Scale Curtiss XP-55 Ascender

[acerc]

Larry, I think we are both on the same page in general, we may disagree as to what extent each role plays. I still say put the plane on a scale as I described. I do this to see how much my models shift from the mfg suggested sweet spot. It is usually not much but occasionally one is off a good bit. My Pitts Eagle is my example, for my idea of proper flight the so called c of g after I set up for flight is out of the mfg'ers suggested range, and when weighed the tail had gained a good bit versus factory specs. I contribute this difference to the fact kit or ARF manufactures purposely build for a user friendly aircraft where as I change that to make the aircraft perform my way. Modified kit or scratch building usually changes the manufactures range and I suspect the changes you made to your Ascender is in the same boat.

 

[Larry B]

Hi Doc,
I am sure you have more "biplane" experience than I do, but I set up my Fiat with the upper wing having more incidence than the lower. From what I read the main reason this is done is because when the airplane stalls the upper wing stalls first, and this moves the center of lift further back because the lower wing is now lifting (this only works if the upper wing is in front of the lower wing!) Now with just the lower wing lifting the center of lift is further aft of the CG which helps to cause a nose down pitch for stall recovery.
The Fiat is my only attempt at a biplane design from scratch, and it seems to fly pretty good so I think I got things right?
Thats the cool thing about this silly hobby, there are no rules! Go with what works for you.
Larry B

 

[acerc]

Doc, a lot of builders do the same, I am not one of them. I learned to fly them to the ground and typically build per full scale and a lot of full scale don't make the same adjustments. Again, my Eagle as an example, is built per full scale as in no engine offset thrust, no incidence on the wings, 1-1/2°+ on stab, per full scale plans of the aircraft. And it flies like it is on rails, lands a bit hotter than typical though, pure enjoyment.
My Cub has, like seen in the pics posted by Larry, an adjustable tail. It is on a servo and mixed a little with throttle to aid in maintaining level flight at different speeds.

 

[Doc]

I follow the reasoning behind positive decalage I just have had good luck with my method. Its true my Nieuport doesn't break when it stalls it just sort of settles, no wing drop tendencies, makes real pretty three pointers. It's real lightly loaded , only 32 oz per sq ft
Doc

 

[Larry B]

Ace,
I understand what you are suggesting, balancing the model on the manufactures recommended CG location. My problem is that when you draw your own plans and design the thing from scratch there is no place to start other than the full scale CG location. In the case of the Ascender that has to go completely out the window because the full scale airplane was not a canard but rather a flying wing with a floating elevator way out in front.
It seems like I pick that absolute worst subjects to try and model

 

[Doc]

Perhaps we should talk about that.
Doc

 

[Pistolera]

Perhaps we should talk about that.
Doc

 

[pawnshopmike]

Perhaps we should talk about that.
Doc

 

[Larry B]

Well today I tore it up. It's repairable but I am beginning to think it may not be worth it. This flight was done with the CG moved back 5/8" more and after making 3 approaches I stalled it. With the CG back this far the nose would not come down even with the application of down elevator which was really strange. As the thing would slow down a bit the nose would rise and then of course there goes your airspeed, also the pitchy tendencies were back but not as bad with the gyro helping out.
I'll have to sleep on it as to what to do with the thing, I would have a really nice electric power set up I could use in something else

 

[Pistolera]

Ahhh sh*t.....sorry to hear that . Take a break and ponder the future!