Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: F4UDOA on July 26, 2000, 03:26:00 PM
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Gents,
I am researching this right now because some issues in the game got me looking at actual flight characteristics of these two A/C in contrast to one another.
Does anyone have drag data IE NACA reports of the Drag coefficients of these two A/C. I have "America's Hundred Thousand" and I believe the information there may be a bit misleading based on the varying speeds the Cdo's were calculated. Based on that text the P-47 had a lower drag Airframe than the F4U. I believe this is wrong based on performance data of the A/C in or out of the game.
In AH currently the F4U-1D out accellerates the P-47 to 300MPH and is equal to it or better at lower speeds with WEP. Also it is faster at sea level with WEP by a full 20MPH 360MPH to 340MPH. These speeds correspond to the actual perfromance data exactly. Why then is it assumed that the P-47 had a lower drag Airframe? It had 14FT less wing area(314Sq Ft vs 300Sq Ft) and a much larger cowl intake compared to the F4U creating allot of additional drag. This is because the F4U had it's oil cooler intakes in the wings.
If the F4U had 350HP(2250HP vs 2600HP) less than the P-47D30 then why is it 20MPH faster at the same Alt?
The P-47D30 weighed 2400lbs more but weight is not as limiting a force in top speed as drag. In fact weight can assist top speed because of the force of momentum.
Does anyone have data or an explanation for this or any NACA data? Pyro/HT?
Thanks F4UDOA
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"In fact weight can assist top speed because of the force of momentum"
I think you are wrong here. All other things being equal, the heavier plane is going to be slower in your test conditions (level flight).
popeye
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Popeye,
That would make sense except when the weight doesn't add drag like a drop tank. Does your plane get faster as it gets lighter. Maybe but not significantly. Were as if you drop a drop tank you can pick up 20mph because of lose of drag. Besides isn't there a law in physics about an object in motion tending to stay in motion?? I'm not an engineer so I depend on guy's like Wells and Niklas for some help on calculations.
Also weight can definitly help speed in a dive. The steeper the dive the greater the assist. In level flight some of that forward momentum assist forward volocity. It has more to do with E-retention than flat out forward speed or acclleration. But I think the brick wall of drag is your greatest inhibitor. It happens when your Cdi(induced drag) and Cdo(zero lit drag) become equal to your available thrust then you no longer accellerate. The problem I see is that the sum of these two drag coefficients is so high in the P-47 that it stops it from accellerating 20mph slower than the F4U. And the F4U has allot less HP. Meaning that the F4U must have less drag. But I need someone to tell me I'm wrong or right here.
Thanks
F4UDOA
[This message has been edited by F4UDOA (edited 07-26-2000).]
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Any additional weight slows the aircraft down. The more weight it has, the more power from the engine must be spent to keep it flying. The more power used to just stay in the air, the less power availble to pull the aircraft through the air.
Originally posted by F4UDOA:
In fact weight can assist top speed because of the force of momentum
Not true. Additional weight will not increase the top speed through momentum. It will slow acceleration through inertia and will also cause speed to be reduced at a slower rate due to momentum.
Sisu
-Karnak
[This message has been edited by Karnak (edited 07-26-2000).]
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At least with one thing weight is helping, crashing through houses (http://bbs.hitechcreations.com/smf/Smileys/default/biggrin.gif)
At least in that case P-47 can infiltrate much deeper into the house than Spitfrie...
But well.. thats the all speed benefit that weight can give, will not stop at first wooden pole.
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Yep, more weight = more lift required = more drag.
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Doug "Pyro" Balmos
HiTech Creations
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Pyro,
Point taken, weight is bad okkayy Mr. Mackey.
A little South Park Humor there.
Anyway if the additional weight is such a factor then why does the P-47 hold E so well and zoom so well. Is it the momentum of the weight?
When you take the three factors involved there are only three questions to ask.
Weight
F4U=12000lbs P47=14400lbs
HorsePower
F4U=2250hp P47=2600HP
Drag
F4U Cdo=? P47Cdo=?
When you consider the F4U is 20MPH faster at sea level then one or both of the other factors is slowing the P47 down.
Also the same factors should affect accelleration, sustained turn rate and climb.
I'm digging for an equation here guy's. Where is the center of the circle?
Thanks
F4UDOA
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Originally posted by F4UDOA:
Pyro,
Point taken, weight is bad okkayy Mr. Mackey.
A little South Park Humor there.
Anyway if the additional weight is such a factor then why does the P-47 hold E so well and zoom so well. Is it the momentum of the weight?
When you take the three factors involved there are only three questions to ask.
Weight
F4U=12000lbs P47=14400lbs
HorsePower
F4U=2250hp P47=2600HP
Drag
F4U Cdo=? P47Cdo=?
When you consider the F4U is 20MPH faster at sea level then one or both of the other factors is slowing the P47 down.
Also the same factors should affect accelleration, sustained turn rate and climb.
I'm digging for an equation here guy's. Where is the center of the circle?
Thanks
F4UDOA
Probably also airframe and propeller has something to do with that..
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The P-47 probably has much more wetted surface area in the fuselage than the F4u and that's what will limit top speed more than anything. The difference in weight is negligable at those speeds. The P-47 has 30-40 lbs more drag due to weight difference. Keep in mind that propwash *adds* drag and with the fuselage being in the propwash, all that extra power and thrust in the P-47 may not be advantageous. In other words, if they used 'pusher' props, they might be 20 mph faster.
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Wells,
I thought you would respond. Doesn't the drag of the fuselage factor into the Cd of the A/C?
I guess the question is why does the same factor that prevents the P-47 from reaching higher speeds allow it to zoom and hold energy so well compared to the F4U? In my offline test the F4U-1D could easily out accellerate the P-47-D30 even with WEP to 300MPH. But it does not hold E as well in turns or zoom as well. I think you already know what I'm thinking Wells since I'm basing this on your equations but I can't duplicate your calculation for the Cdo and Cdi of both A/C.
Fishu,
Consider this, the P-47D25 or later had the 13ft 4 blade Hamilton Standard prop. It was much better than 12 foot Curtiss Prop and slightly better than the 13Ft Hamilton 3blade Standard on the F4U. Even with more horse power and better prop it could not overcome the F4U at sea level. When the F4U-4 used the 4blade prop and increased to 2380HP at 12500lbs the F4U-4 was 380mph at sea level with a 4000fpm climb.
Thanks
F4UDOA
[This message has been edited by F4UDOA (edited 07-26-2000).]
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...because induced drag is prominent in turns, while only about 5% of the total drag at top speed. Everything goes against the F4u in that department. More wing area, higher Clmax, lower aspect ratio, less weight. Say both planes pulled a max turn at 300 mph
P-47 Cdi = 0.111 (note about 5 times greater than the Cd0, based on Clmax of 1.4)
induced drag = 7700 lbs approx
accel (or deceleration) = -7700 * 32.2 /14400 = -17 ft/sec/sec
F4u Cdi = 0.134 (Clmax ~ 1.5)
induced drag = 9700 lbs approx
deceleration = -9700 * 32.2 /12000 = -26 ft/sec/sec
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wells, is it possible that the resulting G load for the f4u in your example would be much higher than for the p47? Donīt you compare for example a 6G turn for the f4u to a 4G turn for the P47 with your calculation?
Can you do the calculation for a 4G turn for both ac, including prop force pls?
niklas
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I think you've run out of variables here (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
If the Hog is faster than the Jug, with less thrust available, the Jug MUST have more drag--no way outta that one.
Zoom climb, OTOH, depends on what kind of zoom you're talking about. Start both planes at max speed, level flight, and zoom, and I'll bet the Hog wins every time. Lighter, more speed to start with, lower stall speed.
But which plane reaches a higher DIVE speed? Zoom from a dive is based on kinetic energy along with the basic thrust/lift/weight properties of the plane. If two planes dive to the same speed, the heavier plane has more KE, right? If the Jug dives to a higher speed than the Hog (not sure, but certainly possible) then it's got an even greater advantage in the initial zoom.
You've also got to consider prop efficiency and supercharger performance at the "top of the zoom" where the plane's performance is being maxed out. Was the Jug's prop a better "climb prop" than the Hog's? Did the blower kick in at the same point.
More data required to get to the bottom of this one, I'd say...
Plus, you have to wonder if the lack of "distinct" turn performance differences in the FMs of the planes has its root in the way drag is calculated or applied in the sim. If so, it'll be hard to match sim plane tests to real plane data.
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Wells,
I think Niklas has something there.
Your calculation is deceiving. It also assumes that pulling a 4G turn in a F4U gives you the same radius as a 4G turn in a P-47. It may be possible to "Out Turn" a
4g pull in a P-47 while only pulling 3G's in an F4U. I see also that the extra weight assist the P-47 in acheiving a lower loss of E. Doesn't that extra weight along with a lower Cl cause it to Slip wider into the turn because of higher centripital force? It's sounds less like E-retention and more like an inability to hold the road. Were as a Spitfire can turn tightly and quickly.
Also looking at your Excel calcs on these two A/C the P-47 Cdi at 300MPH is at 755 and Cdo is at 6980 for a Cd of 7735 while the F4U is at a Cdi of 522 and a Cdo of 5995 for a Cd at 6517. It seems like the F4U has less drag at high speed and more drag/lift at low speed. Shouldn't that be the optimal configuration for a fighter??
Later
F4UDOA
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I wasn't trying to be devious. The F4u has the ability to bleed more E than a P-47. I thought that was the question?
Optimum fighter design is a different topic altogether...hehehe
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Hmm,
The F4u and P-47 are 'optimized' for a speed of about 165 mph IAS. The lift coefficient being roughly 0.55 for the F4u and 0.69 for the P-47 at that speed. Now, if you keep that optimum lift coefficient (angle of attack) at other speeds, you could get something like an optimum G-load.
200 mph = 1.5 g
250 mph = 2.3 g
300 mph = 3.3 g
350 mph = 4.5 g
If you pull more than that, you would be on the 'backside' of the L/D curve, wasting energy.
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I just saw this and have a couple of thoughts on this subject.
First, the CDo of .0213 posted in Dean's America's 100K for the P-47 is for the XP-47 on page 113. The CDo .0251 he posts on page 598 is for P-47D. The CDo for the F4U-1D is .0267.
Second, those CDo values are for 250 mph at SL. Between RN=2x10^^6 and about 20x10^^6 the CDo values steadily decrease, stabilizing to a constant (but uncorrected for compressibility). Look to pg 112 for the example of P-51D CDo vs RN.
q= Dynamic Pressure = Rho*V^^2 = 160 #/sq ft
At 250mph TAS at SL, RN for P-47D = ~ .00237x250x1.467X(7.29)/(3.7373x10^^-7)= 16.9x10^^6
For the F4U, RN at 250mph at SL =~ .00237x250x1.467x(8.12)/(3.7373x10^^-7) = 18.3x10^^6
For the P-51D, RN = .00237x250x1.467(6.63)/(3.7373x10^^-7) = 15.4x10^^6
Go back to pg 112 and pick off CDo for RN=15.4x10^^6 to find .0176. At 10^^20 the CDo (uncorrected for M) is .0156. At that RN, the P-51D is going about 324mph TAS and about 0.42M
Back to your question "what is going on about relative Drag?"
First the Drag(total) = Drag(parasite) + Drag (induced)
Induced Drag CDi= (CL)^^2/(Pi*AR*e); Assume as Dean states e=.85, P-47 AR=7.29, GW =14411; F4U AR=7.83, GW=13698
P47 CL= W/q*S=13698/160*300 = .285; CDi= (.285)^^2/(3.14*5.61*.85) = .00544
P-47 Total Drag Coefficient at 250mph, SL= .0251+.00544 = .03054
Total Drag47 in pounds= CD*q*S = .03054*160*300 = 1466 # (Dean Table 104 has 1485)
F4U CL = 12694/160*314 = .264; CDi= (.264)^^2/(3.14*5.35*.8) = .00488
F4U Total Drag Coefficient at 250mph, SL= .0267+.00488 = .0315
Total Drag4U in pounds= CD*q*S = .0315*160*314 = 1586 # (Dean Table 104 has 1580)
The F4U with 2000HP at SL at 250mph and 80% efficiency has Thrust=.80*2000*550/367.5
F4U Thrust in # = 2394 # (excluding exhaust) (Dean Table 104 has 2400)
The P-47 with same HP at SL has the same Thrust = 2394 # so the delta excess thrust for the P-47 over the F4U is (2394-1466=928# P-47) vs (2394-1586=808# F4U)
So, for these weights and HP and engine and Oswald efficiencies, relative aspect ratios and wing loadings - the Jug should be faster through the M=.55 range. Above that, you will have to look at CD vs RN and the Compressibility Drag rise curve.
Additionally Dean did not look into the relative CD vs CL Form Drag due to Angle of Attack.
For a P-51D at CL=10208/160*233.2 = .27, the Delta CD is .00018
Hope this helps.
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Holy Necro Bump Batman!
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Gents,
I am researching this right now because some issues in the game got me looking at actual flight characteristics of these two A/C in contrast to one another.
Does anyone have drag data IE NACA reports of the Drag coefficients of these two A/C. I have "America's Hundred Thousand" and I believe the information there may be a bit misleading based on the varying speeds the Cdo's were calculated.
The Parasite Drag Coefficients were extracted from the cited References on page 113 of Dean's book for the speeds and SL at the associated RN's. The P-51D data is in fact as it should be for RN=15x10^^6 at 250 mph @SL - namely .0176.
Based on that text the P-47 had a lower drag Airframe than the F4U. I believe this is wrong based on performance data of the A/C in or out of the game.
The game performance may not match real life for a variety of reasons. First, the Oswald efficiency given for the P-47D per flight test report was nearly .9 whereas Dean uses .85 for all (including F4U-1 and F4U-4), so the Induced Drag values for the P-47D will be about 5% less in real life than Dean's calculations.
Second, all Parasite and Induced and Form Drag Coefficients are referenced to each individual wing area. The P-47B (.0215) and P-47D (.0251) have CDo less than the F4U AND have 95% of the wing area. Net Result? Less Parasite Drag in pounds for the P-47's even if CDo was exactly the same.
In AH currently the F4U-1D out accellerates the P-47 to 300MPH and is equal to it or better at lower speeds with WEP. Also it is faster at sea level with WEP by a full 20MPH 360MPH to 340MPH. These speeds correspond to the actual perfromance data exactly. Why then is it assumed that the P-47 had a lower drag Airframe? It had 14FT less wing area(314Sq Ft vs 300Sq Ft) and a much larger cowl intake compared to the F4U creating allot of additional drag. This is because the F4U had it's oil cooler intakes in the wings.
If the F4U had 350HP(2250HP vs 2600HP) less than the P-47D30 then why is it 20MPH faster at the same Alt?
The P-47D30 weighed 2400lbs more but weight is not as limiting a force in top speed as drag. In fact weight can assist top speed because of the force of momentum.
Too many unknown variables to deal with. First, Dean's calculated values are at P-47D GW=13698 which is just about right for a P-47D model lower than P-4D-25. Full internal fuel and ammo, no external wing pylons, 305 total gallons. The Combat Power at SL=2300HP
Second, for that model series, 2300HP was Combat Power and remained constant through 27000 feet. The F4U did not have a Turbo so its power fell off considerably with altitude.
Both the F4U-1 and -4 in Dean's book had .0267 CDo at 250mph SL. The Combat Power of the R2800-8W was 2135 from SL to 12000 feet, and for the F4U-4 the 18W started at 2380 and dropped to 2080 at 23000ft.
The GW of the fully loaded F4U-1 with both Fuse and wing internal tanks plus full ammo was 12,676 pounds.
So, the GW difference between the P47D through the P-47D-20 and the F4U-1 was about 1000 pounds more for the Jug. The Combat Power of the P-47D was 165 HP More than the SL 2135 for the F4U-1. The actual Thrust difference in Pounds was 2300/2135 = 1.077 factor in favor of the Jug. The actual Drag difference in pounds based on the above analysis was ~1470 # for the Jug and 1584 # (CRS from earlier calcs) for the F4U-1 so:
The Jug was a.) faster and b.) had slightly more acceleration than the F4U-1 by the numbers
Does anyone have data or an explanation for this or any NACA data? Pyro/HT?
Thanks F4UDOA
The challenge is to find Performance Reports published by Republic and Vought which have the detailed Drag estimates as f(CD, RN, CL), as well as Power Available and Power Required as f(height, boost, RPM). Then go to the Spitfireperformance threads and gather Flight Test data with given results including references to external racks, GW, etc.
I have the NAA P-51D and P-51H reports
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Thanks for posting. :aok