Turning without loss of altitude

[Bruce Austin]

Hi there fellow gliders guiders and thermal hunters.

I am getting some encouragingly longer (motor off) flights out of my Phoenix 2000.

I am getting the C of G close to optimum, and able to "see" when my glider is close to and entering thermals.

My "downfall" at present is the loss of altitude due to my poor circling techniques.

The phoenix has no dihedral and I am wondering if that is a factor.

However, if there are a few suggestions that might help me, I would be ever so grateful.

I do use the rudder and a bit of aileron to start the turn and feed in a bit of elevator to try to keep the nose from dropping. But generally the nose does drop losing at least two or three meters and sometimes worse.

I have also put in a bit of expo on all of these controls to be less sensitive near the stick centres. I think this has been a wee bit of help.

Perhaps I am flying too close to stalling speed???

Go With the Flow

Bruce

 

Edited By Bruce Austin on 01/08/2016 20:57:09

[The real Ron Truth]

Bruce,

I'm no expert and am experimenting like you. i didn't realise until recently that with thermals comes downdrafts. As soon as you leave a thermal you can hit these and sink several meters.

it is possible you are also close to the stall and a thermal tips the model up and stalls.

[Bruce Austin]

Ah yes Bent rocker, thank you for responding.

I have also made that observation when i am flying straight. As you hit the thermal the plane lifts up bodily, more or less on an even keel, but slightly nose up, and then drops, again on an even keel, on the other side of the thermal. That is to be expected and a great indicator.

My problem, and the question is, that when I bank to turn back to rejoin the thermal, the nose tends to drop and lose altitude. What techniques are needed to reduce the problem????

Go With the Flow

[Kevin Wilson]

Bruce a flat turn is initiated with rudder and the roll countered by opposite aileron.
But I recently had a few flights in a full size glider and the pilot turned on aileron and elevator. He only used rudder to keep the glider clean ie pointing the right way. I commented on the angle of bank and he was not perturbed, stating there was still plenty of wing and lift. I couldn't disagree as he was making a fair ascent.
I was surprised just how much he yanked it round.
We need some glider experts to help us out here.
I enjoy my P2k enormously.

[john stones 1 - Moderator]

No thermalling expert either Bruce, but if you've got the hang of turning flat sounds like you're killing the speed with too much elevator, easy done when models high up, I think you're seeing a slight stall rather than seeing sink.

I do it myself with the same model.

John

[Kevin Wilson]

Also don't forget that as soon as you are rolled over the rudder is pushing the nose down.
Something that I quickly learnt in the flat turn world of indoor flying.
Try turning on aileron and not worry too much about the bank. After all the full size do not flat turn and they go up quite nicely.
I was told the secret with gliding was do everything gently. Each deflection of control surface costs altitude.

Edited By Kevin Wilson on 01/08/2016 22:13:01

[Martin Harris - Moderator]

I'm no model thermalling expert but I did spend several hundred hours thermalling in full size. All turns are balanced - initiated with aileron and rudder together and coordinated to balance the adverse yaw produced by the effects of the ailerons along with appropriate elevator input to maintain correct pitch attitude (i.e. speed) - and flown at well above stalling speed. Full size thermals are quite large - a few hundred feet diameter - the art is to centre in the area of best lift and in some cases in narrow thermals, best results are had at considerably over 45 degrees of bank.

"What do you mean, full size thermals?" I can hear people saying. It's unusual to thermal below five or six hundred feet for two reasons, the first is self-preservation as an inadvertent spin at low altitude is usually fatal and secondly, thermals that low are normally disorganised and bitty. These are the thermals that model pilots are trying to use. It's probably no coincidence that cases of model pilots losing models in thermals where they "can't get down" happen at height and are probably due to trying to escape in a variety of directions and actually staying within the same thermal.

I would think that you are indeed stalling (I know it happens to me sometimes when thermalling my models) but I'm a very occasional model glider flyer so more regular glider guiders may have developed some better techniques that they may share.

Edited By Martin Harris on 01/08/2016 22:58:21

[will -0]

Hi, a couple of points based on hours an hours of thermalling, though again less with the models:

1) you'll tend to slow down when you fly into lift. If you let this get too much you will stall and lose height

2) turning a glider will always increase the sink rate due to a whole bundle of maths but mainly due to the fact that you're now producing more lift than you have to in straight and level.

3) Additionally with a model you're almost certainly side slipping to some extent which is hard to avoid as you]ve no onboard reference for slip. This will increase the sink rate!

[Simon Chaddock]

Like Martin I spent many hours in thermals - or trying to find them - in full size gliders and now thermal models enthusiastically so I will add my observations.

A large part of the skill is recognising when lift is there, which side it really is and doing something about it immediately - before you fly out the other side.

As other have pointed out 'sink' is likely around a thermal so 'going on through' is not a good idea hence the particularly steep initial turn.

From my full size experience thermals, particularly at low altitude, have an inward radial component as well as upward so although the bank may look steep the airflow itself is inclined thus the 'aerodynamic' bank is a bit less.

Most thermals get stronger and narrow a bit as they rise so it pays to maintain a reasonable angle of bank to keep in the strongest lift. Thermals do 'open out' at altitude - frequently in cloud but that is not an area models should get into!

Also remember the wind 'cants' a thermal over at an angle so don't expect to circle in the same spot (viewed from the ground) once you are established. Try and visualise where the thermal started and where it is going. there is likely to be a cloud to mark it. Don't be fooled by the ground wind direction. Thermal activity can play all sort sorts tricks. Look at the direction the clouds are moving.

Finally making good use of thermals requires a degree of 'feel'. Much harder to do from the ground than with your back side in the cockpit - unless of course you have the benefit of a local buzzard to guide you. They are really good at it.

 

 

Edited By Simon Chaddock on 02/08/2016 01:34:48

[The real Ron Truth]

Good points Simon. I was taught to think of thermals as mini tornados always going downwind. You must follow the thermal even if its going away from you. i also learnt that higher altitude thermals are so much more powerful than low level itty bitty ones which dissolve quickly.

I spent a lot of wasted time trying to work low level thermals only to experience the real deal higher up, not much but around 300-400ft.

[Bruce Austin]

Well now glider guys, this has turned into a very helpful exercise, with all these various observations from both "seat of the pants" flyers as well as the "thumb twitchers" like myself.

Kevin you struck a chord with me, about the rudder starting to push the nose down in the bank. I hadn't thought about that, and it is so clear to me that in my case, this could certainly be happening.

I read somewhere that too many guys are flying without using the rudder, so I have been focussed on using it, as that would be the least air disturbing surface.

I do have to say, though, with my Phoenix 2000, the rudder does not seem to have a lot of authority, and I generally do use the ailerons for gentle directional changes also.

It seems that I must trim the elevator down a tad to increase my speed just a wee bit.

Thank you all, for taking the time to try to help me and others improve our flying skills.

Go With the Flow

Bruce

Expo on all surfaces to soften the controls near centre.

Hmmmm, lots more experimentation needed, but isn't that just the joy of this model flying hobby.

Thank you

[russ d]

Hi, if you can find a copy of "Radio Control Thermal Gliding" by Markus Lisken & Ulf Gerber, well worth a read and I found helped with my thermal flying (it's probably a bit old now but the theory's still the same !).

r.

[KiwiKid]

Hi Bruce, yep some good advice here. Just a comment on the Phoenix 2000, a friend of mine has one and I have had a fly of it and it couldn't in all honesty be considered as a great thermaler. Part of the reason you are losing height when banking may be the wing loading, which I think is up around 25+ ounces per square foot. I found the model to be great fun as a roust about park flyer and it makes an excellent slope soarer.

So, you can view it as a good thermal trainer and maybe look at getting something in the future with a lower wing loading to really enjoy the thrill of hooking the those elusive thermals.

Edited By KiwiKid on 02/08/2016 15:49:09

[Bruce Austin]

Yes KiwiKid, I just love the Phoenix 2000. I have been flying it for the last two years, having first started with a Bixler in my sortie into the RC gliding hobby. I am sure you're correct about other better performers. But for a "glider trainer" and a forgiving one at that this is a hard one to beat.

Your preference glider for a bumpy field and hillside landing??? (not to side track this thread, but I am interested in your suggestions for a cash strapped pensioner.)

My best thermal flight to date is over three hours with just over three minutes of motor throttle time using a zippy 1500 3S for "rescue" bursts.

Thank you everybody for all the input. LET THE SUN COME OUT!!!

Go With the Flow

Bruce

[KiwiKid]

Mmmm - tricky. Cash strapped and thermaling pretty much mean sticking to foam based gliders. While the P2K is a bit heavy, it's fuse is built like a baseball bat which certainly provides durability. A model I have seen good reports on is the Multiplex Heron. At 2.4m it is a good size and looks pretty sexy: **LINK**

It would certainly make thermalling easier if the air turned purple or somesuch when it got warm. Here's a pic I took a few summers ago which shows a thermal that formed in an adjacent dirt covered paddock. It picked up some dirt so you can actually see its form and how it drifts off to the right at the top. You can see my flying buddy making a bee line for it. As soon as I had taken the pic I launched my glider and had a real elevator ride. There wasn't much wind and thermal column drifted around for about five minutes before it broke off at the bottom and turned into a bubble and then dissipated. Took me 10 minutes to clean all the dust out of my glider after it landed.