Yet another silly idea with pulsejets...

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Bruno Ogorelec
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Yet another silly idea with pulsejets...

Post by Bruno Ogorelec » Sun Mar 12, 2006 9:27 pm

During World War II, when the jet engine was young, Germans were thinking up all sorts of zany things one could do with it. Being mad but methodical, most of their ideas worked. We all know that the Western and Soviet aerospace industries lived off German ideas for the next 20 years.

One of the bizarre ideas that worked was having a jet engine blow through a gyroplane rotor from below. That would make the rotor rotate, of course. Once it spooled up to high speed, thrust was vectored backwards to make the gyroplane roll along. Given the high speed of the rotor, the thing needed to roll only a few yards to take off. That was the first jet-powered gyroplane I know off. Also, it was one of the few jet-powered gyroplanes to fly, ever.

While this is a neat idea, and one well worth exploring again in my opinion, it has led me to a different proposition -- jet powered flying platform.

Most of you will be familiar with the Hiller flying platform -- one of the few mad gadgets that actually worked well. Its biggest problem was that the military didn't quite know what to do with it. It was an easy target for gunfire, so you could hardly use it with confidence on the battlefield.

I've been thinking about it, however, equipped with a big version of my Constant Flow engine. blowing downwards through the fan at its perimeter, like that German BMW engine blew upwards through the gyroplane rotor.

I have drawn a simple sketch of the idea. The original flying platform had two counter-rotating props but that was because it had to annul the torque reaction of an engine-driven prop. Given that this one is jet-driven, there is no torque reaction and a single rotor is needed. No gearing, either. Much less weight and complexity. Also, my twin combustor engine is just a lot of empty tubing -- must be a damn sight lighter than a piston engine with transmission Hiller was using.

It just might work.

Flying platforms are neat devices -- they are steered by weight shift. You stand upright in the center and lean in the direction you want to travel -- quite instinctive. Lean forward and the platform starts moving forward. Lean left and the platform turns left. Lean back and the platform slows down, stops and starts moving backwards. A bit like Segway.
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Zippiot
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re: Yet another silly idea with pulsejets...

Post by Zippiot » Mon Mar 13, 2006 11:59 pm

it would be very useful for surveying over a hill if it is small enough for a field r/c operation...just a thought to make a vtol r/c craft.
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larry cottrill
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re: Yet another silly idea with pulsejets...

Post by larry cottrill » Wed Mar 15, 2006 3:57 pm

Bruno -

The only thing I think is "silly" about these platforms (other than that they don't work very well under total power failure) is that they generally attempt to utilize THRUST for LIFT. No matter how you slice it, you need a net thrust-to-weight ratio slightly greater than 1.0.

Why not use LIFT for LIFT, as in this attempt to bend a glider wing into a donut? It still won't work in a total power failure, but might make better use of the available power.

L Cottrill
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Flying Donut, plagiarized from Bruno Ogorelec's jet platform and modified to use a lifting foil.
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cudabean
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re: Yet another silly idea with pulsejets...

Post by cudabean » Wed Mar 15, 2006 4:59 pm

I like the idea.

Here's a bit of a variation:
How about a purpose-built annular lockwood that looks like a thin doughnut
configured so that the intake and thrust all take place at the frosting side of the doughnut. Then you mount it "frosting side down". The locky then has a big hole in the middle allowing the fan below to suck unimpeded air (excepting for the pilot). The outer ring of the fan could then transition to a set of more standard looking turbine blades optimized for harnessing the thrust of the lockwood situated just above it.

Marlin

Bruno Ogorelec
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Re: re: Yet another silly idea with pulsejets...

Post by Bruno Ogorelec » Wed Mar 15, 2006 8:49 pm

Larry Cottrill wrote:The only thing I think is "silly" about these platforms (other than that they don't work very well under total power failure) is that they generally attempt to utilize THRUST for LIFT. No matter how you slice it, you need a net thrust-to-weight ratio slightly greater than 1.0.

Why not use LIFT for LIFT, as in this attempt to bend a glider wing into a donut? It still won't work in a total power failure, but might make better use of the available power.
Larry, but the flying platform does use lift for lift. The duct is, in effect, a carefully profiled curved wing. It creates lift even at standstill, by means of the air sucked over the rim, and still more lift as soon as you start moving horizontally. That's a big factor in making the platform work.

I think your layout would only generate lift at standstill. Something very complicated would happen in horizontal flight. In addition, it would cease to be easily steered by weight shift.

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re: Yet another silly idea with pulsejets...

Post by cudabean » Wed Mar 15, 2006 10:00 pm

The scary thing about this though is the reliability. As someone else alluded to in this forum it's like pulsejets have no flywheel. Miss one beat and the the rug is pulled out from under you. Literally, in this case.

Marlin

Bruno Ogorelec
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Re: re: Yet another silly idea with pulsejets...

Post by Bruno Ogorelec » Wed Mar 15, 2006 10:21 pm

cudabean wrote:The scary thing about this though is the reliability. As someone else alluded to in this forum it's like pulsejets have no flywheel. Miss one beat and the the rug is pulled out from under you. Literally, in this case.

Marlin
Not with my Constant Flow engine (http://www.pulse-jets.com/phpbb2/viewtopic.php?t=2752). It uses two combustors and generates symmetrical thrust or lift whether working with just one of them or both. If one goes out, your thrust or lift is cut in half, but the balance is preserved and the remaining half lets you do something -- like deploy a ballistic parachute, or even make a hard but tolerable landing. That's the main reason I developed the concept.

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re: Yet another silly idea with pulsejets...

Post by Zippiot » Thu Mar 16, 2006 5:35 am

well since you are already using fuel for the pj's and the ducted fan provides gyroscopic ballnce, the only issue i see left (i mean major issue hindering liftoff) is power.

so how do we solve this?

simple and complicated! Motorjet!!!

you already got the fuel running, and the ducted fan shooting air downwards, seems like a small step to me.

potential issues i forsee:
1. motorjet uses more of a nozzle than a ducted fan, so if you run out of fuel the efficiency of the fan goes right out the window...
2. motorjets do work, but are usually innefficient. although in this case i see little room for improvement over a motorjet
3. giant flame shooting downwards around the pilot, if the fan stops spinning he/she will cook when it flames out!!!!
4. the nozzle sticks down further than the ducted fan's, so improved landing gear must be used to get it higher up without changing the riders position.


one day these will roam the sky, but in the next 10 years? doubt it...
Sailing Student- How do I know if my life jacket is tight enough?
Me- Can you breathe?
Sailing Student- Yes
Me- Then its too loose!

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