The Optimal Fin Shape For small rockets But will it work for supersonic ones?

[MarkII]

Does this mean the ogive is poor for everything?
Aren't cones ogives and parabolics th only ncs that are commerically availible?

No, there are also conical shapes (simple cones), various types of ellipsoids, spherical shapes and hybrid shapes (combinations of more than one shape). When Semroc's site comes back up (it's down right now), navigate to the nose cones page, and click on various nose cone pictures to get an idea of the variety that are available. Semroc's term "Bezier" refers to blended or hybrid types. (There are also some "cones" that actually consist of two or more individual rocket components on the same piece of balsa. They are mean to be cut apart into their individual parts.)

MarkII

[cjl]

It just breaks mach.

I'd be extremely surprised if that design actually broke mach. Tube fins are extremely high drag compared to standard fins.

[blackjack2564]

Here are the fins and nc from a 24mm proto- type I'm working on.
Guaranteed to break Mach. Just scale it.

Don't want to cut fins and make a nose cone?

Wait till it's released and just put it together and fly 24mm. LOL Even comes with black high temp epoxy and fin alignment guides so you can get them on straight! It will fly on Estes D motors and 18mm Aero tech's. with an adapter. [shameless self promotion here]

You can read about it here.


http://www.rocketryplanet.com/forums...ead.php?t=5969

[luke strawwalker]

I'd be extremely surprised if that design actually broke mach. Tube fins are extremely high drag compared to standard fins.

Yeah, that's an interesting choice...

I read an interesting webpage about a year ago about jet intake designs on supersonic aircraft and the different effects of Mach shockwaves and air intake efficiency. It was a very interesting read because it detailed not only the problems and effects at different flight speeds, but sizing and many of the solutions used, and why they work the way they do.

For instance, the optimum size/shape of the intake changes markedly depending on the flight speed and air density, as it relates to the "local speed of sound" (which varies with air density) and shock wave effects. An intake that is optimal at takeoff is FAR too large at altitude and speed, and therefore extremely draggy. Intakes that are optimally sized for altitude and speed are too small at takeoff, which can result in the compressor blades "stalling" out for lack of air. Also, the supersonic airstream has to slow to subsonic speeds to flow properly through the engine. That is why there are a myriad of intake designs, from the old F-4 Phantom intakes that used a "vane" in front of the intake that moved to divert some of the air going into the intake and manipulate the shock wave coming off it so the shock wave stayed out of the intake itself. The Russian MIGS used a 'half cone' that could slide back into the intake or out further in front of it, reducing the intake size for supersonic flight. The Harrier (among others) use small spring-loaded air doors that open up to admit more air at low speeds, and snap shut at high speeds to reduce the effective intake size. Of course the F-15 and F-14 had those drooping moveable intake 'wedges' that extended up to the front of the wing.

Now how does this apply to the subject of tube fins?? Simply put, the tube fin 'intake' would create a conical shock wave inside each tube fin, which would compress the air as it passed through the shockwave, and when supersonic air goes through a shockwave, it loses energy (to maintain the shockwave) and goes subsonic... so essentially the tubefins would be acting as huge aerodynamic brakes...

Interesting stuff... OL JR

[MarkII]

The Russian MIGS used a 'half cone' that could slide back into the intake or out further in front of it, reducing the intake size for supersonic flight. The Harrier (among others) use small spring-loaded air doors that open up to admit more air at low speeds, and snap shut at high speeds to reduce the effective intake size. Of course the F-15 and F-14 had those drooping moveable intake 'wedges' that extended up to the front of the wing.

The Sled (SR-71 Blackbird) was the premier example of that. It had the ability to vary its engine intakes considerably in response to different phases of its flight profile. When they were running full out, the engines were essentially ramjets.

[OT:] One thing that I found really fascinating about the SR-71 was that the fuselage was intentionally designed to fit together very loosely while the plane was on the ground or in subsonic flight. It would actually leak while it sat on the tarmac and it would give off all sorts of squeaks, rattles and bangs after it took off and was still flying below Mach. Once it got up to speed at Mach 1.5-2, the heat that it absorbed through air friction caused all of the joints to expand and seat themselves properly and the plane became a nice, tight, solid platform. [End OT]

MarkII

[GregGleason]

Here are the fins and nc from a 24mm proto- type I'm working on.
Guaranteed to break Mach. Just scale it...

That is one sweet rocket! Certainly a real hot rod with the good motor.



Is the high-temp epoxy you are planning to use Cotronics?


Greg

[rcktnut]

I'd be extremely surprised if that design actually broke mach. Tube fins are extremely high drag compared to standard fins.

According to RS it does for .12 sec. I figured a better option than breaking some long swept back balsa fins. I wouldn't fly either myself.

[cjl]

According to RS it does for .12 sec. I figured a better option than breaking some long swept back balsa fins. I wouldn't fly either myself.

Yeah, but I don't trust rocksim with standard designs at mach+, much less unusual ones such as one with tube fins.

[blackjack2564]

That is one sweet rocket! Certainly a real hot rod with the good motor.



Is the high-temp epoxy you are planning to use Cotronics?


Greg

The generic version. Still 500 degree high temp, graphite loaded stuff. Pre packed in amount needed for kit. Same thing comes with the Mongoose's

[GregGleason]

The generic version. Still 500 degree high temp, graphite loaded stuff. Pre packed in amount needed for kit. Same thing comes with the Mongoose's

There is a generic version??!!

Do you know the name of the generic version and do they take orders?

Greg

[blackjack2564]

There is a generic version??!!

Do you know the name of the generic version and do they take orders?

Greg

Wildman sells it. I believe he has an exclusive on the stuff,but not sure. Pint kits.

Ask for the Pro-line high temp Black.

[ScrapDaddy]

wow machbusters are starting to have kits; but after this im done with machbusters, on to payloaders

[The EGE]

wow machbusters are starting to have kits; but after this im done with machbusters, on to payloaders

This is gonna get interesting.

Define 'interesting'

Oh God oh God we're all gonna die?

[ScrapDaddy]

My thrEads are going to change to a payloader subject

[blackjack2564]

Gee, I've built Mach busting payloads.

Why not combine the 2?

[ScrapDaddy]

I like how you think but don't think a supersonic payloader is possible on a D21

[cjl]

Definitely not. There's a simple solution to that though:

Use a bigger motor

[ScrapDaddy]

I'll stick with clustered SUBSONIC payloader untill my wallet grows a little