Tank Killer--- update 11/15

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BABAR

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neil_w

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Looks like you have the whole airframe ready to go. How about the fin "can"?
 

BABAR

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Okay, the creative juices are flowing, or perhaps in this case swirling
I have only had one other rocket that just BEGGED for rear ejection more than this one, that was the Uranus Explorer

https://www.rocketreviews.com/umm-me-uranus-explorer-2-scratch-by-tom-markel.html



This one however will have a twist.
First, the nose itself is probably the toughest part of the rocket, so as opposed to other noses, having this one land nose first seems logical.

Second, I put a dowel through the nose as a way of attachment, thinking to add a short segment of body tube either as a shoulder or even a short length of tube THEN a shoulder. But if I just glue it onto the tube, makes it even simpler, and just go eject.

But third, and perhaps most mucho coolo (hey, I don't get out much okay?) I can leave the dowel on, put piston plug an the tail end of the dowel say 3 inches forward of the front no of the engine, then have to long tube inner rear eject simply slide off the piston. Will have to diagram this on my desk top computer to demonstrate. I have never seen this done before, but it seems like it incredibly simplifies the rear end eject mechanism,.
 
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neil_w

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Okay, the creative juices are flowing, or perhaps in this case swirling
I have only had one other rocket that just BEGGED for rear ejection more than this one, that was the Uranus Explorer
I had forgotten that build was also yours.:roll:

Will have to diagram this on my desk top computer to demonstrate. I have never seen this done before, but it seems like it incredibly simplifies the rear end eject mechanism,.
I will await a picture. :)
 

Lowpuller

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I recommend using gas for your rear ejection method..
 

BABAR

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I recommend using gas for your rear ejection method..
There will be sulfuric fumes all right. In fact this is one of my few scratchers (hmmmm, that in itself may be a less than optimal term for a rear ejection model) that will require an engine hook, as within the small initial space for the piston pressure tube the gas pressure will build up pretty fast.
 

BABAR

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Okay, here is diagram. Will probably double wall the BT-5 pressure chamber section, will also have an internal roll of aluminum from a soda can on the inside for flame retardant. Reason is that the ejection charge from the 24 mm engine is being ducted through the BT-5, thus a LOT of heat going through a very small tube. Plus whenever I see an engine fired on a stand so you can watch it, after the ejection charge there is a persistent flame that burns for a few seconds and extends maybe 2 or 3 inches from the forward end of the casing. I think this may be why Kevlar thread attached to motor mount and otherwise unprotected burns through a lot.

Main reason for down-ducting of the BT-50 to BT-5: For me, biggest problem is rear engine eject models in not a lot of space for the recovery device between the engine pod tube and the outer fuselage tube. Downscaling from BT-50 inside a BT-60 to a BT-5 inside a BT-60 gives me a WHOLE lot more space.


The red "shelf" section is sort of a centering ring around the mid portion of the BT-5. It is attached to the BT-5 but NOT to the outer fuselage. It is very loose, mainly serves to nudge the parachute out with the engine pod assembly..

The grey blue "guides" around the motor mount likewise are centering rings attached to Motor Mount BT-50 but not to the outer fuselage. Just keeps the engine pod aligned within the outer fuselage.
 

K'Tesh

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I think there's a possible name for this... John...

[video=youtube;bx86xPHCAuI]https://www.youtube.com/watch?v=bx86xPHCAuI[/video]

As for the rear eject, if it doesn't work, I'd just toss the whole idea into the crapper.
 

bill_s

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View attachment 313611

Okay, here is diagram. Will probably double wall the BT-5 pressure chamber section, will also have an internal roll of aluminum from a soda can on the inside for flame retardant. Reason is that the ejection charge from the 24 mm engine is being ducted through the BT-5, thus a LOT of heat going through a very small tube. Plus whenever I see an engine fired on a stand so you can watch it, after the ejection charge there is a persistent flame that burns for a few seconds and extends maybe 2 or 3 inches from the forward end of the casing. I think this may be why Kevlar thread attached to motor mount and otherwise unprotected burns through a lot.

Main reason for down-ducting of the BT-50 to BT-5: For me, biggest problem is rear engine eject models in not a lot of space for the recovery device between the engine pod tube and the outer fuselage tube. Downscaling from BT-50 inside a BT-60 to a BT-5 inside a BT-60 gives me a WHOLE lot more space.


The red "shelf" section is sort of a centering ring around the mid portion of the BT-5. It is attached to the BT-5 but NOT to the outer fuselage. It is very loose, mainly serves to nudge the parachute out with the engine pod assembly..

The grey blue "guides" around the motor mount likewise are centering rings attached to Motor Mount BT-50 but not to the outer fuselage. Just keeps the engine pod aligned within the outer fuselage.
The one issue I can see is the eject pressure will be very high, probably over 200 PSI except for leaking. The piston won't really seal that well except for gunking making it tight later if it gets that far. If the pressure were somehow reduced the piston area is small so the total ejective force is low, so can't do a lot of that. Other things is I don't see a stop to keep the MMT from moving forward and if the shelf ring intended to be loose and the stop is behind it could hang up. And it's all delicate. What I see is a possibility of just leaving out the piston and dowel and just using the inner tube for bypassing the ejection and also wadding, with probably the shelf ring full diameter and maybe providing the stop. The piston would eliminate the need for wadding but that's the main thing it buys you. Rear eject also works without wadding if there's enough space for the ejection to go to and the shock cord out the back, but I'm not sure if you'll have enough protection without any. As to shielding, if the BT50 tube can be extended at all it would help and I'd probably concentrate on getting some epoxy e.g. JB Weld coasting the corner there. And while it's a big concern having enough space for a parachute with rear eject, your scale is closer to BT50 or even 29 mm (are you sure D size motors are enough?) inside BT55. Inside a long piece of BT60, a long enough piece of BT50 might be fine or a step down to BT20 would be less fragile.

As to rear eject generally, I started off building rockets that stood and landed on their fins and a rear eject that neither stood or landed on its fins, so now I've started to fix that disparity.
 

BABAR

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IMG_0182.jpg
Lucy likes it!IMG_0184.jpg
 
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BABAR

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IMG_5247.jpgIMG_5248.jpg

Primer on. Letters on white primer background, will primer over the letters (white primer), then paint green and pull of letters.
The dots are little stick ons, trying to simulate rivets.
 

BABAR

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Successful Flight of Tank Killer

First flight with rear eject was failure. Thought I was assuring engine retention with an engine hook (I usually use tape) Apparently hook not tight enough, engine ejected, pod didn't. Lawn dart. Interestingly I had two police officers who stopped to watch the flight (park was empty.) They didn't notice anything, thought it was cool. I wasn't ABOUT to say anything.

Rebuilt for forward ejection, Had a great flight on D12-3. Altitude I am guessing about 300 feet. Angled slightly into wind, blew back and landed about 75 feet from pad.

I like the look of this one.

Tank Killer.jpg
 
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