Sunday, April 18, 2010


I've written a very simple simulator to try and do some vehicle optimizations.
Using a very simple drag model... I used the data from page 16 of built a table of mach number and Cd and interpolated. (This is actual data from a 5" rocket, were building a 6" rocket so it seems reasonable)

One of the interesting results is this graph:

It shows peak altitude achieved (y axis in meters) piloted against the equivalent peak drag. The peak drag units here are equivalent velocity at sea level in m/sec. The peak is at 50500m and 303m/sec (165Kft and 677mph)

Another interesting result (from a slightly different run) I'm not using any real fancy integrator and the results vs time steps don't change much:

Time StepAlt

So this means for very crude integration steps you get reasonable results, thus allowing one to use the model for optimization seeking. Right now there are a number of limitations, the model assumes that the ISP does not change as the motor is throttled for peak drag limiting etc... so as I add more detail to the model it will be interesting to see what happens.

Sunday, April 11, 2010

Space Access 10

I had a great time at space access. It was strange to be showing a space access regular the plastic model of the 75lb motor I'm having 3D printed in stainless and the CTO of Lockheed interrupts and asks for my business card. The motors is a 50 to 75 pound regen peroxide hydrocarbon biprop. I've ordered one from the 3D printer and I'll show pictures when I get it. This drawing shows 4 of these tucked into a 6" airframe:

For those of you that follow the blog that was actually the only 100% new picture in my entire presentation. I also talked about restarting my composite tank work that I started in 2006 at the very begining of the blog. (Go back and reread the first few months)

The Technical plan going forward is in several steps. Working on a smaller scale I can do 100% of this plan within my current budget.
1)Build a 4 engine gimbaled monoprop that uses irrigation tubing and HPR style recovery. I expect this to take two months to get ready for first flight attempt, this puts it in the middle of summer so first flight might be delayed until september as FAR in summer is miserable.

1a)In parallel test the bi prop motor I'm having printed.

1b)In parallel develop composite polyethylene lined tanks.

1c)Build some small canards for the 6" airframe and see if we can make it glide with tanks empty.

In no particular order do the following:

Trade out the mono prop motors for the bi-prop. (I'll Probably crash the mono-prop so its probably a series of mono-prop then bi-prop.)

Substitute the composite tanks for Irrigation tubing tanks.(or alternatively put one of Steves Flometrics pistonless pumps in instead of the composite airframe.)

Fly the whole assembly to 100K ft

Fly the vehicle to 100K ft twice in one day.

Seems like a simple list its probably two years work.
The first unpleasant step is to clean up my Garage so I can actually work on anything.

Sunday, April 04, 2010

I hate painting...

I have done a bunch of stuff at FAR, but I've never done the traditional HPR rocket thing.
Some of the next steps (glide back, aerodynamic canard controls) will be done a bit easier with that sort of propulsion. So to be able to order/fly traditional HPR stuff I though I ought to get my Tripoli certification so I can just order HPR motors. Toward that end I built a Giant Leap Liberty 4 kit to do the L1 and L2 qual flights. The Local Tripoli club flew Sat and Sun this week, so I was trying to get it ready for Sunday. On Friday it was done, it just needed paint.

Did I remember to say I hate paint? I put a nice coat of high build auto primer on sanded it all off, repeat three times, its looking pretty nice in its gray primer. Then two coats of white base followed by florescent orange about 10pm last night. Then I went to bed, alas this morning it looks like on the those crinkle paint jobs the white was not dry enough and the orange crinkled.

I took my painting embarrassment out to plaster city to do the qual flights only to discover the motor vendor was only on site Saturday. Arghhhh! Oh and did I remember to say I hate paint.