Glider Wing Warp - Top Model CZ Bliss

[Wasaforumite]

I have a Topmodel CZ Bliss E Glider - an attractive pod and boom with a 2 metre span. I have had it for about 3 years and it is a 'Hangar Queen' because it won't fly properly.

The first two test flights nearly ended in disaster as the plane turned violently to the left. I found a massive twist in the left tip panel. I tried straightening it using weights but the panel is very strong and resisted efforts at correction. I even removed the underside covering and cut all the joints between the ribs and the spar and re-glued them but the twist was in the spar and it had no positive result.

I then complained to the factory, who to their credit sent me a new left panel. That was 2 years ago. Unfortunately, the new panel shows most of the characteristics of the old, It has a 2 degree wash out , whereas the corresponding right panel has no washout. Two more test flights showed that the plane is almost unflyable, as not only do you have to use all the right trim but full right stick to get it to fly straight.

Although I am a reasonably competent builder, I prefer building on a plan and rebuilding the panel seems a daunting and time consuming task and it would be difficult to match the factory finish of the original. The glider is quite sophisticated yet very flawed and I’m stumped as what to do next.

I suppose the easiest thing would be to find some new 2 metre wings. I would rather go to that expense rather than have a useless plane that has cost about £200 to set up.

I would welcome comments and suggestions, please. Especially about the availability of wings.

[flight1]

If i am thinking right you have a center wing section and plug in left and right wing panels / Check the Centre section has no twist.

You mention the right panel as no wash out if so this is properly the 'twisted/ warped panel' plug in the new left panel take measurements then strip the right panels covering adjust to be the same ,then recover without warping it again , when all done it should fly good

Ps  before removing the covering on the right panel you might be able to heat the covering up with a heat gun(carefully) and quickly before it cools hold a twist in the panel the until it cools you might be able to rectify this way(might need to do a couple of times to correct) , harder to explain than do

Edited By flight1 on 17/08/2017 18:18:55

Edited By flight1 on 17/08/2017 18:19:57

[Wasaforumite]

Thanks for your comment. You are correct there is a one piece centre section and two outer panels.

T9 sell them see: https://www.t9hobbysport.com/topmodelcz-bliss-1.97m-ep-light-thermal-glider

I bought mine ages ago from the factory as I couldn't find it in the UK at the time.

When I stripped the original left panel I found that the wood appeared to be very rigid, coarse grained rather dark coloured. (Oak balsa!!) It was not amenable to correction. It would mean a major reconstruction job.

I was intrigued by your comment that the right panel might be at fault with no washout. That means it came with two faulty panels. I would be interested to hear other peoples experiences with Topmodel Gliders. It is to be hoped their more expensive gliders are better than this.

[flight1]

Hi wasa there are two ways of inducing the inboard part of the wing to stall before the tip ( a must for good flight manors) one is to change the angle of attack of the wing at the tip if the same section is used and the other is to change the air foil section at the outer ends to a airfoil that stalls latter than the inner sections .

I believe the bliss e uses washout , might be wrong but maybe not

[John Emms 1]

Whilst I have no experience with the Top Model gliders, it is not unusual, and even quite common to find this with Czech models. The covering on Czech models is always polyester, normally Oracover, but may be polyester Solarfilm. The covering provides the rigidity for the wing panel.

THE techniques is to set an iron to normal shrink temperature. Twist the panel (or part of the panel) affected past the required point. You will see wrinkles appear in the covering. Run the covering iron slightly away from the covering, and over the wrinkles on both sides of the panel until you see the wrinkles go smooth. Let the panel cool a little, and then check the panel for washout. Repeat this until you get the panel exactly as you want it. You may find that slight correction will be required after a week or so, but after that slight correction, the panel will be permanently set.

Whatever you do, do not let a hot iron touch vinyl marking.

This sounds a lot more involved than it actually is - oh, and this is from tech support of a Czech glider company.

[Wasaforumite]

See my picture:

Thanks for your comments. Unfortunately, the Bliss has a laminated spar which is where the warp lies.

[Wasaforumite]

Removing the bottom covering had no effect on the warp. You might expect some change if the tension of the covering was causing the problem. The wing is quite short only about 700mm so the structure wins against the covering. I am sure John's method would work on longer wings but not here. I can't heat the top of the wing because its covered in vinyl decoration. Having been encouraged to remove the covering I am going to see if adding diagonals while holding the wing in a twist will work. I'll post another picture separately as they seem to get pushed into strange places in my text,

[Wasaforumite]

Removing the bottom covering had no effect on the warp. You might expect some change if the tension of the covering was causing the problem. The wing is quite short only about 700mm so the structure wins against the covering. I am sure John's method would work on longer wings but not here. I can't heat the top of the wing because its covered in vinyl decoration. Having been encouraged to remove the covering I am going to see if adding diagonals while holding the wing in a twist will work. I'll post another picture separately as they seem to get pushed into strange places in my text,

[Wasaforumite]

[Wasaforumite]

I'll let the rather excessive glue dry overnight and see if it holds the new twist in the wing. Posting here has stopped me just whingeing about the problem and encouraged me to do something about it!

[John Emms 1]

That wing is pretty much "normal" Czech construction. The laminated spar is EXACTLY of the type used on the Pelikan Swift and Big Swift (except the Swift is balsa, carbon, balsa), and the first job in construction was to do final adjustment on the washout of the tip panels, and adjust the centre panels). In fact, I adjusted one wing panel OVER 10 degrees each way to prove the point.

Where there are vinyl markings, follow the technique, but hold the iron slightly off the surface, and you will see the vinyl adjust with the wrinkles. Where are you? If you are local, I could do it for you.....

I am buying a Obag Donald that I will pick up at the Nats, and know that I will need to adjust the wing panels - it's easy!