Designing a 200lb thrust engine, anything majorly wrong?

mk · Post by mk » Thu Jan 22, 2004 10:21 pm

cbromano wrote:MK-
How did you fasten the spring steel to the valve plate?

I built 4 valve cases from 1mm steel (use stainless if possible), drilled 6 holes per case and welded M4 screws from inside on the cases (it's easier before welding up the cases completely). So they stand like bolts from the cases away. Welding from inside keeps the outer surface nearly untouched, so valves can close completely. [-> see attachement]

The valves are pressed on the cases by the retainer plates, which are fastened with some nuts (here: M4). You see that you will need some kind of retainer anyway. If you just fasten the valves with a screw, the valves would soon getting loose or could even brake near the hole, so it's better or rather necessary to press them along their whole "fastening line" on the cases.

cbromano wrote: Also- I am probably wrong but wouldn't the valves not carry enough momentum to go past a line parallel with airflow? I would think the retainers would not be necessary because the valves move a lot less then petal valves.

Yes, they do just go to a line parallel to airflow, but without retainers they won't bend! This means that they would simply snap behind the screw (or nut) and brake (experiments at piston engines showed this).

mk

cbromano · Post by **cbromano** » Fri Jan 23, 2004 5:11 am

Thanks for the help. The part about the retainer plates makes sense.

Did I read the caption on the image right? You said you used razor blades for the valves?

Thanks again-
CB Romano

mk · Post by mk » Fri Jan 23, 2004 11:51 am

Yes. If you could get some stainless steel (0.12+-0.03mm) it would be better. You get a lot of valve area unable to use, because of the holes in the razorblades .

Mark · Post by **Mark** » Sat Jan 24, 2004 2:24 am

mk wrote:Yes. If you could get some stainless steel (0.12+-0.03mm) it would be better. You get a lot of valve area unable to use, because of the holes in the razorblades .

Yes, but perhaps you get a sharper sound and shave using razor blades.
Mark

mk · Post by mk » Sun Jan 25, 2004 9:19 pm

THIS is the reason for beating someone by a nose!

Perhaps a razor firm would like to give some support...

Viv · Post by **Viv** » Sun Jan 25, 2004 10:22 pm

mk wrote:THIS is the reason for beating someone by a nose!

Perhaps a razor firm would like to give some support...

The "Gillete jet" love it:-)

Viv

TonyG · Post by **TonyG** » Sat Jan 31, 2004 9:16 am

Hi, finally got some time to sit down at my computer, staying busy between school and work.
I would like to offer a great thanks to the advice I have received here, as it will go a long way toward this project. All the tubes have been rolled and I should be able to start tig welding them together next week.
The fuel comsumption rate doesn't bother me, as this isn't something that I will be running too often, and fuel delivery will be by means of pressuring the gas tank with nitrogen, which I have a small bottle of.
I understand the concerns behind building one of this size, but I am one that likes to build things big.
I can't wait to here this engine fire up, I should have it done in the next couple of months if everything goes good without to many distractions. Yes, I don't get much time to work on this, only about 30 minutes or so a day and I have to use part of that time to set things up then do clean up afterwards.

If anyone cares to see a project that 3 of my friends and I built, check this link out: http://amarillonet.com/images/121703fn/9203_512.jpg We threw a 12lb bowling ball about 135 yards with the trebuchet, and built in about a week of late night work.

Viv · Post by **Viv** » Sat Jan 31, 2004 11:36 am

TonyG wrote:If anyone cares to see a project that 3 of my friends and I built, check this link out: http://amarillonet.com/images/121703fn/9203_512.jpg We threw a 12lb bowling ball about 135 yards with the trebuchet, and built in about a week of late night work.

Hi Tony, love the trebuchet I see you went for the later model with the swinging wait.

Did it move much when you let it go,

Viv

TonyG · Post by **TonyG** » Sat Jan 31, 2004 5:32 pm

No, it didn't move much at all, but it was bolted and welded to that trailer, which unfortunately we borrowed from a guy, and had to take the trebuchet off of, but we have another trailer coming that we can permanently mount it to. The guy in the picture is not me, but one of the others that worked on it.
I am working on a webpage that will give more information on this and my other projects, and will put a link to it when I am done.

Mark · Post by **Mark** » Sat Jan 31, 2004 5:57 pm

What is that long rope for the guy is holding? Is that the MSD, minimum safe distance for launching? I use to use a simple piezo sparker and 30 feet of wire when I tested some confined combustion metal devices.
That's a nice black and white photo, brings back memories in college, I spent 2 years shooting in B/W. Sometimes it seems better than color.
Mark

TonyG · Post by **TonyG** » Sun Feb 01, 2004 12:45 am

Yes, the long rope was the MSD for launching the trebuchet as part of the guidelines when we were using it for the school project, otherwise we just use a much shorter steel cable to pull the pin out, a long rope was just attached the steel cable to meet the requirements for the project.
The photograph was taken by a photographer from the local newspaper.