Proposal: L3 competition for airframe-free rockets.

[RGClark]

By airframe-free I mean with no body tube, so for example the fins are connected directly to the motor casing. This would require a great deal of experience to pull off, which is why I’m proposing it only for L3 certified rocketeers.

As discussed in this post, it would result in a radical reduction in the rocket dry mass, and therefore a radical increase in altitude:

Unexpectedly high RASAero estimate for a two-stage rocket.
https://www.rocketryforum.com/threa...te-for-a-two-stage-rocket.145740/post-1783286

Note, with the university student team at USC achieving a flight beyond the von Karman line for suborbital space, it should no longer be considered a “bad word” for amateur rocketeers to discuss the rocket they thus designed also breaking the von Karman line.

The most common way of attaching the fins is by way of a fin can:

Altitude Expectations for a Minimum Diameter 54mm.
https://www.rocketryforum.com/threa...r-a-minimum-diameter-54mm.146209/post-1789560

However, with many experienced rocketeers devising their own methods of managing it, likely more lightweight means could be achieved.

By the way, apparently a term in use for an airframe-free amateur rocket is “subminimum”:

98mm subminimum diameter.
https://www.rocketryforum.com/threads/98mm-subminimum-diameter.162595/

This is because competitions have been mounted for “minimum diameter” rockets. These are when the rocketeer tries to get the wall thickness of the body tube or airframe as thin as possible. So not using a body tube at all is referred to as subminimum. It’s not a very appealing term. So I’m looking for a better term to use.

Bob Clark

 

[manixFan]

Motor case diameter. MCD rocket.


Tony

 

[blackjack2564]

So if this a competition.....what's the prize?

 

[blackjack2564]

So if this a competition.....what's the prize?

 

[3stoogesrocketry]

What is the competition Bob ?

When was the Karmen Line ever a " bad word " ?

 

[MClark]

The term I dislike is "suborbital"
If it doesn’t go in to orbit its suborbital, when I spit it’s suborbital.
What launch are you wanting to victimize with this contest?

M

 

[RGClark]

So if this a competition.....what's the prize?

I’m a proponent of dreaming big. The biggest prize will be when many amateurs exceed the von Karman line, they will then set their sights beyond that.

Robert Clark

 

[RGClark]

What is the competition Bob ?
When was the Karmen Line ever a " bad word " ?

I love your sig file.

Some amateur rocketeers regarded achieving the von Karman line as an unreachable goal for amateurs, prior to the USC student team’s success.
Note that many regarded the earlier CSXT suborbital flight as not really amateur because aerospace professionals took part in the flight:

https://www.rocketryforum.com/threads/csxt-s-class-engine-and-the-karman-line.21215/#post-189713
Robert Clark

 

[Tim51]

I’m a proponent of dreaming big. The biggest prize will be when many amateurs exceed the von Karman line, they will then set their sights beyond that.

Robert Clark

Will you be entering one of your own builds into this competition, or are you just holding the ring for others?

 

[3stoogesrocketry]

I love your sig file.

Some amateur rocketeers regarded achieving the von Karman line as an unreachable goal for amateurs, prior to the USC student team’s success.
Note that many regarded the earlier CSXT suborbital flight as not really amateur because aerospace professionals took part in the flight:

https://www.rocketryforum.com/threads/csxt-s-class-engine-and-the-karman-line.21215/#post-189713
Robert Clark

Yes I am familiar with all of Ky's space shot attempts , as their have been more then 2. . I am also familiar with the USC's rockets over the years . I think your assumption that the Karmen Line being unreachable by a "amature" is extremely miss leading . As to my knowledge , there has still yet to be a true "amature" flight over the karmen line. USC does not count . When a large group of students that are going to a aerospace University , with almost a unlimited budget , with unlimited tooling , build a big ass flying motor (T) impulse that by physics alone will allow it to reach the karmen line . Back to your competition . So there is no competition or prize . Just another thread.

 

[ghostfather]

I've been playing with ideas about building an internal framed rocket with a non-loadbearing external skin. I know, it's nothing new, it's been done before, but I don't see any kits using it. Just want to prove to myself that I can engineer it correctly. Probably K or L range of stresses.

Most of what we fly is where the airframe is the exterior tube, which takes the load. With a submindia design, the motor casing is the airframe. That seems to be what RGClark intended with "airframe-free". Not sure whether an internal frame will save any weight.

I read a design paper from a university rocketry group, flying something for IREC (or another competition) using an internal frame of carbon fiber rods and glassed plywood bulkheads, with their calculations and design goals. Wish I could find that again, it was an interesting starting point for me.

 

[jbr]

I machined a 98mm casing with threads on the end that an AL fin can screwed onto and the top of the casing screwed into the AL body tube
this was done for the OU rocket group
the up part was good, rocket was never seen again

 

[cwbullet]

So if this a competition.....what's the prize?

A double post, a double post by CJ.

I am intqigued. Do you have a drawing or rocksim file?

 

[jbr]

Mike Fisher should be able to make his AL fin can to fit a 3.9" casing instead of his normal one that fits a 4" body tube

the forward bulkhead could be machined with an extension on the top to fit inside an AL body tube

I'm not sure this is a competition, just some extra machining needed and not really very hard to do

 

[RocketRev]

Didn't Dr Rocket basically do this with a 98mm motor for his L-3 cert?

 

[ghostfather]

I have this aluminium fincan waiting for a suitable project. Fits a 98mm CTI casing and the bottom sits on the thrustplate of the casing.
Was intended to have the CF airframe held in place with the internal minimum diameter retainer, but I suppose you could glue this to the casing itself, and make it subminimum diameter.
Good luck finding a place that can make these, as the welding tends to deform the pipe, and then it has to be honed to size. We had a few of these made in a shipyard in Korea, where the could turn them on a lathe made for propellers, for honing the inside.

 

[jbr]

Didn't Dr Rocket basically do this with a 98mm motor for his L-3 cert?

yes and he used to sell the parts, it was a Dr rocket fincan and upper section and nose cone used for this project but they wanted more power than the special lower motor tube provided, mine was an N motor

 

[jbr]

View attachment 440060

I have this aluminium fincan waiting for a suitable project. Fits a 98mm CTI casing and the bottom sits on the thrustplate of the casing.
Was intended to have the CF airframe held in place with the internal minimum diameter retainer, but I suppose you could glue this to the casing itself, and make it subminimum diameter.
Good luck finding a place that can make these, as the welding tends to deform the pipe, and then it has to be honed to size. We had a few of these made in a shipyard in Korea, where the could turn them on a lathe made for propellers, for honing the inside.

https://binderdesign.com/store/page15.html
you can also buy the 60" O motor casing and have Mike make a special fin can to fit it

 

[tfish]

yes and he used to sell the parts, it was a Dr rocket fincan and upper section and nose cone used for this project but they wanted more power than the special lower motor tube provided, mine was an N motor

 

[RGClark]

Mike Fisher should be able to make his AL fin can to fit a 3.9" casing instead of his normal one that fits a 4" body tube
the forward bulkhead could be machined with an extension on the top to fit inside an AL body tube
I'm not sure this is a competition, just some extra machining needed and not really very hard to do

It would be a competition in regards to the altitude achieved, for both single stage and multi-staged.

By the way, you want only experienced rocketeers to take part in the competition because of the possible altitudes reachable on the multi-stage scenario or possible range distance that could happen if the flight goes awry.

Another issue that requires experienced flyers is the difficulty igniting the upper stage(s) when the staging occurs at high altitude.

Robert Clark

 

[RGClark]

With no airframes, multi-stage rockets with N or higher motors, should be able to reach the 100 km von Karman line.

Robert Clark

 

[RGClark]

https://binderdesign.com/store/page15.htmlyou can also buy the 60" O motor casing and have Mike make a special fin can to fit it

I’m curious about the altitudes that were able to be achieved on those airframe-free rockets with high power motors.

Bob Clark

 

[RGClark]

Another thing I’m curious about is in regards to the flyers who have taken part in the minimum-diameter competitions. Presumably they are going through steps also to lightweight their rockets to achieve the high altitude for the competitions.

For those flyers, what would your simulations show if you zeroed out the weight for the airframes or body tubes?


Bob Clark

 

[RGClark]

Actually, the same question applies to any flyer who’s done high power flights with N or higher motors.

What do your simulations show for the altitude when you zero out both weight and thickness of your airframe or body tube?

Bob Clark

 

[RGClark]

So if this a competition.....what's the prize?

I never answered this question. Here’s a proposal

$1,000 - First Prize
$500 - Second Prize
$250 - Third Prize

This is in the range offered here for example for a payload competition:

https://www.soundingrocket.org/2023-sa-cup.html
But what would be the parameters to win? Achievement of high altitude, above the von Karman line, and high velocity, hypersonic, requires high propellant fraction and/or high Isp.

Then two separate competitions, one to maximize propellant fraction, then one to maximize vacuum Isp are proposed, each at those prize levels.

In regards to maximizing propellant fraction it is known using carbon fiber casings can improve it. But by how much? It should be easy to find out because it is known carbon fiber casings can cut the the casing weight in half. But I have been unable to find any quotes among the amateur community where this number is given. Even in the well-publicized launch to the von Karman line of suborbital space by the USC RPL team of Traveler IV, this number, i.e., the propellant fraction, is not given.

Then competition A.) will be to maximize the propellant fraction of a APCP rocket stage. Carbon fiber casing or high strength metals would be required.

The proof is in the pudding, however, so the winning stage would also have to demonstrate flight to high altitude including onboard video and GPS validation of altitude.

Note: that the rocket flight has to be demonstrated is why this is only promoted for teams with L3 certification. Additionally, student teams should have professional safety advisors.

Competition B.) is proposed in an unusual fashion. Here we want to maximize vacuum Isp. But for APCP propellant the sea level and vacuum Isp are pretty much set given a fixed expansion ratio nozzle. But it is a known fact among professional rocket engineers you can’t make the expansion ratio be arbitrarily high for sea level engines because of the phenomenon of flow separation that can damage or even destroy an engine fired at sea level but with a vacuum optimized expansion ratio.

Then the purpose of competion B.) will be to demonstrate adaptive nozzles, aka, altitude compensating nozzles. These are nozzles that can operate at sea level yet can get maximum Isp at vacuum. One version of such nozzle is called the aerospike. But other ways of accomplishing it will be nozzles that physically change their size at high altitude.

Part of the purpose of competition B.) would be the teams showing their creativity in accomplishing the adaptive nozzles.

Note: that flow separation can cause engine RUD, i.e., to CATO, this is also a competition that should only be attempted by teams with L3 certification and for student teams to have professional safety advisors.

Robert Clark

 

[MClark]

Are you putting up the prize money?
When you say "we" who are you referring to?

 

[Igotnothing]

Haven't a good way to attach fins to the rocket motor, yet, without a fin can, but I do have a 100mm motor case and a 100mm body tube in a rocket. Has been hauled to 2 launches but has yet to fly due to weather. So MCD except the fin can.

Also, sugar motor. 4 feet long, maybe a baby N, but Karman line is still magnitudes away.

 

[RGClark]

Are you putting up the prize money?
When you say "we" who are you referring to?

Yes. I'm providing the prize money.

In the phrase:

Competition B.) is proposed in an unusual fashion. Here we want to maximize vacuum Isp.

By "we", I'm just referring to the purposes of the competition.

Robert Clark

 

[LithosphereRocketry]

I never answered this question. Here’s a proposal

$1,000 - First Prize
$500 - Second Prize
$250 - Third Prize

This is in the range offered here for example for a payload competition:

https://www.soundingrocket.org/2023-sa-cup.html
But what would be the parameters to win? Achievement of high altitude, above the von Karman line, and high velocity, hypersonic, requires high propellant fraction and/or high Isp.

Then two separate competitions, one to maximize propellant fraction, then one to maximize vacuum Isp are proposed, each at those prize levels.

In regards to maximizing propellant fraction it is known using carbon fiber casings can improve it. But by how much? It should be easy to find out because it is known carbon fiber casings can cut the the casing weight in half. But I have been unable to find any quotes among the amateur community where this number is given. Even in the well-publicized launch to the von Karman line of suborbital space by the USC RPL team of Traveler IV, this number, i.e., the propellant fraction, is not given.

Then competition A.) will be to maximize the propellant fraction of a APCP rocket stage. Carbon fiber casing or high strength metals would be required.

The proof is in the pudding, however, so the winning stage would also have to demonstrate flight to high altitude including onboard video and GPS validation of altitude.

Note: that the rocket flight has to be demonstrated is why this is only promoted for teams with L3 certification. Additionally, student teams should have professional safety advisors.

Competition B.) is proposed in an unusual fashion. Here we want to maximize vacuum Isp. But for APCP propellant the sea level and vacuum Isp are pretty much set given a fixed expansion ratio nozzle. But it is a known fact among professional rocket engineers you can’t make the expansion ratio be arbitrarily high for sea level engines because of the phenomenon of flow separation that can damage or even destroy an engine fired at sea level but with a vacuum optimized expansion ratio.

Then the purpose of competion B.) will be to demonstrate adaptive nozzles, aka, altitude compensating nozzles. These are nozzles that can operate at sea level yet can get maximum Isp at vacuum. One version of such nozzle is called the aerospike. But other ways of accomplishing it will be nozzles that physically change their size at high altitude.

Part of the purpose of competition B.) would be the teams showing their creativity in accomplishing the adaptive nozzles.

Note: that flow separation can cause engine RUD, i.e., to CATO, this is also a competition that should only be attempted by teams with L3 certification and for student teams to have professional safety advisors.

Robert Clark

What are the requirements for qualification and flight demonstration due date?

 

[BigMacDaddy]

It seems to me that a fincan has a body tube that is affixed to / built with the fins and is shorter than the motor...

Does airframe-free mean that fins, engine, and nosecone must only be connected to each other by the structure of the engine?

You are basically turning your engine casing into your airframe then (assuming definition of airframe means the structure that connects nose cone to fins).

Maybe this actually means that engine combustibles are loaded directly into airframe so maybe this is a engine-casing-free competition (reloads go directly into airframe).