Direct airstart BP motor from Composite motor

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n27sb

N27SB
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Has anyone done a direct airstart to a BP upper stage from a Composite motor ejection charge booster?
 
What size/type of motors are you looking at? You will have to choose your motor carefully for the smallest possible delay. CTI has a much wider of ranges to choose from than AT in this regard.
 
Most composites don't have delays short enough for this. Shortest I can think of are 3 or 4 seconds and you want as close to zero delay as possible.
 
What size/type of motors are you looking at? You will have to choose your motor carefully for the smallest possible delay. CTI has a much wider of ranges to choose from than AT in this regard.
Something like AT F24w-4. This is a really light rocket so it might tolerate up to 4 sec of delay.
I was more interested in if the composite motor would light the upper stage BP
 
I wasn’t ‘t going to post but since I’m busy doing nothing but staring at my build pile, here goes:
First, the stack has to be stable Not too overstable.
The second stage needs to light while vertical. A function of mass and thrust. (ya, fins too, etc)
Thus dictates the booster motor size. Also the coast phase, if you are screaming for altitude. Thus the delay.
Interstate coupling to withstand lateral forces and longitudinal forces to prevent g force collapse.
‘nose’ to ‘tail’ engine interface not so much an issue but the idea is get burning particles from ejection on the booster up inside the booster motor.
if there is any spacing, you may need to vent the coupler to allow the ejection gases to force the burning particles in before it separates. The ignition of the sustainer should separate the stack.
Next is how the booster recovers. Most RSOs take a dim view of it coming in ballistic. It’s hard due to the increased mass of a composite to get it to ‘flutter’ but it can be done.
Lastly, you may augment the booster ejection with 2f powder, as most use the equivalent of 4f pressed into place to generate the gas for recovery. This is ‘chunkier’ so more burning bits travel further.
Yes this has been done. The FSI F100-7 was too much for the min dia sustainer airframe and it shredded at max q after lighting. Pretty desert confetti. Exceeded the speed of balsa. Just my 2 cents worth
 
I've considered a 3d printed funnel in the ejection well to direct the first bits of heat straight up the nozzle and to protect a flap of kevlar as a streamer.... seems plausible that it would work.
 
Maybe like a CTI G46 38/1G, you can drill it down to two seconds. H125 38/2G would work too, 3s delay.
 
To help ensure ignition on the BP motor, I'd also use a section of "fast paper fuse". Ideally you'd use quickmatch but you have to have a LEUP to have that now. Fast paper fuse is almost as good but not quite. Cut a section so that it's near the ejection charge if the APCP motor on one end and the other end is in the nozzle of the BP motor held in place with the normal plastic plug and then taped. The fast paper fuse will light with pretty much any flame source and burns very quickly (0.1 to 0.4 seconds per foot). It'd actually work better with a bit of distance between the motors but not required. I've used it when clustering BP and APCP motors. The APCP motor flame ignites the fuse and that transfers to the BP motors. In the time the APCP comes up to pressure, the BP motors are lit.

https://www.skylighter.com/products/quick-fuse-white-gn1207
 
It *might* be possible to drill a delay grain down to 2 seconds by using a much smaller drill bit, say 3/32". I don't know the tensile strength of a delay grain, but for example, the end of a 3/32" hole at 700 psi would see a force of 4.8 lb (area of hole in in^2 times pressure in lb/in^2). The question remains: would that area (0.0069 in^2) withstand a force of 5 lb? If so, it'd be okay.

It would probably be necessary to face the flat, un-drilled side of the grain to the combustion chamber. If the drilled side faced the chamber, the hole would increase in area during the burn, increasing the force. Unfortunately, facing the flat side to the combustion chamber means that on burn-through, there would still be a lot of the delay grain left to burn, and the flame would come out both ends of the delay. Possible damage to the part of the booster that is ahead of the delay grain.

I've never done this and don't know if it would work in practice.

Best -- Terry
PS: I don't know the size of the bit used to drill delays, but as an example, if the drill (and its hole) is 3/16" in diameter, the force on that part of the grain would be almost 20 lb.
 
I did a D21-4T to a C6-7 in an Estes Mongoose, I just removed the paper cap prior to flight.
It turns out that the D21-4T was closer to a D21-10T so the C6-7 powered the upper stage into the ground.
 
I have incorrectly attempted a sub-4s delay twice so far: the first time I produced thrust at both ends of the motor, ruining the casing and the rocket ( RIP Mustang Sally Ride Can Dance ). The second time I had plenty of delay grain left to go, and I hibachi'ed the forward closure. For this application that's actually a bit promising since I know a needle of flame went up the tube.

When I try it again I'll use BMS foil-lined MMT.

Here's what lead me down this path:
https://docs.google.com/spreadsheet...hej4LvAabA-v/pubhtml?gid=90280042&single=true
EDIT:
Attempt 1 was with the drilled portion facing AWAY from the combustion chamber, standard LARGE-ish drill bit, probably too DEEP.
Attempt 2 was with the drilled portion facing TOWARD the combustion chamber, SMALL drill bit, same DEPTH
 
It *might* be possible to drill a delay grain down to 2 seconds by using a much smaller drill bit, say 3/32". I don't know the tensile strength of a delay grain, but for example, the end of a 3/32" hole at 700 psi would see a force of 4.8 lb (area of hole in in^2 times pressure in lb/in^2). The question remains: would that area (0.0069 in^2) withstand a force of 5 lb? If so, it'd be okay.

It would probably be necessary to face the flat, un-drilled side of the grain to the combustion chamber. If the drilled side faced the chamber, the hole would increase in area during the burn, increasing the force. Unfortunately, facing the flat side to the combustion chamber means that on burn-through, there would still be a lot of the delay grain left to burn, and the flame would come out both ends of the delay. Possible damage to the part of the booster that is ahead of the delay grain.

I've never done this and don't know if it would work in practice.

Best -- Terry
PS: I don't know the size of the bit used to drill delays, but as an example, if the drill (and its hole) is 3/16" in diameter, the force on that part of the grain would be almost 20 lb.
This makes me realize that if you dished the chamber side and domed the chargewell side, you could probably go a tiny bit smaller on the delay for quite a bit of effort.
 
Thank you All for the input.
A 4 second delay may work on a calm day with a vertical flight.
Total weight on the pad is only about 200 g. Rocksim shows a velocity of about 250 mph after the 4 second delay.
Did 3 test burns today and all 3 lit the upper stage.
 
This makes me realize that if you dished the chamber side and domed the chargewell side, you could probably go a tiny bit smaller on the delay for quite a bit of effort.
Domed the chamber side and dished the charge well side, maybe? Seems more reasonable. Though after three fermented malt beverages, I don't know what is and isn't reasonable...:cheers:
 
Domed the chamber side and dished the charge well side, maybe? Seems more reasonable. Though after three fermented malt beverages, I don't know what is and isn't reasonable...:cheers:
I don't see many pressure vessels shaped that way -- that would an interesting set of experiments though, most pressure vessels aren't flying cash-to-smoke schemes, either.
 
dhbarr, we may be talking about the same thing. I think the optimum shape for a delay grain drilled as I described would be like this:
1589655210913.png
Aft end of the grain at the bottom, in contact with the combustion chamber. Someone who knows more engineering/physics than I do, please correct me.
 
I don’t do much with composites, but I do a lot of black powder gap staging (50 inches plus) and I am very uncomfortable with what you are proposing.

Not that all my flights have been a success, but you are doing two thing here. Not just GAP staging, but DELAYED gap staging. The DELAYED part, without the use of electronics to set a precise time or other criteria for sustainer ignition, worries me.

Normal black powder staging is effectively instantaneous at booster burnout. Yes, it is a bit less efficient from an altitude standpoint as there is no “coast” phase, but there is much less concern for a “late” ignition when the stack is potentially not vertical.

Drilling a delay is not an exact science. I am not saying your idea won’t work, I AM suggesting it may not work CONSISTENTLY. IF you try this, and I think you should not, you should definitely lean toward an error of too short a delay rather than trying to nail the perfect “coast time.” Igniting the sustainer earlier will give you a safe flight albeit slightly lower apogee. Igniting the sustainer late will not only give you a definitely lower Apogee but also may give you a perigee which will be a negative number. This is generally consider poor technique.
 
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