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FES underpowered for 18m ship?



 
 
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  #41  
Old September 15th 20, 11:02 PM posted to rec.aviation.soaring
Ramy[_2_]
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Posts: 601
Default FES underpowered for 18m ship?

Cumungus, you forgot to sign your name, so I need to ask: Do you fly from Truckee? Are you familiar with the area, the return methods, ridge soaring spots and landout options? Did you walk the golf course before?
I believe I answered all your questions in my detailed “I screwed up” report. Will you do the same if you screw up, and sign your name?
And back to the subject, using the FES as I described will eliminate this risk completely. Just make your rule of minimum safe altitude at spooner and stick to your rule and you will never need to land in the golf course. And no, one should not enter as low as I did relying on engine. It is not any safer than relying on ridge lift.

Ramy
  #42  
Old September 15th 20, 11:12 PM posted to rec.aviation.soaring
Dave Nadler
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Posts: 1,610
Default FES underpowered for 18m ship?

On Tuesday, September 15, 2020 at 6:02:32 PM UTC-4, Ramy wrote:
relying on engine... is not any safer than relying on ridge lift.


Its considerably less safe...
  #43  
Old September 15th 20, 11:26 PM posted to rec.aviation.soaring
Eric Greenwell[_4_]
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Posts: 1,939
Default FES underpowered for 18m ship?

Dave Nadler wrote on 9/15/2020 3:12 PM:
On Tuesday, September 15, 2020 at 6:02:32 PM UTC-4, Ramy wrote:
relying on engine... is not any safer than relying on ridge lift.


Its considerably less safe...

You must read the ridges much better than I do :^)

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1
  #44  
Old September 16th 20, 12:35 AM posted to rec.aviation.soaring
Kenn Sebesta
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Posts: 48
Default FES underpowered for 18m ship?

Given your apparent claimed knowledge could you please list available COT components and sources for such a glider.
Motor 25 kw
Controller
Interface
Battery system with BMS and charging system
How hard could it be?
UH


I think we're saying the same thing. For the most part, industrial-grade COTS parts for a glider FES-style system don't exist. They are either an order of magnitude larger (cars) or smaller (robotics).

BTW, don't forget the propeller. There aren't many out there for cruising at 50kts while only absorbing 5kW of power.
  #45  
Old September 16th 20, 01:41 AM posted to rec.aviation.soaring
jfitch
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Posts: 1,134
Default FES underpowered for 18m ship?

Yes, that would work. You need a different strategy (and perhaps different discipline) with the FES vs. an ICE. I usually keep trying until I'm a bit over pattern altitude, then fire. There are some other scenarios such as storm cells over intended destination, land somewhere and wait it out, then continue but these are admittedly rare. I believe every retrieve I have done in flying my ASH at Truckee for 20 years would have been as easily done with an FES. Now it just needs to self launch to 3000 AGL and still be able to do those retrieves, and charge itself somehow on the line overnight.

On Tuesday, September 15, 2020 at 11:11:26 AM UTC-7, Ramy wrote:
John, for the Carson relight you are correct if one waits until pattern altitude at Carson. However the strategy should be to relight over spooner the moment you down to your minimum altitude, say 9K. You will need a short run and only 1-2K climb to get to a safe final glide altitude. If you run out of battery before hand you can escape back to Carson.
At least this is what I would do if I have FES.

Ramy

  #46  
Old September 16th 20, 03:07 AM posted to rec.aviation.soaring
2G
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Posts: 1,439
Default FES underpowered for 18m ship?

On Monday, September 14, 2020 at 11:54:00 PM UTC-7, Matthew Scutter wrote:
On Tuesday, September 15, 2020 at 7:29:17 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 9:06:08 PM UTC-7, wrote:
Hi Eric,

I agree with you in principle, that for higher output powers, things must get bigger/heavier. However, I don't think this is the case here. The 2x batteries they use (datasheet below) are spec'd for ~40 kW discharge rate. The more realistic limiting factor might be how quickly they can dissipate heat from the batteries' internal resistance out of the battery compartment, but according to Matthew, this hasn't been a problem.
http://www.front-electric-sustainer....% 20v1.25.pdf

They would have to have a bigger inverter to handle the 40% higher input current when the batteries discharge from 4.2v-3.0v, but these ~20 kW class inverters weigh nothing (1-2 kg) compared to the batteries.
https://www.mgm-compro.com/brushless...e-controllers/

I'd be interested to hear FES's reasoning, or other owners' experiences on why the power dropoff is so significant.

Patrick Grady

I am amazed that this is even being speculated upon. How hard is it to do FES climb performance runs? You simply take off and climb until the battery (or controller) shuts down. Then, you repeat this test 5-10 times. Then you repeat that test for a different glider. Why isn't this data readily available? I can only guess that this test has been done and it is not favorable to FES.

There are many FES installations out there - if you have one, do this test and report the results.

Tom

Not readily available? It's in the flight manual. If I adjust for 5.3kWh vs 4kWh batteries and 350kg weight of the Diana 2, it's ~2000m, which matches my napkin math from partial runs.
As for why owners haven't tried it - it sounds boring...

5.3.4 Powered flight performance
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

5.3.4.2 Cruise flight
The maximum range of powered cruising flight, without the water ballast, is around
100km (62 miles), depending on lift-sink conditions.
The optimum cruise speed and flap position depend on the type of sailplane. Usually,
it is about 90 km/h (48 kts) at around 3000-3300 RPM and 4kW of power with a positive
flap setting, as used in thermals.


And you REALLY believe that? If so, I've got a bridge for sale. No, I want to see the INDEPENDENT verification of this data.

Tom
  #47  
Old September 16th 20, 07:25 AM posted to rec.aviation.soaring
Matthew Scutter
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Posts: 42
Default FES underpowered for 18m ship?

On Wednesday, September 16, 2020 at 4:07:16 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 11:54:00 PM UTC-7, Matthew Scutter wrote:
On Tuesday, September 15, 2020 at 7:29:17 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 9:06:08 PM UTC-7, wrote:
Hi Eric,

I agree with you in principle, that for higher output powers, things must get bigger/heavier. However, I don't think this is the case here. The 2x batteries they use (datasheet below) are spec'd for ~40 kW discharge rate. The more realistic limiting factor might be how quickly they can dissipate heat from the batteries' internal resistance out of the battery compartment, but according to Matthew, this hasn't been a problem.
http://www.front-electric-sustainer....% 20v1.25.pdf

They would have to have a bigger inverter to handle the 40% higher input current when the batteries discharge from 4.2v-3.0v, but these ~20 kW class inverters weigh nothing (1-2 kg) compared to the batteries.
https://www.mgm-compro.com/brushless...e-controllers/

I'd be interested to hear FES's reasoning, or other owners' experiences on why the power dropoff is so significant.

Patrick Grady
I am amazed that this is even being speculated upon. How hard is it to do FES climb performance runs? You simply take off and climb until the battery (or controller) shuts down. Then, you repeat this test 5-10 times. Then you repeat that test for a different glider. Why isn't this data readily available? I can only guess that this test has been done and it is not favorable to FES.

There are many FES installations out there - if you have one, do this test and report the results.

Tom

Not readily available? It's in the flight manual. If I adjust for 5.3kWh vs 4kWh batteries and 350kg weight of the Diana 2, it's ~2000m, which matches my napkin math from partial runs.
As for why owners haven't tried it - it sounds boring...

5.3.4 Powered flight performance
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

5.3.4.2 Cruise flight
The maximum range of powered cruising flight, without the water ballast, is around
100km (62 miles), depending on lift-sink conditions.
The optimum cruise speed and flap position depend on the type of sailplane. Usually,
it is about 90 km/h (48 kts) at around 3000-3300 RPM and 4kW of power with a positive
flap setting, as used in thermals.


And you REALLY believe that? If so, I've got a bridge for sale. No, I want to see the INDEPENDENT verification of this data.

Tom


Only on RAS do you get called biased or asked if you really believe your own experiences owning and operating - couldn't make it up if you tried. Regrettably my certification as an independent standards body is still processing. My only comment on the manuals data validity would be the 4kW is not applicable to all types, the cruising flight power estimate should be scaled like the climb altitude. The heavier HpH Sharks at eGlide this year told me they were cruising with 5-6kW.
  #48  
Old September 16th 20, 03:44 PM posted to rec.aviation.soaring
Darren Braun
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Posts: 20
Default FES underpowered for 18m ship?

With RC front electric gliders you need a soft brake to keep the prop from windmilling in flight. Is that the same engine-not-running drag referred to here? i.e do today's FES have a failure mode like this?
  #49  
Old September 16th 20, 06:34 PM posted to rec.aviation.soaring
Matthew Scutter
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Posts: 42
Default FES underpowered for 18m ship?

On Wednesday, September 16, 2020 at 4:44:36 PM UTC+2, Darren Braun wrote:
With RC front electric gliders you need a soft brake to keep the prop from windmilling in flight. Is that the same engine-not-running drag referred to here? i.e do today's FES have a failure mode like this?


Yes it does, I have had it windmill from inadvertently hitting the power off rather throttling down first a few times. I have no idea how much drag it really is, but I was able to continue climbing in a thermal while I restarted it to then stop it properly.
What I'd really like to see is the ability to actually recharge the batteries via the propeller brake, imagine prestart after a self launch, waiting for the line to open for an hour at cloudbase, slowly charging back up. Maybe someone can do the numbers on the drag that would be induced to charge at 1kW to determine if that's a totally harebrained idea.

Flight manual again:
3.7.2 Power loss during flight
If power is lost during flight, the propeller will windmill. Push the control stick
forward gently, to sustain the desired airspeed! You can perform the following actions to
try and restore power:
1. Check first if you unintentionally switched OFF the power switch!
Warning: This can happen in gliders that thave the landing gear lever and
the power switch located on the same side of the cockpit when retracting
the landing gear, i.e. LAK17A&B FES.
If this happens, switch power switch ON and adjust the throttle.
Note: On earlier software versions (before v2.13), it was necessary to
reduce throttle bar to zero manually; otherwise motor did not start due to
safety. Motor restarted when the throttle was reduced to zero
New versions (from FCU v2.13) automatically reset the throttle!
2. If the power switch is ON:
• Switch OFF the “Power switch” and the FCU.
• Turn ON the FCU and check for strange behaviour.
• If the FCU has no issues switch the power switch ON and try to start the motor.
The motor starts but behaves strangely under power:
• Stop the propeller from the windmilling with the electronic brake..
• When the propeller stops, switch OFF the power switch and the FCU..
If you are not able to stop the propeller with the electronic brake, you will need to land
with a windmilling propeller. Note: it is not possible to stop the propeller by
reducing airspeed. Try to land on both landing wheels simultaneously, to avoid potential
damage of the propeller.
Note: It is probably better to use a grass runway in good condition if one is
available than a concrete runway. If the grass runway is in bad shape, use a
concrete runway if one is available.
Warning: Try to avoid landing into high grass or similar.
Note: The L/D of a sailplane with a windmilling propeller is reduced only by
a small amount. With enough altitude will have enough time to choose a
suitable landing field.
  #50  
Old September 17th 20, 06:58 AM posted to rec.aviation.soaring
Paul T[_4_]
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Posts: 259
Default FES underpowered for 18m ship?

At 06:25 16 September 2020, Matthew Scutter wrote:
On Wednesday, September 16, 2020 at 4:07:16 AM UTC+2, 2G wrote:
On Monday, September 14, 2020 at 11:54:00 PM UTC-7, Matthew

Scutter
wrote=
:=20
On Tuesday, September 15, 2020 at 7:29:17 AM UTC+2, 2G

wrote:=20
On Monday, September 14, 2020 at 9:06:08 PM UTC-7,


=
wrote:=20
Hi Eric,=20
=20
I agree with you in principle, that for higher output powers,

thing=
s must get bigger/heavier. However, I don't think this is the case here.
Th=
e 2x batteries they use (datasheet below) are spec'd for ~40 kW

discharge
r=
ate. The more realistic limiting factor might be how quickly they can
dissi=
pate heat from the batteries' internal resistance out of the battery
compar=
tment, but according to Matthew, this hasn't been a problem.=20

http://www.front-electric-

sustainer.com/Manuals/FES%20BATTERY%20PAC=
K%20GEN2%2014S%2040Ah%20manual%20v1.25.pdf=20
=20
They would have to have a bigger inverter to handle the 40%

higher
=
input current when the batteries discharge from 4.2v-3.0v, but these

~20
kW=
class inverters weigh nothing (1-2 kg) compared to the batteries.=20

https://www.mgm-compro.com/brushless...rollers/33-kw-

medium=
-voltage-controllers/=20
=20
I'd be interested to hear FES's reasoning, or other owners'

experie=
nces on why the power dropoff is so significant.=20
=20
Patrick Grady=20
I am amazed that this is even being speculated upon. How hard

is it
t=
o do FES climb performance runs? You simply take off and climb until

the
ba=
ttery (or controller) shuts down. Then, you repeat this test 5-10 times.
Th=
en you repeat that test for a different glider. Why isn't this data
readily=
available? I can only guess that this test has been done and it is not
fav=
orable to FES.=20
=20
There are many FES installations out there - if you have one, do

this=
test and report the results.=20
=20
Tom=20
Not readily available? It's in the flight manual. If I adjust for

5.3kW=
h vs 4kWh batteries and 350kg weight of the Diana 2, it's ~2000m,

which
mat=
ches my napkin math from partial runs.=20
As for why owners haven't tried it - it sounds boring...=20
=20
5.3.4 Powered flight performance=20
5.3.4.1 Rate of climb=20
The maximum rate of climb is available only for a few minutes

with
full=
y charged=20
battery packs. As battery voltage is reduced, the maximum

achievable
cl=
imb rate is lower.=20
The average rate of climb depends mostly on the type of sailplane

and
i=
ts take-off weight.=20
Maximum attainable altitude gain that in standard atmosphere

conditions=
depends on=20
the type of sailplane, its weight and aerodynamic qualities. To

achieve=
the maximum=20
altitude gain, use about 15kW of power. Do not use full power as

the
ef=
ficiency of the=20
system is lower. Usually, 80-85 km/h is best for the climb with

positiv=
e flap setting (the=20
same setting as used while thermaling). Here are rough

numbers:=20
=E2=80=A2 1600 m (5200 ft) for UL sailplanes at 300kg take-off

weight,
=
i.e. Silent 2 Electro=20
=E2=80=A2 1400 m (4500 ft) for the 18m class sailplanes at

400kg
take-o=
ff weight (without=20
water ballast), i.e. LAK17A FES=20
=E2=80=A2 1200 m (3900 ft) for the 18m class sailplanes at

450kg
take-o=
ff weight (without=20
water ballast); LAK17B FES, Ventus 2cxa FES, Discus 2c FES, HPH

304ES=
=20
=20
5.3.4.2 Cruise flight=20
The maximum range of powered cruising flight, without the water

ballast=
, is around=20
100km (62 miles), depending on lift-sink conditions.=20
The optimum cruise speed and flap position depend on the type of

sailpl=
ane. Usually,=20
it is about 90 km/h (48 kts) at around 3000-3300 RPM and 4kW of

power
w=
ith a positive=20
flap setting, as used in thermals.=20

=20
And you REALLY believe that? If so, I've got a bridge for sale. No, I

wan=
t to see the INDEPENDENT verification of this data.=20
=20
Tom


Only on RAS do you get called biased or asked if you really believe

your
ow=
n experiences owning and operating - couldn't make it up if you tried.


Your command of the English language is limited obviously. You have not
been called biased - it was posed as a question - since you have and
operate a FES glider and voiced an opinion. There is a lot of BS floated
about in gliding often not backed up with substantive data that's all.

 




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