Greg Poehlein responded back with a great new idea of putting a reverse bend in the top of an engine hook.
Thu, October 20, 2011 1:15:23 AM[OldRockets] Re: Estes Engine Hook
From: Greg
To: OldRockets@yahoogroups.com
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If you are planning to use it in a rocket with a body tube of BT-55 or larger, you can still use these hooks. My suggestion is to put a motor block in the tube at the depth you want for an overhang. Then, bend the top end of the motor hook AWAY from the motor tube at a 90 degree angle. Glue the centering ring just behind the hook, so at ejection, the ejection charge will be pulling the motor hook against the centering ring between the motor tube and the body tube. For that matter, you could do the same thing with a standard (2.75") length motor hook as well. Good luck with the build.
Here's what one of these hooks could look like if used on a standard 18mm engine mount tube.While Greg mentioned using this hook in a BT-55 or larger, the hook as shown (with a shorter top bend) could fit into a BT-50 sized tube.
The bend on the right side goes under the nozzle end of the engine. The upper (shorter) bend faces away from the mount and and would sit over the top of the upper centering ring.
The engine hook from the side. Notice how the upper bend of the hook faces out and goes over the top of the upper centering ring.With a "shotgun" ejection charge any movement of the hook is against the top centering ring, not pulling down inside a thin walled BT-20 engine mount tube.
In this example, the upper outward bend of the hook is shorter so it won't overhang the centering ring diameter.
Viewed from the top, you can see the engine block (or thrust ring) in place.
The thrust ring keeps the engine in place during the boost stage.
The lower and upper reverse bend in the engine hook keep the engine in place at ejection.
A simple, brilliant idea. Thanks Greg!
Check out Greg's Project Paper on TRF HERE
Chris, this type of tip is one of the reasons your blog is the best. This is absolutely brilliant!
ReplyDeleteAlong with increased ejection charges, I have experienced a couple of occasions where engines have exploded and forced themselves through the body tube and out the top during flight, bending the upper engine hook out of the way (Luckily I was able to repair and reuse the rockets). Using an engine block instead of a hook up top, this technique would solve that problem as well. I will definitely try this on my next build.
Hi Lonnie,
ReplyDeleteThanks! But, all the credit goes to Greg Poehlein on this one.
You almost have to wonder why engine hooks weren't bent this way from day one!