paintballtommy

ive been thinking about this and think it would be pretty cool. os 30vg in an airplane. spin it to 30 k with a carbon fiber prop with a pretty mild pitch. what say you to that?

soarrich

My Feedback: (98)

Wow, I grew up in Concord.

I was thinking the same thing while in the LHS today, they had a .25 buggy motor there for ~$150, made 2.5hp at 31,000 rpm. they said you can rev it to 50,000 rpm. The box had the HP chart on it, max HP at 31,000, the chart showed it ran out of breath by 33,000 rpm, the 50,000 rpm must be for the guy that doesn't back off in a jump. I didn't believe the 50,000 rpm so they called the manufacturer and he confirmed it.

I saw a .18 that turned either 38,000 or 41,000 rpm, but they where asking $350 for it, it's out of my price range for a .18 that I'd have to cut the extra fins off of.

mikekosatka

My Feedback: (7)

fine if you can find a 2x1 prop!!
LOL
Mike

soarrich

My Feedback: (98)

With 2.7HP I think it'll turn a little bigger prop than that. I really think it would be fun to try, but to cut up a new $350 motor for an experiment is tough for me to do. I do think you could get 200mph out of a electric easily though.

Rudeboy

Not too long ago I saw an advertisement for a "truck".... it had a new breed of engine in it... a .46 that produced 5.0 hp at 23000 rpm... they must be running tetranitromethane through that thing.

Now, you won't hear me saying that 5 hp can't be had from that engine... I just want to see it do that for 5 seconds at a stretch.

In other words: there are .21 engines out there that will put out a genuine 2.7 hp... at +40K rpm.

IMO the 2x1 prop suggestion isn't too far off. When you're finished shaving the head down, you'll have to put on a prop so small it will barely be enough to cool the engine.

Molten pistons will be your share

GregG

My Feedback: (2)

Even thinking of using 2 X 1 prop would be a bit whacked. Spinning at 40k RPM still only gives one a pitch speed of around 40 MPH.

These engines are a viable alternative that I have been looking into. At the local track vehicles powered by them have an unforgettable acceleration and top speed. They all use a tuned pipe that gets curled 'round and 'round to fit into the confines of whatever body they choose to use. I can only imagine how much better that engine would run with a nice straight expansion chamber attached to the port.

I believe that the horsepower numbers that they're throwing out aren't too far off. However, you won't see a one of these using direct drive to the wheels. [sm=lol.gif] One guess how they get that horsepower to the workload. [sm=idea.gif] That's all I'm gonna say.......

Cyclic Hardover

My Feedback: (3)

Maybe you guys can hook up th 2 speed tranny along with it![sm=lol.gif] "Scotty! we need second gear now-or were all gonna die!"

Kmot

My Feedback: (24)

Dude!!

The E-Maxx has a switch selectable two speed gearbox. Can you just picture it? Low gear for take-off/landing. Switch to high gear once in a dive for that 'high speed pass'. [sm=thumbup.gif]

MyWay

With a little work on the head. carb. and special prop nut the OS 18 tz will turn a apc 7x6 at 20000 rpm or a 6.5x5 at 26000 rpm with no internal mods and just an open exhaust. Still have to try a tuned pipe. BTW, it weighs less than 6 oz.

paintballtommy

it would be pretty cool i was drawing up some scetches using a traxxas n4tec 2 speed setup but it would be really big and id have to fab a carrier for the second gearset.

paintballtommy

os makes a 46 vx ducted fan motor. that makes 2.5 horsepower and spins to 23k how hard would that be to throw in a plane. carbon fiber prop etc its rear carb rear exhaust i think it would make for a good layout. im concerned about cooling though.

soarrich

My Feedback: (98)

I think you'll find cooling ISN"T an issue, 200mph wind will cool it nicely! I saw a pylon racer it had a slit 1/8 x 1inch for cooling, a big hole to let the air out though.

Cyclic Hardover

My Feedback: (3)

Any of you guys remember back in the early 70's when Popular Mechanics or Science had articles on little Sabbs or some other small POS of a car and coverted it into a plane?

GregG

My Feedback: (2)

Cooling should not be a problem if it's done right. Have you ever seen the engine shroud on a Bob Violett Modells ducted fan unit? It has a narrow slit in front for air entry and a smooth flowing cover over the entire cylinder and head. The air is released just behind the engine shroud.

bob27s

My Feedback: (19)

It possibly can produce 2.7 hp at 30,000 rpm - but the catch is, you have to GET to 30,000 rpm to produce that power.

The engine's torque curve will decide how fast it can rotate/accelerate a given load.

That is why you will not see a HP rating that is not accompanied the RPM it is achieve at. They are mathematically connected.

It is also for this reason, that for aircraft use, the best practicle way to compair power is using known, practicle, and useful fixed loads (standard prop, or a series of props).

The car installations have the advantage of serious gear reduction - the engine requires very little torque. So the engines can be and are designed for that application. That light torque combined with no/little gyroscopic forces puts less load on the rod, pin, piston, shaft, crankpin - which means construction and design of internal components can be taylored to best achieve the higher rpms. Also, the car engines rarely run at full rated rpm for longer than a handful of seconds. Allowed to run continuously at high rpm (like a fan engine) they would likely self-destruct in short order.

As for the engine cooling, controlled use of the air and air duct/baffle arrangment is what is utilized on the fan engine and racing planes. That little slot and the geometry is much more efficient than many open-air cooling arrangements, even at lower velocities - and it is actually useful for keeping the cylinder temperature UP while flying at higher speeds.

(for reference, the QM40 engines produce somewhere around 2.7 - 3.0 HP at 25-27,000 rpm [info from a reliable dyno test], and that is the in-flight range where the engines turn 7.5x8 size carbon/wood prepared racing props)

paintballtommy

i understand that they do in fact make that power at 30000 i wonder if we can get a torque graph to see how easily they get there

Horsepower = Torque * RPM / 5252 so lets say Torque= (Horsepower/(RPM/5252))
3.0 hp at 28k for the 0s 30 vg car engine
3=T*28000/5252
3= T*5.3313
3/5.3313=T
T=(3/(28000/5252))

Torque at 28000=.5628 correct my math if i am wrong

now lets say we have a motor of approximately equal displacement but designed for airplane use
the os 25 la makes .6 horsepower at 15k so
T=(.6/(15000/5252))

Torque at 15000= .21

lets assume that the 25 la is spinning a 9X5 prop at say 14500 rpm we can assume that at that speed it would be making approximately the same torque as at 15000 rpm. when i look back at this it only takes that motor .21 torque to spin that prop at 14k

the os 30 vg produces more than twice the torque and 5 times the horsepower at less than double the speed.

the 30vg is designed as a replacement for the savage x rc truck motor so lets look at the gearing of the savage motor. if we can find the gear reduction that the savage uses we can figure the torque multiplication provided by it. i know the gears on the motor and the drive gear is 23-32 as per hpi racint cust service. thats 29% reduction which is by no means final drive ratio but my gut feeling is that you would probably be fine spinning a 9x5 prop on a 30 vg all the way to 28 as long as the prop will hold up. the only way to be certain is to see a torque graph and find out jsut how the torque moves through the rpm range. basically what im saying is everyone just says ohh it may make 3 hp at 28 thousand but it has to spin that fast to get there nobody has said anything about the torque curve or how linear it is to the hp curve. 2 strokes are peaky engines but im not gonna jump in and assume that the 30 vg cant make enough power to get that prop spinning to redline

Rudeboy

Well, for starters, your 9" prop is going to have a tip speed of about Ma 0.99 at 28000 rpm...

MyWay

Not to worry. 20k will probably be all it will muster with a 9/5. The only way to know for sure is to run it with the 9/5.

MJD

My Feedback: (1)

And it will take about 5 horsepower to spin it that fast neglecting the huge jump in C-sub-d at the tips as they approach transonic, so the figure is going to be way more than that.

Depending how much credence you put in the various bits of software out there (a good question), 28k and 3HP represents the load of a prop between 8-4 or 8-5, or 7-8. Adding my customary skepticism about manufacturer's HP claims, I would imagine that .30 might spin a 7-7 or so prop at that rpm.

I-Love-Jets

Hello MJD,

you should adjust your estimation downwards to get true 30000 rpms on the ground. A 6.5x6.5 is the ideal prop size for a .28 converted car engine for speed application. That prop size makes such an engine run at its optimum level, i.e. the torque/power peak.

MJD

My Feedback: (1)

I can believe that. A prop that size must look unusual on front of a .30 size engine.. but I bet it sounds cool.

I-Love-Jets

Well I think that depends on the type and design of airframe. Such an prop-engine combination really needs lowest drag solutions...

soarrich

My Feedback: (98)

I-Love-Jets

Please post more pictures of planes like that one! Nice.

MJD

My Feedback: (1)

Ditto that, it's nice to see some airplanes in this forum that really are extreme speed designs for a change.. instead of prop jets, Magnums and Shrikes .


Relax all, just poking fun.