What Are Our Motors "Missing"?

[ClayD]

That page isn't really a good source. Solid fuel is actually much better for long-term storage than liquid fuels are, so storability is an advantage for solids. In addition, liquid fuel boosters are pretty much never reused, while solid fuel boosters are reused already (for example the shuttle SRBs). In addition, not all liquids are throttleable, so they aren't necessarily variable thrust.

Basically, that table is very questionable, and several of its statements are just wrong. That isn't too surprising either, since it just appears to be someone's personal webpage. It does have links to sources, but its sources are broken, so they aren't helpful at all.

We agree..
yeah, thats the google result that has fuel consumption as a disadvantage for solid rockets.

 

[ClayD]

Solid motors are generally good for large amounts of thrust over short amounts of time...the shuttle SRB's give 80% of total liftoff thrust to get the vehicle going to the upper atmosphere, and the liquid engines burn much longer to get the shuttle to orbital speed...im sure there are many engineering equations that are used to figure out the best thrust over time to go into orbit, but i don't know them. Look at the Delta IV heavy...it uses additional liquid engines. It just depends what type of motor is best for the application

ISP is literally a comparison of the impulse/weight of a propellant. Sometimes engines will say theoretical ISP, which assumes perfect conditions. Since this is never the case, the delivered ISP is what actually is delivered. Then there are things like vacuum ISP. Rocket motors have an increase in thrust, for the same propellant being expelled, as ambient pressure drops as the rocket gains altitude, therfore better ISP. Usually, liquid engines will match or exceed solid propellant in ISP, depending on what fuel/oxidizer it uses. For example, don't be fooled by the fact that the SRB's are much smaller and produce much more average thrust than the liquid/main tank assembly. This does not mean they are more efficient than the liquid engines. For one, they burn much longer (need a big tank), and two, the propellant has a different density. Density has nothing to do with ISP. The SSME's, pound for pound (propellant wise) are more efficient than the SRB's, with an ISP around 400.

I will agree here.. Dont feel lucky cause im wrong a lot...

i guess my head is so far up there, i can see for ....

Thanks guys for taking me to university on this.

 

[ClayD]

Just in case anyone is reading what Clay is writing, there are quite a few errors in describing Kn, burn surface, pressure, thrust curve shapes, and Isp's. Just in case.

wait... "errors in describing" The wrong appearance, gramatical errors, or orientation?
:eyepop:

 

[bobkrech]

Now... i am i reading this right...

soo, excuse my dunce or density... But does that mean the propellant density has to do with the propellant type... means the propellant type has to do with thrust generated?

Solid propellant is gas generator. A slow burning propellant needs a larger surface area, or Kn, to generate the same m-dot of gas as a fast burning propellant where m-dot is the propellant mass flow rate per second, e.g. g/s.

The m-dot or propellant mass flow rate per second is simply the volume of propellent burned per second or cm3/s multiplied by the propellant bulk density or g/cm3.

The volume of propellant burned per second is simply the throat area in cm2 times Kn which is the burning surface area to throat area ratio, multipled by the linear burn rate in units of cm/s which gives the volume burned per second, or cm3/s. Density is simple g/cm3 so when you do dimensional analysis you get g/cm3 * cm3/s = g/s which is the mass flow rate.

Bob

 

[jsdemar]

Solid propellant is gas generator. A slow burning propellant needs a larger surface area, or Kn, to generate the same m-dot of gas as a fast burning propellant where m-dot is the propellant mass flow rate per second, e.g. g/s.

The m-dot or propellant mass flow rate per second is simply the volume of propellent burned per second or cm3/s multiplied by the propellant bulk density or g/cm3.

The volume of propellant burned per second is simply the throat area in cm2 times Kn which is the burning surface area to throat area ratio, multipled by the linear burn rate in units of cm/s which gives the volume burned per second, or cm3/s. Density is simple g/cm3 so when you do dimensional analysis you get g/cm3 * cm3/s = g/s which is the mass flow rate.

I thought I heard Clay's head exploding, so I stopped by to see who posted.

 

[rcktnut]

WOW!! Good question, but now I have a headach after reading this thread!!!

We should be so fortunate to have such a wide selection of propellant types to use in our hobby. This is model rocketry, right??? The real ones should out perform us.

I wonder if the model railroad guys discuss ways to improve the engines available to them to haul more freight, like why can't we pull 100 cars if the real ones can???

 

[r1dermon]

WOW!! Good question, but now I have a headach after reading this thread!!!

We should be so fortunate to have such a wide selection of propellant types to use in our hobby. This is model rocketry, right??? The real ones should out perform us.

I wonder if the model railroad guys discuss ways to improve the engines available to them to haul more freight, like why can't we pull 100 cars if the real ones can???

Why not try to push the limit?

 

[troj]

WOW!! Good question, but now I have a headach after reading this thread!!!

We should be so fortunate to have such a wide selection of propellant types to use in our hobby. This is model rocketry, right??? The real ones should out perform us.

I wonder if the model railroad guys discuss ways to improve the engines available to them to haul more freight, like why can't we pull 100 cars if the real ones can???

My guess is some of them do! Much like the prevalence of Kadee couplers over...I think they're called horn hook couplers...with the more serious types

 

[Peter Olivola]

Good guess. Just as there are model rocketeers who obsess over scale details, there are "rivet counters" in model railroading. Any and every aspect of any and every hobby is subject to the tyranny of the true believer.

My guess is some of them do! Much like the prevalence of Kadee couplers over...I think they're called horn hook couplers...with the more serious types

 

[ClayD]

prevalence of Kadee couplers over...I think they're called horn hook couplers...with the more serious types

what??? is that Kah*Dee, or Kay*Dee..

Are you talking about the HITCH coupler?

 

[Tominator 2]

This is a great thread, I have asked the same question. I think that for the materials and motors we are allowed to use, the hobby gets some serious altitude. 22,000 feet on a J?! That's insane when you think about it. I can't think of any hobbies that go that high and as fast as we do with relatively little money.
Just my opinion.
Tom

 

[ClayD]

This is a great thread, I have asked the same question. I think that for the materials and motors we are allowed to use, the hobby gets some serious altitude. 22,000 feet on a J?! That's insane when you think about it. I can't think of any hobbies that go that high and as fast as we do with relatively little money.
Just my opinion.
Tom

Actualy, we are afforded some rediculousness the "industry" isn't.
So if your comparing "space exporation" or even "government weather/altitiude research" to "highpower rocketry"
All of us get to set the agenda to what happens. My hobby boss (wife) is the only one i have to get fiscal and project approval.

 

[Alby]

Good guess. Just as there are model rocketeers who obsess over scale details, there are "rivet counters" in model railroading. Any and every aspect of any and every hobby is subject to the tyranny of the true believer.

I say, as long as it gets off the pad in one piece, it is a working rocket.

 

[RadManCF]

WOW!! Good question, but now I have a headach after reading this thread!!!

We should be so fortunate to have such a wide selection of propellant types to use in our hobby. This is model rocketry, right??? The real ones should out perform us.

I wonder if the model railroad guys discuss ways to improve the engines available to them to haul more freight, like why can't we pull 100 cars if the real ones can???

I'm into model railroading as well as rocketry, and in my experience, that doesn't happen so much, as one engine pulling 100 cars would be considered unrealistic. It usually takes 3-4 engines, depending on how heavy the cars are and how many of them are empty. It probably could be done, but the train wouldn't move very fast, and probably couldn't start if it were on a grade. The key thing here is horsepower to weight ratio. If you want the train to be able to move fast, like if its a piggyback train, add more engines. If you're just moving cars around in a yard, you won't need as much power.

 

[Peter Olivola]

2.5 cars per driven axle.

I'm into model railroading as well as rocketry, and in my experience, that doesn't happen so much, as one engine pulling 100 cars would be considered unrealistic. It usually takes 3-4 engines, depending on how heavy the cars are and how many of them are empty. It probably could be done, but the train wouldn't move very fast, and probably couldn't start if it were on a grade. The key thing here is horsepower to weight ratio. If you want the train to be able to move fast, like if its a piggyback train, add more engines. If you're just moving cars around in a yard, you won't need as much power.

 

[edwinshap1]

I say, as long as it gets off the pad in one piece, it is a working rocket.

isn't the idea to get it back in one piece? or is the addage "You don't need a recovery system to fly a rocket. You only need a recovery system to fly a rocket twice." in effect here

 

[Bullpup]

Some of us in the hobby are working on reproducing these rockets.
Here is my dart project:
Project High Jump Photos

This is a case bonded O motor. The only real difference between this and a true Super Loki dart is fin size and case wall thickness. I am using 6061 AL with a 0.125 wall. I could run .083 if I did a custom mill run of 7075 AL tube but it is not a standard tube. So it comes down to cost. I suffered a burn through this year but hope to have that resolved by next year.

36 lbs of APCP
Total weight of rocket at liftoff 67 lbs
Dart weight 9 lbs

I will get it to work. Its just not a full time job.

And a plug for Adrians electronics... as they are in both booster and sustainer.

Geoff

 

[Adrian A]

And a plug for Adrians electronics... as they are in both booster and sustainer.

Geoff

Thanks, Goeff. In case you don't already know, make sure you send in your sustainer's Raven (and your booster's Raven, too, while you're at it) to get the firmware upgrade to 2.4 for proper operation over 65,000 feet.

https://www.rocketryforum.com/showthread.php?t=27666

 

[powderburner]

I was interested in your project and was looking forward to seeing the pix:

Here is my dart project:
Project High Jump Photos

I got nothin'
Is this another photo page that you have to join up/log in to see anything?

 

[Tominator 2]

Thats because its his google plus account. It's google's answer to facebook.

 

[Bullpup]

I updated the link to go to Picasa link... should work for anyone...

and here are some great proofs from Photos by Nadine. She does a great job and is a wonderful person.

Proofs from Photos by Nadine

 

[Bullpup]

Thanks, Geoff. In case you don't already know, make sure you send in your sustainer's Raven (and your booster's Raven, too, while you're at it) to get the firmware upgrade to 2.4 for proper operation over 65,000 feet.

https://www.rocketryforum.com/showthread.php?t=27666

Will do Adrian, the booster Raven was damaged. Too many G's on the landing pulled most the chips off the board. :wink:

Hope to fly one well over 100k next year if I get all the bugs worked out of the system. Building 3" 18,000 ns motor and 4" O motor to do it with. Both should be able to do it. The O motor next year will be a faster burning version too so I am planning for some issues with that as I will be going Mach 3.5+ next year. Thinking it may be time for a solid AL nose cone and ditching the composit one.

Geoff

 

[Alby]

isn't the idea to get it back in one piece? or is the addage "You don't need a recovery system to fly a rocket. You only need a recovery system to fly a rocket twice." in effect here

Hahahahaha... Very true..

 

[Bullpup]

Posted some more pictures here:

Project High Jump (Loki Dart knockoff)

 

[stickershock23]

Posted some more pictures here:

Project High Jump (Loki Dart knockoff)

wow that really doe look a lot like a TRUE loki dart.. really similar to the viper's too.. nice.

 

[Alby]

Posted some more pictures here:

Project High Jump (Loki Dart knockoff)

Out of curiosity, why are there holes at the back of the rocket/motor?
I'm sure they are serving some functional purpose.

Thanks,

 

[Alby]

Out of curiosity, why are there holes at the back of the rocket/motor?
I'm sure they are serving some functional purpose.

Thanks,

Doh.. Nevermind. I see its a bunch of screws.

 

[gregm]

Posted some more pictures here:

Project High Jump (Loki Dart knockoff)

Very interesting project Geoff!!

I've been quite intrigued with the idea of building an HPR Super Loki motor since I began reading the report about them. The thing that surprised me most was the relative simplicity of the original propellant formula.

What is the total impulse of your O motor and the delivered ISP of your propellant (if you don't mind me asking of course)?

Hope all goes perfectly next year, look forward to hearing about it.

Greg

 

[Bullpup]

Very interesting project Geoff!!

I've been quite intrigued with the idea of building an HPR Super Loki motor since I began reading the report about them. The thing that surprised me most was the relative simplicity of the propellant formula.

What is the total impulse of your O motor and the delivered ISP of your propellant (if you don't mind me asking of course)?

Hope all goes perfectly next year, look forward to hearing about it.

Greg

The formula delivers an ISP of about 200 in a 2 grain 38mm test motor. The motor held 17,000g of propellant so that would be 34,000ns but I suspect the delivered ISP to be higher on this large of a motor. 36,000ns is probably in the ball park. I'm building a couple of half scale versions of it now to test on the test stand with a slightly changed design and a faster formula to get the performance closer to the original.

 

[gregm]

The formula delivers an ISP of about 200 in a 2 grain 38mm test motor. The motor held 17,000g of propellant so that would be 34,000ns but I suspect the delivered ISP to be higher on this large of a motor. 36,000ns is probably in the ball park. I'm building a couple of half scale versions of it now to test on the test stand with a slightly changed design and a faster formula to get the performance closer to the original.

Hope you will share your test results!

Definitely would love to follow the progress of your project.

Good luck,
Greg