Author Topic: Turn rate and radius questions (Read 4112 times)

GScholz · « **Reply #60 on:** May 18, 2003, 11:28:04 PM »

Wing loading isn't the only factor you have to consider with regard to turning ability. How much AoA could the wing take before stalling? Focke Wulf had excellent aerodynamicists as shown by the very effective aileron design. Lbs/sq.feet wing loading numbers don't tell you how effective that wing was in producing lift. As an example; the P-51's wing was a laminar flow airfoil design which decreased drag, but was less tolerant to high AoA compared to a conventional airfoil. Higher AoA produces more lift at the expence of bleeding more E, a typical 190 trait.

dtango · « **Reply #61 on:** May 18, 2003, 11:54:12 PM »

This thread won't go away

. For grins I did some acclerated stall limit testing on the F4U-1D.

Flight parameters: 25% fuel, alt around SL.

Constant-G tests for lift limit. As prescribed in the US Navy Flight Test Manual - holding constant bank angle in level turn until speed slowly decays to point of stall. Calculated bank angle for 3g's was ~70 degrees at 173 mph TAS. Flight test results: 3g stall at 168-174 mph. Film attached below.
F4U-1D Constant-G Test

Pull-up tests. Wings level pullups holding 3g's. Rapid deceleration made data collection and analysis hard to conduct. The results show this difficulty: 3g stall around ~162-190 mph. Film attached below.
F4U-1D Pull-up Test

Between the two types of tests the constant-g was more reliable vs. the pullup test to collect data on though tricky as it is. The constant-g tests closely match what Badboy's EM chart indicate.

Tango, XO
412th FS Braunco Mustangs

Guppy · « **Reply #62 on:** May 19, 2003, 01:50:13 AM »

Quote

Originally posted by GScholz
Wing loading isn't the only factor you have to consider with regard to turning ability. How much AoA could the wing take before stalling?

Another interesting question is what happens when the critical AOA is reached. If the aircraft has a severe stall with little warning, then it will be difficult for any but the most skilled to extract its maximum turn performance (especially in a low-level stallfight).

The Focke-Wulf 190 seems to have been noted as especially bad in this respect, despite its aerodynamic excellence in other areas. A computational analysis (Lednicer, 1995, in the Royal Aeronautical Society Journal) concluded that "the aerofoils and twist used on the Fw 190, combined with the wing's elastic properties are the cause of the aircraft's harsh stall characteristics."

F4UDOA · « **Reply #63 on:** May 19, 2003, 09:44:48 AM »

Dtango,

Thanks for actually listing to what I'm saying.

I looked at your film on the digital viewer and your results are very good.

I don't know if you looked through the external viewer or not but I would say you canstant 3G was about 170MPH and the pull up was about 190MPH at 3G.

Two things.

1. The Chart I am using for comparison is from the F4U-1 flight limits chart I posted not Badboy's EM chart. Badboys chart is based on AH.

2. Your test was at 25% fuel which in an F4U-1D is 11,000LBS. Or 1,000lbs less than the 12,000LBS specified in the Accelerations chart I posted. All of the Test I performed were at 75% fuel which is still underweight but not nearly so much.

Using the meathod from the P-51 chart to determine the F4U max G at a given weight multipy the charts weight by the G factor then devide by the new weight.

So 12,000lbs * 3G = 36,000lbs / 11,000LBS = 3.27.

So basically your increasing your G load by about 27% with every 1,000lbs.

I may seem like I'm being Zealous here for what may not seem like a huge difference but it is rather significant.

The problem is this. Some A/C in WW2 were excellent turning A/C ala the Spit, Zero, Hurri and some were moderate F4U, F6F, P-51, 109 (late) and some were poor P-47, FW190. The first group of excellent turning A/C IMHO are very well represented in there ability. IMHO the latter two groups are lumped into a parity of turning ability that is not realistic.

This can be seen in the 1G stalls and the accelerated stalls which are almost identical depending on loading.

What I would like to see is simple to define at least in the American A/C is to have stalls occur as the P-38, P-51, F6F, F4U as they should be. I do not have the data for the Euro types but I'm sure HTC does.

dtango · « **Reply #64 on:** May 19, 2003, 12:42:14 PM »

Heyas,

So why doesn't the AH stall limits match the chart you posted for the F4U-1D? There could be hundreds of reasons. I think it's a bit premature to make the claim something is off. Let's just do some further triangulation here.

Going by the posted chart if we have 3g stall speed of 160mph at 10k ft. Running the math we get 1g stall then at 92mph TAS at 10,000 ft. Running the calculations for 92mph at 10k we get a sea level stall speed of 79 mph TAS.

What do you have a for a 1g stall speed of a F4U-1D, 12,000 lbs, at SL clean? Does it match the 79 mph?

The only data I have comes from the "Joint Fighter Conference" which I just have the figures and don't know the flight parameters (weight etc.).

Tango, XO
412th FS Braunco Mustangs

GScholz · « **Reply #65 on:** May 19, 2003, 03:31:52 PM »

Quote

Originally posted by Guppy
Another interesting question is what happens when the critical AOA is reached. If the aircraft has a severe stall with little warning, then it will be difficult for any but the most skilled to extract its maximum turn performance (especially in a low-level stallfight).

The Focke-Wulf 190 seems to have been noted as especially bad in this respect, despite its aerodynamic excellence in other areas. A computational analysis (Lednicer, 1995, in the Royal Aeronautical Society Journal) concluded that "the aerofoils and twist used on the Fw 190, combined with the wing's elastic properties are the cause of the aircraft's harsh stall characteristics."

Yes the 190 had very bad departure charecteristics, especially the snap-roll was deadly at low alts. I think it would be fair to say that the 190 pilots were apprehensive about pushing the envelope in turning fights ... unlike us virtual pilots

I've seen LW guncam footage of an 190A8 who completely out flew a P47 in a turning fight at medium alt, turned inside him after three or four circles and scored hits. Must have been a good pilot in that A8.

I think the relative pilot quality of the two airforces were a greater factor in 44-45 than the qualities of their airplanes. Again this is not something we see in AH. That the LW was able to offer any effective resistance at all late in the war is quite amazing considering the odds stacked against them.

F4UDOA · « **Reply #66 on:** May 19, 2003, 03:45:46 PM »

I like triangulation, lets play.

The chart when CAS is corrected the 3G stall at 10K is 164MPH. The math I think you are doing is deviding by the square of the G force. So the square of 3G's is 1.73, so take 164 devided by 1.73 = 94.7MPH power on stall which corresponds very well to quoted power on stalls in the F4U CAS.

Your question is if you take that to sea level does that sound right? That being the 72MPH CAS to TAS.

The answer is no of course not. The chart I posted is IAS not TAS.

[However a subject for another thread is that clmax goes way up with increase in power and prop wash in 1G flight. So at higher power settings the 1G stall can be much lower than what is quoted.]

TAS speed is always going to be higher than IAS at higher alts. Thats why stall speeds are always quoted in IAS. The pilot can't sit there with a conversion chart while flying.

The chart does have a margin of error built into it for variations in stall as altitude increases. However at sea level it should be at the low end of that chart.

Urchin · « **Reply #67 on:** May 19, 2003, 03:48:04 PM »

I thought the F4U-1D was *the* worst turning US plane because of the spoiler on the wing, it gave the wing a poor life coeffiencent which kinda offset the moderate wingloading. According to AHT that is the way it was, even the P-47 turned better.

F4UDOA · « **Reply #68 on:** May 19, 2003, 04:12:00 PM »

Urchin,

Unknowingly you are the cause of this post. You outturned me in a flat turn when I thought I had you dead to rights when you were in a 190A.

Frances Dean who wrote AHT used a calculation to come up with a turning index using the CLmax of each AC clean no flaps. Oddly enough the Clmax for the F4U he used was 1.48 and is correct. However the Clmax used for the rest of his A/C are all way off to high. The P-47 Clmax he has listed as 1.93. That would give the P-47D at 14,300LBS a 1G stall of 97.5MPH clean no power. Not likely.

In fact no WW2 fighters that I am aware of had a Clmax of over 1.6 with no flaps. Mr.Dean quotes 5 a/c over 2.0 and two over 1.8. In fact the only one even close in the F4U.

While Mr.Dean was alive I visited him in his home and asked him via Email where his lift coeeficients came from. he said he calculated them from the 1944 fighter conferance(which he also published). Unfortuately the confernace results are all over the place if you have a copy you may notice that stalls in Knots and MPH are used interchangeable between A/C. Also take a look at the FG-1 stall. It is at 130Knts and is the same exact A/C as the F4U-1D. If he had used the FG-1 stall speed you would be saying the best turning WW2 fighter instead.

FYI, all except the first 800 F4U's made had the spoiler strip installed at the factory. The others were retro fitted. Even with the spoiler strip the quoted stall speeds are virtually the same as the F6F-5 and generally much lower than the Army types.

Urchin · « **Reply #69 on:** May 19, 2003, 05:14:27 PM »

What kind of turn was it? Generally I'll try to get someone to overshoot and set up a nose to nose turn so that they fly in front of me.

I'm not sure that in a nose to tail turn the 190A5 will out-turn a F4U-1D.

Interesting stuff on AHT, by the way.

dtango · « **Reply #70 on:** May 19, 2003, 08:09:07 PM »

Yes, the equation I used for my calculation is:
Vs-accelerated = Vs * sqrt (g-load)

Hmmm something is askew with your chart then. If the chart you posted was IAS then you wouldn't have a difference in accelerated stall limit velocities for varying altitudes hence the curves plotted the way they are.

Tango, XO
412th FS Braunco Mustangs

F4UDOA · « **Reply #71 on:** May 19, 2003, 08:12:29 PM »

Urchin,

I did some test in the FW190A5. With the light gun package it is actually very difficult to bleed enough energy to get down below 180MPH. It makes a very fast circle at about that speed. I usually try to fly it when Buff hunting but because of the climb, dive accleration and roll I think it is a great dogfighter. I probably spend more time in Luftwable rides than you think. I usually do it for a specific mission though.

I don't have accelerated stall numbers for the FW190A5 but I do have the FW190A5 vrs F4U and F6F report. You can say the AFDU type data is Navy bias but there was one piece of data to consider. The A/C had a flight limits restriction card in it when captured.

The restrictions are as follows

466MPH below 10K
426MPH 10k to 16,400ft
360MPH 16,400ft to 25K

Also the common 1G stall speed is generally accepted at 110MPH.

Based on that you can calculate the 3G stall at 190MPH.

This is actually modeled pretty closely in AH. The problem I have have is that I believe that the F4U is modeled almost exactly the same in regards to accelerated stalls at gross weight.

As Dtango showed in his test you can do better in an F4U as long as you don't bring any fuel.

F4UDOA · « **Reply #72 on:** May 19, 2003, 08:21:01 PM »

Dtango,

Sure it does? It has 10, 15, 20, 25, 30K??? Is that what you mean?

BTW, It says Indicated Airspeed in Knots right in the middle of the chart.

Urchin · « **Reply #73 on:** May 19, 2003, 08:34:38 PM »

F4UDOA, I actually think the 190A5 might be a little overmodelled. At least as far as the stall speeds go. I remember reading that the 190A4 had a listed stall speed in 'clean' configuration of 110 mph I think (might have been 120), and a 'dirty' stall of 99 mph. I can get it down to 100 mph no problem without stalling it. The only difference as far as I know between the 190a4 and the 190a5 was some radio equipment, I think. So I can't imagine why the 190a5 would have such a drastic difference in 1g clean stall speed.

I haven't really done any 'tests' other than flying as slow as I can go.

dtango · « **Reply #74 on:** May 19, 2003, 08:36:54 PM »

Here's another check. Let's compare Clmax figures. Let's go with Clmax figure of 1.48 for the F4U-1D.

CLmax based on AH Model:
3g stall speed: 170 mph
Weight: 11,000 lbs
Resulting Clmax: 1.45

CLmax based on Chart:
3g stall speed: 164 mph (corrected)
Weight: 12,000 lbs
Resulting Clmax: 1.69

Looks like the AH model is closer to the 1.48 figure you've quoted as well.

Tango, XO
412th FS Braunco Mustangs