Author Topic: P-51 Airfoil and Turn Performance  (Read 34023 times)

Offline dtango

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P-51 Airfoil and Turn Performance
« Reply #30 on: August 18, 2007, 01:04:03 AM »
Fair point about the 109 slats when flaps aren't deployed.  But it really depends on cl/cd and other values HTC has used with respect to flaps vs. not.  

On this point you've hit the nail on the head about guessing at performance.  It applies to both of us though.  Neither of us know what values HTC has used.  I'm just saying without some more definitive data to show otherwise it is just as likely that the flight model is "right" vs. "wrong" based on the math.

You mention the RAF report (reports?) on the Mustang III.  I take you absolutely seriously.  However the issue for me is without more data about how the tests were done there isn't enough information to know the relevance from these reports.  For instance, was the Mustang III running on 150 octane fuel?  Were the tests done above 20k?  Were they with flaps or no flaps?  Etc. etc.  We both know all of these could have dramatic impact on how we would intepret the reports.

If we had some wind tunnel or flight tested cl/cd polars representing flaps down conditions for the respective aircraft in question, then I think we would have something more solid to work with to do some mathematical sanity checks.

On the topic of trying to confirm the FM through the math, this is actually a soap box issue for me so please allow me to rant for sec on the topic :D!  So I don't have any notion that I can actually confirm the flight characteristics vs. the HTC flight model.  If I go down this path, in the end it becomes nothing more than a comparison of how I've chosen to model something vs. how HTC has chosen to model something.  Like you've said, a complete waste of time!  The best I can hope for is to do some overall physics sanity checks vs. some nitty gritty confirmation that the FM is 99.5% correct.

BTW, I also agree with your P-51 comment on Cd rise with Cl, but the bottom line there is that I don't think any of those drag polars are with flaps deployed.

Tango, XO
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« Last Edit: August 18, 2007, 01:06:19 AM by dtango »
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Offline Stoney74

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P-51 Airfoil and Turn Performance
« Reply #31 on: August 18, 2007, 01:09:38 AM »
Quote
Originally posted by Widewing
You gents are trying to use formulas to confirm the flight characteristics of code... Don't waste your time. You cannot assume that the dynamics match the real aircraft as you have no idea what data is used in the model. HTC isn't talking or telling us what their parameters are. Thus, you are guessing at best.


Guess I was thinking that perhaps the code HTC made samples some of these same equations to create the vectors used to move the planes around.  After that one thread where he posted pictures showing the lift vectors during the stall, I think we can safely assume that many aerodynamic characteristics of the planes are modelled using some type of math.  Otherwise the flight model wouldn't behave so realistically.  Continuing, if they keep updating the code with better equations to simulate those effects, while the data on the individual planes remain static, it could create some of the effects that degrade the P-51 performance.  I don't think they're purposely "porking" the plane.  I could be totally wrong, obviously, but regardless, its an interesting academic exercise.

Offline dtango

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P-51 Airfoil and Turn Performance
« Reply #32 on: August 18, 2007, 01:17:57 AM »
Quote
What I find very confusing is that in level flight, the P-51s have less drag than the 109s, even with full flaps. I test this by cutting power and timing speed loss. the 109K-4 slows much faster that the P-51D. Yet, when turning, drag rises rapidly in the P-51s and lift degrades, but not in the 109s..


Sorry Wide, I missed this statement.  I hear ya.  Two things to consider:  (1) prop drag.  (2) variation of Cd with Cl (either as changing oswald efficiency or a delta_profile_drag increment with increasing Cl).

I know I know, you already have issues with the AH prop drag :D!  I'll spare us diving into the mathematical details!

I am very confident they model #2.

Tango, XO
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Offline bozon

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P-51 Airfoil and Turn Performance
« Reply #33 on: August 18, 2007, 06:42:43 AM »
Quote
Originally posted by Widewing
What I find very confusing is that in level flight, the P-51s have less drag than the 109s, even with full flaps. I test this by cutting power and timing speed loss. the 109K-4 slows much faster that the P-51D. Yet, when turning, drag rises rapidly in the P-51s and lift degrades, but not in the 109s..
 

This tests mostly viscous drag and windmilling prop, per mass. Induced drag is the more important at high AoA and low speeds, I think.

Quote
Something is rotten in the drag modeling of the Mustangs.

Or perhaps it is the only corrent one...
We are arguing something that I have never seen a direct test of. In no performance tests was turning ability considered with full flaps - the "maneuver" setting at best. I still seriously doubt that full flaps was that effective in any plane. The no-flaps AH FM seen about right.
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Offline Viking

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P-51 Airfoil and Turn Performance
« Reply #34 on: August 18, 2007, 06:51:45 AM »
A few anecdotes:



"BF109 was very good, very high scale fighter plane. If was superior to our Yaks in speed and vertical combat. It wasn`t 100% superiority, but still. Very dynamic plane. I`ll be honest with you, it was my dream during my war years, to have a plane like this. Fast and superior on vertical, but that didn`t happen.
Messer had one extremely positive thing, it was able to be successful fight Yak`s at 2000m and Aircobras at 6000m. This is truly unique ability and valuable. Of course, here Yak and P-39 were inferior. As far as combat on different altitudes, BF109 was universal, like La-5.
Me109 was exceptional in turning combat. If there is a fighter plane built for turning combat , it has to be Messer! Speedy, maneuverable,(especially in vertical) and extremely dynamic. I can`t tell about all other things, but taking under consideration what i said above, Messerschmitt was ideal for dogfight. But for some reason majority of german pilots didn`t like turn fight, till this day i don`t know why.
I don`t know what was stopping them, but it`s definitely not the plane. I know that for a fact. I remember battle of Kursk where german aces were starting "roller-coaster" rides where our heads were about to come off from rotation. No, seriously... Is it true it`s a common thing now that Messer wasn`t maneuverable?
Interviewer: Yes.
Heh.. Why would people come up with something like this... It was maneuverable...by god it was."
- Major Kozhemyako, Soviet fighter ace.


"My flight chased 12 109s south of Vienna. They climbed and we followed, unable to close on them. At 38,000 feet I fired a long burst at one of them from at least a 1000 yards, and saw some strikes. It rolled over and dived and I followed but soon reached compressibility with severe buffeting of the tail and loss of elevator control. I slowed my plane and regained control, but the 109 got away.
On two other occasions ME 109s got away from me because the P 51d could not stay with them in a high-speed dive. At 525-550 mph the plane would start to porpoise uncontrollably and had to be slowed to regain control. The P 51 was redlined at 505 mph, meaning that this speed should not be exceeded. But when chasing 109s or 190s in a dive from 25-26,000 it often was exceeded, if you wanted to keep up with those enemy planes. The P 51b, and c, could stay with those planes in a dive. The P 51d had a thicker wing and a bubble canopy which changed the airflow and brought on compressibility at lower speeds."
- Robert C.Curtis, American P-51 pilot.


"Thomas L. Hayes, Jr. recalled diving after a fleeing Me-109G until both aircraft neared the sound barrier and their controls locked. Both pilots took measures to slow down, but to Hayes' astonishment, the Me-109 was the first to pull out of its dive. As he belatedly regained control of his Mustang, Hayes was grateful that the German pilot chose to quit while he was ahead and fly home instead of taking advantage of Hayes' momentary helplessness. Hayes also stated that while he saw several Fw-190s stall and even crash during dogfights, he never saw an Me-109 go out of control."
- Thomas L. Hayes, Jr., American P-51 ace, 357th Fighter Group, 8 1/2 victories


The most delightful features of the Messerschmitt were, first, in spite of its remarkably sensitive reaction to the controls, the ship showed no disposition to wander or "yaw" as we call it; neither was there any tendency to "hunt". It was a ship where the touch of a pianist would be right in keeping with the fineness of the response. And, likewise, I am sure that any ham-handed pilot who handled the controls in brutal fashion would soon be made to feel ashamed of himself.
Seldom do we find a single-seater that does not stiffen up on the controls as the ship is pushed to and beyond its top speed.
In about cruising speed, a movement of the control stick brought just exactly the reaction to be expected. And at high speed, wide open, the control sensitivity checked most satisfactorily.
Then I wanted one more check and that was at the bottom of the dive where the speed would be in excess of that ship's straightaway performance. So down we went about 2,000 feet with the air speed indicator amusing itself by adding a lot of big numbers - to a little over 400 mph. A gentle draw back on the control effected recovery from the dive; then up the other side of the hill.
- US Marine Corps major Al Williams.


"Indeed many fresh young pilots thought they were pulling very tight turns even when the slats were still closed against the wing. For us, the more experienced pilots, real maneuvering only started when the slats were out. For this reason it is possible to find pilots from that period (1940) who will tell you that the Spitfire turned better than the Bf 109. That is not true. I myself had many dogfights with Spitfires and I could always out-turn them.
One had to enter the turn correctly, then open up the engine. It was a matter of feel. When one noticed the speed becoming critical - the aircraft vibrated - one had to ease up a bit, then pull back again, so that in plan the best turn would have looked like an egg or a horizontal ellipse rather than a circle. In this way one could out-turn the Spitfire - and I shot down six of them doing it."
- Erwin Leykauf, German fighter pilot, 33 victories.


“- How did the slats behave in such a situation, did they go in and out?
 It depended on speed, if you pulled more they came out, then back in
- The slats came out completely, never half-way?
 I never came to watch them so intensely. You just knew they had come out, you could see them and feel that the lift increased pretty much."
- Antti Tani, Finnish fighter ace. 21,5 victories.


"Inexperienced pilots hesitated to turn tight, because the plane shook violently when the slats deployed. I realized, though, that because of the slats the plane's stalling characteristics were much better than in comparable Allied planes that I got to fly. Even though you may doubt it, I knew it [Bf109] could maneuver better in turnfight than LaGG, Yak or even Spitfire."
- Walter Wolfrum, German fighter ace. 137 victories.


Two P-51 shootdowns with three-cannon Messerschmitt 109 G-6/R6:
"I got both in a turning battle, out-turning them. We did several times 360 degrees until he became nervous, then pulled a little too much. His plane "warned", the pilot had to give way a little and I was able to get deflection. When I got to shoot at the other one, the entire left side was ripped off.
- So you did several full circles, you must have flown near stalling speed. Did you fly with "the seat of your pants" or kept eye on the dials? What was the optimum speed in such a situation, it was level flight?
It was level flight and flying by "the seat of your pants". What should I say, I should say I was doing 250kmh and the Mustang must have more than 300kmh. That is why I was able to hang on but did not get the deflection.
- And you was flying a three cannon plane?
Yes, but I did fly another one as mine was under maintenance. It was the experience that counted. Experience helped to decide when you had tried different things.
- In which altitude did these Mustang dogfights take place?
It must have been about 2000m."
- Kyösti Karhila, Finnish fighter ace. 32 victories.


"I cast a quick glance at the machine and then climbed up after the other enemy aircraft. Damn, he could turn! Finally I was sitting behind him. I turned so tightly that condensation trails formed behind both wingtips and my Me shuddered on the verge of a stall more than once. Fortunately, the 109 turned extremely well.
The whole air battle took place at a very low altitude. I sat behind the Russian like a shadow, and now and then I succeeded in hitting him.......
He (Russian pilot) turned sharply, leaving a heavy vapor trail, and dove away towards the northeast.......... I cut him off and closed in at high speed. My airspeed indicator was showing more than 750 km/h.
I opened fire rather too soon, but he didn't change direction, instead he put his nose down briefly so that I was suddenly a level higher than he was. I put my nose down as well, but as I was about to fire he pulled up again, and this time I ended up below him."
- Helmut Lipfert, German fighter ace. 203 victories.


The 109 should out-turn and out-fight the P-51 with ease ... because it did.
« Last Edit: August 18, 2007, 06:57:09 AM by Viking »

Offline Benny Moore

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P-51 Airfoil and Turn Performance
« Reply #35 on: August 18, 2007, 07:04:12 AM »
See Rule #4, #5
« Last Edit: August 20, 2007, 11:19:28 AM by Skuzzy »

Offline Viking

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P-51 Airfoil and Turn Performance
« Reply #36 on: August 18, 2007, 07:28:59 AM »
See Rule #4
« Last Edit: August 20, 2007, 11:19:13 AM by Skuzzy »

Offline Benny Moore

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P-51 Airfoil and Turn Performance
« Reply #37 on: August 18, 2007, 07:39:39 AM »
See Rule #4, #5
« Last Edit: August 20, 2007, 11:19:45 AM by Skuzzy »

Offline Viking

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P-51 Airfoil and Turn Performance
« Reply #38 on: August 18, 2007, 11:04:21 AM »
See Rule #5
« Last Edit: August 20, 2007, 11:19:59 AM by Skuzzy »

Offline Stoney74

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P-51 Airfoil and Turn Performance
« Reply #39 on: August 18, 2007, 11:16:49 AM »
Quote
Originally posted by Viking
The 109 should out-turn and out-fight the P-51 with ease ... because it did.


Don't know if you read the rest of this thread, but we're not even talking about P-51 versus 109 turn performance.  We're talking about the flight model of the P-51 and you're more than welcome to participate, if you have anything relevant.

Offline Viking

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« Reply #40 on: August 18, 2007, 11:33:35 AM »
Quote
Originally posted by Stoney74
Don't know if you read the rest of this thread, but we're not even talking about P-51 versus 109 turn performance.


Widewing's posts seem to contradict that. He constantly compares the turning circle of the P-51 with that of the 109K, and comments that it is somehow wrong. I just chimed in to say my bit on behalf of the 109. Is the flaps on the P-51 porked? I don't know; they very well might be.

Offline Widewing

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« Reply #41 on: August 18, 2007, 12:50:39 PM »
Quote
Originally posted by Viking
Widewing's posts seem to contradict that. He constantly compares the turning circle of the P-51 with that of the 109K, and comments that it is somehow wrong. I just chimed in to say my bit on behalf of the 109. Is the flaps on the P-51 porked? I don't know; they very well might be.


I have no issues with the 109s, as many aircraft saw a boost in flaps-out turn performance with the drag update last summer. What bugs me is that the P-51s apparently don't get a proportional increase in CLmax when they use flaps, and the type of flap is very similar to that of the 109s. I used the 109K-4 as a typical example of a fighter that benefited from the drag update.

My regards,

Widewing
My regards,

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Offline PanzerIV

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P-51 Airfoil and Turn Performance
« Reply #42 on: August 18, 2007, 05:43:11 PM »
Although the P51s wing loading wasn't high, the wing lifting was low, thus increasing turn radius, put flaps down 1 or 2 notches and it can turn nicely.

Offline 1K3

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« Reply #43 on: August 18, 2007, 06:06:39 PM »
In turning radius, I'd put P-51s in the same class as the Fw 190.  Both P-51 and Fw 190 have very good controls, but at slow speed they're pigs.

Offline Badboy

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« Reply #44 on: August 18, 2007, 07:35:38 PM »
Quote
Originally posted by Widewing
Have a look at this graphic and tell me if you think that a 13,457 lb P-47D-25 should out-turn a fuel light, 8,604 lb P-51B.


Here is an EM diagram for the P51D and P47D25 both with full flaps. It shows that the P51 has a better sustained turn rate, but a slightly wider radius.



You can see the relationship between the sustained turn radius and rate better in this diagram, which also includes the P51B.



You can see from this that both the P51D and the P51B have higher sustained turn rates and can therefore out turn the P47D25 at full flaps when they both have 25% fuel. The P-51B has a better sustained turn rate and a smaller radius, which doesn't agree with your original graphic.

In general, a similar type of flap design can have a very different effect on wings of varying profile and planform. Their relative position, size and integration with the main wing can yield significantly different results.

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