Some may think this should be in the spad forum. But, it fits better here for me. Thank you in advance for your in-put.

I have gutter plane (gutter downspout, coraplaste design) that is really fun to fly. The problem with the plane is; with throttle set around mid, and plane trimmed to level flight. When you accelerate the plane climbs (at full throttle it will go to the moon, and will continue to loop) and with deceleration it noses over hard. At mid and above throttle, inverted, the plane noses towards earth. Oh, and if it makes a difference, it will flat spin like a frizzbie.

A little background on the design. It is short (regional maker design), I call it my Indy car plane. the fuse is 30" plus a OS FX.46 out front, and 2.5 inches of elevator out the rear. The wing is coreplaste 48" wingspand (totally symmetrical) and 11" wide plus 2.25" alieron. The wings leading edge is 5.5" back from back of the OS 46. The distance between the tailing edge of the alieron, and the leading edge of the horizontal stab is approximately 10". The horizontal stab ends at the approximate end of the fuse.

I have moved the CG back and forth some. I lifted the rear of the wing by .25" to change the angle of attack.


HEELLLP.......

Almost sounds like too little down thrust. check degree of d.thrust.Report back to this forum with d.t. in degrees.
There are many who are more qualified than me who will respond. Wing incedince?. You may get better response after the football games are over. HAPPY NEW YEAR!!

not the sharpest tack in the box,Fredsedno

Does sound like an engine thrust problem. Check out this trim chart at the Palos RC site...

http://www.palosrc.com/instructors/trim-chrt.htm

--Bill

Somewhat engine downthrust but mostly the CG is too far foward by the sounds of it.

Use a thicker than normal washer under the engine mount lugs where the rear bolts go through. Or if you've got a mount then add a wedge shim that puts the engine to 2 degrees downthrust compared to the flat bottom of the wing.

Next comes flight testing and what is called the dive test. You're going to trim the model for around mid RPM's (whatever throttle stick position that is) and trim the elevator for level flight. Then punch it over into a 60 degree dive from good height and let go of the sticks leaving the engine at the same throttle setting. Watch how the model pulls up from the dive. I'll bet it comes back to level and then noses up pretty quickly. That means it is too nose heavy and you're carrying too much elevator trim to compensate. So move the CG back about 1/2 inch and try again. As close to using the same throttle setting as you can manage but it's not really critical. Keep moving the CG back and retrimming in some down trim for hands off level and then do the dive test until the model shows that it is trying to lift the nose but it's not really doing it or it takes a LONG time to pull back to level from the dive. Avoid getting to where it just wants to straight line all the way in or where it wants to tuck to an even steeper dive. That's too far and you need to move it ahead a little.

On a large chord wing like this (the ailerons are part of the wing chord so you've got a 13.25 inch chord) moving the CG by 3/8 to 1/2 inch at a time to find the right ballpark is OK. Once you get in the range to can find tune the handling by shifting it an 1/8 to 1/4 one way or the other.

The reason it's more about the CG than the engine thrust is that if the model was dead neutral then even with the engine in line with the wing it would not nose up at all It would just accelerate. Going for a degree or two of downthrust just helps compensate for the usual amount of stability that most folks prefer. Don't try to mask the issue with downthrust. Add in a little by all means but then do the dive tests to set the CG location.

To get a head start on what you have and where your model's neutral point is (that would be the most rearward CG you should try under any circumstances) go look for the CG calculator link in the stickies in the Scratch Build forum.

Take the measurements that're required by this website and plug 'em in. There are 9 measurements and I think you've mentioned most of them. Then plug in a Safety Margin of 10% and click the button. Read out the CG location. Then replace the 10% with 20% and click again. The CG location that gives will pair up with the first one to give you an excellent idea where the safe CG range lies on your design.

http://www.geistware.com/rcmodeling/cg_super_calc.htm

The value of these established formulas is huge for situations like yours. It gives you absolutely dependable direction as to the safe range for the CG. It allows you to isolate and possibly reject the CG location as a player in your problem.

Hi bbellfly
All of my planes now are SPADS so I'm familiar with what you are facing. It does not appear you built a known model. Without some side view, top, and front photos anything we can offer is just a wild guess. Here is my wild guess based on my SPAD experience: The first time I built a symetrical wing (mine had all been flat bottom wing or slightly symetrical) I mounted it like a flat wing and experienced the types of problems you reported. For the plane to fly "normal" the wing incidence must be near zero. It sounds like you may have five or more degrees of positive incidence. When looking at the wing from the end, a line from the leading edge (LE) to the center of the TE) must be parallel to the horizontal stab and engine mounting surface. Small adjustments from this general rule may then be required to fine tune the plane. Others may chime in with contrary information. You will have to decide what to believe. You will find the information at spadworld.net much more useful and very believable. I suggest you build from a known plan to get experience before you try your own design. spadtothebone.com has many great and proven designs. If you want to build something different search for my Flying Lawnmower or Canard at this site.

These are shots taken. The wing is just laying on top and not fastened down for pics. Thanks for advice....

Also there is down and right thrust, if you think of the fire wall being flush with the edges of the gutter tube at the front. I have it set with top and left side flush. And, the bottom right corner is back in side the tubing about .25" These left's and right's are looking down the gutter tube towards the motor.

The wing has a ruler inside to make it symetrical. And, this is not a design of mine. It is a plane that is sold at the Perry GA R/C Show from a regional builder for many years. The wing is held in place by many rubber bands, usually 7 per side.

Part of this sure looks like you've got a VERY big wing and not a lot of horizontal tail or tail length. But being symetrical you should be able to get away with it.

For this sort of model with a symetrical wing and a small tail on a short fuselage like this you're best to treat it as a flying wing. That means 0-0-0 on the engne, wing and tail angles and go for a CG at 20 to 23%. Work from there to optimise the CG based on the dive testing described above.

Looking very hard at those pictures, there doesn't appear to be a saddle for the wing to tuck it's diamond airfoil into. The profile of that wing is what's called a diamond airfoil. And for it to sit properly on the drainpipe fuselage, there should be some kind of structure on the bottom-center of the wing, or on the fuselage. There isn't anything on the fuselage in the pictures. And from what the pictures show of the wing, if there is a special structure under it, it doesn't extend to the LE of the wing for sure.

When you strap on that wing, how does it orient itself to the fuselage?

Does the bottom-center of the wing look just like the top-center of it? Is there nothing extra under there?

Hi bbellfly
I wanted a photo of the end of the wing so I could determine if it is symetrical. A symetrical wing, when viewed from the end, with an imaginary line drawn from the LE to the center of the TE deviding the wing into two halves, has an airfoil shape at the top halve as well as at the bottom halve; thus the name symetrical. From your photos I am GUESSING that your wing is not symetrical. If it is flat it can sit flat against the flat fuselage. If it is symetric or simi-symetric, the TE must be raised so a line from the LE to the TE is parallel to the top of the fuselage. The wing appears to be much larger than it needs to be; it may belong to a larger plane. Or maybe the plane was meant to be a 3D plane. Those planes fly a bit different than "standard" planes, and the difference is accepted to get the 3D features. I suggest you contact the person who built the plane to get advice. Also, compare it to designs on spadtothebone.com. The short tail makes this plane difficult to trim in pitch. Increasing the horizontal tail area by 50% may give you the needed improvement. I recently was forced to do that with the vertical stab on my SPAD CoroCub to correct a tendency to nose over during landing.

Yes, the plane was designed with 3D in mind. When I purchased it 4 yrs ago, the builder told me (when I asked him if it was capable of hovering) his son had been hovering his regularly.

I will try and take the side view of the wing tomorrow. But, the wing is symetrical. Inside of the wing is nothing more than a yard stick glued on edge. It is approximatly inline with the pointed edge of the wing. If the wing were opened up (unglued at the back and both ends) it would be exactly the same measurement on both halfs. It would be like a hot dog bun.

As for a wing saddle, the orange piece atop the wing (coroplaste also) wraps around and under 2.5", both front and back. This keeps the wing resting on the gutter pipe evenly, with out crushing the bottom in the center of the wing.

To save you the trouble of taking the picture...........

In my drawing there are two dark green areas between the bottom of the wing and the downspout. If they were wedges, they would support the wing parallel to the fuselage. What does that job on your airplane? Is there something like those green wedges between the wing and the fuselage now?

On my wing, the orange piece (coroplaste 4" wide) on top of the wing, wraps around the wing and extends approximately 2.5" on the under side, both LE and TE. This supports the front and rear of the wing against the fuselage. The wing may not sit exactly parallel (LE and TE) to the fuselage, but it's so close you can't see it with the naked eye. In your diagram your wing is diamond shaped, mine is a little more rounded, both top and bottom.

Where is the CG?

It's been mentioned by a couple of us because it matters.

When an airplane trimmed for level flight climbs with an increase in power, and dives with a decrease in power it very often has the CG too far forward. It can be other things as well, but a too far forward CG is a good bet. The airplane is lugging around a CG that can be handled by the tail at cruise with the help of the engine. The pitch is balanced at that speed, but when the airplane speeds up, the tail trim works better with the increased airspeed. And that tail that has been pushing down some at cruise speed now pushes down even more. And the airplane starts to pitch more and more up. So now you slow it down below the cruise speed and now that horizontal tail trim doesn't work as well at the slower airspeed. And the CG simply pushes the nose down.

The tail on that airplane really looks marginal for the job it's being asked to do. When they're too small the CG range is very narrow. The CG range is where the CG can be, front to back, on the wing and the airplane fly ok. The range can be increased by increasing the size of the tail or moving the tail farther back. Or you can simply plug the numbers into that CG Locator and find out where that size tail, that far back, needs the CG range to be. And move the CG into it.

How far back from the wing LE is the CG?

If you want to tame the plane down so it flys more "normal", you could move the tail back a distance that you could decide from studying similar planes. One way to do it is shown on http://www.rcuniverse.com/forum/m_6735417/tm.htm. It is then common with SPADS to move the wing to get the CG location you need. I suggest that the MODERATOR move this whole topic to the SPAD section.

I have built and flown several SPAD designs and I had a similar problem with a FX-Bandit. I had it set up with the ailerons slightly drooped a couple of degrees down. Kind of liking flying with a few degrees of down flaps. At high speeds it would climb like crazy but at landing speeds I had to hold a lot of up elevator. All this changed when I set the ailerons at a couple of degrees up and the problem got better and vanished at about +5 degrees. Might give it a try.

I agree. Reflexing the rons up a bit has solved this problem on many ,many SPADs.