Ram Air for a HL?

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ZSartell
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Ram Air for a HL?

Post by ZSartell » Tue Aug 10, 2004 7:52 pm

This is an idea of mine that I have been thinking about for a while. How could you get ram air for a HL? The obvious idea would be to put an arrray of deflectors to turn the air around and force it into the intake,but this would most likely create less power than required to compinsate the added wind drag. I know a lot of you have designed Pulse Jets completely around that Coanda effect although I'm not sure if anyone has actually built one that worked. I'm proposing using the Coanda effect to force a little bit more fresh air in front of both intakes of a HL and even more at higher speeds. The amount of power it would add would most likely be minimal if it was anything at all, but it would not create any more drag on the engine. Below is a drawing of my idea. Tell me what you think...
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steve
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Post by steve » Wed Aug 11, 2004 12:02 am

larry just posted this in the "Great Engines" thread:

http://www.pulse-jets.com/phpbb2/download.php?id=1409
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ZSartell
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Post by ZSartell » Wed Aug 11, 2004 12:10 am

It seems I am always one step behind.

jmhdx
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Post by jmhdx » Wed Aug 11, 2004 7:18 pm

Does a straight lockwood type engine, when travelling fast enough, have almost no output through the intake. I think when ram pressure is high enough all the expanding gases will exit through the rear. Mike Everman amongst others has blown out the flame before. If you want ram air without increases in drag it is the only way to go. A low speed u-bend or mushroom might be usefull, then move it out the way at speed.

Mike/stella artois.

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Re: Ram Air for a HL?

Post by Mike Everman » Thu Aug 12, 2004 3:50 am

Yeah, Mike! I want to put my thrust stand in the back o the truck and hang the engine off the side. At least I can get ram assisted data up to maybe 80 mph...
Mike
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hinote
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Post by hinote » Thu Aug 12, 2004 4:29 am

jmhdx wrote:Does a straight lockwood type engine, when travelling fast enough, have almost no output through the intake. I think when ram pressure is high enough all the expanding gases will exit through the rear.
My research shows that the exit velocity at the front of the L-H family is pretty high--well above Mach .5 at peak; the actual velocity depends on the pulsejet under consideration.

It's been well documented that increased forward velocity will boost the output of a straight L-H engine (due to the effects of ram-air at the intake) but it WON'T stop the thrust-producing effects at the front of the engine.

The simplest (and most effective) way to handle this effect (IMHO) is to keep the engine straight, and use a flow rectifier (the "recuperator" as used in the Escopette is the most obvious version of this) to get the thrust going in the proper direction. It isn't necessary to get the recuperator out of the way for higher speeds when a proper pressure-recovery duct is utilized.

An alternative method is to "u-bend" the engine, and then deal with feeding air to the front of the engine. There's good ways to do this, too- but I think the straight engine/recup combo is the way to go. Of course, this means the Chinese configuration (with its rear-facing intake) is compromised regarding this particular aspect of pulsejet performance.

M., are you watching?--how about chiming in on this?

As usual, I would welcome discussions about this particular design compromise.

Bill H.
Acoustic Propulsion Concepts

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Re: Ram Air for a HL?

Post by Nick » Thu Aug 12, 2004 9:36 am

Mike Everman wrote:Yeah, Mike! I want to put my thrust stand in the back o the truck and hang the engine off the side. At least I can get ram assisted data up to maybe 80 mph...
Mike , now that i want to see, how about a film?

Nick

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Re: Ram Air for a HL?

Post by Mike Everman » Thu Aug 12, 2004 2:39 pm

Now that I think about it, Nick, being in the back of my truck going 80 gives me the heeebie jeeebies, so I'll stick with calibrating my leafblower! Better chance of video, too.
Mike
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Re: Ram Air for a HL?

Post by Mark » Thu Aug 12, 2004 2:47 pm

How about a short test run while parachuting? You could get going 120 mph easily enough and test everything out. Just keep the flames away from your cords.
Mark

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Re: Ram Air for a HL?

Post by Mike Everman » Thu Aug 12, 2004 6:03 pm

bill wrote:My research shows that the exit velocity at the front of the L-H family is pretty high--well above Mach .5 at peak; the actual velocity depends on the pulsejet under consideration.
Bill, you need a pressure differential to make for the exit velocity, and the ram air makes for "quasi-hammer" pressure at the inlet. I have a graph around here somewhere, but memory says that it's less velocity than you'd think to effectively plug the intake during combustion. It didn't take that much air blown in to make the puffs out the front go away, according to the back of my calibrated hand, of course. (I think you were on speaker phone when I did that on Kazooenstein! LOL)
Mike
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Re: Ram Air for a HL?

Post by Mike Everman » Thu Aug 12, 2004 6:09 pm

Oh, yeah, which raises the question for me, and requires a simple test, but it seems you might want to move the fuel feed up the intake as ram air increases, so mixing occurs more to the front and combustion stays forward in the CC.

Bill and I noticed that the hot spot moved down the CC when we shortened the engine (49" starting length, 42" shorter length; essentially the exhaust throat gets moved from 29% of over-all length, to 33%). I suspect my next test is to use a fuel stinger and move it up the intake on this shorter engine. Hmmmm. Faaaascinating.
Mike
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Re: Ram Air for a HL?

Post by yipster » Thu Aug 12, 2004 7:12 pm

How about a short test run while parachuting? You could get going 120 mph easily enough and test everything out. Just keep the flames away from your cords.
first thing that came to mind was: if any time left in that jump you could once started try to turn the pj 180 degrees.
the guy that could not open his chute asked another privat going up fast but got he wasnt a paratroper but mineclearer.
did really see chutes go up once, when closer i saw they were launched as kites from jeeps

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Re: Ram Air for a HL?

Post by mk » Thu Aug 12, 2004 7:52 pm

hinote wrote:It's been well documented that increased forward velocity will boost the output of a straight L-H engine (due to the effects of ram-air at the intake) but it WON'T stop the thrust-producing effects at the front of the engine.
I'd agree to that opinion.
Starting my engines with the torch and the hot-air gun there is (now was...) needed an "overlap" for heating up. While forcing air into the engine, an unsteady airflow out of the intake was noticable (intake mouth was nearly completely covered with the flared nozzle!). This airflow even blew out the torch flame "without problems", when it got to close to the intake mouth.
These engines, I'd say, are rather "blown out" than "stopping" intake outflow through ram-air affects.

Well, some data or rather experiences from an aircraft or a car powered test would be interesting, of course.
mk

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Re: Ram Air for a HL?

Post by Mark » Fri Aug 13, 2004 1:13 am

I was thinking if Charlie the hurricane comes this way, I could do some ~110 mph wind testing with my Dynajet. The last good hurricane here, I smoked a cigar in the eye of the hurricane and the sun came out briefly. Speaking of cigars, Cuba is set to get hit, imagine all those rare, valuable cigars, hand-rolled on the thighs of virgins.
Mark

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Re: Ram Air for a HL?

Post by tufty » Fri Aug 13, 2004 7:40 am

Mark wrote:Speaking of cigars, Cuba is set to get hit, imagine all those rare, valuable cigars, hand-rolled on the thighs of virgins.
Mark
You evacuate the cigars, I'll take the virgins.

Simon

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