I have a great planes 27% cap 232 with an os 160 on it. Flies well full throttle , when inverted it noses down pretty hard. On landings cut throttle and it ballons until it stalls. I'm not comfortable adding down on landings. Checked cg set at 5.75 inches from LE. Any suggestions?

Take the plane to altitude, and fly it straight and level. Cut the power. What does the model do? If it tends to balloon up, that is, pitch upward, then you have too much downthrust. You'll also likely notice that the model will tend to pitch down if you go from a low-powered level flight to a high-powered level flight.

When the model's flying at high power in level flight, and you chop the throttle, it should tend to "coast" level for a bit and then gradually pitch down to maintain airspeed. If you're in low-power level flight and you abruptly add throttle, the model should start to accelerate forward and gradually pitch upward into a climb.

If you go from low power to high power you have to add up elev. for level flight. When flying at full throttle ,and then cut back it will coast level for a little bit then the nose will begin to climb like it is tailheavy.

When you say it noses down when inverted are you trying to say that the nose drops towards the ground or it is pushing towards the belly?

From what you're saying above if it's pushing to the belly when inverted I'd say it's tail heavy.

The way to test is trim for level flight at about 1/4 throttle then push over to a vertical dive and let go of the stick. If it pulls up you're nose heavy and have too much up trim to compensate. If it trys to tuck to the belly then that confirms that you're tail heavy and are running with down trim to compensate. For an aerobatic model of this sort it should run a true vertical line with little or no nose up tendency but definetly no tucking.

When inverted it noses toward the ground.

G'day Mate,
And you need lots of DOWN elevator to keep it level, right!, then it is NOSE heavy, & you have lots of up elevator trim to keep it level, when upright.
You did trim it, at full throttle, for straight & level flight, then test it.

To me your plane is tail heay. CG at 5.75 inches from LE is a lot and you should tell whether you measured it by the wing root, half way or by the wing tip.
Besides the engine is a light weight one, which may cause the plane to have a balooning attitude.
At full throttle the engine tends to pull the plane toward different directions than the ones the plane would fly according to its aerodynamic and balance, this effect may confuse you.
For aerobatics and your comfort you should have a neutral attitude plane.
Check the allignement of the tail surfaces in respect of the fuselage and wing.
Check the engine thrust angle.
Put a ballast (1 pound should make you understand the case) onto the firewall.
At full throttle trim the control surfaces to straight and level then, hands off, (in a zero wind day) make a perfectly vertical dive at idle (of course) and then a perfectly vertical climb at full throttle and see what the plane attitude will be.
If this will work for you, afterward try to reduce the ballast weight by moving the things inside the fuselage, including the engine, as much forward as you can.

If it drops the nose to the ground when inverted resulting in needing some down to hold level then that indicates that it's biased nose heavy from the neutral point.

The dive test will show you how much it's nose heavy by how quickly it tries to rotate from vertical. Ideally for a truly aerobatic model like a CAP it should hold the vertical line or only try to nose up slowly.


.... and don't forget to pull up before it lawn darts itself....

Either tail heavy or too much down thrust.

Tail heavy if:
when you fly full throttle and then cut it it dosen't immediatly balloon, but balloons as the plane slows down. Try adding some nose weight to see what happens. Or just force yourself to push on landing. A nose heavy plane will do the same thing in reverse. Look up the term "flight path stability" if you have an aerodynamics book.

Too much down thrust:
if the change in elevator trim required is immediatly correlated with throttle possition.

Sometimes these taildragger models are designed with a ground attitude that is too high for their own good. If you combine that with a pilot that likes to land REALLy slow you get a situation where the plane is landing at a post stall ( or very high) angle of attack. After the model touches down, it instantaneoulsly transitions to horizontal translation (the ground forces it to) and the ground attitude becomes the new angle of attack which is now a very high but pre-stall angle of attack, and the wing's lift now is higher than before touch down! The model takes off again, goes into stall, touches down, takes off, etc., etc.

Taildragger aircraft make bouncing landings because they do not have the nose high enough when the main wheels touch down. For a given speed, increasing the angle of attack of the wing will increase lift, as long as the angle is below the stalling angle. When a taildragger is a bit fast, the mains will touch first. This causes an "up" force upon the aircraft forward of the CG. The nose is pitched upwards, increasing the angle of attack. The aircraft "balloons" into the air. It can then stall and pitch down dramatically. If the speed is high enough at the next touchdown, then the process repeats. Many times, though, the model winds up on its nose after one or two repeats of the bouncing.

If the stall angle is high enough, a taildragger can actually touch tailwheel first. This results in a landing that "sticks". That's because for the speed, when you touch tail first, the wing's angle of attack is reduced, and so lift is reduced. The model cannot bounce back into the air...regardless of the actual touchdown speed.

Lowering lift when you reduce angle of attack on landing is why a "stuck" landing happens when tricycle-geared airplanes touch mainwheels first and then lower the nosewheel to the ground. Lift is reduced. Works well for full-size aircraft. If the model is set up so that it's slightly nose-low on the ground, landings will be easy to make without bouncing.

An excellent reference about how airplanes fly (full-size or models) is the book "Stick and Rudder" by Wolfgang Langeweische. A classic book that describes flight from the pilot's viewpoint. It about full-size aircraft, but the principles all apply to models as well.

A tailheavy CAP-will "balloon" if you chop throttle on approach - the reson is that the thrust and braking (not breaking) is well above centre of drag (the wing ) I set my CAPS- always- at 0-0-0- and with the cg aft they are not really great flyers but at about 27% cg they become great fun - good tumbles quick recovery great snaps n stuf and very litle tuck on knife
the balloon tho happens when cg goes aft 30% cg. just too darn sensitive to the CAP high thrust line setup.
But --it's a CAP- if I wanted a YAK -there are a blue jillion of em on the market .
th so called 3D setups -with exag. aft cg, wreck the manners of lots of designs
save it for the foamies. then flip n flop till your heart's content.

Hanson... The engine/drag combo has something to do with it but it is much more related to flight path stability and how the wing and tail moments work out.

The quick and dirty: As speed decreases the moment created by the wing decreases, if this moment decreases faster than the tail force decreases you end up pitching the plane up.

sure- opposing forces - On the CAP ,a big prop w/ flat pitch suddenly slowing creates a pretty effective brake -as far as prop braking goes

I have had a gaggle of Caps all sizes mostly scratch built ones and the prop disc braking , with a bit of pitch up, etc., is more noticable than the typical pattern setup -
Have you flown many of these designs?

Yes, I have flown many, many low wing planes, and a few caps as well. I am actually working on a cap x right now. As I stated:
if it happens as soon as the engine is cut back or on a down line it is due to breaking, but if it happens when the airspeed decreases it is due more to the moments. Any plane with an aft cg will balloon on landing. A funtana, Ucan do, ucan do ep, four star, pw extra, edge, kyosho pitts, decathalon, and even the little delta ep will do it.

yes - -a plane with more forward trim is more stable -in all respects . - the BRAKING force is more evident tho with very high thrust lines on low wing stuff.
It is all about lever arm and forces .

Sorry, but I have not read this whole thread and please excuse any redundancy of this post.

It has been stated that tail heaviness and down thrust are factors and I agree but to a great extent it is a “cap thing due� to the comparably high thrust line coupled with a higher than normal horizontal in relation to the very low wing.

When power is applied the pulling force will have the effect of pulling the nose down and during prop breaking the nose will be forced up.

try this:
move the cg back on a high wing plane and see what happens. It will balloon on landing.

BTW it happens in full scale planes too where the breaking force isn't nearly as high due to the high pitch props. also look up the term flight path stability.

yes -
braking - to apply a stopping force

Just explain why a high wing plane does the same thing when the cg is aft????

The braking force is pulling the nose down but it still will balloon!!

All true... but the ballooning effects are much less pronounced on a Yak 54, for example, than a Cap. The Cap's ballooning tendency is much greater than many of the other aerobats. Of course, there are many other factors such as cord width at root, just to highlight another factor.

Fair enough.

Can a spelling bee fly?

Dick, with the modern miracle of spell checkers, we know longer half too worry about weather or knot hour words are spelled wright.

I fergat-