Jims Little 3 Lb Thermojet

[Eric]

Your engine is the slight deviation based on the materials I had at hand. The intake is from .44" ID tube instead of the plans .50" ID. So about 1/16" of an inch.

Though it probably runs like Mag's .50 engine with out the flare, without the flare they will probably draw the same volume of air.

Eric

[mag]

The Exhaust on my engine is flared but the intakes are not until now, maybe I do it someday. Let´s wait what frequency mk is telling us :D

And for the part what Im doing with it, Im not a modell plane builder so Im doing just the testing thing. I will maybe sell it to a friend which is as model plane freak.

[mk]

#####

Note because I cannot edit my post anymore:

The formerly send soundfile analysis might be in error wrt. frequencies of larger order. Especially the closed pipe frequencies may be affected!

As said, it was my first attempt.

#####


From the new video provided by "mag", the OCF peaks at 219.63 Hz. With harmonic content visible up to the 16th (!) order. Now this likely to ba a result of the staedy-state operation for the suspicious, but constant, fueling rate.

Larger differences by changing frequencies could be well surpressed due to the longer, warmed-up steady state operation.

A beat frequency is still superpositioned, and about in the same range as in the earlier records.

So far for now.

Could you please measure the length of your engine, "mag"?

[mag]

thanks mk, complete length is 56cm. The Engine eric build for jim is a little bit faster cause of the shorter length i think.

[Jim Berquist]

Eric: Class Room " Thermojet 101" The processes there of

Make this thread a class room so we can all learn.

We can do the experiments with the augmentation. We could do the things you did not have time for......

MK: can do his Acoustic evaluations.

Mag: Can improve his Engine and we can all learn! I can improve my engine and learn.....

Your only task would be to assign a task and evaluate results.

Jim

[Eric]

Also once you get the flares on the intakes and get it running at peak performance it will run a bit hotter and pick up in frequency too.

I will think of some other experiments you could do with the engine.

Maybe use it to cook some shishkabobs with it, the pressure waves from the exhaust tenderize the crap out of the meat, and yes I have done this myself :)

Eric

[Jim Berquist]

Eric:

How do you handle all of the people from Canada at the lake about 5:00 pm ....

White Base in foil takes about 10 minutes per side....

If you stuff them with garlic and onions could be a bit longer..

You do have white bass in pennsylvania don't you......

Jim

[Jim Berquist]

Eric:


Seriously

Give us ideas on how to make them blast!!!!!!

I will give it a shot! And do my best. All you have to do is add directions and suggestions....

You are a Teacher, You Just Don't Know it Yet!!!!

Jim

[thecheat]

just a note... my PJ is starting to take shape! I need ONE item.... a big enough piece of 20gauge sheet metal.... Besides that, I'm finding the fabricating surprisingly easy! Well done Eric! With the help of cone-layout and some scissors, a pipe and a vice, gloves and a hammer, the pieces take shape pretty easy!

Here are some pictures of the pieces, they are: intakes, Cone for CC to tailpipe, CC, tailpipe flare.

PS: I'm getting better at the welding!

[mk]

As suspected (red letters) before, my extracted closed pipe frequencies are more and more seeming off. Hmmm, learning by doing. I have to check and evaluate that again. Unfortunately I do not have much time to spend on pulsed combustors right now. However the lower end open pipe frequencies, together, with OCF appear to be correct.

[Jim Berquist]

The cheat:

Looking good to me!

What do you need to complete it? Materials for the tail pipe?

After you complete yours, we will have three to compare on runs. How long did it take you to role the intake tubes? Did you cut to length and role or role and trim as required? I have never done it?????


Jim

[Jim Berquist]

Thecheat:

Can't you find some .5 inch intake tube?

Looking good!

Your intake tube is a bit ruff on the out side! Clean it out with a rat tail file on the inside..

Make it run!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I wish I could weld as good as you do!!!

Mine has spatters and junk

Lots of fun HHHeeaaa?

Jim

[thecheat]

Lotzes of frustration! (note that I have never even gotten a jam jar to get selfsustaining... meh)

Ok, pictures! I've gotten the jet together, did a trial run, and... it won't self sustain! Actually, it won't get to combusting properly either... with the forced air.

I am using a shopvac for a forced air source
I am using roscoinjectors (please check pictures)
I am leaving the sparkplug on
The dimensions should be near to exactly the specs (I'll check when it cools)
The CC WAS getting very warm (discolored and smoked off any spots of paint very quickly

What might the problems be?





Here's what I'm getting, the air is applied, I turn up the gas (with spark on) it gets to a point and BANG! then some thrumming (quiet) I continue to turn up the gas until the engine blows out. Turn it back down, and find a spot where the thrumming is loudest. The engine gets REALLY warm, and continues howling. Once or twice it stepped up a couple notches or so... but even then, not close to what I think it should sound like.

I'll post a vid in a minute or so... anyways, I really want to get this thing working, thanks for any help in advance!

PS: oh, and the intakes took only a minute to roll, they were pretty easy!


EDIT: here's a vid...

http://s19.photobucket.com/albums/b154/ ... trial1.flv

[Eric]

It looks and sounds good, just need to do a few small things differently to get it going.

First if you have a nozzle for the shop vac, the kind with the skinny slot opening that will cause the air to be blown out at a much higher speed, that will give you the starting air you need.

Also the injectors might need to be positioned near the front of the intake, that way they have more length to mix the fuel in the intake and wont take up a lot of the intake area.

When you get the higher starting air speed, you will be able to turn the fuel up without it flaming out. The main problem was you werent getting fast enough air, so the quantity of fuel you could give it was rather limited before it would go too rich.

At the point of 1:30 in the video you had it to the point where it was almost about to run, just need a little more fuel and the buzzing will be louder and stronger, and much more smooth, and a little more beyond that and it will take right off and sustain and then you will be sure it is running, if people run away from it, it is running :D

Jam jars can be quite a pain, I can turn a straight tube into a pulsejet easier than I can get a damn jam jar to run. Its always either too humid, too cold, or the planets are not aligned right.

Eric

[Eric]

Oh yea, the injectors are fine for getting it running, but if you smash the ends totally flat with a hammer, and then give it a few taps on the edge you can get them to open up so that you have a very thin slot.

The tighter the slot the more speed you get from it, and the better the mixing will be, but you have to keep them open enough that you get fuel.

You should get it going the next attempt!

Eric