What is the correct CG.

What is the correct CG for a Sterling Ringmaster?

RINGMASTER. Kit plans show CG at 2 1/4" from LE. Full UP elevator and full DOWN elevator are both 39 degrees on my airplane. I think 30 deg would be better. I put the longest control horn I could get on the elevator and the elevator is 39 deg with the linkage in the last hole. Full UP elevator and full DOWN elevator are both 39 degrees. I had an OS Max 25 LA with a 9x6 prop on it CG was about 2". It flew good but a little bit fast about 70 mph. I changed the prop to 10x4 now it flies like its tail heavy. I put a heaver McCoy 35 engine with a 10x6 plastic prop on the airplane its .56 ounces heaver than the OS Max 25. CG is 1.5" from LE not 2.250 like the plans call for. The tail flops up and down when it flies. Next I put a heaver Fox 36x on the airplane 1.185 ounces heaver than the OS 25 LA. Its still tail heavy. The airplane turns so sharp it stalls out half way around the loop and falls like a dead butterfly. When I straighten out the elevator the airplane picks up speed and flies again. The Ringmaster has a flite streak elevator and stabilizer. Canopy is different too. I have moved the engine out to the very tip of the fuselage. CG is now 1.25" from LE. I have not flown it yet. Each time CG was checked with no fuel in the tank. It seems like the fuselage was designed a few inches too short.

[photo not recovered: abcde.jpg]

FLITE STREAK. Brodak plans show CG 1" from LE. Full UP elevator and full DOWN elevator are both 30 degrees on my airplane. I had an OS Max 25 LA on this airplane and it flew great. With a 9x6 prop its a little bit fast about 70 mph. I tried a 10x5 prop and a 10x4 prop it flies even better and slower. I tried a Fox 36X with a 10x6 prop its a bit fast so I changed the prop to 10x5. CG is 1.5" from LE not 1" like the plans with the Fox 36x engine. Loops are large 20 foot circles with the Fox 36x. When the engines stops the airplane slows down very quick and falls out of the sky like a brick bends the landing gear every time. It must have a lot of drag and a poor glide ratio. Each time CG was checked with no fuel in the tank.

>What is the correct CG for a Sterling Ringmaster?
>
>RINGMASTER. Kit plans show CG at 2 1/4" from LE. Full UP
>elevator and full DOWN elevator are both 39 degrees on my
>airplane. I think 30 deg would be better. I put the
>longest control horn I could get on the elevator and the
>elevator is 39 deg with the linkage in the last hole. Full
>UP elevator and full DOWN elevator are both 39 degrees. I
>had an OS Max 25 LA with a 9x6 prop on it CG was about 2".
>It flew good but a little bit fast about 70 mph. I changed
>the prop to 10x4 now it flies like its tail heavy. I put a
>heaver McCoy 35 engine with a 10x6 plastic prop on the
>airplane its .56 ounces heaver than the OS Max 25. CG is
>1.5" from LE not 2.250 like the plans call for. The tail
>flops up and down when it flies. Next I put a heaver Fox
>36x on the airplane 1.185 ounces heaver than the OS 25 LA.
>Its still tail heavy. The airplane turns so sharp it stalls
>out half way around the loop and falls like a dead
>butterfly. When I straighten out the elevator the airplane
>picks up speed and flies again. The Ringmaster has a flite
>streak elevator and stabilizer. Canopy is different too.
>I have moved the engine out to the very tip of the fuselage.
> CG is now 1.25" from LE. I have not flown it yet. Each
>time CG was checked with no fuel in the tank. It seems like
>the fuselage was designed a few inches too short.
>

This is classic Ringmaster performance. You definitely need to slow the controls more - to about 1/2 of what you currently have. Just putting on more nose weight will help, but it will likely still have a problem. You can help by narrowing the handle spacing, but I think it will be better if you slow down the controls in the airplane instead.

It should be pretty easy to put an extension on the elevator horn. Use the existing holes in the horn with through bolts to hold it.

Gary, you changed the design by installing the FS stab and elevator on the Ringmaster. You may notice that the tail end of the fuselage is shorter than the FS. The shorter tail moment should have a larger horizontal tail, not smaller. This would require moving the CG forward to give decent stability in level flight. You wrote "The tail
flops up and down when it flies". Is it fluttering? Is the aft end of the fuselage twisting? Is the pushrod flexing in level flight? You need to clarify this issue, so we might understand what you are seeing.

A few general rules of trimming may prove useful. 1) Adjust airspeed with pitch, adjust rpm with diameter or blade area. 2) If the model pitches nose up after engine shutdown, the CG is too far aft. If the nose pitches down after shutdown, the CG too far forward. 3) Slower controls are better for precision flying. 4) Lightweight models fly better and generally last longer because they avoid the ground more effectively. Steve

Even with the Streak tailfeathers, 30º still is too much. 20º is more like it.

Did you use the closest hole to the pivot pt. on your bellcrank?

I will try to answer all your questions.

The linkage on the Flite Streak is out all the way to the last hole.

Example. If the Flite Streak were flying 20 ft off the ground when the engine quits it will go maybe 1/2 way around the circle slowing down very fast. The airplane reaches a point where the wing no longer produces lift and it falls almost as if I had dropped it from the top of a step ladder. It comes down like a parachute. If I nose dive to the ground it doesn't have far to fall when it lands.

Tomorrow I will build an elevator control horn about 2" long and adjust the linkage out to where ever it needs to be for 20 deg on the Ringmaster elevator.

It seems to me when building an airplane the bell crank should have a STOP. There should be a limit to how much the bellcrank can move. That way there is no problem with to much elevator movement. My bellcrank is 3.250" long. The lead outs are 3" apart on the bellcrank. The linkage hole is 5/8" from center.

The tail of the Ringmaster goes up and down as if I were pulling the control line handle back and forth very fast. The airplane flies in a SNAKE pattern after doing a loop its hard to get the airplane under control.

YES... I changed the design. I think the canopy, tail and elevator on the Ringmaster are ugly so I changed it. Nothing wrong with that. I have a friend that loves Ringmasters he built a Ringmaster with Spitfire wing tips, a Ringmaster Japaneese Zero, a Ringmaster Stearman Biplane, a Ringmaster P-38 with 2 fuselages, and several others. lol, the guy is Ringmaster crazy.

LAST EDITED ON Jan-02-04 AT 10:36 PM (CDT)
 
>It seems to me when building an airplane the bell crank
>should have a STOP. There should be a limit to how much the
>bellcrank can move. That way there is no problem with to
>much elevator movement.

No - blocking the controls is a completely different deal than slowing them down. If you block them instead of slowing them down, you get too "binary" a response. Slowing them down is the right answer.

BUT - I may amend what I said earlier. When people state their total control throw, the usual basis is how much they get with full hand movement. I think you are actually describing the total throw with the bellcrank hard over. Given your stated bellcrank setup, I would think your control rates are not too far off ideal. I would guess, given a 3" bellcrank with a 5/8 pivot distance, that an elevator horn height (center of hinge pivot to pushrod hole) of maybe an inch and a quarter should be about right. With a 3.25" handle spacing, this will give you about 22 degrees for 45 degrees of handle motion, which sounds reasonable. The current height is about .75, correct?

I would also be curious to know the handle spacing - I'm going to bet it's a 4" and that's almost certainly too big for the 3" bellcrank. For sure, it will really fall off at the ends of travel. If it is 4", I would narrow that first, before slowing the controls as the airplane end - because the bellcrank "pegs out" at only 48 degrees of handle angle.

I am not sure why going from a 9-6 to a 10-4 prop should make the plane fly tail heavy, unless the 10-4 is a lot lighter than the 9-6 prop (just the opposite to my experience, at least with APC props). Tail heaviness has nothing to do with the plane stalling, rather it manifests itself as being unstable. It does sound like you are overcontrolling the plane. Also you didn't give the plane weight, and I am wondering if it is a bit heavy. That does make the wing have to generate more lift for a fixed loop diameter. That causes the pilot to increase the angle of attack to generate the extra lift, at least until the wing stalls out.

I would go back to the original CG, as shown on the plans and slow down the controls. One other thing is that the Ringmaster isn't going to turn like the FliteStreak.

Look at the controls like this: If you use a 3" BC, you use a 3" handle spacing, then say a 3/4" elevator horn, so put the pushrod at the 3/4" hole on the bellcrank (assuming there is one), and you have 1:1 control ratio through the whole scheme. If you crank your wrist 15 deg. up, you get 15 deg. of up elevator, etc.

This isn't tough, it's basic Jr. High science at most. This is one reason why for precision flying, you are better off with a 4" bellcrank. It allows you to use wider handle spacing, and less likely that you'll get the thing flying on just one line, which is not a good idea.

I agree with you about having limit stops on your bellcrank, but would limit the bellcrank to more like 45 degrees up/down, and simply so that if a line breaks on pulltest, the controls would not overload the control system at the horns and hinges. Other may disagree, but that's another subject, for another time. Your hand is supposed to limit the controls while flying. If your hand gives it too much control, then the CG is too far aft, or your controls are too quick. Adjust, Grasshopper. Steve

A short coupled heavy plane will have a tendancy to hunt in level flight. How thick is the stab an elevator, 1/8" balsa could be flexing when you come out of a loop.

A 20 ft loop is not a large loop, the standard size loop flown in competition is @48 ft (5ft to 45 degrees) on 60 ft lines. Sounds like you are overcontrolling the plane, try doing loops that almost go to the top of the circle and see how the plane flies when you exit. Do you have the hinge line sealed, if so unsealing it will reduce the effectiveness of the elevator and calm the plane down.

What size bellcrank did you use? What hole in the bellcrank do you have the pushrod in? The standard procedure is to use at least a 3" bellcrank and install the pushrod only @ 1/2" from the pivot point. There is no need to install a stop when you set the bellcrank up this way.

You should be able to whip the flite streak for 2 or 3 laps from 20 ft altitude. If the plane is yawed out a lot this will cause the plane to slow down quickly. How heavy is the plane, a profile has a lot of drag due to everthing being exposed, a very light plane has low inertia and since you have installed twin LG will loose speed quickly. Are you giving a little up elevator to extend the flight, this causes a nose up attitude and shortens the glide, a little down elevator will actually result in a better glide and smoother landing.