Exhaust Piping & Radiators

[KJ_Lesnick]

I know race cars have to some extent shaped their radiators to conform to the meredith effect, have any tried to capitalize on exhaust thrust in anyway?

[PR19_Kit]

Depends how you define 'race car'.

In current F1 cars it'd be illegal because the exhaust has to exit at a defined point clear of the bodywork. Other formulas may differ of course.

There's a discussion on just that subject here, dated back in 2013 and majoring on F1 cars though.

http://www.f1technical.net/forum/viewtopic.php?t=15179

[Hobbes]

Spitfire exhaust thrust was only 70 lbs (on the Spitfire Mk I), from a 27-litre engine developing 1030 shp. Later marks with more efficient exhausts and more power developed more thrust.
In a car, the exhaust gases are badly matched to the car's speed [1] so the effect will be less pronounced than in an aircraft.

The effect is used in extreme cases, e.g. top fuel dragsters have their exhausts pointed upwards, as the 8000 shp engine will produce 800 lbs of downforce that way.

1: compare to the low efficiency of early turbojets at low speed.

[kitnut617]

Spitfire exhaust thrust was only 70 lbs, from a 27-litre engine developing 1030 shp.

This is straight out of the Rolls Royce Heritage Trust book, 'Rolls Royce and the Crecy'. "A Merlin obtains about 150lb of thrust from it's exhaust."

Where the exhaust thrust works best though is at high altitude, an aircraft with a Crecy which was predicted to put out nearly 350lb of thrust, flying at those altitudes it was expected to increase the aircrafts speed by nearly 50mph.

[Hobbes]

The 150 lbs would have been for a later Merlin mark, I suspect.

The Crecy was specifically developed to increase exhaust thrust, with exhaust valves opening very early (IIRC while combustion was still going on).

[kitnut617]

The Crecy didn't have valves per say, it had sleeve valves. The book says, the port opened instantly ----

Incidentally,  the fuel was not mixed in the supercharger, just straight compressed air came from the supercharger and then fuel was injected at the right moment from the top.

[Dizzyfugu]

The turbo-charged R-3350 was definitively built around extra thrust from the exhausts, and many other aircraft/radial engines received in the course of WWII modified exhaust systems with single pipes for added thrust. One obvious case is the Mitsubishi A6M, and I also think that the Vought F4U's system for its R-2800 was changed accordingly from the -1 to the -4 version.

Additionally, the radiator system on some aircraft with liquid-cooled engines was also designed to generate extra thrust. The P-51's belly tunnel is one of these cases I know of.

[PR19_Kit]

Additionally, the radiator system on some aircraft with liquid-cooled engines was also designed to generate extra thrust. The P-51's belly tunnel is one of these cases I know of.

The Mustang's cooling system is THE classic example of the Meredith Effect at work, but apparently even the Hurricane's and Spitfire's systems used it as well.

[KJ_Lesnick]

Depends how you define 'race car'.

In current F1 cars it'd be illegal because the exhaust has to exit at a defined point clear of the bodywork.

I did not know that.  However, I suppose it would be useful on any sports-scar being able to use the radiator to generate thrust through a ram-compression process, and use the thrust of the exhaust pipes to push the car along/negate cooling drag

Other formulas may differ of course.

There's a discussion on just that subject here, dated back in 2013 and majoring on F1 cars though.

http://www.f1technical.net/forum/viewtopic.php?t=15179

I did find something interesting in there regarding NACA research on high speed flight...