Thin wings?

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Turd Ferguson

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That was Wittman’s O&O Special (Sort of a long-range Tailwind on steroids; O&O = Oshkosh to Ocala …).
I agree. The plane was NOT a tailwind. Other than some visual resemblance, the airplane had nothing in common with the increasingly popular tailwind.


This topic was understandably batted around among the Tailwind folks – As best as I recall, by the time of the delamination, the fabric/wing attachment was almost 20-year old, so although the chain of events that led to catastrophic failure was real enough, it took years to actually develop… regrettably some of the old hands remember someone noting the start of the delamination (just a bubble at the time), and bringing it to Steve’s attention – he apparently said he’d fix it soon
It's quite possible the NTSB arrived at the wrong conclusion with regard to the probable cause. The airplane may have first experienced airframe flutter, which caused the already detached fabric to be pulled from the plywood wing surface. There is no conclusive evidence either way in which order the events of the accident occurred. Having seen the airplane about a yr and a half before the accident, I can confirm the wing fabric had several places were it was not bonded to the plywood wing surface. The fabric was still quite taut and not any more subject to flutter than a wing without an underlying plywood skin. SW knew this which is why he continued to fly the plane in that condition - it's not a concern that would warrant grounding the plane. The finish was also mottled as reported but that too is more a cosmetic issue than a safety issue.

Put another way, had SW used unmarked (uncertified) fabric, there would have been no covering process manual to reference and the NTSB would not have had any evidence that the fabric was improperly applied.

apologies for the diversion......
 

SVSUSteve

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It's quite possible the NTSB arrived at the wrong conclusion with regard to the probable cause. The airplane may have first experienced airframe flutter, which caused the already detached fabric to be pulled from the plywood wing surface. There is no conclusive evidence either way in which order the events of the accident occurred. Having seen the airplane about a yr and a half before the accident, I can confirm the wing fabric had several places were it was not bonded to the plywood wing surface. The fabric was still quite taut and not any more subject to flutter than a wing without an underlying plywood skin. SW knew this which is why he continued to fly the plane in that condition - it's not a concern that would warrant grounding the plane. The finish was also mottled as reported but that too is more a cosmetic issue than a safety issue.

Put another way, had SW used unmarked (uncertified) fabric, there would have been no covering process manual to reference and the NTSB would not have had any evidence that the fabric was improperly applied.

apologies for the diversion......
No apologies need since I was the one who derailed the thread there and plus, it's interesting to hear your input. It's a case I have always wondered about so it's nice to have some additional insight into it.
 

WonderousMountain

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Have you looked into the Daedalus style airfoil. Good performance at low Reynolds. If you're using flaps, it's important to make sure they are effective with the foil you're investigating.

LuPi
 

BBerson

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Thanks For analyzing and I made some changes,Kindly advise on this,I would like to design a
All metal single seat Aircraft high wing tricycle gear Tractor engine,I have got access to CNC machine,
Aircraft will have wing span of 5.4mts and 1.3mts chord,To minimize stall it got 60% span flaps 30% of chord,
Total aircraft weight 60Kgs Including ZDZ360 Quad engine drirect drive 36' 16' three balde carbon,
Including Me and 20litrs fuel TOW will be 140kgs,
wing loading is 20kgs sqm,
Flaps do not minimize stall. Actually the opposite, flaps can cause a sharp stall break.
Have a look at the airfoil characteristics in the book: THEORY OF WING SECTIONS.
 

dcstrng

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There is no conclusive evidence either way in which order the events of the accident occurred...
Sorry for the digression, but thanks for sharing the explanation/description, you obviously had firsthand knowledge – always been fascinated by the O&O, but what I know about it is distinctly 3rd-hand lifted off the TW forum… we had a couple of TWs and a Cougar where I used to hang around many decades ago (mid-Ohio), but in my few early 90s trips to Oshkosh, I never met Steve… met several other of the EAA gentry, but always regretted not taking the time to listen in on a Wittman seminar or something…
 

Aviatorzaki77

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Your engine (a 35 hp UAV/Giant Scale Model engine) is not cheap and I don't have any ideaof it's reliability. You could put together an ordinary ultralight with a proven engine for less.!

I have compered to an ultralight engine, weight number goes about 40 kgs with prop & reduction for rotax 502,
And ZDZ360 with prop comes around 12kgs with every thing included ignition battery mufflers ,
28 Kgs weight saving on engine alone, thin wing design will save further 5 kg, and my own weight is 72kgs,
Wing Span is almost half of an average ultralight IE 5.4mts, total wing area is 7sqm so 30-40% lighter the UL wing,
length will be 4mts where as 6mts for average part 103 aircraft,
Over all weight 60Kgs is not unrealistic but with careful design it can be achieved,
wire bracing and carbon fiber reinforcement at load-point in wing spar and fuselage will do the trick,
Engine will not run at max even for 3 mins for Takeoff and initial climb,
And for level flight it hardly needs 16 Hp that 3800-RPM at that power U can run forever
By just monitoring ETG,

Further criticism is highly appreciated to correct myself.
 
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Aviatorzaki77

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Flaps do not minimize stall. Actually the opposite, flaps can cause a sharp stall break.
Have a look at the airfoil characteristics in the book: THEORY OF WING SECTIONS.
Flaps are not used as brakes. Flaps are used to increase and maintain lift at slower speeds. During the flare the flaps change horizontal energy to vertical energy that is used to decrease the sink rate prior to touchdown. Fowler type flaps, as on Cessnas, deflect air downward and the gap created on flap deployment helps increase airflow over the wing's trailing edge. In the flare the flaps allow an energy conversion from horizontal to vertical. The air is reflected downward into the ground effect region. This allows the aircraft to be slow, nose high and controlled as it floats to touchdown.

controlling flap operation on aircraft
 

bmcj

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Flaps are not used as brakes. Flaps are used to increase and maintain lift at slower speeds. During the flare the flaps change horizontal energy to vertical energy that is used to decrease the sink rate prior to touchdown. Fowler type flaps, as on Cessnas, deflect air downward and the gap created on flap deployment helps increase airflow over the wing's trailing edge. In the flare the flaps allow an energy conversion from horizontal to vertical. The air is reflected downward into the ground effect region. This allows the aircraft to be slow, nose high and controlled as it floats to touchdown.

controlling flap operation on aircraft
But if you read further:

Flaps contribute primarily to the landing approach angle by increasing the 'braking effect' of drag. The drag is used initially to increase the approach angle without a corresponding increase in speed. There is no appreciable (required or created) change in approach speed as distinguished from no-flap speeds. When the approach slope is changed into the roundout and flare, speed is quickly decreased. It is this decrease in speed, the horizontal slowness of possible ground contact that protects the aircraft structure. The more flaps available and used, the slower the speed, the slower the touchdown and shorter the rollout.
Flaps change the lift and drag profile of the airfoil. Small amounts of flaps can enhance lift, but typically add some drag too. A large flap deployment is almost always done to increase drag, not lift, for approach angle control. Complex flaps like you see on an airline can be designed to augment lift greatly, but they still add drag.
 
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Aviatorzaki77

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But if you read further:



Flaps change the lift and drag profile of the airfoil. Small amounts of flaps can enhance lift, but typically add some drag too. A large flap deployment is almost always done to incrase drag, not lift, for approach angle control. Complex flaps like you see on an airline can be designed to augment lift greatly, but they still add drag.

SO I have to limit my flap angle, That is what a pilot has to do use flaps for lift or brakes,
 

SVSUSteve

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SO I have to limit my flap angle, That is what a pilot has to do use flaps for lift or brakes,
The big limit is probably going to be, with the thin section, how much space you have for the mechanism to deploy the flap. The other limit is probably going to be the pitching moment.
 

bmcj

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SO I have to limit my flap angle, That is what a pilot has to do use flaps for lift or brakes,
Use a little bit of flaps for increasing lift for slow flight and (maybe) shorter takeoff. Use more flaps to increase lift for slow flight while adding drag to allow you to decend steeper without picking up speed. Use all of the flaps to add drag for a very steep decent (you don't need the extra lift of partial flaps for slow flight if you are in a nose down steep decent).

The stall behavior with flaps is very much going to depend on which aircraft you are in. Each has its own unique behavior.
 

WonderousMountain

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Thin wings have later trailing edge separation drag rise compared to greater thickness, perform better during high Cl and mush stall. For very light planes where spar weight is low (like birds) there is something to be gained by wings sub .12C thickness. We all know what laminar and fat leading edge foils with high CL flap arrangements, alternative choices take a bit more thought for the indoctrinated. The question is are you getting some gains over common arrangements or following a skinny rabbit to the middle of nowhere. Enter does not work... LuPi
 

Aviatorzaki77

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The big limit is probably going to be, with the thin section, how much space you have for the mechanism to deploy the flap. The other limit is probably going to be the pitching moment.
Flap Mechanism is electrical most probably window glass geared motor it will be installed internally at wings main spar,
I will give you the drawings very soon, And Pitching Movement will be around 30 Degrees,
 
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SVSUSteve

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Flap Mechanism is electrical most probably window glass geared motor it will be installed internally at wings main spar,
I will give you the drawings very soon, And Pitching Movement will be around 30 Degrees,
You do know the pitching moment is not the same thing as the flap angle, right?

By window glass, do mean silicate glass or am I misreading that?
 

WonderousMountain

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Looking forward to the drawings,

How quickly does the electric servo work? I would suggest less than 3second for full reversal. Although I have preference for mechanical actuators.

LuPi
 
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