Rocket Science

[cessna170bdriver]

I know just enough about rocket science to be truly dangerous. (Ya wanna motor that develops as much thrust as a 170, but only weighs a pound or two? We got 'em.)

Miles

That motor sounds pretty good. What's the range on one of those?

Hmmm….

Assuming a 170 takes about 75% of 145hp to go 120mph (176 ft/sec), and has about 80% propeller efficiency, about 270 lb of thrust is required for cruise.

A pretty good liquid rocket has a specific impulse (thrust divided by propellant mass flow rate) of about 400. If my arithmetic is correct, that rocket would require 270/400=0.68 pounds mass of fuel per second to generate equivalent thrust of a 170 in cruise. Assuming the fuel used weighs around 8lb/gallon, that’s a about 0.085 of a gallon per second, or about 305 gallons/hour. Ignoring the fact that you can’t shove that flow rate through a 170s (3/8” ??) fuel lines, the 38 gallons usable fuel would last less than 7.5 minutes, or less than 15 miles!!

Any of you who really are rocket scientists feel free to check the assumptions and math. This wouldn't be the first time I've screwed up a calculation like that.

Miles

[iowa]

we had a fellow in town
who put a turbine engine
on his homebuilt.
it worked great!!
only trouble was
that it ate him out of house and home in fuel!!
he went back to the standard engines
dave

[GAHorn]

I know just enough about rocket science to be truly dangerous. (Ya wanna motor that develops as much thrust as a 170, but only weighs a pound or two? We got 'em.)

Miles

That motor sounds pretty good. What's the range on one of those?

Hmmm….

Assuming a 170 takes about 75% of 145hp to go 120mph (176 ft/sec), and has about 80% propeller efficiency, about 270 lb of thrust is required for cruise.

A pretty good liquid rocket has a specific impulse (thrust divided by propellant mass flow rate) of about 400. If my arithmetic is correct, that rocket would require 270/400=0.68 pounds mass of fuel per second to generate equivalent thrust of a 170 in cruise. Assuming the fuel used weighs around 8lb/gallon, that’s a about 0.085 of a gallon per second, or about 305 gallons/hour. Ignoring the fact that you can’t shove that flow rate through a 170s (3/8” ??) fuel lines, the 38 gallons usable fuel would last less than 7.5 minutes, or less than 15 miles!!

Any of you who really are rocket scientists feel free to check the assumptions and math. This wouldn't be the first time I've screwed up a calculation like that.

Miles

Miles ... Is that a private company job you have there? Or is it a gov't grant/subsidized gig you have? Are any of us paying for this kind of information?
If so, we'd appreciate it if you would check your work a little more closely. (A 170A/B only has 37 gals of useable fuel. Of course, to be accurate you did say "170s" so it's possible you meant a ragwing, which would have 33.5 gals of useable fuel, and that would mean we might have to split the difference. Unless, of course, you meant total fuel for a ragwing, in which case you'd still have missed it by half-a-gallon. Either way, it's still not good enough for this forum's eagle-eyes, albeit it might do for gov't-work.)

[cessna170bdriver]

...we'd appreciate it if you would check your work a little more closely. (A 170A/B only has 37 gals of useable fuel. Of course, to be accurate you did say "170s" so it's possible you meant a ragwing, which would have 33.5 gals of useable fuel, and that would mean we might have to split the difference. Unless, of course, you meant total fuel for a ragwing, in which case you'd still have missed it by half-a-gallon. Either way, it's still not good enough for this forum's eagle-eyes, albeit it might do for gov't-work.)

I can count on the fingers of one hand the number of times I've used more than 30 gallons on a single leg, and I use the (placarded) fuel selector by the Braille method, so I took a guess. Anyway, whats 0.39473684210526315789473684210526 miles amongst friends?

Miles

[cessna170bdriver]

This is part of a Rocket that should do significantly better on fuel.

Miles

[flyguy]

MILES IS KAREN GONE ON A LONG TRIP OR SUMPIN

IT DOANT TAKE A ROKET SCEITNESTS (SP) TO SEE YOU HAVIN TOO MUCH TIME ON URE HANS

[johneeb]

I know just enough about rocket science to be truly dangerous. (Ya wanna motor that develops as much thrust as a 170, but only weighs a pound or two? We got 'em.)

Miles

That motor sou ...

Miles,
Does the engine you are developing for the 170 look like the ones on this rig? Hard to tell if the engines are jets or rockets.
http://jet-man.com/playervideo.swf?video=jetman2007.flv

[cessna170bdriver]

Miles,
Does the engine you are developing for the 170 look like the ones on this rig? Hard to tell if the engines are jets or rockets.
http://jet-man.com/playervideo.swf?video=jetman2007.flv

I can't get to that site, as it seems to be blocked by the Air Force server. (God forbid we should see a propulsion video on our computers here at the Propulsion Directorate of the United States Air Force Research Laboratory )

If it's the one I think it is, it is a hydrogen peroxide-powered back pack. They call it a jet (correct by at least one of the dictionary defintion of the word: per Merriam-Webster, a usually forceful stream of fluid (as water or gas) discharged from a narrow opening or a nozzle), but isn't a turbine, nor is it airbreathing.

They work because hydrogen peroxide, H2O2 is fairly unstable and readily dissociates into water (steam), oxygen and copious amounts of heat, especially in the presence of a catalyst, like silver or manganese. They are essentially self-powered steam generators. The trick is to keep this from happening before the peroxide gets to the chamber.

That outfit isn't practical for personal transport for the same reason that it wouldn't be practical on an airplane: the extremely high fuel flows required for usable thrust precludes attaining usable range. A I remember, the duration of that peroxide jet pack is about 20 seconds, and it took many runs to piece together the video you see.

Here at the lab we're looking into it a possible replacement for the highly toxic fuels currently used for satellite maneuvering thrusters that only have to operate for seconds (or even milliseconds) at a time.

Miles

[johneeb]

Miles,
You have to get a look at the link. It was filmed in Switzerland and the pilot straps on a folding wing that has four small engine mounted on it. He launches in flight from a Helio Curior (I think).

[AR Dave]

WOW! I want to do that!

Pilatus Porter

[GAHorn]

I believe those 4 engines are originally designed for the radio-control airplane market and have been adapted. I've been informed by one of the guys here at work that theres a sizeable model B-52 with EIGHT of them!

[johneeb]

WOW! I want to do that!

Pilatus Porter

Thanks Dave, I have got to learn my Pilatuses.

[GAHorn]

Why did Pilatus Pontificate?

[doug8082a]

I believe those 4 engines are originally designed for the radio-control airplane market and have been adapted. I've been informed by one of the guys here at work that theres a sizeable model B-52 with EIGHT of them!

Correction... there WAS "a sizeable model B-52 with EIGHT of them"

http://www.teambanana.co.uk/b52rob.wmv

[N1478D]

WOW! I want to do that!

Wouldn't that be a fun way to harvest squirrels along Petit Jean Creek!