Most efficient vertical flight speed?

I stated, not implied.

Until now it was not even possible to judge if your profile was buildable.

Assuming 54mm solid, still probably not.

The fatter the rocket the less likely your 20 second burn is going to fly anywhere near vertical.

You have not stated you assume the use of active guidance.

I assume you at least are doing minimal mass, minimal drag minimal diameter configuration so perhaps it will only arch over after 17 seconds instead of 9.

My practical experience (I used to have a TRA CERTIFIED long duration motor BTW), is that there is a trade-off for performance and burn time and how vertical the unguided flight is.

I have found 15 seconds is stretching it.

Free advise.

We all know the impractical is optimal.

Wait till you see it in reality. :)

Reality bites.

I flew a flight with two E6's on a mildly windy day. I launched it slightly WITH the wind so it arced back to vertical. Each of the two motors were stepped thrust and 9 seconds burn. That's 18 seconds with two steps.

It was a record of 80ns 1992 M, but it was very difficult to achieve.

Good luck.

Jerry

There is nothing wrong with that. ;)

I'm amazed that you apparently came to such a profound conclusion using such a crude tool. You could probably do better using F-M, but I recommend that you use a RK-4/5 ODE solver.

No PDE's. Think in terms of MR/HPR solid rocket motors, except that we are going theoretical. It is an exercise to get you think about how the form of optimal thrust might change with different constraints.

You can't really design a motor to deliver optimum thrust, but there are some things you can do to get closer to optimum thrust. You can't really have thrust through a fixed nozzle at high constant ISP at both the high boost thrust and low sustain thrust. Of course in practice you get the initial boost from a stage, or strap ons. You could get constant ISP at constant chamber pressure and thrust, but even if you could essentially turn the thrust on and off, you would have transient loses. The 15 second burn time limit is artificial, but it comes from a real regulatory constraint.

You might be able to throttle a hybrid over a suitable range, but that is still a heavy clunky lower performance motor.

Realistically, you can optimize the initial propellant grain geometry to get a thrust profile that is better than nothing.

Alan

EACH E6 was an Aerotech 24mm 40ns E6 motor. E6-0 to E6-8.

Let's spoon feed the masses:

-Fred Shecter NAR 20117

Ok, but in your previous post you stated that:

"Each of the two motors were stepped thrust and 9 seconds burn. That's 18 seconds with two steps."

Am I wrong in saying that you are stating that the E6 motor in question has a burn time of 9 seconds?

A motor with a 9 second burn and 6N average thrust is a 54Ns 'F' class motor.

The file Fred just posted a link to states the burn time as 6 seconds.

Why I am bothered about this I don't know, but hey, this is RMR after all :)

Correct. I believe they are now on the Apogee website.

It used to be a USR relabel item.

E6 is its "name".

Good. They need it.

So in conclusion, said 'E6' is not actually an E6! I guess 'the average thrust is less than 6N' would have answered my question :)

Sounds like Rocket Services "F36" territory here Niall ;)

Fred Shecter posted a link to the NAR cert sheet on the motor.

Jerry

I view motor designations as having, in practice, a somewhat arbitrary element to them - rather like firearm cartridge "caliber" designations.

-dave w

Yup, and that data sheet did in fact describe a 38Ns E-class motor with an average thrust of just over 6N and a burn time of just over 6 seconds - an accurate designation.

Anyway, doesn't really matter an awful lot! As Darren said, check out the thrust curve of a Rocket Services 'F36' - I think that *is* an E6! (Just with a massive initial spike).

While from a 'purist' point of view the average thrust number should be accurate, for motors with high initial thrust an 'adjusted' or 'advisory' designation has its merits.

I believe that means the "new" version uses a different propellant than the "old" version.

I also flew pre-production E6's known then as E5's. I flew it in an approx 2.5" x 24" rocket which with very careful pad set-up went almost perfectly vertical, but the flight was slower than any I have seen since.

Gary was there. It was his prototype.

The rocket was later the first rocket flown at LDRS-1.

Jerry

That's 18

question has

Niall, Please excuse Jerry. He was mearly taking liberties with the truth as instructed by his co-worker in his company of less than two individuals.

steve

I'm amazed you can make that statement since you haven't seen the tool, nor have I haven't pasted any of the code. :-) Using ODE's (or going the PDE approach) have limitations via assumptions and simplifications you have to make. Using a finite interval method, it's very easy to adjust for atmospheric density, drag coefficent (as a function of Mach), propellant weight reduction, decreased gravity (for space shots), etc...

Dave

I should not have not have called your tool crude as I have not seen it. It may be quite effective, but your brief description of it did not convey its adequacy or effectiveness. I have to admit that I don't know exactly what you mean by your finite interval method. Nevertheless, I stand by my recommendation to sport rocketeers to use fourth order Runge-Kutta-Fehlbeg numerical integration with fifth order step size control to numerically integrate Ordinary Differential Equations, thereby solving sport rocket trajectory problems (an Initial Value Problem). It is easy to incorporated all the model featured that you mentioned and more directly into the differential equations without "adjustment".

Once again, even HPR models are not capable of space shots. You can model the gravity field if you want, but constant gravity suffices for sport rocket work, and even much of professional rocket work.

My "crude" comment was not intended as a put down. Rather, I am more impressed by the skillful use of simple tools and the drawing of insightful conclusions thereof, than by unskilled use of more sophisticated tools. Again, I have not seen your tool, so it may not be "simple".

Alan

Good point.

simplifications

No hard feelings. :-)

from a high altitude balloon before... (aka rockoon). Under the right conditions and with a little luck, it's possible to hit the 100km mark with something in the "L" motor range.

Dave