Hybrids 2019

Previous Threads:

Hybrids 2015
Hybrids 2016
Hybrids 2017
Hybrids 2018

Why another year in hybrids? Especially with interest nearly non-existant? Because 2019 marks the 10th anniversary of the NAR & TRA winning the lawsuit against the ATF, where-by removing APCP from the explosives list. This is the proverbial line in the sand, marking the time which we begin to see the decline of hobby based hybrids. Why you say? Because, of the 4 or 5 manufacturers that supplied our hobby, there is one left. One who still believes, and is trying to support us, and provide new hybrids for the small market. I am referring to Contrail Rockets.

Recently I was browsing YouTube for the latest hybrid videos that had come out in 2018... contrary to the traffic here on this forum for the topic, hybrids, specifically research hybrids, are alive and well. Small research companies and universaties are still building, testing and flying the latest in hybrid technology. I have wtched videos on rockets flown on parrafin and HTPB fuels, acryllic, PVC and even coffee. Most interesting are the 3D printed fuels. Watching these videos late last night, I ran across my own video of a parrafin test I was a part of... so yeah, lets give this topic another year to discuss.

It would seem that hybrids are thriving in the research world, rather than the commercial hobby industry. So, if you are indeed researching hybrids and or tri-brids, please post up the research in the proper research forum. But be sure to share your videos and flights here in the Hybrids forum. So, without further ado:

Another flying season gone-by, and a new one is just ramping up... what are your goals for flying hybrids during the 2018 flying season? Anything and everything hybrid related is welcome!

* Motors
* Vehicles
* Ground Support (GSE)
* Research motors discussion (within the limits of a non-research forum)
* Electronics
*Altimeters; Vent sensors; GPS etc etc
* Commercial/Professional advancement hybrid discussion
* College development (i.e. TUDelft etc etc)
* Events/Launch coverage
* New flyer questions

I'm continuing my quest to complete my collection of all top-end 54mm injectors that were commercially available. I'm about halfway? The purpose, at some point, will be to do cold fliw comparisons.

So is it really only contrail, i know skyripper has been gone for some time, is there anything for Rattworks?

I've acquired an inventory of RATTWorks hardware, and am looking forward to building out and testing my GSE this spring. My hybrid airframe is mostly ready to go. Perhaps later this year I'll be ready for a flight. Why fly hybrids? Why not? I like new challenges.

I have downsized my hybrid goals; I sold off all of the smaller hybrid hardware (29mm & 38mm) as I just do not have the time or interest to build small dual deploy rockets for these small hybrids. I have lots of larger airframes, all of which are capable of the 54mm sized hybrids I have left, specifically the SkyRipper and Alpha Hybrid motors.

Tougher still will be venues local to me that will allow me to fly the motors, since the motors are past TRA cert, and NAR lifetime cert is in question.

Given a person has to be level 2 to fly hybrid anyway, just fly them at any TRA research launch.

Bill, when you get ready to do your hybrid I'd be interested. I don't make it to Battle Park nearly enough. I'm presuming that is where you'll fly?

I've got my own EX hybrid, though no GSE. THRP-1 thread on the research forum, and mentioned somewhere in this forum on a previous Hybrids of 201x thread. If I get the time and motivation I could finish the airframe and cast another fuel grain and preheater grain.

Gerald

ericm541 said:

So is it really only contrail, i know skyripper has been gone for some time, is there anything for Rattworks?

Click to expand...

I ran across this bit of info on the RATTWorks website:

Note: due to overwhelming demand in the aerospace industry, RATTWORKS rocket motors & reloads indefinitely out of production.

Click to expand...

DRAGON64 said:

I have downsized my hybrid goals; I sold off all of the smaller hybrid hardware (29mm & 38mm) as I just do not have the time or interest to build small dual deploy rockets for these small hybrids. I have lots of larger airframes, all of which are capable of the 54mm sized hybrids I have left, specifically the SkyRipper and Alpha Hybrid motors.

Tougher still will be venues local to me that will allow me to fly the motors, since the motors are past TRA cert, and NAR lifetime cert is in question.

Click to expand...

I must correct myself; I emailed TRA motor cert committee, and they have told me that ALL current hybrid motors on the cert list can be flown at launches. I made an assumption that motors had a 5-year cert terms before needing to be re-certified, and that is not the case. So yes, older SkyRipper, RATTWorks, West Coast and Alpha Hybrids reloads (if previously certified), are still accepted at current launch venues.

I asked arocket but they've been silent so far.

Is Krytox 205/206 the correct grease here?

I use 205 on my hybrids, this is what I purchased from Pratt Hobbies many many years ago. Pratt still sells it at $35 per .5oz

https://pratt-hobbies.com/proddetail.asp?prod=KRY-5

I've sold my 29 mm RattWorks motor hardware to fellow club members. I am focusing on my Contrail 38, 54 and 75 mm hardware from now on. I have had several great flights with the 38 mm 36" motor over the last year. I will be using the 54 mm 28" motor at our next HPR launch in late June. Hopefully the 75 mm motor will fly in September.

Here is my extended Double Shot 2nd stage on a Contrail 38mm 36" motor with a J246-HP grain and medium nozzle at our last HPR launch in April. The flight was with a redundant dual deploy configuration. A Featherweight GPS Tracker was installed in the nosecone. The darker mid section is the required extension to accommodate the 36" motor tube. The flights with this configuration have been impressive.

I still have a K cylinder, but due to the weight and keeping it cool in the summer, I have given up hybrids
I even designed and flew my own 38 and 54mm several years ago
APCP is so much easier to prep and fly

I've been doing a lot of motor testing. I don't fly rockets much, but I test a lot of motors. Lately I've been working on a 'boosted' hybrid. It starts off with a finocyl APCP motor that is cast inside a custom hybrid fuel grain. It burns for ~2.5 seconds with about 300 pounds thrust and then an engine controller opens a valve to the nitrous tank and the motor then transitions to around 6 seconds of 200 pounds of thrust in hybrid motor. I was looking for a way to fill up some of the core space in a traditional hybrid. Typically this means a large core to get the surface area required in a hybrid. I decided I'd try filling that space with traditional APCP and see what happens. So far I've just tested the APCP motor three times to get a thrust curve so that I can program parameters on when the nitrous valve will open.

Edward

How about 3D printed Grains of ABS, PETG, or PLA?

Some students I'm involved with did some 3D printed grains on an I-class two-ish years ago. They used 440cc nitrous tanks filled to 300 grams of N2O. I don't remember anything spectacular in terms of performance about the grains compared to machined plastics (PVC, ABS, Nylon, Delrin, HDPE, LDPE) I do remember that the grains were less dense than machined plastic grains. I also remember that they tended to delaminate and leave the wall opposite the test stand schmeared with plastic residue.

Edward

Any one here good at using Todd Moore’s hdas spreadsheet ? Or know of a different simulation tool?

I would like to try to reverse sim a motor that I built and flew this past weekend . I can’t seem to post video to share the results.

The motor was 3” diam. 6ft tall used an 18” pvc grain.

What was the ID? 2.75? How much room did your internals take? Off the cuff I'd estimate 3.5" for the nozzle, 2" for the forward closure, 1.5" for the mid-bulkhead, total of 7". 72"-18"-7" = 47" of nitrous oxide, less 10% for ullage space, 42.3" total nitrous length. That is 251.25 cubic inches (4117 cubic centimeters). Based on that nitrous amount I'd estimate between 6600-7200Ns total impulse.

Edward

Yes tube id was 2.75

Nozzle /nozzle washer - 1.68” long
Injector is 1.230” long
Fwd bulkhead is 1”.170 recessed the vent tube fitting to get maximum fill
Grain length was 16-3/4 ( not sure why I was thinking 18” )
2.740 diameter, 1.437 core wish I would have got a weight before we launched it

Burn time was 15 seconds.

That increases the volume to 273.5 cubic inches/4482 cubic centimeters. New range of 7100-7800 Ns. I'd estimate you had between 7-9 seconds of liquid burn and the remaining was blowdown of the vapor out of the 15 seconds. If you used a straight drilled orifice U/C valve I'd lower those values based on injector efficiency. If you used a RATTWorks star injector those number are in the ballpark.

Edward

I used 4 - 1/8 injectors canted outwards .

The 15 seconds was burn time during liquid phase , using the time on the video from first motion until you could hear it start the blowdown.

I’ll try to post the video later.

Just knowing hybrids, a fifteen second burn time with four 1/8" injectors and that mass of nitrous seems optimistic. You really can't tell when you run out of vapor by sound, a nitrous tank pressure reading is the best way because you can see the 'knee' in the curve as it runs out of liquid.

Your motor has a 1/4" diameter equivalent orifice. I have a motor with a 3/16" equivalent orifice and 5650 cubic centimeters of nitrous volume. On the test stand it varies between 9 and 11 seconds of liquid burn time depending on the nitrous starting density - I've fired the motor 5 times, thrust, chamber pressure and nitrous tank pressure recorded each time.

Your motor has a larger injection orifice and less nitrous oxide. Unless you are running a very high At/Ai it seems unlikely to have 15 seconds of liquid burn.

Edward

You probably burned out at a few thousand feet. Sound speed is approx 1100fps. You need to subtract a few seconds if you are going by sound, due to linear distance at the time that sound occurred. I'd say closer to 12 seconds liquid burn from the video. Accelerometer data will tell provide much better accuracy than my eyeball stopwatchless guess.

If your injectors used tubing, the actual orifice diameter may not be your injector diameter but the tubing ID.

Also temperature can make a considerable difference in the results. Pressure varies strongly with temperature for N2O if you don't otherwise controll it.

Also(#2) - 4x 1/8" injectors is not exactly equivalent to a 1/4" injector. The drag coefficient will be slightly different, all else being equal. The larger is more efficient.

Gerald

Gerald,

Area equivalent they are the same.

If you want to split hairs, then yes more smaller orifices don't equal the larger orifices due to friction losses. 95% of hybrid fliers don't put their motors on a test stand, so I'm making a generalization so it is more understandable. Most also don't do injector testing to measure the Cd and Cv of the orifices. Most hybrid fliers use the orifice diameter as a way to measure parameters.

The larger orifice is more efficient at moving mass through it, but I'd argue less efficient depending on the motor size. I'd rather use multiple .050 orifices instead of a single 0.25" orifice on most motors.

Edward

The wocket only went to 1800ft

It was 3/16 tubing .125 id


I’m just happy it worked, now that I know it works I can try to fine tune things and try to get real data next time . It was a fun upscale from the 6ft 38mm I did last year.

Danh said:

Click to expand...

Did that weathercock or was that the camera angle?

Edward

We angled it out that way ... away from the “lake?” And away from the flight line

Here’s a pic from liftoff .

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.