P-270 Moskit Soviet supersonic ramjet powered anti-ship cruise missile

[techrat]

I thought about doing this as one of my next kits...

Well, let me know when you're there. You're somewhere in my neighborhood (Northen NJ), and we met in person at the last METRA, so let me know and we'll give it a whirl.

 

[BigMacDaddy]

Well, let me know when you're there. You're somewhere in my neighborhood (Northen NJ), and we met in person at the last METRA, so let me know and we'll give it a whirl.

I am still a bit stuck on whether or not the airframe diameter reduces in the middle or just expands in the rear. Wish I could find a definitive answer from someone who has seen the model in person or from some pictures that make this totally clear.

 

[BABAR]

For now, I am going to stick to my previous design... I did find a good picture of the rear of the rocket.

View attachment 523755

Not particularly interesting but does suggest I can recess my engine some to increase stability. I am going to try recessing it 1/2 the diameter of the body tube (around 2cm) based on the Apogee article about GDS. I am not going to be totally aggressive on stability assumptions but I do think that the base of this model is draggy enough that I can use the base drag trick (I also think that OR is not totally taking into account the drag or other aerodynamic benefits of those pods). So end result is I am going to drop my nose weight down to 1oz (sorry to shift off metric just for nose weight but I use fishing weights).

View attachment 523754

Call me crazy (everybody else does). It would greatly complicate the build, but if you left the forward ends of the outboard open (or put small central ramjet partial cones it, leaving the partially open just like a real spike nozzle) AND you ducted the flow INTO the core tube, you COULD Recess the motor at least half a main tube width, maybe even more, as it WILL act a bit like the Lil’Augie. So you could actually have some useful function from your simulated ramjets.

also agree with @techrat , even completely open those tubes are far too long to function as tube fins and would act like solid cylinders or worse.

@neil_w , is there a maximum length To diameter ratio for tube fins beyond which they completely lose function?

 

[Cape Byron]

It would greatly complicate the build, but

My brother from another mother...

 

[BigMacDaddy]

Call me crazy (everybody else does). It would greatly complicate the build, but if you left the forward ends of the outboard open (or put small central ramjet partial cones it, leaving the partially open just like a real spike nozzle) AND you ducted the flow INTO the core tube, you COULD Recess the motor at least half a main tube width, maybe even more, as it WILL act a bit like the Lil’Augie. So you could actually have some useful function from your simulated ramjets.

also agree with @techrat , even completely open those tubes are far too long to function as tube fins and would act like solid cylinders or worse.

@neil_w , is there a maximum length To diameter ratio for tube fins beyond which they completely lose function?

I do not understand GDS or ducting very well. From what I read, if you have intakes forward of CG it destabilizes the model (GDS intakes being approximately equal to fins in their effect on CP). Intuitively it does seem that a ramjet style rocket would pull air in from the front and push it out the rear and that this would create a more stable flight.

In my model, the 3D printed parts are hollow and I was planning to recess the motor some so it would actually be pretty easy to add holes from the ramjet tubes through the airframe to the ignition area so that those parts would intake gasses. However, I think that the resistance that we already discussed would lead to most air being pulled in from the rear of rocket.

 

[BABAR]

I do not understand GDS or ducting very well. From what I read, if you have intakes forward of CG it destabilizes the model (GDS intakes being approximately equal to fins in their effect on CP). Intuitively it does seem that a ramjet style rocket would pull air in from the front and push it out the rear and that this would create a more stable flight.

In my model, the 3D printed parts are hollow and I was planning to recess the motor some so it would actually be pretty easy to add holes from the ramjet tubes through the airframe to the ignition area so that those parts would intake gasses. However, I think that the resistance that we already discussed would lead to most air being pulled in from the rear of rocket.

hmmm, hadn’t thought about the intakes relative to the CG. Agree that tailward of CG would be BETTER than forward, not sure if that’s ESSENTIAL.
i have included a pic of the Lil Augie, I built one scratch and it worked well. Not sure where opening is relative to CG, I don’t think I added any nose weight, eyeballing it looks like it would be near or slightly ahead of CG. (Remember the Augie was CHAD-staged, so there are two motors, the booster is completely within that larger outer body tube.) The Augie intake however is huge.

also unsure if the size/surface area of this four outboards would be adequate even if you leave them totally open.

I believe at least one other TRF member has posted about successful GDS using side ports. There’s an article on it here from Apogee

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www.apogeerockets.com

personally I Think without the ramjet cones the rocket loses a lot of its character, but I do always say, “it’s YOUR rocket, as long as it is safe the only person you have to satisfy is YOURSELF (and maybe the RSO but only if you launch at a club!)”

the outboards will definitely strengthen the airframe, so you could cut some pretty large sideports (to keep Uncle Krushnic at bay) in the main body if you can live with the cosmetic changes. Moving the motor mount forward has a big plus for stability. Downsides are it decreases your space for recovery gear, and as I remember it, the Augie was a bit of a challenge to get motors in and out. Suspect the ports also cause at least mild additional drag, but obviously this isn’t designed for Karman line challenging anyway.

looking forward to the build!