Valveless for R/C Flying?

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Tony~
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Valveless for R/C Flying?

Post by Tony~ » Sun Dec 19, 2004 3:47 pm

Is there any valveless design that would work on a R/C Plane? I have trouble finding valvematerial, thats why I want to use a valveless design.

Maybe if you could scale down the Chinese or the shortlady. What do you think? And also, it should be prefered if it worked with liquid fuel..

Anthony
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Re: Valveless for R/C Flying?

Post by Anthony » Sun Dec 19, 2004 7:03 pm

Well, the FWE for the moment has a low T/W ratio, so does the Elektra. I'd suggest an Escopette or the Escopeta version, those seem to be the most appropriate ones.
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Tony~
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Re: Valveless for R/C Flying?

Post by Tony~ » Sun Dec 19, 2004 9:22 pm

But aren't they very big? Can you scale them down?

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Re: Valveless for R/C Flying?

Post by Mike Everman » Sun Dec 19, 2004 11:24 pm

Tony, thrust is proportional to exit area, and there is an optimal exit area for a given combustion chamber diameter, so really for all intents it's proportional to CC area. Area changes with the square of the radius, so thrust reduces dramatically when you scale down. In the best case, a half scale FWE would have 1/4 the thrust, if you could get it to run at all. Small engines very quickly become useless for anything but noise, and getting a small one going gets high praise from this group, because it is so difficult to do.
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Tony~
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Re: Valveless for R/C Flying?

Post by Tony~ » Sun Dec 19, 2004 11:57 pm

So an design with valves would be the way to go? Like the "Atom Jet"?

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Re: Valveless for R/C Flying?

Post by larry cottrill » Mon Dec 20, 2004 10:05 pm

Tony~ wrote:So an design with valves would be the way to go? Like the "Atom Jet"?
Tony -

There are a few things running in favor of valved engines for flight. One is: so far, I don't think any of us have seen a valvless engine that successfully carburetes liquid fuel - for liquid without carburetion, you've got to add the weight of a pump and batteries; for vapor fuel, you've got to add the weight of a pressurized tank or cylinder. Another one: So far, I don't think we've seen a valveless engine that delivers enough power for its bulk [size] to compete with a valved engine. My FWE design could probably be built light enough for a reasonable T/W ratio, and MIGHT be capable of carbureting liquid fuel in the near future - but it's as big around as a Dynajet, slightly longer, and only delivers about 1/4 the thrust! Of course, I hope it will eventually be much better developed, but for right now, that means you would have to get carburetion perfected AND build a large, super light airframe just to hold it properly. The drag would keep you from getting to any really impressive speeds.

No, I don't like it - but that's just the way things seem to be for the present. Here's an old article of mine on the pitfalls of pulsejet power for model vehicles. It's a bit dated, and was written for someone interested in R/C autos, but it lists most of the design points that need to be thought through:
http://www.jetzilla.com/Vol01Num01/jetZ ... #Article_1

L Cottrill

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Re: Valveless for R/C Flying?

Post by steve » Mon Dec 20, 2004 11:45 pm

Larry, here is an idea that I have been toying around with:
as you are aware, sometimes pressurized fuel tanks made from surgical tubing and inflated with fuel are used in aerobatic CL models. I propose that one of these fuel "bladders" be connected to a needle valve and then connected to a length of steel tubing wrapped around the combustion chamber of your valveless engine and then to the fuel injector inside the intake. The engine would be started using propane and a seccond injector that would be held inside the intake for startup and then removed. Once the engine is running on propane and has heated up a bit, start turning down the propane while turning on your liquid fuel untill the propane is completely off.

so there you have it- no chance of air in the fuel line, inverted flight capable, possibly more efficient then using propane, and lightweight too! Granted, the startup might be a little tricky to master, but the result is well worth it in my opinion. I can see no obvious reason why this could not be made to work and am considdering building it myself on the half size (or half thrust) FWE that I might build.

what do you think?
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Re: Valveless for R/C Flying?

Post by larry cottrill » Tue Dec 21, 2004 1:38 am

Steve -

Actually, I've thought about something like it but without the bladder tank, using chamber-driven pressurization. I definitely want to try a vaporization coil for liquid fuel.

Remember that the surgical tubing [or any unmodified latex bladder] will only take alcohol fuel, so your choices will be limited - still, methanol makes a fine fuel and is readily available.

Here's another way I thought of trying it: Arrange enough conduction between the chamber and the intake pipe that the pipe gets good and hot after an initial warmup period of a few seconds. The hot part could include a turned brass venturi, if desired. Deliver the liquid fuel so it hits the inside surface of the tube and evaporates instantly from the hot metal wall! You'd just need to be sure the wall stays hot enough so the cooling effect of the fuel evaporation doesn't kill the effect. "Crude but effective," as I like to say. Again, you would use a temporary vapor supply for startup.

I think something like that would work wonderfully for Butane, which comes in very lightweight pressurized aluminum cans. Of course, all such arrangements [in fact, all pressurized fuel systems] need an inertially-activated "crash valve" for emergency shutoff.

L Cottrill

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Re: Valveless for R/C Flying?

Post by Mark » Tue Dec 21, 2004 1:55 am

I was thinking the same thing, you could do a surgical tubing inflated like what's his name in Oregon, and that could be your fuel pump, a collapsing tank of rubber. Then too you could make a feedback mechanism that ran off the heat of the engine to pressurize the fuel line with valving to control the heat that drives the reaction and you would need a way to control just how much fuel pressure you need. Feedback mechanisms seem plausible for fuel feed but I don't think I have seen anyone governer that reaction yet. That is, drive the reaction with heat, pressurizing the fuel tank to just the right amount safely.
Mark
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Re: Valveless for R/C Flying?

Post by jmhdx » Tue Dec 21, 2004 9:16 pm

Mark wrote:I was thinking the same thing, you could do a surgical tubing inflated like what's his name in Oregon, and that could be your fuel pump, a collapsing tank of rubber. Then too you could make a feedback mechanism that ran off the heat of the engine to pressurize the fuel line with valving to control the heat that drives the reaction and you would need a way to control just how much fuel pressure you need. Feedback mechanisms seem plausible for fuel feed but I don't think I have seen anyone governer that reaction yet. That is, drive the reaction with heat, pressurizing the fuel tank to just the right amount safely.
Mark
There's plenty of spare heat alright! Anything that makes use of it will improve the overall efficiency. I would bravely sujest the fuel, prefererbly gasoline, was stored in a cylindrical container around the exhaust pipe. It would be vapourised and pressurised by the heat and would only require a regulator between it and the injector. Again no(almost) moving parts and an aerodynamic solution.
Still it's all simple on paper.
Mike.

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Re: Valveless for R/C Flying?

Post by Mike Everman » Tue Dec 21, 2004 11:24 pm

...just boil gasolene in a red hot container that you make yourself...

"shut it off! shut it off!"

the worst thing is that it will collapse the engine tube, unless you can relieve the pressure somehow. I think you're better off with the Russian pressurization of the tank with cc pressure fed to the tank. too simple, and you're not sending oxy up the line, or fire, it just works. I am of the opinion that you needn't have a check valve, either, just a small diameter copper tube. (the pressure average in the cc is something like +5psi above ambient, certainly not enough to pop a pet coke bottle)
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Re: Valveless for R/C Flying?

Post by steve » Wed Dec 22, 2004 3:35 am

that would definately work, but you would run the risk of gas bubbles in your fuel line disturbing fuel flow and killing the engine. The biggest advantage of the pressurized bladder is that there are no gas bubbles in it to begin with, so you don't have to worry about the engine dying prematurely, even when inverted or during some other acrobatic manuver.

funny story, I once ran out of fuel while inverted on the very first flight of a new model that I had designed. Once the engine cut out all I could do was watch it slowly glide downwards while still inverted. Ill leave the rest to your imagination ;-)
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Re: Valveless for R/C Flying?

Post by larry cottrill » Wed Dec 22, 2004 4:02 am

steve wrote:funny story, I once ran out of fuel while inverted on the very first flight of a new model that I had designed. Once the engine cut out all I could do was watch it slowly glide downwards while still inverted. Ill leave the rest to your imagination ;-)
Steve -

The first time you want to invert any stunt model, pull it up for a half loop and try to level it at the top of the loop and fly it high around the circle. Of course, this means you have to turn a little faster with it. If it quits, grit your teeth and IMMEDIATELY pull full UP to complete the loop [i.e. the downward half loop], level out and glide your plane in with normal control.

Of course, this is easy when you're just sitting here at the computer thinking about it ... ;-)

Just remember: Whatever happens, you're always going to see it later on in slow motion, anyway, so analysis will be straightforward.

L Cottrill

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Re: Valveless for R/C Flying?

Post by Mike Everman » Wed Dec 22, 2004 6:22 am

Oh, Steve, I feel your pain. I lost a wing on a super chipmunk and it went down in an old folks home. I was young, so I ran. I watched the papers to see if I'd hurt one of the blue haired clan, but no news, so I went over there a few days later and the janitor gave me my gear, having crashed on the edge of the roof somewhere. Broke the engine in half. I dreamt in those days over and over about calmly putting my one winged racer into a knife-edge and bringing it back to me for a less risky ditch. Ha ha. That would have been something. I'd have been looking around for witnesses: "Hey! Did anyone see that????" It would have been worth the loss of the plane! My aunt lives in that very home now.
Mike
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