M15E--Doubled-Up!

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hinote
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M15E--Doubled-Up!

Post by hinote » Sun Jan 22, 2006 1:09 am

Here's the latest iteration of my M15E "simple-build" engine.

I decided to install a u-bend; the easy interchangeability of intake components was being degraded by the inability to take direct thrust readings. I didn't want to have to develop a decent flow rectifier ("recuperator") as part of the project--there's already plenty to do.

Although my larger engines have been difficult to mount when bent like this, the current engine is going to be really simple. It's an issue of the better inherent rigidity of the smaller tubing.

This motor is quite compact considering its ability to produce up to 12 lbf thrust.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."
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M15E ubend first photo.JPG
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Mark
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re: M15E--Doubled-Up!

Post by Mark » Sun Jan 22, 2006 1:48 am

That's a good amount of thrust I think. Not bad for the size!
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re: M15E--Doubled-Up!

Post by Mike Everman » Sun Jan 22, 2006 1:49 am

Very nice. What's the CC diameter again?
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hinote
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Re: re: M15E--Doubled-Up!

Post by hinote » Sun Jan 22, 2006 2:01 am

Mike Everman wrote:Very nice. What's the CC diameter again?
3-inch OD exhaust tubing, 14 ga.

ID is 73.0 mm.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

hinote
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Re: re: M15E--Doubled-Up!

Post by hinote » Sun Jan 22, 2006 4:13 am

Ben wrote:Wow, it looks small now that you've bent it. Even more impressive. I think it will fulfill its objectives nicely. Did you put the bend in a specific spot?

About the perfect size for a bicycle engine, too...
Velocities are lower, in the forward part of the "throat" tube.

I used all of the tubing that was part of the u-bend as shipped, and welded it to a 1-inch stub remaining on the forward parts of the motor.

It would seem to be better optimized with the bend a little farther forward--but the pictured result was just too convenient to ignore.

Now, I can give it a test run and compare it wth my baseline performance. It's going to be interesting.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

Zippiot
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re: M15E--Doubled-Up!

Post by Zippiot » Sun Jan 22, 2006 4:23 am

wut is the fuel? and the total length of the jet?
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hinote
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Re: re: M15E--Doubled-Up!

Post by hinote » Sun Jan 22, 2006 4:38 am

Zippiot wrote:wut is the fuel? and the total length of the jet?
Prop.

1525.3 mm.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

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re: M15E--Doubled-Up!

Post by Zippiot » Sun Jan 22, 2006 4:40 am

that is a lot of thrust off of a tiny pj with propane, major props man major props
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re: M15E--Doubled-Up!

Post by Bruno Ogorelec » Sun Jan 22, 2006 8:15 am

Very, very nice!

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re: M15E--Doubled-Up!

Post by mk » Sun Jan 22, 2006 12:14 pm

Amazingly amazing where your designs are developing to, Bill!

Interesting findings all over the place here. Man, when should I just find the time for running over the contents sufficiently?
mk

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re: M15E--Doubled-Up!

Post by Mark » Sun Jan 22, 2006 4:12 pm

One thing I like to do is a volume test; I don't know why but it's something that is easy to do and maybe there is something to be gleaned from knowing the volume of your device. I did it with my Dynajet - just unscrewed the head and with the flat of my hand sealed one end and filled it with water and poured the water into a measuring cup.
I also filled my little Logan with water one day. Because plumbing pipe is kind of thick, it was funny how very little water it actually held, less than 75 ml.
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Re: M15E--Doubled-Up!

Post by hinote » Mon Jan 23, 2006 12:02 am

hinote wrote:Here's the latest iteration of my M15E "simple-build" engine.
I decided to install a u-bend
Here's today's photo of the project.

For all of you who finish an engine like this and think it's time to go out and run it--I offer the following:

The mount for your engine is very important! It must absorb and re-transmit the forces of the engine, and allow for the substantial longitudinal expansion that occurs when it gets hot (this little engine expands about 1/2-inch, for example).

The mounting you see here is complete; it took about as long to create as the engine!

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."
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M15E u bent on mount 2.JPG
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re: M15E--Doubled-Up!

Post by Bruno Ogorelec » Mon Jan 23, 2006 10:53 am

A classy mounting, too. Bill, your engines are the Cadillacs of the pulsejet world by now.

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Re: M15E--Doubled-Up!

Post by larry cottrill » Mon Jan 23, 2006 1:50 pm

hinote wrote:The mount for your engine is very important! It must absorb and re-transmit the forces of the engine, and allow for the substantial longitudinal expansion that occurs when it gets hot (this little engine expands about 1/2-inch, for example).
Bill -

Something I've always wondered about, but somehow I've never (I think!) gotten around to asking:

On these 'bent' engines, is there any tendency for them to "straighten" (or otherwise distort) when hot? Or do they stay pretty much parallel (or at whatever small angle you manage to build them to)? Should you try in any way to support or align the overhanging part of the tailpipe, or just let it 'float'? Does it reliably stay perfectly aligned after several runs and cool-downs?

Obviously, the thermal expansion isn't going to be uniform over the whole tailpipe, since the temps will vary considerably!

Are you saying that this one actually expands & contracts 1/2 inch in its present, bent form (I would be astounded!), or is that the figure for its former, straight length?

I must agree that the "finished product" is very nice, incidentally - I should have said so before now.

L Cottrill

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Re: M15E--Doubled-Up!

Post by hinote » Mon Jan 23, 2006 4:03 pm

Larry Cottrill wrote: Something I've always wondered about, but somehow I've never (I think!) gotten around to asking:

On these 'bent' engines, is there any tendency for them to "straighten" (or otherwise distort) when hot? Or do they stay pretty much parallel (or at whatever small angle you manage to build them to)? Should you try in any way to support or align the overhanging part of the tailpipe, or just let it 'float'? Does it reliably stay perfectly aligned after several runs and cool-downs?

Obviously, the thermal expansion isn't going to be uniform over the whole tailpipe, since the temps will vary considerably!

Are you saying that this one actually expands & contracts 1/2 inch in its present, bent form (I would be astounded!), or is that the figure for its former, straight length?
Thanks for the compliments, guys.

I've attached several images, for purposes of discussion.

First, a detail of the exterior mounting at the u-bend of the Ecrevisse C. SNECMA did it in an elegant way, of course--minimizing the amount of metal used, and maximizing its structural effectiveness.

My experience with the u-bend has been documented before; I experienced a severe collapse there, during an extended hot run. Now, I use an exterior support across the legs of the u-bend to prevent that.

There's some similarity between SNECMA's mount and mine, actually; you can see the same triangulation in the base legs--to take the thrust loads out.

The other image shows a detail of the photo posted at the top of this thread; the articulating links shown are offset to a surprising extent, given the mild heat showing in the duct metal. In particular the link at the tail end (left) is pretty well deflected. My figure for expansion (1/2 inch) is a guess--but is probably about right, at full heat.

Larry, the tailpipe runs so cold it isn't structurally compromised; however, you have to be careful not to place the articulating link too far forward, or the overhanging weight will cause a reverse bend in the hot area further forward--just from the offset center of gravity.

I've experienced a severely bent-up motor, as a result of rigidly mounting it.

The depicted mounting system is quite adequate--but quite overweight, because it's built from hardware store angle iron. For application to an aircraft, for example--it could probably be made stronger but at something like 1/5 the weight by using proper chromoly tubing and sheet.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."
Attachments
Ecrevisse mount detail.JPG
Ecrevisse mount detail.JPG (36.19 KiB) Viewed 5821 times
art link detail.JPG
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