Yep, positive static stability is a GOOD thing! Gotta keep CG in front of the AC, or bad things will happen...
I understood on Saturn V the fins were to add stability in case of an abort.
Quote from: kyle_baron on 01/24/2010 03:56 pmFins could also be placed at the base of the rocket, unless you can think of a reason why they shouldn't be. No need, only extra weight and drag.This is what is used. The scoops are on right and left of the base of the stage
Fins could also be placed at the base of the rocket, unless you can think of a reason why they shouldn't be.
I congradulate Jim for comming up with a simple, yet practical solution for the base heating problem, concerning the RS-68 engine! Well done.
Quote from: kyle_baron on 01/25/2010 01:36 pmI congradulate Jim for comming up with a simple, yet practical solution for the base heating problem, concerning the RS-68 engine! Well done.That isn't a solution. The base heating problem is radiant heat from SRB. The scoops are for base recirculation issues.
Maybe in combination with heat dissipating fins on the RS-68 nozzles,
As you stated, the SRB heat radiation problem isn't likely to be solved, short of extending the perimeter of the base to cover the RS-68 nozzles, that are nearest to the SRB exhaust.
That model rocketry magazine also describes shock cords, which don't apply to SRBs, so you have to watch how you extrapolate some information you come across.
I come back to what Jim said: the problem is radiant heat, and the problem exists beyond the atmosphere where scoops and boattails no longer matter.
Not to discourage your thinking, but Jim mentioned radiant heat specifically because redirected air is a solution to the wrong problem.
The air traveling thru the scoops must be traveling at sonic speeds with in the boat tail. And could be directed downward to the RS-68 nozzles by short ducts. I disagree about the problem existing beyond the atmosphere, because we're talking about the 1st stage only.
Quote from: kyle_baron on 01/29/2010 03:20 pmThe air traveling thru the scoops must be traveling at sonic speeds with in the boat tail. And could be directed downward to the RS-68 nozzles by short ducts. I disagree about the problem existing beyond the atmosphere, because we're talking about the 1st stage only. First stage does leave the sensible atmosphere
On page 3, I found a picture of a Boat Tail on a Model Rocket:http://www.2020vertical.com/nar_edu_cd_dev/lessons/apogee/Reports/Rocket_parts.pdfBoattailBoattail is a drag reducing part on the back of the rocket.It helps direct airflow around the base of the rocket. In effect,it keeps the flow smooth, which reduces the aerodynamic dragand allows the rocket to fly higher into the air.Hmmmm.... Combine a Boat Tail with air scoops, and what do you have? A possible solution to base heating, for the RS-68 engine?
Quote from: Jim on 01/29/2010 03:30 pmQuote from: kyle_baron on 01/29/2010 03:20 pmThe air traveling thru the scoops must be traveling at sonic speeds with in the boat tail. And could be directed downward to the RS-68 nozzles by short ducts. I disagree about the problem existing beyond the atmosphere, because we're talking about the 1st stage only. First stage does leave the sensible atmosphere Does a sensible atmosphere exist, before the SRB's fall away? I agree that there is a "point of diminishing returns" for the air scoops, as the rocket gains altitude.
You do realize this is why the DIRECT proposals using the RS-68 had a boattail, yes?
The issue with Ares V having one is due to the sheer # of engines. DIRECT had, at most, 3 engines on an 8.4m core. A 10m core would not add enough width, and the engines would burn out before they had used that much fuel, and would be unable to lift that size anyways.
I'm guessing for stability, but are there other reasons? What would be the result in air pressure, if an SRB were placed between 2 fins?