What's the minimum realistic climb rate that should be acceptable for self-launch? I've heard things like 1:4 ratio of thrust to MTOW (where thrust is approximated as 3x motor/engine power), but planes like the Silent 2 Electro and miniLAK FES seem to exceed this somewhat, with the miniLAK FES having a ratio approaching 1:5.5. The S2E's flight manual publish a climb rate somewhere around 400fpm, and just based on the numbers I would expect the miniLAK FES to be around 300fpm.

The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.

And gas-powered craft might have 500fpm at sea-level, but they certainly can't attain anywhere near that at higher (density) altitudes.

So while all this sounds slow, when I compare to stall speeds I find that self-launch gliders' overall performance is generally 2-3x better than the FAA's minimum requirement of 200'/1nm for instrument flight (that's the closest I could find to a hard and fast rule for climb rates). So it would suggest that quick climb rates aren't necessary if the forward flight speed is very low.

So what's the right real-world response? Is there a certain absolute minimum for safe glider flight, or is it better to have a great climb angle rather than a great climb rate?

On Sunday, April 26, 2020 at 1:38:33 PM UTC-4, Kenz Dale wrote:
> What's the minimum realistic climb rate that should be acceptable for self-launch?

I can just tell you my experience with two different ships. My first self-launch was a Silent-IN Club. I got 400 fpm. Flew it for several years and put 500 hours on it. Great intro bird for self-launch.

But, my second self-launch is a DG-400. I get between 600-700 fpm at a much steeper angle. Immensely more comfortable. The oh crap period on climb out is much shorter. Love my 400.

Kevin
92

On Sunday, April 26, 2020 at 1:38:33 PM UTC-4, Kenz Dale wrote:
>>...that quick climb rates aren't necessary if the forward flight speed is very low. <<

Seems like it would depend on where and when you want to takeoff. Some airports have shorter runways with sink, strong wind and wind shear close to the ground on good soaring days. Slow speed over the ground leaves me in the sink for a longer time. Low climb rate leaves me in the wind shear for longer. Low airspeed and windshear seem like a bad combination.

On Sunday, April 26, 2020 at 1:38:33 PM UTC-4, Kenz Dale wrote:
> What's the minimum realistic climb rate that should be acceptable for self-launch? I've heard things like 1:4 ratio of thrust to MTOW (where thrust is approximated as 3x motor/engine power), but planes like the Silent 2 Electro and miniLAK FES seem to exceed this somewhat, with the miniLAK FES having a ratio approaching 1:5.5. The S2E's flight manual publish a climb rate somewhere around 400fpm, and just based on the numbers I would expect the miniLAK FES to be around 300fpm.
>
> The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.
>
> And gas-powered craft might have 500fpm at sea-level, but they certainly can't attain anywhere near that at higher (density) altitudes.
>
> So while all this sounds slow, when I compare to stall speeds I find that self-launch gliders' overall performance is generally 2-3x better than the FAA's minimum requirement of 200'/1nm for instrument flight (that's the closest I could find to a hard and fast rule for climb rates). So it would suggest that quick climb rates aren't necessary if the forward flight speed is very low.
>
> So what's the right real-world response? Is there a certain absolute minimum for safe glider flight, or is it better to have a great climb angle rather than a great climb rate?

CS 22 - Certification Specifications for Sailplanes and Powered Sailplanes - has standards.

"CS 22.51 Take-off
(a) For a powered sailplane the take-off distance at maximum weight and in zero wind, from rest to attaining a height of 15 m must be determined and must not exceed 500 m when taking off from a dry, level, hard surface. In demonstration of the take-off distance, the powered sailplane must be allowed to reach the selected speed promptly after lifting off and this speed must be maintained throughout the climb.
(b) The selected speed must not be less than;
(1) 1·3 VS1, or
(2) any lesser speed, not less than 1·15 VS1, that is shown to be safe under all reasonably expected operating conditions, including turbulence and complete engine failure.
CS 22.65 Climb
(a) For a powered sailplane the time for climb from leaving the ground up to 360 m above the field must not exceed four minutes with:
(1) not more than take-off power;
(2) landing gear retracted;
(3) wing-flaps in take-off position;
(4) cowl flaps (if any) in the position used in the cooling tests.
(b) For self-sustaining powered sailplanes, the maximum altitude that can be sustained must be determined."
https://www.easa.europa.eu/sites/default/files/dfu/CS-22_Amendment 1 revised.pdf

On Sunday, April 26, 2020 at 12:24:31 PM UTC-7, Dan Daly wrote:
> On Sunday, April 26, 2020 at 1:38:33 PM UTC-4, Kenz Dale wrote:
> > What's the minimum realistic climb rate that should be acceptable for self-launch? I've heard things like 1:4 ratio of thrust to MTOW (where thrust is approximated as 3x motor/engine power), but planes like the Silent 2 Electro and miniLAK FES seem to exceed this somewhat, with the miniLAK FES having a ratio approaching 1:5.5. The S2E's flight manual publish a climb rate somewhere around 400fpm, and just based on the numbers I would expect the miniLAK FES to be around 300fpm.
> >
> > The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.
> >
> > And gas-powered craft might have 500fpm at sea-level, but they certainly can't attain anywhere near that at higher (density) altitudes.
> >
> > So while all this sounds slow, when I compare to stall speeds I find that self-launch gliders' overall performance is generally 2-3x better than the FAA's minimum requirement of 200'/1nm for instrument flight (that's the closest I could find to a hard and fast rule for climb rates). So it would suggest that quick climb rates aren't necessary if the forward flight speed is very low.
> >
> > So what's the right real-world response? Is there a certain absolute minimum for safe glider flight, or is it better to have a great climb angle rather than a great climb rate?
>
> CS 22 - Certification Specifications for Sailplanes and Powered Sailplanes - has standards.
>
> "CS 22.51 Take-off
> (a) For a powered sailplane the take-off distance at maximum weight and in zero wind, from rest to attaining a height of 15 m must be determined and must not exceed 500 m when taking off from a dry, level, hard surface. In demonstration of the take-off distance, the powered sailplane must be allowed to reach the selected speed promptly after lifting off and this speed must be maintained throughout the climb.
> (b) The selected speed must not be less than;
> (1) 1·3 VS1, or
> (2) any lesser speed, not less than 1·15 VS1, that is shown to be safe under all reasonably expected operating conditions, including turbulence and complete engine failure.
> CS 22.65 Climb
> (a) For a powered sailplane the time for climb from leaving the ground up to 360 m above the field must not exceed four minutes with:
> (1) not more than take-off power;
> (2) landing gear retracted;
> (3) wing-flaps in take-off position;
> (4) cowl flaps (if any) in the position used in the cooling tests.
> (b) For self-sustaining powered sailplanes, the maximum altitude that can be sustained must be determined."
> https://www.easa.europa.eu/sites/default/files/dfu/CS-22_Amendment 1 revised.pdf

When reading the manufacturer's sales brochure, remember that the advertised climb will usually be for standard atmosphere at sea level. For gas engines, the climb rate will be significantly less if you plan to fly in the US western states in summer.

Thanks, Dan, you knocked it out of the park with this answer.

> CS 22 - Certification Specifications for Sailplanes and Powered Sailplanes - has standards.
>
> "CS 22.51 Take-off
> (a) For a powered sailplane the take-off distance at maximum weight and in zero wind, from rest to attaining a height of 15 m must be determined and must not exceed 500 m when taking off from a dry, level, hard surface. In demonstration of the take-off distance, the powered sailplane must be allowed to reach the selected speed promptly after lifting off and this speed must be maintained throughout the climb.
> (b) The selected speed must not be less than;
> (1) 1·3 VS1, or
> (2) any lesser speed, not less than 1·15 VS1, that is shown to be safe under all reasonably expected operating conditions, including turbulence and complete engine failure.
> CS 22.65 Climb
> (a) For a powered sailplane the time for climb from leaving the ground up to 360 m above the field must not exceed four minutes with:
> (1) not more than take-off power;
> (2) landing gear retracted;
> (3) wing-flaps in take-off position;
> (4) cowl flaps (if any) in the position used in the cooling tests.
> (b) For self-sustaining powered sailplanes, the maximum altitude that can be sustained must be determined."
> https://www.easa.europa.eu/sites/default/files/dfu/CS-22_Amendment 1 revised.pdf

My Stemme gets 800 ft/min at 8,000' density altitude but it's
turbocharged. :-D If I'm repositioning for a safari or such, I climb
straight up to 18,000' MSL and cruise at 140 KTAS.Â* But it sure isn't a
fingertip light ship to fly. :-(

On 4/26/2020 4:44 PM, Kenz Dale wrote:
> Thanks, Dan, you knocked it out of the park with this answer.
>
>> CS 22 - Certification Specifications for Sailplanes and Powered Sailplanes - has standards.
>>
>> "CS 22.51 Take-off
>> (a) For a powered sailplane the take-off distance at maximum weight and in zero wind, from rest to attaining a height of 15 m must be determined and must not exceed 500 m when taking off from a dry, level, hard surface. In demonstration of the take-off distance, the powered sailplane must be allowed to reach the selected speed promptly after lifting off and this speed must be maintained throughout the climb.
>> (b) The selected speed must not be less than;
>> (1) 1·3 VS1, or
>> (2) any lesser speed, not less than 1·15 VS1, that is shown to be safe under all reasonably expected operating conditions, including turbulence and complete engine failure.
>> CS 22.65 Climb
>> (a) For a powered sailplane the time for climb from leaving the ground up to 360 m above the field must not exceed four minutes with:
>> (1) not more than take-off power;
>> (2) landing gear retracted;
>> (3) wing-flaps in take-off position;
>> (4) cowl flaps (if any) in the position used in the cooling tests.
>> (b) For self-sustaining powered sailplanes, the maximum altitude that can be sustained must be determined."
>> https://www.easa.europa.eu/sites/default/files/dfu/CS-22_Amendment 1 revised.pdf

--
Dan, 5J

On Sunday, April 26, 2020 at 10:38:33 AM UTC-7, Kenz Dale wrote:
> What's the minimum realistic climb rate that should be acceptable for self-launch? I've heard things like 1:4 ratio of thrust to MTOW (where thrust is approximated as 3x motor/engine power), but planes like the Silent 2 Electro and miniLAK FES seem to exceed this somewhat, with the miniLAK FES having a ratio approaching 1:5.5. The S2E's flight manual publish a climb rate somewhere around 400fpm, and just based on the numbers I would expect the miniLAK FES to be around 300fpm.
>
> The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.
>
> And gas-powered craft might have 500fpm at sea-level, but they certainly can't attain anywhere near that at higher (density) altitudes.
>
> So while all this sounds slow, when I compare to stall speeds I find that self-launch gliders' overall performance is generally 2-3x better than the FAA's minimum requirement of 200'/1nm for instrument flight (that's the closest I could find to a hard and fast rule for climb rates). So it would suggest that quick climb rates aren't necessary if the forward flight speed is very low.
>
> So what's the right real-world response? Is there a certain absolute minimum for safe glider flight, or is it better to have a great climb angle rather than a great climb rate?

As a practical matter, the climb angle should significantly exceed the glide angle with the engine not operating but deployed, at the density altitude of your field. That way the engine cannot take you to a place you can't get back from. If your dirty glide is 20:1 @ 50 knots, that's 260 ft/min so you'd want a climb rate of 350 or so. The C22 climb criteria (1200 ft in 4 min) suggests a minimum climb rate of 300. That'd be real minimum for me. FES may be slower climbing but also cleaner gliding with a failed motor, so a step back and a step ahead.

I'd be careful of brochure or owner claimed climb rates. Look at the IGC files to be sure. I get about 880 ft/min at sea level and about 530 at 9000 ft density altitude (averaged over many flights, from IGC data - I wrote an app to analyze multiple files automatically).

On Sunday, April 26, 2020 at 10:38:33 AM UTC-7, Kenz Dale wrote:
> What's the minimum realistic climb rate that should be acceptable for self-launch? I've heard things like 1:4 ratio of thrust to MTOW (where thrust is approximated as 3x motor/engine power), but planes like the Silent 2 Electro and miniLAK FES seem to exceed this somewhat, with the miniLAK FES having a ratio approaching 1:5.5. The S2E's flight manual publish a climb rate somewhere around 400fpm, and just based on the numbers I would expect the miniLAK FES to be around 300fpm.
>
> The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.
>
> And gas-powered craft might have 500fpm at sea-level, but they certainly can't attain anywhere near that at higher (density) altitudes.
>
> So while all this sounds slow, when I compare to stall speeds I find that self-launch gliders' overall performance is generally 2-3x better than the FAA's minimum requirement of 200'/1nm for instrument flight (that's the closest I could find to a hard and fast rule for climb rates). So it would suggest that quick climb rates aren't necessary if the forward flight speed is very low.
>
> So what's the right real-world response? Is there a certain absolute minimum for safe glider flight, or is it better to have a great climb angle rather than a great climb rate?

hi guys i was wondering why most of the groups on google groups are from 6or 7 years ago\

Kenz Dale wrote on 4/26/2020 10:38 AM:
> What's the minimum realistic climb rate that should be acceptable for self-launch? I've heard things like 1:4 ratio of thrust to MTOW (where thrust is approximated as 3x motor/engine power), but planes like the Silent 2 Electro and miniLAK FES seem to exceed this somewhat, with the miniLAK FES having a ratio approaching 1:5.5. The S2E's flight manual publish a climb rate somewhere around 400fpm, and just based on the numbers I would expect the miniLAK FES to be around 300fpm.
>
> The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.
>
> And gas-powered craft might have 500fpm at sea-level, but they certainly can't attain anywhere near that at higher (density) altitudes.
>
> So while all this sounds slow, when I compare to stall speeds I find that self-launch gliders' overall performance is generally 2-3x better than the FAA's minimum requirement of 200'/1nm for instrument flight (that's the closest I could find to a hard and fast rule for climb rates). So it would suggest that quick climb rates aren't necessary if the forward flight speed is very low.
>
> So what's the right real-world response? Is there a certain absolute minimum for safe glider flight, or is it better to have a great climb angle rather than a great climb rate?

I don't think you should pay any attention to estimated thrust. What you want to
know is the climb rate, and that is always given by the brochure or handbook, and
most owners know about what their plane really does.

Based on 25 years of flying my ASH26E, I want at least 500 fpm at the weight I
would normally expect to fly. Don't use MTOW, as that gives you a very distorted
picture if you compare a Silent 2 Electro with a GP15, which can fly at a far
higher wing loading than the Electro.

The GP15 is rated at 865 fpm (large battery, 705 lbs takeoff weight, 8.4 lb/ft2).
That's a lot better than an Electro or miniLak, two of the gliders I considered
before deciding to buy the GP15. Compare it to my ASH26E, which is around 600 fpm
at the same wing loading, and drops off at higher density altitudes. So, the GP15
should be significantly better at places like Minden, Ely, and Parowan, as it's
electric propulsion does not lose nearly as much power at those places.

The maximum weight I expect to fly at (1010 lbs) gives a 12 lb/ft2 wing loading,
and I estimate the climb rate would be about 600 fpm.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On 4/26/20 11:38 AM, Kenz Dale wrote:

>
> The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.
>

Given that there are approximately 0 Jeta's flying in the hands of real
customers, the lack of complaints may not be surprising.

You should always be cautious comparing specs of vapourware gliders to
those of gliders in the field, since in the first case the glossy
brochures are sometimes not encumbered by nasty things called facts.

-Dave

Even if CS22 only requires approximately 1.5 m/s (~300 ft/mn) at sea level ISA, this is really not comfortable.
I get bearly 250 ft/mn when taking off from high altitude airport (5700ft) with the Ventus 2 CM and it is OK but not a pleasant experience! Especially in mountainous environment.

Anything below 400 ft/mn at sea level will result in uncomfortable performance during hot days and/or high altitude.

Concerning electric performance, the motor itself does not lapses with altitude. Therefore, at given rpm, the thrust loss is pretty much proportional to the effect of air density variation on the prop.

The rule of thumb you propose is very rough and would only approximate sea level static.

For climb performance you really need to model the prop and get an estimate of thrust at typical climb speed.
Because FES and GP have relatively small diameter props, they are highly loaded and the GP has an efficiency advantage with the 3 blades.
If you run the analysis, you find the GP15 should have a sea level ISA climb rate of ~500 ft/mn at 470 kg, which is pretty good since you are taking off at 60 kg/m2!

kinsell wrote on 4/26/2020 11:37 PM:
> On 4/26/20 11:38 AM, Kenz Dale wrote:
>
>>
>> The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb
>> for powered flight. Yet, I don't hear anyone complaining.
>>
>
> Given that there are approximately 0 Jeta's flying in the hands of real customers,
> the lack of complaints may not be surprising.
>
> You should always be cautious comparing specs of vapourware gliders to those of
> gliders in the field, since in the first case the glossy brochures are sometimes
> not encumbered by nasty things called facts.

The first one was at the SSA convention, then taken to it's new home in Oregon.
The virus situation has complicated and delayed the licensing, but the owner
expects to fly "soon". The factory (and many other businesses) in Poland has been
locked down (and still is) for over a month, which has delayed the April delivery
of the next two units to the USA, and that delay will likely ripple through the
other orders for many months. The prototype has flown for at least two years.

Bringing a new glider to market on time is difficult, even for established
manufacturers. 25 years ago, Schleicher surprised both myself and the US dealer
when they added a year to the delivery date for my ASH26E.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Sunday, April 26, 2020 at 11:59:57 PM UTC-4, Eric Greenwell wrote:
> Kenz Dale wrote on 4/26/2020 10:38 AM:
> > What's the minimum realistic climb rate that should be acceptable for self-launch? I've heard things like 1:4 ratio of thrust to MTOW (where thrust is approximated as 3x motor/engine power), but planes like the Silent 2 Electro and miniLAK FES seem to exceed this somewhat, with the miniLAK FES having a ratio approaching 1:5.5. The S2E's flight manual publish a climb rate somewhere around 400fpm, and just based on the numbers I would expect the miniLAK FES to be around 300fpm.
> >
> > The GP 15 Jeta has a ratio of 1:6.3, which is far lower than the rule of thumb for powered flight. Yet, I don't hear anyone complaining.
> >
> > And gas-powered craft might have 500fpm at sea-level, but they certainly can't attain anywhere near that at higher (density) altitudes.
> >
> > So while all this sounds slow, when I compare to stall speeds I find that self-launch gliders' overall performance is generally 2-3x better than the FAA's minimum requirement of 200'/1nm for instrument flight (that's the closest I could find to a hard and fast rule for climb rates). So it would suggest that quick climb rates aren't necessary if the forward flight speed is very low.
> >
> > So what's the right real-world response? Is there a certain absolute minimum for safe glider flight, or is it better to have a great climb angle rather than a great climb rate?
>
> I don't think you should pay any attention to estimated thrust. What you want to
> know is the climb rate, and that is always given by the brochure or handbook, and
> most owners know about what their plane really does.
>
> Based on 25 years of flying my ASH26E, I want at least 500 fpm at the weight I
> would normally expect to fly. Don't use MTOW, as that gives you a very distorted
> picture if you compare a Silent 2 Electro with a GP15, which can fly at a far
> higher wing loading than the Electro.
>
> The GP15 is rated at 865 fpm (large battery, 705 lbs takeoff weight, 8.4 lb/ft2).
> That's a lot better than an Electro or miniLak, two of the gliders I considered
> before deciding to buy the GP15. Compare it to my ASH26E, which is around 600 fpm
> at the same wing loading, and drops off at higher density altitudes. So, the GP15
> should be significantly better at places like Minden, Ely, and Parowan, as it's
> electric propulsion does not lose nearly as much power at those places.
>
> The maximum weight I expect to fly at (1010 lbs) gives a 12 lb/ft2 wing loading,
> and I estimate the climb rate would be about 600 fpm.
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

At 8.5 lb wing loading an ASW-24E, on engine power of 17KW, gets 300 ft/ minute.
25KW should get it to about 450. These are the numbers I expect with my electric conversion. Color me skeptical that the GP15 is going to get 600. I don't doubt it will be very good, but think projections are optomistic.
FWIW
UH

On Monday, April 27, 2020 at 10:57:39 AM UTC+2, jld wrote:
> Even if CS22 only requires approximately 1.5 m/s (~300 ft/mn) at sea level ISA, this is really not comfortable.
> I get bearly 250 ft/mn when taking off from high altitude airport (5700ft) with the Ventus 2 CM and it is OK but not a pleasant experience! Especially in mountainous environment.
>
> Anything below 400 ft/mn at sea level will result in uncomfortable performance during hot days and/or high altitude.
>
> Concerning electric performance, the motor itself does not lapses with altitude. Therefore, at given rpm, the thrust loss is pretty much proportional to the effect of air density variation on the prop.
>
> The rule of thumb you propose is very rough and would only approximate sea level static.
>
> For climb performance you really need to model the prop and get an estimate of thrust at typical climb speed.
> Because FES and GP have relatively small diameter props, they are highly loaded and the GP has an efficiency advantage with the 3 blades.
> If you run the analysis, you find the GP15 should have a sea level ISA climb rate of ~500 ft/mn at 470 kg, which is pretty good since you are taking off at 60 kg/m2!

I can see how it's easy to do an analysis of climb performance relative to weight, but did you / do you need to account for impact of higher wing loading (increased stall speed / sink rate)?
I'm also curious whether there's a similar effect for higher altitude takeoffs via stall/sink speeds, other than air density on the propeller.

You will probably get more than the ASW24E.
The very high drag from the pylon with engine, like the ASW24E, reduces the glider L/D below 20, which start to have a significant effect on climb performance. This is probably a 100-150 ft/min difference.
It is more difficult to get the published power rating from 2 strokes carburated engines than it is from electrical motors.

Concerning GP15, its pylon is very low drag and most important, it is very light.
For climb performance it is not the wing loading but the weight which drives climb performance. To takeoff at 8.5 lb/ft2 with the ASW24E you need to be at 425 kg. With the GP15, you only need to 330 kg for the same wing loading.
Because of the available shaft power, drag and weight differences, I have no doubt the GP will have at least a 30% climb advantage with similar takeoff conditions.

wrote on 4/27/2020 6:08 AM:
> On Sunday, April 26, 2020 at 11:59:57 PM UTC-4, Eric Greenwell wrote:
....
>>
>> The GP15 is rated at 865 fpm (large battery, 705 lbs takeoff weight, 8.4 lb/ft2).
>> That's a lot better than an Electro or miniLak, two of the gliders I considered
>> before deciding to buy the GP15. Compare it to my ASH26E, which is around 600 fpm
>> at the same wing loading, and drops off at higher density altitudes. So, the GP15
>> should be significantly better at places like Minden, Ely, and Parowan, as it's
>> electric propulsion does not lose nearly as much power at those places.
>>
>> The maximum weight I expect to fly at (1010 lbs) gives a 12 lb/ft2 wing loading,
>> and I estimate the climb rate would be about 600 fpm.
>>
>> --
>> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
>> - "A Guide to Self-Launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
>
> At 8.5 lb wing loading an ASW-24E, on engine power of 17KW, gets 300 ft/ minute.
> 25KW should get it to about 450. These are the numbers I expect with my electric conversion. Color me skeptical that the GP15 is going to get 600. I don't doubt it will be very good, but think projections are optomistic.
> FWIW
The wing area of the ASW 24E is 110 ft2, for a weight of 935lbs (8.5 lb wing
loading); the wing area for the GP15 is 84 ft2 , for a weight of 714 lbs (also at
8.5 lb wing loading). The GP15 motor power is 30kW during the launch (the 25 kw is
maximum continuous operation). With 24% less weight and 76% more power, it should
easily beat 600 fpm.

I have compared the brochure values for the AS 34 and Gp15 as a "reality check",
and determined the GP15 values gave climb rates similar to the AS 34 when adjusted
for wing loading and weight. That's not the same as a flight test, but at least
the engineers at the two companies are using the same handbook :^)

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

"With 24% less weight and 76% more power, it should easily beat 600 fpm"
Don't forget the lower drag due to streamlined pylon compared to traditional installations like ASW24E.

The equation to determine climb rate is relatively simple, the main unknown is the thrust delivered by the prop at ~25-30 m/s climb IAS.

For the GP15, modeling a decent 1 meter 3 blades prop gives 550 N thrust at 30 m/s climb IAS with 25 kw on the shaft, sea level ISA.
AT 325 kg (722 lbs) TOM, L/D of 40 due to pylon, the climb rate should be ~4.3 m/s (~850 ft/mn).

Modeling the ASW24E with the same equation and following assumptions:
Thrust 450 N at 26 m/s IAS with 17 kw on the shaft (just a guess, using 20% higher prop efficiency than the GP due to larger prop diameter)
Weight 425 kg and L/D with pylon out 25
the climb rate is estimated at ~1.7 m/s (~340 ft/mn)

Even if these estimations are for sea level ISA, GP15 with such a high climb rate should perform very well even at high altitude in summer.
With the large battery packs and such a high climb rate, the GP15 should deliver an excellent climb altitude of ~4500 m with above assumptions and a 10% energy reserve. This is a very good differentiator!

On Monday, April 27, 2020 at 1:57:39 AM UTC-7, jld wrote:
> Even if CS22 only requires approximately 1.5 m/s (~300 ft/mn) at sea level ISA, this is really not comfortable.
> I get bearly 250 ft/mn when taking off from high altitude airport (5700ft) with the Ventus 2 CM and it is OK but not a pleasant experience! Especially in mountainous environment.
>
> Anything below 400 ft/mn at sea level will result in uncomfortable performance during hot days and/or high altitude.
>
> Concerning electric performance, the motor itself does not lapses with altitude. Therefore, at given rpm, the thrust loss is pretty much proportional to the effect of air density variation on the prop.
>
> The rule of thumb you propose is very rough and would only approximate sea level static.
>
> For climb performance you really need to model the prop and get an estimate of thrust at typical climb speed.
> Because FES and GP have relatively small diameter props, they are highly loaded and the GP has an efficiency advantage with the 3 blades.
> If you run the analysis, you find the GP15 should have a sea level ISA climb rate of ~500 ft/mn at 470 kg, which is pretty good since you are taking off at 60 kg/m2!

Another way to look at it is, how does it climb relative to a towplane? They are engine powered and suffer from altitude sickness as well. With a low drag electric, if you can out climb the towplane at high density altitude they you are relatively better off, regardless of the absolute numbers.

Last year I took two tows behind a Pawnee, climb rate to 1000 ft was 353 ft/m on one and 625 on the other, average 451. On the next 6 days I did self launches, averaging 573, the lowest was 439 and highest 796. This is all at Truckee, density altitude usually between 8800 and 9400 ft. A strong self launcher will beat the tow plane.

On Monday, April 27, 2020 at 2:22:15 PM UTC-4, jfitch wrote:
> Last year I took two tows behind a Pawnee...

Reminds me of a western tow a couple years ago...

The task will open in 15 minutes.
CD, can you hold that, YO is still at 1600 feet on tow.
.... and 5 minutes later ...
The task will open in 15 minutes.
CD, can you hold that, YO is still on tow, 1500 feet and descending.
IIRC, I gave up at 1300 feet, pulled the release, and climbed out...

Some of you were in the air waiting...

I really would like to second Steve message.
Because the prop used on existing self launchers have very little speed Range, their pitch is selected to provide a narrow compromise between takeoff speed and climb speed.
This allows to have sufficient thrust during takeoff run, but reduces the climb speed.
From my precedent message, it is not pleasant at all, especially when density altitude gets high and the feeling gets worse with low IAS and less than 3 knots of climb.

Modern props with significant ESR effect (Extended Speed Range) could be used to improve the situation without compromising performance (you would still get the higher drag from the pylon/engine).

When looking at the GP prop, they seem to be using modern airfoils which should exhibit the necessary ESR effect (good question to ask GP)
Because of the low drag pylon and better electric motor speed/torque control, the climb rate should be good over a large speed range compared to existing combustion engine self launchers.

On Monday, 27 April 2020 15:46:46 UTC-6, Dave Nadler wrote:
> On Monday, April 27, 2020 at 2:22:15 PM UTC-4, jfitch wrote:
> > Last year I took two tows behind a Pawnee...
>
> Reminds me of a western tow a couple years ago...
>
> The task will open in 15 minutes.
> CD, can you hold that, YO is still at 1600 feet on tow.
> ... and 5 minutes later ...
> The task will open in 15 minutes.
> CD, can you hold that, YO is still on tow, 1500 feet and descending.
> IIRC, I gave up at 1300 feet, pulled the release, and climbed out...
>
> Some of you were in the air waiting...

I was laughing reading this YO as I remember it vividly. You and your Arcus and UGLY the tow plane just did not mesh well. No fault on either end of the rope, sometimes combinations just do not function well.

The look on your face a day or two later when I had UGLY pull onto the runway in front of your glider before waving it off was priceless.

FWIW UGLY the tow plane is/was a Calair and was the work horse at Morgan UT airport for years. It has been retired after hitting power lines on the way to Nephi a couple of ago. Both pilot and aircraft survived but aircraft had to be retired.

I also agree with Eric. Having been flying an ASH26e and recently a
Ventus self-launcher I have never been in the slightest concerned about climbing at around 54 knots. It is totally different from being on an aerotow.. I would definitely not want to trade climb rate for climb speed. The only thing to be very aware of is the pitch change when the propulsion stops before the engine is retracted.

I used to self-launch in an Arcus M and many other types. I was happy that the Arcus had a significant margin between best climb RPM and redline. IIRC about 400rpm margin.
In turbulent conditions, close to the ground, I could maintain 63kts while climbing.

I guess the same applies to the DG1001M and Quintus, but I don't remember precisely.

Redline is a serious concern in the DG600M. Probably a little less so in the DG400.

Aldo Cernezzi

The typical slow self launch climbout speed arguably makes a self launch more hazardous than an aerotow or a winch launch until above 500ft, which takes a couple of minutes. The climb speed is lower than the typical approach speed, and the speed would drop fast, due to the nose up attitude, the flap use for climb, and the sudden windmill drag, which will try to increase the pitch-up for a mast design. I find it best to approach at Minden in my ventus 2cxM at a speed much higher than the climbout speed: I approach at 70kts in summer, due to the typical changeable, windy conditions, only slowing in the last 50ft.

wrote on 4/28/2020 8:16 AM:
>
> The typical slow self launch climbout speed arguably makes a self launch more hazardous than an aerotow or a winch launch until above 500ft, which takes a couple of minutes. The climb speed is lower than the typical approach speed, and the speed would drop fast, due to the nose up attitude, the flap use for climb, and the sudden windmill drag, which will try to increase the pitch-up for a mast design. I find it best to approach at Minden in my ventus 2cxM at a speed much higher than the climbout speed: I approach at 70kts in summer, due to the typical changeable, windy conditions, only slowing in the last 50ft.
>
My experience is much different than yours. I think self-launch in my ASH26E is
safer than towing or winch, because I am in complete control. There is no chance
miscommunication, no chance of entanglement with a rope or parachute, no need to
fly formation or operate at a very high pitch attitude.

At the places I fly, I can land straight ahead from less than 100' agl, and do a
180 back to the runway over 200' agl - the same numbers I would use for a typical
tow. At 600 fpm climb, that's only 10 seconds of "aw snap!" if the engine stops
between 100' and 200', same as for a tow. If the engine quits (never has), I will
just nose down to keep the speed correct, then use my pre-determined plan for the
situation, same as if I was being towed. I've practiced this at altitude, examined
the IGC file, so I'm confident it would work as well as it would with a tow failure.

I've flown at Minden, Ely, and Parowan many times over 25 years with the 26E, and
never had a problem with handling turbulence on takeoff; I do land as you do in
the often much more turbulent afternoon.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Tuesday, April 28, 2020 at 10:25:27 AM UTC-7, Eric Greenwell wrote:
> wrote on 4/28/2020 8:16 AM:
> >
> > The typical slow self launch climbout speed arguably makes a self launch more hazardous than an aerotow or a winch launch until above 500ft, which takes a couple of minutes. The climb speed is lower than the typical approach speed, and the speed would drop fast, due to the nose up attitude, the flap use for climb, and the sudden windmill drag, which will try to increase the pitch-up for a mast design. I find it best to approach at Minden in my ventus 2cxM at a speed much higher than the climbout speed: I approach at 70kts in summer, due to the typical changeable, windy conditions, only slowing in the last 50ft.
> >
> My experience is much different than yours. I think self-launch in my ASH26E is
> safer than towing or winch, because I am in complete control. There is no chance
> miscommunication, no chance of entanglement with a rope or parachute, no need to
> fly formation or operate at a very high pitch attitude.
>
> At the places I fly, I can land straight ahead from less than 100' agl, and do a
> 180 back to the runway over 200' agl - the same numbers I would use for a typical
> tow. At 600 fpm climb, that's only 10 seconds of "aw snap!" if the engine stops
> between 100' and 200', same as for a tow. If the engine quits (never has), I will
> just nose down to keep the speed correct, then use my pre-determined plan for the
> situation, same as if I was being towed. I've practiced this at altitude, examined
> the IGC file, so I'm confident it would work as well as it would with a tow failure.
>
> I've flown at Minden, Ely, and Parowan many times over 25 years with the 26E, and
> never had a problem with handling turbulence on takeoff; I do land as you do in
> the often much more turbulent afternoon.
>
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
> - "A Guide to Self-Launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Hi Eric, your points are all true, and on balance I prefer a motorglider. But just not for the first minute of takeoff. Although I don't feel personally endangered, an engine failure would probably force me to sacrifice my motorglider to preserve my safety. From 200ft, starting nose up at best climb speed (51-54kts), flaps +2 and engine windmilling, I very much doubt I could do a safe 180 in my glider (Ventus 2cxm). I've I've never dared try it, and I've never heard of anyone trying it. In contrast, simulated aerotow failures from 200ft in gliders is practiced as part of standard training. Similarly, a winch failure at any time should be able to be safely handled.

wrote on 4/28/2020 2:56 PM:
> On Tuesday, April 28, 2020 at 10:25:27 AM UTC-7, Eric Greenwell wrote:
>> wrote on 4/28/2020 8:16 AM:
>>>
>>> The typical slow self launch climbout speed arguably makes a self launch more hazardous than an aerotow or a winch launch until above 500ft, which takes a couple of minutes. The climb speed is lower than the typical approach speed, and the speed would drop fast, due to the nose up attitude, the flap use for climb, and the sudden windmill drag, which will try to increase the pitch-up for a mast design. I find it best to approach at Minden in my ventus 2cxM at a speed much higher than the climbout speed: I approach at 70kts in summer, due to the typical changeable, windy conditions, only slowing in the last 50ft.
>>>
>> My experience is much different than yours. I think self-launch in my ASH26E is
>> safer than towing or winch, because I am in complete control. There is no chance
>> miscommunication, no chance of entanglement with a rope or parachute, no need to
>> fly formation or operate at a very high pitch attitude.
>>
>> At the places I fly, I can land straight ahead from less than 100' agl, and do a
>> 180 back to the runway over 200' agl - the same numbers I would use for a typical
>> tow. At 600 fpm climb, that's only 10 seconds of "aw snap!" if the engine stops
>> between 100' and 200', same as for a tow. If the engine quits (never has), I will
>> just nose down to keep the speed correct, then use my pre-determined plan for the
>> situation, same as if I was being towed. I've practiced this at altitude, examined
>> the IGC file, so I'm confident it would work as well as it would with a tow failure.
>>
>> I've flown at Minden, Ely, and Parowan many times over 25 years with the 26E, and
>> never had a problem with handling turbulence on takeoff; I do land as you do in
>> the often much more turbulent afternoon.
>>

>
> Hi Eric, your points are all true, and on balance I prefer a motorglider. But just not for the first minute of takeoff. Although I don't feel personally endangered, an engine failure would probably force me to sacrifice my motorglider to preserve my safety. From 200ft, starting nose up at best climb speed (51-54kts), flaps +2 and engine windmilling, I very much doubt I could do a safe 180 in my glider (Ventus 2cxm). I've I've never dared try it, and I've never heard of anyone trying it. In contrast, simulated aerotow failures from 200ft in gliders is practiced as part of standard training. Similarly, a winch failure at any time should be able to be safely handled.

Surely, there is a period after takeoff when you can still land straight ahead
without damage? In my usual locations, I can be as high as 100' and still do that
- what about your locations?

You can simulate an engine failure during a launch at a safe altitude. I've done
at 2000'-3000':
- set your flight recorder to 1 second intervals, to get the best flight trace data
- at altitude, configure the glider for takeoff: gear down, flaps normally used
- line up on a long, straight road or similar
- establish a steady, full power climb at your normal climb speed
- climb for 200' or so, then set throttle to idle, and do a 180 degree turn,
lining up on the that road
- repeat the test, but this time, turn the ignition off, then turn as before

After you are done flying, you can download the flight trace to determine how much
altitude you lost. From that, you can judge how high you want to be before making
a 180 degree turn. I was surprised at how little altitude loss there was during
the turn. Ditto for my friend in his DG400, when he tried it. I don't know how
well a Ventus 2CXM will do, but I suspect it's not any worse than a DG400;
regardless, it gives you actual numbers to work with.

Some will point out a 180 degree turn leaves you offset from the runway, and you
need to do more turning to line up. Yup - unless you drift away from the runway
during your climb, making a 180 degree sufficient to line you up with runway.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

I've had two Rotax 912 seizures in a Pipistrel Sinus.Â* In each case I
was at or below 200' AGL.Â* In both cases I turned back and landed safely
without undue concern other than being extremely ****ed off. In the
first case, the engine seized so quickly that the 6 bolts holding the
prop onto the hub sheared and the prop windmilled like a pinwheel almost
separating from the aircraft.

In the second event, I noticed reduced climb rate, and reduced pitch.Â*
Then the RPM dropped slightly.Â* At that point, again at or below 200'
AGL and still over the runway but too far down to land straight ahead, I
started to turn back.Â* About half way through the turn it threw a rod
through the crank case, filling the cockpit with smoke and covering the
windscreen with oil.Â* I landed on the parallel taxiway.

The root cause for both failures was that Pipistrel replaced the hose
from the oil cooler to the oil pump with one with internal wire bracing
and did make note in the Illustrated Parts Breakdown.Â* When the hoses
were replaced with Rotax recommended hoses at 5 years, the hose in
question, having a tight bend, collapsed when it heated up starving the
engine.Â* The wire braced hose would not have failed that way.

On 4/28/2020 3:56 PM, wrote:
> On Tuesday, April 28, 2020 at 10:25:27 AM UTC-7, Eric Greenwell wrote:
>> wrote on 4/28/2020 8:16 AM:
>>> The typical slow self launch climbout speed arguably makes a self launch more hazardous than an aerotow or a winch launch until above 500ft, which takes a couple of minutes. The climb speed is lower than the typical approach speed, and the speed would drop fast, due to the nose up attitude, the flap use for climb, and the sudden windmill drag, which will try to increase the pitch-up for a mast design. I find it best to approach at Minden in my ventus 2cxM at a speed much higher than the climbout speed: I approach at 70kts in summer, due to the typical changeable, windy conditions, only slowing in the last 50ft.
>>>
>> My experience is much different than yours. I think self-launch in my ASH26E is
>> safer than towing or winch, because I am in complete control. There is no chance
>> miscommunication, no chance of entanglement with a rope or parachute, no need to
>> fly formation or operate at a very high pitch attitude.
>>
>> At the places I fly, I can land straight ahead from less than 100' agl, and do a
>> 180 back to the runway over 200' agl - the same numbers I would use for a typical
>> tow. At 600 fpm climb, that's only 10 seconds of "aw snap!" if the engine stops
>> between 100' and 200', same as for a tow. If the engine quits (never has), I will
>> just nose down to keep the speed correct, then use my pre-determined plan for the
>> situation, same as if I was being towed. I've practiced this at altitude, examined
>> the IGC file, so I'm confident it would work as well as it would with a tow failure.
>>
>> I've flown at Minden, Ely, and Parowan many times over 25 years with the 26E, and
>> never had a problem with handling turbulence on takeoff; I do land as you do in
>> the often much more turbulent afternoon.
>>
>>
>> --
>> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
>> - "A Guide to Self-Launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
> Hi Eric, your points are all true, and on balance I prefer a motorglider. But just not for the first minute of takeoff. Although I don't feel personally endangered, an engine failure would probably force me to sacrifice my motorglider to preserve my safety. From 200ft, starting nose up at best climb speed (51-54kts), flaps +2 and engine windmilling, I very much doubt I could do a safe 180 in my glider (Ventus 2cxm). I've I've never dared try it, and I've never heard of anyone trying it. In contrast, simulated aerotow failures from 200ft in gliders is practiced as part of standard training. Similarly, a winch failure at any time should be able to be safely handled.
>

--
Dan, 5J

"You can simulate an engine failure during a launch at a safe altitude. I've done
at 2000'-3000':
- set your flight recorder to 1 second intervals, to get the best flight trace data
- at altitude, configure the glider for takeoff: gear down, flaps normally used
- line up on a long, straight road or similar
- establish a steady, full power climb at your normal climb speed
- climb for 200' or so, then set throttle to idle, and do a 180 degree turn,
lining up on the that road
- repeat the test, but this time, turn the ignition off, then turn as before"

You cannot do that last bit in an Arcus M - when you turn the engine off it commences the prop lowering process. In the ASH 26 I had before I did try this sort of stuff and would have been confident of a turn back from 200 foot. I think it would also be fine in the Arcus. However from my club's small grass field I am vulnerable to a potentially damaging off field arrival from about 50 foot to about 200 foot.

The only relevant power failure I have had was in the Arcus just after lift off, at 5 foot or less off the ground. There was a drive belt failure, and the glider plonked down rather heavily on the ground - instead of the lift component of the engine power I now had no power and a high drag prop mast.. Happily no damage done other than by the flailing drive belt(s). Since then I have tried to stay just above the ground until achieving say 55 knots.

In the Arcus while best climb rate is supposed to be about 52 knots, you can climb quite a lot faster without over-revving and without much sacrifice of climb rate - and there is a rev limiter which you could only hit in level flight, probably about 90 knots.

waremark wrote on 4/29/2020 1:03 PM:
> "You can simulate an engine failure during a launch at a safe altitude. I've done
> at 2000'-3000':
> - set your flight recorder to 1 second intervals, to get the best flight trace data
> - at altitude, configure the glider for takeoff: gear down, flaps normally used
> - line up on a long, straight road or similar
> - establish a steady, full power climb at your normal climb speed
> - climb for 200' or so, then set throttle to idle, and do a 180 degree turn,
> lining up on the that road
> - repeat the test, but this time, turn the ignition off, then turn as before"
>
> You cannot do that last bit in an Arcus M - when you turn the engine off it commences the prop lowering process. In the ASH 26 I had before I did try this sort of stuff and would have been confident of a turn back from 200 foot. I think it would also be fine in the Arcus. However from my club's small grass field I am vulnerable to a potentially damaging off field arrival from about 50 foot to about 200 foot.
>
> The only relevant power failure I have had was in the Arcus just after lift off, at 5 foot or less off the ground. There was a drive belt failure, and the glider plonked down rather heavily on the ground - instead of the lift component of the engine power I now had no power and a high drag prop mast.. Happily no damage done other than by the flailing drive belt(s). Since then I have tried to stay just above the ground until achieving say 55 knots.
>
> In the Arcus while best climb rate is supposed to be about 52 knots, you can climb quite a lot faster without over-revving and without much sacrifice of climb rate - and there is a rev limiter which you could only hit in level flight, probably about 90 knots.

That 50' to 200' "window of discomfort" is disturbing, but would be still be there
when using a climb speed a few knots higher than the "speed for max climb rate"
that Steve M is looking for. It does sound like the Arcus M would be much more
suited to Steve's flying than the N3D, unfortunately at a much greater cost.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Wednesday, April 29, 2020 at 1:03:12 PM UTC-7, waremark wrote:
> "You can simulate an engine failure during a launch at a safe altitude. I've done
> at 2000'-3000':
> - set your flight recorder to 1 second intervals, to get the best flight trace data
> - at altitude, configure the glider for takeoff: gear down, flaps normally used
> - line up on a long, straight road or similar
> - establish a steady, full power climb at your normal climb speed
> - climb for 200' or so, then set throttle to idle, and do a 180 degree turn,
> lining up on the that road
> - repeat the test, but this time, turn the ignition off, then turn as before"
>
> You cannot do that last bit in an Arcus M - when you turn the engine off it commences the prop lowering process. In the ASH 26 I had before I did try this sort of stuff and would have been confident of a turn back from 200 foot. I think it would also be fine in the Arcus. However from my club's small grass field I am vulnerable to a potentially damaging off field arrival from about 50 foot to about 200 foot.
>
> The only relevant power failure I have had was in the Arcus just after lift off, at 5 foot or less off the ground. There was a drive belt failure, and the glider plonked down rather heavily on the ground - instead of the lift component of the engine power I now had no power and a high drag prop mast. Happily no damage done other than by the flailing drive belt(s). Since then I have tried to stay just above the ground until achieving say 55 knots.
>
> In the Arcus while best climb rate is supposed to be about 52 knots, you can climb quite a lot faster without over-revving and without much sacrifice of climb rate - and there is a rev limiter which you could only hit in level flight, probably about 90 knots.


I'm curious why motorglider pilots don't practice that at 200ft agl, as all student pilots do on aerotows as part of normal training.

> I'm curious why motorglider pilots don't practice that at 200ft agl, as all student pilots do on aerotows as part of normal training.

FYI- the L/D of the Arcus M with mast extended and engine not running is approximately 13:1 with a sink rate in level flight of 495 fpm. Do you want to try a turn back to the runway with those numbers?

On Wednesday, 29 April 2020 17:29:52 UTC-6, wrote:
> > I'm curious why motorglider pilots don't practice that at 200ft agl, as all student pilots do on aerotows as part of normal training.
>
> FYI- the L/D of the Arcus M with mast extended and engine not running is approximately 13:1 with a sink rate in level flight of 495 fpm. Do you want to try a turn back to the runway with those numbers?

Come on Mark, 1980 vintage hang glider performance. Not an issue, could probably do a 360!

> Come on Mark, 1980 vintage hang glider performance. Not an issue, could probably do a 360!

Straight from the Schempp-Hirth Arcus M Flight Manual. Dave Nadler calls it "Plummet Mode."

When we converted four Arcus M gliders to jet power, we measured 38:1 with the engine extended but not running.

wrote on 4/29/2020 5:36 PM:
>
>> Come on Mark, 1980 vintage hang glider performance. Not an issue, could
>> probably do a 360!
>
> Straight from the Schempp-Hirth Arcus M Flight Manual. Dave Nadler calls it
> "Plummet Mode."
>
> When we converted four Arcus M gliders to jet power, we measured 38:1 with the
> engine extended but not running.

38:1 -- is that with the jet engine extended, gear retracted?

I'm astounded a 20M high performance, 50:1 glider can only manage 14:1 with the
pylon out. Is that in landing configuration with the gear extended, also? My 18M
ASH26E is much better than that (about 20:1) with the pylon up and gear extended.
Do you have any idea what makes it so terrible? That's like a PIK 20E!

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

38:1 -- is that with the jet engine extended, gear retracted?

Yes- gear retracted, engine extended but not running.

The biggest cause of the terrible performance of the Arcus M with the prop and pylon up is the fact that the two huge 6 ft. long doors remain open and the big engine bay and the rest of the hole in the fuselage gives all those draggy little air molecules a place to run around before finally jumping out.

The ASH-26E appears to have smaller doors and a smaller engine bay, and possibly less drag because of this.

And for those of you who still don't believe, 495 fpm is 8.25 feet per second. 60 knots is 101.27 feet per second. 101.27/8.25 = 12.275.

At 13:17 30 April 2020, wrote:
>38:1 -- is that with the jet engine extended, gear retracted?
>
>Yes- gear retracted, engine extended but not running.
>
>The biggest cause of the terrible performance of the Arcus M
with the prop
>=
>and pylon up is the fact that the two huge 6 ft. long doors
remain open
>and=
> the big engine bay and the rest of the hole in the fuselage gives
all
>thos=
>e draggy little air molecules a place to run around before finally
jumping
>=
>out.
>
>The ASH-26E appears to have smaller doors and a smaller
engine bay, and
>pos=
>sibly less drag because of this.
>
>And for those of you who still don't believe, 495 fpm is 8.25 feet
per
>seco=
>nd. 60 knots is 101.27 feet per second. 101.27/8.25 =3D
12.275.
>
Just out of interest the electric 20m Antares20E which has a
"book" L/D of 56:1 does 30:1, engine out and prop windmilling,
gear retracted. The main engine doors are closed when the engine
is erected. The prop is stopped by the "electronics", if it throws a
wobbly the pilot has no way to stop the prop. The prop is 2m
diameter, two blades. The engine is direct drive to the prop so the
engine would have had to seize up for the prop to be stopped &
erected. The circuit & landing are a bit of a non event, rather like a
K13.
I've never experienced "plummet mode" in an Arcus; the
DG400/800 plummet rather well.
Dave Walsh

L/D with pylon out highly depends on IAS.
On a Ventus 2 CM with gear up, failed spindle drive, prop stopped, I was getting ~18 L/D at 50 kts. This was dropping fast below 15 L/D when accelerating above 55 kts.

On Thursday, April 30, 2020 at 7:15:04 AM UTC-7, Dave Walsh wrote:
> At 13:17 30 April 2020, wrote:
> >38:1 -- is that with the jet engine extended, gear retracted?
> >
> >Yes- gear retracted, engine extended but not running.
> >
> >The biggest cause of the terrible performance of the Arcus M
> with the prop
> >=
> >and pylon up is the fact that the two huge 6 ft. long doors
> remain open
> >and=
> > the big engine bay and the rest of the hole in the fuselage gives
> all
> >thos=
> >e draggy little air molecules a place to run around before finally
> jumping
> >=
> >out.
> >
> >The ASH-26E appears to have smaller doors and a smaller
> engine bay, and
> >pos=
> >sibly less drag because of this.
> >
> >And for those of you who still don't believe, 495 fpm is 8.25 feet
> per
> >seco=
> >nd. 60 knots is 101.27 feet per second. 101.27/8.25 =3D
> 12.275.
> >
> Just out of interest the electric 20m Antares20E which has a
> "book" L/D of 56:1 does 30:1, engine out and prop windmilling,
> gear retracted. The main engine doors are closed when the engine
> is erected. The prop is stopped by the "electronics", if it throws a
> wobbly the pilot has no way to stop the prop. The prop is 2m
> diameter, two blades. The engine is direct drive to the prop so the
> engine would have had to seize up for the prop to be stopped &
> erected. The circuit & landing are a bit of a non event, rather like a
> K13.
> I've never experienced "plummet mode" in an Arcus; the
> DG400/800 plummet rather well.
> Dave Walsh

Someone please correct me if I am wrong but I believe only 4 Arcus E's were sold and one of those was written off in an accident?

On Wednesday, April 29, 2020 at 5:07:37 PM UTC-7, Ron Gleason wrote:
> On Wednesday, 29 April 2020 17:29:52 UTC-6, wrote:
> > > I'm curious why motorglider pilots don't practice that at 200ft agl, as all student pilots do on aerotows as part of normal training.
> >
> > FYI- the L/D of the Arcus M with mast extended and engine not running is approximately 13:1 with a sink rate in level flight of 495 fpm. Do you want to try a turn back to the runway with those numbers?
>
> Come on Mark, 1980 vintage hang glider performance. Not an issue, could probably do a 360!

As one who has flown many vintage 1980 hang gliders, 13:1 was a dream that we could never achieve! 5 or 6:1 was more typical. 8:1 for the very high end.

The math is, a 50:1 glider at 1000 lbs has 20 lbs of drag. The dynamic pressure of 50 knots is about 8.5 lbs/ft^2. To get to 13:1 you need to add 57 lbs of drag or about 6.7 sq ft of flat plate area. A spinning 5 foot prop is 20 sq ft, not flat plate but pretty high drag coefficient. So it is plausible. On an ASH26 with a stopped prop at 20:1, it's just like landing a clean 2-33 or 1-26. Students do it all the time.

On Thursday, April 30, 2020 at 12:34:24 AM UTC-4, Eric Greenwell wrote:
> I'm astounded a 20M high performance, 50:1 glider can only manage 14:1
> with the pylon out.

Why? Its only been explained here, like a thousand times?
In addition to open engine bay, the large radiator is a lot of drag.

The published min sink rate is at IIRC blue line.
Are you really going to attempt a turn-back at blue line?
No margin, and speed decays VERY rapidly with any inattention and all this drag.

Plummet mode in ArcusM is really not as bad as some older contraptions.

On Wednesday, April 29, 2020 at 5:15:43 PM UTC-4, wrote:
> On Wednesday, April 29, 2020 at 1:03:12 PM UTC-7, waremark wrote:
> > - climb for 200' or so, then set throttle to idle, and do a 180 degree turn,
> > lining up on the that road
> > - repeat the test, but this time, turn the ignition off, then turn as before"

> I'm curious why motorglider pilots don't practice that at 200ft agl

Because we prefer not to die.

On Thursday, April 30, 2020 at 10:48:55 AM UTC-4, Jonathan St. Cloud wrote:
> Someone please correct me if I am wrong but I believe
> only 4 Arcus E's were sold and one of those was written off in an accident?

Those are correct numbers (at least as of a few months ago).

Dave Nadler wrote on 4/30/2020 1:43 PM:
> On Thursday, April 30, 2020 at 12:34:24 AM UTC-4, Eric Greenwell wrote:
>> I'm astounded a 20M high performance, 50:1 glider can only manage 14:1
>> with the pylon out.
>
> Why? Its only been explained here, like a thousand times?

Well, probably because this is the first time I've seen it documented with numbers
from the flight manual. If I had a glider that sank at 500 fpm because the pylon
was extended, I'd sure mention it.

> In addition to open engine bay, the large radiator is a lot of drag.
> The published min sink rate is at IIRC blue line.
> Are you really going to attempt a turn-back at blue line?

First, I would try it at altitude, as I have in my ASH26E. If that worked out, as
it did for my ASH26E, then I would be willing to turn back at the blue line in an
emergency. What do you think is the minimum safe altitude for a turn-back at blue
line in an Arcus M? What do other Arcus M pilots think is a safe altitude?

> No margin, and speed decays VERY rapidly with any inattention and all this drag.
>
> Plummet mode in ArcusM is really not as bad as some older contraptions.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

At 20:45 30 April 2020, Dave Nadler wrote:
>On Thursday, April 30, 2020 at 10:48:55 AM UTC-4, Jonathan St.
Cloud wrote:
>> Someone please correct me if I am wrong but I believe
>> only 4 Arcus E's were sold and one of those was written off in an
>accident?
>
>Those are correct numbers (at least as of a few months ago).
>
The Arcus E has a pretty high wing loading; the one that crashed was
flying near Barcillonette in the southern French Alps, it appears to
have spun in. Neither pilot survived. It's not known whether the wing
loading was a significant factor.
Spinning any open class glider seems to be a hazardous. JM Clement,
who has very extensive gliding experience, is of the opinion that
none of them can be safely spun.

Le vendredi 1 mai 2020 17:15:05 UTC+2, Dave Walsh a écritÂ*:
> At 20:45 30 April 2020, Dave Nadler wrote:
> >On Thursday, April 30, 2020 at 10:48:55 AM UTC-4, Jonathan St.
> Cloud wrote:
> >> Someone please correct me if I am wrong but I believe
> >> only 4 Arcus E's were sold and one of those was written off in an
> >accident?
> >
> >Those are correct numbers (at least as of a few months ago).
> >
> The Arcus E has a pretty high wing loading; the one that crashed was
> flying near Barcillonette in the southern French Alps, it appears to
> have spun in. Neither pilot survived. It's not known whether the wing
> loading was a significant factor.
> Spinning any open class glider seems to be a hazardous. JM Clement,
> who has very extensive gliding experience, is of the opinion that
> none of them can be safely spun.

The Arcus is not an Open Class glider.
Spinning an Open Class glider is suicidal. The moment of inertia of the wings is 3-4 times higher than that of a 15 m glider, but the rudder isn't. That makes that stopping the rotation takes significantly more time than in a small ship, and during this unstalling process the ship starts to accelerates. After the rotation has stopped, there are two choices: Exceeding v_ne, or exceeding max g-load above v_d.
Stupid enough to have been there and done that, lucky enough that the glider was stronger than the designer had expected.

On Friday, May 1, 2020 at 8:27:07 AM UTC-7, Tango Whisky wrote:
> Le vendredi 1 mai 2020 17:15:05 UTC+2, Dave Walsh a écritÂ*:
> > At 20:45 30 April 2020, Dave Nadler wrote:
> > >On Thursday, April 30, 2020 at 10:48:55 AM UTC-4, Jonathan St.
> > Cloud wrote:
> > >> Someone please correct me if I am wrong but I believe
> > >> only 4 Arcus E's were sold and one of those was written off in an
> > >accident?
> > >
> > >Those are correct numbers (at least as of a few months ago).
> > >
> > The Arcus E has a pretty high wing loading; the one that crashed was
> > flying near Barcillonette in the southern French Alps, it appears to
> > have spun in. Neither pilot survived. It's not known whether the wing
> > loading was a significant factor.
> > Spinning any open class glider seems to be a hazardous. JM Clement,
> > who has very extensive gliding experience, is of the opinion that
> > none of them can be safely spun.
>
> The Arcus is not an Open Class glider.
> Spinning an Open Class glider is suicidal. The moment of inertia of the wings is 3-4 times higher than that of a 15 m glider, but the rudder isn't. That makes that stopping the rotation takes significantly more time than in a small ship, and during this unstalling process the ship starts to accelerates. After the rotation has stopped, there are two choices: Exceeding v_ne, or exceeding max g-load above v_d.
> Stupid enough to have been there and done that, lucky enough that the glider was stronger than the designer had expected.

I used fly a Nimbus 4 (best damn glider ever!) and one day while lowish over the local house thermal it started to rotate on me. I was slow on purpose (dry) as I wanted to see how slow it would thermal when I hit small bit turbulence and started to rotate. I smashed the stick to the instrument panel and stood on the opposite rudder. I had it flying in a quarter turn. Would not want to try that wet and perhaps not as keyed up for any problems. I only flew the nimbus without water a few times and frankly spinning anything full of water has all sorts of potential for heartache and hydraulic issues.

The Arcus is not an Open Class glider.

The Arcus E may not be strictly "Open Class" I don't know the strict
definition of "open". But the point I was trying (unsuccessfully) to
make is that the 20m wings are heavy maybe even heavier than
some true open class traditional gliders?
Anyone who has tried to pick up an Antares20E wing will understand.
Arcus E wings have 72 batteries plus associated mounting hardware,
each battery has a heating mantle, there are control electronics
boards every third battery plus the wiring & cooling hardware. As far
as I know it has exactly the same system as the Lange built Antares
20E. (Lange built the "E" bit of the Arcus).
Each battery weighs a little over a kilo so the whole lot possibly
weighs 80-85 kilos, add two pilots and you get high wing loading.
I understand the Arcus with full water ballast is pretty predictable;
maybe a pilot with Arcus E experience could comment on the
handling characteristics.