Planing for next years speed weekend, (1/2 scale Argus)

[erik]

Sorry i haven't responded before now, did have a lots of work and overtime.
This weekend the whole team met and discussed the project and different designs.
We made some changes:
First we are not going to use the ice yacht, instead we are going to mount the motor in a old stripped down and modified Yamaha et 400 t/r snowmobile.
Here is a picture, its not my picture but its the same model.


PyroJoe: With this new vehicle i don't think multiple engines is a alternative, and Johansson is right, there is many small design flaws in my last build that we hopefully is going to fix with this new design.
I am not sure , but i think a more easy starting design would be preferable because we are going to start and use the engine in cold weather.
So, do you think the design i posted will work well for a easy starting engine with a decent performance?
Here is a modified version with a flare on the tailpipe.
http://hv4all.com/pulsejet/2011/drawing ... 29rev1.PNG

Viv:
I don't think i have room for a full size engine, but i must say its tempting...

[PyroJoe]

I think you will be disappointed with the frequency, which will probably have the engine performing at a slow pace. I would shave some CC resonant volume and increase the tail as seen in the bottom modified one(below in the PDF).

I can't make the decision of what the power band/range should look like so what would be best is to start at tail length of 1700 mm and cut 25mm off at a time and take careful notes on ease of starting, throttle range, balanced with the thrust developed. You will need to decide which works best to fit your need.

According to the scaling it can run with a tail length as short as 1400mm, with overall length at 2300mm, but that is with a spot on valve/grid setup and very little range.

I know I mentioned it before, but the noise level will be considerable, even for a pulse jet.
(on a off chance that it hit peak power, the engine mounts would need to withstand approx. 1819 N plus some factor of safety)

[erik]

Thanks, i think i will give your version a try.
Do you think i could make the tailpipe 1400mm and then make a slightly larger pipe that's slides over it, so i can try different lengths from 1400mm to 1700mm by just sliding the pipe back and forth?
Do you know what frequency its going to operate on with the different lengths, so i can design my red-valves accordingly?

[PyroJoe]

The sliding pipe would be a good idea, you could also make it with a flare if you like. Frequency is a tough one, nothing is giving a accurate answer, most are showing in th 50cps range.

I suspect the resonant volume will try to cycle at around 70cps with a draggy grid setup, and it would probably be easy to attain up to 85cps with a moderately draggy grid. With a high flow/low drag grid it may shift higher by a considerable amount.

Of course as the cycles per second climb, so will the fuel requirements.

Best I can tell the lengths will only change a few cycles one way or the other. The grid drag represents the more difficult part to establish frequency. At least that is what I see from my perspective.

A clear tail recording of her first run will tell how she perceives the grid. Any idea of how much area the opened valves would represent?

Any one else want to take a shot at the frequency?

[PyroJoe]

Remember on the sliding pipe to have leeway for thermal expansion. Don't want to wrinkle/distort the main tailpipe.

[Rocket Man]

Thanks, i think i will give your version a try.
Do you think i could make the tailpipe 1400mm and then make a slightly larger pipe that's slides over it, so i can try different lengths from 1400mm to 1700mm by just sliding the pipe back and forth?
Do you know what frequency its going to operate on with the different lengths, so i can design my red-valves accordingly?

It is much easier to cut the tail pipe off than to make it longer or make a slide pipe. I would build the flare at the end of the tail pipe so it can be clamped on. Do a test run with a long tail pipe then cut off some of the tail pipe, clamp on the flare and do another test run. You can cut the tail pipe off several times and do several test runs using the flare each time.

Disadvantage to a short tail pipe is, engine is harder to start, engine may be harder to keep running.

Fast take off is the key to winning any race. Once your out front it is easier to stay there than to over take another vehicle.

[erik]

Hello again, i am back from the dead.
I just want to show my progress in this build.
The valve grid and first diffusor

[erik]

Machining the diffusors

[erik]

Some sheet metal work, starting with 5m2 of 2mm stainless steel.
Here is a link to our site.
http://svarthaletracing.se/

[Viv]

Wicked work Eric

Viv

[Mark]

Does it matter if you stagger the seams or not? On my tiny Bailey Jet I noticed the three sections the seams are staggered. And in this V-1 photo it looks like the seams don't all line up. Would some kind of fatigue resonance occur if they did?
http://en.wikipedia.org/wiki/File:V1_La ... uxford.JPG

[PyroJoe]

Looking good!
Is the area of the front square of the combustion chamber the same as the circle of the back?
How much area does the open valve grid represent when compared to the tail pipe area?
Wow thats a big engine.

[erik]

Thanks.

Mark: The seams will be stagger, in the picture the parts is not welded together, the tailpipe is actually hanging.

PyroJoe: Yes, they have the same area within about 5%
Open valve grid area is 550.8cm2 and tailpipe area 730cm2, so about 75%

Here is this weekends work, more parts for the diffusor grid, and my team mates made the first of 15 valve blocks.

[Mark]

Pretty fancy. Now for the reeds.

[PyroJoe]

Excellent.