Typical BP Engine Thrust Curve

[jqavins]

Maybe this is old news to most of you, and it surely is to some. But it's new to me.

Ever wonder why most BP engines' thrust curves look the way they do? With that big initial spike, then fairly constant thrust until burn-out. Sure, it's really handy for getting good rod exit speed, but how does it happen?

Well, while looking for something else, I stumbled on this NASA page with an animation and explanation that reveal all. And it's really simple. Almost unavoidable, actually.

 

[jmasterj]

That's a cool animation that nicely demonstrates how it works.

It is pretty simple when you think about it - more burning area equals more thrust. After you're through the initial core-burning part, it's a end-burner and the thrust stays pretty much constant for the remaining burn. Look at an A10 and an A3 and compare the depth of the core, and then the two thrust curves. Or just watch the animation you linked, lol.

 

[lakeroadster]

That's great, thanks for posting it Joe. I created some screen shots. The video steps through the animation so quick I had trouble viewing the profiles.

 

[lakeroadster]

So, not that I would ever do this, but wouldn't drilling a small hole up through the center of the black powder (like a composite motor) keep the preferred conical shaped profile moving upward and thus provide more power?

 

[heada]

Compare to a fully cored BP motor like the B14

 

[lakeroadster]

Compare to a fully cored BP motor like the B14

Rocketeer's Corner: Testing a bit of the past​

 

[lakeroadster]

Compare to a fully cored BP motor like the B14

Rocketeer's Corner: Testing a bit of the past​

View attachment 531946

 

[jqavins]

Yup. That engine was discontinued after I failed to get going in the hobby and before I became active 30is years later. I do wish I could get ahold of some B14-0s.

 

[smstachwick]

Yup. That engine was discontinued after I failed to get going in the hobby and before I became active 30is years later. I do wish I could get ahold of some B14-0s.

Advances in miniaturizing staging electronics could make the same kind of rockets possible with composite boosters staged to BP sustainers. There isn’t anything extremely high thrust in the B range currently but I’d bet a Q-Jet C18 could get one of those triple stacks off the pad. I suspect it will never be as simple as BP staging, though.

A C18-4 electronically staged to an A8-0 staged to an A8-5 would be an impressive build and a fun flight.

 

[cerving]

Advances in miniaturizing staging electronics could make the same kind of rockets possible with composite boosters staged to BP sustainers. There here isn’t anything extremely high thrust in the B range currently but I’d bet a Q-Jet C18 could get one of those triple stacks off the pad. I suspect it will never be as simple as BP staging, though.

A C18-4 electronically staged to an A8-0 staged to an A8-5 would be an impressive build and a fun flight.

You'd probably need to use an A8-0 in the upper stage too, with electronic deployment. A 5 second delay probably wouldn't be enough.

 

[jmasterj]

Once I need electronics, I'm not designing for black powder anymore. The nice part about black powder staging is the simplicity. Once that's lost, I'm out.

 

[jqavins]

Advances in miniaturizing staging electronics could make the same kind of rockets possible with composite boosters staged to BP sustainers. There here isn’t anything extremely high thrust in the B range currently but I’d bet a Q-Jet C18 could get one of those triple stacks off the pad. I suspect it will never be as simple as BP staging, though.

A C18-4 electronically staged to an A8-0 staged to an A8-5 would be an impressive build and a fun flight.

Also just one more reason to wish someone would import the Klima engines.Their D9-0 could lift some heavy multistagers off the pad quick, and it's a "standard" 18⨯70 mm.

 

[jmasterj]

Also just one more reason to wish someone would import the Klima engines.Their D9-0 could lift some heavy multistagers off the pad quick, and it's a "standard" 18⨯70 mm.

I think the barrier is Klima not wanting to certify them, not the lack of a willing importer.

 

[smstachwick]

You'd probably need to use an A8-0 in the upper stage too, with electronic deployment. A 5 second delay probably wouldn't be enough.

That depends on your parameters. I’m playing around with a BT-55 design in OR and with all the weight and drag, the ideal delay is right about 4 seconds. It might be even less when the second stage ignition system is factored in, but my experience with this kind of thing is insufficient to know how to simulate it.



I am almost certain that somebody else can think of a way of doing this that can squeeze out some more coast time, especially by replacing that bulky 9V and thus allowing a narrower tube. But from what I can see, -5 or even -3 is sufficient for this design.

Of course, this design loses much more by introducing complexity than it gains in potential. I think a 24mm lower stage with a BP booster motor is a far better option for most, unless one is looking for a difficult-on-purpose project.

 

[Tom Flint]

So, not that I would ever do this, but wouldn't drilling a small hole up through the center of the black powder (like a composite motor) keep the preferred conical shaped profile moving upward and thus provide more power?

You wouldn't increase the total impulse of the motor, but a cored motor would produce more thrust over a shorter burn duration. Estes has already done this with the A10, B8, B14, and partially cored C5 motors. If your drilled an endburning motor to make it into a coreburner, however, the motor would likely cato because you would increase the burning surface area without also increasing the nozzle throat area. Note the larger nozzle size on the A10 vs the A3, or the C5 which has a partial core to produce a higher initial thrust spike, vs the endburning C6.

 

[jqavins]

So, not that I would ever do this, but wouldn't drilling a small hole up through the center of the black powder (like a composite motor) keep the preferred conical shaped profile moving upward and thus provide more power?

Pet peeve: referring to this motor having more "power" than this other one. Really? Higher thrust, all else being equal, always correlates with more energy transferred to the rocket per unit time if your thrust to weight ratio allows for launch, but people often seem to mean more total impulse, or sometimes they mean more total energy. Please, either carefully use the right word for what you mean, or, if you're not sure which you mean exactly but just want to "more go", then say "more go", or "more oomph" or something like that.

 

[lakeroadster]

Pet peeve: referring to this motor having more "power" than this other one. Really? Higher thrust, all else being equal, always correlates with more energy transferred to the rocket per unit time if your thrust to weight ratio allows for launch, but people often seem to mean more total impulse, or sometimes they mean more total energy. Please, either carefully use the right word for what you mean, or, if you're not sure which you mean exactly but just want to "more go", then say "more go", or "more oomph" or something like that.

Come on Joe, it's a forum, not a college thesis or Professional Presentation. Sometimes I feel like blocking you, for bitch slapping me.

Geeze, get a grip.

 

[jqavins]

Sorry, I didn't mean it personally. I never mean to bitch slap anyone. I'm truly sorry that I've offended, insulted, or upset you. I quoted your post only because it was the one, after many others by many people, that finally made me feel compelled to post, certainly not to attack you.

As a forum, it's in large part about educating each other. We're the folks who are allowed to wear the T-shirts that say "Yes, as a matter of fact I am a rocket scientist." I just think we ought to discuss rocketry topics in a manner suited to that statement. This was a "rocket sciencey" thread from the start.

 

[rharshberger]

Sorry, I didn't mean it personally. I never mean to bitch slap anyone. I'm truly sorry that I've offended, insulted, or upset you. I quoted your post only because it was the one, after many others by many people, that finally made me feel compelled to post, certainly not to attack you.

As a forum, it's in large part about educating each other. We're the folks who are allowed to wear the T-shirts that say "Yes, as a matter of fact I am a rocket scientist." I just think we ought to discuss rocketry topics in a manner suited to that statement. This was a "rocket sciencey" thread from the start.

But most of us are in the hobby for fun, not being politically, grammatically correct or even using scientific/engineering terminologies. Not picking on you or anyone but OCD/pet peeves gets the best of us all occasionally.

 

[shockie]

I think the barrier is Klima not wanting to certify them, not the lack of a willing importer.

Klima told me it was the cost of liability insurance .

That might well make their products too pricey and therefore uncompetitive in pricing compared to.our domestic producers.

The Initial tests to just get all the DOT paperwork can easily top $10k.

 

[jmasterj]

Klima told me it was the cost of liability insurance .

That might well make their products too pricey and therefore uncompetitive in pricing compared to.our domestic producers.

The Initial tests to just get all the DOT paperwork can easily top $10k.

All kinds of barriers, I suppose. Maybe the next person who takes a boat to Europe can bring some back, lol.

 

[Ez2cDave]

So, not that I would ever do this, but wouldn't drilling a small hole up through the center of the black powder (like a composite motor) keep the preferred conical shaped profile moving upward and thus provide more power?

It would provide more thrust for a shorter period of time.

However, the diameter of the nozzle throat, if too small, might cause the motor to over-pressurize and CATO.

Dave F.

 

[mh9162013]

I think in most contexts, nitpicking is just that. But for rocket engines, nitpicking takes on greater importance.

For example, what is a more powerful engine? One that provides more thrust? Or one that has more total impulse? And trying to figure out what someone is really trying to say can sometimes be confusing

Although in the case of @lakeroadster, I think it was clear that he was using the term "power" in the context of an engine having more thrust or "oomph."

 

[lakeroadster]

Thread Drift Engage... Since you brought up this topic @jqavins

Low Power Rocketry.... Mid Power Rocketry.... High Power Rocketry....​

​

What does "Power" refer too?​

​

Should there be a push to "redefine" these to LIR, MIR, HIR? (My vote is no, hell no)​

 

[smstachwick]

Power is the ability to perform work at a specific rate. “More powerful” to mean “higher thrust” would be accurate, even if various other factors, like a reduction of total impulse from the removal of propellant, reduce the rocket’s altitude.

 

[Alan15578]

Pet peeve: referring to this motor having more "power" than this other one. Really? Higher thrust, all else being equal, always correlates with more energy transferred to the rocket per unit time if your thrust to weight ratio allows for launch, but people often seem to mean more total impulse, or sometimes they mean more total energy. Please, either carefully use the right word for what you mean, or, if you're not sure which you mean exactly but just want to "more go", then say "more go", or "more oomph" or something like that.

Sometimes standardized testing can be a bitch slap. They will ask you to explain somthing in your own words so that they know you understand something and are not just parroting what you read. But if you say "more power", that means something technically different and you may not receive full score points. I love a motor with more giddy-up that makes my rocket go like a bat out of hell.

 

[lakeroadster]

Sometimes standardized testing can be a bitch slap. They will ask you to explain somthing in your own words so that they know you understand something and are not just parroting what you read. But if you say "more power", that means something technically different and you may not receive full score points. I love a motor with more giddy-up that males my rocket go like a bat out of hell.

I think Kramer's definition of "Giddy-Up" just may be a bit different, than that of a rocketeer.

 

[mh9162013]

Thread Drift Engage... Since you brought up this topic @jqavins

Low Power Rocketry.... Mid Power Rocketry.... High Power Rocketry....​

​

What does "Power" refer too?​

​

Should there be a push to "redefine" these to LIR, MIR, HIR?​

Hmmm, that's a good question.

Generally speaking, HPR > MPR > LPR in terms of both thrust and total impulse, right? Sure, there might be an "MPR" motor that has more thrust than a "HPR" motor (even if it's just for a split second). But in that case, the MPR motor would certainly have lower total impulse than the HPR motor.

So is there a technical term that diffentiates, yet encompasses, the concepts of thrust and total impulse? Probably not, otherwise it wouldn't be a technical term (or term of art), right?

 

[rharshberger]

LPR, MPR , and HPR are generalized classes of rocketry. LPR is motors from A-D impulse, MPR is motors of E-G impulse, and HPR is for motors of H or higher impulse. Those impulse ratings are defined by the letter designation system for each letter grade of motors G motors are only in the range of 80.01 to 160.00 total Ns, irrelevant of the amount of giddy-up (thrust) they produce.

 

[lakeroadster]

LPR, MPR , and HPR are generalized classes of rocketry. LPR is motors from A-D impulse, MPR is motors of E-G impulse, and HPR is for motors of H or higher impulse. Those impulse ratings are defined by the letter designation system for each letter grade of motors G motors are only in the range of 80.01 to 160.00 total Ns, irrelevant of the amount of giddy-up (thrust) they produce.

Sure, right. No worries.

My point (other than the one on my head) is why the use of the word "Power"? Why not LIR - MIR - HIR? I guess because, arguably, the word "Power" rolls off the tongue and sounds better.