Fly-by-wire and gliders

On Thursday, October 30, 2014 6:13:41 PM UTC-7, Dan Marotta wrote:
so...* You want to eliminate all the
things that make soaring challenging?

Dan Marotta
On 10/30/2014 6:04 PM, Ramy wrote:



While I am not looking forward for any automatic controls, I agree with the OP that FBW will significant improve performance. I believe the lost of performance due to inaccurate pilot input, un centered yaw string (heavy foot), non optimal flap position (I estimate I am flying in non optimal flap position maybe 30% of the time especially when doing a lot of transitions), flying too slow/too fast etc hurts performance more than the difference in glide performance between modern gliders.

Ramy

No no, I don't want this, just agreeing with the OP that this will indeed improve performance, but in the account of fun and challenge.

Ramy

On Friday, 31 October 2014 02:04:10 UTC+2, Ramy wrote:
While I am not looking forward for any automatic controls, I agree with the OP that FBW will significant improve performance. I believe the lost of performance due to inaccurate pilot input, un centered yaw string (heavy foot), non optimal flap position (I estimate I am flying in non optimal flap position maybe 30% of the time especially when doing a lot of transitions), flying too slow/too fast etc hurts performance more than the difference in glide performance between modern gliders.

Ramy

Yes and we have to remember that whole concept of conventional glider with tail has built-in-drag as elevator pushes the tail down all the time instead of giving only occasional control inputs. I bet there is several extra % of drag right there, as is in the large wetted area of long rear fuselage and rudder, which is only needed to counteract the yaw created by aileron drag. Flight controls have to be designed to have nice feel and harmony. Would there be more aerodynamically optimal geometries if this would be a non-issue? You could program any control feel you wish to joystick.

New wingprofiles (current are from nineties BTW, Ventus 2 & ASW 27 etc.) could be used with more narrow area of optimum angle-of-attack as FBW could nail it indefinetly while thermalling.

One could speculate with safety aspects as well. FBW would be easily programmed with unability to stall. Think about it, only coordinated turns, if you pull the stick while thermalling low, nose would go up until close to stalling angle of attack but not an inch more.

I believe hardware is coming cheaper and easily available as this is all stuff that UAVs use right now. You probably got most of the required sensors in your pocket right now. And I bet that at least some Akaflieg have studied this concept already.

Would we want FBW controlled glider? Did we want glider made from glassfibre instead of wood during 60s? Electrical varios during 70s? Or GPS in 90s? PW5? (No wait, no-one wanted that.)

THEY ALL RUINED THE SPORT when introduced, remember?

One thing to consider is what will happen when the FBW will fail from some reason and you end up with pilots who don't know how to fly manually as happened to AF447.

Ramy

On 10/31/2014 3:22 PM, Ramy wrote:
One thing to consider is what will happen when the FBW will fail from
some reason and you end up with pilots who don't know how to fly
manually as happened to AF447.

Ramy

Are you saying that simply pushing the "Return to Gliderport" button
might not always be an option?

Vaughn

FBW is the only reasonable way to get rid of the tail surfaces. That's easily 20% of the total drag and an easy 10% of the weight. All in all, I would think a 35-50% increase in performance is possible, once one can deal with the huge issues of implementing a FBW.

20+ years ago, I flew this Speed Canard ( http://en.wikipedia.org/wiki/Gyroflug_Speed_Canard ) . No tail stabilizer, no FBW, and flying it didn't require any special skill (I've never had any ;-) ). Nice to fly. It actually even wouldn't stall.
I guess this proves that instability is actually not a problem. Indeed, if the speeds unwillingly increases, we don't wait for stability to correct, we pitch up ourself well before !
Or do I get it wrong ?

On Tue, 04 Nov 2014 01:53:34 -0800, Francois VG wrote:

20+ years ago, I flew this Speed Canard (
http://en.wikipedia.org/wiki/Gyroflug_Speed_Canard ) . No tail
stabilizer, no FBW, and flying it didn't require any special skill (I've
never had any ;-) ). Nice to fly. It actually even wouldn't stall.
I guess this proves that instability is actually not a problem. Indeed,
if the speeds unwillingly increases, we don't wait for stability to
correct, we pitch up ourself well before !
Or do I get it wrong ?

As I understand it, the main problem with flying wings is that, contrary
to popular superstition, they are not particularly efficient due to the
reflexed wing sections that are often used on flying plank designs, i.e.
no or minimal sweepback, and the often extreme amounts of wash-out that
many swept wing designs need to be stable.

In the competition free flight model world, which requires models to be
auto-stable since they are not remotely controlled, you never see flying
wings in competition with conventional layouts and the designs flown in
specialist tailless competition classes have clearly inferior performance.

Its also noticeable that contemporary 'tailless' high performance gliders
and light aircraft such as the Genesis II, Gyroflug Speed Canard and
VariEZE are *not* tailless designs.

If anybody on the list has flown a true tailless glider, such as the
Hortens or the French Fauvel designs, it would be interesting to hear how
they rate their performance against similar conventional designs.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

"...no tail stabilizer..."

What do you call that canard? ...And those vertical thingies on the
wing tips...

Dan Marotta

On 11/4/2014 2:53 AM, Francois VG wrote:
20+ years ago, I flew this Speed Canard ( http://en.wikipedia.org/wiki/Gyroflug_Speed_Canard ) . No tail stabilizer, no FBW, and flying it didn't require any special skill (I've never had any ;-) ). Nice to fly. It actually even wouldn't stall.
I guess this proves that instability is actually not a problem. Indeed, if the speeds unwillingly increases, we don't wait for stability to correct, we pitch up ourself well before !
Or do I get it wrong ?

I've been intrigued by the no horizontal stab idea for that reason. A clever fellow implemented a simple control system on a model sailplane and was able to achieve this. He explains the design problem really well too. Here's the page for those interested.
http://www.charlesriverrc.org/articl...lke_asfwpp.htm

I wonder what performance hits there may be while thermalling? This is a problem that the Genesis I/II faces.

I'd love to try it on a model glider, but not on full-scale. Too easy to imagine what happens if the angle of attack sensor vane fails... aka the X-31 crash and so on...

On Saturday, November 1, 2014 7:17:12 AM UTC-4, J. Nieuwenhuize wrote:
FBW is the only reasonable way to get rid of the tail surfaces. That's easily 20% of the total drag and an easy 10% of the weight. All in all, I would think a 35-50% increase in performance is possible, once one can deal with the huge issues of implementing a FBW.

Show me a soaring bird without movable tail surfaces, then I might consider it!

Mike