Two D15 grains makes a ???

"I feel a great disturbance in the force!"

Reply to
Alan Jones
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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.

Reply to
Jim Yanik

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.

Reply to
Jim Yanik

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 psi

Add 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

Reply to
Kevin Trojanowski

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!

Reply to
Impakt

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

Reply to
Impakt

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.

Reply to
Jim Yanik

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.

Reply to
Jim Yanik

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

Reply to
Gary C. Rosenfield

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!

Reply to
Bob Kaplow

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!

Reply to
Bob Kaplow

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!

Reply to
Bob Kaplow

Bingo!

BTW, where does burnsim come from?

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Reply to
Bob Kaplow

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.

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Has some great computer programs and text info and is a great place to start for beginners like me. For for the price (Cheap) it's well worth it.....a bargain even.....A wealth of info.

------

(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

Reply to
CJC

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-Kevin

Reply to
Kevin Trojanowski

  1. Generally, HPR starts with H motors (>160Ns). But there are some other scenarios considered HPR.
  2. Any single motor with more than 62.5g of propellant (the case of the G33)
  3. Total (combined) motor propellant mass > 125g (eg, cluster)
  4. Total rocket weight in excess of 1500g

  1. Motor with average thrust in excess of 80N (eg, F101, G125)

  2. Total (combined) impulse > 320 N (eg, cluster of three G80's, which also exceeds the propellant mass threshold)

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

Reply to
Doug Sams

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.

Reply to
Jim Yanik

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

Reply to
Kevin Trojanowski

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

Reply to
Gary C. Rosenfield

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.

Reply to
Impakt

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