Dora climb rates

[Crumpp]

Ok you have a lot of "if's" there.

 

Not really...in fact they are pretty common ones with new type development.

 

what what is the actual climb rate of the Dora at 1.8 ata,

 

Physics says it will be in the vicinity of this:

 

Quick climb swag at 1.8ata @3250 rpm using a Jumo 213 power chart with n = .85; climbing just above the stall like the pathological climb test's we see in this thread:

 

Something like Maximum Angle of Climb at SEA LEVEL reproducing the test climb profiles found in this thread:

 

[(1827thp*550) - (308thp*550)] / 9038lbs = 92.4fps x 60 = 5546fpm = 28 m/s

 

[(1827thp*550) - (308thp*550)] / 9370lbs = 89.1fps X 60 = 5349.73 = 27 m/s

 

Now let's do it at Best ROC speed ~300kph

 

[(1827thp*550) - (367thp*550)] / 9038lbs = 88.8fps X 60 = 5330fpm = 27 m/s

 

[(1827thp*550) - (367thp*550)] / 9370lbs = 85.6fps X 60 = 5141fpm = 26 m/s

 

That is 11% using a quick very rough SWAG from the 22.9 m/s Focke Wulf publishes in their calculated performance.

 

It very much agrees with what Yo-Yo is saying.

[Pilum]

 

Physics says it will be in the vicinity of this:

 

Quick climb swag at 1.8ata @3250 rpm using a Jumo 213 power chart with n = .85; climbing just above the stall like the pathological climb test's we see in this thread:

 

Something like Maximum Angle of Climb at SEA LEVEL reproducing the test climb profiles found in this thread:

 

[(1827thp*550) - (308thp*550)] / 9038lbs = 92.4fps x 60 = 5546fpm = 28 m/s

 

[(1827thp*550) - (308thp*550)] / 9370lbs = 89.1fps X 60 = 5349.73 = 27 m/s

 

Now let's do it at Best ROC speed ~300kph

 

[(1827thp*550) - (367thp*550)] / 9038lbs = 88.8fps X 60 = 5330fpm = 27 m/s

 

[(1827thp*550) - (367thp*550)] / 9370lbs = 85.6fps X 60 = 5141fpm = 26 m/s

 

That is 11% using a quick very rough SWAG from the 22.9 m/s Focke Wulf publishes in their calculated performance.

 

It very much agrees with what Yo-Yo is saying.

 

 

You keep saying that your calculations agree with what Yo-Yo is saying Crumpp but how can you be so certain of that? Do you agree Yo-Yo? Do you really think that a sea level climb rate of 28 m/s for the Dora at 1.8 ata is reasonable and what we should expect to see in DCS?

Edited March 8, 2015 by Pilum

[Crumpp]

how can you be so certain of that?

 

Because I have actually checked it out and ran the math?

 

The track is in this thread Pilum.

 

When the DCS model is flown as per the POH instructions for a climb it gives good agreement with the Kennblatt performance at Steig u Kampfleistung.

 

That indicates that the FM parameters are good and any climb performance realized above that power setting is the result of the additional power of 1.8ata @ 3250 rpm with MW50.

 

That is backed up by the math.

 

If I ran the math and it was not in agreement, then I would be posting a thread asking why.

 

I would also be able to back up my claim with the formula and theory I was using.....

[Kurfürst]

Anyway, it could be very interesting what basic values calculates your code for sea level for 3000 rpm and 3250 MW-50.

 

 

It's very interesting fact: for 3000 rpm as I use jet thrust for Vy estiimation - I get TEST FLIGHT Vy curve. As I null this thrust - I get German estimations you referred to as "real curves".

 

That pretty much clears the issue up. :thumbup:

[USARStarkey]

Because I have actually checked it out and ran the math?

 

The track is in this thread Pilum.

 

When the DCS model is flown as per the POH instructions for a climb it gives good agreement with the Kennblatt performance at Steig u Kampfleistung.

 

That indicates that the FM parameters are good and any climb performance realized above that power setting is the result of the additional power of 1.8ata @ 3250 rpm with MW50.

 

That is backed up by the math.

 

If I ran the math and it was not in agreement, then I would be posting a thread asking why.

 

I would also be able to back up my claim with the formula and theory I was using.....

 

Pilum also ran the math, its doesnt agree with yours, and unlike yours it was the product of careful computer simulation....not SWAG

[NineLine]

Pilum also ran the math, its doesnt agree with yours, and unlike yours it was the product of careful computer simulation....not SWAG

 

Ok guys, enough is enough, submit your evidence if you like, but there is no need to be insulting of anyone elses... bottomline is that Yo-Yo will have the final say on what goes into these FMs, and I personally trust that he cares to get them as close as possible with all given information available...

[Crumpp]

Pilum also ran the math, its doesnt agree with yours, and unlike yours it was the product of careful computer simulation....not SWAG

 

A colored chart and an unwillingness to discuss the theory/math behind it is neither math nor evidence.

 

:smilewink:

[USARStarkey]

A colored chart and an unwillingness to discuss the theory/math behind it is neither math nor evidence.

 

:smilewink:

 

:megalol: colored charts eh? I guess only your SWAG is evidence then.....lol. Perhaps if it was in black an white you'd understand it better.

[sobek]

Enough is enough. Maybe we can rivisit this later if the need arises.

[Pilum]

The effects of exhaust thrust on Dora performance

 

Propeller driven aircraft in WW2 such as the Fw-190D9 that did not have an exhaust driven turbocharger like the P-47 but instead used a compressor to attain higher than atmospheric boost pressures as a rule had carefully designed and tuned exhaust stubs. The reason for this is that there is a substantial amount of thrust to be gained by directing the exhaust gases from the engine to the rear thereby adding this to the thrust of the propeller.

 

Taking the Junkers Jumo 213A that powered the Fw-190D9 we have modeled in DCS as an example, how much exhaust thrust did this engine produce? Well if we assume a high boost scenario with the engine producing around 2100 hp, the exhaust thrust would be in the order of 1400 N which is quite significant.

 

This exhaust thrust is especially welcome and significant at high speeds since it is close to speed independent, i.e. the 1400 N in exhaust thrust the Jumo 213A engine produced at standstill is present also at high speed. This becomes especially important to increase top speed performance since the propeller engine thrust is inversely proportional to speed, i.e. Tp= (n x P)/v, where n=propeller efficiency, P=Engine power and v=TAS.

 

Applying this to derive a C++ calculated top speed for the Dora including exhaust thrust under these conditions the top speed is circa 615 Km/h with, while the top speed without exhaust thrust is around 580 Km/h. So, when looking at historical data it will be quite obvious if exhaust thrust is included or not since the speed difference is so substantial.

 

However, the exhaust thrust also has a significant impact on climb performance as the attached simulation figure shows. The solid blue line shows the climb rate with exhaust thrust and the dashed line without exhaust thrust. As can be seen, the sea level climb rate with exhaust thrust is around 22.6 m/s while without exhaust thrust accounted for it is reduced by 2.8 m/s to circa 19.8 m/s.

 

Consequently, since exhaust thrust is such an important contributor to the overall performance of a WW2 type compressor driven aircraft in both top speed and climb, these effects are absolutely necessary to include in any meaningful performance estimate and which is also why all performance estimates I have ever seen have always included this effect.

Edited March 9, 2015 by Pilum

[Crumpp]

In conclusion......Yo-Yo is correct.

 

By your estimation exhaust thrust accounts for a 14% increase in climb performance.

 

So, Focke Wulf's estmate of 22.9 m/s without exhaust thrust and ballparking your 14% increase means ~26 m/s.

 

engine producing around 2100 hp

 

And the engine produced ~2250hp in the first gear and 2150 in the second gear. I used the 2150hp for my estimate.

 

The fact you have removed exhaust thrust from your estimate and when you add it to your C++ simulation it equals Focke Wulf's estimate without exhaust thrust is telling.

 

Probably something else going on with your simulation or assumptions, Pilum.

 

If you would share the formula's you are using, we might be able to solve it and help out.

 

:smilewink:

 

Consequently, since exhaust thrust is such an important contributor to the overall performance of a WW2 type compressor driven aircraft in both top speed and climb, these effects are absolutely necessary to include in any meaningful performance estimate and which is also why all performance estimates I have ever seen have always included this effect.

 

Leaving it out would ensure your estimate is conservative and hits the 10% performance variation range Focke Wulf, GmbH guaranteed by contract to the customer.

Edited March 9, 2015 by Crumpp