Bi-Plane Stall Behaviour

[Ultralights]

today i was asked a question by a student that i couldn't answer, after watching the red bull pits arrive at bankstown, i was asked if a Bi plane has 1 wing set at a lower angle of incidence to reduce the nose drop or loss of lift/control in the stall? i can see what the student was thinking, if the upper or lower wing was set a lower AOI then at the stall, only one wing will stall, and the other providing lift (until it stalls itself)
yes, the lesson was stalling, and i understand the washout, chord twist, and other design features designed to make the stall more controllable, but bi-plane stall characteristics has me stumped.

[chimbu warrior]

There are probably as many different wing combinations as there are biplane types, so the short answer is that there is no one rule for biplanes.

Considering that there are staggerwings (not just the Beech model of that name), sesqiplanes, and various other configurations, stall characteristics would vary greatly.

[djpil]

Curtis Pitts original patent info is online (http://musclebiplane.org/htmlfile/pittspat.html)and should be enough for you to impress any student about wing design of the Pitts.

[Green gorilla]

Dont know about fullsize but with rc aircraft the top wing is 0 to -1 and the bottom wing +1.

[Ultralights]

now that patent paperwork was a very informative read!

[Spanner Turner]

Oh Goody!

One of my 'favourite' words that I picked up during my apprenticeship (yes.... I know it's sad that I have fav words) is the term "decalage".

:D :D

This describes the difference in the angle of incidence between the top and bottom wing on a biplane.

If the upper wing has a higher angle of incidence (relative to the a/c longitudinal axis) then it has 'positive' decalage. Vice versa for 'negative' decalage.

:ok:

Due to different "incidence" angles therefore AOA is different between the wings so a stall is much less dramatic. i.e with one wing in the stall you have only "lost" approx half of your lift instead of nearly all lift during a stall in a single aerofoil aircraft.

:ok:

[SystemsAreGo]

the wings so a stall is much less dramatic. i.e with one wing in the stall you have only "lost" approx half of your lift instead of nearly all lift during a stall in a single aerofoil aircraft.

Agreed.. A certain wallowing sensation occurs with the stall. Then you kick in full rudder, pull the stick and hold on. :eek:

On another note, try flying level inverted and you will be amazed at how much forward pressure is required. Goes to show that symmetrical wings aren't quite as effective as they look due to upright rigging.

Good question Ultralights :ok:

[judge.oversteer]

I thought decalage refers to the difference between the angle of incidence of the top and bottom wings whereas stagger refers to the fore/aft horizontal positioning relationship of the wings! i.e. Tiger Moth +ve stagger, Beech 18 -ve stagger.

Apologies if I'm wrong.

JO

[SystemsAreGo]

Decalage - Decalage is the angle between the chord line of the upper plane and that of the lower plane and is positive when the top plane is at a greater angle of incidence than the bottom.

Taken from * Decalage - (Aviation): Definition (http://en.mimi.hu/aviation/decalage.html)

[solowflyer]

Saw a tiger Moth at an airshow perform what was called a falling leaf where it appeared to float down verticaly and wallow from side to side like a falling leaf. Has this manouver have anything to do with the stalling properties of the bi plane, It looked very impressive.

[ROB-x38]

If the upper wing has a higher angle of incidence (relative to the a/c longitudinal axis) then it has 'positive' stagger.

Every definition of stagger i've seen relates to the relative position of each wing and has nothing to do with angle of incidence or 'riggers' angle. ie: Agree with the judge.

As far as "decalage" goes I think the generic definition is simply something like different angles of incidence between aerofoils. It doesn't specify whether those aerofoils are the top and bottom wings of a biplane, or more commonly, the mainplane and tailplane - longitudinal stab issues.

[Mustangbaz]

hey i've done that in a Warrior 2, it just mushes (technical term) down, but you have to hold the column all the way back to the stops, on a side issue has anyone else flipped an Archer upside down :} (incipent spin testing before ppl test) we laughed so hard we tried again :E

[Spanner Turner]

Sorry for all who read my original post #6.

I'd had a few and typed stagger where I meant decalage. :{

I was going to explain the difference between them both and had both definitions in my pea brain, then decided to just stick to the original question r.e decalage yet mashed both definitions together. :ugh:
You can now see with the change of just those two words it reads correctly.

Sorry to all. My post #6 has been rectified.


judge.oversteer, SystemsAreGo and ROB-x38 were all on the ball. :D
Sorry gentlemen.

:ok:

[joehunt]

I flew the Grumman Ag Cat 600, years ago and it was a beautiful docile aircraft to fly. You could do a max rate turn, pull a bit more and watch the top wing stall and it would just shudder, shake and wallow. Needed the ball in the middle of course.

Up until that time, there had been no fatal Ag accidents in Ag Cats, ever recorded. I would not be surprised if that still stands today. Says a lot for the design of the aircraft, does it not?