Puller concept...

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Bohica

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Just an idea I am fooling around with...



Oops...that top BT-20 is 130mm long...not 13!:D
 
I once built one similar to this one I found on EMRR-
https://www.rocketreviews.com/reviews/scratch/mystery_rocket.html

Watch out for those dowel rod spars! Make sure they are attached
securely and aligned perfectly so there isn't any undue stress.

You might have to extend the spar length on your design. The lower body tube
might introduce a <a href="https://www.rocketreviews.com/cgi-bin/flattips/glossary.cgi#347">Krushnic Effect</a>, or get burned apart after a few flights.
 
A slight variation on the concept. This is actually a two-stage rocket with a cluster of 3 engines in the lower stage. It's a combination of a puller and a CHAD.
 
Originally posted by TeenRocketNerd
make sure to use high heat spray paint and/or foil tape. :)

If this prototype proves out I will be using high heat type at the fin tube inlet and some heat resistant paint on the rest of it.
 
Originally posted by brianc
I once built one similar to this one I found on EMRR-
https://www.rocketreviews.com/reviews/scratch/mystery_rocket.html

Watch out for those dowel rod spars! Make sure they are attached
securely and aligned perfectly so there isn't any undue stress.

You might have to extend the spar length on your design. The lower body tube
might introduce a <a href="https://www.rocketreviews.com/cgi-bin/flattips/glossary.cgi#347">Krushnic Effect</a>, or get burned apart after a few flights.

The spars will be treated for heat resistance and they are dead straight...

After studying the available data on the Krushnic effect I have determined that it should not be a factor in this design. Thanks for the tip BTW, I had never heard of the Krushnic effect before your post...
 
Originally posted by Bohica
Just an idea I am fooling around with...



Oops...that top BT-20 is 130mm long...not 13!:D
Woah, i misread that to be a min dia. L staged to a wee little motor... I was gonna say...
Reed
 
Neat looking design, and, no worries about nose weight:) I'm looking forward to your flight test results. Mainly, how the lower tube holds up to the heat.
 
Originally posted by astrowolf67
Neat looking design, and, no worries about nose weight:) I'm looking forward to your flight test results. Mainly, how the lower tube holds up to the heat.

Me too!:D:D:D If it does'nt rain all day I will try it on an A8 this evening.
 
You might not even need fins on the lower section, visit:

https://www.rocketreviews.com/contest/virtual_rockets8/levison_twin_boomer.jpg

The struts are 0.246mm diameter body tubing and also serve as launch lugs. The struts are just coated with plain Krylon lacquer paint over a coat of white autobody primer. The struts got slightly singed on their inner edges after a few launches.

Bruce S. Levison, NAR #69055
 
Well I got in one quick launch this evening on an A8-3. It was so smooth it was boring.:D About 150' with a very sloooowwww spin...maybe twice around on the way up. The lower tube suffered no damage at all nor did the spars.

I am putting this one down as definately "do-able" and I will build a nice "finished" version over the winter.

I love it when a plan comes togethor!
 
Originally posted by brianc
You might have to extend the spar length on your design. The lower body tube might introduce a <a href="https://www.rocketreviews.com/cgi-bin/flattips/glossary.cgi#347">Krushnic Effect</a>, or get burned apart after a few flights.
Provided the lower tube is open at both ends, the Krushnic Effect won't happen. The motor could even be inside the lower tube.

If the motor is too far up inside a closed tube, the exhaust gas expands into the tube and reduces pressure to below atmospheric, causing air to be sucked up from the bottom end. Venting the tube above the motor will allow air to be sucked in from the vents, preventing the Krushnic Effect. A design like Bohica's, with an open tube below the motor, can even augment the thrust. I'm not sure what length or diameter of tube is best, but I do know that some research was done into this.
 
Neat personal project, Gerald.
Cool concept. :cool:

Definitely got my curiousity. Now I'm wondering if 29mm is
do-able. Might be too much heat for multiple launches, though.

-Chris
 
Thanks Chris...It worked...at least once.:D Before I build a "dress" version I am going to look at high heat paint options.
 
Originally posted by Bohica
Before I build a "dress" version I am going to look at high heat paint options.

Brass (thin-walled) tubing used for the spars might help a bit.
I also agree with the use of foil (muffler) tape on the I.D. of the lower BT. Then, heat paint it! Might be just the ticket.

Just thinkin' out loud :rolleyes:

-Chris
 
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