[] Beginner from England here with difficulty ... My Christmas build Tiger Trainer 40 (60" span) and powered by TT 54 4 stroke motor, running 11 x 7 prop consistently balloons up in the air when either in to wind or, increased throttle - my instructor tells me so many things at once I lose it and he takes over the buddy box controller - My question to you knowledgeable folk is how do I prevent this ballooning - I have added nose weight - I have trimmed with slight down elevator - what should In do ??? Thankyou for any responses .... Regards, Rob.[8D]

It could be a number of things.

There may be insufficient down thrust -- you can test that by shimming the engine mount.

It could be an incidence problem. You can test that by shimming the trailing edge of the wing upward with a tongue depressor under the the wing where it fits on the wing saddle.

It may be tail heavy -- you are addressing that already

The ailerons may be incorrectly configured. The aileron linkage should be adjusted so that the trailing edge of the ailerons are NOT depressed below the trailing edge of the wing. Try trimming them so that they are reflexed slightly above the trailing edge of the wing.

Only do one thing at a time.

Good luck & get back to us.

Thankyou britbrat I will try these things (one at a time) - presumably the engine downthrust means I need to shim the back of engine ??

How does the plane balance?

I use washers between the mount and the firewall. In this case use one washer on each side at the top of the engine mount. Most standard sized washers are thick enough to give you about 1 degree of thrust.

how bad is this ballooning? couldnt it just be the normal lift created by more airflow over the nonsymetrical wing of the trainer?

Yes. You can either shim the entire mount (shim stock placed transversely across the mount behind the top edge) --- or you can place some shim material beneath the engine lugs, at the location of the rear mounting bolts, to tip the engine forward.

While a small amount might be seen due to this, the amount of ballooning he is indicating is excessive and needs to be fixed. Hard to train if you are constantly fighting trim. Needs to be fixed, like I said before.

Trainers are basically made to do that. Its a safety thing, if the plane is ine trouble, hit the throttle and it will climb! This gets the plane higher than the ground and hopefully there is nothing in the air to hit such as tall trees. Unfortunately this also results in the plane ballooning in fast turns or when gusts hit the plane on landing. You will learn to get control of the ballooning in the turns and all you need is to get more stick time for that. Thats why most clubs prefer to train new flyers when the winds are fairly light. It also is why once you are able to handle the faster speeds of the low wing planes with semi. sym. wings you don't want to go back. They handle the wind much better and don't jump up in the air if a wind gust hits it, unless its really windy and then they just slow down. [8D]

Still asking about balance! Nose heaviness cold be a factor.

That could do it as well because of the excessive up-elevator trim required. That one would be more speed sensitive than throttle setting sensitive. We don't have enough information yet.

Gents etc .... Thankyou for the interest being shown. In answer to MODE ONE, "how does the plane balance?" - the C of G balance is about spot on, however this of course is with empty tank and because TT cleverly give you a tank that will NOT move forward beyond the leading edge of the wing, I suspect that in flight with fuel the plane is probably tail heavy.
In answer to RICH D "How bad is the ballooning?" - well, when flying in to wind at say 50% throttle, it rises at an angle circa 45 degrees. The elevator is trimmed with downward incidence to try to cure this, which is not working 100% and is not ideal. Whilst I recognise that this trainer has lots of dihedral and will 'float', its current tendency to balloon makes learning to fly very very difficult .....

The tank does not need to be forward of the leading edge, just forward of the CG to maintain "nose heavy" rather than tail heavy.

NOw I am confused about where the fuel tank is located. Most fuel tanks are mounted right behind the firewall of the engine. This places it well well in front of the leading edge of the wing on every plane that I have seen. OR am I reading the inormation wrong!??![X(]

I'm also confused about the fuel tank location. Looking at the Tiger Trainer manual, the fuel tank is not specified, but appears to be mounted directly behind the firewall, which would put the back of the tank near the leading edge of the wing, and well forward of the CG. With a TT 54 Four stroke on the nose, as well as added nose weight, this plane should be nose-heavy as all heck!

I seriously suspect its either wing incidence or horizontal stabilizer incidence. Try the popsicle stick under the trailing edge of the wing, as well as making sure the ailerons are not reflexed down.

Just as a note, the tail heavy plane will not just climb with wind and speed. It will have a tendency to snap up or down with wind gusts, and be VERY hard to control. Small movements of the elevator either up or down will cause rapid changes in the planes attitude. Further, when banking in a turn, the tail will tend to drop. The wing incidence however, could easily cause the ballooning behavior.

Brad

Branston, I have the same airplane. We use it for a "club trainer", and it had the very same ballooning problems that you describe. It already had plenty of engine down thrust, so I shimmed the trailing edge of the wing about 1/8" and that solved the problem. It is a very nice flying trainer now.........RS

TT Trainer is a flat bottomed wing like RCM trainer if I'm not mistaken. Efficiency of these aerofoils mean that small increases in either airspeed, thrust and angle of attack will effect large changes in rates of ascent causing the 'balllooning' you describe. If the incidence angle of the wing is mistakenly cut into the wing saddle at the 'factory' marginally higher than it should be as it commonly is on ARFs, the problem is exacerbated.

Secondly, overpowering the models (excess thrust) doesn't help either, but that's beyond the 'ken of the aerodynamically and instructionally illiterate who sell you the stuff, and many albeit good intentioned who would 'advise' or 'instruct' in good faith. A case fof the blind leading the blind, except the one doing the leading often isn't aware he is.

Make sure you've got the recommended downthrust angle factored in, though it shuold have been factored into the firewall with the TT ARF. However bear in imnd that downthrust is a poor aeromodelling kludge which will only work at one particular power setting and flight attitude, and for any particular model is set at an angle intended for the intended engine to be used in that model at a single power setting usually determined to be full power in straight and level flight. So if you are using an engine developing greater thrust and pulling the aircraft faster at full power than that down thrust angle was calculated for, eg:TT FS-54, you will need If you will need to increase it, which will of course exacerbate the differential when you aren't at full power. In either case, you will have to trim out the changes in power and speed with greater trim changed required more often with increased downthrust angles and more powerful powerplants in a model with a wing like this really intended for moderate plain bearing powerplants like an O.S. 40LA, TTGP42 or Enya SS40.

Nose weight won't assist your 'ballooning' situ at all. Adding nose weight alters the CofG forward, which willl make the model more pitch stable and less responsive to elevator effectively increasing the degree of trim or elevator input you will need to make. This is immaterial because it's not pitch instability which is the root cause of your apparent balloning problem.

On very gusty and windy days two factors will affect and exacerbate the sensation of ballooning. One is real and the other illusionary. On gusty days when poiinted into wind, the RAF or relative air flow often actually strikes the wing at a slightly increased angle of attack due to orographic effect which we can't escape given our proximity to mother earth and the friction layer in the nature of our ordinary operation. This creates additional lift (increased ROC or rate of climb) and the aircraft climbs unless we reduce power and counter it with a little down elevator and trim it out. Again the efficiency of the aerofoil on the TT trainer accenuates this climb even with a small AoA increase. The second is due to increased climb gradient or angle of climb as your model tracks over the ground. The groundspeed is severely reduced up wind compared to downwind and is visually noticable from your perspectvie though the actual airspeed remains effectively constant. Thus you see the aircraft appear to balloon or gain a lot of height in comparison with distance travelled over the ground when flying upwind. The apparent 'ballooning' is an illusion due to model gaining greater height in the same time but over a shorter distance increasng the climb gradient and steepening the climb angle due to that differing groundspeed upwind caused when flying into a moving air mass (wind) heading in the opposite direction over terra firma. THis of course provides the illusion that the model is climbing faster when it really isn't, well, not caused by that anyway, but by the changed trust-line and increaased effective AoA. All conribute to making the model appear to balloon and climb like a rocket. Even properly set up flat bottom winged models in such conditions are annoying to the veteran flyer, and posiitivily disconcerting to the confused and struggling beginner.

All you can do with your current setup is try and understand what is happening so you can counter the effects as necessary by inputting the correct corrective inputs in to counter the effects described. Those physical realities described are always present, but are markedly reduced with a symetrical aerofoil and higher wing loading type. The problem is exacerbated by overpowering the model usually attributable to a beginner receiving poor purchase advice and not infrequently, poor instruction both unfortunately all too prevalent in the hobby.

In answer to 'bkdavy' and 'fast sky' questions re fuel tank position, whilst the build manual illustrates the tank almost immediately behind the firewall, regrettably the fact is it just will not pass through the structure of the fuselage to get there - hence it lives directly under the front section of the wing with approx 80% of it in front of TT's C of G point with the remaining 20% behind it .... Thankyou 'sigrun' for the very informative technical case - I shall print off and study at leisure!
This Sunday I will try (UK weather permitting) with rear edge of wing shimmed up approx 1/8" as suggested and hopefully my instructor will not feel the need to become so agitated with either the performance of the plane or its 'ground pilot ...

Pleasure. Summarised in a succinct sentence, all that says by way of explanation is the TTT wing design is going to ensure it's gonna' do that to some degree anyway, which is worsened by (a) strong gusty winds, (b) using more powerful an engine than intended for the design, and (c) incorrect wing incidence cut into the saddle at the factory (not uncommon).

Shimming the rear of the wing up as someone has already suggested will decrease the wing incidence relative to the thrust line, LOF and and RAF effectively reducing the exaggeration of that ballooning characteristic. ie: It'll fly better.

If your instructor is truly becoming "agitated" with you and conditions, find a good instructor. If with the plane, don't proceed until you fix it. Trying to teach with a plane as you describe is nigh on an impossible ask in the worst cases. He shouldn't be. Been there done that. Pointless proceeding until the model's flight characteristics are corrected.

Well, there was no flying at the field today - far too much rain - will try the mods next Sunday as we are promised a dry day ... ha! ha!

The stock tank should fit in the correct location. Have you substituted a replacement tank?

In reply to Bruce 88123, the tank came as standard in the kit and whilst capacity fine (22 minutes @50% throttle), the size and shape means it will just not fit forward unless I cut out significant sections of ply bulkhead ...