Death of the 13.5m class?

http://www.spr.aero/wcc-main-news/e-...-for-electric-
gliders.aspx

At 08:13 23 December 2017, Paul T wrote:
http://www.spr.aero/wcc-main-news/e-...-for-electric-
gliders.aspx



Rebirth of the (e) standard class. If only we could retrofit FES units to
existing standard class gliders (please)!

On Saturday, December 23, 2017 at 9:00:08 AM UTC-5, Chris Davison wrote:

If olnly we could retrofit FES units to
existing standard class gliders (please)!

problem is weight -- the weight hit on an 18 m (or bigger span) glider matters a lot less than on a 15, and then as they have better L/D you need less total power to sustain them (although don't forget the impact of gross weight)

It's worth going through the numbers just to see what's going on -- first, take the optimistic case:

The power required to fly level is just

P = m * g * v / (L/D)

Taking an 18 m glider at 400 kg gross weight, coming home at 60 kts ≈ 30 m/s and an L/D of 40 yields 2.9 kW (before motor and propeller losses) ... taking 3.2 kW as battery output required would be reasonable.

The very best Lithium-sulfur batteries are now around 400 Wh/kg, but 200 is more typical of common Lithium batteries.

So if you wanted 60 nm return range @ 1 hour cruising time you'd need 16 kg of standard lithium batteries. Motor and propeller for this power will add 4 - 5 ... so up around 20 kg ... sounds good, right?


But if you look, people aren't fitting FES that wimpy. Pilots will want more than 60 nm return range and will want to come home FASTER, also have more margin for sink or headwind en route. The real FES units being put into gliders just about double all the numbers, and that becomes a real load on a 15 m glider ... and L/D at cruise matters, the 18 m ships win there too.

Better batteries are the only thing that can change the equation.

On Saturday, December 23, 2017 at 10:01:38 AM UTC-5, wrote:
On Saturday, December 23, 2017 at 9:00:08 AM UTC-5, Chris Davison wrote:

If olnly we could retrofit FES units to
existing standard class gliders (please)!

problem is weight -- the weight hit on an 18 m (or bigger span) glider matters a lot less than on a 15, and then as they have better L/D you need less total power to sustain them (although don't forget the impact of gross weight)

It's worth going through the numbers just to see what's going on -- first, take the optimistic case:

The power required to fly level is just

P = m * g * v / (L/D)

Taking an 18 m glider at 400 kg gross weight, coming home at 60 kts ≈ 30 m/s and an L/D of 40 yields 2.9 kW (before motor and propeller losses) ... taking 3.2 kW as battery output required would be reasonable.

The very best Lithium-sulfur batteries are now around 400 Wh/kg, but 200 is more typical of common Lithium batteries.

So if you wanted 60 nm return range @ 1 hour cruising time you'd need 16 kg of standard lithium batteries. Motor and propeller for this power will add 4 - 5 ... so up around 20 kg ... sounds good, right?


But if you look, people aren't fitting FES that wimpy. Pilots will want more than 60 nm return range and will want to come home FASTER, also have more margin for sink or headwind en route. The real FES units being put into gliders just about double all the numbers, and that becomes a real load on a 15 m glider ... and L/D at cruise matters, the 18 m ships win there too..

Better batteries are the only thing that can change the equation.

I'm converting a Std class ASW-24E right now from existing engine to electric.
Weight of motor, battery, controller, and prop is 78 lb. Lift mechanism being reused adds another 8. Engine, fuel tanks and other stuff coming out is about 68 lb.
I'm getting 25 kw instead of 17kw at the price of 10 lb and obviously reduced range. Full power run time will be about 12 minutes.
The net weight gain by having the electric stuff in vs pure glider raises my wing loading .8 lb per square foot.
FES alternative in this ship would be about 10 lb lighter.
FWIW
UH

On Saturday, December 23, 2017 at 1:22:04 PM UTC-8, wrote:
On Saturday, December 23, 2017 at 10:01:38 AM UTC-5, wrote:
On Saturday, December 23, 2017 at 9:00:08 AM UTC-5, Chris Davison wrote:

If olnly we could retrofit FES units to
existing standard class gliders (please)!

problem is weight -- the weight hit on an 18 m (or bigger span) glider matters a lot less than on a 15, and then as they have better L/D you need less total power to sustain them (although don't forget the impact of gross weight)

It's worth going through the numbers just to see what's going on -- first, take the optimistic case:

The power required to fly level is just

P = m * g * v / (L/D)

Taking an 18 m glider at 400 kg gross weight, coming home at 60 kts ≈ 30 m/s and an L/D of 40 yields 2.9 kW (before motor and propeller losses) ... taking 3.2 kW as battery output required would be reasonable.

The very best Lithium-sulfur batteries are now around 400 Wh/kg, but 200 is more typical of common Lithium batteries.

So if you wanted 60 nm return range @ 1 hour cruising time you'd need 16 kg of standard lithium batteries. Motor and propeller for this power will add 4 - 5 ... so up around 20 kg ... sounds good, right?


But if you look, people aren't fitting FES that wimpy. Pilots will want more than 60 nm return range and will want to come home FASTER, also have more margin for sink or headwind en route. The real FES units being put into gliders just about double all the numbers, and that becomes a real load on a 15 m glider ... and L/D at cruise matters, the 18 m ships win there too.

Better batteries are the only thing that can change the equation.

I'm converting a Std class ASW-24E right now from existing engine to electric.
Weight of motor, battery, controller, and prop is 78 lb. Lift mechanism being reused adds another 8. Engine, fuel tanks and other stuff coming out is about 68 lb.
I'm getting 25 kw instead of 17kw at the price of 10 lb and obviously reduced range. Full power run time will be about 12 minutes.
The net weight gain by having the electric stuff in vs pure glider raises my wing loading .8 lb per square foot.
FES alternative in this ship would be about 10 lb lighter.
FWIW
UH

I dunno. Seems to me that ultimately most gliders will be fitted with some sort of MOP. Having a race where use of the motor to avoid a landout and continue on course (with a time penalty) is ultimately easier and fairer to score than trying to equate miles to MPH - along with all the attendant methods of day devaluation, etc.

Imagine a scoring system where you get 5 minutes added to your time on course for every minute you run your MOP. If you did a 4 knot climb under power for 15 minutes to get home it would cost you about an incremental hour, so you'd only be inclined to use it when the alternative is landing out.

I'm sure there are all kinds of corner-cases to think through in terms of impact on strategy and of course it's only fair if everyone has a roughly equivalent capabilities. A reliable motor would also be pretty important. Landing out because your motor didn't start would end your contest in a world where everyone else can motor home at a cost of 100 points or so rather than 400 points. Because of the need for ubiquity, I don't see it in mainstream contest flying anytime soon.

I think it's interesting. Bring on the FES kits!

Andy Blackburn
9B

There is a war against landing out. Or at least creeping cultural change against landing out. Remember kids if you let land outs slip from being a normal thing they will eventually be forbidden.

On Saturday, December 23, 2017 at 4:50:23 PM UTC-7, Andy Blackburn wrote:
On Saturday, December 23, 2017 at 1:22:04 PM UTC-8, wrote:
On Saturday, December 23, 2017 at 10:01:38 AM UTC-5, wrote:
On Saturday, December 23, 2017 at 9:00:08 AM UTC-5, Chris Davison wrote:

If olnly we could retrofit FES units to
existing standard class gliders (please)!

problem is weight -- the weight hit on an 18 m (or bigger span) glider matters a lot less than on a 15, and then as they have better L/D you need less total power to sustain them (although don't forget the impact of gross weight)

It's worth going through the numbers just to see what's going on -- first, take the optimistic case:

The power required to fly level is just

P = m * g * v / (L/D)

Taking an 18 m glider at 400 kg gross weight, coming home at 60 kts ≈ 30 m/s and an L/D of 40 yields 2.9 kW (before motor and propeller losses) ... taking 3.2 kW as battery output required would be reasonable..

The very best Lithium-sulfur batteries are now around 400 Wh/kg, but 200 is more typical of common Lithium batteries.

So if you wanted 60 nm return range @ 1 hour cruising time you'd need 16 kg of standard lithium batteries. Motor and propeller for this power will add 4 - 5 ... so up around 20 kg ... sounds good, right?


But if you look, people aren't fitting FES that wimpy. Pilots will want more than 60 nm return range and will want to come home FASTER, also have more margin for sink or headwind en route. The real FES units being put into gliders just about double all the numbers, and that becomes a real load on a 15 m glider ... and L/D at cruise matters, the 18 m ships win there too.

Better batteries are the only thing that can change the equation.

I'm converting a Std class ASW-24E right now from existing engine to electric.
Weight of motor, battery, controller, and prop is 78 lb. Lift mechanism being reused adds another 8. Engine, fuel tanks and other stuff coming out is about 68 lb.
I'm getting 25 kw instead of 17kw at the price of 10 lb and obviously reduced range. Full power run time will be about 12 minutes.
The net weight gain by having the electric stuff in vs pure glider raises my wing loading .8 lb per square foot.
FES alternative in this ship would be about 10 lb lighter.
FWIW
UH

I dunno. Seems to me that ultimately most gliders will be fitted with some sort of MOP. Having a race where use of the motor to avoid a landout and continue on course (with a time penalty) is ultimately easier and fairer to score than trying to equate miles to MPH - along with all the attendant methods of day devaluation, etc.

Imagine a scoring system where you get 5 minutes added to your time on course for every minute you run your MOP. If you did a 4 knot climb under power for 15 minutes to get home it would cost you about an incremental hour, so you'd only be inclined to use it when the alternative is landing out.

I'm sure there are all kinds of corner-cases to think through in terms of impact on strategy and of course it's only fair if everyone has a roughly equivalent capabilities. A reliable motor would also be pretty important. Landing out because your motor didn't start would end your contest in a world where everyone else can motor home at a cost of 100 points or so rather than 400 points. Because of the need for ubiquity, I don't see it in mainstream contest flying anytime soon.

I think it's interesting. Bring on the FES kits!

Andy Blackburn
9B

Use of a motor get distance points from start cylinder to motor on. Pilot and crew save a retrieve effort.

Mike

On Saturday, December 23, 2017 at 5:10:19 PM UTC-8, wrote:
There is a war against landing out. Or at least creeping cultural change against landing out. Remember kids if you let land outs slip from being a normal thing they will eventually be forbidden.


Sound like all that "War on Christmas" talk - 'tis the season - LOL.

I promise you - landing out will never be banned. Do it every day you fly if it pleases you to do so. Just don't ask me to be your retrieve buddy.

;-)

9B

On Saturday, December 23, 2017 at 4:50:23 PM UTC-7, Andy Blackburn wrote:

Imagine a scoring system where you get 5 minutes added to your time on course for every minute you run your MOP. If you did a 4 knot climb under power for 15 minutes to get home it would cost you about an incremental hour, so you'd only be inclined to use it when the alternative is landing out.


Since the

On Saturday, December 23, 2017 at 4:50:23 PM UTC-7, Andy Blackburn wrote:

Imagine a scoring system where you get 5 minutes added to your time on course for every minute you run your MOP. If you did a 4 knot climb under power for 15 minutes to get home it would cost you about an incremental hour, so you'd only be inclined to use it when the alternative is landing out.


Easy fix. Since the motor is to prevent the land-out score it this way:

Starting Motor = Land Out.

The benefit is avoiding the inconvenience of the land out. Back to the airport in time for BBQ and beer, hope for better the next day.