FES climb rate question.

[JM LN]

Hi everybody.
I would like to know the opinion of a owner of a HPH Shark with FES.
Which is the true climb rate?.
Somebody has proven to use FES like a supplement tow mechanism?. I mean, how efficient is take a tow to 300 or 400 m and later start FES to climb at 900 or 1000 m.

Thank you very much.

Juan.

[Peter F[_2_]]

So you're spending 150k Euro on your glider then trying to save a few Euro
per launch on the tow?

The climb rate of a FES glider easily beats the traditional Turbos but do
you really want to use up the limited duration of the batteries in this
phase of the flight?

You'd be better off taking the higher tow & saving the FES for the retrieve
if needed.
Or take the lower tow & soar

PF

At 22:27 07 October 2020, JM LN wrote:
>Hi everybody.
>I would like to know the opinion of a owner of a HPH Shark with FES.
>Which is the true climb rate?.
>Somebody has proven to use FES like a supplement tow mechanism?. I mean,
>how efficient is take a tow to 300 or 400 m and later start FES to climb
at
>900 or 1000 m.
>
>Thank you very much.
>
>Juan.
>

[Matthew Scutter]

On Thursday, October 8, 2020 at 12:00:07 PM UTC+2, Peter F wrote:
> So you're spending 150k Euro on your glider then trying to save a few Euro
> per launch on the tow?
>
> The climb rate of a FES glider easily beats the traditional Turbos but do
> you really want to use up the limited duration of the batteries in this
> phase of the flight?
>
> You'd be better off taking the higher tow & saving the FES for the retrieve
> if needed.
> Or take the lower tow & soar
>
> PF
> At 22:27 07 October 2020, JM LN wrote:
> >Hi everybody.
> >I would like to know the opinion of a owner of a HPH Shark with FES.
> >Which is the true climb rate?.
> >Somebody has proven to use FES like a supplement tow mechanism?. I mean,
> >how efficient is take a tow to 300 or 400 m and later start FES to climb
> at
> >900 or 1000 m.
> >
> >Thank you very much.
> >
> >Juan.
> >
You'll get at least 2m/s dry. But like PF says, better to take a tow to 400m and use the FES straight and level until you find a thermal. It's much more efficient in level flight than climbing.

[JM LN]

El jueves, 8 de octubre de 2020 a las 12:00:07 UTC+2, Peter F escribió:
> So you're spending 150k Euro on your glider then trying to save a few Euro
> per launch on the tow?
>
> The climb rate of a FES glider easily beats the traditional Turbos but do
> you really want to use up the limited duration of the batteries in this
> phase of the flight?
>
> You'd be better off taking the higher tow & saving the FES for the retrieve
> if needed.
> Or take the lower tow & soar
>
> PF
> At 22:27 07 October 2020, JM LN wrote:
> >Hi everybody.
> >I would like to know the opinion of a owner of a HPH Shark with FES.
> >Which is the true climb rate?.
> >Somebody has proven to use FES like a supplement tow mechanism?. I mean,
> >how efficient is take a tow to 300 or 400 m and later start FES to climb
> at
> >900 or 1000 m.
> >
> >Thank you very much.
> >
> >Juan.
> >
Thank you Peter.
The idea is not to take a tow and release early.
Now I have a turbo discus and all my tow are at 500 or 600 m, but if the day is weak and lose the fisrt thermal when I start the turbo at 300 m I usually can not climb. Whe this happen the zone near the aerodrome is dead even you find descendet air and usually the mountain works, but it is a litle far away. I was thinking in this kind of situation. If I will move to a FES glider I want to be sure it can climb at 2m/s, and you can travel to the mountain gaining height.
Regards.

[Mana]

> You'll get at least 2m/s dry. But like PF says, better to take a tow to 400m and use the FES straight and level until you find a thermal. It's much more efficient in level flight than climbing.

On the Shark, based on a test flight I think that you will get less than 2m/s as it is a heavier glider than Matthew's Diana 2 :-).

From the FES manual:
5.3.4.1 Rate of climb
The maximum rate of climb is available only for a few minutes with fully charged battery packs. As battery voltage is reduced, the maximum achievable climb rate is lower. The average rate of climb depends mostly on the type of sailplane and its take-off weight. Maximum attainable altitude gain that in standard atmosphere conditions depends on the type of sailplane, its weight and aerodynamic qualities. To achieve the maximum altitude gain, use about 15kW of power. Do not use full power as the efficiency of the system is lower. Usually, 80-85 km/h is best for the climb with positive flap setting (the same setting as used while thermaling). Here are rough numbers:
•1600 m (5200 ft) for UL sailplanes at 300kg take-off weight, i.e. Silent 2 Electro
•1400 m (4500 ft) for the 18m class sailplanes at 400kg take-off weight (without water ballast), i.e.LAK17A FES
•1200 m (3900 ft) for the 18m class sailplanes at 450kg take-off weight (without water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH 304ES

[2G]

On Thursday, October 8, 2020 at 1:14:30 PM UTC-7, Mana wrote:
> > You'll get at least 2m/s dry. But like PF says, better to take a tow to 400m and use the FES straight and level until you find a thermal. It's much more efficient in level flight than climbing.
>
> On the Shark, based on a test flight I think that you will get less than 2m/s as it is a heavier glider than Matthew's Diana 2 :-).
>
> From the FES manual:
> 5.3.4.1 Rate of climb
> The maximum rate of climb is available only for a few minutes with fully charged battery packs. As battery voltage is reduced, the maximum achievable climb rate is lower. The average rate of climb depends mostly on the type of sailplane and its take-off weight. Maximum attainable altitude gain that in standard atmosphere conditions depends on the type of sailplane, its weight and aerodynamic qualities. To achieve the maximum altitude gain, use about 15kW of power. Do not use full power as the efficiency of the system is lower. Usually, 80-85 km/h is best for the climb with positive flap setting (the same setting as used while thermaling). Here are rough numbers:
> •1600 m (5200 ft) for UL sailplanes at 300kg take-off weight, i.e.. Silent 2 Electro
> •1400 m (4500 ft) for the 18m class sailplanes at 400kg take-off weight (without water ballast), i.e.LAK17A FES
> •1200 m (3900 ft) for the 18m class sailplanes at 450kg take-off weight (without water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH 304ES

Sounds like a very marginal self-launch system and is really just a decent self-retrieve (turbo) setup.

Tom

[[email protected]]

Dne pátek 9. Å™Ã*jna 2020Â*vÂ*2:54:13 UTC+2 uživatel 2G napsal:
> On Thursday, October 8, 2020 at 1:14:30 PM UTC-7, Mana wrote:
> > > You'll get at least 2m/s dry. But like PF says, better to take a tow to 400m and use the FES straight and level until you find a thermal. It's much more efficient in level flight than climbing.
> >
> > On the Shark, based on a test flight I think that you will get less than 2m/s as it is a heavier glider than Matthew's Diana 2 :-).
> >
> > From the FES manual:
> > 5.3.4.1 Rate of climb
> > The maximum rate of climb is available only for a few minutes with fully charged battery packs. As battery voltage is reduced, the maximum achievable climb rate is lower. The average rate of climb depends mostly on the type of sailplane and its take-off weight. Maximum attainable altitude gain that in standard atmosphere conditions depends on the type of sailplane, its weight and aerodynamic qualities. To achieve the maximum altitude gain, use about 15kW of power. Do not use full power as the efficiency of the system is lower. Usually, 80-85 km/h is best for the climb with positive flap setting (the same setting as used while thermaling). Here are rough numbers:
> > •1600 m (5200 ft) for UL sailplanes at 300kg take-off weight, i..e. Silent 2 Electro
> > •1400 m (4500 ft) for the 18m class sailplanes at 400kg take-off weight (without water ballast), i.e.LAK17A FES
> > •1200 m (3900 ft) for the 18m class sailplanes at 450kg take-off weight (without water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH 304ES
> Sounds like a very marginal self-launch system and is really just a decent self-retrieve (turbo) setup.
>
> Tom
HI
stefan langer discus capabilities of Shark FES in some of his videos, I dont remenber exact number but you can try wach it.
https://www.youtube.com/user/SLSoaring

[kinsell]

On 10/8/20 6:54 PM, 2G wrote:
> On Thursday, October 8, 2020 at 1:14:30 PM UTC-7, Mana wrote:
>>> You'll get at least 2m/s dry. But like PF says, better to take a tow to 400m and use the FES straight and level until you find a thermal. It's much more efficient in level flight than climbing.
>>
>> On the Shark, based on a test flight I think that you will get less than 2m/s as it is a heavier glider than Matthew's Diana 2 :-).
>>
>> From the FES manual:
>> 5.3.4.1 Rate of climb
>> The maximum rate of climb is available only for a few minutes with fully charged battery packs. As battery voltage is reduced, the maximum achievable climb rate is lower. The average rate of climb depends mostly on the type of sailplane and its take-off weight. Maximum attainable altitude gain that in standard atmosphere conditions depends on the type of sailplane, its weight and aerodynamic qualities. To achieve the maximum altitude gain, use about 15kW of power. Do not use full power as the efficiency of the system is lower. Usually, 80-85 km/h is best for the climb with positive flap setting (the same setting as used while thermaling). Here are rough numbers:
>> •1600 m (5200 ft) for UL sailplanes at 300kg take-off weight, i.e. Silent 2 Electro
>> •1400 m (4500 ft) for the 18m class sailplanes at 400kg take-off weight (without water ballast), i.e.LAK17A FES
>> •1200 m (3900 ft) for the 18m class sailplanes at 450kg take-off weight (without water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH 304ES
>
> Sounds like a very marginal self-launch system and is really just a decent self-retrieve (turbo) setup.
>
> Tom
>

These gliders are sustainers only.

[kinsell]

On 10/12/20 8:46 AM, kinsell wrote:
> On 10/8/20 6:54 PM, 2G wrote:
>> On Thursday, October 8, 2020 at 1:14:30 PM UTC-7, Mana wrote:
>>>> You'll get at least 2m/s dry. But like PF says, better to take a tow
>>>> to 400m and use the FES straight and level until you find a thermal.
>>>> It's much more efficient in level flight than climbing.
>>>
>>> On the Shark, based on a test flight I think that you will get less
>>> than 2m/s as it is a heavier glider than Matthew's Diana 2 :-).
>>>
>>> Â*From the FES manual:
>>> 5.3.4.1 Rate of climb
>>> TheÂ* maximum rateÂ* of climbÂ* isÂ* availableÂ* onlyÂ* forÂ* aÂ* few
>>> minutesÂ* withÂ* fullyÂ* charged battery packs. As battery voltage is
>>> reduced, the maximum achievable climb rate is lower. The average rate
>>> of climb depends mostly on the type of sailplane and its take-off
>>> weight. Maximum attainable altitude gain that in standard atmosphere
>>> conditions depends on the typeÂ* ofÂ* sailplane,Â* itsÂ* weightÂ* and
>>> aerodynamicÂ* qualities.Â* To achieve the maximum altitudeÂ* gain, use
>>> aboutÂ* 15kWÂ* ofÂ* power. DoÂ* notÂ* useÂ* fullÂ* powerÂ* asÂ* the
>>> efficiencyÂ* ofÂ* the systemÂ* isÂ* lower. Usually, 80-85Â* km/h isÂ* best
>>> for theÂ* climb with positive flapÂ* setting (the same setting as used
>>> while thermaling). Here are rough numbers:
>>> •1600 m (5200 ft) for UL sailplanes at 300kg take-off weight, i.e.
>>> Silent 2 Electro
>>> •1400Â* m (4500Â* ft)Â* forÂ* theÂ* 18mÂ* classÂ* sailplanesÂ* atÂ* 400kg
>>> take-off weightÂ* (without water ballast), i.e.LAK17A FES
>>> •1200Â* mÂ* (3900Â* ft) forÂ* theÂ* 18mÂ* classÂ* sailplanesÂ* atÂ* 450kg
>>> take-off weightÂ* (without water ballast); LAK17B FES, Ventus 2cxa
>>> FES, Discus 2c FES, HPH 304ES
>>
>> Sounds like a very marginal self-launch system and is really just a
>> decent self-retrieve (turbo) setup.
>>
>> Tom
>>
>
> These gliders are sustainers only.

Looks like the Silent 2 is rated for self-launch.

[Eric Greenwell[_4_]]

kinsell wrote on 10/12/2020 11:40 AM:
> On 10/12/20 8:46 AM, kinsell wrote:
>> On 10/8/20 6:54 PM, 2G wrote:
>>> On Thursday, October 8, 2020 at 1:14:30 PM UTC-7, Mana wrote:
>>>>> You'll get at least 2m/s dry. But like PF says, better to take a tow to 400m and use the
>>>>> FES straight and level until you find a thermal. It's much more efficient in level flight
>>>>> than climbing.
>>>>
>>>> On the Shark, based on a test flight I think that you will get less than 2m/s as it is a
>>>> heavier glider than Matthew's Diana 2 :-).
>>>>
>>>> *From the FES manual:
>>>> 5.3.4.1 Rate of climb
>>>> The* maximum rate* of climb* is* available* only* for* a* few minutes* with* fully* charged
>>>> battery packs. As battery voltage is reduced, the maximum achievable climb rate is lower.
>>>> The average rate of climb depends mostly on the type of sailplane and its take-off weight.
>>>> Maximum attainable altitude gain that in standard atmosphere conditions depends on the
>>>> type* of* sailplane,* its* weight* and aerodynamic* qualities.* To achieve the maximum
>>>> altitude* gain, use about* 15kW* of* power. Do* not* use* full* power* as* the efficiency
>>>> of* the system* is* lower. Usually, 80-85* km/h is* best for the* climb with positive flap
>>>> setting (the same setting as used while thermaling). Here are rough numbers:
>>>> •1600 m (5200 ft) for UL sailplanes at 300kg take-off weight, i.e. Silent 2 Electro
>>>> •1400* m (4500* ft)* for* the* 18m* class* sailplanes* at* 400kg take-off weight* (without
>>>> water ballast), i.e.LAK17A FES
>>>> •1200* m* (3900* ft) for* the* 18m* class* sailplanes* at* 450kg take-off weight* (without
>>>> water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH 304ES
>>>
>>> Sounds like a very marginal self-launch system and is really just a decent self-retrieve
>>> (turbo) setup.
>>>
>>> Tom
>>>
>>
>> These gliders are sustainers only.
>
> Looks like the Silent 2 is rated for self-launch.

As is the miniLak FES, also a 13.5M glider. It works well for them because they are lighter
than the 18M gliders.

--
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

[Mana]

As is the new LAK 17c FES https://www.youtube.com/watch?v=rxe6DIfPKb4

More prop clearance, 16s batteries and higher max RPM for 2.5 m/s climb rate. The angle of attack of the wing is smaller, back to what it was on the 17a (vs the 17b that was based on the fuselage of the LAK 19)

> >> These gliders are sustainers only.
> >
> > Looks like the Silent 2 is rated for self-launch.
> As is the miniLak FES, also a 13.5M glider. It works well for them because they are lighter
> than the 18M gliders.
>
> --
> Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)

[[email protected]]

On Monday, October 12, 2020 at 3:18:05 PM UTC-5, Mana wrote:
> As is the new LAK 17c FES https://www.youtube.com/watch?v=rxe6DIfPKb4
>
> More prop clearance,

Looks like keeping the tail down is interesting at 1:30 in the video.
What does the POH ask you to do with the stick?

If you use it to hold down the tail and hit a bump, then how high can the tail bounce before entering lawn mower mode?

Technically self launch, but with grass or tiger country, the tow line didn't look all that long and having the batteries full seems wise.

[waremark]

Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud.

Any idea what the endurance is of that aircraft?

As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that.

[2G]

On Friday, October 16, 2020 at 7:11:13 AM UTC-7, waremark wrote:
> Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud.
>
> Any idea what the endurance is of that aircraft?
>
> As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that.

I would like to know if it can even launch to 2,100 ft without the motor/controller overheating.

Tom

[John Foster]

On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
> Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud.
>
> Any idea what the endurance is of that aircraft?
>
> As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that.

Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move.

[2G]

On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote:
> On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
> > Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud.
> >
> > Any idea what the endurance is of that aircraft?
> >
> > As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that.
>
> Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move.

My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500. If you do the math, this works out to 454 mph, well below the speed of sound. Few GA aircraft have props that go supersonic, and you can really tell those few that can.

Tom

[Kenn Sebesta]

> Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move.

You're right that a fair amount of noise comes from the prop, and in particular that petrol vs electric won't change this.

However, I do not agree that it's because of breaking the sound barrier. Good prop design will keep the max tip speed below 0.6-0.7 Mach at max RPM and flight speed. It would be extremely hard to spin a well-specced prop fast enough that you'd see tips breaking the sound barrier. In an airplane which doesn't have a prop specifically designed to work transsonic (which AFAIK is pretty much any airplane outside of a handful of research ones), the prop loses so much efficiency as the tips approach Mach that you either actually slow down or dramatically increase the required engine power.

[Eric Greenwell[_4_]]

John Foster wrote on 10/16/2020 4:53 PM:
> On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
>> Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud.
>>
>> Any idea what the endurance is of that aircraft?
>>
>> As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that.
>
> Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move.
>
The longer the propeller, the slower it turns.

--
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

[andy l]

On Saturday, 17 October 2020 at 00:53:50 UTC+1, wrote:
> Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move.

It does happen, but rarer than you think. The Harvard is an example that comes to mind.

For me, the only one. Maybe design has moved on a bit since then

[Martin Gregorie[_6_]]

On Fri, 16 Oct 2020 16:53:48 -0700, John Foster wrote:

> Much of the noise you hear from any propeller-driven aircraft comes from
> the tips of the propeller breaking the sound barrier. That won't
> change between an electric vs petrol engine.
>
True, provided that the prop diameter, number of prop blades and RPM are
the same.

> The longer the propeller, the faster the tips move.
>
True only if the RPM stays the same.

The quietest propeller-driven aircraft I've heard is the Antares 20 - it
uses a large (2m diameter), slow turning two blade propeller. From 50m to
the side all you can hear as it accelerates past you on take-off is a
quiet fluttering/puttering noise.

At the other end of the scale, for shear prop-generated racket you can't
beat a CRESCO top-dressing aircraft - but you'll need to visit NZ during
the top-dressing season to hear that, unless your local jump club has a
CESCO PAC-750, which is probably just as loud.


--
Martin | martin at
Gregorie | gregorie dot org

[Dan Marotta]

The CalAir A-9b, for instance...

On 10/16/2020 8:50 PM, 2G wrote:
> On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote:
>> On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
>>> Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud.
>>>
>>> Any idea what the endurance is of that aircraft?
>>>
>>> As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that.
>> Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move.
> My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500. If you do the math, this works out to 454 mph, well below the speed of sound. Few GA aircraft have props that go supersonic, and you can really tell those few that can.
>
> Tom

--
Dan, 5J

[Dan Marotta]

To follow up, if my simple arithmetic is correct, a 94 inch propeller
spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second.Â*
According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a
typical summer density altitude of, say, 8,800' MSL, the CalAir's prop
tips are supersonic.

But I may have screwed up the math...

On 10/17/2020 10:09 AM, Dan Marotta wrote:
> The CalAir A-9b, for instance...
>
> On 10/16/2020 8:50 PM, 2G wrote:
>> On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote:
>>> On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
>>>> Take-off performance looks impressive. I was surprised by the
>>>> amount of noise - sounded not unlike a petrol engined aircraft as
>>>> it passed the camera, although presumably it is actually much less
>>>> loud.
>>>>
>>>> Any idea what the endurance is of that aircraft?
>>>>
>>>> As the owner of a petrol self-launcher, I like to know that I have
>>>> enough endurance for a launch to 2,100 feet (700 m), a relight if
>>>> necessary, and a reasonable self-retrieve later if necessary. I
>>>> will stick to petrol until batteries can cope with at least that.
>>> Much of the noise you hear from any propeller-driven aircraft comes
>>> from the tips of the propeller breaking the sound barrier.Â*Â* That
>>> won't change between an electric vs petrol engine.Â* The longer the
>>> propeller, the faster the tips move.
>> My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500.
>> If you do the math, this works out to 454 mph, well below the speed
>> of sound. Few GA aircraft have props that go supersonic, and you can
>> really tell those few that can.
>>
>> Tom
>

--
Dan, 5J

[Mike Reid]

Your math seems correct, but the speed of sound varies with temperature, and not pressure, so if your density altitude is 8800' because it is 90º F, then the speed of sound is 1252 fps and the tips are subsonic.

Mike

[Dan Marotta]

Thanks for that!Â* But come to Moriarty and listen to the unholy racket
that the CalAir makes.

On 10/17/2020 2:21 PM, Mike Reid wrote:
> Your math seems correct, but the speed of sound varies with temperature, and not pressure, so if your density altitude is 8800' because it is 90º F, then the speed of sound is 1252 fps and the tips are subsonic.
>
> Mike

--
Dan, 5J

[Martin Gregorie[_6_]]

On Sat, 17 Oct 2020 16:38:14 -0600, Dan Marotta wrote:

> Thanks for that!Â* But come to Moriarty and listen to the unholy racket
> that the CalAir makes.
>
Louder than these?

https://www.youtube.com/watch?v=XSGYL3j5EXo
(105.5 dB at 50m 400hp piston)

https://www.youtube.com/watch?v=YOTwJ1ASz1c
(750hp turboprop)


--
Martin | martin at
Gregorie | gregorie dot org

[2G]

On Saturday, October 17, 2020 at 9:16:27 AM UTC-7, Dan Marotta wrote:
> To follow up, if my simple arithmetic is correct, a 94 inch propeller
> spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second.Â*
> According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a
> typical summer density altitude of, say, 8,800' MSL, the CalAir's prop
> tips are supersonic.
>
> But I may have screwed up the math...
>
> On 10/17/2020 10:09 AM, Dan Marotta wrote:
> > The CalAir A-9b, for instance...
> >
> > On 10/16/2020 8:50 PM, 2G wrote:
> >> On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote:
> >>> On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
> >>>> Take-off performance looks impressive. I was surprised by the
> >>>> amount of noise - sounded not unlike a petrol engined aircraft as
> >>>> it passed the camera, although presumably it is actually much less
> >>>> loud.
> >>>>
> >>>> Any idea what the endurance is of that aircraft?
> >>>>
> >>>> As the owner of a petrol self-launcher, I like to know that I have
> >>>> enough endurance for a launch to 2,100 feet (700 m), a relight if
> >>>> necessary, and a reasonable self-retrieve later if necessary. I
> >>>> will stick to petrol until batteries can cope with at least that.
> >>> Much of the noise you hear from any propeller-driven aircraft comes
> >>> from the tips of the propeller breaking the sound barrier.Â*Â* That
> >>> won't change between an electric vs petrol engine.Â* The longer the
> >>> propeller, the faster the tips move.
> >> My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500.
> >> If you do the math, this works out to 454 mph, well below the speed
> >> of sound. Few GA aircraft have props that go supersonic, and you can
> >> really tell those few that can.
> >>
> >> Tom
> >
>
> --
> Dan, 5J

What MG has such a prop? That is about 2.4m, 0.85m larger than the ASH26/31..

Tom

[Dan Marotta]

Not a motor glider.Â* The Callair A-9
<https://www.google.com/search?q=callair+a9&safe=active&rlz=1C1CHBD_enUS892US893&sxsrf=ALeKk01KWvhDfRd1SaXXBOzZmMichhcvyA:160323510 8039&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiTmOyYpMTsAhUFQ80KHQUmC9IQ_AUoAXoECAcQA w&biw=1536&bih=722&dpr=2.5#imgrc=L7sDan_WSLAatM>
is an ag-plane.Â* I did some research and it seems the prop diameter is
84 inches instead of 94 inches.Â* I thought I measured it, but that was a
long time ago...

On 10/19/2020 6:53 PM, 2G wrote:
> On Saturday, October 17, 2020 at 9:16:27 AM UTC-7, Dan Marotta wrote:
>> To follow up, if my simple arithmetic is correct, a 94 inch propeller
>> spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second.
>> According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a
>> typical summer density altitude of, say, 8,800' MSL, the CalAir's prop
>> tips are supersonic.
>>
>> But I may have screwed up the math...
>>
>> On 10/17/2020 10:09 AM, Dan Marotta wrote:
>>> The CalAir A-9b, for instance...
>>>
>>> On 10/16/2020 8:50 PM, 2G wrote:
>>>> On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote:
>>>>> On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
>>>>>> Take-off performance looks impressive. I was surprised by the
>>>>>> amount of noise - sounded not unlike a petrol engined aircraft as
>>>>>> it passed the camera, although presumably it is actually much less
>>>>>> loud.
>>>>>>
>>>>>> Any idea what the endurance is of that aircraft?
>>>>>>
>>>>>> As the owner of a petrol self-launcher, I like to know that I have
>>>>>> enough endurance for a launch to 2,100 feet (700 m), a relight if
>>>>>> necessary, and a reasonable self-retrieve later if necessary. I
>>>>>> will stick to petrol until batteries can cope with at least that.
>>>>> Much of the noise you hear from any propeller-driven aircraft comes
>>>>> from the tips of the propeller breaking the sound barrier.Â*Â* That
>>>>> won't change between an electric vs petrol engine.Â* The longer the
>>>>> propeller, the faster the tips move.
>>>> My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500.
>>>> If you do the math, this works out to 454 mph, well below the speed
>>>> of sound. Few GA aircraft have props that go supersonic, and you can
>>>> really tell those few that can.
>>>>
>>>> Tom
>> --
>> Dan, 5J
> What MG has such a prop? That is about 2.4m, 0.85m larger than the ASH26/31.
>
> Tom

--
Dan, 5J

[2G]

On Tuesday, October 20, 2020 at 4:45:35 PM UTC-7, Dan Marotta wrote:
> Not a motor glider.Â* The Callair
> A-9 is an ag-plane.Â* I did some research and it seems the prop
> diameter is 84 inches instead of 94 inches.Â* I thought I measured
> it, but that was a long time ago...
>
>
>
>
> On 10/19/2020 6:53 PM, 2G wrote:
>
>
>
> On Saturday, October 17, 2020 at 9:16:27 AM UTC-7, Dan Marotta wrote:
>
>
> To follow up, if my simple arithmetic is correct, a 94 inch propeller
> spun at 2,700 rpm achieves a tip speed of about 1,107 feet per second.Â*
> According to NASA, 1,100 fps at sea level is the speed of sound.Â* At a
> typical summer density altitude of, say, 8,800' MSL, the CalAir's prop
> tips are supersonic.
>
> But I may have screwed up the math...
>
> On 10/17/2020 10:09 AM, Dan Marotta wrote:
>
>
> The CalAir A-9b, for instance...
>
> On 10/16/2020 8:50 PM, 2G wrote:
>
>
> On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote:
>
>
> On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
>
>
> Take-off performance looks impressive. I was surprised by the
> amount of noise - sounded not unlike a petrol engined aircraft as
> it passed the camera, although presumably it is actually much less
> loud.
>
> Any idea what the endurance is of that aircraft?
>
> As the owner of a petrol self-launcher, I like to know that I have
> enough endurance for a launch to 2,100 feet (700 m), a relight if
> necessary, and a reasonable self-retrieve later if necessary. I
> will stick to petrol until batteries can cope with at least that.
>
>
> Much of the noise you hear from any propeller-driven aircraft comes
> from the tips of the propeller breaking the sound barrier.Â*Â* That
> won't change between an electric vs petrol engine.Â* The longer the
> propeller, the faster the tips move.
>
>
> My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500.
> If you do the math, this works out to 454 mph, well below the speed
> of sound. Few GA aircraft have props that go supersonic, and you can
> really tell those few that can.
>
> Tom
>
>
>
>
> --
> Dan, 5J
>
>
> What MG has such a prop? That is about 2.4m, 0.85m larger than the ASH26/31.
>
> Tom
>
>
>
>
>
> --
>
> Dan, 5J

That is a big difference and means that the tip speed is 675mph, well below the speed of sound.

Tom