Exhaust Thrust ????

[Crumpp]

Actually, there are several photos from 2010, although the photo of the purported engine definitely isn't a BMW 801

 

It is a Jumo 213 for the Dora 9, which was next on the list after Little Missy.

[Friedrich-4B]

Added; a report on the design of carburettor air scoops and their effect on fuel-air metering; although not directly related to exhaust thrust, it shows the importance of the incoming airflow to the engine's overall performance:

[[DBS]TH0R]

Thought this would be interesting to share:

 

(When making a short-field landing, move the mixture control to idle-cutoff after touchdown. This eliminates the thrust produced by an idling Merlin. Propeller inertia and windmilling prevent the monstrous "flywheel" from stopping quickly. As the Mustang slows and you begin to see individual blades, return the mixture to auto rich. The engine restarts nicely and in time to taxi.)

 

http://www.aopa.org/News-and-Video/All-News/2007/August/1/North-American-Aviation-P-51D-Mustang

[Kelevra]

great find thanks

[RAZBAM_ELMO]

The struggles of Dora owners not knowing what a mixture control lever is lol.

[DieHard]

... and to add to that, there is even coolant radiator thrust (cold air entering into the radiator, warms up, expands, leaves at the back creating some pressure). Its basically a miniature jet engine, only here you do not heat up the air by burning fuel but by cirvulating hot fluid in the radiator. Of course its not that great thrust, but its still thrust and at high speed, where the propeller starts to struggle to convert its motion into thrust it can be more significant and at the very least, it makes up at least some of the drag the radiator system creates. On some designs, such as the P-51 its even claimed to provide a net positive thrust. Though this is debated back and forth, it still shows that how important careful designing of the radiators were to the overall design.

 

There are a few engine charts that show this effect - this one is for the DB 601Aa series, the top line showing the equivalent horsepower of the engine output PLUS the exhaust thrust at 600 km/h. It IS a significant boost, adding the equivalent of about 100 horsepower due to exhaust thrust (Rückstossenergie).

 

Out of interest, this power curve also shows the effect rammed power (Stau, Staudruck on the right, given at different pressures, equivalent to specific speeds/atmoshpeheric conditions). When the airplane travels very fast, it slams a lot of extra air into the supercharger air intake - in effect, its own motion provides a lot of "free" supercharging. That is why aircraft higher rated altitudes at high speed compared to slow speed climbing conditions.

 

In Cub Scouts I made a boat, propelled by a candle fastened on the boat, heating air in a copper coil wrapped around the candle. It was not fast, but it did propel the little boat.

Edited April 13, 2015 by DieHard

[Bucic]

The struggles of Dora owners not knowing what a mixture control lever is lol.

:D

[Teapot]

... I dont claim to understand half of it, but its still cool :)

 

Well you're understanding a lot more than I do.

 

Most of the time I feel a bit like a caveman sitting in a corner listening to all the propeller head talk ... and when the graphs are trotted out pfffft! not a hope ... eyes glaze over and I catch myself playing with the HOTAS ... ah saved by an airshow youtube video ... and yeah, I can *understand* raw visceral power. Maybe I'm just a bogan :lol:.