"I feel a great disturbance in the force!"
"I feel a great disturbance in the force!"
Kevin Trojanowski wrote in news:6k5ne.61946$sy6.5371@lakeread04:
The larger throat reduces the chanber pressure to compensate for the added burn area of the longer grain.
For a slot-core motor,the area of the ends rapidly lessens in effect.
kaplow snipped-for-privacy@encompasserve.org.TRABoD (Bob Kaplow) wrote in news:fS67cPWq+ snipped-for-privacy@eisner.encompasserve.org:
with the D15 nozzle throat diameter,I suspect?
What sort of core does it have? It's not an end-burner,is it? I thought it was a slot-core grain.Or were you referring to the 2 extra grain ends?
My point is that the F39 has the highest impulse and probably the highest chamber pressure of all the 24/40 loads.So a double D15 (if the nozzle throat was set to what an E28 is) would not exceed the case pressure limits.IMO,the key is the nozzle throat diameter.
Since the OP said he kept the D15 nozzle unaltered,he probably did overstress his casing.
To give an idea of how much of a difference it can make, I ran a sim in BurnSim of the "Fast" propellant that's included.
1" grain, 0.6" dia, slot 0.1" wide, 0.5" deep, nozzle throat 0.1" Max Kn 199 Max Pc 436.02 psiAdd a second identical grain and the numbers change to Max Kn 399 Max Pc 1466.37 psi
The different is significant
On the 2 grain, change the nozzle throat to 0.14" and the numbers become Max Kn 203 Max Pc 451.71 psi
-Kevin
I thought that HPR starts with J's and that G is the top end of MPR. Learn something new every day.
THATS WHY I HAVE TO YELL!
Hmmm, The F24 has more surface area...I've never noticed the nozzels being different...so maybe drilling the nozzel to the same dia as the F24 nozzel would be safe?
Cheers
Kevin Trojanowski wrote in news:IT8ne.61973$sy6.15271@lakeread04:
Yes,it doubles the burn area,and reduces the chamber volume(with no change in nozzle aperture).
So if he had altered the nozzle aperture to what an E28 reload used,the case pressure would have been acceptable? (comparable to an E28's case pressure?)
Let's calculate for a single grain with a length equal to the 2 original slugs,for both size nozzle apertures.Let's compare the double slug pressure to the single larger slug to see what difference the separate double slugs extra burn area makes.
snipped-for-privacy@mail.iinet.net.au (Impakt) wrote in news: snipped-for-privacy@news.iinet.net.au:
I thnk they are trying to tell you that unless you have a program like BurnSim,you have no idea what effect you achieve with the changes you make,and so;to not do this. You could make the nozzle TOO big,and actually lose performance,or not big enough and blow your casing apart.
In article Xns9667D82B8C84Fjyanikkuanet@129.250.170.83, Jim Yanik at snipped-for-privacy@abuse.gov. wrote on 5/31/05 7:16 PM:
Yes.
I think he means that grain is not cut in half (with the extra end area), it's one single longer grain.
Gary
All the MR reloads are C slot. And the F39 is barely an F, 49 NS.
The increase in initial burn area of 2 D15 grains is probably greater than the F39. A D15 has a .104 nozzle, or .0108 in^2 throat. An F39 is .166 and .0276 respectively, 2.6 times the nozzle size. It is amazing that it didn't blow.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
The F24 has LESS than twice the surface area of a D15 (length double, ends the same) and about TWICE the throat area. You fully doubled the burn area with no change in nozzle size.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
I'd have gone to the F39 nozzle, to account for hte extra expoed ends in the middle of the grain.
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
Bingo!
BTW, where does burnsim come from?
Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!
I don't know about burnsim but a few yrs back I picked up CP Tech's "HOW TO MAKE AMATEUR ROCKETS" book / video / software set 2nd edition.
------
(To Impakt) - If you're serious about modifying or building motors get some amateur books etc. and start reading! The info gained is invaluable and for the cost of a few blown cases... :-)
Clint
-Kevin
At a NAR or TRA sanctioned launch, any of these 6 scenarios requires NAR/TRA HPR certification. And the TRA is indeed present in Oz, so it could apply to you (if you attend a TRA launch)
In the US, items 3 and 4 require FAA waivers, so even if someone is running an independent launch, they must still abide by those rules.
Surely Australia has similar airspace rules and regulations, no?
Anyway, in the States, besides H and higher motors, there several other ways to be flying HPR.
Doug
kaplow snipped-for-privacy@encompasserve.org.TRABoD (Bob Kaplow) wrote in news: snipped-for-privacy@eisner.encompasserve.org:
IMO,with the E28 nozzle,that extra area would not make a significant difference. Or one could paint an inhibitor on the ends in the middle,glue the 2 slugs together.
That assumes that I'm using numbers that match the propellant properties; unless Gary wants to give me the a and n numbers for his propellant, what I've done is as indicative as anything else.
-Kevin
In article hutne.26810$iU.17218@lakeread05, Kevin Trojanowski at snipped-for-privacy@nospam.cox.net wrote on 6/1/05 7:42 PM:
For Blue Thunder, a = .0474, n = .321.
Gary
No..this was a once off thing because I was agro about geting 21 crap motors. I've never noticed the nozzels being different so I thought what I did was the same as joining two grains that come with some RMS reloads.
I like rocketry but I dont have time to get serious with any of it. Not to the level that other guys here are anyway.
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