high stabs? full scale airfoils?

[mmcconville]

	Quote: Originally Posted by Bam Bam
	Q for mike, how much higher is the stab on the H9 35% 260? i heard these planes fly very true and am considering getting one if i can find one in oz (distibutor O'reilly doesn't seem to want to get me one for at least six months!!!) i like the nice big wing area!

Bam Bam. Tes the 260 is very true. When the Cg is correct, the pitch coupling is very minimal as is roll coupling.

Going from memory, I believe I ended up putting the stab around 6mm to 12mm above the wing center line. The prototype had a little higher stab, but I lowered it to reduce coupling a little.

[Bam Bam]

i belive the weight of a plane would also make a difference to the way it fly's along with c.g.?
If it's lighter it should fly better with less coupling yeah? or not?

[mmcconville]

Not really. Weight will effect elevator trim slightly, which effects pitch coupling but a slight CG change will eliminate that.

[Mithrandir]

I had a Jekyl years ago and I kinda did an anhydral thing to the stab... it was popular back in the dark ages... (1970's and 80's)...
anyway... the plane was the only plane I ever had that truly had ZERO pitch coupling.... it had adverse roll coupling... but just a little baby amount.... and being a pattern plane, I never got it to like 45 degrees of beta.... (Like my avatar)... so who knows what would happen at that extreme angle....

But worse then coupling, is coupling that is really nonlinear, or very speed dependant, or very "Beta" dependant... or worse yet,.... coupling that changes sign (or direction) as a function of beta... rumor has it that one of the more expensive all composite bad ass planes has a KE coupling that goes positive-negative-positive as you go from zero beta to 50 degrees beta.....

Bottom line in my book... consitant and predictable are virtues to be treasured!!!

[Bam Bam]

i dig that! Very true! thats what i am really chasing i guess, consistancy.
and of all the planes iv'e had, including the 50cc's and 100cc's was the fliton extra 330 freestyle! obviosly not as nice as a 100cc, but it had the best flight characteristis and manners of any plane i have flown! in a .46 size glow!!!

[03fomoco]

One other consideration given in fullscale is ground clearance. Pretty sure there is an FAA requirement for this also?

[kjkimball]

I can attest to the lack of coupling in the full scale model 12 Ti-12. In our test flights, the airplane was rigged for hands and feet free flight level and high cruise speed, say 190 mph. Knife edge flight left or right wing down had zero pitch coupling. It did not want to go to the canopy or to the wheels in level knife edge or in a knife edge climb. Wings level same speed hands off the stick and input full left or right rudder made a flat skidding turn, no roll, no pitch deviation. From 230mph 5 g pull to vertical, hands and feet off controls on the vertical line, the airplane continues straight up until stops and simply flops over pointing vertical down and did not deviate off the vertical downline as it gained speed. Pilot reported he felt it would drive straight in if he did not make control inputs.

So, this is an example of an airplane that has a high stab and some of the arrangement issues pointed out above to allow pesky humans to ride in it that has near zero coupling. This shows that some full size airplanes can fly like a model and do not count on the pilot to "correct" the coupling issues.

Some other notes on this airframe is that the wings and stab are all +2 deg incidence while the engine is zero down and 2 deg left thrust (russian backwards rotation engine). CG at about 27% MAC.

[flying skunks]

well said Kevin , if you are flying a well designed and built plane you should not have any KE coupling issues ..

[Mithrandir]

	Quote: Originally Posted by kjkimball
	.................Some other notes on this airframe is that the wings and stab are all +2 deg incidence while the engine is zero down and 2 deg left thrust (russian backwards rotation engine). CG at about 27% MAC..............

Interesting!!!

How much static margin do you have??? Did you do a broad CG sweep in test flight to find "The Sweet Spot"?

Did you experimentally arrive at the incidence and thrust line???

[sukhoi26mx]

	Quote: Originally Posted by kjkimball
	I can attest to the lack of coupling in the full scale model 12 Ti-12. In our test flights, the airplane was rigged for hands and feet free flight level and high cruise speed, say 190 mph. Knife edge flight left or right wing down had zero pitch coupling. It did not want to go to the canopy or to the wheels in level knife edge or in a knife edge climb. Wings level same speed hands off the stick and input full left or right rudder made a flat skidding turn, no roll, no pitch deviation. From 230mph 5 g pull to vertical, hands and feet off controls on the vertical line, the airplane continues straight up until stops and simply flops over pointing vertical down and did not deviate off the vertical downline as it gained speed. Pilot reported he felt it would drive straight in if he did not make control inputs. So, this is an example of an airplane that has a high stab and some of the arrangement issues pointed out above to allow pesky humans to ride in it that has near zero coupling. This shows that some full size airplanes can fly like a model and do not count on the pilot to "correct" the coupling issues. Some other notes on this airframe is that the wings and stab are all +2 deg incidence while the engine is zero down and 2 deg left thrust (russian backwards rotation engine). CG at about 27% MAC.

Very cool! That's a pretty amazing set of accomplishments for any airplane, but especially so for a biplane. Great work!

The Sukhoi I fly, OTOH, has coupling galore with its high stab and low wing. Oh well, still suits me.

Scott

[Bam Bam]

pretty interesting stuff! i always wondered if full scale had the same amount of coupling issues as our models? i guess it is a rare thing then to have a scale model that flys with all pure inputs (no ke coupling or roll coupling)! since our imac planes are modeled after full sized planes and the fact that the ideals for full size are so different from our models, we made never get the perfect setup with the 10% rule!

What we need is someone to make a full size pattern plane with 3d style elevators, rudders & ailerons so we can use them for imac!

42% passort anyone!!!

[kjkimball]

	Quote: Originally Posted by Mithrandir
	Interesting!!! How much static margin do you have??? Did you do a broad CG sweep in test flight to find "The Sweet Spot"? Did you experimentally arrive at the incidence and thrust line???

The CG range for this design from birth in 1993 when Curtis Pitts designed the airplane has always been 15%-28%MAC. We have test flown from 15% to 30% in the 2 seat model 12 aircraft. In the case of the python and Ti-12, we did not have to make tests with varied CG since I knew what to expect based on the 2 seater. The ti-12 will operate between 24-28% MAC throughout all its flight payload conditions.

The incidence and thrust values are all exactly as first designed in 1993 3 years prior to the first flight of the Curtis Pitts prototype model 12 in 1996. We have changed none of this throughout production of the airplanes and kits. This Model 12 design has the right combination of design elements to work very well. The airplane is big yet fast. Agile yet able mild mannered when needed.

RC models of the model 12 and variants are scattered in how well they fly. In most cases, the full scale model 12 has lower coupling than RC versions that have "fixes" built into the design. Quique's design seems to be the best handling of all the model 12 type airplanes. He made dozens of changes most of which even spot on RC designers have not picked up on. His design has coupling just about like what we see in the full scale python and Ti-12.

[toc pilot]

The answer to your disire to have everything scale and in scale places and also to have a plane with NO mixing is easy! The BH Yak 55M! lol...

But seriously, this is the main reason I love this Yak! The wing and stab placement is right where it needs to be and it is scale. There is no mixing required and it flys GREAT! Check out the pics and see for yourself. The Yak is a great choice regardless of the manufacturer!

[Mithrandir]

	Quote: Originally Posted by toc pilot
	The answer to your disire to have everything scale and in scale places and also to have a plane with NO mixing is easy! The BH Yak 55M! lol... But seriously, this is the main reason I love this Yak! The wing and stab placement is right where it needs to be and it is scale. There is no mixing required and it flys GREAT! Check out the pics and see for yourself. The Yak is a great choice regardless of the manufacturer!

all we need now is someone to distribute a 40% ARF for about $1399.00

hint....... hint....... hint.....

[King Snake]

A high stab helps pitch authority on full scales, as well.