Thrust

[J_A_B]

I see a lot of people comparing WW2 planes using "power to weight".  But seldom do I see anyone use "thrust to weight" for a WW2 plane, yet TTW is a much more useful measurement.

Horsepower, in and of itself, means nothing.  It is that combined with the propeller that moves the plane.  

Take two version of the Spitfire 1--one has a fixed-pitch 2 blade prop, the other has a variable-pitch 3 blade prop.  Do they perform the same?  Obviously not--yet they have the same power-to-weight ratio.

Which brings me to my question:   Exactly how much thrust do these planes produce?  Knowing that figure would be much better for determing what kind of maneuvers they could perform.

J_A_B

[Zigrat]

thrust varies with speed, power does not

[Midnight]

Well, the point here is still valid.

The airfoil design of the props used should have a big difference on the performance.

HP to WEIGHT ratios would be fine if all the planes used the same airfoil prop with the same number of blades.

------------------
"Wing up, Get kills, Be happy"

Midnight
13th TAS
midnight@13thtas.com

"I see you have made your decision. Now let's see you enforce it." -Brandon Lee (The Crow)

[funked]

Thrust is a pain in the bellybutton to calculate for these planes.  The best numbers anybody has are still going to include a lot of assumptions and estimates, i.e. guesses.

AFAIK there was not an in-flight test of any of these planes with strain gauge or other device on the prop shaft for a direct measurement.  I've seen photos of ground tests of this sort but thrust at zero speed is not thrust at flying speed.

Even if you could actually figure out how much thrust the prop is exerting, there is still thrust from exhaust stacks which is significant on some of the planes.

[J_A_B]

A rough figure would be great.

If it is possible to test this using the planes in AH, thats fine--tell me how.  As I said, I'm happy with a ballpark figure, and the AH planes are close enough to reality to satisfy me.


I'm just curious how these planes stack up in terms of total thrust.  


In partucular, I am willing to bet that some planes with a high level of horsepower, actually have LESS total thrust than some less powerful planes--which explains some seeming anomolies of performance.

Knowing even a ballpark figure of TTW for these planes would give me a much better idea of what these planes could do relative to each other.   It isn't what I think of as vital knowledge....just interesting to know.


J_A_B

[funked]

A rough figure would be something like:  
T=(0.8*hp*550)/(V*5280/3600)

T is thrust in lbs
hp is power in horsepower
V is true airspeed in mph

[This message has been edited by funked (edited 02-21-2001).]

[juzz]

Using that calc we get(at s/l top speeds)

P-51D: 1382lbs
Fw 190A-5: 1465lbs
Spitfire F.IX: 1486lbs
Spitfire VC: 1416lbs
Me 109G-10: 1622lbs
Me 109G-6: 1313lbs
Me 109G-2: 1301lbs
Me 109F-4: 1181lbs
Typhoon Ib: 1760lbs
F4U-1D: 1875lbs
La-5FN: 1542lbs

Hmmm, exactly how does the G-6 make more thrust with the exact same engine and prop as the G-2...

SO, some thrust:weight ratios then

P-51D: 0.137
Fw 190A-5: 0.170
Spitfire F.IX: 0.198
Spitfire VC: 0.218
Me 109G-10: 0.216
Me 109G-6: 0.188
Me 109F-4: 0.194
Typhoon Ib: 0.156
F4U-1D: 0.150
La-5FN: 0.213

So what does this mean - that the Spitfire VC should accelerate and climb better than the Me 109G-10? I knew it was porked!  

[This message has been edited by juzz (edited 02-22-2001).]

[M.C.202]

Funked said:

>A rough figure would be something like:
T=(0.8*hp*550)/(V*5280/3600)

> T is thrust in lbs
> hp is power in horsepower
> V is true airspeed in mph

So:
.8*750=600(yes 750hp)*550=330,000

398*5280=2101440/3600=583.7333..=

330,000/583.7333= 565.32667 (rounded)


The numbers are for the S.A.I.207

This would give it almost no drag to hit 398mph??

??? Hell, I don't even do old math well :-)

Then again, it's after midnight :-)



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M.C.202
Dino in Reno

[juzz]

565lbs is "almost no drag"?

BTW: There was a 1940 Russian fighter prototype with two 220hp engines that did 422mph at 19,000ft.  

[funked]

Maximum thrust does not occur at maximum speed Juzz.  Look at the function I wrote that is good (assuming the 0.8 efficiency is valid) at any speed.  

But you probably knew that, nerd.

And the efficiency is most definitely not constant.  But J_A_B specifically requested a rough figure.  

[Jimdandy]

I'm glad to see someone else is talking about thrust to weight.

juzz, I know these are ruff calculations but you might be seeing an improvement of the prop between the G-2 and G-6.

This is from one of my other posts. It deals more with props in the transonic region but talks about prop efficiencies:

"Damn niklas even as rusty as I'm I can still pull one out of my a..  I was right about the efficiency of the prop near M1. Here is a NACA study on the subject. It is looking at prop tip speeds as we had talked about a while back. http://naca.larc.nasa.gov/reports/1950/naca-report-999/  
It even explains some of the things you were seeing with the prop data. It explains why they went to the wide bladed props. It appears they are able to play with the shape of the prop and get higher critcal Mach numbers.

Jimdandy,
You might interested in this story about supersonic (actually, transonic) props.
 http://home.att.net/~historyzone/Fisher.html  

My regards,

Widewing


[This message has been edited by Jimdandy (edited 02-22-2001).]

[This message has been edited by Jimdandy (edited 02-22-2001).]

[Sundog]

Or to clarify what Zig said, the thrust varies greatly with speed (i.e.- it is much higher at low speeds than at high speeds for a propellor driven aircraft) and for a piston engined aircraft, power is a constant. So, from an aircraft analysis perspective, thrust loading offers a 'relative' indication of performance. As stated previously, because there are so many variables that come into play with regards to propellor design, P-Factor, Blockage, etc., power loading is an easier number to calculate. If you wanted thrust to weight ratio, you would typically need 'flight test' data, that most companies wouldn't want to share for propietary reasons and would be much harder to come by from foreign nations. Whereas horsepower and weight numbers were much easier to gain access to.


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Sundog
VMF-111 Devildogs
'Criticism is always easier than craftmanship.'

[Jimdandy]

 

Originally posted by Sundog:
...If you wanted thrust to weight ratio, you would typically need 'flight test' data, that most companies wouldn't want to share for propietary reasons and would be much harder to come by from foreign nations. Whereas horsepower and weight numbers were much easier to gain access to...

Your right but we are talking about obsolete planes so I don't think that's a factor here. The factor in getting the data is more the 50+ years since the data was produced. Also the fact that a lot of the non US plane data was destroyed. I wouldn't be surprised that a bunch of this data still exists but where. Thrust to weight might show more clearly why some of these planes performed as well as they did at lower speeds and altitudes. I sure wish we could find the data. The site that Widewing supplied me with above gives some hint of the differences in performance of the German and US planes and that it might just be the prop design that was a major factor.

[funked]

Sundog as I said above, AFAIK they did not have a way to measure thrust in flight during the war.

[J_A_B]

Thansk for the replys, this is what I wanted to know.  It gives me a much better idea of why these planes perform as they do.

J_A_B