Yes, a thrust block will need to be in the sustainer, but nothing in the booster. A few Estes kits like the Apogee II had an engine block on the back end of the booster to keep it from kicking out during staging, just the opposite of a traditional thrust block.

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I love sanding.

That's true. Also, the Estes Loadstar still uses a rear-mount engine block in the booster stage. The Quest Navaho AGM uses engine hooks, but I've never flown one.

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NAR# 94042
SAM# 0078

The Quest Zenith II uses hooks also, as does the classic Estes Omega with gap staging.

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I love sanding.

Does it work OK without the tape?

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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

I've built several with engine hook's. Both the upscale's I'm fixing to start on will have engine hook's. The Rip Roar made by Apogee is the built like this. I have started using vent hole's in mine to assure I light the next stage properly.

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Multi Stages Rock
Kevin

Correct; that rear-mounted block was what I was referring to. With it installed, there is no way that Jeff's scenario, in which the booster motor was ejected at staging but the booster unit itself remained attached, would ever happen. When the booster motor disconnects from the sustainer at staging, it takes the whole booster unit with it. Since the booster motor does not have an ejection charge, it does not need to be as firmly held in the booster unit as a friction-fitted motor in a single-staged rocket would require, because it doesn't need to resist being kicked out by an ejection charge. It does need to have some friction on it, though, to keep the booster unit that surrounds and houses it from flying off and being left behind at lift-off.

MarkII

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SAM # 0011

Engine hooks can be used for both motors if gap-staging is used, because the motors don't actually touch each other in that set-up. For direct-staging (taping the booster motor to the sustainer motor), the rear-mounted thrust block in the booster stage unit is the way to go. Estes Industries used a special thrust block (EB-20B) in the Astron Midget for this; basically, it was a thin ring that was cut from a BT-20 coupler. It did the job perfectly, and was narrow enough to avoid getting burned by the booster motor's exhaust plume. If you are scratch-building, you can get this part from Semroc. They also have the longer version, EB-20A.

See Step 4 of the K-40's instructions and step #11 of the Flight Prep sequence in the attachments.

MarkII

Attached Thumbnails

   

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SAM # 0011

The easiest way to stage a model rocket is to dispense with the first stage airframe altogether. As with the British Skylark 7 and Skylark 12 sounding rockets (see http://www.sat-net.com/serra/skylar_e.htm and http://news.bbc.co.uk/2/hi/science/nature/4490253.stm ), using a short and finless first stage works perfectly well if the second stage is long enough and/or has a sufficiently heavy payload that the second stage's fins can stabilize the vehicle. This reduces both dead weight at launch and drag.

From the standpoint of drag, this method is best suited to minimum-diameter rockets, although I have successfully staged wider models such as the 25 mm diameter Quest Tracer using finless first stage motors. The first stage motor is simply butt-joined to the second stage motor and the joint is wrapped with a single layer of cellophane tape.

This method even works with second stages that use motor clips. The clip is simply flexed out of the way to insert the second stage motor into the second stage rocket's body tube (or motor mount) just as one would do when flying the rocket as a single-stage model. When the second stage motor ignites and blows off the spent first stage motor, the flexed motor clip snaps back into place to retain the second stage motor in the model. (Although I've never had a second stage motor fail to be retained by the motor clip, a small rubber band slipped over the rear end of the second stage motor would ensure that the motor clip would snap back into place--the rubber band would do its job long before heat soaking through the second stage motor case might cause the rubber band to lose its elasticity.)

To make the spent finless first stage motor more visible while falling and after landing, it can be spray painted with bright fluorescent colors or aluminum paint, or the motor could be wrapped with aluminized mylar tape.

I hope this information will be helpful.

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NAR #54895 SR

The IRIS sounding rocket, among others, used a small finless booster. It got the rocket going off the pad at ignition and burned out before the IRIS had even cleared the launch rail, falling away as the rocket, with its sustainer motor ignited, left the rail. It sort of resembled the Tiny Tim booster for the Wac Corporal in appearance, but was shorter.

What you are describing is called CHAD staging (CHeap And Dirty), and it has been used in model rocketry for decades. It doesn't work with all designs, though, because it shifts the CG rearward and lowers the stability margin. If the booster motor has a large enough mass, this could be a problem. And often the booster motor IS fairly massive, because it has a lot of work to do.

Semroc has a finless booster kit (the Booster-16 engine mount) that can be used with rockets that have a 1.64" (ST-16) diameter, such as the Centurion. I would imagine that with a very slight amount of trimming it can also be used with BT-60 based rockets, too.

I'm glad that you mentioned this method, Black Shire, because it is a very viable option for staging any rocket that is stable enough to be able to handle the extra mass in the tail. Someone on this forum mentioned to me a couple of years ago that the Estes Maxi Alpha was a terrific platform for CHAD-staging.

MarkII

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SAM # 0011

Thank you, Mark II, for posting the meaning of "CHAD." I'm familiar with the term, but I didn't remember what words it stood for.

Your description of the ARC (Atlantic Research Corporation) IRIS reminded me that ARC's ARCON sounding rocket (see: http://www.designation-systems.net/...app4/arcon.html and www.astronautix.com/lvs/arcon.htm ) actually did fly with a finless booster attached, although it wasn't a true first stage because the booster and the ARCON sustainer were ignited simultaneously and burned in parallel (like the Aerobee booster and sustainer). As with the Aerobee, the ARCON's "slip-fit" booster remained attached to the sustainer during its burn because its thrust was much greater than that of the sustainer, and drag plus the sustainer's exhaust separated the booster as soon as it stopped thrusting.

Semroc sent me one of their finless ST-16 first stage kits as a bonus item. With its high frontal area/weight ratio, it should land fairly gently. Now we just need A10-0Ts for it...

The three-stage British Skylark 12 (see: http://www.sat-net.com/serra/skylar_e.htm ) got me thinking--a scale (or sport scale or semi-scale) model of it could use not only a finless first stage, but by canting its second stage fins to make the model spin like the full-scale vehicle, the third stage (also finless, which would be gap-staged in the model) could be flown "live" without fins by using spin stabilization. The weight of the third stage motor up near the nose of the model would give the model an excellent stability margin even with the finless first stage.

Also, the Japanese (formerly ISAS, now JAXA) SS-520 two-stage sounding rocket (see: http://www.isas.ac.jp/e/enterp/rock...ing/ss520.shtml and http://www.jaxa.jp/projects/rockets...ts/index_e.html ) has a finless second stage that is stabilized by the spin imparted to the rocket by its first stage fins. An SS-520 model with a spin-stabilized gap-staged finless second stage would also have a very good stability margin due to the weight of the second stage motor up near the rocket's nose.

__________________
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