Jet Fighter vs. Propeller Fighter Turning Characteristics

[Soren]

Holtzauge,

I know that book, and it's based on memory and wrong data.

The Cd0 of the Me-262 couldn't have been that high.

Plus NACA has lower Cd0 figure for the P-80.

Davparlr,

The P-80 wasn't faster than the Me-262, the Me-262 was faster than the P-80. The P-80A of 1945 with its 17.1 kN engine had a top speed of barely 800 km/h.

As for thrust vs speed:

P-80A top speed at 17.1 kN: 792 km/h
Me-262 top speed at 17.6 kN: 870 km/h
P-80C top speed at 24 kN: 965 km/h

I don't see how the P-80 is cleaner at all.

A good place to read on: ch11-2

A direct comparison: app-a3

As can be seen the Me-262 is able to reach higher Mach levels with lower thrust than the P-80A.

 

[Soren]

The aspect ratio for the 262 is ~ 6.9 to 5.85 for the 51

7.23 vs 5.85

Just to be exact

 

[Holtzauge]

Deleted

 

[Holtzauge]

7.23 vs 5.85

Just to be exact

I used 6 for both aircraft to arrive at a BALLPARK figure to show that the Cdo figures differed so much that the contribution of the induced drag was INSIGNIFICANT in the comparison.

Assuming Cl at around 0.1:

Aspect ratio 7.27:

Cdi= =0.00055033

Aspect ratio 5.85:

Cdi=0.00068015

Base on a Cdo of 0.02 and 0.017 respectively this becomes a staggering 2.75% and 4% of total drag.

Of course if you want to take it one step further you can work out the Cl at max speed and find a difference there if you like. Maybe it's closer to 0.2 than 0.1 and will of course differ for both aircraft. However, this will not change the fact that the drag figure of 0.02 for the Me262 is higher than the 0.017 for the P51 IRRESPECTIVE if induced drag was included or not.

 

[Holtzauge]

Holtzauge,

I know that book, and it's based on memory and wrong data.

The Cd0 of the Me-262 couldn't have been that high.

Plus NACA has lower Cd0 figure for the P-80.

If surprised you claim Hoerner is wrong. He was a career aerodynamicist in Germany during the war and his credentials gave him a position in the US after the war.

Please explain where he got it wrong and what the numbers should be

BTW: Still waiting for your sources claiming the Cdo for the Me262 was lower than the P51 and that the 0.02 figure is "waay" to high as you claim.

 

[HoHun]

Hi everyone,

For the sake of the discussion, I have added a twin-engined jet fighter not entirely unlike the Me 262 to the diagram.

Interestingly, the generic twin-engined jet fighter matches the turn performance of the generic single-engine jet fighter fairly accurately.

The basic observations on the characteristics of jet propulsion can be seen to apply to the twin-engined jet as well.

Not that the actual Clmax value does not have the same significance for jet fighters as for propeller fighters. An increased Clmax value would extend the graph to the left. For the propeller fighter, that would result in an increased sustained turn rate, but the jet fighters at the left end of the graph are below maximum sustained turn rate anyway. Accordingly, increasing Clmax would only decrease turn radius - at a decreased sustained turn rate.

Regards,

Henning (HoHun)

 

[davparlr]

Davparlr

The P-80 wasn't faster than the Me-262, the Me-262 was faster than the P-80. The P-80A of 1945 with its 17.1 kN engine had a top speed of barely 800 km/h.

I'll need very reputable reference on this. Every source I have says the P-80A used the J-33/I-40 (40 stands for 4000 lbs thrust (17.8 kN)) engine and was capable of 558 mph at SL. Those references include documentation I have and all the searches of the internet including the NASA document listed.

P-80A top speed at 17.1 kN: 792 km/h

See above.

Me-262 top speed at 17.6 kN: 870 km/h

This is at 6 km, not SL.

A good place to read on: ch11-2

A direct comparison: app-a3

As can be seen the Me-262 is able to reach higher Mach levels with lower thrust than the P-80A.

All I see is that the Me-262 can make .76 Mach at 20k, and the P-80 can make .75 Mach at 30k. There is no mention of the thrust generated by either aircraft at those altitudes. All we do have is static thrust at SL and top speed and associated Mach at SL, which shows the P-80A substantially faster in both than the Me-262 with only 32 lbs of thrust different.

 

[Soren]

Holtzauge,

He used incorrect base data, that's all. His calculations are all good, no problem there.

A Cd0 of .20 makes no sense really, considering just how fast the a/c is. Also NACA figures are different, with the P-80 having a lower Cd0 than the P-51.

Looking at the data available and disregarding the figure I remember reading somwhere, I have calculated the Me-262's Cd0 to be in area of .015.

Moving on to the effect of increases in AR;

The real difference of 7.23 vs 5.85 in AR is as follows (Assuming similar Cl e):

(1.3^2)/(pi*5.85*.80) = 0.114945237
(1.3^2)/(pi*7.23*.80) = 0.093005482

That's a difference of 23.6%, a pretty noticable advantage I'd say.

When it comes to the Cdi, the AR is the dominant factor.



Davparlr,

Read up on the P-80A, it didn't reach past the 792 km/h at alt, and 898 km/h at SL, and the P-80A's in actual service by 45 didn't even reach that speed. I will find the reference for you, will dig it up in my archive this week.

The Me-262A-1a with 17.6 kN of thrust reaches 838 km/h at SL and 870 km/h at alt. (And 900 + km/h in British speed trials) And according to US comparative tests the Me-262 climbed and accelerated faster than the P-80.

 

[davparlr]

Davparlr,

Read up on the P-80A, it didn't reach past the 792 km/h at alt, and 898 km/h at SL, and the P-80A's in actual service by 45 didn't even reach that speed. I will find the reference for you, will dig it up in my archive this week.

Well, I'll wait patiently. There seems to be lots of evidence that the P-80A was capable of 558 mph at SL with 4000 lbs of thrust.

And according to US comparative tests the Me-262 climbed and accelerated faster than the P-80.

This is the test no one seems to have a copy of?

 

[Holtzauge]

Holtzauge,

He used incorrect base data, that's all. His calculations are all good, no problem there.

A Cd0 of .20 makes no sense really, considering just how fast the a/c is. Also NACA figures are different, with the P-80 having a lower Cd0 than the P-51.

Looking at the data available and disregarding the figure I remember reading somwhere, I have calculated the Me-262's Cd0 to be in area of .015.

Moving on to the effect of increases in AR;

The real difference of 7.23 vs 5.85 in AR is as follows (Assuming similar Cl e):

(1.3^2)/(pi*5.85*.80) = 0.114945237
(1.3^2)/(pi*7.23*.80) = 0.093005482

That's a difference of 23.6%, a pretty noticable advantage I'd say.

When it comes to the Cdi, the AR is the dominant factor.



Davparlr,

Read up on the P-80A, it didn't reach past the 792 km/h at alt, and 898 km/h at SL, and the P-80A's in actual service by 45 didn't even reach that speed. I will find the reference for you, will dig it up in my archive this week.

The Me-262A-1a with 17.6 kN of thrust reaches 838 km/h at SL and 870 km/h at alt. (And 900 + km/h in British speed trials) And according to US comparative tests the Me-262 climbed and accelerated faster than the P-80.

Soren, the Cl is not 1.3 at high speed. I used 0.1-0.2 because this is the BALLPARK range for both the Me262 and P51 at high speed:

L=W= 0.5 * ra*v**2*Cl*S

P51: I'm a metric guy so I'll use the following numbers:

W=4177 Kg
Vmax=201 m/s at 9.4 Km altitude
S=21.8 sqM

4177*9.81=0.5*0.43*210**2*Cl*21.8

This gives Cl=0.198 not Cl=1.3 like you assume. So again, induced drag is just a few percent of total drag at max speed. Agreed?

As to the Me262 Cd0, I checked what I got on this and found the following document:

AAF (Army Air Force) F-TS-1569, translation of "Der Einfluss starkerer Triebwerke auf die Flugleistungen von Tl-Jaegern" by Hubner.

In this report a number of factors affecting jet a/c performance are treated. However, the interesting thing is that for comparison the numbers for the Me 262 are listed on page 4:

Me 262 Cd0* S (m2) 0.460
S (m2) 21.79

So by a simple division we arrive at...........0.02111

So it seems the Germans themselves calculated with Cd0=0.02 in their performance estimates on the Me262. Still think 0.02 is to high?

 

[Soren]

Holtzauge,

I used the higher Cl figures because I was under impression that we where talking turning comparisons here, not straight flight.

The Cd0 of 0.021 seems way too high. Could you post the document?

At any rate this doesn't go against the fact that the jets are much slicker a/c than the piston engined a/c, which is why the pilots note the much better energy retention in tight turns.

 

[Holtzauge]

Holtzauge,

I used the higher Cl figures because I was under impression that we where talking turning comparisons here, not straight flight.

The Cd0 of 0.021 seems way too high. Could you post the document?

At any rate this doesn't go against the fact that the jets are much slicker a/c than the piston engined a/c, which is why the pilots note the much better energy retention in tight turns.

Soren, You keep coming back with an opionion that 0.02 is to high. You are of course entitled to your opinion but you seem to lack anything to support this claim other than your feelings on the subject.

Given that the Germans themselves used 0.02 as the Cd0 figure for the Me262 I'm more inclined to go with that unless you can come up with anything substantial to support your claim that it is lower than the Mustangs.

 

[Soren]

Holtzauge, just post the document please.

Btw, the German put a P-51 in a windtunnel as-well, so it would be interesting to see what figures they got there.

As for the figures in Hoerner's book, well they differ from the NACA's own figures, and not because he calculated wrong but because he used wrong figures. Otherwise how could he get the P-80's Cd0 figure to be higher by 0.007 compared to that by NACA ?

 

[Holtzauge]

Holtzauge, just post the document please.

Btw, the German put a P-51 in a windtunnel as-well, so it would be interesting to see what figures they got there.

As for the figures in Hoerner's book, well they differ from the NACA's own figures, and not because he calculated wrong but because he used wrong figures. Otherwise how could he get the P-80's Cd0 figure to be higher by 0.007 compared to that by NACA ?

Why should I post the document? It's from my private collection. Do you have any problem with the text I quoted below:

AAF (Army Air Force) F-TS-1569, translation of "Der Einfluss starkerer Triebwerke auf die Flugleistungen von Tl-Jaegern" by Hubner.

In this report a number of factors affecting jet a/c performance are treated. However, the interesting thing is that for comparison the numbers for the Me 262 are listed on page 4:

Me 262 Cd0* S (m2) 0.460
S (m2) 21.79

If anyting is unclear with this I can explain it to you.

Let's recapitulate:

I provided a Cd0 figure of 0.02 for the Me262 based on Hoerner (see previous post above). You said Hoerner was wrong. I provided another unrelated source saying the same thing (see quote above).

So far you have provided no references only your feelings what the results should look like.

I'll be happy to continue this discussion when/if you provide something substantial.

 

[Soren]

Why should I post the document? It's from my private collection.

And ? Is there something in it you don't want us to see ? Is it secret ?

Doesn't inspire allot of confidence Holtzauge.

Let's recapitulate:

I provided a Cd0 figure of 0.02 for the Me262 based on Hoerner (see previous post above). You said Hoerner was wrong. I provided another unrelated source saying the same thing (see previous post above).

And I provided sources which contradicted these: NACA.

Also until you provide the document which you claim to have we cannot know wether it's true or not, or wether you've read it properly, now can we?

So far you have provided no references only your feelings what the results should look like.

I beg your pardon ? I provided figures from NACA, figures which showed significantly lower figures for the jets.

I'll be happy to continue this discussion when/if you provide something substantial.

Right back at you.

 

[Holtzauge]

And ? Is there something in it you don't want us to see ? Is it secret ?

Doesn't inspire allot of confidence Holtzauge.



And I provided sources which contradicted these: NACA.

Also until you provide the document which you claim to have we cannot know wether it's true or not, or wether you've read it properly, now can we?



I beg your pardon ? I provided figures from NACA, figures which showed significantly lower figures for the jets.



Right back at you.

So it was as I suspected: You are implying that I am misquoting or hiding something. Well you can take a hike buddy. You have provided nothing substantial in this thread and now you resort to personal attacks and insinuations.

Goodbye.

 

[Soren]

Personal attack ??

All I asked was for you to post the document. Is that a personal attack ?

I've posted my references, so it's only fair that you post yours.

And I'm not implying anything, but now I do find it strange that you just don't post the damn document.

 

[Sweb]

What's this thread about again? Turn rates piston vs turbine? Graphs presenting this against that? Seems scientific enough, though we have a little conflict going above. But, if I was to mix it up with a jet I'd simply throttle back, horse it in a bit to get the lead or cause the jet to assume the larger turning radius to keep his all-too-sacred airspeed. The jet, once airspeed is bled off, takes much longer than me to regain it with his slow spooling turbines. Mine is just the opposite. I'll always be able to risk airspeed for advantage in such a mix-up where the jet's only advantage is his speed. If he tries to turn at my speed he'll drop like a stone and I'm on him immediately, especially considering the types suggested in this thread. Speed is not necessarily the primary component off a turning fight. Jet-to-jet, prop-to-prop all bets are off but for the thread topic an internal combustion engine, propeller driven machine will always turn inside a jet. If I bleed off speed I can turn tighter because I've lessened the G's on man and machine, and the machine that recovers it's airspeed better is the winner in this sort of fight. This whole concept involves only the turning maneuver for illustration. Try a typical piston-engined snap-roll in a jet the likes of a 262 - no can do. Such a maneuver would expose the jets tail feathers every time.

If this is to establish which machine can hold speed better in a turn then the jet will clearly win over the dynamics of a propeller every time unless maneuvers involving certain angles of attack cause flame-outs at high power settings where inlets are oblique to ram air. This, of course, must involve machines of similar - dang near identical - flight characteristics, power to weight ratios and drag coefficients regardless of powerplant installed if the turning radii are to mirror each other in the model. In other words, only the powerplants are different otherwise the comparison loses its focus.

 

[Corsair82pilot]

From a fighter pilot's point of view, it doesn't matter what type of aircraft it is, jet or prop. What matters is energy management. That is the most important aspect of flying fighters. When it come to a turning fight, the aircraft that can maintain his energy level at the slowest airspeed in a turn will most likely win the fight. This is how it works.
If two aircraft are turning, and one can maintain a six G turn at 250 kts and the other must fly at 420 kts to maintain a six G turn, the slower aircraft will have the faster aircraft in his sights all day long.
No matter how fast you go the G force determines the turn radius. That means that as the speed increases for a given G force, the turn radius increases. The turn rate (time to complete the circle) remains the same for both aircraft. The aircraft with the smaller radius will have the guns solution. One of my earlier posts describes a turning dog fight I had in an F-4E against an F-86. ( see my earlier post Your Funny, Humorous or Incredible Military Stories - Page 14 - Aircraft of World War II - Warbird Forums) I was stupid to try to turn with him (or an F-16, 18, 15) But an F-4 could out run all of the above and do a 180 and shoot them in the lips with a missile. You have to know your aircraft and the capabilities of your adversary's aircraft to determine how you will fight him.
Of course all fights are not turning dog fights, so the parameters of the fight and the experience of the pilots has a lot to do with the outcome.

 

[Corsair82pilot]

What's this thread about again? Turn rates piston vs turbine? Graphs presenting this against that? Seems scientific enough, though we have a little conflict going above. But, if I was to mix it up with a jet I'd simply throttle back, horse it in a bit to get the lead or cause the jet to assume the larger turning radius to keep his all-too-sacred airspeed.

You are thinking in two dimensions instead of three. If the jet pilot has half a brain he will take the fight out of plane and lose his ground speed while maintaining his airspeed. By that I mean he will alter his track by turning vertical (up or down) so his closure speed on you slows while he maintains his airspeed in a different vector. He will turn but keep you in his sight in his canopy and when the closure rate is correct he will turn again and gun your brains out while you are trying to get your power up again. The whole time he will keep his energy level up and not worry about regaining it.