Accelerated Stalls

Discussion in 'Flight Test Data' started by mad_max, May 11, 2008.

  1. mad_max

    mad_max Member

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    Does anyone know of data, pilot notes, etc about accelerated stalls for the various fighter aircraft of WW2? I've mostly only found information about the "normal" stall, but not much about accelerated stalls.

    It's well known that a hamfisted P-51 pilot can get himself into a real butt puckering spin during accelerated stalls, but what about other fighters? Lots of hearsay out there, but not much in the way of facts that I can find. I'm hoping someone else can direct me where to find some information on them.
     
  2. timshatz

    timshatz Active Member

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    I think they may be talking about high speed stalls. Most stalls happen at low speed when the wing stops flying. You just drop out of the sky and, usually, one wing down.

    But a high speed stall is where you're angle of attack to the wind flow exceeds the ability of the wing to create lift. For example, if you are buzzing along at 300mph and you yank the stick back very hard, the aircraft could stall with loss of lift over the wings. Band news if you are in fighter as the thing will probably start to tumble, really bad news in a GA aircraft as you'll probably lose your wings.
     
  3. mad_max

    mad_max Member

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    Thanks for the reply Timshatz. I know what an accelerated stall is. What I wanted to know is does anyone have information on other WWII fighter and the reaction of the airframe to an accelerated stall.

    I used the P-51 as it had a vicious accelerated stall and test pilots noted this and described what the airframe does. A "normal" stall is noted about alot of airframes, but not about accelerated stalls.

    I've read that the 190 would react with a snap out, but took 4-5k to come out of, but wasn't so vicious of a spin.

    I'm looking for sourcesof test pilots or pilot notes about how others airframes react.
     
  4. drgondog

    drgondog Well-Known Member

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    The acclerated stall characteristics of the Mustang were two fold and primarily dependent on the airspeed at which the 51 entered the high AOA scenario. The most vicious characteristics were caused by the oft mentioned 'aft cg' condition of a full fuse tank down to 20-25 gallons.

    I don't recall reading of similar violent departures for 109s - perhaps because the LE deployed quickly at that threshold of stall and enabled control at the extreme AOA for non-deployed slats

    The ones I have heard and seen referenced are the Spit high speed turn 'control reversal' issue created by an aeroelastic twist of the wing in the outer tip area - I recall but do not remember that the issue was largely solved with the clipped wing XIV. Do not quote me on this

    The 190 issue was mentioned in the oft discussed Lednicer Report in which he cited a German study on the causes of the fw 190 'snap' at low speed/high G turn.

    That scenario was described (i don't read German) as also an aeroelasticity issue but the problem was headlined at the outer/upper wing torquing due to aeroelasticity and locally increasing the tip AOA - causing the stall - and snapping to inside. I have posted the Lednicer Report and specified the Focke Wulf report somewhere.

    The only experience I had with an accelerated stall was once and it snapped in and down into a tight spin, recoverable but scary for first time with enough altitude - but not on the deck unless extremely lucky and skilled.. on the other hand the 51 gave plenty of advanced warning with elevator shaking, and you just let off the back pressure a tad.

    The experienced guy would be the one that didn't quite back it off enough but just before it snapped on him, eased the pressure enough to still get the stall but have enough control to quickly cut the power and recover - say in 500-1000 feet.
     
  5. Soren

    Soren Banned

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    Actually the Fw-190 recovered very quickly from accelerated stalls, while the P-51 often took a lot of altitude to recover.

    The reason for the Fw-190's violent stall is attributed to the fact that its wing featured an elliptical lift distribution (Generated with specific amount of washout), and fully elliptical wings inherently feature very violent stalls.

    Crumpp has plenty of info on this if you want a further explanation.
     
  6. drgondog

    drgondog Well-Known Member

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    http://www.ww2aircraft.net/forum/polls/allied-tests-captured-bf-109-s-12456-4.html

    Note Page 89 discussing the harsh stalling characteristics of the Fw 190 and note the reference to (14) "Gross, P; "Die Entwicklung der Tregwerk Konstruction Fw 190", Bericht 175 der Lillenthal - Gesselschalt 2 Jan 1944"..as well as Brown's comments.

    In the discussion the report by Lednicer discusses the theory from that report that the Fw 190 CLmax is attained at the same angle of attack for inner 40% and that elastic deformation shifts the load distribution outward, causing more of the wing to reach stalling Clmax faster... all related to high G manuevers and IIRC at relatively low speeds (not sure of this)

    Another note for your attention, Soren, is Figure 2-page 86, which plots Calculated Wing Loading as a function of Semi Span. In that plot Lednicer shows the theoretical 'eliptical' wing load distribution to contrast the Spitfire IX, the Mustang and the Fw 190.

    You may notice that a.) the Spit wing is closest to eliptical wing loading and that the Fw 190 is the worst example of elliptical wing loading - a direct contradiction to your statement above.

    Further you may notice that the wing loading of the Spifire is superior in distibution over the Mustang out to 90% of semi span, and that the 51 is superior to the Fw 190 out to 80% where the two converge and cross but remain close.

    You also may notice that Lednicer discusses 'suction' distribution over the wings of the P-51B and D as the same but that the 'suction' distribution of the P-51D canopy is superior to the P-51B. but then you may not. You may still believe 'suction' is drag in his report.

    In an earlier thread on the "Allied tests of the Me 109" you claimed that the LE slats on an 109 deployed gradually and gently at low AOA - which is untrue for any 'pressure' actuated LE Slat unless the airfoil specifically stalls at a low AOA - which is not true for a 109.

    I would have to check but I seem to remeber you trying to use the improved 'delta' Cl derived from Slats as part of a discussion to prove that a 109 had a higher Clmax and would outclimb a Spit - and Claidmore (I believe) correctly noted that slats aren't a factor in climb unless you are at stall point

    Time after time you blurt something out that is so outrageous it makes one scratch one's head and ask 'why'?

    Soren, why don't you stick to what you really DO know? You know a lot about a lot of things but aerodynamics and fluid mechanics and structural mechanics are not in your tool kit.

    Regards,

    Bill
     
  7. Soren

    Soren Banned

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    Sorry but that's complete BS Bill, and just another one of your feeble attempts at lying to benefit your own arguments. But in this post the proof of your incompetance will be presented. (I know its rough but you brought it on yourself by continuing your rants)

    First of all I never claimed the Bf-109 climbed faster because of a higher Clmax granted by the slats. The Clmax of the 109's wing without the slats is around 1.52 - 1.55, as demonstrated in windtunnel tests at Charlais Meudon where V24 demonstrated a Clmax of 1.48 WITHOUT slats (none were fitted).

    Note: V24 was a Friedrich with shortened wings and a wing area of 15.2 m^2and a lower wing AR.

    The Bf-109 climbs better than or similarly (incase of 109 K-4 vs Spit IX +25lbs/sq.in.) to the Spitfire because of a lower power loading. And that's all I have ever argued.

    And as for Lednicers report, well it doesn't show pressure distribution under G's you nimwit! Did you suddenly forget about the effects of aeroelasticity mr. expert ? Yep yet another piece of evidence that you're nothing but an amateur within the science of aerodynamics and clueless within many of its fields, you've proven it plenty of times before and now you've just verified it again. Want evidence ? OK I'll give you a sample:

    Bill earlier claimed that aerolasticity and its effects was an unknown science in WW2, almost witchcraft in his own words! Well fact is (and this is mentioned in nearly every book about aerodynamics and its history used for educational purposes), that aeroelasticity, its effects and how to benefit from these was a very well understood science even by the early 1930's, at this time even the Russian aerodynamics department TsAGl having its own bunch of scientists specializing within this field, one of them was M.V.Keldysh.

    And now that we're talking about aeroelasticity;

    Fact is that under G's the Fw-190's wing achieved an elliptical lift distribution because of a smart and purposeful combination of airfoil type and washout, all intended to take advantage of the effects of aeroelasticity. Focke Wulf AG intentionally designed the wing to benefit from the effects of aeroelasticity, testing various wing configurations with various degree's of washout to pinpoint the perfect combination. The goal was optimal lift distribution under G's, and this was pursued to achieve the best L/D ratio in turns and a quick recovery in spins.

    But since you're so clueless on this subject Bill perhaps you should take a talk with Gene about this as he was the one to first forward this information ???

    Now as for your claim that aerodynamics is not in my toolkit, well I'd say it's atleast as much in my toolkit as it is in yours my amateur friend, infact it has just been proven that it is more in my toolkit.

    Anyway Bill keep up your cowardize ways and lie as much you like, from this point on you will be ignored and the cause for that is that you're a liar and a prick.

    Have a good day.
     
  8. Micdrow

    Micdrow “Archive”
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    Enough is enough, keep the subject on track and stop with the insults. Difference of options is one thing when backed with documentation but insults will not be tolerated from both of you.
     
  9. drgondog

    drgondog Well-Known Member

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    Soren - help me understand your qualifications to dismiss mine?

    Help me understand the credits you received academically or even Industry experience in the following:

    Fluid Dynamics
    Aerodynamics of Wings and Bodies
    Stability and Control of Vehicles in Flight
    Aircraft Performance and Flight Dynamics
    Properties of Materials
    Airframe Structures
    Subsonic and Supersonic Aerodynamics
    Heat and Mass Transfer
    Boundary Layer Theory
    Aeroelasticity

    Static and Dynamic Analysis
    Vector and Tensor Analysis
    Calculus
    Calculus of Variations
    Control Theory
    Matric Theory
    Advanced Numerical Methods
    Differential Equations

    I have at least 3 hours credit in each of those subjects prior to my BS and MS Degrees in Aero. I might note that my MS GPA was 3.9 on a scale of 4.0

    I did not perform to that standard as an undergrad because I screwed around a lot and played football (although my coaches may dispute the latter) and 'party'

    My primary airframe experience from 1968-1974 was in Advanced Aerodynamics (primarily pressure distribution modelling-exactly what Ledicer did with VSAERO, but not as sophisticated as VSAERO) at Lockheed, Airframe Design and Structures (balance of hand crank and NASTRAN modelling at Bell.

    Had to demonstrate that every stress calculation done by NASTRAN was analogous to conventional and approved analytical methods to be accepted by US Army for the Huey and the Cobra that I worked on). If you want to chat on-line on either of these subjects, let us chat.

    For you to demonstrate that my observations are unfounded by education and theory, or not grounded in experience, you may feel free to show me how you know this to be true by submitting your own education and experience.

    This might be about the sixth or seventh time since I posted my Diploma that I asked you for this small favor. What say you?

    If you are left at somewhat of a loss relative to such credentials would you please refrain from casting aspersions on my own?

    Thank you.
     
  10. Glider

    Glider Well-Known Member

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    Trying to get back on topic I do know that the Spitfire Pilots notes (all the versions that I have found) go to some trouble to warn pilots about its handling in a high speed stall flipping the aircraft onto its back.

    That said I would have thought that a high speed stall is certain to get your attention, by its very nature its fast and varied in its effect due to the differences caused by the attitude in which its entered.

    Certainly I have been flipped in a fairly modern glider, finding myself upside down, heading for terra firma and horribly close to the VNE. If that can happen to a glider with its wing design and slow roll rate, it can happen to most aircraft.
     
  11. Soren

    Soren Banned

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    A couple of Cessna's have this problem as-well, some having the nasty habbit of flipping onto their backs on the turn in for the landing approach. Apparently there is no warning of the stall with the flaps down, not good considering the critical AoA is lowered by the deployment of the flaps. Fortunately recovery is quick though.
     
  12. drgondog

    drgondog Well-Known Member

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    Education.. experience in the airframe biz Soren?
     
  13. kool kitty89

    kool kitty89 Well-Known Member

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    .... Just take it to PM, there's no good reason to do that publicly, particularly on completly unrelated topics which continue to be sidetracked. (and in at least one case closed, for this specific argument)
     
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