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FES underpowered for 18m ship?



 
 
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  #51  
Old September 18th 20, 03:16 AM posted to rec.aviation.soaring
2G
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Posts: 1,217
Default FES underpowered for 18m ship?

On Tuesday, September 15, 2020 at 11:25:21 PM UTC-7, 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:
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.


Oh, so you admit that the manual is wrong - my bad!

Tom
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  #52  
Old September 18th 20, 10:16 AM posted to rec.aviation.soaring
andy l
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Default FES underpowered for 18m ship?

On Friday, 18 September 2020 at 03:16:19 UTC+1, 2G wrote:
On Tuesday, September 15, 2020 at 11:25:21 PM UTC-7, Matthew Scutter wrote:



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.

Oh, so you admit that the manual is wrong - my bad!

Tom


Are you actually interested in this subject or not?

A friend has a Ventus 2 with a FES

I asked him about time or distance endurance, and I'm inclined to believe someone I've known for over 30 years, without needing certified statements from other witnesses, plus half their curriculum vitae, as suggested by some over-argumentative type on here.
  #53  
Old September 19th 20, 03:13 AM posted to rec.aviation.soaring
2G
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Posts: 1,217
Default FES underpowered for 18m ship?

On Friday, September 18, 2020 at 2:16:26 AM UTC-7, andy l wrote:
On Friday, 18 September 2020 at 03:16:19 UTC+1, 2G wrote:
On Tuesday, September 15, 2020 at 11:25:21 PM UTC-7, Matthew Scutter wrote:



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.

Oh, so you admit that the manual is wrong - my bad!

Tom


Are you actually interested in this subject or not?

A friend has a Ventus 2 with a FES

I asked him about time or distance endurance, and I'm inclined to believe someone I've known for over 30 years, without needing certified statements from other witnesses, plus half their curriculum vitae, as suggested by some over-argumentative type on here.


I am VERY interested in this subject. You have me waiting with bated breath - what are your friend's results?

Tom

  #54  
Old September 20th 20, 07:24 PM posted to rec.aviation.soaring
[email protected]
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Default FES underpowered for 18m ship?

That is definitely the future and awesome idea Matthew,

Pasi

On Wednesday, September 16, 2020 at 8:34:19 PM UTC+3, Matthew Scutter wrote:
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.

  #55  
Old September 22nd 20, 10:37 PM posted to rec.aviation.soaring
waremark
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Posts: 336
Default FES underpowered for 18m ship?

'I can climb quickly from 200m to 400m (500 - 1200ft) then have
enough left for 75km in stillish air. Low power is more efficient so
if you recognise the day is dying earlier you don’t need to invest
the charge in climbing so range is much better. It will never
match the range of a conventional turbo but will always get you
away from a farmer’s field to an airfield near home.'

Are you saying that you would cruise home level at 1,200 foot above the ground? Depending on the terrain you are flying over, how can that enable you always to have somewhere to land if the motor dies? In my petrol self-launcher, even over fairly flat land, I would typically climb at least to 3,000 foot before leveling off and cruising home at 85 knots (if I am not feeling impatient I generally climb as high as I need to glide home).
  #56  
Old September 24th 20, 02:50 PM posted to rec.aviation.soaring
Kevin Neave[_2_]
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Posts: 68
Default FES underpowered for 18m ship?

It's a different mindset. With your self launcher, and my conventional
turbo, if you start the engine you drive home.

With my FES if I need to climb I only climb as little as possible, then I'm
back in the "Soaring" game to get as close to home as I can. I just have
the option of setting my glide angle to something more favourable. And in
the UK will almost certainly have the option of an Airfield on the way home
if I need it

If the engine dies then I'm still in the same situation all of us are in,
so I don't fly over unlandable terrain with or without the FES running
(I'll make an exception for the Solent)

Flying in the UK 1200ft normally gives a pretty wide choice of fields

KN



At 21:37 22 September 2020, waremark wrote:
'I can climb quickly from 200m to 400m (500 - 1200ft) then have
enough left for 75km in stillish air. Low power is more efficient so
if you recognise the day is dying earlier you don=E2=80=99t need to

invest
the charge in climbing so range is much better. It will never
match the range of a conventional turbo but will always get you
away from a farmer=E2=80=99s field to an airfield near home.'

Are you saying that you would cruise home level at 1,200 foot above the
gro=
und? Depending on the terrain you are flying over, how can that enable

you
=
always to have somewhere to land if the motor dies? In my petrol
self-launc=
her, even over fairly flat land, I would typically climb at least to

3,000
=
foot before leveling off and cruising home at 85 knots (if I am not
feeling=
impatient I generally climb as high as I need to glide home).


  #57  
Old September 24th 20, 04:02 PM posted to rec.aviation.soaring
Stephen Struthers
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Posts: 20
Default FES underpowered for 18m ship?

At 13:50 24 September 2020, Kevin Neave wrote:
t's a different mindset. With your self launcher, and my conventional
turbo, if you start the engine you drive home.

With my FES if I need to climb I only climb as little as possible, then I'

back in the "Soaring" game to get as close to home as I can. I just have
the option of setting my glide angle to something more favourable. And
i the UK will almost certainly have the option of an Airfield on the way
home if I need it

If the engine dies then I'm still in the same situation all of us are in
so I don't fly over unlandable terrain with or without the FES running
(I'll make an exception for the Solent)

Flying in the UK 1200ft normally gives a pretty wide choice of fields

KN

Ok so the UK stops North of Hadrian's wall !!

Like to see you soar round my neck of the woods at 1200 ft AGL lol

(apologies for post hijack)





 




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