Fisher Research K3800

[RocketFeller]

This Saturday our upscale Dragonfly will go up at NXRS on a Fisher Research K3800. 1200 pounds of thrust at the start with a regressive burn should get her off the pad like a scalded cat.

The rocket is about forty pounds, so it should really move...

 

[djs]

Take Video? Also more info about this K3800 motor?

 

[amellrotts]

In for info

 

[RocketFeller]

There will be video, although probably fairly distant. We have an onboard camera, so hopefully we will get something good!

As far as the motor goes, I'm sure Mike will be able to give a lot more information than I can. It is a fast propellant (obviously!) and the grains are cut quite short (I believe there are seven). It is a 98mm case that Mike made for us. Something like 2200 NS impulse in .61 seconds. I am already clenching in anticipation...

 

[Binder Design]

Here's the Burnsim screenshot. 8 grains. Cute little motor. Scale is loaded motor weight.

 

[gerbs4me]

Can't wait to see the video of this flight!

 

[RocketFeller]

Mike is the only person I know who would consider a 98mm motor with a half ton of thrust a "cute little motor". It is about 1/4 as long as what he usually builds, but come on...

 

[Loki Research]

By chance, is the propellant color a mustard yellow or a rusty brown? ;-)

I'm assuming you've ground tested this Mike, but aren't you a bit concerned about the web thickness being greater than the grain length and having propellant shear away under the combination of high G load plus the high mass flow rate?

 

[CORZERO]

I have a bad feeling about this one... Please get quality video of the launch. And no smoke trail videos! Keep the vehicle in the frame as it ascends. Or as the pieces ascend, whichever...

 

[3stoogesrocketry]

By chance, is the propellant color a mustard yellow or a rusty brown? ;-)

I'm assuming you've ground tested this Mike, but aren't you a bit concerned about the web thickness being greater than the grain length and having propellant shear away under the combination of high G load plus the high mass flow rate?

My votes on the rusty brown Scott . I too am curious as to how the motor will not shear the grains .

Eric

 

[neil_w]

Sorry if this is a dumb question, but my LPR-oriented brain is having a hard time sorting this out: why one would want to use such a motor? That's 30:1 thrust/weight off the pad. Is the idea to just get it to vault off the pad (!) but then limit total altitude? What is the predicted altitude BTW?

 

[djs]

why one would want to use such a motor? That's 30:1 thrust/weight off the pad.

I've flown my wildman interceptor sport on an I800 vmax, which is like a 70:1 thrust/weight ratio. I can't answer to what RocketFeller is thinking, but my answer is "because it looks way cool when the rocket goes from there to.... way up there, in a blink of an eye". Sure- max altitude is nice, but you don't run a top fuel drag racer in the 24 hours of lemans either

@RocketFeller- do you have any concerns with such a high thrust motor and fin flutter, given the shape of the fins?

 

[CORZERO]

I've flown my wildman interceptor sport on an I800 vmax, which is like a 70:1 thrust/weight ratio.

I took a 2lb (built) Estes Phoenix to a 60:1 with a CTI H410 with no problem. Much smaller scale though. RocketFeller's rocket is on a different level in terms of size. The thing is huge. Like, really huge. In all dimensions. My concern is the motor and motor mount ripping through the centering rings, going vertical through the airframe and leaving the rocket on the pad. Unless some serious strength was incorporated into the design I fear structural failure of the airframe. 1200lbs of thrust unleashed in half a second is no joke. That's not an engine burn, that's a freaking controlled detonation.

 

[dhbarr]

Looking at the build steps that tank is going to crush a hole in the sky. Hope someone has a high-speed camera you can leave at the pad!

 

[ActingLikeAKid]

Excited to see the results.

 

[Binder Design]

I can't answer to what RocketFeller is thinking,

Motor is my call. I've had this design for a bowling ball loft motor for a few years, figured it would be a good test.

 

[Binder Design]

aren't you a bit concerned about the web thickness being greater than the grain length and having propellant shear away under the combination of high G load plus the high mass flow rate?

Not super concerned about it due to the short length of the motor. g's won't be that high comparative to what I'm used to seeing. We shall see.

 

[Binder Design]

I have a bad feeling about this one...

We really have no idea what it's going to do until we push the button. That's why it's called research. I wanted to do a long burn M, but Dan wanted to keep it conservative on this first flight, so I decided on a K with the initial thrust of an M. That way we can test the structural integrity for future bigger flights. That's how the motor decision was made.

 

[Binder Design]

Is the idea to just get it to vault off the pad (!) but then limit total altitude? What is the predicted altitude BTW?

If we were concerned about altitude this would be a much different rocket. It's only going about 2,000 feet.

 

[noffie79]

I'll be watching. Good luck guys!

 

[Binder Design]

I'll be watching. Good luck guys!

Thanks! The math works, we'll see if the physics can keep up.

 

[CORZERO]

This project certainly has my interest. Looking forward to the flight report and videos/pictures. Good luck tomorrow!

 

[pyrobob]

Count me in. This sounds really cool!

 

[RocketFeller]

I can't wait! Personally, I think everything will hold together, but I don't know much. As I have been telling the kids, it will be an awesome flight or a spectacular failure. If we wanted to just build a rocket and fly it that would be easy. This will be a good test of our design and building methods. This time tomorrow we'll know how well we did!

 

[djs]

So did this go up today? Did everything stay together?

 

[CORZERO]

Your audience patiently awaits...

This really is a worthy endeavor. We are curious. Please post a worthy after action report!

 

[burkefj]

Saw the flight, at the end of the burn it looked like it spit some some flaming grain pieces that made a nice firework show but burned out before they hit the ground, rocket coasted straight, backslid and ejected nicely with what looked like a very large rocketman chute, nice slow motion deployment. I dont think it made 2k feet but I'm sure Dan will chime in with data.

 

[rharshberger]

Saw the flight, at the end of the burn it looked like it spit some some flaming grain pieces that made a nice firework show but burned out before they hit the ground, rocket coasted straight, backslid and ejected nicely with what looked like a very large rocketman chute, nice slow motion deployment. I dont think it made 2k feet but I'm sure Dan will chime in with data.

Did it sound like a shotgun going off? That much impulse in that little time it almost has to be loud.

 

[burkefj]

Not to me, it actually looked sort of majestic, not scalded cat, it was very pretty even if not perfect motor performance.

 

[noffie79]

Not to me, it actually looked sort of majestic, not scalded cat, it was very pretty even if not perfect motor performance.

Glad to hear it! Looking forward to hearing some data from the flight.