I just cracked open a old 1278 Estes Vigilante to build. In looking at the booster and sustainer with the tape two engines together method, I would like to switch them to having engine hooks for both motors. This would create some gap between the motors due to hook and motor block in booster engine. I have done this before in a Semroc Texas Firefly with no issues, as it was designed that way, but not sure if there are any issues with my approach, so thought I would ask advice from the more experienced builders.

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Build floor: Estes Pro Series Jayhawk, Estes LTV Scout

In paint:
Estes Interceptor II

Ready for 1st flight: Custom Rockets Bullet, Semroc/Centuri Renegade, Semroc Laser X, Estes Beta Launch Vehicle, MPC Flare Patriot, Estes Nimbus, Estes SR-71, Estes Nebulon Warrior, Semroc Ruskie, Estes Nike -X, Estes Mini-Shuttle Clone. Estes Renegade, Estes Big Red Max, Estes Phoenix, Fliskits Shadowlord, Custom Rockets SAM-X, thanks Texas Winds and rain.
Austin TX

Put some vents in the stage couplers so it has enough time to ignite the upper stage instead of just blowing off the booster. You want the sustainer to "push off" the booster.

__________________
When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !

GH beat me to it. Some vents are certainly in order so that the second stage gets lit before the first stage pops itself off.

That said, at least one model I have built and flown, the Quest Zenith II, has motor hooks for both stages and no interstage venting. Yet it seems to work. The stage coupler fit in the base of the sustainer is pretty snug, though.

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Bernard Cawley
NAR 89040 L1 - Life Member
SAM 0061
AMA 42160
KG7AIE

So just to be clear, a couple of holes punched thru the booster engine mount so the gas can escape while it ignites the sustainer and then pushes away the booster?

__________________
Build floor: Estes Pro Series Jayhawk, Estes LTV Scout

In paint:
Estes Interceptor II

Ready for 1st flight: Custom Rockets Bullet, Semroc/Centuri Renegade, Semroc Laser X, Estes Beta Launch Vehicle, MPC Flare Patriot, Estes Nimbus, Estes SR-71, Estes Nebulon Warrior, Semroc Ruskie, Estes Nike -X, Estes Mini-Shuttle Clone. Estes Renegade, Estes Big Red Max, Estes Phoenix, Fliskits Shadowlord, Custom Rockets SAM-X, thanks Texas Winds and rain.
Austin TX

NOT the engine mount, the sides of the stage coupler need a couple 1/4" holes drilled.
Drilling a couple vent holes thru each centering ring between the BT-55 and BT-20 can work/help too.

__________________
When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !

I should have said centering rings. That is how its done on the Texas Firefly. See attached. I also like to put 2 balsa supports between the centerings as well, just to provide rigidity etc.

Attached Thumbnails

 

__________________
Build floor: Estes Pro Series Jayhawk, Estes LTV Scout

In paint:
Estes Interceptor II

Ready for 1st flight: Custom Rockets Bullet, Semroc/Centuri Renegade, Semroc Laser X, Estes Beta Launch Vehicle, MPC Flare Patriot, Estes Nimbus, Estes SR-71, Estes Nebulon Warrior, Semroc Ruskie, Estes Nike -X, Estes Mini-Shuttle Clone. Estes Renegade, Estes Big Red Max, Estes Phoenix, Fliskits Shadowlord, Custom Rockets SAM-X, thanks Texas Winds and rain.
Austin TX

That "Texas Firefly" method of holes in the centering rings should work fine for venting.
It should work without the side-holes in the stage couplers.
You could use one or other method fine, whichever you prefer.
I went "overkill" on the Astron Omega clone I built and did both...lol

The balsa supports for the centering rings are fine, but overkill for anything 18mm short of flying on a lot of old-school B14 boosters or single stage on composite D21s/D24s.

Remember, real vintage kits get fins and cones filled/finished with Dope Balsa Fillercoat and Sanding Sealer, no water based baloney.

__________________
When in doubt, WHACK the GAS and DITCH the brake !!!

Yes, there is such a thing as NORMAL, if you have to ask what is "NORMAL" , you probably aren't !
Failure may not be an OPTION, but it is ALWAYS a POSSIBILITY.
ALL systems are GO for MAYHEM, CHAOS, TURMOIL, FIASCOS, and HAVOC !