Hybrids 2019

Joshua F Thomas said:

Is there a 'Hybrid Systems 101' thread or resource?

Not that I'm going to be using one any time soon, but relevant to my interests as a physics/chemistry major.

Click to expand...

Here is a good place to start.

https://www.aspirespace.org.uk/

not much is left for information
https://pratt-hobbies.com/

Putting a vehicle together to fly this hybrid this year (if weather and time permits...)





Burn time in the video was short due to problems we were having with filling (using chilled N2O and pressurant) where vent was getting blocked. Also filling from chilled N2O bottle is very difficult due to the N2O in the flight tank warming up and hence the pressure differential dropping very low.

Self pressurised version of the short tank (750mm) will be approx 1000N thrust and 8s burn time.

Initial assembly



Motor is integral part of the airframe, and since the CC is smaller than the tank it allows me to run a nice boat tail fincan design which will assist with drag reduction.

Cad model



Further development of this concept will be a longer tank (1800mm) allowing a much longer burntime and significantly increased altitude and velocity.

Currently working on Fincan, recovery hardware and electronics mounting.

Further static tests with HDPE fuel grain instead of PVC will be done as well prior to flight.

Very nice Strud! Would love to see that fly. All the best with the development of this beauty.

Hi voyager1, should be a fun one...

Not sure what's wrong with the images, only some of them are showing....

Some of it on the test stand





Nozzle

Where are you located?

Gerald

In the land downunder, where making your own APCP is a much harder option.....

strud said:

Hi voyager1, should be a fun one...

Not sure what's wrong with the images, only some of them are showing....

Some of it on the test stand

Nozzle

Click to expand...

Forum doesn’t like google drive, at least the mobile version.

I was thinking of pointing you to my own research hybrid thread, but it is locked up behind the Research forum. It is a chilled nitrous M, called THRP-1 (Tiny Hybrid Rocket Project).

If you make an opacified fuel grain of a mix of rubber of some form and wax such as Parrafin, you can alter the regression rate by altering the mixture proportions. An added advantage is the wax may form a thin film over the nozzle and provide a great deal of cooling. It works that way in mine. Mine does not have a post-combustion chamber. If the wax is beaded, the resulting mini-cratered grain surface during the burn promotes turbulent mixing and likely tones the nasty acoustics down in the combustion chamber, greatly smoothing the burn. Your hybrid shows lots of pulsing during the burn which is not unusual. The zero fog content (solids and/or liquids) in the combustion chamber gas mix tends to lead to that from all the research I've read. It's just like a liquid motor in that respect. In contrast, mine burns super smooth. Just something worth trying if you are going to be experimenting with grain material. Though it could also be you have borderline sufficient pressure drop through the injectors?

Nice nozzle.

Welcome to the dark side!

Please keep documenting what you are doing!

Gerald

https://www.rocketryforum.com/attachments/somewhat-assembled-resized-jpg.313745/
https://www.rocketryforum.com/attachments/coupler-nearly-completed-jpg.313930/
https://www.rocketryforum.com/attachments/injectors-installed-jpg.315124/
https://www.rocketryforum.com/attachments/tank-assembly-completed-jpg.315140/
https://www.rocketryforum.com/attachments/fully-assembled-thrp-1-motor-jpg.315412/
https://www.rocketryforum.com/attachments/3-29-2017-11-57-03-pm-png.315991/
https://www.rocketryforum.com/attachments/core-from-nozzle-end-jpg.315990/

Hi Gerald,

Looks like I need to get access to the research section then....

Pressure drop across injectors is > 300psi (Ullage > 800 and Pc 500) for that test burn.
I think that a lot of the instability comes from the PVC fuel and the lack of any damping mechanisms.

I intend to go to a swirl injector for next tests and change to HDPE in the short term. Longer term contemplating using a fuel similar to the team in the Netherlands ie majority Sorbitol with addition of wax and Aluminium.
Swirl injectors have shown in many papers to improve regression and reduce instabilities (will dig up some of the papers).

Darned near anything beyond blasting the oxidizer straight down the core is an improvement! Mine uses impinging streams. One person here uses showerhead which is probably better.

Is your 800psi measured or guesstimated from temperature, or assumed? Nitrous has a severe relationship between temperature and pressure. That's why I stabilized the pressure and temperature in mine (chilled), so I could get reproducible results. Plus it increases the nitrous density a lot so I get more oxidizer in the tank. It does make ignition a $%@#!

And yes, certainly making your own fuel grain with additives such as Aluminum or other metals will provide a metal and metal oxide fog in the combustion chamber which will help dampen the acoustic energy. I highly recommend it. But Al might not be the best choice in a small N2O motor. I expect most of it would get ejected as melted blobs rather than burned, robbing ISP. The gas characteristics are less optimal for burning than is the case for APCP so the aluminum will burn slower so it will need even more residence time.

Anyway so far I like wax beads in rubber. The burned surface in one of the pics I linked shows why. Flow down the core will be very turbulent. I don't need swirl or other methods of mixing the flow better. The grain surface does it for me. I haven't seen others do it this way but likely it isn't original.

I don't think you can get access to the Research forum if not a US citizen. Sorry. But it won't hurt to ask.

Gerald

Here is a chart from an old test where we ran a pressurant with regulator and chilled N2O. Injector was inpinged pairs.

https://drive.google.com/open?id=0B7tnRi_PndLeLVVqWmUxY0tnR2FTOHp2aVdqcE4tTkRnZks4

Some of that oscillation is from the test stand but some obviously from the motor.

I intend to investigate using chilled N2O and dissolved O2 as pressurant, basically a higher temp version of Nytrox. There is an improvement in pressurisation performance but a slight reduction in density....

As you say, unlikely that I can make it onto the research forum due to non-US citizen.

Will send you a pm

Shouldn't it be possible to mix wax-rubber, all-rubber, aluminum-rubber and pour a tequila sunrise?

Damping function, dwell time, nozzle cooling, small form factor.... I don't actually know what I'm talking about, just speculating.