stall recovery

[Spice Cat]

Evening team,

I have been flying my HK Skyeye on FPV and have managed to stall three times now. Normally its on the cross wind leg when preparing for landing.

This is high rear mounted and facing motor type glider with a large wing chord.

Normally it's the left wing that drops and then she spirals in. What action do you recommend as I understand the engine placement and thrust angle can have an effect of flight characteristics.

Any recovery will have be done with the goggles on by the way.

Regards.

Edited By Spice Cat on 06/07/2016 18:54:26

[cymaz]

Start with a lateral balance check. And add weight to the light wing uunit the model balances level.

[trebor]

Can't you slip them off when coming in to land when your lined up ? Sounds like your coming in too slow.

[Peter Miller]

Simple, make a faster approach. The stall is caused by too slow an approach and too high an angle of attack.Come in faster which will mean that you do not have to have the nose so high. No stall.

Edited By Peter Miller on 06/07/2016 19:11:56

[Martin Harris - Moderator]

You need to learn to judge airspeed by attitude. Make sure there's a recognisable part of the airframe in the camera view and relate that to the horizon. Consider re-trimming a little nose down from normal cruising trim - preferably once you get into your landing circuit - and use your competent observer to prompt you if the model's attitude starts to get nose high.

If you do drop a wing, use rudder to pick it up, not ailerons (if the model has them) and move the stick forward to un-stall the wing.

[PatMc]

I agree with Peter & Martin up to Martin's last sentence.

Trying to pick a wing up with rudder when near the stall is the best way to enter a spin, use ailerons [or co-ordinated rud + ail] instead but don't get close to the stall on approach anyway.

When I was learning to fly full size gliders in Slingsby T21 & T31 the landing approach was the fastest part of the flight apart from the winch launch.

Edited By PatMc on 06/07/2016 19:35:06

[Martin Harris - Moderator]

Once a wing drops, using aileron increases the angle of attack of that part of the wing, deepening the stall and adding in-spin drag at the wing tip. When I instructed in gliders, great emphasis was put on recovery from the incipient spin (i.e. wing drop) by using opposite rudder. In fact, most training gliders would actually require the application of out-spin aileron in order to provoke a full spin!

Edited By Martin Harris on 06/07/2016 19:41:34

[PatMc]

Using rudder causes a yaw which increases the stall speed, if you're near to the stall that risks a spin. That's the recipe for spin entry when doing aerobatics.

Best not to be near stall speed in the first place when close to the ground.

[Martin Harris - Moderator]

I agree with your second paragraph!

However, if a wing drops at low altitude in any aircraft I'm in, I would have a violent disagreement with any pilot who tried to pick the wing up with aileron!

Or maybe the BGA instructors course and every written treatise I've read on the subject were wrong and I survived multiple incipient spin demonstrations and practices by pupils somewhat miraculously!

Edited By Martin Harris on 06/07/2016 20:11:30

[Denis Watkins]

Just to add, too forward a C of G can cause some models to induced spin quite easily. Double check the C of G, and not so much of this "nose down attitude" that is often quoted.

Ideally, set the model level with the horizon

[Biggles' Elder Brother - Moderator]

Sorry Denis - but I just don't understand that at all! Would you care to expand on:

a) How a forward CoG induces a spin?

b) How being nose down is problem with regard to stalling and/or spinning?

BEB

[Martin Harris - Moderator]

Judging the correct attitude will depend on the camera position...

[Martin Harris - Moderator]

I was given dispensation to fly with an overly forward C of G when an exceptionally large individual turned up for a week's course. Spinning was not an option - it was difficult enough to get enough elevator power to flare for the landings - extra speed and precise timing was key so teaching landings was a challenge to say the least!

[Spice Cat]

Thanks everyone!. It seems to me that I am slowing things down too much. As for taking off the googles; noooooo that's the best part!

I'll keep the speed up and use the rudder. Would it be advisable to feed in power too???

[trebor]

Have you got the hang of landing this without the goggles on ?

[Spice Cat]

Yes, but I seem to manage better landings with them on!!

[Martin Harris - Moderator]

Posted by Spice Cat on 06/07/2016 21:06:29:

Thanks everyone!. It seems to me that I am slowing things down too much. As for taking off the googles; noooooo that's the best part!

I'll keep the speed up and use the rudder. Would it be advisable to feed in power too???

That's something you'll find debate over due to torque and slipstream effects - apparently the RAF don't advise any power changes and aerobatic pilots often use power to aid recovery. Opinion differs in other circles...

Edited By Martin Harris on 06/07/2016 21:14:02

[Denis Watkins]

I am fully aware that I do not fit in with the clique on this site, and that my comments are stripped down and criticised frequently, but I love flying and being an instructor, and from experience and learning, I know much of what I write to be the truth and hopefully of some use and help to someone. Its nice reading through the site and believing that one can help in someway. I be gone now, never to darken your doorstep again, thankyou

[Martin Harris - Moderator]

Don't take BEB's correction to heart - but perhaps you should know that he is a university professor and teaches aerodynamics. We all get things wrong from time to time but it doesn't mean your opinions aren't valued.

I'm unaware of any cliquiness on the site - there are those who express strong and forthright opinions, sometimes correctly and sometimes not - they will be challenged and corrected but no-one I'm aware of takes sides...

Edited By Martin Harris on 06/07/2016 21:24:24

[Biggles' Elder Brother - Moderator]

SC - we are in danger here of perpetuating the myth that stalling is caused by flying too slowly - it isn't!

Only one thing causes a stall - having too high an angle of attack - ie too "nose-up". That is 100% the cause and so the only solution is to reduce the angle of attack - nothing else will work. More speed? No. More power? No. Only dropping the nose will recover a stall.

There is a good reason why people get confused about this and think that the cause is low speed. As you reduce speed your lift drops off. So you tend to pull back, increasing the angle of attack of the wing and so enabling the wing to make more lift so you can hold your altitude. But as we know, there is a limit to this process - take the AoA too far, beyond the critical value for your wing profile, and you stall.

Did the low speed cause the stall? No. It was a provoking and accompanying factor true - but it was not the cause. The cause was you pulling the nose up too high and detaching the airflow from the upper surface of the wing. So the only way you can fix this is to let the nose come down, and so allow the air to re-attach and get the lift back.

If you doubt this - then consider; you can stall your model at full throttle, maximum speed in a dive! Speed is no defence against stalling! If the AoA is too high the wing will stall - no matter how fast you are flying!

BEB

[trebor]

Posted by Spice Cat on 06/07/2016 21:11:30:

Yes, but I seem to manage better landings with them on!!

Must be really difficult to get your speed and hight right !

[Biggles' Elder Brother - Moderator]

Posted by Denis Watkins on 06/07/2016 21:14:14:

I am fully aware that I do not fit in with the clique on this site, and that my comments are stripped down and criticised frequently, but I love flying and being an instructor, and from experience and learning, I know much of what I write to be the truth and hopefully of some use and help to someone. Its nice reading through the site and believing that one can help in someway. I be gone now, never to darken your doorstep again, thankyou

Denis - I did not mean to offend you - In fact I didn't even disagree, I merely asked you to expand on your views - I'm interested in why you think what you do! Surrely that's not confrontational?

BEB

[Spice Cat]

Posted by Martin Harris on 06/07/2016 21:17:18:

Don't take BEB's correction to heart - but perhaps you should know that he is a university professor and teaches aerodynamics. We all get things wrong from time to time but it doesn't mean your opinions aren't valued.

Second that. It appears to me that not everyone agrees on aerodynamic principles indeed as I understand it there is some chap working on turbulence and if he cracks it it will revolutionize wing design. Indeed I found it amusing that there are scientists that still believe the earth is flat. The Flat Earth Society is still going strong and I understand you by a tee shirt from them.

I am interested to hear what you have to say about the c of g as I have moved the battery around a bit and it's a bit of a lump.

Regards.

Edited By Spice Cat on 06/07/2016 21:28:47

[Spice Cat]

Posted by Biggles' Elder Brother - Moderator on 06/07/2016 21:24:36:

Posted by Denis Watkins on 06/07/2016 21:14:14:

I am fully aware that I do not fit in with the clique on this site, and that my comments are stripped down and criticised frequently, but I love flying and being an instructor, and from experience and learning, I know much of what I write to be the truth and hopefully of some use and help to someone. Its nice reading through the site and believing that one can help in someway. I be gone now, never to darken your doorstep again, thankyou

Denis - I did not mean to offend you - In fact I didn't even disagree, I merely asked you to expand on your views - I'm interested in why you think what you do! Surrely that's not confrontational?

BEB

Don't call me Shirley.....

[Biggles' Elder Brother - Moderator]

BEB