enginehistory.org

[aburhoe]

Hi all,

I’m looking for info regarding the amount of thrust obtained from the exhaust of unlimited racers, or any aircraft. It seems the phenomena is accepted to exist, but I’ve never seen any data that can correlate a specific mass of airflow through the engine with an amount of thrust.

Thanks!

Aaron

[wpearce]

Hello Aaron,

Since no one else had responded I'll toss some info out.

I do not know the formula for calculation or how it is measured but, in "The Rolls-Royce Crecy" by Nahum, Foster-Pegg and Birch, it gives a comparison of the jet thrust from the Merlin vs the Crecy.

From the book, the Merlin is listed as 150 lbs of thrust which gave it 241 net hp from the exhaust. The Crecy had 350 lbs of thrust which gave it 865 net hp. These numbers are from straight exhaust, not with a turbo.

A racing Merlin uses larger stacks than a stock Merlin but also has 120+ even 130+ manifold pressure. I do know know what thrust is generated from a racing Merlin.

From "Reno for Gearheads", Graham White wrote: "It has even been argued that anything in excess of 100 inches does not produce any additional power to the propeller, however the aircraft will fly faster when running in excess of 100 inches. The argument presented is the fact jet thrust from the exhaust stacks is increased at the higher manifold pressure resulting in a higher air speed."

There is more out there, but I just can't remember where.
_________________
Bill Pearce

www.oldmachinepress.com

[aburhoe]

Hi Bill.

Everything that I’ve seen so far doesn’t show calculation or measurement. I’m sure you’d be dying to do these types of experiments with your plane, right??

Thanks, I’ll pick up the book.

Aaron

[jschauer]

Somewhere in the NASA/NACA archives is a report on this, but I can't locate it. Perhaps one of you can remember how to get to the website?

[kmccutcheon]

[wpearce]

I remember seeing a few formulas but I can't recall where or if they really pertained to exhaust thrust. I'll see what I can scare up in the coming days.

As for the plane, it is not mine. I'm just a lowly crew-type-person but I appreciate you having a look. I'm not sure if it will be ready by Reno.
_________________
Bill Pearce

www.oldmachinepress.com

[wpearce]

I think I just found the NACA document...

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19930091844_1993091844.pdf
_________________
Bill Pearce

www.oldmachinepress.com

[aburhoe]

A gem of an article!

Thanks Bill, and all who responded.

Aaron