<span style="font-family: Comic Sans MS">so i got around to taking the LT flying this weekend.she isballooning in flight when i go full throttle. i have an LT-25 with an O.S. .32 motor with a 10x6 prop. (can't everhave too much power)the CG is set per instruction. it never did thisalot before, but then i never really pushed the envelope with it. i normally fly around at about 1/2 throttle, but now when i push it to full, the plane wants to climb like crazy, and requires mucho down trim. other thresholds are great as far as not trying to bank or yaw when i push it up, just the climbing deal. i couldn't imagine the wing being twisted. it looks fine, anyway. the only time i noticed it was on takeoff, i never really had to input much elevator for her to get in the air. i guess just the normal amount. is this not normal? am i getting too much ground speed, thus inducing the ballooning on takeoff?and she tracks straight on the ground. aside from wing incedence and down thrust on the motor, is there much else to do? i'm looking for maybe a couple other known secrets to try as well, that maybe won't effect the flight when i am putting around at 1/2 stick. i don't want to need up trim.i want to get used to flying a little faster, before busting out the RV-4 again (spent a couple years in the hangar) or the SMP. it's not that it's hard to handle, but just annoying adjusting the trim to speed up or slow down. i even moved the fuel tank under the CG, so that wouldn't effect it when the level started getting low, with the servos in front. (that was done way before this ordeal though)</span>

Your sating it is climbing when you add power going from half to full throttle and from straight and level flying? All flat bottom wing planes do this, it's nothing strange at all, very normal with a high wing trainer type of plane. The wing generates lift and the more speed the more lift you will get. It's the nature of trainers.

Sounds like you have overpowered a trainer and now it balloons at full throttle, mission accomplished...?

You can increase the engine downthrust and play a little with wing incidence (shim trailing edge) or you put the engine in something more suitable with a symmetric wing.

Hi crash bandicoute
I wish you could use normal punctuation so I can follow your post easier. Ballooning at take off can be caused by having the front gear a little short (assuming it is a tricycle gear plane). The main wing will have negative incidence which generates a down force keeping your plane from taking off, until you overpower that with your up elevator at which point your plane will balloon up.

This is why any high wing airplane (all airplanes will respond to power changes with pitch changes) especially a cabin type which has the thrust line lower in the center of mass, normally will use a fair amount of down thrust (literally pointing the crankshaft at an angle downward).

What you are doing when trying to fly level at high power is forcing it beyond its trim speed. This will cause the airplane to become less stable in pitch and generally make you look bad just like a beginer.

Your airplane will never fly well and always look terrible in flight if you don,t pull the throttle back. Now having the extra power is indeed wonderfull and is very useful if you learn how to use it. Learn that throttle, never fly past the trim speed in level flight, use the power in your up lines and off the power on the downlines. You start to learn to use that throttle, then you will start impress your Buds. That airplane can do a great aerobatic routine.

There is nothing worse than some guy with a well powered trainer blasting around at full throttle trying to impress his friends but in reality he is just showing how little he knows. Don,t be that guy. learn to use the throttle

John

I believe you are talking about a Sig Kadet LT - 25.
The O.S. .32 makes me think that you want it flying more as a sport plane than as a trainer.

aside from wing incedence and down thrust on the motor, is there much else to do?

Not really, but go in full playing with the incidence first (reducing the difference in angle between the wing and stab), and the thrust angle later (increasing thrust down if needed).

Trainers by their nature are trimmed out to fly level at one speed. When trimmed out this way, they lift the nose when in a dive due to excess speed, as well as lower the nose when left in a climb and slowing down. It suppose to make them easy to fly for the rank beginner. The airfoil used by trainers is a small part of the reason, but not really the primary reason.

This "self recovery" mode of operation is driven mostly by the decalage and the balance of the model. The incidence of the wing relative to the thrust line, and the angle of the horizontal stabilizer determine the decalage. Having the airplane balanced out "nose heavy" is the other factor that increases the effect that speed has on climbing.

Most trainers have a fairly wide band of permissible CG ranges. You will dramatically improve your pitch/speed problem by moving the CG to the rear of the range. On some designs, even operate slightly behind the "approved" range. Then removing much of the excess decalage will give the result you are seeking.

Other things you can do if you find your trainer too tame. Cut down the wing area by one rib in both panels will increase the wing loading and speed. I've done that to an LT-40 in the past.

I've also remodeled the airfoil of a Goldberg Eagle 63, making ribs that glued to the bottom of the wing to make a semi-symmetrical airfoil. Just remove the covering on the bottom, and glue them on beside the existing ribs (about half the camber of the upper surface).

Or you can replace the wing entirely with a wing from another airplane. I put a 400 square inch symmetrical wing from a das little Stick on a Eagle 63. Interesting test flight ensued, since I didn't remove enough of the down thrust.

Any questions?

I had a similar problem with an electric glider and the cure for it was to mix the elevator with the throttle. From memory (it was some time ago) I had about a 30% mix of down elevator at full throttle but start off with a small % and work up, not the other way round. For the glider though I aimed for a fairly gentle climb at full throttle, not straight and level.

The bottom line is that you're asking the plane to do something it's not designed to do. Burning holes in the sky is what Ugly Sticks are made for. The good news is that you have a trainer that you're used to. Learn loops, barrel rolls, stall turns, Immelmans, and cuban 8's with it, using the extra horsepower to pull your up lines. When you get your first sport plane, you'll be amazed at the speed range once you get it set up right.

Hi,
All of the previous is good advice. Try trimming the plane out at a higher throttle setting and make that your cruise speed. It will still climb if you increase the throttle above that level.
Also in keeping with the LEARN TO USE THE THROTLLE theme try setting the level flight throttle setting much LOWER and learn to do things like low and slow figure eights without ever leaving the area directly above the runway. One wheel touch and goes are fun two.
Practice axial rolls, the rudder will be required to get it right. Also try inverted and see if you can fly the complete circuit.
Good luck!

Your simplest solution is to just increase the down thrust on the engine. If it flys well under normal power without excessive elevator changes, then just increase the down thrust angle which is usually easy to change by adding some washers or spacers under the appropriate mounting bolts.

I fixed the ballooning problem on a trainer of mine by decreasing the wing incidence. It's very easy to do. Just raise the trailing edge of the wing with a popsicle stick or two until the plane behaves the way you want. If I remember correctly, I used two. Once you figure out the correct amount, you can replace the popsicle sticks with a more permanent solution. My trainer flew great afterwards. RS

I had a similar problem with my trainer. Overpowered it and it took the better part of 10 flights to get it sorted out.

I do prefer to stick to the recommended engine range on new models now.

I also had to decrease the wing incidence (lift the trailing edge), add more donwthrust and right thrust and then ultimately had tp trim it for 1/2 throttle flight and used a mix to add elevator beyond that setting.

1. power range for motor selection is .25-.32. so, unfortunately, at the top of the range. maybe a bigger pitch on the prop, but i'm not sure what the max recommended is. but still we have the speed/lift increase. AARRGGGHHHHH!!!!!
2. i'm getting bored with this thing and, i guess, more curious of the difference of speed of the bigger .40 size motor. not that i'm going from a .25 to a .60 or .90.
i don't remember what it was like flying the RV-4. it was twice a couple of years ago. scared the crap out of me though. luckily my buddy took the sticks and landed her. that could've gotten real ugly quick.
3. 90% of my flying is at 1/2 or 2/3 throttle, and requiring more trim above that. i'm not really into hot doggin' yet, as i know the plane won't do it. i just want to push the speed some times to see what it will actually do.
4. the slow flight capability of this thing is amazing. i can darn near get the thing slow enough to fly that i'm tempted to harrier her in. the stall speed is beautiful on it. if i walk a little fast, i can keep up with it and grab it out of the air insteadof
landing it. but i think that's right before the stall. not a good thing at 5 feet off the deck. my normal buzzing around the plane flies more than amazing.
5. i guess i am asking a bit much of it. the inverted thing is kind of fun, but needs a lot of down trim to keep it going good. i think i got some dislexia (?) with the coordinated turns upside down. i start going back to the bank and yank bit, cuz i
can't figure it out for some reason. or i guess yank and push...


but i'll try the incidence change with the popsicle sticks after the throttle/elevator mixing if i can figure that one out on my radio. i'll post this coming weekend what works best, or that i crashed (pics will be included), the RV-4. NOT!!!it's such a little hotrod!!! thanks for all the tips and advice.

Hi!
First of all you have to trim the plane at full power! At this setting it should fly straight!

Then as you probably know, all high winged trainers using a flat bottom (nearly a Clark Y airfoil) or semi symetrical airfoil, should have the engine set with a little (1-2 degrees) down trust.That's very important.

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You stated you are using a O.S. .32. That would be the .32SX. It's no normal sport .32. It's a screaming little power house. Generally considered the size of a .25 with the power of a .40. They were rather pricey in their day. Great motor, but not a good application in this case.</p></font>

Hi Crash - I had one of these planes before and powered it with an OS Max FP .25 and most of the time flew 1/2 throttle. I'd have to agree with others on this thread that you are a little overpowered. However, if you read some of the other threads on this plane, there are folks who have stuck a .46 on the front - why - I don't know - guess they just feel the need for speed. It is a great plane that will hold your interest past being a trainer. Wish I still had mine.

G'day Crash. My LT-25 is now in retirement or having a rest. Like all planes it is a compromise. It is a trainer and so is heavily compromised to meet the needs of a trainer. It was never meant to go fast.

It has lots of dihedral. This makes it more stable for the new pilot but makes aerobatics untidy and makes it prone to problems in cross wind landings.

It is light for its size and so has a low wing loading. This means it can fly slowly which is very important for a learner. More time to think.

It is quite large. This makes it easy to see but as it has a low wing loading and dihedral it gets pushed around in cross winds.

It has a flat bottom wing. This means it generates lots of lift at low speeds but as you add speed, it generates lots more lift and so your "problem". I used to trim mine for half power or so. If you do trim for high power you will find it will fall like a stone when you pull the power off for landing.

Mine has had various engines in it over its career. It started with a 30 four stroke which was just about perfect, graduated to a 46 Leo (vastly too much but we could fly it happily for hours on FAI (no nitro) fuel). And has had other engines too. We put the 46 in because it was the only engine available at the time. It worked but it spoiled the plane overall.

If you want to go faster then it is time for a new plane. How about a Stick of some sort. They are a really great second aircraft and they will fly fast. Or our club's workhorse, the World Models Skyraider Mach II low wing trainer. They go like stink, are cheap and I hate them but that's just me. Everyone else loves them.

Keep having fun. That is what it is all about.

Oh yes, next time you are flying it in the wind, see if you can get it to fly backwards. Reduce the power to near idle, and gradually pull in more and more up until it slows right down. It will then hang there like a kite. You have to do this pointing directly into the wind. If all goes well, it will then start to fly backwards. Cool. You will find as you slow that the controls do become rather mushy but this is to be expected.

Cheers

Mike in Oz

I bought a Great Planes Escapade ARF as a second plane and love it. Plenty fast with just a .36, cheap, easy to build, easy to fly, nimble.
I have a Sig Kadet Jr which has had an OS25FP, Irvine 25 (wow, really powerful), and a Thunder Tiger GP25. It ballons too but it isnt terrible, probably has plenty of down thrust.

<span style="font-family: Comic Sans MS">wow... never knew that. i figured it was just another motor between my .20 FP and the .40 FX. that would explain past occurances with other planes. OOPS! so maybe i'll try the down thrust before messing with the incedence of the wing and such. i was looking at maybe a tiger 2 for an intermediate plane before finishing the SMP. i really don't care much for the 4*'s. i got a wrecked one to fix up for a friend and wasn't impressed with about half of it. but i think i'm more into the look of the plane than not. i guess as long as it does it's job. thanks for the hot tip on the motor. that really explains a lot...</span>

First, as stated in several posts above that is a common aerodynamic function of airplanes operating within the realm of subsonic convergent airflow. The machine, when "trimmed" is only trimmed for the airspeed at which such "trim" is applied. Any deviation from that airspeed, deviation from balance (such as the Flt attendants walking up and down the aisle ), deviation from power setting, and a few other things will require an adjustment to trim. That is a fact, Jack!

For your specific model let's explore several items. 1. moving the Center of Gravity (CG) AFT as one so presented is absolutely the most wrong that can be attempted. On a wing such as your model has, the Center of Pressure (CP) will always be right in the vicinity of 25% of the Mean Aerodynamic Chord (MAC). Any CG aft will proportionally decrease stability of the machine. Therefore CG forward will proportionally increase stability. Any CG within the 25-30% of MAC will result in a nice stable aircraft that will maneuver well. Do not confuse the previous statement with certain applications of CG for specific desired functions that a learned pilot may desire. BTW, MAC can be used as the average chord in models because the difference is none to very little.

2. Adding/reducing power simply changes airflow over the control surfaces - changing trim - and changing airspeed which changes trim.
3. The chord line of the horizontal stabilizer is the real aerodynamic longitudinal reference, not the one drawn on a plan for reference. Therefore, if as offered above, you raise the wing's Trailing Edge, all you do is apply a negative wing incidence, which simply makes the horizontal stab the same as adding down elevator. The stab applies down force on the wing, such force being proportional to the square of the airspeed. Not a bad thing.

4. Now with a slow airplane such as a high wing trainer, flat bottom airfoil, the very best application which works quickly and efficiently is engine downthrust. You can experiment and find a down-thrust setting that will allow you to trim for level flight at your desired power setting and airspeed. Now when you add power, the engine will be pulling more down which helps offset the additional wing lift created by an airspeed/power increase. When you retard throttle for landing/slowing, the up-trim set for cruise (offsetting the down-thrust) will be less effective, thus the nose will not want to drop out of the sky and your machine will ease into the glide with less stick pressure required.

Therefore disregard all the fixes other than experimenting with downthrust to find a setting which you like. It may never be perfect, but it will allow far better flying than any else you can find. CG at 25 -28% edge of the chord back from wing Leading Edge and your problems will be minimal if any at all. Remember that most model airplanes have a moment arm of about 1 to 4, I unit forward of CG and 4 units aft of CG. I ounce in the tail needs 4 ounces in the nose to offset. That is too simple for full scale load planning but close enough for toy airplanes.
I suggest tapered plywood behind the engine mounting rather than washers which will eventually tighten into the wood and cause engine loosening.
Good luck.

ON a related note.
If my plane flies tail down at cruise even though it is balanced and trimmed straight would you raise or lower the leading edge wing incidence to correct it?
My last trainer did this and it was found the ailerons were adjusted improperly, both were slightly up, this plane has been checked and they are not.

I would increase the incedence of the tail plane.  But that is a major job once epoxied in place.

You would have to both increase engine downthrust and also increase the main's incedence to raise the tail in flight.

There is a way to think about the problem that clarifies the solution.

What is your goal? It is to have the fuselage level at cruise, right. Since no matter what you do, the wing will always fly with the AOA that produces the appropriate amount of lift, and it is in control and is always going to set the same angle, forget about changing the wings incidence. Simply think about adjusting the fuselage to the wing.

Think about adjusting the fuselage to be what you want. It's tail down now? OK, move the tail up where you want it. That's easier to see in your mind, right.

How far down is the tail in cruise? Let's say 7 degrees. OK, change the wing's incidence by 7 degrees. Which way? If the tail of the airplane is going "up", the trailing edge of the wing is going "down" and the leading edge is going......... see?

Simple?

No, actually it's not.

The horizontal tail is stuck to the fuselage. And it's now going to be flying about 7 degrees differently.

If you really want everything arranged the most efficient way, you're going to have to change the horizontal tail's incidence when you change the wing's. Not simple is it? Aerodynamics isn't sound byte simple. Never was.