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  #21  
Old 10-12-2010, 05:10 PM
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For correctness the aircraft was the Yokosuka MXY-7 Ohka, or Cherry Blossom. Navy personnel dubbed it the Baka, idiot or fool. The training version of the aircraft was painted bright red-orange upper surfaces, while the operational version was overall gull gray. If you model the version painted overall gray, then a CATO is a close to scale flight.
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  #22  
Old 10-12-2010, 05:27 PM
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Here's a couple of thoughts:

1.) Although this is not shown in the diagram, I wonder if the wadding is supposed to go in front of the pod rather than along side of it, as the diagram shows. Packing a bit of wadding into the tube ahead of the motor pod might prevent the recess.

2.) [incorrect] I suspect that making the pod-less rocket glide will give it a less realistic recovery, rather than a more realistic one. The Baka was a rocket plane, a very crude and flimsy one that had little in the way of glide trim. The rocket motor gave it speed and range, but shortly after the motor burned out the Baka went into a steep dive. The rocket motor was meant to get it to the target, and then the pilot was to steer his plane toward a ship as it plunged down to the sea. Designing a plane so that it would be flyable in a controlled glide following a rocket boost involves some rather sophisticated engineering, and the Baka definitely did not have any. It took the Germans quite some time to develop the Heinkel He-176 and the Messerscmitt Me-163, and they just barely got them into production before the war's end. The Baka was by no means comparable to these designs, nor was it built anywhere near as well. If the Kamikaze pilot even managed to regain consciousness following the brutal rocket boost, he had nothing but extremely rudimentary controls to guide it during the high-speed dive.[/incorrect]

If I was to build this design, I would put a rather large spill hole in the second parachute so that as the rocket returned to ground nose first, it would not build up enough speed to be unsafe. A small parachute with a spill hole would probably be more effective than a streamer in preventing it from swinging back and forth so that the descent would at least somewhat resemble a dive bombing run.
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Last edited by Mark II : 10-13-2010 at 10:37 AM.
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  #23  
Old 10-12-2010, 05:35 PM
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Quote:
Originally Posted by Mark II
1.) Although this is not shown in the diagram, I wonder if the wadding is supposed to go in front of the pod rather than along side of it, as the diagram shows.
That's not wadding, that's a PK-12 chute shown in the pic.

Doug

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  #24  
Old 10-12-2010, 05:50 PM
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There is also a more legible version of the plan in Jimz. Note also that in the images below there are both the planned thermojet powered version - with intakes, and the triple rocket version. The trainer version with skid is also illustrated.

http://www.spacemodeling.org/JimZ/eirp_70.htm
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Last edited by jharding58 : 10-12-2010 at 06:12 PM.
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  #25  
Old 10-12-2010, 06:24 PM
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Quote:
Originally Posted by Doug Sams
That's not wadding, that's a PK-12 chute shown in the pic.

Doug

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Oops, you're right. OK, then here's another thought. I'm wondering if the motor is actually recessed as far into the body tube as it looks in the diagram. The motor tube is 8.65" long, and the motor hook projects 0.75" back from the end of it. This makes the pod effectively 9.4" long. The BT-60 body tube is 11" long. The shoulder of the BNC-60L was probably about 0.75" long, so that reduces the internal length of the airframe to 10.25". Two NCW-2 nose weights are attached to the base of the nose cone with a screw eye, so these further reduce the interior length by some unknown amount. If one doesn't include them, then the motor nozzle would be recessed 0.85" into the airframe when the pod was inserted. If the nose cone weights and screw eye reduce the interior length by another 0.25", then the recess is brought down to 0.6".

The instructions indicate that the CG location is especially critical with this design, so perhaps the effective recess was designed with that in mind. It probably cannot be completely eliminated. In light of the fact that the airframe is BT-60, I wonder if the flame jet from a circa-1970 Estes rocket engine would expand to a diameter of 1.595" before it reached 0.6" from the nozzle exit. If not, then the Baka most likely would not have been damaged by the recessed engine.
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  #26  
Old 10-12-2010, 07:07 PM
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I would go by your dimensions than the quarter view in the drawing. The dimensions for the aft end of the cockpit and the trailing edge of the wing are 4.5" and 5.5" respectively. They appear to be dead on in the drawing.

Given that the eye fits into the motor tube the distance from the rear edge of the BNC to the first centering ring of the piston is probably 1/8" loaded. NCW-2 were barely 7/16th diameter. Shoulder on the original Estes BNC-60L is 5/8". So the available swept volume of the BT would be (11" - (1/8"+ 5/8")=10.25.

BT-20B is 8.65" plus the .75" overhang of the hook is 9.4" which puts the aft end of the motor recessed around .85" - give or take the radius of the bend in the hook... although the drawing appears to place it around 1.3
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Last edited by jharding58 : 10-12-2010 at 07:25 PM.
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  #27  
Old 10-12-2010, 10:01 PM
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Default Ohka Model 22

The Ohka Model 22, which was powered by a thermojet (also called a motorjet, a ducted fan driven by a reciprocating engine) has possibilities as an air-augmented ducted rocket model and as a (horizontally-flying) ducted Jetex or ducted Rapier powered model. Below are a few links to photographs and information on the Ohka Model 22:

http://www.nasm.si.edu/collections/...id=A19480180000
http://tanks45.tripod.com/Jets45/Hi...o-22/Ohka22.htm
http://www.travelco2neutral.com/Kug...Flying_Bomb.htm
http://en.wikipedia.org/wiki/Ohka
http://www.airliners.net/photo/Japa...Ohka/1488133/L/
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  #28  
Old 10-13-2010, 06:51 AM
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Quote:
Originally Posted by Mark II
I created this thread to divert the off-topic discussion from here and place it in its own thread. The discussion concerns the design for a model of the Japanese Baka that was published in Vol. 10, No. 3 of the Estes Model Rocket News.

Just about that entire thread through post #25 is taken up with the OT discussion, so I'm not going to bother providing links to the relevant irrelevant posts from there.



Thanks for doing that, I was going to do the same thing, but didn't get back to the computer soon enough, my apologies to the OP in the other thread.
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  #29  
Old 10-13-2010, 07:44 PM
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My "Mo' Skeeter" features a "power pod" design like the Baka, but uses a single chute and recovers like this:



I'm sorely tempted to make a look-alike version of this design by getting a set of Saki fins from Carl and mating them to an 11" BT-60 with a Bertha cone. Rather than using two chutes, I'd probably use a single chute like with the Mo' Skeeter. To avoid needing too much noseweight, I'd also probably move the "wings" back a bit, about halfway between the given location and the tail of the rocket (or maybe a bit forward of that).

I'm not a scale person... I just like interesting designs.
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  #30  
Old 10-13-2010, 10:07 PM
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To extend upon an earlier comment - if you were to retain the spit mount and then use a small clear chute for the airframe you would have a quite prototypical descent.
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Last edited by jharding58 : 10-14-2010 at 04:07 PM.
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