Low-speed F4U

[dtango]

Not in terms of airflow over the wing.  250 MPH IAS is the same no matter what altitude your at, but to acheive 250 MPH IAS at a higher altitude, you would have to have a faster TAS since the air is lighter up there.

WW, that is odd.  Perhaps the control surface model in AH2 is based upon TAS?  Would that make the roll rate calculate correctly if you pretended the TAS was actually the IAS?

Hmm, I think you misunderstand me.  TAS at 250mph IAS 27K is a lot faster than TAS at 250mph IAS ASL. 

TAS is the actual airspeed of the aircraft with respect to the air through which it flies thus the airspeed that determines the aerodynamic forces on the airplane.  TAS is the actual airflow speed over the aircraft.  AH better model it's aerodynamic forces based on TAS not IAS otherwise it would be completely wrong.

Tango, XO
412th FS Braunco Mustangs

[dtango]

Air density - As illustrated in Widewing's P-38 roll chart, at the same true airspeed because of the reduced density of the air the higher you go the roll rate would be lower because we're not able to generate the same amount of lift at a lower altitude.[/i]  Thus if the aileron is deflected the same amount then assuming the exact same true airspeed but different altitudes the plane at a higher altitude rolls slower.  This is what Widewing's P-38 chart shows.

I noticed something confusing I wrote that I can't edit now in a previous post.  The bolded italics should read "because we're not able to generate the same amount of lift compared to a lower altitude". 

Cheers!

Tango, XO
412th FS Braunco Mustangs

[SectorNine50]

Not necessarily, roll rates should be modeled on the IAS because of the air density change.  Control surfaces have much less control power in lower density air than in the more dense low altitude air at the same TAS, same goes for lift off the wing.  Because the air is lighter, you are technically flowing less of it over the wing at higher altitudes at the same TAS because there are fewer air molecules per unit^3 up at those alts.  The pitot reflects this by showing a slower IAS.  This is also why the aircraft will always stall at the same IAS, no matter what altitude your at.

IIRC, TAS is just ground speed corrected for wind.  So 250 MPH TAS is the same no matter what altitude your at.  250 MPH IAS is much faster at higher alts than at sea level.

[dtango]

Where to start.  Let me use an example to demonstrate instead of trying to explain via theory.  Here's a blow up of Widewing's P-38 roll rate chart.



Points A and B are where the P-38's roll rate is the same at 10k as it is at 20k.
Point A IAS=169 mph, TAS=203 mph, roll_rate=60 dps
Point B IAS=153 mph, TAS=215 mph, roll_rate=60 dps

Points A and C are for the P-38 at the same IAS (169 mph IAS). 
Point A IAS=169 mph, TAS=203 mph, roll_rate=60 dps
Point C IAS=169 mph, TAS=237 mph, roll_rate=70 dps

So here we have the P-38 at the same IAS (169mph) at either 10k or 20k.  Notice that the P-38 actually rolls better at 20k vs. 10k when we compare the same IAS (169mph) at 10k and 20k.

If you want to know why that's the case, that's harder to explain easily (I can't think of a way at the moment).  It has to do with the complexity embedded in the relationship I mentioned earlier:

steady_roll_rate = roll_helix_angle * 2 * V (in TAS) / wing_span

...specifically the complexity of the factors that affect roll_helix_angle.

Tango, XO
412th FS Braunco Mustangs

[SectorNine50]

Hmm, while it doesn't makes 100% sense to me, I'll take your word for it.  I'll look into why this is on my own time so you don't have to type up a huge explanation just for me.

[BnZ]

Ummm...okay, don't laugh at my ignorance for me asking this guys...

What would make Corsair models have bad torque problems compared to other WWII fighter aircraft? The horsepower/weight ratio isn't too extreme compared to alot of other planes. This is even the case with the F4U-4. So what made it so nasty at low airspeed/high power settings? Abrupt stall, lack of longitudinal stability?

[SgtPappy]

The power-weight ratio has absolutely nothing to do with the torque roll AFAIK.
I assume it's just the aircraft's geometric design.

If everyone flew P-38's we wouldn't need this conversation

[BnZ]

The power-weight ratio has absolutely nothing to do with the torque roll AFAIK.
I assume it's just the aircraft's geometric design.

If everyone flew P-38's we wouldn't need this conversation

Uh...forgive my ignorance, but I don't understand how the power of the engine in various aircraft can have NOTHING to do with torque roll at high power settings.

Wouldn't more power turning the prop make for more powerful opposite reaction?

[dtango]

Points A and C are for the P-38 at the same IAS (169 mph IAS). 
Point A IAS=169 mph, TAS=203 mph, roll_rate=60 dps
Point C IAS=169 mph, TAS=237 mph, roll_rate=70 dps

Correction to my last post.  Point C roll_rate = 65 dps not 70.  I can't divide right .

Tango, XO
412th FS Braunco Mustangs

[Saxman]

BnZ,

I think the F6F and P-47 were more stable because of their taller fuselage reduced torque effect.

[mensa180]

The F4U1 with full flaps has the same turn radius as an A6M5 without flaps. Consider that.

Close, but not the same.

[mtnman]

I'm also wondering if torque truly "builds" as power is applied or whether torque effect is reduced as a throttle setting is maintained.  I don't know, I'm just guessing here..

Crazy analogy- If I squeeze the trigger on my power drill, I feel torque try to twist the drill in my hand.  The effect is greatest (from what I can tell) when I squeeze it suddenly and completely, but then as I continue to hold the trigger torque seems to lose some/most of it's effect.  It actually feels like less torque, and more of a "gyroscopic" effect.  And if I slowly squeeze the trigger I feel very little torque effect.

Anybody understand what I mean?

I would guess a similar effect happens with an airplane engine.  Further complicated of course by the propeller, and again by the fact that the pitch/resistance of the propeller changes.

I would also expect that an airplane (let's just use the F4U, since it's the subject of the thread) flying at say 100 mph would react differently to a smooth application of full throttle, versus a sudden application of full throttle.  The plane would be flying the same speed in both cases, same AoA, etc, but I would expect different torque "effects".

Can anyone explain/elaborate?  I have zero expertise here, I'm hoping someone else can throw some facts out for me.

MtnMan

Another consideration- even in the slow turnfight scenario, we're still talking about an airplane that's moving at 100-120 mph, which is still pretty fast in reality.  That's a lot of "mass in motion"- what kind of effect would torque really exhibit?  I honestly don't have any idea, but I wonder if I expect more than would occur in reality?  I'd guess the wings would have an effect of reducing felt torque as well.

[SectorNine50]

The thing about the F4U's wings that supposedly made it awful at low speeds, but great at high speeds, was the fact that they were "seagulled."  That design of wing made it so the aircraft didn't compress in high speed dives, problem is, as I'm sure you can imagine, at low speeds when putting a lot demand on the wings, the air slides off the tips due to the angle of the wing.  This causes the lifting effect of the wing to drop sharply and suddenly if pushed too far.  So if you're pushing the aircraft to it's limits in a stall, than add ANY more throttle, your going to add more pressure to the outside wing, which eventually, will give due to lack of lift.  On top of that, if you do tip-stall, it seems that the F4U recovers incredibly quickly and easily in-game.  From what I've read, in real life stalls are VERY scary in an F4U.

The only reason you don't notice it on a power drill is because it's not at the limit of your hold.  Assuming the drill is powerful enough, if you put it in an object that is trying to twist against you're hold to the extent of your strength, and you give it just a little more torque, your arm isn't going to be able to hold it at that position any more, so it'll twist.

Your technically getting the same overall amount of torque when applying slowly as quickly, but when applying slowly, your muscles have time to react.  In a sudden tip-stall scenario, it'd be more like just flooring the drill because it's so sudden most of the time.

However, all this info is based upon what I have read, so please feel free to correct me if I'm wrong.

[colmbo]

The thing about the F4U's wings that supposedly made it awful at low speeds, but great at high speeds, was the fact that they were "seagulled."  That design of wing made it so the aircraft didn't compress in high speed dives, problem is, as I'm sure you can imagine, at low speeds when putting a lot demand on the wings, the air slides off the tips due to the angle of the wing.  This causes the lifting effect of the wing to drop sharply and suddenly if pushed too far.

Not true.

The wing design was to reduce drag and allow a shorter gear leg while still getting adequate prop clearance.  The gull wing reduced drag by having the wing root at a right angle to the fuselage.  All wings "lose" some lift near the tip due to the tip vortice.  The out wing panels of a Corsair don't have a great deal more dihedral than many other designs, it's just exaggerated by the gull wing shape.

[SectorNine50]

Not true.

The wing design was to reduce drag and allow a shorter gear leg while still getting adequate prop clearance.  The gull wing reduced drag by having the wing root at a right angle to the fuselage.  All wings "lose" some lift near the tip due to the tip vortice.  The out wing panels of a Corsair don't have a great deal more dihedral than many other designs, it's just exaggerated by the gull wing shape.

Was actually just looking over the Wiki on it when I got the notification of your post and saw that little bit of information.  Guess you can't believe everything you hear!  Wonder if the compression bit has any merit though?  Seems plausible.

I did know that all planes had that tip vortice effect, but from what I understood before, it was worse on the F4U.  Now I read the Wiki and it tells me that the seagull design affected "elevator authority," and was fairly bad before that spoiler, that was mentioned earlier, was installed.  Perhaps I misunderstood the fellow I was speaking with on the subject.

Sorry 'bout that, good to get things straight though!