Author Topic: Question about Flaps Deployed at High Speeds.. (Read 2601 times)

Kweassa · « **on:** January 01, 2003, 01:45:56 PM »

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.

......

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?

Toad · « **Reply #1 on:** January 01, 2003, 02:41:46 PM »

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.

AKDejaVu · « **Reply #2 on:** January 01, 2003, 04:22:09 PM »

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

Shiva · « **Reply #3 on:** January 01, 2003, 05:59:08 PM »

Quote

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.

udet · « **Reply #4 on:** January 01, 2003, 07:06:17 PM »

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.

dtango · « **Reply #5 on:** January 01, 2003, 08:47:06 PM »

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

Kweassa · « **Reply #6 on:** January 02, 2003, 05:10:18 PM »

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?

AKDejaVu · « **Reply #7 on:** January 02, 2003, 05:14:31 PM »

Random failures never go over well.

I'd also caution against trying to model something without any data to back it up.

AKDejaVu

hitech · « **Reply #8 on:** January 02, 2003, 06:05:08 PM »

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

Toad · « **Reply #9 on:** January 02, 2003, 08:06:33 PM »

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.

Kweassa · « **Reply #10 on:** January 02, 2003, 10:03:30 PM »

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.

Kweassa · « **Reply #11 on:** January 02, 2003, 10:06:06 PM »

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?

Toad · « **Reply #12 on:** January 02, 2003, 10:11:57 PM »

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.

Wotan · « **Reply #13 on:** January 02, 2003, 10:14:38 PM »

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.

funkedup · « **Reply #14 on:** January 02, 2003, 10:58:54 PM »

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.