Announcement

**spacegrrrl** · 11-10-2005, 11:52 AM

Re: How fast can you go with 1650 hp ?

One thing that a lot of people don't seem to realize is just how much change in HP it takes to affect top speed. It really points to the fact that there is way more to gain with drag reduction than engine tweaking. Of course at some point you have to do both to be the fastest! :-)

(For a perfect example look at AT-6 speeds, the increase from stock speeds is all subtle airframe cleanup.)

Michele

**MMPerk** · 11-10-2005, 09:09 PM

Re: How fast can you go with 1650 hp ?

Very good point. Isn't there a computation somewhere about how much more drag is created by going faster? I thought for sure there is a formula for that. Like the man said, "Speed is just a matter of how much money you want to spend." Though this was said about things on the ground, the rule applies to aircraft. "How fast do wanna go, and how much money do you have?"

Lonnie

**stuntflyr** · 11-10-2005, 09:51 PM

Re: How fast can you go with 1650 hp ?

There is another thing a lot of people miss about top speeds that are very important.
The altitude that that speed was recorded.
An Me-109K was a high altitude interceptor, right Juke? It has a top speed of over 450 mph, but it wasn't measured at Reno, at 5000 feet. It was done at that airplane's optimum altitude. Usually the "critical altitude" for the engine. That is the altitude that is the highest the engine will make maximum hp. I understand the supercharger in the DB 605's were fluid driven so the blower rotor doesn't have a fixed rotational speed for given crankshaft rpm. That would mean the supercharger would be able to turn faster for the same crank speed due to the reduced forces of the air as it becomes less dense the higher airplane climbs. Theoretically this would give the engine a bit of an edge on a fixed geared set-up like most allied engines.
Most WWII airplanes like the P-51, P-38, P-47, Spitfire MK14 etc had their top speeds recorded at high altitudes (high twenties to mid thirty thousands). This will enable a high True Air Speed (TAS) with a hp rating much less than is necessary to propel a modern racing plane at 5000 feet to the same speeds.
Chris...

**First time Juke** · 11-11-2005, 02:10 AM

Re: How fast can you go with 1650 hp ?

Chris,

I guess K-4 was at its best @ 19 000 + ft. Fast climer.

Messerschmitt ME 109

http://www.chuckhawks.com/me-109.htm

The "K" was the final effort to clean up the aerodynamics of the Bf 109 and standardize the various factory and field improvements that had appeared in previous models. In this it was similar to the previous "F" model, which it resembled. Gone were the unsightly cowl bulges of the Gustav. The most numerous variant, the K-4 of which over 700 were produced, featured a pressurized cockpit and the improved visibility "Galland" canopy. It was a formidable fighter, comparable to the best Allied fighters at the end of the war. An astonishing achievement when you think about it. The K was to outlive the Third Reich, serving in the Spanish Air Force into the 1960's (by which time it had been re-equipped with Rolls Royce engines!).

Also the first 109 was equipped with a RR Kestrel engine.

109 K-4 vs. Spitfire XIV

Spitfire Mk XIV versus Me 109 G/K

http://www.spitfireperformance.com/spit14v109.html

Spitfire Mk XIV versus Me 109 G/K performance comparison, wartime flight trials and data analysis.

rgds,

Juke

**Blue Foam** · 11-11-2005, 10:27 AM

Re: How fast can you go with 1650 hp ?

Originally posted by Juke

This brings another question ...why did 400 more hp:s only give 20 more km/h
Aerodynamics seem to overtake power here in this case.

Within certain limits, for sub-transonic aircraft using propellers the speed varies with the second order of drag or thrust. Since their is an additional velocity factor in the HP vs. thrust equation, speed varies with the third order of HP. Other factors come into play when the HP change takes the prop into or out of an efficient part of its operating envelope, or as a highly loaded aircraft sees a non-linear change in its induced drag with velocity.

In english, take square root of the drag change or the cube root of the HP change and this will appoximately equal the speed change. Within limits.

**First time Juke** · 11-14-2005, 02:56 AM

Re: How fast can you go with 1650 hp ?

Just to emphasize the 109 F-4 qualities;

All G-models G-1 => G-6 at least were slower than F-4/Z. In fact also K-4 in practise did not go beyond 709 km/h.

So the added 400 hp:s did not cover the lost aerodynamics of new fairings in the bulged K-4 with added 300-400 kg:s.

-------------------------------------------------

I read the Bill Sweetman book HIGH SPEED FLIGHT and he tells that Allison V-1710 was test runned @ 2800 hp:s . Anyone know what was the weight of a Allison V-1710 ?

Page not found – British Columbia Aviation Museum

http://www.bcam.net/engines/allison.htm

He also tells a tale about R-4630 ( 70 litres ) runned with 4500 + Hp:s and saying that GoodYear Corsairs raced at over 500 mphs ?