Hybrids For 2015

Upper bulkhead re-machined, though not finished. It doesn't have the double bolt circle threaded holes yet, or the external lightening. The through-hole is for the valve, and the blind hole is for attaching a bolt (or anything else) if desired.

When it is done I'll post some better pictures, including the valve.

Gerald

Gerald,

Do you have a complete sketch of how this is all going together. I'm not quite seeing the whole picture.

Edward

I never made a complete sketch. Computer models, paper sketches... Nothing I want to provide at least until the motor is proven to work! When I get the upper bulkhead completed I'll take some shots of the full set of parts (except injector assembly which I haven't started yet) which should show everything pretty well. With work expected to be heavy over the next few weeks it might take me a week or two to get there. I'm really only getting about one day to machine each week.

The motor tube is in two segments. The lower segment - the combustion chamber - is shown in my post #125 on this thread. At that point the coupler was not fully machined. The portion showing machining on the outside was the part that plugs into the top end of the combustion chamber. Later I showed the more complete coupler. The tank tube looks much like the combustion chamber just much longer at 40 something inches. It plugs onto the upper half of the coupler. The bulkhead from a couple posts back plugs into the top of the tank tube and is also retained by bolt pins. The nozzle is much like any commercial graphite full diameter nozzle for a 76mm motor, except I re-machined it to my specifications. This gave it a shorter throat (perhaps half commercial length) and a much shorter overall length.

A custom phenolic liner (same size as normal 76mm) goes in the combustion chamber and has the fuel grain cast in place. I haven't cast it yet as I need to make casting bases and get a mandrel ready, and get some lamp black. Going by memory, the liner is 13 7/8" long but I might be mis-remembering the inches part.

A roughly 2" section of 54mm custom phenolic liner (I forget the exact length offhand) is used for a short precombustion chamber in the bottom side of the coupler. I am planning to line this with a thin layer of a smoke formula for a little extra preheating for the first second or two of the burn. Being a chilled nitrous system, this motor may have ignition stability issues otherwise. Or it may be fine without it. I'm not using extreme chilling.

There will be a valve on top of the upper bulkhead which sets the flight tank pressure and therefore the nitrous density and temperature once the tank is filled and allowed to reach steady-state conditions through bleed-off / chilling. It's wasteful of nitrous but it is a simple way to refrigerate it. More advanced would be to cycle the boil-off back to a heat exchanger to pre-chill the input nitrous. That would greatly up the efficiency. If I do a larger version of this motor I may consider doing that.

There is a small lip at the bottom of the motor tube plus a groove for an optional spiral ring. So it can be retained like normal from the rear for sticking in a bigger rocket if desired. Or a fin can can be slid on for minimum diameter flights.

When assembled, the motor looks much like a Contrail 76mm motor, differing in the number and type of bolts, and the lengths of the tubes. Internal details are of course different. This is a little bigger (and likely lighter) motor than Contrail's largest 76mm setup, and should give more total impulse.

Gerald

PS - The tank should be somewhere around 3700cc capacity and the nitrous is densified somewhat by chilling a bit. Quick back of the envilope computation... I should compute out the real volume as-machined. External dimensions are not much different than Contrail's 75mm longest motor - just a tiny bit longer for the tank and of course the valve sticking out the end. It is closer than I'd realized. The main difference is the thinner walls so more tank volume and less tank mass. Although, I wouldn't be surprised if my coupler weighs more as it is longer to stabilize the tubes better for minimum diameter projects. Overall the motor will be lighter. Anyway it should be a small M with unenhanced fuel grains, ballpark M1000 ignoring the tail of the burn.

jderimig said:

Edward,

Putting performance aside, what about effect? Would a heterogeneous fuel like wax or htpb give any additional "excitement" to the burn? How to wax fuels and HTBP fuel compare in "coolness" factor? (I am guessing MagTef is really cool).

Edit: here's a pic of my hetereo grain idea. Outside section would be HTPB. What could I put in the wagon wheel sections for burn coolness factor?

Click to expand...

Have these grains been tested and/or flown yet?

DRAGON64 said:

Have these grains been tested and/or flown yet?

Click to expand...

Grains are made and hoping to fire to fly em Oct or Nov.

Well, I've used a K bottle (75 pounds) of nitrous testing. I've decided that I really don't care for building rockets, just making motors. I've tested the hybrid with a 4 pound Nitrous tank and 7 pound Nitrous tank. Performance was good and now I want to try a 12 pound tank.

Edward

AlphaHybrids said:

Well, I've used a K bottle (75 pounds) of nitrous testing. I've decided that I really don't care for building rockets, just making motors. I've tested the hybrid with a 4 pound Nitrous tank and 7 pound Nitrous tank. Performance was good and now I want to try a 12 pound tank.

Edward

Click to expand...

A K-bottle? You have been busy. My daughters marching band season comes to a close today with her final competition, and then I can get back at it!

Yea, I've had some time since September and found a test site that is much closer than before (15 minutes away). I did 4 tests with the four pound tank and then 6 with the seven pound tank and then did two more with the four pound tank. So far everything is looking good. I just need to order the 12 pound tank and machine a new casing (5" vs 4") before I test that. Maybe over the winter I'll build a rocket for the four pound tank.

Edward