@drgondog,
you're probably right, but...
I say probably, because I calculated with overall pressure (dynamic + static) for 700km/h @7km as ~0.52 kg/cm^2, which is negligible, according to
this chart.
Also Rechlin flight test, lists DB605A's power as
1355 hp, at 5.7km, which corresponds with my calculations.
The discussion necessarily is focused on Drag. The reason I don't fool around with high speed/high altitude data as much as SL is that I KNOW there is a significant delta due to compressibility - which results in a higher parasite drag total for that particular aircraft (109K, P-51B/D/H, FW 190D9, P-47D/N, etc) than indicated for incompressible flow. In addition Power available for the max speed run is always questionable as only manufacturer tables for a mid range performing new engine is available.
When I did the calcs on a 700K/hr with the Hp you presnted in the zuegeister report - the parasite drag was way off for the derived thrust - for any version of a 109 for any report I have ever seen - and no explanation regarding reducing flight data for compressibility - hence my strong remarks about dragging a red herring into the discussion. having said that I boneheaded the Max V pickoff for the P-51 for -39 Allison at 5K instead of the SL I quoted.
The revised Cdtotal @5K = .01727, the CL =.0143, the Cdi=.00094 and calculated Cdparasite= .01633 which is very close to published P-51 Parasite drag for incompressible flow. The Mach number at 363 for 5 K at STP = 363/33.42*Sqrt(500.2) + ~.48M so it is just short of entering compressible flow..
However, it's still unclear where is that pressure measured and which pressure line corresponds with what speed and calculated values from Datasheets you linked, may be correct indeed.
A few more points, though...
First, I've noticed you substitute wing area in drag formula and you can't do that if you wanna calculate absolute drag or comparable drag coefficients, for different aircraft.
Of course I can 'do that' just as I set aside a wetted drag result to provide context. As to context, every flat plate drag calculation is expressed as a function of wing area as a first cut - simply because drag on a wing is such a high percentage of parasite drag - independent on induced drag or high AoA Vortex drag. Ditto for succeeding calcs on friction, gaps, protrusions, exhaust stacks, cannon barrels becaue that aero wanted to get all the duckies in one frame of reference - and wing area is THE common frame of reference. For what it is worth I gave the 109F-4 the benefit of the doubt and used Hoerner's figures for his text book example on a 109 - even though I penalized the 51 by using .85 for e and applied it to the AR for the CDi calc. Hoerner reduced his AR by only 5% instead of 15% like my 51 calc (and e=.85 is the standard for Preliminary design until the designer intruduces something funky like winlets)
The reason is that wing area value disregards fuselage component of drag and you can have differently aspected wings within same area, both of which produce misleading results.
I agree subject to the above. For these two birds the wing efficiency, per se is reasonably close as the induced drag increment due to rounded tip versus the 51 tip/chord ratio sets up a reasonaly close spanwise lift distribution, the aspect ratios are close. The 51 has a slight delta due to washout, the 109 has some issues due to wheel wells - not to mention the drag buckets otherwise called radiators.., slats and aileron gaps that the 51 does not have
Second, there are two main propeller parameters, exit velocity and the air mass.
Since, propeller's thrust equals air mass times exit velocity, you end up with two types - fast (smaller mass over faster speed) and slow (larger mass over slower speed).
So, you can have equal nominal thrust, but different net thrust lapse over the speed curve and "fast" type can yield more net thrust on the right hand part of the envelope, producing faster plane.
I didn't have time to examine all propellers involved, but I hope I will, if I get the time.
Have at it. You can play with variables to arrive at eta for Thrust calcs all day long, playing with RPM, tip Dia, airspeed (particularly at >.5M for tip transonic potential effects) if you want to build a sophisticated model - then find your model doesnts agree with enough flight test results. If you dare to slip into Low speed/High Power/High CL calcs for Prop efficiency you are deep into a world of non linear foolishness because you will need a very sophisticated Navier Stokes model with varying meshes to remotely Attempt to extract vortex drag, asymmetrical influences and deep into combined laminar/turbulent flow regions (that alter) so you may want to flip in a little chaos theory for Boundary layer assumptions.
Or you could stick with the generally accepted preliminary design equations and calc. I'll stick with the latter with full understanding regarding where and why they fart and fall down
Now as for the top speeds, they're not bogus, but flown at
E-stelle in Rechlin.
Here's the AtA1.3 (which we know for sure), flight record for
109G-1 and I already linked AtA1.42, one.
Derived graph
109G-2, a model without pressurized cockpit, flew 666km/h at AtA1.30, so it's a fair guess it surpassed 700km/h at AtA1.42 and not marginally.
Once again - anything at .5-55M during WWII introduces noticable instrumentation errors and there is no mention of algorithms or even attempts to make TAS corrections, nor is there any reason to suspect wht the actual Power delivered happened to be, nor any prop efficiency or actual exhaust thrust measurements available to separate fact from opinion assumed from assumed facts or opinions extracted from places the sun doesn't shine. I don't care about boost - that isn't an aero variable, it isn't a prop efficiency variable, it is marginally an exhaust thrus variable if consistently tested and validated - only the 'real Hp' delivered is interesting because that is the basis for free body diagram to solve for gross Drag. Yes?
To conclude.
Calculated power for Kurfurst's datasheets, still remains open though and I'd appreciate any input toward solving that question, although I suspect them being correct.
(would be helpful if someone could translate this
chart's text only, but in the context)
Cheers