Short Lady Build Log

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sid_raptor
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Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 4:48 pm

Hi all!

First allow me to introduce myself. My name is Sid. I have a degree in mechanical engineering from The University Of Brighton and i currently live and work in Mozambique.
I have access to a small workshop mostly used for industrial equipment repair. I have been interested in pulse jets since i was in school but never had the opportunity to actually build one. So a few days ago i thought why not build one now! After all i do have access to welding equipment!

So after searching through the internet and doing a little reading, i decided to build Larry Cottrill's Short Lady design.

I am going to post a few pics of my build in progress and the final results here and hopefully will get some good advice along the way!
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 4:54 pm

Here is what i have done so far!

I do have access to welding equipment but not much in the way of equipment for making stuff out of sheet metal, so ive had to improvise a lot.

I started with buying a long steel pipe for the tailpipe and a 1mm steel plate.

The first thing i built was the cone. I started by tracing the outline on a sheet of 1mm steel and made it slightly larger than the intended dimension.
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IMG-20140507-WA000.jpg
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 4:58 pm

Next, i cut the rough outline using a disc cutter. After that i used an angle grinder to sand it down to the proper dimensions and used a file to give it a smooth finish.

I was then ready to roll the cone!
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 5:02 pm

Now came the tricky part! I had never rolled a cone before and i had little idea what i was doing.
I started by giving it a little curve by bending it with my hands. Then i put a steel pipe in my bench vice and hammered the piece to give it a slightly better curve. I then repeated the process along with applying heat from a welding torch until i had a cone shape.
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IMG-20140507-WA0006.jpg
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 5:05 pm

After a bit more hammering to get the shape right, i tack welded 3 points on the seam to hold it in place. I then welded the seam in 2 passes using an electric welder with welding rods. I tried to be careful and not let too many welding beads form inside the cone but a few did turn up in the end. I am going to try to file them down a bit later.
After welding, this is what the final cone looks like.
Attachments
IMG-20140507-WA0008.jpg
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 5:09 pm

I then cut the tailpipe tube. I left it a bit longer than the design specified and i will correct that at a later stage. I welded the cone on to the tailpipe and it seemed to form a nice fit. I had filed the inside of the tail pipe at the joint with the cone prior to welding to form a smooth transition, but a few welding beads seemed to form there too.
Attachments
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 5:19 pm

And now for the dome!!!!

I cut a rough circle out of 1mm steel the same way i had done for the cone. I tried to sand it down into a somewhat circular shape using an angle grinder but it just was not working. I suddenly had a (Dangerous) idea and seeing no other alternative i tried it out.

Now, i have minimal experience working with sheet metal and i don't know if what i did was the correct way of doing things. I call this method the Spinning wheels of death and i do not recommend anyone try it without proper saftey equipment and enough room to duck or run should things go downhill.

First i took the roughly circular plate and drilled a hole in the centerpoint. I then put a bolt through the hole and tightened it with a nut.

Then, i put the nut into a hand drill and locked it down as tight as i could manage. I then put an angle grinder on the work bench, grinding disc facing upwards and got a friend to hold it tight and operate it.
I ran the angle grinder and spun up the drill and grinded the spinning circular plate on the spinning grinding disc. It was a bit scary but in no time i had a nice circular plate for the dome!

However i do not want to try this method again. If anyone has any tips on how to do this better without fancy equipment, I would really like to know!
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IMG-20140508-WA0001.jpg
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 5:24 pm

Aaaand Thats all for today!

tomorrow i am going to work the circular plate into the dome and start work on the intake pipe!

I have a few questions and any help would be appreciated!

1) Would small welding beads inside the CC hinder the performance?

2) I tried to make the transition from the cone to the tail pipe as smooth as possible but i did end up with a few welding beads there. They are a bit hard to reach and file down so will they make a difference?

3) How accurate must the curvature of the dome be in this engine? I read through the entire design and first build threads by Larry and Steve and i came off with the impression that it does not need to be perfect, just close enough

4) will a difference of a few mm between the plans and the actual construction cause problems?

5) Can i start this engine by using a blow torch to heat the CC till its red hot and then pumping the gas and air?
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Thu May 08, 2014 5:25 pm

Oh and Thanks a lot for having me on the forums!
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zono
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Re: Short Lady Build Log

Post by zono » Fri May 09, 2014 4:24 pm

Hi,

great to hear from new members! I try to give some answers :
1) Would small welding beads inside the CC hinder the performance?

no

2) I tried to make the transition from the cone to the tail pipe as smooth as possible but i did end up with a few welding beads there. They are a bit hard to reach and file down so will they make a difference?

no problem

3) How accurate must the curvature of the dome be in this engine? I read through the entire design and first build threads by Larry and Steve and i came off with the impression that it does not need to be perfect, just close enough

depends, in my opinion best shape of the dome is a spherical cut, because focused waves concentrate in the focus of the spheric radius

4) will a difference of a few mm between the plans and the actual construction cause problems?

yes, normally diameters are very critical, and tengths are critical. It will run, but with less performance

5) Can i start this engine by using a blow torch to heat the CC till its red hot and then pumping the gas and air?

better preheating through the inlet with your injector with low throttle (small fire)
good luck, zono
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sid_raptor
Posts: 31
Joined: Tue May 06, 2014 8:43 pm
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Location: Maputo, Mozambique

Re: Short Lady Build Log

Post by sid_raptor » Fri May 09, 2014 6:25 pm

So i was mostly busy with work today and did not have a chance to do much on the engine. Still i managed to start building the intake pipe.
Now i am a bit confused about this. i see 2 versions of the plans. one asks for a 21 mm pipe while the other asks for 19mm. I only managed to find a 20mm pipe and im using that. Will this make things harder in the future?

I know it looks a little ugly tight now and i have not finished grinding it down. Will try to have this finished tomorrow
Attachments
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Fri May 09, 2014 6:28 pm

zono wrote:Hi,

great to hear from new members! I try to give some answers :



good luck, zono

Thanks a lot for the answers! I plan to spend some time in the shop tomorrow and i should have some nice progress to show!

Hopefully i will get it to start soon!
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Wed May 14, 2014 5:21 pm

sorry for the lack of updates on the build! I have been busy with work stuff but i should have a lot of things to show tomorrow!!!!
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Sun May 18, 2014 9:34 am

Ok Here goes!

I have been pretty busy with work and other things but i did manage to get some work done!

First of all i would like to apologize for the sheer ugliness of the intake flare.....i tried to grind it down but this was all i got. The dimensions seemed correct though.

Apart from that, i managed to finish everything in the engine itself. Now i am going to build a stand and i am waiting for my propane tank!

If i try to run the engine on Butane, will it make a big difference?
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sid_raptor
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Re: Short Lady Build Log

Post by sid_raptor » Sun May 18, 2014 9:40 am

The dome on the other hand came out rather nicely! And this is what the engine looks like with all the bits and pieces attached....

I made the fuel line out of an old car brake line and used a regular car spark plug.
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