Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Dragon Tamer on July 27, 2013, 10:27:03 PM
-
This is just a quick question (I say that but it will probably turn into a 5 page thread anyway). A spit 8 in a dive, at what speed does it compress? I chased a spit down yesterday and my jug compressed but the spit was still pulling away from me and actually pulled out of the dive without any noticeable dampening on it's performance.
-
It doesn't. The Spit was capable of diving to higher speeds than any other WWII aircraft, even the Me262. It has aileron control problems at speed, but the elevators work just fine, too well in some cases.
-
Several planes have higher critical Mach numbers than the P-47 (Spitfires, Bf 109's, FW 190's, P-51's do -- not sure if there are some others).
Critical Mach (where compressibility starts) depends (to sort of a first-order approximation) on t/c where t is thickness of airfoil at thickest part, and c is chord. That smaller the t/c, generally, the higher the critical Mach.
Not all planes with small t/c will be able to get to critical Mach before failure of some other part of the airplane, though. For example, a Ki-84 or Zero might have a low t/c compared to a P-47, but they break apart at very high speeds.
-
It doesn't. The Spit was capable of diving to higher speeds than any other WWII aircraft, even the Me262. It has aileron control problems at speed, but the elevators work just fine, too well in some cases.
I question the control authority the Spitfires have at high speeds. It just seems like the controls should be quite heavy at some of the speeds you see Spitfires diving to.
-
As a long time Spit pilot the practical top speed in a dive is ~480-500 mph IAS but you have to pull out gently so as not to break a wing. Spits don't compress. You can push the numbers I stated higher but at the risk of losing a wing. A steady gentle pilot might see 550.
When the dive is over Spits hold E just as they do in a turn. Where some other planes (P-47's for example) use weight to create E for a run or a zoom climb Spits do so through aerodynamics (i.e. low drag).
Full span spits get quite heavy in roll authority at those speeds, particularily the Spit I but also the XIII and XIV. The V and the XI don't seem to lose as much, most likely due to the lower power (i.e torque) vs the VIII or the XIV. The I's fabric covered wings flex hampering it's roll ability at speed.
There's planes that are both faster and slower in a dive than a Spit but, like every other flight charachteristic, the Spit is among the top of the line; not the best but right up there.
-
the spitfire wing was amazing.
:salute R.J Mitchell
-
I question the control authority the Spitfires have at high speeds. It just seems like the controls should be quite heavy at some of the speeds you see Spitfires diving to.
After about 450-500 you cannot roll in a Spit VIII or Spit XIV because the ailerons are so heavy. The elevators did not get heavy, and that imbalance of control forces caused more than one Spitfire pilot to pull back to fast and lose his wings. The light elevator control to extremely high speeds is historical.
In reality the longer aileron Spitfires, like the IX and XVI, sometimes also suffered aileron reversal at high speeds, where pushing the stick to the right caused the Spit to roll to the left and pushing left caused it to roll to the right. The shorter ailerons in the Mk VIII and Mk XIV were a fix for that. The root cause was the force of the air at high speeds causing the thin wings to twist a bit.
-
The shorter ailerons in the Mk VIII and Mk XIV were a fix for that.
I thought about the ailerons being a more likely culprit in roll authority in those two varients than engine torque last night after I posted but I'd already shut down for the night. Glad someone interjected.
-
Wasn't the cause of heavy control surfaces just the airflow over it (trying to push it to the most aerodynamic position)?
Now please correct me if I'm wrong on the above, but it seems like the above would make heavy controls pretty universal. I'm not saying that it should be as heavy as a 109,but the near full authority they have just instinctively seems quite unlikely.
-
Wasn't the cause of heavy control surfaces just the airflow over it (trying to push it to the most aerodynamic position)?
Now please correct me if I'm wrong on the above, but it seems like the above would make heavy controls pretty universal. I'm not saying that it should be as heavy as a 109,but the near full authority they have just instinctively seems quite unlikely.
Well, Supermarine had to put counterweights on the elevators to make them heavier after several Spit Vs were lost when pilots pulled out of a dive too rapidly due to overloading the wings. At some point it will enter full compression, but until then the elevators remained light.
The Spit XIV comparative notes mention that its elevators were noticeably heavier, but still easy to move.
-
Any idea of the aerodynamics behind this? Or will I have to wait for my physics class this fall?
-
Any idea of the aerodynamics behind this? Or will I have to wait for my physics class this fall?
No, I don't know the cause. I doubt it was intended as when the Spit was designed aircraft engineers knew very little, if anything, of the effects of those speeds.
I know the US dinged the Spitfire for imbalanced controls when we evaluated it. Ideally for smooth operation you want elevator and aileron forces to be similar so that the pilot isn't having to change the force on the stick, pulling hard to either side and gentle to the rear when rolling into a turn for example.
-
Any idea of the aerodynamics behind this? Or will I have to wait for my physics class this fall?
:airplane: I don't know the engineering behind this, but I do know the shape of the fuselage has a lot to do with the forces acting on elevator and rudder. Some fuselages were either shorten or length added, depending on how the aircraft was acting and what the design engineer was trying to accomplish.
-
Any idea of the aerodynamics behind this? Or will I have to wait for my physics class this fall?
Basic physics won't cover it, but it will start to give you the fundamentals to understand more about aerodynamics.
There are some aspects of performance that are easier to estimate based on generally available measurements of the airplane (things like drag based on coefficient of lift, wing aspect ratio, etc.)
Then there are things that are not at all easy to estimate because they depend on subtle, detailed aspects of design that are not easy to model. Control force and effect vs. speed is in that category. Not all designs result in higher force per g as speed increases. Some designs started to get lower force per g at high speeds and had to address that as a problem if the effect was too significant lest pilots inadvertently overstress the airframe to the point of failure.
Here are some books on such things if you are interested in the math details:
[PH] Airplane Performance Stability and Control, by Courtland D. Perkins and Robert E. Hage.
[VM] Theory of Flight, by Richard Von Mises.
[RS] Fundamentals of Flight, Second Edition, by Richard S. Shevell.
[BM] Aerodynamics Aeronautics and Flight Mechanics, Second Edition, by Barnes W. McCormick.
[JA] Introduction to Flight, by John D. Anderson, Jr.
-
The Spitfire was unmatched in dive speed in WWII.
-
V2 in the last part of its flight profile did :old: :neener:
-
True, but I'd rather fly a Spitfire given the choice... ;)
-
Basic physics won't cover it, but it will start to give you the fundamentals to understand more about aerodynamics
It's a physics course tailored for Aerospace engineers, so it might get into fluid mechanics pretty well. But not sure.
And thank you.
-
It's a physics course tailored for Aerospace engineers, so it might get into fluid mechanics pretty well. But not sure.
And thank you.
That's a good foundation, but I don't think it would get into the meat of aerodynamics, aircraft modeling, stability and control, etc. Those topics can fill up many more courses and can stretch throughout BSE and MS coursework.
-
Yeah, ASU is said to have a few fairly brutal courses for juniors and seniors. At least within my discipline.
-
Real quick and dirty: Compressibility and localized supersonic airflow affected different aircraft differently; shock waves form deflecting the air away from the wing and fuselage surface, disrupting the normal flow of air over the wings and control surfaces. The turbulent air flow can cause the control surfaces to vibrate or even oscillate between its extremes of deflection like the ailerons on the P-47 and 109. However, the important fact is that since conventional ailerons and elevators work by changing the curvature of the whole airfoil (wing) they don’t work when the airflow is separated and turbulent. For all intents and purposes the wing is stalled behind the region where the shock impinges on the surface of the wing. You can move the control surfaces to their maximum deflection and they will do nothing. On some planes the controls become lighter after the wing airflow enters compressibility, still the controls remain ineffective. The turbulent air flow over the wing also incurs an aerodynamic stall and abrupt loss of lift, which leads to the aircraft diving steeper without the pilot being able to do anything about it. This is often refereed to as "Mach tuck".
(http://upload.wikimedia.org/wikipedia/commons/e/ed/FAA-8083-3A_Fig_15-9.png)
-
It's almost impossible to lawn dart a spit from 14k :old:
-
A nice comment on P-38's and compressibility:
http://www.youtube.com/watch?v=5J0lEHyKInw
-
It's almost impossible to lawn dart a spit from 40k :old:
fixed
-
Well they have to fix the A8 in AH then...
quote author=GScholz link=topic=351707.msg4651089#msg4651089 date=1375055981]
The Spitfire was unmatched in dive speed in WWII.
[/quote]
-
Well they have to fix the A8 in AH then...
quote author=GScholz link=topic=351707.msg4651089#msg4651089 date=1375055981]
The Spitfire was unmatched in dive speed in WWII.
Sorry, how does that follow?
-
I think that some point to the Spitfire's max dive speed as being a result of low drag. The Spitfire had a significantly higher drag coefficient than the P-51. Its wing, however, had an excellent low chord to thickness ratio, delaying the onset of compressibility. On the same horsepower, the P-51B was more than 30 mph faster than the Spitfire IX.
A Spitfire PR recorded Mach .91 in a dive. However, that would not have been possible, except that the prop shaft failed and the propeller came off. Indeed, a major limiting factor in prop driven aircraft speed is t(http://[img])[/img]he propeller itself. Generally speaking, at very high speeds, it's little more than a circular speed brake. The issue for Spits in combat was not maximum velocity, but the rather leisurely dive acceleration rate (in comparison to the P-47 and Mustang).
(http://www.wwiiaircraftperformance.org/wade-dive.jpg)
Test pilot Herb Fisher more than a hundred test dives in a P-47D, testing standard and high mach propellers. His P-47 would reach a terminal velocity of Mach .81 with the standard Curtiss-Wright prop. Using the lower drag designs, he could manage Mach .83. Ultimately, that was terminal velocity for the P-47. Critical Mach was .73, whereupon a shockwave would begin to form. Light buffeting would begin at Mach .71 and full boogie shake at critical mach.
(http://www.mediafire.com/convkey/2209/grq49z73u42zk62fg.jpg)
-
A8 can fly 620mph in a dive and pull-up keeping its parts, never ever seen a spit do that with elevators intact in AH. if statement above is true, A8 needs to lower its max dive speed.
Sorry, how does that follow?
-
A8 can fly 620mph in a dive and pull-up keeping its parts, never ever seen a spit do that with elevators intact in AH. if statement above is true, A8 needs to lower its max dive speed.
Or Spits need their elevators strengthened...
-
A8 can fly 620mph in a dive and pull-up keeping its parts, never ever seen a spit do that with elevators intact in AH. if statement above is true, A8 needs to lower its max dive speed.
Yes. I also fly the A8 quite a bit in-game and 600 in a dive's easy. A Spit can come close with proper trimming but it won't get there without shedding a wing so if Spits were the fastest divers IRL then something needs to be remodeled. I've never lost an elevator due to speed (at least in a Spit... I've lost them in Ki-84's and A-20's and a few others on more than a few occasions)
Or Spits need their elevators strengthened...
The elevators are very responsive at every speed but are part of the problem in that they allow you to shed wings easily.
-
Took me about 5 minutes to test. (Select Germany terrain, air spawn, set wind with 127 mph updraft, climb to 30k, roll over into vertical dive.)
I did about four dives vertically to the deck from 30k, well into compressibility, peaking out at Mach 0.81 in the Spit IX.
No problems whatsoever.
Which Spit version do you guys say has problems?
-
Only problems I've had in diving Spits is that they roll very badly, if at all, at high speeds and the Mk XIV breaks its wings off very easily.
I've never lost control surfaces in a Spit due to speed.
-
I think blackout is the bigger problem than control surfaces at that point. You're pretty much forcing yourself into a level target for whoever is on your tail.
-
I tested most of the fighters for dive speed and handling.
I did this offline, using the TA map. Air spawning at 30k from field A3.
The fastest diving prop fighters are the P-51B and P-51D. Only these two could attain Mach .83
The Fw 190D-9 managed Mach .82, as did the Ta 152H.
Everything else was slower, typically between Mach .80 and Mach .81, except for the P-38s, Typhoon, and Hurricanes. They all maxed out at around Mach .77 or slightly less.
The Ki-84 and Ki-43 both reached Mach .80, before things began falling off. Ditto for the P-40s.
The Brewster and the I-16 both reached Mach .80 without damage, and the Yak-9U managed Mach .81 and suffered no damage (unlike the Yak-3, which breaks up at that speed).
The max for all Spitfires was Mach .81, but they had the best elevator authority (along with the N1K2-J). No trim was required to pull out of the dive. Likewise for the F6F-5, which will pull out hands off at Mach .81.
I have a film... a long film, if anyone is interested...
http://www.mediafire.com/download/j3pxqdndwc78v4w/Dive_tests.ahf (http://www.mediafire.com/download/j3pxqdndwc78v4w/Dive_tests.ahf)
-
I have a film... a long film, if anyone is interested...
I am, thank you :aok
-
Only problems I've had in diving Spits is that they roll very badly, if at all, at high speeds and the Mk XIV breaks its wings off very easily.
I've never lost control surfaces in a Spit due to speed.
Try a Spit 1 from 20k in the TA. 70' +. Hold onto your elevators. :)
(Edit - throttling back not NO throttling back)
-
I tested most of the fighters for dive speed and handling.
Excellent! <S>
-
One thing to note about the dive film... Even though it may appear that a fighter is increasing speed as it begins to pull out of the dive, Mach is decreasing. Most understand that Mach is altitude dependent. I used E6B, which shows Mach regardless of altitude.
Terminal speed in terms of MPH (ignoring Mach) can only be determined by flying each aircraft into the ground. Except, of course, those which have already come apart. :D
One thing you can count on... Should you be flying a P-51D and run into a horde of P-47Ms at 30k, you can bug out with impunity. The P-51D will dive faster, all the way down to the deck. After that, it takes a very, very long time to burn off the energy acquired in the dive. On the other hand, the P-47s cannot retain E like the P-51D and the Mustang will be long gone. RunStang, indeed!
-
Try a Spit 1 from 20k in the TA. 70' +. Hold onto your elevators. :)
(Edit - throttling back not NO throttling back)
(http://imageshack.us/a/img842/7067/5yp2.png)
(http://imageshack.us/a/img442/8065/9c3o.png)
(http://imageshack.us/a/img9/8688/6r1q.png)
(http://imageshack.us/a/img51/7169/8rjw.png)
(http://imageshack.us/a/img829/4536/25c4.png)
(http://imageshack.us/a/img28/8025/8ygd.png)