US Rocket "Two The Limit"

Hello Everyone,

My son and I have recently built the US Rockets "Two the Limit" kit (18oz). Its a 29mm 2-stage rocket that is setup for direct staging. My concern is that the kit was originally designed to use the US Rockets F20 motors which are not available. This leaves me with either the Estes E16 or F15 motors. I've used OpenRocket to simulate the flight of the rocket using two F15 motors and am concerned. The F15's take a while to build to maximum thrust and looks like it will be fairly slow off the rail.

Does anyone have experience with these kits/F15 motors? Any thoughts?

Thanks

How long is the motor tube? Just use a composite motor in the booster stage, 24(with an adapter) or 29mm.
Also use a rail instead of a rod at a longer length.

kclo4 said:

How long is the motor tube? Just use a composite motor in the booster stage, 24(with an adapter) or 29mm.
Also use a rail instead of a rod at a longer length.

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Thanks for the reply.

The motor tube is fairly short (6"?). I'd considered a composite booster but don't have any experience using composite motors to light BP motors. Is it reliable?

It never occurred to me to swap the launch lugs for rail buttons. That will be much better since I can get an additional 4 ft before it leaves the rail. This add ~40% more speed at the top of the rail.

From what I've read, using APCP motors for direct staging is unreliable due to the ejection charge caps. Instead of bursting and scattering hot clay and residue like a BP motor, the ejection charge covers may block the hot stuff from entering and lighting the sustainer. I will of course defer to anyone who has tried this method and has empirical evidence to the contrary.

Nytrunner said:

From what I've read, using APCP motors for direct staging is unreliable due to the ejection charge caps. Instead of bursting and scattering hot clay and residue like a BP motor, the ejection charge covers may block the hot stuff from entering and lighting the sustainer. I will of course defer to anyone who has tried this method and has empirical evidence to the contrary.

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Seems like piercing a hole of approx. sustainer nozzle throat diameter would make sense?

The important consideration here would be to use an appropriately shirt delay to ensure the upper stage has time to come up to pressure before any wobble is introduced.

dhbarr said:

Seems like piercing a hole of approx. sustainer nozzle throat diameter would make sense?

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Have you had success with composite boosters in direct staging? I'm curious about all non electronic staging methods.
I think its more of the disk (or whatever shape) obstructing the debris path. The pressure gets out, but the hot gas and particles are deflected randomly. To truly get a similar result as BP motors your hole may theoretically have to be as big as a BP motor inner diameter (which probably means your charge isn't contained anymore).

Nytrunner said:

Have you had success with composite boosters in direct staging? I'm curious about all non electronic staging methods.
I think its more of the disk (or whatever shape) obstructing the debris path. The pressure gets out, but the hot gas and particles are deflected randomly. To truly get a similar result as BP motors your hole may theoretically have to be as big as a BP motor inner diameter (which probably means your charge isn't contained anymore).

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I've read positive results written up on another rocketry resource, which included techniques for drilling strain relieved delay grains to get below 4s interstage timings ( not manuf. approved; EX )

Presumably whatever interstage coupler one us using ( e.g. sellotape ) would provide as much containment as a friction fit cardboard cap, which would be removed when assembling the stack.

I intend to try these methods over Thanksgiving, will try not to get so into it that I neglect to take notes & pics

If you look at the recent technical report on high-speed photos of delay burnthrough, you'll find that it's already a random chaotic mess and flame billows quite a ways up the interstage.

You might try something like this, using a a modified* ejection charge in a 29 mm composite booster engine to a 29 mm black powder engine in the sustainer.

*This modification would be to omit the red plastic ejection cap and instead use a bit of cotton or a small wad of tissue paper to retain the ejection charge, using only about half of the black powder charge. Use the shortest delay in the booster (4 seconds) and if possible, drilled 1/16 inch deep to reduce the delay down to 2 seconds but not more. Whether this constitutes any violation of NAR or Tripoli rules I do not know, but I know it will work.

[video=youtube;Zse-T3uYgz8]https://www.youtube.com/watch?v=Zse-T3uYgz8[/video]

This is great info. May the scientific method continue to dispel tribal knowledge!

It'll probably be awhile.before I try staging, but knowing there's been some groundwork should certainly help when that time comes.

tmacklin said:

You might try something like this, using a a modified* ejection charge in a 29 mm composite booster engine to a 29 mm black powder engine in the sustainer.

*This modification would be to omit the red plastic ejection cap and instead use a bit of cotton or a small wad of tissue paper to retain the ejection charge, using only about half of the black powder charge. Use the shortest delay in the booster (4 seconds) and if possible, drilled 1/16 inch deep to reduce the delay down to 2 seconds but not more. Whether this constitutes any violation of NAR or Tripoli rules I do not know, but I know it will work.

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A possible variation for covering the powder well could be to make a burst diaphragm from aluminum foil, then tape it around the sides of the powder well. In theory the aluminum should break and peel open (maybe create a small pin prick to get it started) allowing the flaming particles access to the sustainer motor.

Wow! I didn't think it was possible up direct stage using a composite motor. I'm super-interested in this too.

BDB said:

Wow! I didn't think it was possible up direct stage using a composite motor. I'm super-interested in this too.

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I have heard of it being done, but only AP to BP not AP to AP.

Of course, tampering with the AP motor is against the NAR Model Rocket Safety Code.

Here's a thread about my experimentation on this subject that was posted on YORF. (Fast forward to post 25 and onward that are applicable to my post here on TRF.)

https://forums.rocketshoppe.com/showthread.php?t=12147&page=1&pp=10

The "red cap" on Aerotech ejection well serves two purposes. First is to contain the black powder and prevent spillage, and second is to provide enough containment to create a small explosion sufficient to eject the laundry. By substituting a weak, burnable material for the red plastic cap, the ejection charge merely burns rapidly rather than exploding and thereby communicates the fire to the sustainer engine. :smile:

aerostadt said:

Of course, tampering with the AP motor is against the NAR Model Rocket Safety Code.

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My posts on this subject were for informational purposes only. I would hope that RCS/Aerotech would pursue this idea, test and ultimately produce reliable composite booster engines to compliment their existing mid-power products.

tmacklin said:

You might try something like this, using a a modified* ejection charge in a 29 mm composite booster engine to a 29 mm black powder engine in the sustainer.

*This modification would be to omit the red plastic ejection cap and instead use a bit of cotton or a small wad of tissue paper to retain the ejection charge, using only about half of the black powder charge. Use the shortest delay in the booster (4 seconds) and if possible, drilled 1/16 inch deep to reduce the delay down to 2 seconds but not more. Whether this constitutes any violation of NAR or Tripoli rules I do not know, but I know it will work.

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Fascinating! Would the light-off even be better if one substituted the 4F BP with 2F or even pyrodex since you want more slow burn and scatter than a quick flash?

tmacklin said:

Here's a thread about my experimentation on this subject that was posted on YORF. (Fast forward to post 25 and onward that are applicable to my post here on TRF.)

https://forums.rocketshoppe.com/showthread.php?t=12147&page=1&pp=10

The "red cap" on Aerotech ejection well serves two purposes. First is to contain the black powder and prevent spillage, and second is to provide enough containment to create a small explosion sufficient to eject the laundry. By substituting a weak, burnable material for the red plastic cap, the ejection charge merely burns rapidly rather than exploding and thereby communicates the fire to the sustainer engine. :smile:

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:clap: I have heard may hand waiving claims through the years and your efforts are the only ones that offered proof. I'm glad someone is doing this even if I never try it.

jrkennnedy2 said:

Fascinating! Would the light-off even be better if one substituted the 4F BP with 2F or even pyrodex since you want more slow burn and scatter than a quick flash?

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Possibly, but that would require more experimentation. The grain size must be small enough to fall through the passfire hole in the ejection well without blocking it. I do know that in black powder flintlock firearms, FFFF black powder is typically used as the primer in the flash pan for that same reason. I would also think that the greater the gap between the ejection charge and the nozzle of the sustainer engine, the more powder would be necessary to insure ignition.

I believe that the shortest stock delay used in Aerotech RMS engines is 4 seconds. In small or lighter rockets, this should provide plenty of momentum to maintain a vertical flight before staging without any modification to the ejection system other than substitution of the plastic ejection cap with a burnable material like cotton or tissue paper. An Aerotech F52-4 or G64-4 to an Estes F15-8 might make an interesting flight in something with a total lift off weight of 24-26 ounces.

Whether elimination of the ejection cap in favor of a combustible wadding constitutes "tampering" under NAR rules is for others to decide.

rstaff3 said:

:clap: I have heard may hand waiving claims through the years and your efforts are the only ones that offered proof. I'm glad someone is doing this even if I never try it.

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Thanks Dick. Sometimes, people extend all five fingers while waiving at me. :wink:

rstaff3 said:

:clap: I have heard may hand waiving claims through the years and your efforts are the only ones that offered proof. I'm glad someone is doing this even if I never try it.

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Ted dreams of things that never were and says "Why not ?" :grin:

This PDF has great staging AP motors to BP motors info. Similar to above, more detailed directions.

View attachment staging bp to ap copy.pdf



Under conclusions you will find the only real drawback, was not being able to drill delay grain for more specific time.

Now that drilling delay grains, to shorten delay time, is an accepted practice....a little testing with the pyrogen head off a standard igniter, makes this method a no-brainer.

There is a lot of interesting material here which looks like it could open possibilities in the future. But as for this rocket it was a bit breezy Friday and since we had concerns, we decided to leave the booster stage behind and fly it with a single Aerotech F40. Unfortunately, the motor CATO'ed about 30 above the pad.