Exhaust thrust

[rookie]

If we're still talking TF engines here, don't forget that nitro can be a mono-propellant and I believe may be injected in near-hydraulicing proportions..

This is pretty insane. http://www.youtube.com/watch?v=xGTbQuhhluY


Shawn

Yep, lots of fuel...they did a demonstration where they had to use a fire hose to replicate the amount of fuel the pump moves.

[SchmidtMotorWorks]

The fuel pump has a 116 GPM capacity but has a return line so some of it goes back to the tank.
A garden hose is about 10-15 GPM.

I don't know if it is still true but at one time the gears in those pumps were taken out of Chevy oil pumps. They would buy pallets of them, take the gears out, bore them for larger shafts and throw the housings away.

[digger]

someone must know the mass flow rate of fuel and air of TF then its pretty easy to work out.

if it was liquid like water passing through the engine then i think it just scales proportional to density

[SchmidtMotorWorks]

someone must know the mass flow rate of fuel and air of TF then its pretty easy to work out.

if it was liquid like water passing through the engine then i think it just scales proportional to density

I can probably get the numbers tomorrow.

[allencr267]

Aircraft were playing with exhaust thrust in the late 30's, called it 'ejector exhaust'.
Wiki has something about the Rolls-Royce Merlin'd Spitfire getting an extra 10mph.
http://en.wikipedia.org/wiki/Rolls-Royc ... r_exhausts
and Flight magazine has a 1940 article
http://www.flightglobal.com/pdfarchive/ ... 00876.html

[RednGold86Z]

OP here, heck, all I was trying to figure out was what kind of force might come out of a 600 or 700 hp gas motor so I could put it to good use by either venting it through one of the steps on the boat bottom or a diffuser of some sorts on the transom to clean some of the turbulance right at the sterndrive . On 30 ft plus hulls, acceleration out of the turns is always so mello dramtic and boring compared to you car and bike guys. Anyway to break the waters surface tension on that large of wetted surface is a plus for us. Large amounts of thrust coming from under our steps could really screw our handling or help if not done right. Looks like some trial and error is in order.

I will say posts coming from all the various forms of racing have given me some lucrative avenues to research and I want to thank everybody for participating with their thoughts and experiances. The outlaw and circle track guys have given me some neat ideas. You TF guys if I had your exhausts to play with I wouldn't need propellors !

a 400CI engine at 10000rpm 100% VE flows 0.65 kg/s of air. the air exit two 3" pipes with a velocity of 62m/s. this creates a force of 0.65*62 = 40N (10lb) someone check my math PLS

I'm getting much higher exhaust velocities... Remember the exhaust is no longer air, and no longer at 25C. A rough approximation though would just be the intake volume flowrate * (T2/T1). I get an exhaust volume flowrate of a little over 75300 L/min at 773K, which works out to about 137 m/s through two 3" pipes (I also calculated .686 kg/sec using 25C air and 12.5:1 AFR), getting 94 N and 21.15 lbs force.

When I calc a 1.015L cylinder (1 cyl on a top fuel 500CID), at 8400 RPM, 2.75" pipe, 4.5bar of boost (550kPa manifold pressure), 1253K exhaust, 1.5:1 AFR (stoich would be about 2.63 for 90%nitro, 10%methanol), I get about 63 lbs force PER CYLINDER. That's about 504 lbs total. There are many areas where this could have error (such as the calc show the AVERAGE flow), but you can see it's not little, but not thousands of pounds (wikipedia shows about 800-1000 lbs).

If I calculate it at mach 1 in each pipe, they produce 119 lbs of force, or 955 total, but mach 1 won't happen for all 720 degrees of crank rotation.

[digger]

OP here, heck, all I was trying to figure out was what kind of force might come out of a 600 or 700 hp gas motor so I could put it to good use by either venting it through one of the steps on the boat bottom or a diffuser of some sorts on the transom to clean some of the turbulance right at the sterndrive . On 30 ft plus hulls, acceleration out of the turns is always so mello dramtic and boring compared to you car and bike guys. Anyway to break the waters surface tension on that large of wetted surface is a plus for us. Large amounts of thrust coming from under our steps could really screw our handling or help if not done right. Looks like some trial and error is in order.

I will say posts coming from all the various forms of racing have given me some lucrative avenues to research and I want to thank everybody for participating with their thoughts and experiances. The outlaw and circle track guys have given me some neat ideas. You TF guys if I had your exhausts to play with I wouldn't need propellors !

a 400CI engine at 10000rpm 100% VE flows 0.65 kg/s of air. the air exit two 3" pipes with a velocity of 62m/s. this creates a force of 0.65*62 = 40N (10lb) someone check my math PLS

I'm getting much higher exhaust velocities... Remember the exhaust is no longer air, and no longer at 25C. A rough approximation though would just be the intake volume flowrate * (T2/T1). I get an exhaust volume flowrate of a little over 75300 L/min at 773K, which works out to about 137 m/s through two 3" pipes (I also calculated .686 kg/sec using 25C air and 12.5:1 AFR), getting 94 N and 21.15 lbs force.

When I calc a 1.015L cylinder (1 cyl on a top fuel 500CID), at 8400 RPM, 2.75" pipe, 4.5bar of boost (550kPa manifold pressure), 1253K exhaust, 1.5:1 AFR (stoich would be about 2.63 for 90%nitro, 10%methanol), I get about 63 lbs force PER CYLINDER. That's about 504 lbs total. There are many areas where this could have error (such as the calc show the AVERAGE flow), but you can see it's not little, but not thousands of pounds (wikipedia shows about 800-1000 lbs).

If I calculate it at mach 1 in each pipe, they produce 119 lbs of force, or 955 total, but mach 1 won't happen for all 720 degrees of crank rotation.

so the numbers are good enough for the ballpark ( i used density 1.2kg/m3 for exhaust gas as i wasnt sure what temp it would exit the end of pipes).

[MadBill]

I intend some day to get real data by running the exhaust of a stout dyno mule through some flex pipe into a 90°elbow pointing vertically and resting on a weigh scale...

It may be many hundreds of pounds on a TF car, but my SWAG is 15-20# for 500 HP.

An inspired S.W.A.G. is as good as a sharp pencil...

[Kevin Johnson]

I am just glad that the gent that had his pants blown off and legs severely burned did not breathe in whatever it was and in whatever kinetic state.

[John Wallace]

I am just glad that the gent that had his pants blown off and legs severely burned did not breathe in whatever it was and in whatever kinetic state.

Pedregon on starting line at Indy?

[rookie]

I am just glad that the gent that had his pants blown off and legs severely burned did not breathe in whatever it was and in whatever kinetic state.

Pedregon on starting line at Indy?

Yep, this one here. http://www.ar15.com/forums/t_1_5/1087115_.html