Hybrids For 2015

Where did you find your polyethylene powder? Mostly what I've seen is either quite high prices or quite large quantities.

Gerald

I will have to look at the manufacturer. They make powders for powder coating/melt coating steel items like dishwasher racks. It was not a small quantity, I had to buy a 100 pound cardboard keg of it. That was almost 8 years ago and I'm down to about 20 pounds left.

Edward

I finished the required lathe portion of the machining for the coupler today. It still needs bolt/pin holes. That part weighs a bit more than I'd like at somewhere around 31oz. I may go back to it later and skeletonize it to drop a few ounces but I might just be lazy and leave it alone. The part is probably a bit more complex than average as it includes accomodation for a precombustion chamber with its own liner. The nozzle is completed. I haven't started the injector assembly, or the upper tank bulkhead assembly. When assembled this motor is going to be about 5' long.

I hope to have it essentially done in a couple weeks. Then I'll be looking for the first opportunity for a static test.

Gerald

Below is a picture of the "ignition" grain for my EX-Hybrid to be used with 54MM Skyripper hardware.

This grain holds 2 pyrodex pellets against the 3/8 nylon fill tube that the SR injector uses.



The wagon wheel grains will stack below these and I will probably weld them together with acetone.

PS. Anyone know how to edit the

Also can someone with a Skyripper54 motor measure the nozzle throat for me? I have misplaced that nozzle and need to make another one.

I can measure my 54mm SRS tomorrow. I would fill the central port of the pyrodex pellet with silicone. It will make them burn much longer.

Edward

jderimig said:

Also can someone with a Skyripper54 motor measure the nozzle throat for me? I have misplaced that nozzle and need to make another one.

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AlphaHybrids said:

I can measure my 54mm SRS tomorrow. I would fill the central port of the pyrodex pellet with silicone. It will make them burn much longer.

Edward

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I have one also. It is in new unused condition. I can check it this evening when I get home from work.

DRAGON64 said:

I have one also. It is in new unused condition. I can check it this evening when I get home from work.

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Thanks all!

The nozzle with my 54mm hardware reads .563 in the throat.

Mine measured 9/16 (.5625) at the throat.

Edward

DRAGON64 said:

The nozzle with my 54mm hardware reads .563 in the throat.

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AlphaHybrids said:

Mine measured 9/16 (.5625) at the throat.

Edward

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Thanks guys.

I'm ending up using bolts for pins in this hybrid. Not really my first choice but probably necessary given how I designed it. I have lots of bolts on hand, and nothing appropriate. Figures. So last night I ordered the bolts and a good tap as my taps in that thread were worn. Dull taps don't work well with aluminum. I'll likely be milling, drilling, and tapping this weekend.

Heck, I might even cast the first fuel grain this weekend. I'm ready to do that now and it is a much quicker job than APCP. I'm not doing anything fancy with the grain for the first burn. Not even any casting tube, just bonded straight into the liner.

I'll try to get some pictures sometime soon. It's starting to look pretty cool.

For those who have done EX hybrids - anodizing of any importance, or just skip it?

Gerald

G_T said:

I'm ending up using bolts for pins in this hybrid. Not really my first choice but probably necessary given how I designed it. I have lots of bolts on hand, and nothing appropriate. Figures. So last night I ordered the bolts and a good tap as my taps in that thread were worn. Dull taps don't work well with aluminum. I'll likely be milling, drilling, and tapping this weekend.

Heck, I might even cast the first fuel grain this weekend. I'm ready to do that now and it is a much quicker job than APCP. I'm not doing anything fancy with the grain for the first burn. Not even any casting tube, just bonded straight into the liner.

I'll try to get some pictures sometime soon. It's starting to look pretty cool.

For those who have done EX hybrids - anodizing of any importance, or just skip it?

Gerald

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You have any pics to share of your work?

Not yet. I'm doing the machining at a friend's place where between the two of us we have a decent small shop. He has an Atlas lathe and I a Bridgeport mill. My camera gear though is at my place.

I have one of my first 54mm hybrid motors - the I250 that the case has over 100 firings on it. Never anodized. Looks the same on the inside as when I machined it. The outside has some scratches, but still performs fine.

Edward

I was hoping that would be the case. Hybrid exhaust products and residue should be nowhere near as corrosive as APCP products. Good, then no delay or expense for anodizing!

I did run into one no-fun issue when doing the first test assembly. I machined the surfaces to have essentially zero clearance for maximum stability when the motor is used as the min diameter airframe. Unanodized aluminum galls unanodized aluminum very easily. They locked. It took a little work to get the coupler separated from the tank tube. Afterwards I took off about .0015" from the coupler (radius) and then there were no issues. I probably could have gotten away with only taking off 0.001".

Gerald

AlphaHybrids said:

John - I worked with a college group competing in ESRA this past year and they built a very nice hybrid. They did 3-inch subscale tests of many grains/fuels. They did do one of something very similar to the wax/wagon wheel grain. They found that they could get better performance from plain HTPB with 50% powdered wax in a finocyl shape. For the finocyl they used foam and melted it out with acetone after. I kept trying to convince them to do HTPB, Teflon and Magnesium.

Edward

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Edward,

I am thinking of a variant of your suggestion and wagon print in a different mode. I was thinking two concentric rings of wagon wheel cavities. The inner one filled with wax and the outer ring with HTPB with additives. The thought being having a high regression rate at the start of the burn and lower near the end to better match the O/F ratio as the tank pressure drops.

Any thoughts?

--john

I think that a simple geometry is much easier to control than having multiple types and bands of fuels. I've tried wax on the inside and HTPB on the outside. For the sizes we fly, I couldn't tell a performance difference. The college group did notice a big difference going from a single circular port to a finocyl port. I think that the regression rate would matter more when action time increases. Anything under 15 seconds or so and I go simple.

The average regression of a 50% powdered wax/50% HTPB grain with ~1 pound/second of oxidizer flowing was 0.128 inches per second.


Edward

AlphaHybrids said:

I think that a simple geometry is much easier to control than having multiple types and bands of fuels. I've tried wax on the inside and HTPB on the outside. For the sizes we fly, I couldn't tell a performance difference. The college group did notice a big difference going from a single circular port to a finocyl port. I think that the regression rate would matter more when action time increases.

Edward

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So is the finocyl port just a surface area to port area play?

How about a twisted finocyl to get a little swirl action?

Yes, you increase surface area of the port, but through the regression you can actually keep it surprisingly constant. On a 127mm motor I have the surface area only increases by 10% from initial to end conditions.

I've done a twist on them, didn't notice a difference. To get the most out of our hybrid motors w/o investing a lot of time in design there are four main things that you should do. Pre-combustion chamber, post combustion chamber, multi-orifice injection and a neutral grain geometry.

I'd rank the pre and post combustion chambers as something that you should do on each motor. I noticed a 10% increase in performance from a single center injector to multiple injectors. I have a spread sheet that calculates what I term active area, the area of nitrous readily available to combine with fuel. Imagine a garden hose of oxidizer, the stuff in the middle won't react easily because it is insulated. Break that into 12 1/8" holes and you can see how you have much more active area.

Edward

On an ISP basis I can see the utility of pre and post combustion chamber. My question is for a fixed length motor what is the better use of the volume, pre/post combustion chamber or more fuel/oxidizer?

Add length to the motor You would have to do some testing on the particular motor, but my guess is oxidizer wins out. You almost always have too much fuel. The college group cut out the pre and post combustion chambers to add more fuel in one test and then they added them back in the next test. I never saw the data from that test but I'm guessing it was significant enough. One caliber pre and 1.5 post is what It typically use. After 2 post you see diminishing returns AND you have to insulate that area well.

All of this may only add 10-15% more to your total impulse. The gains are small, but when you are firing a 20,000 Ns motor the extra 3000 Ns is worth it.

Add 5-10% oxidizer to your fuel and you can do the same with almost no modifications.

Edward

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?

Wax, HTPB, a bit of PVC. Run at a lower and stable pressure, no hybrid flatulence.



On the left, copper oxide, parlon, HTPB. On the right, Wax, Asphaltum.



HTPB, PVC.



HTPB, Wax.



HTPB, Zinc, Magnesium.

Edward, your motors are always so photogenic... now about those long lost videos. Do you have any images of the I-250?

Every image above is of the I250.

www.alphahybrids.blogspot.com has videos.

Edward

AlphaHybrids said:

Every image above is of the I250.

www.alphahybrids.blogspot.com has videos.

Edward

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Confused, are we jsut talking hardware? Otherwise, how many different fuels are there for the I-250?

This is all the I250 hardware. There is only one reload certified for the I250 and it looks a lot like the HTPB/Wax reload.

I rarely fly certified reloads, even my own. All of these are of research tests and flights.

Edward

AlphaHybrids said:

This is all the I250 hardware. There is only one reload certified for the I250 and it looks a lot like the HTPB/Wax reload.

I rarely fly certified reloads, even my own. All of these are of research tests and flights.

Edward

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That begs another question then; do you have any spare casting tubes that you could sell me? Or maybe you could source me what you have used so that I might cast some of my own reloads? email me if you could...

Here is a PDF with fittings that can be used for a pyrovalve. I've clouded the fittings. I've used these in my last generation of pyrovalve to hold a piston back using light oil. The plug melted through, released the oil, the piston dropped to expose injectors.

Edward

View attachment Parker Poly-Tite.pdf