Hybrid ignition questions - GOX

[bigandy]

Morning all,

First of all, I'm new around here. I came across the forum whilst searching for some information on Micro-hybrids, and there seems to be a wealth of knowledgable people here I've been playing around with small model rockets, and RC rocket gliders for a good few years, and I have decided that it is time to scale things up a bit, and start using some bigger motors. I have decided to have a shot at firing some Hybrid powered rockets, using the Skyripper 29mm casing to begin with.

I have a slight issue though, in that the preheater grains are pretty difficult to get hold of in Wales, UK. There is a UK supplier, but they cannot post them out, only use specialist couriers which cost many £! So, I'm looking at GOX type ignition. I understand the theory, but have never seen it in practice, especially on a Skyripper type motor (where the nylon fill tube must be ruptured by the heat of ignition). Does anyone know if this has been accomplished succesfully in the past? If so, what was the ignition system? I can't help think that the Hypertek high voltage style ignition seems quite neat, but will it ignite the PVC or Polypro Skyripper fuel grains? Or do I need something that burns a bit hotter to beginwith (like a E-match and wire wool coupled with GOX).

Finally, does starting a Hybrid on GOX, use much oxygen up? I can get hold of small canisters of oxygen, about 400ml at 120Bar, for a reasonable amount of money, but if it is going to take one of them per firing, then that is going to work out expensive. What sort of flow rate and pressure is normally used?

Cheers
Andy

 

[Gillard]

Hi Andy,

Welcome to TRF, there are quite a few Brits here.
Can't help you with the hybrid stuff, except to say that you are best off turning up to a club launch where there will be someone that flys hybrids and get them to talk you through it.
The next two big launches in the UK are IRW, which is up in scotland and is happening this week, and Midland Sky on the 17-19 September (in the midlands!).
Don't know if anyone at FOG is a hybrid flier
As a bonus, vendors will be at both events - Richard from Rocketstore is your best bet for hydrids.
Hope someone here at TRF can help you out with your questions.

 

[karlbaum]

I personally use pyro ignition. West Coast Hybrids has pyro free plans for monotube motors. https://westcoasthybrids.homestead.com/West_Instruction_Sheet1.pdf

I am no expert on pyro free but I would think that the combination of GOX and steel wool would creat quite a melting fireball since you have the fuel of iron and nylon tubing (nitrous fill line) and pure oxygen for an oxidizer. By the way, for an experiment take a 9 volt battery and touch it to steel wool and you will have ignition, add cotton and you will have a fire.

You will also need the proper ground support https://westcoasthybrids.homestead.com/new.html

You may want to start with 38mm motors so you can fit the GOX tube in the nozzle. Check out the nozzle throat diameter and nitrous fill line specs before buying the motor.

Also check out Rocketry Planet for another good forum.

Cheers!

 

[ROCKet STAR]

Hi Andy,

I know that there has been a fair bit of work done in the UK on hybrid ignition methods (i'm from the UK, i'm in Australia now though), due to the fact that there used to be much tighter restrictions on APCP and cutting up motors to produce preheater grains etc. I have heard of a number of people sucessfully using GOX ignition in monotube hybrids. I dont believe that GOX ignition uses a huge amount of oxygen, but the one thing you need to consider is the extra GSE required to achieve GOX ignition though. As well as the bottle of oxygen, you will need a regulator for it, a solenoid valve for initiating the flow of the GOX on the pad etc...

For my hybrids I use APCP preheaters as I find it much less bother. For the 29mm stuff you only need 24mm grains to make your preaheaters (I use blue thunder propellant). The 24mm reloads come in packs of three and you will get about 5 preheaters from each grain. So your pack of reloads will go a long way. I guess it just comes down to what you deem the most economical.

 

[WiK]

Just saw this post, must've missed it whilst at IRW! Another way to ignite them without having to use GOX, or cut AP grains, is PIC, a slow and hot burning fuse. We (just) managed to light a 38mm skyripper with it last week at IRW (pic). Of course, you still have the same problems with acquiring the stuff as it also has to be shipped by expensive hazmat courier.

If you're in Wales, maybe you could try getting along to a FOG club launch (https://www.fogrocketry.org.uk/) near Redwick? Or as Gillard suggested, the Midland Sky launch in a couple of weeks, which will be the best place to get ahold of AP grains or PIC.

Cheers,
Phil

 

[andytherocketeer]

As Wik says, quite a wodge of PIC and an e-match "worked". Not perfectly, but it lit. Apparently it seemed that the fill tube ripped out of the compression fitting (according to Colin), but I didn't see that close up.

I'd suggest the cutting a fuel grain and an igniter method, since this is what the SRS preheaters are afaik. Need an RCA still (in the UK), but 1 AP reload should last for many flights. Best to pick one up at an event.

As for GOX, you don't need much. I think the EARS GSE only uses small cans of GOX. Best to speak to Mike R. of EARS, since he specced and built it. I think it's designed for Hypertek hybrids, but instead of connecting to the Hypertek fillstem, you'd connect it to a (metal?) tube which goes up inside the grain alongside the SRS fill tube. Then you need space for ignition wires. Don't know if e-match in GOX would work? The usual Hypertek way is HV arc across bare ends of (cheap) twincore cable in the GOX flow.

 

[bigandy]

Hi folks,

Thanks for the input, it's much appreciated. I've ordered one of the little dispoable oxygen cylinders and regulators that are used in the micro welding/brazing sets (oxy-turbo sets) to have an experiment with differnet ways of igniting motors. The disposable cans are pretty expensive for the amount of oxygen they contain (about £20 for 110litres), but the alternative is hiring a cylinder from BOC at about £85 a year (assuming one fill of about 1100 litres of O2).

I've got soem e-matches and steel wool to try, and I have also rigged up a spare ignition from a model aircraft engine to try the HV arc method. I quite like the sound of HV arc ignition, something to do with danger I guess! I'll have to see how much GOX is used for each method, and decide from there, as I would really like to keep the motors pyro free to keep the landowners where I can launch from, happy.

Cheers
Andy