Outsides are larger than the Insides

I now have 2 planes that exibit this behavior: outside loops are larger than the inside loop. I really have to struggle during outside square loops. As the result, I've pankacked both planes upside down.

I've tried adjusting the handle so that it would be perfectly perpendicular to the lines. I've checked the maximum deflection angles: all about equal. On one of the planes the down line is in front while on the other one it's in the back so I would guess that doesn't matter. My other planes don't have that behavior so it's not a pilot error(or is it?).

What else can I check?

When I had the reverse of your problem, it was due to having unplanned downthrust built into the engine mount. Maybe you have upthrust? Mine was cured with a 3 degree shim.

>When I had the reverse of your problem, it was due to having
>unplanned downthrust built into the engine mount. Maybe you
>have upthrust? Mine was cured with a 3 degree shim.
>
>Jim Thomerson

Thanks Jim for the pointer, I'll check it tonight. What is a good way to check trust angle of a motor on a finished plane?

Are they profiles or full body (upright or inverted engines)? We have asked this before, but check to make absolutely certain that the flap (if any) and elevator both line up at neutral at the same time.

Something you may not have checked (and it is a little late) is to see if the belcrank is at neutral when the flaps (if any) are at neutral. If no moveable flaps, then make sure the belcrank is at neutral when the elevator is at neutral.

How much movement do you have in your flaps (or elevator)? Too much is just as bad as too little, but this can be controled by the spacing on your handle.

Can you get any slop in the flap pushrod when you pull on the leadouts? (Or if you lock the leadouts, can you get any slop in the flap?)

What is the weight and area of the two planes? Give a little more information and also check to make sure the thrust line is at neutral.

A final (dumb) question: How are you holding the handle at neutral? Is it possible that you are not able to move your hand as much in the "down" position as you do in the up?

You might also check for negative stab incidence or positive wing incidence.

Steven,

How is the 'neutral' bias of your handle? I like to be holding slightly up on the handle when flying level. That way when you give it down it turns immediately and makes square outsides corners much crisper. It will also make the insides larger/outsides smaller, which helps me since I just started intermediate recently. Also, you could adjust the handle with more throw on the down line.

You may simply have more up throw in your elevator than down. Make sure the flaps and elevators are truly at zero/zero and that the wing and horizontal stab chord lines are aligned with each at zero/zero. Then check the engine for up or down thrust and make it zero. The handle is next for bias. I just finished a new stunt ship and had the same. I have an adjustable elevator pushrod and have dialed out the up elevator until now I have equal throws and equal turns.

Steven:

Where do you live? I know you were at the Wrentham contest, I was too.

If geography permits, perhaps we can fly together.

Rick Campbell

Thrust line misalignment, pushrod flexing, control bias (bellcrank neutral with flaps/elevator neutral), flap/elevator misalignment, incidence or warp issues, could be the problem, or several of the above. Lots of ways to have this happen. I would suggest getting a Robart Incidence Meter (or two) and give the models thorough inspection, but if you can't remove the flaps and elevators, this can limit the usefulness. Best to do this during construction. The easiest thing to try is adjust the pushrod between the flap and elevators. One turn on the clevis made a huge difference on Jerry Day's Brodak Cardinal. Handle adjustments can also make a huge difference. Steve

Hi Rick!
I live in Stoughton which is about 20 minutes from the Wrentham field. I primarily fly at the Wingbusters club. The grooming of that field is amazing!

I checked the trust line on one of the planes last night. The motor is DEFINITELY pointing up! Since the plane is flapless and everything looks aligned AND it flies straight in either direction, the thrust angle is an obvious culprit! Thank you everyone for the pointers!

I will check out the other plane as soon as it's back in one piece.

Isn't it nice to speculate? We have given you many ideas (well, others can use them) and it is one "simple" solution. Is this a profile, by the way?

I guess there is a big moral here for everyone (and we all make our share of "goofs"). Check, double check, and make sure everything is square in the building process. A little extra care here makes trimming a lot easier.

I remember Matt spending a couple of hours one night measuring and shimming and had everything set up on accurate blocks ready to glue and then decided to let it rest over night so he could give it one final check the next day before gluing. Meanwhile, I came along and picked it up to examine his "progress" (not knowing he had it on accurate shims ready for gluing.)

Whoops!

Both planes are profiles. The flapless one is a Ukey with 550 wing area! The other one is a Pathfinder but I havent't put it back together yet to check things out.

I think Homer Simpson said it best when he said: "Doughhhh!"

>I think Homer Simpson said it best when he said: "Doughhhh!"
>
>Steven Yampolsky

Hey, I like the way you spelled that. Let's blame Doug!

LAST EDITED ON Jun-20-03 AT 12:53 PM (CDT)
 
I saw that too...I was wondering if someone would see that...

Yeah I will take the blame....

Leonard,

I was going to tell him to slide the outside line further away...

ALAS, I HAVE FAILED!

After all these years of writing over and over again about the inconsistencies of turn performance which can be tracked directly to unsealed hinge lines and not a single mention of the problem in 14 responses to a question on unequal turns.

Sure, the thrust line could be slightly out of rig and it is well worth while to make it right. Unless, however, it is grossly out of whack it probably won't solve a turn problem that involves "crashing" while trying to do outsides.

Steven, on a flapless design the first things to check will be: No 1, Center of Gravity (measure how far back from the leading edge it balances on your fingertips when picked up on your finger tips halfway out each wing; and, at that point measure the distance from the leading edge to the trailing edge. The distance aft of the leading edge to the balance point divided by the length of the chord will give you the CG in percentage of the average chord). No 2, make sure that the hingeline is sealed so that high pressure air can't move through the gap to the lower pressure side and throw away the lift you need form the tail to make the ship maneuver.

The CG on your flapless design should be at right around 15% of the average chord, the hingeline should be sealed and the pushrod should be supported so it can't bend under compression (a flexing pushrod on your ship with a front up line could well cause the symptoms you describe on down control). If such an airplane is straight and has reasonable power it "will" turn more or less the same inside and outside.

The flapped ship is a much more complex animal in this area and needs a lot more analysis. The unflapped ship should be a no brainer.

Let us know how things work out.

Ted Fancher

The elevator hinge line is sealed. I haven't checked the CG since I didn't think that would affect the turning radius's.

I don't know about this "sealing the hingeline" thing, Ted. I think we should just blame Doug.

Seriously, I hadn't considered sealing the hingeline since there was a problem between insides and outsides. If the insides were doing fine, then I would think the outsides... (Am I trying to think too much?) I suppose it is possible if the incidences are off (which would be a problem in itself) of if the hinges are such that there is a larger gap one way than the other.

Interestingly, on only one plane that Matt has built recently did sealing the hingeline make any noticeable difference. And that was one that he refinished and ended up with considerable gap after resanding. On all the others he fits the hingeline "fairly" close (and I know, those air molecules are quite small) and sealing didn't do anything that we could tell. On one we were trying to get more "kick" out of the tail. He sealed the hingeline. Nothing. My own feeling is that if the hingeline is fairly tight, there won't be any appreciable difference. I would agree, however, that there could be differences in lift amounts, especially on flap planes, that could affect trim. Sealing the hingelines could be a help, but it also adds some stiffness, so it is a double edged sword. But it is always worth a "try and see".

On the pushrod, most pushrods pull in the "down" position, and since it is the outsides where he is having trouble I sort of discounted that. Still, if the horn is on top...? It does make a viable question to ask. Every time we make assumptions that "this is not the problem" we get ourselves into trouble.

LAST EDITED ON Jun-22-03 AT 02:36 AM (CDT)
 
>>I think Homer Simpson said it best when he said: "Doughhhh!"
>>
>>Steven Yampolsky
>
>Hey, I like the way you spelled that. Let's blame Doug!

I checked my other plane that was flying large outside loops and found was the culprit was!

1) the controls were rigged as such that when the elevators were neutral, the flaps were a pointing down a little. This means that the elevator would get a LOT more help from flaps on the inside loops!
2) The metal wire at the end of the CF pushrod(flap to elevator), slides in and out when pressure is applied. My guess is when doing full deflection maneuvers, it slides just a little. Since I'm a beginner, I generally fly inside maneuvers. The pushrod kept sliding just a little, every time I flew causing even further misalignment.

With that fixed, I flew the Pathfinder yesterday and my initial impression is that the insides are as tight as the outsides.

Thank you guys for helping me out!

>I checked my other plane that was flying large outside loops
>and found was the culprit was!
>
>1) the controls were rigged as such that when the elevators
>were neutral, the flaps were a pointing down a little. This
>means that the elevator would get a LOT more help from flaps
>on the inside loops!
>2) The metal wire at the end of the CF pushrod(flap to
>elevator), slides in and out when pressure is applied. My
>guess is when doing full deflection maneuvers, it slides
>just a little. Since I'm a beginner, I generally fly inside
>maneuvers. The pushrod kept sliding just a little, every
>time I flew causing even further misalignment.
>
>With that fixed, I flew the Pathfinder yesterday and my
>initial impression is that the insides are as tight as the
>outsides.
>
>Thank you guys for helping me out!
>
>Steven Yampolsky

Hey, Steven,

Now you've got me scratching my head. Your original post said your outsides were larger than your insides and this last one said that now the insides are as tight as the outsides. Can you let us know which statement was correct?

If the flaps were down with neutral elevator I would expect the outsides to be quicker and smaller. Trimming them to neutral at the same time I would expect the insides to get more responsive and the outsides less so...which, I think, is what you just said.

>Now you've got me scratching my head. Your original post
>said your outsides were larger than your insides and this
>last one said that now the insides are as tight as the
>outsides. Can you let us know which statement was
>correct?

Me English not good so much . I meant to say that it looked like the outsides are just as tight and easy to turn as the insides.

>
>If the flaps were down with neutral elevator I would expect
>the outsides to be quicker and smaller. Trimming them to
>neutral at the same time I would expect the insides to get
>more responsive and the outsides less so...which, I think,
>is what you just said.

Now you've got me stumped. The way I see it is that with the same amount of up elevator, the flaps are down more with the ship right side up. Upside down, the same amount of up elevator results in less down of the flaps. Wouldn't that translate to larger outsides?

>Now you've got me stumped. The way I see it is that with the
>same amount of up elevator, the flaps are down more with the
>ship right side up. Upside down, the same amount of up
>elevator results in less down of the flaps. Wouldn't that
>translate to larger outsides?

I think you are right. Your original quote was:

>1) the controls were rigged as such that when the elevators
>were neutral, the flaps were a pointing down a little. This
>means that the elevator would get a LOT more help from flaps
>on the inside loops!

A plane set up like this will glide well after the engine quits. Try the opposite, and it glides like a rock. But to get the plane flying neutral, you will need to dial in (at the handle) a little down elevator to counter the flaps (which will now go partially up). But you have a lot more "up" control available than you have "down", because part of the down deflection of the elevator is countering the effects of the flaps.

As set up originally you have better insides than outsides. Now you should have things more even.

(Something a lot of people don't consider, however, is the location of the belcrank. If the belcrank is not at neutral when the flaps are at neutral, there will be a bias when the plane is flying level giving more (or quicker) control in one direction over the other. When constructing your plane, make sure the belcrank is at neutral when the flaps are at neutral, and then make sure the elevators line up perfectly with the flaps. You got it.)

Steven,

Drop the trailing edge of the elevators with neutral flap until the turns are balanced. All of my Mustunts and both of my Sea Furys turned tighter inside and required elevators adjusted downward until the turns balanced. Both NATs winning Sea Furys had about 3/16" down elevator trim. After building 5 straight airplanes needing down elevator adjustment, I started using stabilizer incidence instead and never looked back. I published the first intentional use of stabilizer incidence in my Mustang article in 1978.

Steven,

It's a common problem. I'm pretty sure that the flap blanking the elevator on down has something to do with it. Let the TE of the elevator dangle about 1/8" below its neutral position and I think you will like it better.

Some clever folks use stab incidence to compensate..

[photo not recovered: 3e69bb3870f12ad5.jpg]

"I'm not cheap, but I am on special this week."

>Steven,
>
>Drop the trailing edge of the elevators with neutral flap
>until the turns are balanced. All of my Mustunts and both
>of my Sea Furys turned tighter inside and required elevators
>adjusted downward until the turns balanced. Both NATs
>winning Sea Furys had about 3/16" down elevator trim. After
>building 5 straight airplanes needing down elevator
>adjustment, I started using stabilizer incidence instead and
>never looked back. I published the first intentional use of
>stabilizer incidence in my Mustang article in 1978.
>
>Al

Am I missing something, Al? This is what he has got, right?

>1) the controls were rigged as such that when the elevators
>were neutral, the flaps were a pointing down a little. This
>means that the elevator would get a LOT more help from flaps
>on the inside loops!

If the flaps are down when the elevators are at neutral and you bring the flap up to neutral, then you bring the elevator down.

Yup! Sometimes the simplest answer is the best. Add down elevator as necessary with neutral flap. (or if you prefer, down flap with neutral elevator works the same way). You aren't getting help from the flaps. You are simply trimming greater elevator total deflection on down which will tighten outside turns with little negative effect on the airplane's overall characteristics.

>Yup! Sometimes the simplest answer is the best. Add down
>elevator as necessary with neutral flap. (or if you prefer,
>down flap with neutral elevator works the same way). You
>aren't getting help from the flaps. You are simply trimming
>greater elevator total deflection on down which will tighten
>outside turns with little negative effect on the airplane's
>overall characteristics.
>
>Al

What I was saying, Al, is that is the way he had it. By accident he had the trailing edge of the elevator drooping with neutral flap. I am thinking he needs to line these up.

I understand what you are saying, but I think you were desigining for a problem due to the height difference between the root of the wing and the height of the stab. (I don't know, I am guessing.) But this is what he has and he has got a problem.

It is possible, also, that his belcrank is not at neutral with neutral flaps and that he is getting more (or faster) deflection one way than the other.