Elektra II Runs Unbelievably Well!!

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Jim Berquist
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elektra II

Post by Jim Berquist » Tue Jun 05, 2007 3:39 am

I want to launch the little beast that Eric built. 3lb thermojet. 2 meter glider just for loft. This one could be better retro made out of 20 some gage S.S.??

Jim
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larry cottrill
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Re: elekra II

Post by larry cottrill » Tue Jun 05, 2007 11:52 am

berquistj@peoplepc.com wrote:I bet that will scamper better then my biggist cockroach..

Anyone want to wager? I say 4lbs...What is the engine weight? Hell it may be able to fly!!!!
Actually, it does resemble a dragonfly or maybe a giant mosquito (in the front-view photo, with its Champion proboscis). It would look pretty cool, I think, with tandem dragonfly type wings.

I believe that flight IS possible with such an engine, but it would take expert building of the airframe for strength and lightness. That EMT tailpipe must be a couple of pounds by itself. For 1.25 inch pipes, I always use very lightweight tubing (TV antenna mast tubing) probably less than 1mm thick. That's why Mark had trouble "squeezing it in" the width of the box - the EMT is NOMINALLY 1.25 inches ID, but is really significantly larger. The tubing I use is 1.25 inch OD, almost exactly (very close to 32mm OD).

To me, the ideal vehicle to demonstrate this motor would be a hydroplane, built just a bit longer than the engine itself, with the engine mounted low in an insulated half-tunnel up the center. Another cutesy-pie watercraft I thought of would be to just put two aircraft-style pontoons on the engine - the world's noisiest water skimmer. Airplane pontoons are nothing more than super-slim hydroplanes - you would set them up so the CG of the craft is right on the step. My friend and neighbor, the late Fred Lock, gave me a little skimmer that needed a prop engine when I was a kid, but i never tried it. The pontoons were stepped but flat-bottomed (by that, I mean the bottom surface of each pontoon was straight across from side to side). That was in the 1950s - a much better pair could be designed today for something like Mark's jet.

L Cottrill

Mark 42
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Post by Mark 42 » Tue Jun 05, 2007 2:39 pm

While I was on my sick day yeterday I went to the hardware store,
and next door is a hobby shop.

They had a couple of R/C hydros, and I immediately realized I could
put my engine in one of them.

Then I saw a tunnel hull, which is less geometry critical, and I realized
I will be building one someday.

As for flying the Elektra II... use the exhaust as a fuselage. Weld on the
wing root sections of thin steel and make the rest of the wings of aluminum. Empennage can be made in the same way.
The problem then becomes only where to put R/C gear if you don't
make it a U-Control plane.

Here are a few more pictures...
(notice the tether attach loop on the rear axle for thrust measurement)

Image

Image

Image

Image

Jim Berquist
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elektra II

Post by Jim Berquist » Tue Jun 05, 2007 3:17 pm

Good looking set up Mark. This is going to be fun to watch..

Jim
Last edited by Jim Berquist on Tue Jun 05, 2007 9:05 pm, edited 1 time in total.
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Mark 42
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Post by Mark 42 » Tue Jun 05, 2007 3:30 pm

My garage floor has a very slight downhill slope towards the door.
It's just enough to almost overcome the friction of the wheels.

The problem is that this means the exhaust will be pointing into
the garage (towards the back wall) instead of out the door!

I will use the heat shield (still attached to the 2x2 frame) as
a blast fence, but all the noise is gonna be pointed at the back
of the garage. Should be interesting.

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Post by Mark 42 » Tue Jun 05, 2007 5:45 pm


larry cottrill
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Fast Boats

Post by larry cottrill » Wed Jun 06, 2007 11:52 am

Mark -

Man, those are some good-looking fast boats! I think my choice for a jet-propelled craft would be a scale-up of that rather small tunnel-hull model (the one that was shown unpainted). But, there are a lot of pretty neat plan sets just in the few links you posted.

In practical terms, you will probably have your fuel cylinder forward, or forward and beneath, your engine - and thus, probably forward of the CG. Though I am no boat designer, I would think that (as in aircraft) you would want the correct CG with the tank empty in this case, so that you go from a nose-heavy to a neutral condition during the run and never end up in a tail-heavy situation. In other words, you want to check your finished boat CG with an empty cylinder, not a near-full one. As I've said before, you MUST provide an emergency cutoff valve besides the throttle valve. Since "in flight" trim is mostly a high-speed concern, this could be handled with small aerodynamic planes, I would think. I would mount the engine with the intake beneath the tailpipe.

Man, I hope you do go ahead and build something like this someday, just for my own selfish reasons: I'd get a tremendous kick out of seeing an Elektra engine really move something out, and I just think a sleek hydro would be an ideal test platform. Do you think the throttleable range seems adequate for this application?

L Cottrill

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Post by Mark 42 » Wed Jun 06, 2007 2:32 pm

The Hydromite is actually not a true tunnel hull, but a hydroplane.
It does use the same effect to some degree, but rides on the water
on 3 points as well as on a cushion of air under the center.

The tunnel hulls have the sponsons going full length, like a catamaran
(The AquaRacer and AquaRod). The reason I lean towards them is
because they are less sensitive to CG changes.

I'll have to keep my eyes on ebay to see if an old beater or unfinished
hydroplane kit comes up for auction.

I could probably use a pair of paintball gun CO2 tanks for fuel.
The problem is how to orient them so that the propane gas is
extracted and not the liquid. But if I do actually build a boat
I will run it on something like a mix of kerosene & white gas.
Maybe use a pressure tank or electric fuel pump to pressurize fuel.

I found my fishing scale yesterday, but still ahve a couple of things
to do before I do thrust measurements... I need to find my picture
hanger wire for the tether (string would melt, though I may heat
test some dental floss). I'll post the results, of course.

pezman
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Stogie puffin' bunny

Post by pezman » Wed Jun 06, 2007 5:55 pm

In profile this PJ looks like an elongated bunny puffing on a large white cigar.

Mark 42
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Post by Mark 42 » Wed Jun 06, 2007 6:08 pm

Your psychologist must really wonder about you... ;)

Jim Berquist
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Post by Jim Berquist » Wed Jun 06, 2007 6:30 pm

No Ink Spots for him! HeHe!!!!!


Jim
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Post by tufty » Wed Jun 06, 2007 6:45 pm

Mark 42 wrote:But if I do actually build a boat
I will run it on something like a mix of kerosene & white gas.
Maybe use a pressure tank or electric fuel pump to pressurize fuel.
Use something like argon, propane or butane to pressurise. Something safe, something that won't make a combustible mixture with the fuel *inside the tank*. By which I mean "make sure it can't burn inside the tank". Propane / butane may seem like an odd choice, but they need an external oxidant in order to burn - worst case is that, whilst you have pressure, you get a big flame external to the tank, not an explosion inside it. Go from "moving bomb" to "fire hazard".

The problem with pressurised fuel systems driven by external gas tanks is that you need a containment vessel of some type, and that itself becomes a bomb. Really, I'd start with a removable propane feed, and have a bladder setup fed from the pressure of the cc via a one-way valve (i.e. fill the bladder "pressure vessel" with combustion byproducts, which are as near to inert as you are gonna get). Your containment vessel, as long as it is flameproof, can be pretty flimsy, it's only gonna have to deal with 1.5atm or so, so it's less bomblike, and you can build in "weak spots" to provide a "safe" failure mode.

Simon

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Post by Mike Everman » Wed Jun 06, 2007 7:19 pm

I was going to use a Bic lighter, bond some hypodermic tube to the nozzle, pressurize one of those stout coke PET bottles by putting a rubber band around the trigger.
Then, Bob's your uncle!
Mike
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Mark 42
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Post by Mark 42 » Wed Jun 06, 2007 7:37 pm

Mark 42 wrote:Your psychologist must really wonder about you... ;)
I realize now that you all might think this applies to you.

I know this because I returned to this thread, read it, forgot for a few
seconds that I was the one who wrote it, and thought it was directed at me.

Yes, the propane propellant makes sense.
If it's good enough for hairspray, it's good enough for a fuel system.

If I can just use a 1 pound propane cylinder laying on its side
for my fuel system (with a tube and a valve) I won't need to
worry about doing something more complex.

One problem is that most valves are a bit stiff to operate, which
may mean a standard R/C servo won't have enough torque (force).

I did come up with another idea... I'm using a small hose for part of
my fuel feed (about 4 feet of it). If I increase that to 30 feet or so,
I can stand with a propane cylinder (I have a 10 pounder) and just
spin using the hose as a tether and let the drangonfly bunny smoker thingy
go around in circles like a U-Control plane.

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Post by tufty » Wed Jun 06, 2007 7:43 pm

Mike Everman wrote:I was going to use a Bic lighter, bond some hypodermic tube to the nozzle, pressurize one of those stout coke PET bottles by putting a rubber band around the trigger.
Then, Bob's your uncle!
As it happens, a PET bottle would be good, as long as you could keep it away from / shielded from the heat. Score it along its length to provide a sensible failure point.

A bic lighter, though, might be underspecified.

:)

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