Re: Propellant Breakthroughs?

Well, my suggestion was with respect to folks who wanted a "low cost minimum GSE setup" for motors in the "D through G" (i.e., model rocket) range: my intent is to examine whether the traditional solenoid setup is inherently necessary in order to safely operate hybrids in this size range, or if there are ways to do without it. (I.e., I'm not trying to start a safety flamewar, or to propose avoiding necessary safety precautions, but to examine potential alternatives.)

It looks like the pressure ratings of the best available small bore nylon hose (DOT rated air brake tubing) are in the 1000-1200 psi range (for diameters ranging from 1/8" to 5/16")... copper "refrigeration" tubing, 1/4" OD x .030" wall, is rated at 1400 psi. I'd say it's a "wash" with respect to pressure rating; either should be adequate. Restraining the "away" end is prudent in any case, especially with a "remote tank" fill: even if the tank supply is successfully valved off, there's going to be some venting of the hose contents between the motor and the valve.

-dave w

Reply to
David Weinshenker
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Think how much nitrous would be wasted after each flight. 100'x 1/4" seems like quite a volume of gas to waste each flight.

Reply to
Dave Grayvis

Some people are actually trying to make a *living* selling this hardware. That means *realistic* markups over cost, or people go hungry.

Machine shop time is at roughly $50-$80/hour, depending on where you are. For small runs, some CNC shops prefer to do manual machining, rather than invest in the setup time for a CNC run. On the larger motors, a set of parts can easily take a manual machinist a couple of hours to produce--if they're doing a quality job. So that's $100-$160 just for the labour, and another $50 for material. So, where is the price gouging, exactly?

This reminds of the thread of a few months ago, where someone was whining that they shouldn't have to pay R&D costs, property lease costs, staffing costs, coffee, photocopying, and other costs when they purchase a motor. So, if that isn't factored into the cost of the product, how exactly are those costs going to get covered, while maintaining the viability of the business? It's not a charity...

Reply to
Marcus Leech

Dave, your basic quest is a good one, and I support it 100%...among other reasons, becasue I've been wondering whether I should put some money into the ProPoly 22mm hybrids and get them out on the market. If we can do a true model rocket hybrid (G or smaller, under 1 pound flight weight) then it will be a lot more attractive with minimalist GSE. I've put a lot of thought into this, but I am not really happy with anything I've come up with. I have an outstanding source for valves that are of excellent quality, but unless I can start ordering more than 10 at a time they're going to stay at $89 retail; facts of life. I even looked at putting a car door lock (worm gear) actuator on a manual valve out at the pad, but by the time you're through you've spent more than $89 for a cobbled-up setup.

This is going to be an interesting year for hybrids. Todd's SkyRippers are coming onstream, and I've been able to help Marcus get the PentaMAX line going (plus some other top secret projects we'll tell you about at LDRS...hee hee hee!). I would like to move to the 22mm line next, since Marcus came up with a very clever solution to the flow restriction problem. GSE is a big part of that, and I welcome your starting this thread. Comments are also welcome at the hybridrocketmotors Yahoo group, and once we get flyhybrids.org straightened out and back on the air there'll be a discussion board there too.

Doug Pratt up to eight working fingers on the keyboard!

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Reply to
Doug Pratt

no one is stopping you from making casing for sale, are they?

feel free to make an offer, some of us might buy.

somebody? get off yer lazy butt and do it yourself.

armchair entrepenuers, sheesh.

Reply to
tater schuld

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Reply to
Jerry Irvine

alternatives.)

Ahh... got it.

Minimalist Hybrid GSE for filling a hybrid needs to have a fill and dump valve (IMO)... and as Doug points out, these ain't cheap. (Doug's valves are the ONLY ones I've found that work well during long fills, and don't need an excessive amount of current). They're the best I'm aware of on the market, and I should've given a link to

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when I mentioned them. ;)

The only way I can see to reduce the cost of GSE is to investigate the idea of canning the 'fill process' at the launch pad altogether.... perhaps using a tank that is filled at the local hot rod store?

Something like a 'sneaky Pete or something...? I think they're something like 10oz and use nylon hose and would greatly increase the safety aspects.

This would eliminate the cost of a NOS fill tank (again, the most inexpensive and sexiest that I've been able to find were at

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). ;)

This would also eliminate the need for expensive valves, a fill tank, and long hosing... a savings of about $400... not counting the electronics to actuate the valves.

Reply to
Mark

I feel GSE is very low priced. If you can't afford it personally, get several in the loop to buy a club system.

that method has worked all around me for hundreds of miles.

Doug sells some of the best systems at a very low price guys.

Reply to
almax

What's a "Sneaky Pete?" I thought Sneaky Pete was booze that destroyed you the day after you drank it.

One approach for very small model-rocket size hybrids is to do without the dump valve, since they will vent themselves dry in under two minutes, but I don't like it because (a) it's a safety compromise and (b) people might be tempted to use it on bigger motors.

Thanks very much for the kind words. My valves are made by the guy who supplied valves to all the "Fast and Furious" movies. He's taught me a lot. We're working on something that is being field tested now, to solve the long wait for filling M motors; they're based on valves he has put in monster trucks.

Doug Pratt up to typing with seven fingers

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Reply to
Doug Pratt

Actually yes they are stopping people. Aerotech contacted a buddy who owns a machine shop and made a couple hundered of these and told him to quite selling them. We couldn't find a patent number on the casing but where told they are still a patentened part. We always shoot for $75.00 per hour machine time. There is nothing to these so I understand everybodys views, but I still think that they are way too high.

Reply to
Russ Wizinsky

Technically the motor cert is only good for the case type assembly it was tested with... after all, this is part of the "safety" certification, not just the grains. But it always has been a vague area of allowance at both NAR and TRA activities, to allow other case brands. Personally, I like PVC or composite wound cases, as to more fully comply with non-metallic content... and it tends to be cheaper by far... but that doesn't mean much considering some composites are stronger than some structural metals.

~ Duane Phillips.

Reply to
Duane Phillips

LOL... perhaps it is... but the 'Sneaky Pete' I've heard of is a small nitrous system installed into 'street machines'... hot rodders... very available... much used... the bottle is around $70.

Yeah... I'm with you... the safety issues are important to me. You already make the safest minalmist system on the market, IMO. Given the cost of the valves, I don't understand how you make enough profit on the MRL2 to stay in business... must be a 'loss leader'.

I really like the valves... I really like your GSE...

... in order to solve the long fill time vs. battery life of the GSE for the M fills, I've added a Capacitor and Resister to the electrical path of the fill solenoid. The valves need about 3 amps to engage (under pressure), but the holding current is very small (less than an amp). The Cap supplies the initial energy, the Resister limits the current draw on the battery to keep it open. If you charge the GSE battery first (with the cap), the first

3 amps are free. ;)

We've been able to do 4 M fills (and one dump) in several static tests on a single charge... and the charge was still decent on the battery... that's about 40 minutes of fill\dump time.

Would that include 'thumbs'? ;)

Reply to
Mark

Well, if you're thinking about "Dr. Rocket" and "Aerotech", it's really all the same hardware - the same production facility makes both of them, and they're identical until the final coloring and labeling.

Aren't some non-metallics more hazardous than many metals, if the case does burst? A flying spray of fiberglass splinters or PVC fragments could be more dangerous than a banana-peeled metal tube. (I believe this is why PVC pipe is considered undesirable for high pressure compressed air: if something does happen, sharp pieces go flying - and they're not visible on the X-rays...)

Suppose your non-metallic case got popped by a load of those spongy Texas J350 grains, for example.

-dave w

Reply to
David Weinshenker

What situations bring about the need for a rapid dump for safety reasons?

-dave w

Reply to
David Weinshenker

Really spicy food on an empty stomach?!?

David Erbas-White

Reply to
David Erbas-White

You mean those technically uncertified, rule breaking, example making, Texas J350s, which required improper handling via again uncertified field modification to be safe?

I don't think the danger level is more or less than with metal, what with proper safety distances; it has made the arguement historically moot.

These same safety rules also made the technically uncertified popping J350s "safe".

~ Duane Phillips.

Reply to
Duane Phillips

Well, yeah, but you don't need a solenoid valve for that!

-dave w

Reply to
David Weinshenker

Mis-fires at the launch pad... the heater grain not igniting... not following the checklist... the usual.

Ya gotta have a dump valve... one wants that NO2 out of there as quickly as possible in case of a problem... it's just not a 'safe situation'... 8lbs at

900psi... temperature\pressure sensitive anesthetic fluid\gas... the sun is rising... the temperatures and pressures are increasing... what to do, what to do?

Don't know how long 8lbs of NO2 would take to vent to atmosphere through a

3-5mil hole.... especially if the fill valve is jammed open because of a speck of sand... but it's a whole lot longer than I'm willing to wait! ;)

Maybe it's just the 'control freak' in me... perhaps I'm just anal... but if I want to tell that rocket to 'dump' then I need the capability to do so (for whatever reason).

'Safety First'.

Reply to
Mark

Very interesting. That is very similar results to the testing I did when I went to the 3000 mAh ni-mh battery in the RTLS. Four M flights seems like a Good Day to me! And there's always field-charging; the charge jack is wired directly to the battery pack, so a jumper from an external battery to the charge jack works fine, as we found out last year at NYPOWER with Robert DeHate's flight. I'm also playing with a solar panel glued inside the box lid. Hate to waste all that ambient solar energy!

I'm getting ready to announce a new valve option for M fliers. The BFV has more than twice the orifice diameter of the standard, and it draws

3.2 amps. Haven't tried it with an M yet, but it sure fills an H70 fast...like 40 seconds.

Doug Pratt

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Reply to
Doug Pratt

Funny thing about a battery sitting out in the sunshine not collecting any of it, especially in Arizona. Had the same idea when I saw the RV chargers at Harbor Fright.

That sounds encouraging. I thought some of the other fittings were going to be a limiting factor in fill rate. Had you tried a solenoid saver circuit to drop the draw down? Big -FILL- Valve? :o

Joel. phx

Reply to
Joel Corwith

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