P-47D and Spitfire Mk9 turn performance

[Pilum]

Since we will soon have both the P-47D and the Spitfire Mk9 in DCS and there has recently been a discussion about different methods doing turn estimates based on EAS or TAS, I did an estimate using TAS and got the following results:

 

Spitfire Mk9 Merlin 66 at +18 boost, maximum sustained loadfactor at 175 KEAS, n= 3.52 sea level, n=2.77 at 20000 ft.

 

Thunderbolt P-47D-10 56” boost, maximum sustained loadfactor at 175 KEAS, n= 2.54 sea level, n=2.08 at 20000 ft

 

However, as indicated in a couple of figures you posted earlier Crumpp, it looks like your EAS method yields very different results: Compare both at 175 KEAS for example, here it looks like the P-47D with n=3.5 will outturn the Spitfire Mk9 with n=3.2? Again, altitude is not given in the figures and you were referring to results for 20000 ft in your post but maybe the figures refer to sea level after all?

 

Is this the performance you expect to see in DCS then Crumpp? The 56” P-47D having better sustained turn performance than the Spitfire Mk9 +18 boost at 175 KEAS ?

[bongodriver]

:music_whistling:

 

Rate of Turn

The rate of turn (ROT) is the number of degrees (expressed in degrees per second) of heading change that an aircraft makes. The ROT can be determined by taking the constant of 1,091, multiplying it by the tangent of any bank angle and dividing that product by a given airspeed in knots as illustrated in Figure 4-48. If the airspeed is increased and the ROT desired is to be constant, the angle of bank must be increased, otherwise, the ROT decreases. Likewise, if the airspeed is held constant, an aircraft’s ROT increases if the bank angle is increased. The formula in Figures 4-48 through 4-50 depicts the relationship between bank angle and airspeed as they affect the ROT.

NOTE: All airspeed discussed in this section is true airspeed

 

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2004.pdf

 

http://aviation.stackexchange.com/questions/2871/how-to-calculate-angular-velocity-and-radius-of-a-turn

[Crumpp]

Holtzauge,

 

Again, I would be happy to answer your questions about the mechanics of an EAS turn plot.

 

Is steady state turn performance determined by the Power Available to Power Required relationship?

 

The answer is yes.

 

So, why do you not believe that at some point, an engine that creates some 2800 hp from sea level to 30,000+ feet does not outperform an aircraft engine that has lost 50% of its power available by 30,000 feet.

 

The altitude that occurs at I do not know but I would place it at around 30,000 feet for a normal Merlin 66 +18 Spitfire as guess.

 

All this depends on which P-47 you select and which Spitfire variant. Why this is such an emotional issue for you is beyond me.

 

This is my last attempt at reason with you.

[Pilum]

Holtzauge,

 

Again, I would be happy to answer your questions about the mechanics of an EAS turn plot.

 

Is steady state turn performance determined by the Power Available to Power Required relationship?

 

The answer is yes.

 

So, why do you not believe that at some point, an engine that creates some 2800 hp from sea level to 30,000+ feet does not outperform an aircraft engine that has lost 50% of its power available by 30,000 feet.

 

The altitude that occurs at I do not know but I would place it at around 30,000 feet for a normal Merlin 66 +18 Spitfire as guess.

 

All this depends on which P-47 you select and which Spitfire variant. Why this is such an emotional issue for you is beyond me.

 

This is my last attempt at reason with you.

 

OK, that's great because it is difficult to understand how you use EAS Crumpp so it would be good if you explained how it should be used.

 

First of all I thought the P-47 engine produced 2300 hp at 56" boost? You now mention 2800 hp?

 

And secondly, I understand that different Spitfire and P-47 variants behave differently but the question here was the P-47D at 56" boost relative the Spitfire Mk9 at +18 boost right?

 

And thirdly, concerning the altitude, I'm not sure I understand? Are the KEAS turn rate figures you posted for sea level, 20,000 or 30,000 ft?

Edited December 21, 2014 by Pilum

[Barrett_g]

Um.... I hate math... And I couldn't care less about all this Spitfire vs. Thunderbolt stuff... But I notice you guys keep mentioning P-47D.... As if it's one definitive model. You guys realize that there are dozens of different "D" models, right?

 

P-47D-1 through... P-47D-23... I believe... Were all "razorback" models. Onwards up to the P-47D-40 were "bubbletop" models.

 

When you are making comparisons remember that a P-47D-1 is vastly different than a P-47D-40. The plane being modeled by DCS is the P-47D-30.

[Pilum]

Um.... I hate math... And I couldn't care less about all this Spitfire vs. Thunderbolt stuff... But I notice you guys keep mentioning P-47D.... As if it's one definitive model. You guys realize that there are dozens of different "D" models, right?

 

P-47D-1 through... P-47D-23... I believe... Were all "razorback" models. Onwards up to the P-47D-40 were "bubbletop" models.

 

When you are making comparisons remember that a P-47D-1 is vastly different than a P-47D-40. The plane being modeled by DCS is the P-47D-30.

 

Yes, there were as you say many versions of the P-47D. The same goes for the Spitfire Mk9. However, in this case if you look at the attached figures it is well defined: P-47D-22 at 56" boost and Merlin 66 Spitfire Mk9 at +18 boost.

[Friedrich-4B]

The altitude that occurs at I do not know but I would place it at around 30,000 feet for a normal Merlin 66 +18 Spitfire as guess.

 

Definitely a guess; the Merlin 66 still produced over 1,000hp at 30,000 feet.

 

All this depends on which P-47 you select and which Spitfire variant.

 

:huh: Pilum specified the P-47D-10 and the Spitfire L.F. Mk. IX, so that's quite clear. Crumpp specified the P-47D-22, using 56" Hg, but failed to mention that this block number was the first to be equipped with the bigger diameter, paddle-bladed propeller, so there would have been variations - albeit small - in turning capabilities.

 

The main variations for the Spitfire L.F Mk IX were normal or clipped wings, or C or E armament.

 

Just for interest the attached file is from the P-47D Pilot's Training Manual:

Edited December 22, 2014 by Friedrich-4/B
P-47D and Mk IX variants quite clearly specified for the thread

[sobek]

Gentlemen, if you can not stop the bickering, you will forfeit your posting privileges. We've had it up to our ears with your nonsense.

 

Tread *very* lightly now.

[JtD]

I've made two quick estimates for the P-47 turning at 20k feet myself. Input data may vary a little bit from the quoted figures above. Wrongly using EAS (as in TAS=EAS, sea level) I end up at 3.2g, correctly using TAS I end up a little over 2g. So clearly, EAS / TAS is the key issue in the debate.

Edited December 22, 2014 by sobek

[Pilum]

:huh: Pilum specified the P-47D-10 and the Spitfire L.F. Mk. IX, so that's quite clear. Crumpp specified the P-47D-22, using 56" Hg, but failed to mention that this block number was the first to be equipped with the bigger diameter, paddle-bladed propeller, so there would have been variations - albeit small - in turning capabilities.

 

Well I checked my assumptions in the C++ simulation code and it turns out I had the paddle prop modeled for the D10 already: The reason was I was using P-47D-10 trial data from WW2Aircraftperformance.org where they tested both toothpick and paddle blades on the D-10 model and I tuned the model after the paddle prop so my "D-10" estimate should be quite comparable to the D-22 unless there are other big differences that I'm unaware of?

 

I've made two quick estimates for the P-47 turning at 20k feet myself. Input data may vary a little bit from the quoted figures above. Wrongly using EAS (as in TAS=EAS, sea level) I end up at 3.2g, correctly using TAS I end up a little over 2g. So clearly, EAS / TAS is the key issue in the debate.

 

Yes, I agree. I think the different approach in EAS/TAS usage may well be the key here as you say. While EAS can be used as well, the conversions between different altitudes requires careful handling of the density factor sigma if you are using EAS since this otherwize can lead to strange results.

 

Anyway, If Crumpp simply answers the three questions I have asked him in post #4 I'm sure we will find out why the figures attached in post #1 shows the Thunderbolt outturning the Spitfire at 175 KEAS (aircraft variants and conditions as defined by himself).

[Crumpp]

Definitely a guess; the Merlin 66 still produced over 1,000hp at 30,000 feet.

 

Here is an analysis using 1000 bhp from the included chart.

 

Here is where I got the weight and speed data from:

 

http://www.spitfireperformance.com/bs543.html

 

This is the P47D-10 at 56"Hg and the report I got the power, weight, and speed data.

 

http://www.wwiiaircraftperformance.org/p-47/P-47D-10_43-75035_Eng-47-1652-A_Addendum1.pdf

 

I used .85 Propeller efficiency for both aircraft. That will affect the specific numbers but it will not affect the performance trends just the data on individual points. It will shift the curve on both aircraft equally without changing the basic shape.

 

You can see that the P47 at altitude is a performance monster and supreme high altitude dog-fighter compared to its contemporary designs. It has a much larger maneuvering envelope and can sustain a 60 degree bank where the Spitfire cannot sustain any bank angle at all.

 

IIRC,the P-47 was designed to protect and intercept the second generation of pressurized high altitude bombers like the B-29 under development at the time. The turbochargers additional weight was more than compensated for at the altitudes these bombers cruised. Germany discovered the B-29's development and worked on an interceptor the BV-155.

 

http://www.aer.ita.br/~bmattos/mundo/ww2/blhom-und-voss_BV155.htm

 

That project was dropped when it was realized a turbocharged piston engine was a waste of money and time when you had jets. Jet engines gain efficiency with altitude and the Me-262 was almost 100 mph faster than the P-47D-10 at 30,000 feet.

 

As a design, the P-47 is really interesting. Republic gambled on the second generation of bombers pushing combat into the lower stratosphere. It did not happen on the timeline of the war except in the last few months of the Pacific War. IMHO, had Republic's gamble turned into reality in the European Theater, the P-47 would have been the worlds greatest dog-fighter.

Edited December 22, 2014 by Crumpp
replaced acceleration chart as I discovered a velocity conversion error

[Barrett_g]

IMHO, had Republic's gamble turned into reality in the European Theater, the P-47 would have been the worlds greatest dog-fighter.

 

I still consider the P-47 to be the greatest dog-fighter. Simply because it was deployed earlier in the war, when the Luftwaffe still had well trained pilots, intact factories producing superior fighters, and good quality gas.

 

The P-47 fought and won against the best of the best. After the P-47 crippled the Luftwaffe, it let the P-51 take over against younger, newly trained pilots, airplanes built by un-trustworthy slave labor, and fuel shortages.

[Crumpp]

I still consider the P-47 to be the greatest dog-fighter.

 

With the quality DCS seems to be putting out, I am looking forward to buying it!

[JtD]

A 13234 lb P-47 would either need twice the power it had or propeller and wing efficiencies in excess of 100% in order to maintain a load factor of near 2.5g at 30000 feet. Your calculation is again wrong, proper figure is in the region of 1.8g. The Spitfire IX, even the L.F. version, can still turn inside the P-47 and stay there, but this relative performance is also evident from your own chart.

[MiloMorai]

Why is a 1942 Spitfire

 

BS543 IX 3534 R-R M61 FF 22-10-42 R-RH Cv IX M61 23-10-42 AFDU Duxford 8-11-42 AAEE 13-12-42 M66 (RM10SM) install comparison trials with BS534 and BS551 see BS534 for details CRD VA 22-2-43 403S 9-6-43 611S

being compared to a 1944 P-47D?

 

Wouldn't

 

MA648 Vc CBAF M63 R-RH Cv LFIX M66 23-5-43 install with SU MkII fuel injection pump AAEE 21-10-43 trials with pump ros 2-2-44 CRD R-R 22-9-44 SOC 2-7-45

 

be a more representative a/c?

[JtD]

I don't think so, since the LF IX with Bendix carburettor was the most numerous model produced in 1944. I also think this topic is less about relative performance, and more about the misconception of a P-47 being able to maintain load factors in excess of 3g at 20000 feet, where the true figure is somewhere around 2g. Odd relative performance is just a result of that.

[Kurfürst]

Wouldn't

 

MA648 Vc CBAF M63 R-RH Cv LFIX M66 23-5-43 install with SU MkII fuel injection pump AAEE 21-10-43 trials with pump ros 2-2-44 CRD R-R 22-9-44 SOC 2-7-45

 

be a more representative a/c?

 

Serial production Mark IX/M66s were not fitted with SU MkII fuel injection pump.

[MiloMorai]

These results compare favorably with those of other Spitfire LF Mk. IX aircraft, which fact is attributed chiefly to the higher full throttle height obtained with the S.U. pump.

 

The air intake was of a new type, designed to combine the temperate and tropical versions.

 

The SU made no appreciable difference in performance.

[Kurfürst]

Which is probably why this experimental setup on the MA 648 testbed was not bothered to proceed with and be put into serial production on existing models, hence in my opinion its largely irrelevant to the subject matter.

[Friedrich-4B]

These results compare favorably with those of other Spitfire LF Mk. IX aircraft, which fact is attributed chiefly to the higher full throttle height obtained with the S.U. pump.

 

The air intake was of a new type, designed to combine the temperate and tropical versions.

 

The SU made no appreciable difference in performance.

 

The S.U injection pump is an aside, otherwise MA648 was representative of mid-late production Spitfire L.F. Mk IXs. The "new" type of air intake was the lengthened carburettor intake duct incorporating a Vokes Aero-Vee filter; this was standardised on the Mk VIII in mid-1943 and the Mk IX a few months later.

 

The dimensions of the air intake scoop, compared with that normally fitted to the Spitfire IX are:-

 

MA648:

Frontal area: 39 sq.ins.

Distance from nose of intake to back of elbow

(measured along upper surface): 45 ins.

 

Standard:

Frontal area: 35 sq.ins.

Distance from nose of intake to back of elbow: 11 ins.

 

Edited December 23, 2014 by Friedrich-4/B

[MiloMorai]

The S.U injection pump is an aside, otherwise MA648 was representative of mid-late production Spitfire L.F. Mk IXs. The new type of air intake was the extended carburettor intake duct, incorporating the Vokes Aero-Vee filter, that was standardised in early 1944.

 

:thumbup:

[Pilum]

Ok Crumpp, so now we have your chart for 30,000 ft but you still have not answered the question about the charts in post #1.

 

Are they for sea level or 20,000 ft?

[Kurfürst]

The S.U injection pump is an aside, otherwise MA648 was representative of mid-late production Spitfire L.F. Mk IXs.

 

So in other words, if weren't for MA 648 being an experimental testbed with a non-representative injection pump, it would be representative of serial production machine, aside from that it isn't.

 

Looking at the performance figures obtained in testing with the testbeds and experimental machines, it becomes obvious why experimental configurations are preferred at times for being representative - they performed better than the actual aircraft delivered to units. ;)

 

BS.543 prototype w. experimental propeller and overly rich mixture - 407 mph at 22100 ft

MA.648 testbed w. experimental SU injection pump - 411 mph at 21100 ft

 

BS.310 serial production aircraft - 404 mph at 19500 ft

JL.165 serial production machine - 388 mph at 19300 ft.

 

Its worth noting that the testbeds due to their configuration achieved

 

The official specs for the Mark IX.L.F. was an 404 mph, probably based on the BS 310 testing results, with a tolerance of 3 %. None of the serial Mark IX LF tests apart from the BS 310 trials referred to in other docs (w/o the testing details) I have seen ever managed to reach these official specs - all other testing of actual serial production machines yielded top speed results in the 390 - 400 mph range, i.e. trials by R-R, RAAF, and VVS.

Edited December 23, 2014 by Kurfürst

[JtD]

Given that JL.165 was only tested at 25lb boost, are you sure you want to insist that it was a serial production machine?

[Kurfürst]

There is nothing unusual in serial production machines being used for testing by the manufacturer, often repeatedly. Its saves money for the company. A fighter aircraft wasn't cheap back then, nor it is today.