Climbing out of turns issue

[Colin Anderson]

Previously my plane had a tendency to climb as it straightened out of a turn, after which it levels off slightly higher in the exit than that of entry.

On rechecking the CG I felt it was to far aft, following the fitting of a new tailplane and a different electric motor. I've since corrected this and the plane now balances slightly nose down. I have some down and side thrust added to the motor. I also checked the decalage and this is 0, using a semi symmetrical wing and a flat tailplane.

The plane is perfect in the glide, with slight elevator down trim; which it doesn't really need. With the now corrected CG the plane now flies much better. However, it still climbs slightly straightening out from the turn before settling into level flight. I was flying today in flat calm, so I don't think this is to do with coming into wind (it's in both directions) and it doesn't do this when turning in the glide.

My thought is that the plane needs more down thrust. What do you guys think?

[Mike Bell]

Hi Colin. If the c of g and wing incidence are correct then down thrust could help. If you open the throttle in level flight does it nose up then? If so it could be thrust line. Also try the dive test to confirm c of g ie from level flight nose down into a 45 degree dive and neutralise the controls. If it keeps going in the same direction without a pronounced climb or steepening of the dive, the c of g is probably good.

Mike

[Dave Hopkin]

Check you are not mentally keeping a little up elevator as you exit the turn

[Denis Watkins]

There are a couple of things to consider Colin, but 1 st may I ask if your model has a flat bottom wing?

[Biggles' Elder Brother - Moderator]

Colin,

in a turn the lift produced by the wing is divided between two tasks:

1. One, upward, component of the total lift is supporting the weight of the aircraft - as usual.

2. A second, inward, component is providing the centripedal acceleration and actually turning the aircraft.

This obviously requires more total lift than simple level flight whe only the first component is needed. We get this extra lift by increasing the main wing's angle of attack during the turn by pulling a little up-elevator.

However, if when we unbank and straighten-up the aircraft on coming out of the turn, we still have some of this additional angle of attack in, then we will have a surplus of lift. The upward lift will now exceed the downward weight and as a result the aeroplane will climb.

It could be that the model is hanging on to its slight "nose-slight-up" attitude a littkle longer than we want, with the associated higher AoA.

You're simpliest solution may be to just be a little more "positive" in letting out the up-elevator held in the turn - perhaps even with a tiny touch of over-correction to down.

I have found that not everything can be "trimmed out" for all aircraft - sometimes you just have to adapt your flying style a little and that's the essence of skill!

BEB

[john stones 1 - Moderator]

Yep i like that, trim it out with your thumbs

[Colin Anderson]

Thank you all for your replies. Where to start?

1. The model is Chapter One, an electric high wing trainer.

2. The wing is semisymmetrrical, with minimal dihedral.

3. Decalage is 0.

4. My first thought was that it was me, keeping pressure on the stick to keep the nose up in the turn, so I deliberately didn't apply any elevator during the turn and let go of the stick the moment the wings levelled.

5. It doesn't occurr in the glide, even when I put the nose down to gain speed.

6. This characteristic only appeared after replacing the tailplane and motor, following a crash; suggesting that I've unwittingly changed the previous setup.

7. I'll try the 45 degree test - power on or off? I've tried a shallow dive only and, under these circumstances the plane self corrects.

[Don Fry]

point 4 does not compute. Trainers like yours climb under power. It's a safe mode. If it turned with level flight without loss of hight, it must have too much power on. Then when straightened will climb. See BEB's technical whyfore, above.

Try a bit of throttle management during the turn. You may be simply getting a bit better in seeing deviations in flight as you get more experienced.

[Colin Anderson]

Donald. It does drop its nose in a turn, but then climbs as it comes out of it, without me applying any elevator. If I leave the stick and throttle alone it climbs briefly then settles into level flight. And yes, it does climb under power, as it should and the more power I give it the faster and higher it climbs.

I must admit, I'd not actually thought of your last point. You might very well be right. 😊

[Biggles' Elder Brother - Moderator]

Yes Donald is spot on. I'm afraid the test in 4 doesn't prove anything.

You see in "normal" (that is to say fully manual) flight if you are flying straight and level then enter a turn with no up-elevator - you must descend. Simply because now, because the lift is shared with the centripetal force, there isn't enough lift left over to support the weight - so we descend. If you now straighten up you will stop descending and this may look like a climb - relatively speaking. Possibly?

On the other hand, if you don't descend in such a "no-elevator" turn then you must be applying more power as Donald suggests, this increases your airspeed and so your lift goes up - by the square of the speed.

BEB

[Biggles' Elder Brother - Moderator]

Actually, analying deeper, if you do a no-elevator turn, you will descend as I say. But you will also probably gain speed as you trade potential energy for kinetic energy. This means you exit the turn slight faster than you entered. This could result in a zoom (short term temporary climb) which stops once the drag kicks in and slows the aircraft back to its equilibrium speed for the throttle setting you have.

That would explain what you see.

BEB

Edited By Biggles' Elder Brother - Moderator on 16/12/2016 20:57:30

[Colin Anderson]

BEB. Thanks. The way you describe it is a pretty accurate description of what I am seeing. What do advise? Is this then, simply a question of modifying my flying technique?

[Biggles' Elder Brother - Moderator]

Yes I think so. You will find some models do this kind of thing - and some don't. Gaining experience as a flyer is all about getting used to all these little "features" that some models display.

As you progress you will get to flying precision aerobatic models - one of the reasons they are so popular with pilots is that they are very neutral in their handling and don't sjhow this sort of "character". They just go where youy point them.

But at the other extreme if flying scale models is your bag they they have tons of "character" and when we say they are "challenging" to fly we generally means lots of features such like this. The irony is that top aerobatics pilots are often praised as "great pilots" - while the guy that flies a very smooth and realistic routine with a WWI fighter, whilst praised for his building ability, often his flying goes unnoticed. But in my book his skill, in coping with 20 "features" like you describe and "hiding" them so the model flies well, though less noticeable, is every bit as high as the flashy aerobatics pilot!

BEB

[john stones 1 - Moderator]

Like a duck paddling upstream, all looks calm on the surface, but works being done you don't see, that's the best bit though

Edited By john stones 1 on 16/12/2016 23:14:48

[Colin Anderson]

Thanks BEB that is indeed encouraging. I shall persevere. I've come a little ways since you advised me a while back on my Cub. I'm still learning; although, at present I'm flying electric, until I get better. I've changed clubs since (from Slough to Maidenhead) because the first one had no instructors. I got past the buddy box and graduated to solo. I still get things wrong on occasions, when my enthusiasm gets the better of my skill.

Thanks, as always for sharing your knowledge. It's appreciated.

[Biggles' Elder Brother - Moderator]

Its what the forum's all about Colin - helping each other. We're all learning - we're just at different points on the curve that's all!

BEB

[Colin Leighfield]

BEB's spot on about the learning curve. I'm on the other side of it and getting worse.

[Bob Cotsford]

You and me both Colin! This zooming was a standard characteristic in the old days when slower flying 3 channel trainers that had evolved from single channel or free-flight designs ruled. I'd forgotten about it until I tried some vintage cabin models for a change of pace.

[Ben B]

Most people pull elevator in turns and consequently the "climbs after turning" phenomenon is pure artefact. There's a variation on a theme about flat-bottomed wings climbing when turning into wind. To me this is just people pulling more elevator to compensate for the ground speed vs air-speed difference and to prevent drift, they then fail to release the elevator at the correct time and it climbs. A plane circling around a drifting hot air balloon would not demonstrate this behaviour- it's all to do with the pilot being on the ground.

[Colin Anderson]

Thanks for the fascinating insight Bob. It would appear that, at least for the time being, I should leave well alone.

[Denis Watkins]

Don't loose sight guys, with the novice in mind, that a flat bottom wing is able to land more slowly than a similar sized counterpart with a symmetrical wing, and is favoured on many high wing trainers

[Peter Christy]

Colin: Does your model have ailerons, or is it rudder / elevator / throttle?

If you are turning it on rudder, then when coming out of a banked turn, the rudder will also act as a slight "up elevator" (look at the model, and think about it!).

If you do have ailerons, do you have any differential on them? Given equal area and throw in both directions, it is not unusual for ailerons to produce "adverse yaw" - ie: to yaw the aircraft in the opposite direction to the roll. On models, it is generally fairly minimal, but might account for what you are seeing. The solution is to have more "up" than "down" aileron. This is usually easily achieved by offsetting the links on the servo disk slightly.

On the glide, when the model is descending anyway, the effect of either of the above may not be so noticeable, but at the end of the day, you may just have to live with it and learn to fly with its quirks!

I have a scale helicopter with a mechanical flybar-less system, and it behaves a bit like a Sopwith Camel, pitching the nose up when turning in one direction, and down in the other - and quite markedly too! There's nothing I can do to trim it out - I just have to live with it, and be careful when turning onto final approach in the "nose down" direction!!!

--

Pete

[Colin Anderson]

Hi Peter,

My model has ailerons and yes I do have differential on them. The rudder on this plane appears to be pretty ineffectual when it is in the air and I only ever use it on take off (it's linked to the tailwheel) - but then I built it with less dihedral than it was designed with (because I'd learnt to fly with a Wot4).

It is because the plane doesn't "zoom" coming out of the turn on the glide that I assumed that this action was down to not enough down thrust. I also noticed that as I make the turn on finals, when I'm throttling back to lose height, it doesn't exhibit this behaviour either.

I shall persevere and learn its foibles. 😊

[Mike T]

Colin,

Everything you've said in your several posts on this thread leads me to conclude that you have a very nicely set up aeroplane! It's doing exactly what I would expect under power in turns, ditto on the glide. You don't appear to have to input huge corrections to maintain height, or juggle the throttle to maintain an even rate of descent on 'finals'.

Sometimes you just have to learn to live with perfection...

[Colin Anderson]

Mike,

Finals used to make me nervous, 'cause that meant landing. But recently everything seems to be coming together and on my last flying session, in spite of what I've posted here, my plane - Chapter One - made the approach and landing very easy; although I am picking calm days until I gain more confidence.