The following statement may be of interest to you. It was sent to me over a year ago when I was working on a 1/45 Gemini Titan with closer scale motors. The last paragraph should be of interest. You might would want to do some testing first if you want to consider two 18mm motors back to back. Would be a longer motor tube. Could use engine blocks when only using single motors. Just a idea, that’s all. I choose not to try it.

It was a rather short-lived "thing" in NAR competition in the 1976-79
> timeframe and was first demonstrated by Trip Barber. It allowed, for
> example, the use of a "B" class motor in a smaller diameter tube than
> "standard" 18mm B motors...obviously giving one an edge in competition. It
> was eventually prohibited from competition and quickly disappeared because
> it was both not a widely known modification and there was little need
> outside of competition. However, for serious scale modelers, competition or
> not, there is a desire in many cases to have the scale motors as true to
> scale as possible even with a model rocket motor housed inside.
>
> There were some interesting combinations of tandem motors (which, BTW, only
> works with "black powder" motors. For example, a standard 18mm motor fits
> inside a standard 24mm casing. This combination allowed use in most models
> designed for 24 mm motors without modification to accommodate the longer
> motor since the 18mm "front" motor would pass right through the engine block
> or forward engine hook tang. It also meant that you didn't have to have a
> slightly larger engine tube since there was no need to "overwrap" the joint
> with glass cloth. Of course, a smaller motor firing down through a larger
> motor reduced the sum of the impulse delivered by the two motors vs. if they
> were not "tandemed" but you still picked up performance nevertheless.
>
> Also, you didn't want to tandem a high thrust motor with a large nozzle
> above a lower thrust motor with a smaller nozzle. That would almost
> guarantee a rupture at the joint between the motors. Tests did show
> (surprisingly) that there was little performance lost by tandeming two
> identical engines. In other words, say, two 10n/sec C motors did in fact
> almost sum up to 20n/sec or basically a full D black powder motor in an 18mm
> casing (though it was twice as long).

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If the Sky is the Limit, then,
why is there Footsteps on the Moon?
=======================

I just got back from Lexington, KY, and my Boyce Gemini builder’s kit was waiting for me. I’ll lay the stuff out tomorrow.

__________________
Never trust an atom. They make up everything.

4 out of 3 people struggle with math.

Chemically, alcohol IS a solution.

NAR# 94042
SAM# 0078

Blue Thunder propellant would give you realistic-looking exhaust plumes, though.

__________________
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

But we need toxic orange smoke at ignition...



.

__________________
I love sanding.

That can be arranged for, too (and without immediately-lethal [alveoli-dissolving] and longer-term carcinogenic and mutagenic effects), by igniting orange HVAC duct testing smoke generators (see: https://superiorsignal.com/smoke-products/smoke-pellets ^and^ https://www.google.com/search?sxsrf...HTktDXwQ4dUDCAw [these have also been tried, with good results, as Jetex & Rapier jet motor replacements]) just before the models' Blue Thunder propellant motors are ignited. This would be like the MRC Concept II model rocket kits, whose two--or three--FX smoke motors are electrically ignited (the FX System Dual Launch Control panel has two sets of ignition buttons, see: http://www.ninfinger.org/rockets/nostalgia/mrccat.html ) some time--up to ten seconds--before the models' propulsive 18 mm rocket motors are ignited, for greater scale realism.

__________________
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

The toxic part is what I like.

__________________
I love sanding.

Here's what's in the box:

Attached Thumbnails

             

__________________
Never trust an atom. They make up everything.

4 out of 3 people struggle with math.

Chemically, alcohol IS a solution.

NAR# 94042
SAM# 0078

Very nice! Can't weight to get mine. I'll order mine next Tuesday the way things or looking.

Thank you for sharing!

__________________
=======================
If the Sky is the Limit, then,
why is there Footsteps on the Moon?
=======================

When I was younger (and my lungs were, too), and I could sleep soundly in a room that was redolent of materials such as--or containing--solvents, non-water-based paints, strong acids and bases, noxious products of combustion, and so forth, I considered that ability a matter of pride, but:

Beginning in the late 1990s, when even < 30 milliliter, curing mixtures of polyurethane resin prepolymer and isocyanate made me feel tightness in my chest, I knew that my youth-conferred seeming invincibility in the face of life (as we know it)-hostile chemicals was at an end. Now that my lungs can no longer inflate fully (due to Ankylosing Spondylitis progressively reducing the available chest cavity volume that my lungs can inflate into, by bending my spine and body forward so that I increasingly--in profile--resemble a letter "C"), I am palpably aware of the ambient air and its temperature, pressure, and levels of humidity and included impurities, as even moderately "off-spec" atmospheric parameters now easily make the difference between well-being and wearying, labored breathing. (I have contemplated building [another--I'd built one many years ago] a toy train transformer-powered water-splitting electrolysis machine, to generate clean, comfortably cool oxygen [with the hydrogen being vented outside].)

__________________
Black Shire--Draft horse in human form, model rocketeer, occasional mystic, and writer, see:
http://www.lulu.com/content/paperba...an-form/8075185
http://www.lulu.com/product/cd/what...of-2%29/6122050
http://www.lulu.com/product/cd/what...of-2%29/6126511
All of my book proceeds go to the Northcote Heavy Horse Centre www.northcotehorses.com.
NAR #54895 SR

I like the TOXIC orange cloud effect as well.
Hydrazine, wasn't it ?
GOOD STUFF.

__________________
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, and HAVOC !