Asymmetric wing incidence angles

Discussion in 'Aviation' started by gaussianum, Feb 15, 2006.

  1. gaussianum

    gaussianum Member

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    I've seen all kinds of statistics for aircraft, but I've never seen the differing incidence angles for each wing. They are necessary to counter engine torque rolling effects, as I understand it. They are probably small, which would explain why they are seldom mentioned.

    Does anyone have this information, for the wuergers and the Messerschmitts?

    Best Regards
     
  2. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    What you are referring to is also known as "wash in and wash out." Many aircraft had this designed into them, others could have it adjusted by essentric bushings installed at where the wing or other surfaces mount to the fuselage. If this is published at all it would be mentioned in the aircraft maintenance manual....
     
  3. gaussianum

    gaussianum Member

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    Thanks for the quick reply, FlyboyJ.

    I guess I'll have to dig deep into original aircraft maintenance manuals...:)
     
  4. Soren

    Soren Banned

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    The Spitfire and FW-190 both have 2 degree's of washout, while the Bf-109 has none as it doesn't need it because of the slats. Its there to delay tip stalls which can be dangerous.
     
  5. evangilder

    evangilder "Shooter"
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    Didn't the F-8 Crusader also have a variable angle of incidence?
     
  6. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Yep - the whole wing was "Jacked Up" duirng landing...
     
  7. gaussianum

    gaussianum Member

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    Thanks Soren

    After some more research, I don't think washout is what I'm looking for. It changes the wing's stall characteristics, but it doesn't add any net lift to the left wing, since it's symmetric, from what I gather.

    My guess is that, when you look at aircraft data, the wing incidence is the average of the left and right wing incidences.

    The difference between them is probably under 1 degree, which explains why it is rarely mentioned. I'm going to look for some typical values.

    Regards
     
  8. Soren

    Soren Banned

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    No problem Gaus, I haven't been able to find any data on asymmetric wing incidence angles for these aircraft, and Im not sure if they even had this actually.
     
  9. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    On some light aircraft I've worked on this is mentioned in the maintenance manuals but seldom mentioned as a value. Cessna uses eccentric bushings (as I mentioned earlier) and you adjust them on the inboard attach fittings. You need to fly the aircraft and do the actual adjustment by trail and error.

    I also know some aircraft actually had the vertical stabilizer off centered to counter torque. I believe this was true for the AD Skyraider and I think I heard this to be true for the Corsair.

    A YAK-9 was restored when i was working at Mojave a few years ago, a friend of mine worked on it. When completed an "asymmetry check" was done on the wings and airframe (this is done by hanging plumb-bobs off points on the aircraft and measuring the distance between them) and If I remember that one I actually think there was a twist built into the airframe....
     
  10. gaussianum

    gaussianum Member

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    Yes, I think that's the key to the problem. It's probably the stabilizer, not the wings.

    You're a pilot aren't you? From your experience as a pilot, or from footage you may have seen, what would happen if a fellow lost his vertical stabilizer? The aircraft would not only yaw, but also roll, wouldn't it?
     
  11. Soren

    Soren Banned

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    Interesting.
     
  12. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    I am a pilot gauss - I think if you lost everything, vert. stab and rudder, you would yaw and roll, no directional control, and probably would spin. If there was something left you might survive if you could counter the directional instability...

    A friend of mine was doing crop dusting in Canada a few years ago. He hit power lines and they took off all his vert stab and left half the rudder. The crazy sob actually landed on a road and inspected the damage. He then got back into the aircraft and flew it back to his base!!!!

    I think he was flying an Ayres Thrush, pretty beefy crop duster....
     
  13. JonJGoldberg

    JonJGoldberg Member

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    If an aircraft is properly trimmed for cruise flight and we increase thrust then it will climb and if we reduce thrust it will descend. But how this progresses is not at all straight-forward. The reaction to changing power, without the pilot touching the control column, depends on whether the cg is above, below or in-line with the line of thrust.

    For aircraft with a very high power-to-weight ratio, the possibility of a torque stall exists. I see the most visually striking likely scenario as a sudden application of full power in an aborted landing, where the airspeed has been allowed to decay below the safety speed. The torque of the engine and inertia of the large heavy propeller tends to twist the aircraft around the propeller shaft and the consequent roll may increase the AoA of the down-going wing past the critical AoA. If that happens the wing loses lift, accelerating the roll and the aircraft loses height very rapidly.

    Since both conditions reflect the cause of what you believe requires remedy by differences in wing incidence, as you are looking for supporting evidence, I’d like to offer the possibility that since both reasons for asymmetrical wing incidence are within the control of the pilot, are highly variable, it is impossible to find an asymmetrical fixed wing incidence that offers a better soultion to this 'problem' than a symmetrical one; or if it is possible, the design is flawed in a major way.

    There was a NASA ‘asymmetrical wing’ study, and an aircraft built, I do not recall it’s name, that featured a ‘shoulder’ or parasol wing that pivoted as a single entity, making the wing asymmetrical to induce great increases in turn performance.

    As for the tail off set thing, I’ll look into it, and repot if I find something, but I doubt I will, for the same reason given to the wings.

    Airframes with built in ‘twist’ as mentioned and ‘measured’ in postings above, are usually easily found in aircraft on the ground as the airframe is usually ‘straight’ only when in level non-inverted flight at 1G, at specified ‘normal weight, speed density air’. The ‘twist’ is the built in airframe ‘s response to being ‘unloaded’, or they are signs of an over stressed, or improperly serviced aircraft; or it is a B&V asymmetrical design.

    I’m glad to see that it has been realized; a rudder is not there to off-set torque, but is generally used to correct ‘slew’. I believe that since ‘normal’ flight means non-inverted, some of us may need reminding of the fact that the lines of force from effects of engine/prop torque may not necessarily be correctable by off-setting elevators, wings, or rudders, alone; and since there should only be a need to correct for ‘normal’ flight occurrences, where there steady application of torque can be ‘trimmed’ by using all three controls, or at times easier still the flight stick rudder pedals, as it becomes one of the many ‘factors’ involved in maintaining ‘stable’ flight; or we must be talking of a ‘winged’ aircraft such as the F-5U ‘Flapjack’, where the torque effects were too complicated to overcome, ‘till recently. If we are talking of helicopters… please disregard.
     

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  14. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    I don't quite undertand what you're trying to say, but I could tell you there are a great many aircraft built with a "twist" within their structure. Asymmetry ckecks are done after major repairs or after a hard landing. Some manufactures have numbers to verify if the aircraft is "straight" or out of tolerance

    The rudder coordinates a turn and maintains directional stability, period - flying 101
     
  15. gaussianum

    gaussianum Member

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    This is where I got the asymmetric wing incidence information:

    http://www.djaerotech.com/dj_askjd/dj_questions/propeffects.html

    Don Stackhouse says:

    From what you are saying, torque is always counteracted by the pilot; so, when the craft is flying straight and level, at cruise speed, one feels no torque because the ailerons are adjusted to compensate for it. So, when the controls are neutral, the ailerons are already off-centred to begin with?,

    On another forum, and also from the DJ Aerotech pages, I learned that the stabilizer has an angle, relative to the craft's roll axis.

    Someone also told me that the Ju-88's stabilizer was an airfoil.

    Making a vector diagram, I can conceive of a large vertical airfoil's torque counteracting the engine torque. But the main contribution would probably be a yawing one, not rolling.

    I think the propwash itself counteracts a bit the engine torque. But that is not enough; when you are taking off, you feel both a yawing and rolling force to the left, with a clockwise-rotating engine, from the pilot's viewpoint. The yawing is caused by the propwash hitting the tail, but the rolling is to the left, so the engine is dominating.

    But you don't feel the roll, at cruise speed. Unless the stabilizer acts as a wing, or the wings are asymmetric, or the controls (ailerons) are off centered to begin with, I can't see how torque is counteracted in such a situation.

    Maybe you're right; the ailerons are probably already trimmed from the start.

    Perhaps FlyboyJ could confirm that?

    Great story you told earlier, by the way.Typical pilot heroics:)
     
  16. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Here's a few things I'll try to answer based on your post...

    On takeoff, steep turns and at high angles of attack (approaching stall) is where you're going to really feel torque on an aircraft with harmonized controls. On light planes (the majority I fly) you will hold in right rudder during take off and while performing what you call a take off stall. In a steep right turn you will need less right rudder because of p-factor and the opposite when you go right.

    Some aircraft do have the ailerons adjusted so they too are counteracting torque, and again this could also be achieved by "wash-in/ wash out." Through out all this the rudder is used to maintain directional stability and coordinate a turn...
     
  17. JonJGoldberg

    JonJGoldberg Member

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    FLYBOYJ: Posted: Sat Feb 18, 2006 6:57 pm
    ..."The rudder coordinates a turn, period - flying 101."

    Tell that to the Wind or a '47 pilot during take off, or the unlucky pilot caught in a spin, see if they buy this...

    In low power aircraft, and gliders a long established means in controlling the longitudinal axis is to use a fin, or vertical stabilizer, which has a symmetrical airfoil section or just a flat plate, mounted at the rear of the aircraft and which applies a restoring moment to realign the longitudinal axis with the airflow. Note that restoring moment does not realign the aircraft with its original flight path; after restoration the aircraft will be aligned with a different flight path depending on the amount of original displacement.

    If you want to control these forces you build a rudder. The rudder is the control surface attached to the fin and is the vertical equivalent of the elevators. Pressure on the left pedal causes the rudder to deflect to the left so that the fin/rudder act together as a cambered airfoil producing an aerodynamic force pushing the tail to the right and consequently the nose swings left, i.e. the aircraft yaws left (yaw is a much better tem than slew; I apologize for its use in my previous post). The amount of yaw, at a given airspeed, is dependent on the degree of rudder deflection of course it is primarily dependent on the moment arm and rudder area. The aircraft will continue yawing if the rudder deflection is held by the pilot but, as the aircraft turns, the wing on the outside of the turn must be moving faster than the inner wing and thus generates more lift. The increased lift will raise the outer wing and the aircraft will enter a banked turn, but will tend to be skidding out because the bank angle will not be correct for the turn as we know that that only one bank angle will produce the desired radius or rate of turn for a particular airspeed (I do not know this to be fact, but slipping skidding are some of my most favorite ways to induce a miss by my adversary, while flying a sim, because I show one bank angle, but perform a maneuver more suitable for another).

    Because of drag and other effects, aircraft perform much better if their longitudinal axis is accurately aligned with the flight path or the relative direction of airflow. If not aligned then the aircraft velocity will have both a forward component and a slight lateral component. That bodily sideways movement is called slip or skid. Flying instructors may use the expressions slip and skid in situations when the airplane is banked and is ‘over-rudder-ed’ towards the lower wing (skidding) or ‘under-rudder-ed’ towards the lower wing (slipping).

    FlyboyJ you are referring to this, I hope, nothing personal now… but to you we are done right? Wrong…

    In high power aircraft, yaw (much more correct than slew, the use of which I apologize) can be induced by torque, such as during take off, and can only be corrected by the application of rudder, such as in a tail dragger with the rear wheel up…

    And what about the guy in a two engine aircraft with one engine out…

    I'm not so clear why on landing rudder could not be applied, as in my sim... ‘so’ since I’m no ‘real pilot’, I can not say this is fact, but during landings, especially carrier landings, using rudder is a mighty handy thing, but the in pilot’s manuals, not a one mention rudder during landings, drifting is recommended, even in cross winds.

    gaussianum,
    I gotta check into you post, but with regard to control settings being at 'neutral', what do mean? If the ailerons were ' off-centered' to begin with, for the reasons you state, or imply the posting states, why would there be a need for adjustment at all? So no the adjustment, or trim to the 'neutral' controls are due to the real time 'exact' requirements, to compensate for… torque, and or other factors, not because they are off center, but because they are on center.

    Anyway some images from flight manuals downloaded or purchased that seem relevant…
     

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  18. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    JJ - you're making this more difficult than what it actually is! A 47 pilot on take off is experiencing P factor, he squeezes in right rudder - he's controlling DIRECTIONAL STABILITY!!! ;)

    If you get into an accidental spin, its because you didn't apply enough right rudder and listen, here it is again CONTROL DIRECTIONAL STABILITY!!! ;)

    In a low power aircraft, you'll still have p factor...
    JJ - listen the rudder controls directional stability and coordinates the turn - its simple....
    Its actually referring to "Stepping on the ball" and nothing personal... ;)

    JJ again you're making this much more complicated than it is - on higher performing aircraft (say a P-47) once the tail is up you're continually squeezing in right rudder and maintaining directional stability, more than likely using the runway center line as reference - its that simple!
    That's a bit different - it depends if the aircraft has counter rotating engines and if there is a "critical engine." I could explain that on another post....

    You do use the rudder on landing and especially in cross winds, listen carefully, here comes that magic term - "Directional stability" Pilot 101...
    Most high performance pilots manuals are not going to go into on how much rudder you shuld apply on landing, you lean that as a student, it like learning how much you lead your car when you turn. By the time you're flying a P-47 (back in the WW2 days) its assumed you're proficent enough to know this....

    Remember JJ - not all aircraft have trim around each axis, most light aircraft just have elevator trim. You check the adjustment on them because cables stretch and contract, they will go out and you will feel a difference in the way the plane flies
     
  19. JonJGoldberg

    JonJGoldberg Member

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    gaussianum,
    Sorry dude!!! This article is very bad news, in my opinion (but FlyboyJ seems to like it, so maybe I should reconsider).

    From Your Article
    “…The tendency to yaw on takeoff and climb is due almost entirely to P-factor and slipstream effects. The only direct contribution that torque makes to yawing in the early part of takeoff roll is perhaps a slight increase in the rolling friction of one main wheel because the torque is causing it to carry more weight than the other wheel. Strictly speaking, torque applies a rolling moment to the plane, NOT a yawing moment.”

    He is trying, for some reason to say that the engine prop are always at a 90 degree angle to the direction of flight, and therefore can only produce a rolling effect. This is not true, thrust angle, and P-factor aside; because although the prop and engine are spinning in the same direction and are affixed to the aircraft in the same location, relative to say our author, the A-36 pilot, sitting in his cockpit, the relationship of the torque forces at play are not the same when viewed from the perspective of say Earth’s gravity, momentum, or rate of change to our aircraft’s direction of travel. For example, when your nose is straight up, as opposed to during take off, the prop has no P-factor, you, the pilot see the effect of torque as being the same as when on the ground in relationship to your aircraft, to an observer planted on the Earth, torque rotation changed from being a vertical force, to one that is horizontal. What is happening to the aircraft is similar to your experience, if you were holding a spinning bicycle wheel by the ends of the axel, as you change rotation, by swiveling (yawing) the axel, from horizontal to vertical, what is happening to our pilot is the view from near center of the axel.

    So I stopped reading from where I ended my quote.

    Flyboy J,
    Sorry, I’m from NYC, and it’s normal for us to bark a bit more than most over nothing… I think you are an OK guy, and a pilot at that, as is the A-36 pilot, a contributor to G’s referred posting… I am just a self taught pixel playing wanna be... Am I being thick? Help me please…

    P-factor I think is can be defined as seen (very cleverly) here… http://yarchive.net/air/airliners/p_factor.html

    I’m not trying to say that P-factor is not an included dynamic force in the least; what I am sayin’ is so is prop torque. That rudder is applied not only ‘coordinate a turn’ a phrase I now see on your post to have expanded to include directional stability, which if I saw as included, I honestly didn’t, as it is lacking within my last post, I would not have generated my response, as we would be in agreement for the most part (at 50% my glass is half full). So I would like to apologize for being ‘difficult’.
     

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  20. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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    Hey no problem JJ - here's something to think about...

    Imagine a line in front of the nose of you re aircraft, like the center line of a runway - whether it be a P-38, P-47, etc. Any maneuver you complete you're going to roll into a desired heading, that being that imaginary line. Because of P-factor, prop torque, cross winds etc, you're as you roll toward that desired heading one of there factors are going to send you "off the line." You coordinate with the rudder....

    On landing that imaginary line turns into the runway center line. You may use a combination of aileron and rudder to maintain that center line "right between your legs" if you're sitting in a single seat aircraft - As you go to land and start to flare you slowly "squeeze out" these inputs when you're a few feet above the ground so you don't land with the nose angled when referenced to the runway center line. By not doing that you're planting the landing gear "twisted" and you could damage the landing gear....


    Good post of the flight manuals, but like I said earlier they are written for the pilot that has several hundred hours and are not always going to mention thinks like coordinating controls (rudder ) for maintaining directional stability.

    Many WW2 pilots jumped into these beast with just a few hundred hours and sometimes were not proficient (when compared to today's standards) and were already in combat. The biggest non-combat killer back then was spin/ stall and it's still the same for many lower time pilots today.

    There's always a joke made about a flight instructor screaming at his student - 'RIGHT RUDDER, RIGHT RUDDER,' or 'STEP ON THE BALL, STEP ON THE BALL,' this emerging from what was shown here...

    Remember JJ - I'm from Staten Island, we're "homies" I know where you're coming from! ;)
     
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