Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Kweassa on January 01, 2003, 01:45:56 PM
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What would exactly happen when flaps are either a) deployed at high speed, or b) already deployed when the plane reaches high speed?
I'm curious of what would happen, because I did a simple test during discussions about flaps in 1C:Maddox's IL-2 forums.
Now, I've heard the flap modelling had some problems in IL-2, but I was surprised to find out how seemingly, undeniably porked they were when the test results were as following:
1) When the flaps are deployed before high speeds are reached, the flaps jam at approximately 750kph(460mph)
2) When flaps are deployed after high speeds are reached, the flaps jam at approximately 750kph(460mph)
3) With maximum throttle and WEP engaged, in a 45 degrees dive with full flaps engaged, at speeds of approximately 680kph(418mph), the lift force generated by the flaps actually pushes the plane upwards up to a degree which the pilot cannot fight it even when pushing the stick forward in full deflection.
The flaps are so strong that they endure the 680kph(418mph) dive, ignores the pilot input of stick forward full deflection, and pushes the nose pitch upwards and reduces speed.
4) With full flaps engaged, only a near-vertical dive reaches speeds over 700kph(430mph) and makes it possible to get the flaps jammed.
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So I'm curious.. let's say a certain plane has flap deployment maximum speed limit at 200mph.
1) If a plane deploys its flaps at 210mph, will it immediately jam? Or is the 200mph line something like the "expiration date" on milk cartons? A maximum "safety" line, no guarantee what would happen if flaps are deployed over that 200mph line?
2) If the same plane attempts to deploy its flaps at 400mph, will it instantly jam or tear off?
3) If the plane already has flaps deployed at 180mph, and then crosses over 200mph line, will the results be somewhat different than when the flaps were deployed after the limit was reached?
4) Can any WW2 plane in a full flap configuration endure a 418mph dive without the flaps breaking off?
5) If we just assume there's a flap that can endure high speeds, is it possible that during a 45 degrees dive at high speeds the lift force generated by the flaps just pushes the plane's pitch upwards, denying the full forward deflection input?
6) The test I have done, in order to reach high speeds quickly, started off from 10000 meters, making it easy for the plane to just dive and catch speed. Would there be differences in how the flaps can endure pressure at high alts and low alts?
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There isn't any simple answer to this stuff. It will vary from aircraft type to aircraft type and it will probably vary within aircraft type as well.
For example, deploying flaps at high speeds (assuming they will fully deploy, which is quite an assumption to begin with since THAT would probably vary between types and within type) would have varying effects between plane types simply based on where the flaps are with respect to center of lift just for one example of a variable.
The whole "blow off/become damaged" situation is another somewhat random thing. On some planes within in specific type they might jam during deployment or retraction. On another of the same type one or both flaps might depart the aircraft. Then toss in a little battle damage to the outside hinge of one flap on one side. It's quite possible that even "normal" flap deployment speeds might be too much in that case.
So, what I'm saying is there isn't any simple answer.
There is a limiting speed for flaps in every airplane that has them AFAIK. This limit is there because of the possiblily of damage to the aircraft and/or the possiblity of control problems.
Overspeeding flaps is a bad thing. It may or may not be catastrophic. But because there are so many variables, it would be hard to make a generalized statement about it or even a generalized damage model for it.
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I've always thought that this was the main driving force behind HTC's "auto retracting" flaps. I don't know how much data was gathered on aircraft to indicate what effect flaps would have at speeds that high... but I can't imagine there is all that much data on the subject.
Real life pilots didn't have the option to "just try things out for giggles". If something had a defined limit, they tended to stay inside of that limit to avoid being killed. Some would push the edge of that limit, but I wonder how many blew right by it and on into "ludicrous speed".
Basically, you run into the problem that nobody really knows what affect it would have since nobody has recorded data on it. But people will try it anyways because in games there are no penalties for it. The only real question becomes wether or not you chose to model something despite having no data, or if you take the "model common sense" aproach and not allow the super extreme situations at all.
AKDejaVu
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Originally posted by AKDejaVu
Real life pilots didn't have the option to "just try things out for giggles". If something had a defined limit, they tended to stay inside of that limit to avoid being killed. Some would push the edge of that limit, but I wonder how many blew right by it and on into "ludicrous speed".
Well, except for the test pilots, who were expected to do stupid things to make sure that the plane wasn't going to do something ugly.
I remember a story I heard, possibly apocryphal, about the first military test pilot to fly the F-16 prototype. At one point while sitting on the apron, he wondered "What would happen if I did this?" and hit the gear-retract switch. The gear retracted, dropping the plane onto the concrete. Squat switches were hurriedly added to the design, preventing the gear from retracting if there was weight on the wheels.
Interestingly, the presence of squat switches has also caused accidents with military aircraft. One of the flashy things that pilots will do is to hit the gear-retract switch as they start their takeoff roll; as long as there is weight on the gear, nothing happens, and the gear will retract the moment the plane leaves the runway. However, if a gust of wind blows past the plane, it can momentarily achieve enough lift to unload the squat switches, and the plane settles onto its underbelly when the gust passes, not having achieved enough speed to remain flying. The practice of hitting the gear-retract on the ground for the 'instant-retract' effect has been banned several times during and after Vietnam; pilots will still do it.
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remember, deploying flaps also changes the picthing moment of the wing, requiring extra trim. I don't think I've seen that modelled in any sim.
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Udet- In AH when I deploy flaps in the P-51D I have to compensate with either more elevator trim or physically holding the stick forward to attain straight flight. Otherwise the nose of the P-51 continues to rise. Isn't this modelling the pitching moment with flaps deployed?
I'm with Toad regarding the modelling of flaps being deployed beyond rated airspeeds. If you're going to be realistic with the physics then there's a whole heck of a lot more to evaluate and model in terms of affects on a/c structure, flight, etc. besides just having your flaps tear off.
Tango, XO
412th FS Braunco Mustangs
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Then here's another question guys.
1) would you guys agree the 750kph(460mph) jamming speed as portrayed in IL-2 is too extreme?
2) To the best of your knowledge, and logical thinking, if you were modelling the flaps how would you make it respond to varying speeds they are deployed? No intention of criticism to AH, just curious what you guys think about this issue. Random failures above limit speed? A "buffer" speed zone until it breaks off?
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Random failures never go over well.
I'd also caution against trying to model something without any data to back it up.
AKDejaVu
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Its modeled in AH udet, infact some planes will pitch up some down.
I know my RV wants to go nose down past 10 deg flaps.
HiTech
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1. Maybe. Fastest flap limit I've seen so far in my career was 250 kts for 1st flap setting. Doesn't mean it would jam or fall off; it could be limited there because maintenance requirement goes up or something. But the P-511 could deploy combat flaps (10) up to ~400 which is pretty fast. So I'd hate to be definitive. The flap limit data for each airplane is out there in its flight manual I would think.
2. Pitch moments after deploying are going to vary by aircraft and are aerodynamic features of the FM, I'd think.
For the rest, you'd have to have the limit speeds for each aircraft from the tech order. Then you'd probably have to have a randomized failure rate and the type of failure would have to be random as well. Jammed, Jammed and bent, departed aircraft and you have to apply this randomly to each side. A lot of stuff for a minor aspect of the sim.
Now that I've thought about it here, I can see why a "blow up" solution is much easier to implement and really is an acceptable (to me anyway) gameplay "solution" to the problem. Particularly when you are first trying to get a game up and running. Random failures could easily wait for a later time.
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Ah... I think I get it. That would explain the auto-retract issue I guess.
Since there isn't any official data on how the flaps may or may not endure high speeds, there isn't any way to model it "accurately".
About this discussion in IL-2 forums, there was a brief subject on abuse of using flaps during maneuvering. Since the flaps can endure such high speeds in IL-2, people would deploy full flaps as an overshoot mechanism during combat, which often presents a problem of people using methods which real life pilots would almost never try.
Thus, I guess it makes sense modelling in an unrealistic, artificial "hard limit" on flap deployment would ironically help the game feel more realistic in turn. It seems it is simular to the combat trim issues. Difference in game and reality which makes it necessary for a game play concession to exist.
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Another question:
about the combat flaps on USAAF planes such as P-51s and P-47s.. are they designed for "combat" purposes intentionally? Meaning, are they designed tougher than normal flaps so they may deploy at speeds near 400mph? Or, are they no different from other types of flaps other fighters may use?
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Well, I don't really know the answer.
I'll say this. 10 degrees of combat flaps on a P-51 don't really stick out much. So the loads on them at 10/400 might not be as high as full flaps at approach speed. Obviously, though, the flaps are the same flaps for both combat and approach. They were probably just "built to take it" in the case of combat flaps.
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Kweassa I have even seen folks put their gear down at over 600km/h (372mph) with full flaps and they pull straight back on their stick.
That and trim assisted turns and manuvers are gamey as hell.
HTC and Crew really set the standard in several things. Although "combat trim" sounds gamey its far better then what they have in il2. Same with flaps.
However I had hoped at one that with the auto retract flaps in ah that "flap damage" could be incorporated into the DM as well.
at XX speed if flaps are out they auto retract.
If over xx speed deployment of flaps will cause them to jam or be damaged. But since theres no real data to establish at what speed and/or what degree of damage it works well the way it is.
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This is just a data point and it probably doesn't apply to all the WW2 planes.
But,
On a modern airliner the flap and slat actuators have force limiting devices which will keep them from extending when aerodynamic loads are too high.
However they also have an anti-backdriving device which means that they won't auto-retract from aero loads.
I really have no idea how much of this applies to AH planes though.
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That's part of the problem with this airplane stuff. To every generalization, there's an exception.
Some of the newer Boeings have a "blow up" feature from the last notch of flaps to the next to last if you overspeed at full flaps.
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ja, the modern airliner solution seems probably a bit advanced for AH planes, except maybe the 262 (which most modern airliners seen to be based around)
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Part of the problem with the flap modelling question is that it is a bottomless topic. There are many variables in how the flaps worked at all in AH that are not modelled.
For instance.
The F6F had electric flaps. As far as I know they were only two position either half or full deflection with is not modeled here and they were also much slower to extend and retract than hydrolic flaps. But they were in fact real "Blow up" flaps as modelled in AH.
The F4U had 5 position hydrolic flaps but were also "blow up" flaps which would redeploy after speed was lost. Also it had an "overload release mechanism" which would protect against use at excess speeds. In addition there was a "combat flap" setting of 20 degrees which could be used up to 200knots.
So basically there are many pieces of the flap puzzle to solve before you can address one feature.
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Just checked my F6F flight manual.
1. They were electronically controlled but actuated by 4 hydrolic pumps.
2. They were 2 postion flaps. Full up or full down.
3. The manual states they were low drag flaps whatever that means.
4. This is what I mean by bottomless subject(and I don't mean with no pants on). The F6F had blow flaps that independant of the Hydraulics and would push the flaps up from 50 degrees at 93knots to 15degrees at 150knots. This feature could not be controlled from the cockpit!! Aslo the flaps cannot be extended at speeds in excess of 170knots.
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460 mph sounds very high as a limit to me. I cannot recall a real world aircraft that I've flown that has a flap speed anywhere near that high....speed/dive brakes maybe, but not flaps. In my experience the purpose of flaps are to enhance low speed handling characteristics, and to reduce angle of attack (high nose up) at low speeds (approach to landing). There's not much logic to their functioning for this purpose at such hig speeds.
What I relate here applies to general aviation, corporate jet and commercial aircraft types, and not to war birds per se. But, I cannot envision why they would have incorporated flaps that operate at such high speed into their design either. Can anybody point out a real world design in which 460 mph flaps (Vfe = 460 kts) exist?
Navy49
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Hey F4UDOA, is that manual from an F6F-3 or an F6F-5?
Also, how did the flaps work? I'm not too familiar with the interior of the F6F. I know that, in the P-38 for example, the flap lever only had 3 positions--up, "maneuver" and down--but regardless of that fact you could set the flaps at any setting in between that as well. OTOH, with a plane like the Spitfire all you could do was up ro duwn since the switch was basically a toggle switch.
J_A_B
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Originally posted by Toad
That's part of the problem with this airplane stuff. To every generalization, there's an exception.
Some of the newer Boeings have a "blow up" feature from the last notch of flaps to the next to last if you overspeed at full flaps.
That would almost certainly have to be a function of the control system, not a feature of the anti-backdriving mechanism. I.e. it measures airspeed and commands the flaps up one notch if you overspeed.
Although I'm sure some nerd somewhere could design a load sensitive mechanism that overrides the anti-backdriving only at full flaps position.
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It'd be helpful if HiTech could give us his opinion.
I'm not demanding an explanation or an answer here! I don't even have the slightest idea whether AH should change or not! :)
I'm just wondering what HiTech feels about this issue. I'm wondering if there's a helpful answer to how he feels about the flap deployment speeds and variables like his explanation on the combat trims which were very helpful and reasonable.
Despite all the helpful explanations, I'm still very confused and the picture is very unclear how the flaps might react when deployed over suggested limits... :o
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JAB,
Believe it or not that manual is for both the F6F-3 and F6F-5. It list different restrictions for both varients.
The up/down flap lever is exactly as you describe it in the Spit. Simply a toggle switch. However it does state (maybe like the P-38) that the flaps can be in any variation of settings as they blow up from 50 degrees. You just can't set them that way from the cockpit. I have a P-38 manual as well, I will have to compare the two.
The F4U on the other hand had a 5 position flap lever.
In the 1944 Joint Fighter Conferance book the pilots had some very interesting conversations on flap types including blow up flaps and their use. That book gives you the best idea of what the feelings of the time were about everything from flaps, guns, gun sights, dive flaps etc. They pulled no punches.
I have manual for the
F6F-3/5
F4U-1
P-38F-L
P-47N
P-63
I will compare all of there flap types.
FYI, not to change the subject but our flaps still do not provide enough lift. This can be verified very quickly by checking full flap stalls on the digital readout in the film viewer. They aren't even close.
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F4UDOA - what do expect the lift to be?
Tango, XO
412th FS Braunco Mustangs
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As a slight sidenote to this thread's original intent, perhaps you could scan the pages relating to the F6F flap operation and E-mail it to HTC?
HTC seems to have info which syggests the F6F had miltu-position flaps...not only does the AH F6F have such flaps, but as you might recall the WarBirds one did too. If they're mistaken, it's up to us to prove it :)
J_A_B
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Funk, I probably have the books in the attic but it's abit to esoteric for a stick monkey's interest. ;)
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Same here on the interest part. :)
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BTW Kweassa - Andy Bush wrote a nice article on flaps on SimHQ that sheds some more light on it all. More stuff covered there than the questions asked here but good stuff at any rate.
SimHQ Flaps Article (http://www.simhq.com/simhq3/sims/features/flaps/index.shtml)
Tango, XO
412th FS Braunco Mustangs
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Dug through various documents to find some info about the flaps on our various planes
From eric Schillings notes on the P-40:
8. Wing Flaps - The wing flaps are operated hydraulically by either the hand pump or an electrically operated pump. The selector handle is located on the port side of the cockpit beside the pilot's seat and moves fore and after; - forward for "Down" and after for "Up" and neutral for "Off". The hand operated hydraulic pump (see para. 7) may be worked back and forth to raise or lower the flaps after the up or down position has been selected on the handle. The flaps may be operated manually in order that partial setting may be obtained more easily. With aid loads on the flaps they will close automatically as soon as the selector switch is moved to the "Up" position.
[ES: our flap control lever had a push button on the end which had to be depressed in order to move the flap handle out of the neutral position. When placed in the up position, the little finger was used to turn on the electric hydraulic pump. The same switch was used to acctuate the hydraulic pump both for the Flaps and Gear.]
NOTE: - Flap selector lever cannot be set to "Up" position until undercarriage lever has been returned to neutral. [ES: We did not have this type of flap control.]
Below:from the Mustang handbook (Export P51 for UK):
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Sorry, can't figure adding more than one pic at a time.
This is cut and pasted from the Hurricane manual:
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This is typical of all Spitfire manuals that i have:
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This is from the Typhoon manual.
The Tempest says the same, except:
max speed with flaps down is 160mph, and 210mph at 20 degrees flaps
Changes of trim -
Flaps up: Initially nose down, finally nose up
Flaps down: Nose down (During the first 20 degrees of flap movement the change of trim is marked)
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And our Mosquito Mk VI
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More info on the Mosquito, it occurs to me that this is at least as relevant as the actual flap settings. If anyone's interested i can dig out max flap speeds, etc. for the others, and look for flap settings and limits on other planes, but i don't want to clutter up this topic unless there's a demand?
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im sure most of u know that place, but to reminde u all:)
http://www.zenoswarbirdvideos.com/main.html
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Dtango,
If you check the P-38, P-51B/D, F6F and F4U full flap stall speeds at the loading used in the manual you will find that they are all off. Some of them are off with no flap set so it may not be just the flaps that are set wrong.
I tested this at one point although I do not have the results in front of me using the digital speed read out I found the stalls were significantly further off with flaps than without.
For instance in the F6F and F4U manuals they list the stall speeds at the weights of 11,250LBS for the F6F and 11,300LBS for the F4U engine on at idle as reccomended in the manual. I take the fuel load that leaves me with the weight as close as possible and hold the nose level until stall. You can choose not to hold the nose steady but it will only adjust the stall by a few MPH and I am not talking about a few MPH.
The Flight manual stall for the F6F is approx. 74MPH in the clean condition!!! The AH F6F cannot fly even close to that slow speed. In the full flaps position from the manual stall speed is listed at 50Knots however the CAS correction table adds about 6.5knots to the speed with 80Knots indicated so I'm guessing that the full flaps stall is around 65MPH. Without flaps the CAS correction chart actually reflects a slower speed than indicated!
The F4U is also subject to the same. Power on stall 11,300lbs should be 84knots in the clean condition or 97MPH and full flap stall is at 66 knots or 76MPH which is about 15MPH slower than AH allows. The CAS correction chart acctually shows a reduction in speed at stall in both conditions of about 2 to 3 Knots.
This explains to a great degree why it is so hard to get a F4U off the carrier deck. The stall is simply too high for liftoff.
The P-38 manual shows a power off stall clean of 100MPH and full flaps at 76MPH. The CAS correction chart does bring those numbers up showing a correct speed of 100MPH when 83MPH is indicated in the clean condition and 89MPH with full flaps. So stall is harder to calculate.
The P-51D 9,000LBS shows stalls of 101MPH and 94MPH respectively power off. These numbers would come down about 5MPH with power. Again I think they are just to high.
Anyway I know AH can't expect to be perfect but sometimes I think parity is the goal and not accuracy.
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JAB,
I have known about the F6F flap situation for quite some time. The reason I haven't said anything is this.
It is allot easier to get an A/C porked in here than to get one fixed. For instance the F6F should stall about 76MPH with no flaps. So if I complain about both which one do you think will get fixed first? I don't wan't to be the guy who "porked" the F6F.
For all of the posting I have done on the F4U I have never really had anything fixed. The F4U-1D is different than it was but HTC made the C hog heavier, modeled the -1D with drag from external stores regardless of loadout that slows it about 10MPH and the F4U-4 still climbs about 400FPM to slow all with data I have provided. They ignore the positive and change the negative. And the funny thing is that I think the C-Hog data is wrong. I think it should be much lighter than it is and I have data to prove it.
So what have I really done except run my mouth and pork the A/C I'm trying to fix.
So I'm going to relax on this until I can get 5 minutes to talk to HT or Pyro. I whish they hadn't killed that Q&A forum so fast.
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F4UDOA:
I have clean CLmax for the F6F-5 listed at 1.41. Using this figure at ~11,300 lbs weight stall speed should be ~96-97MPH.
If I run the calcs backwards using a stall speed of 74MPH I get a CLmax of a whopping 2.41.
Flight testing in AH taking the F6F-5 with 25% fuel which gives me a ~11,300 lbs of weight I seem to get a stall at ~97MPH. CLmax calculations give me about 1.40 which seems to be in line with the CLmax figures quoted for the F6F-5.
Tango, XO
412th FS Braunco Mustangs
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OK, Tango.. 'fess up. This stuff is a bit more than a hobby with you isn't it?
;)
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LOL Toad :D. What was it that you said? Something about being a bit too esoteric??
Hey, I need something to do in between the times my 2 year old gets up every 5-10 min trying to find a way to avoid bedtime when it's time for him to go to bed!
Tango, XO
412th FS Braunco Mustangs
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Somehow I get the feeling you are intimately familiar with Bernoulli and Ernst Mach and all the rest of those guys.
I bet you even know what Keuffel and Esser made. ;)
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LOL! Bernoulli and Mach - yeah I think those guys are more like the crowd funked hangs out with :D.
Keuffel & Esser! LOL! Now that is truly "classic"! Them things were before my time thank God! Of course I always envied the guys and gals that got to use Mathcad for calculus! Man, what happened to old fashioned pencil and paper slaving away to integrate something??? ;)
Tango, XO
412th FS Braunco Mustangs
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Originally posted by dtango
Hey, I need something to do in between the times my 2 year old gets up every 5-10 min trying to find a way to avoid bedtime when it's time for him to go to bed!
Hey, that's exactly how I got my callsign :)
Badboy
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Hehe Badboy - I'm confused though! So were you the parent trying to put the youngster to bed or were you the youngster trying to avoid bedtime? Or were you the parent that was paying your youngster to avoid bedtime as an excuse to stay up later!
Tango, XO
412th FS Braunco Mustangs
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F4udoa: You sure your not readying the cas ias table backwards?
HiTech
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Hitech,
No I'm sure HT. I'm reading it right out of the F4U, F6F and P-38 manuals.
For the F6F it has two CAS correction tables. One for the F6F-3 and one for the F6F-5. The one for the F6F-5 reads as follows.
Flaps retracted
100Knots subtract 5 knots
120Knots subtract 6.5 knots
140Knots subtract 7 Knots
Flaps extended
80 Knots Add 6.5 Knots
100 Knots Add 4.5 Knots
120 Knots Add 2 Knots
The F4U Manual is for the -1 and -1D series.
The manual list the indicated airspeed, corrected airspeed and the correction in Knots.
Flaps retracted
90 knots IAS = 88Knots -2Knots
100Knots IAS = 99Knots -1Knot
110Knots IAS = 110Knots 0Knots
300Knots IAS= 308Knots +8Knots
Flaps extended
70Knots IAS = 67Knots -3Knots
80Knots IAS = 78Knots -2Knots
89Knots IAS = 100Knots -1Knots
100Knots IAS = 100Knots 0Knots
110Knots IAS = 111Knots +1Knots
These two birds stall way too high according to these charts with flaps and the F6F stalls way too high period. The F4U stall is more modestly off with no flaps. But with flaps there is about a 15% to 20% difference between AH and the manual.
I think this is why the F4U carrier takeoff is sooo difficult.
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Dtango,
I think you are falling into the same trap I just did doing the same calculations.
Here is the calculation I am doing for the F4U.
Cl = Lift * 391 / (V^2 * Area)
= 11300 * 391 / (97^2 * 314)
= 1.49
But if I use 76MPH (the F4U full flap stall) as the speed my CLmax comes out to 2.4 something which is to high. The reason is because you are not adding the extra wing area to the 314 created by the flaps. If you did the number would be approx 1.90 (power on).
The F6F as you pointed out is coming up with a very high Cl max of 2.4 with no flaps.
Here is the F6F power on at 11,250LBS no flaps power on.
Cl = Lift * 391 / (V^2 * Area)
= 11,250 * 391 / (74^2 * 334)
= 2.4
This page shows A/C#5 the F6F to have a Clmax prop idling of Approx 1.9. full flap. This would be higher if the A/C had airflow as there is no wind over the wing. Based on the F4U pre-spoiler clmax of 2.30 I would assume the F6F's to be slightly higher. But I agree 2.4 no flap seems to high and must be a pitot tube error.
Even with that the F4U and F6F stalls are too high even with an questionable Clmax for the F6F.
(http://naca.larc.nasa.gov/reports/1945/naca-report-829/index.cgi?page35.gif)
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Not sure what you mean about fallling into the same trap :). The calcs I ran for the F6F-5 was with no flaps based on your quoted no flap stall speed for the F6F-5 at 74 mph.
I have the same NACA report. Here's another one to look at as well (very large).
NACA Report 824 (http://naca.larc.nasa.gov/reports/1945/naca-report-824/index.cgi?page067.gif)
It shows the F6F-5 (model XV in chart) clean with a Clmax of 1.6. If I use this figure I get a stall speed of 90mph which is pretty different from 74mph. My point is that I couldn't say that there is something wrong with the AH F6F-5 FM when the physics don't agree with the numbers you have quoted.
So why the difference in the Clmax figures even quoted by NACA for the F6F-5?
Perhaps the following:
(1) the NACA 829 report you are pointing to was meant to study the effects of stall characteristics and factors - not a report to to determine exact Clmax of a certain airframe but to determine what influences the change in Clmax for a given airframe.
(2) The NACA 824 report difference uses a simplified approach for calculating the average CL across the span of the wing resulting in the 1.6 at rn of 5.0 x 10^4. The 1.41 figure was I believe from using modern CFD wing analysis software now that we have computers that can make those computations.
I haven't commented on the F4U. BTW- model XIII in the 824 report is an F4U with the Clmax figures for the various flight conditions. Cool stuff. You might try running some of the calcs with that data to see what you come up with for the F4U and see how that matches with other data you have.
Tango, XO
412th FS Braunco Mustangs
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Now you realy lost me F4UDOA wing area increasing with flaps? The f6f didn't have fowler flaps.
HiTech
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BTW pulled out the f6f manual. Somthing is realy strange in the -5 IAS to CAS conversion table. The flaps up / flaps down entry dosn't seem to pass a smell test because the direction of IAS to CAS reverse with flaps up & flaps down to AOA increase.
HiTech
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HT,
Your right on both things.
1. The F6F does not use fowler flaps but they are extention flaps. And I believe they extend as well as deflect. Similar to the F4U if you look at Dtango's link.
2. The stall speeds listed in the F6F manual are a little fishy. But even with a calculated stall of 90MPH clean and 76MPH dirty it still does not match AH.
3. The F4U data is correct and does not match either. 11,300 is a little less than 50%fuel. You still can't fly into the 80MPH range regardless of fuel or ammo load in either the -1 or -1D/C.
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And in the F6F FLight Operations manual. It show dirty power off stall at 80mph with 11,000 Lbs. This equates to an MaxCL of about 2.0. Now the chart with stall speeds is not labled IAS or CAS. If its IAS per there conversion table it realy should be around 90mph CAS. Belive our CLMax is around 1.98.
Just curious where you got a clean stall speed of 74 mph.
HiTech
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HT,
Look in your Pilots Flight operations manual for the F6F page 44.
Section 18 paragraph B. Stalling
Clean Power on- 62Knots
Clean Power off- 64 Knots
LG&Flaps down- power on- 50Knots
LG&Flaps down- power off- 53Knots
????????????????????????????????
Are the manuals different?
Don't see the weight listed now. Must have been looking at the spin characteristics listed beneath. Never the less they are very low speeds.
BTW the slotted flaps definitely extend as well as deflect increasing wing area. Scews up the cl max calculation a bit.
Dtango,
In the NACA report 824 your looking at the wrong bird. A/C XV is a FW190A. A/C XIV is the F6F and A/C XIII is the F4U.
But I still can't tell how your reading the Clmax from that data.
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BTW,
What is geometric washout?
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F4UDOA:
The 824 report shows the F6F with just slotted flaps with no extension (model XV with airfoils 23015.6 and 23009 in the report). I am not at home so can't reference USA's 100,000 to check to see what it says there.
The difference between CLmax 1.6 vs. 1.41 could be attributable to methods for deriving the pressure distribution across the wing (e.g. simplified in the NACA report vs. CFD s/w approach). I can't speak to the difference in accuracy this may introduce and would be hesistant to make the claim the F6F FM is off until I could settle this in my mind.
The 824 report also shows the F6F with dirty CLmax of 2.48-2.5.
HT - are you saying the F6F-5 in AH has a dirty CLmax of 1.98?
Tango, XO
412th FS Braunco Mustangs
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F4UDOA Look at page 59.
HiTech
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Geometric washout = wing twist.
Hmmm, XV is the FW-190? The F6F has airfoil root and tips of NACA 23015.6 and NACA 23009. Interestingly enough the FW-190 has pretty much the same - 23015.3 23009. I didn't check the AR's against the AR's shown so you might be right - XV is the 190. Model XIV I didn't think was the F6F because of the root and tip airfoils listed there weren't the right ones for the F6F (unless I'm not translating the NACA designations correctly).
I'm reading CLmax in the next to the last column.
I just realized something as well. The RN listed are pretty low too since RN's for the velocities we look at are typically in the 10^6 range not 10^4. Heh, not sure we can use these charts anymore until someone reads through the report to try and make sense of it all.
Tango, XO
412th FS Braunco Mustangs
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Page 59!!!
What the fark is that??
The numbers on page 44 must be without seats and a bunch of helium balloons or something?
Honestly dude were looking at the same manual. I can't even imagine what gives there?
But as long as your looking at that chart notice the ground run for takeoff in a 25Knots wind at 12,000LBS is about 320FT. That's before you hit the control tower on the CV.
Also notice in the F4U manual page 64 the stall speed power off is 74knots at 11,000LBS and the takeoff run at 12,000LBS is aound 340ft. Much sooner than AH allows.
Dtango,
I see all the Clmax numbers on the right side there. I just don't know which one is no flap and which one is full.
Also it shows slotted extensor flaps for the F4U and F6F. I'm pretty sure that's a 190A with the plain flaps.
Let me know what you think of that doc when you get a chance.
Thanks
Guys!
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Ahh lets finish this topic first? I would tend to belive the Page 59 chart, it passes smell test, other speeds don't.
HiTech
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Ageed,
However even the page 59 chart should be compared to the existing FM. As well as the fact that the AH F6F has multi position flaps contrary to the manual.
I have run several test today. The question I have about the FM is what do you consider a stall? The AH FM tends to mush forward and loose altitude before stalling or wing break. I believe the stall begins when you can no longer hold the horizon. Correct?
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When you can no longer maintain 0 decent.
HiTech
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Now this is way over my league... :)
Carry on!
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Something I have gathered from years of watching these threads..
Pilot manuals and engagment anecdotes and after action reports were not written to develop a sim from where they.
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Actually Pongo the pilots manuals are probably the single best source of data because it was written for the pilot. Not to sell warbonds or for the propaganda department. Just to keep some poor dudes powder dry.
HT,
If that is correct then the stalls definitely need some adjustment. Especially with flaps. I know that flap lift has already been changed in 1.04 I believe.
Kweassa,
It's all your fault!!
Actually it's been a great thread. Especially the part about the P-47 flaps extending like fowlers. I learned allot about flaps in this thread.
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So what are the figures on page 59 of the F6F-5 Pilots Manual?
Regarding NACA Report 824 - disregard the data for the models shown as a report of CLmax figures for actual a/c. The tests were models and airfoils of different configurations in the 19 foot tunnel at Langley. After reading through it they were used as a way to do an estimation and compare of differences between the 2-D airfoil data they were deriving and 3-D wings to see if there was general agreement between the data. The models weren't specifically a given a/c but just different models with different wings, types of flaps and flap configs.
Tango, XO
412th FS Braunco Mustangs
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Dtango,
On the previous page in the same manual it listed the stall speeds for the F6F clean at approx 64Knots and with flaps down at 50knots.
Then page 59 has a graph of stall speeds which is a much higher range. Totally contradicting data in the same manual. Very strange.
However even the pg 59 data is significantly different than AH with flaps.
Remember the stall in HT words begins when you can no longer maintain a 0 rate of decent which is what I was testing to begin with.
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Btw I would have described is slowest speed that you can maintain level flight. But F4UDOA was talking about keeping is nose on the horizon and thats not how the test is normaly done.
Btw make sure the ball is right in the center when testing. Normal procedure is watch the VSI as the plane slows down , maitaining level flight, Then when it departs i.e. stalls check the speed.
HiTech
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F4UDOA:
Can you provide the speeds listed? I'm interested in just having the data. Or if you can scan the page in question and post it. That would be great. Thanks!
Tango, XO
412th FS Braunco Mustangs
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Nice thread guys! :)
Its SOOOO nice to see an intelligent discussion without, all the rest of the normal crap.
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Heya Verm
long time!!
Dtango,
I have a scanner but I can't jam my manual into it. I will make a run to a copy machine a copy the chart for you.
The listed speeds on page 44 under stalls are
Pilots Flight operations manual for the F6F page 44.
Section 18 paragraph B. Stalling
Clean Power on- 62Knots
Clean Power off- 64 Knots
LG&Flaps down- power on- 50Knots
LG&Flaps down- power off- 53Knots
And the CAS correction chart for the F6F-5
Flaps retracted
100Knots subtract 5 knots
120Knots subtract 6.5 knots
140Knots subtract 7 Knots
Flaps extended
80 Knots Add 6.5 Knots
100 Knots Add 4.5 Knots
120 Knots Add 2 Knots
This data is completely contradicted by the chart on page 59. It is bizzarre.
HT, I will film and post my test.
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Hey F4UDOA ! I'm still around, just been busy. I haven't flown in months and months, but I still try and catch the interesting threads on the BBS, which are few and far between it seems. Just been teaching myself a new and interesting hobby ! :)
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F4UDOA:
I'm interested in the data on page 59 too. Thanks!
Tango, XO
412th FS Braunco Mustangs
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Hitech,
Here are my test results for stalls as follows.
Method of test
1. Hold A/C level until it can no longer maintain 0 rate of decent.
Conditions
1. 25% fuel
2. No ordinance
3. Full Ammo
F6F-5
Full weight 12,483LBS
Adjusted Weight 11,358LBS
Measured clean stall 101MPH
Measured Full flap stall 85MPH
No flap Calculated Clmax 1.30
Film F6Fstall (http://mywebpages.comcast.net/markw4/F6Fstall.zip)
F4U-1D
Max weight 12,175LBS
Adjusted weight 11,108.5LBS
Measured stall no flap 103MPH
Measured stall full flap 91MPH
No flap Calculated Clmax= 1.30 Same as F6F, is this a coincedence? Should be 1.49 according to NACA post spoiler strip.
Film F4U1Dstall (http://mywebpages.comcast.net/markw4/F4U1Dstall.zip)
F4U-1
Max Weight 12,835LBS
Adjusted Weight 11,210.5lbs
Measured stall no flap 103MPH
Measured stall full flap 89MPH
No flap calculated Clmax= 1.32 This should be higher than 1.49 as it is pre spoiler strip F4U with harsher stall.
Film F4U1Stall (http://mywebpages.comcast.net/markw4/F4U1Stall.zip)
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Hitech,
Are you calculating your Clmax for these birds assuming that slotted flaps do no extend to incease wing area??
If you are I think that is part of the issue because I can absolutely prove otherwise on the F4U.
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Did a few more flight tests of the F6F-5 myself with 25% fuel.
I agree with F4UDOA - if we are using HT's definition of not being able to hold VSI=0 as a stall then I can't explain why the F6F-5 seems to be stalling around 101-102 TAS mph around 300 ft alt. This seems a little high for the stall speed to me.
Here are a couple of things I found of interest however:
(1) Using alt-x and speed set at 100 mph I keep getting the F6F-5 speed with VSI=0 holding at 101-102 TAS mph at 100-300 ft alt. Is the film viewer speed just a hair off?
(2) I can maintain flight with the VSI needle just a hair under 0 (~.5-1 fps decent) and if I use the definition of a stall when I have a departure of control (wing tip over etc.) then I can maintain flight to 93-96mph TAS at 100-200 ft alt before I have departure of control. (I used this definition in my earlier tests).
Maybe what we are seeing in the AH F6F-5 is the modelling of the differences in lift distribution across the wing? CL figures for a wing is the average of the lift distribution across the wing. In reality the 3D lift distribution across a wing is not constant but varies from station to station so you may actually have local stalls at different regions on the wing but not lose control of the aircraft.
Of course this is pure conjecture on my part on HTC FM's. I'd be interested if HT or Pyro has any further comment on this.
Tango, XO
412th FS Braunco Mustangs
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flap-deployement at high speed? that isnt even possible :p
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Punt,
HT, don't end the dialog now.
It's like having a conversation with someone on a cell phone and the phone cuts out.
Just say something like "I'll look into it" or "Bugger off" or something.
Dtango,
Thanks for running test. Notice one more thing. The stall really doesn't change with fuel load. With 25% fuel The F6F is getting close to 11,000LBS. That's 1,500LBS under takeoff weight and the stall is about the same. Climb rate does increase proportionate to weight but stall does not. Very interesting.
I want to shoot off all ammo and see what the stall is.