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Pumpkin drop event

tail booms and t tails

#1
I have been building and designing for some small amount of time and I find myself quite fond of single boom pushers. I'm not sure why i like them protection for the prop and simple nose to repair on impact probably weigh in.
the problem I've found is that the combination of t tail and tail boom was a bit... flexible.. the prop wash from my 9-5 on the e flite 480 made my stabilizers seem a bit under stable. My current tail boom is a arrowshaft from Wal-Mart ,poltruded carbon, I think
and while it never bent.. it twisted. It looked as if my tail boom had rotated in the fuselage. Then it returned to normal when I stopped accelerating
this fact and a bit to windy day led to this particular parambulator being up for repairs or a complete rebuild.
I am looking for options for a new tail boom.
I love my t tail... is it a bad choice for this configuration?
I fear the weight of building a foam Box tail boom
what do y'all use?
Is the tail too long? Is it too short?
wingspan is 74"btw
 

Attachments

AkimboGlueGuns

Biplane Guy
Mentor
#2
Nice work on your design. It would be pretty easy to just build a foam boom. This shouldn't really effect your overall weight if you eliminate the weight of the carbon. Otherwise a square piece of carbon would resist rotation a bit better. You could also try using stronger adhesives on your carbon boom. Keep the tail vertical and use foam safe epoxy of wood glue (something very strong that won't melt the foam) and make to "welds" along the piece of the boom that connects with the fuselage.
 

johnmw

propulsion impromptu
#3
imho,
the weak (and possibly flex) point could be the elbow on the fuselage, if design could be improved i'd suggest adding some vertical structure in that gap between belly and wing mount.
the distance from tail to wing should be fine, and the twist can't be helped much with such design.
theoretically, on a same material and cross section, the longer the boom the more twist will be apparent.
it could be optimized with sturdier built, etc. of course, like square boom as pointed out above.
another point would be to reinforce your boom mounting to the fuselage, looks pretty thin from the pic, though looks great.

just my 2cts.
 
#4
When I designed it I meant for a v of foam to fill that area. With the fold near vertical between motor mount and lower fuselage I like how it looked so much I did with out...
I'ma bit of a blinking bulb when it comes to bright ideas.
my current solution is a nearly solid fusalage up front, only room for electronics.
this has the bonus of being tough. i don't think its clever. Ten layers of foam board sandwiched together
I'm planning out a foam boom. Hollow as seams best.
Also it looked like the boom rotated in the fusalage. That isn't actually what's happening. I was trying to describe the twisting.
the boom is glued in the center of a K of foam with 4 beads of glue spread between the sheets it seams very secure
 
#5
The only real way to prevent twisting is to increase the diameter of your tail boom. This could mean buying a wider and thinner walled carbon boom but its probably more practical to just make a foam tube. You can still use the carbon arrowshaft to farther reinforce the foam
 
#6
How about wooden dowels or square stock?
I'm thinking pine. Balsa is hard to find for me.
what are the anycopters booms?
the arrowshafts aren't really easy to find in different sizes. The cheap ones , like I'm using, are biggest.
the more expensive ones get smaller. Some more expensive ones are woven carbon as opposed to the non woven ones I have.
I am hoping to find something better where could I source square carbon tubes. Preferably big enough that I can run servo extension through instead of 're wiring servo.
Current servo busted gear. I think this happened in transport. Do y'all think these small servos are a bit to small for this size of plane?
The are eleven gram hitecs. I'm mounting the elevator way back so adding weight would be an issue again
Would long pushers be better?
What would shortening the boom do to the plane.
the tail is currently to long for a single she at of foam to stretch the fusalage. A foam boom?
How would y'all do this?
I think of an octagon starting larger in front the tapering but. I'm not sure how strong this would be I must test
 

johnmw

propulsion impromptu
#7
How about wooden dowels or square stock?
I'm thinking pine. Balsa is hard to find for me.
what are the anycopters booms?
i think it's basswood, i could be wrong.

the arrowshafts aren't really easy to find in different sizes. The cheap ones , like I'm using, are biggest.
the more expensive ones get smaller. Some more expensive ones are woven carbon as opposed to the non woven ones I have.
I am hoping to find something better where could I source square carbon tubes. Preferably big enough that I can run servo extension through instead of 're wiring servo.
Current servo busted gear. I think this happened in transport. Do y'all think these small servos are a bit to small for this size of plane?
The are eleven gram hitecs. I'm mounting the elevator way back so adding weight would be an issue again
personally i think it's rather pointless to make one part of the plane bulletproof while the rest aren't.
unless it disturbed the flight so much, then i'll leave the twisting boom be.
perhaps just strengthen it more with hot glue etc.
9g servo should suffice imho.

Would long pushers be better?
What would shortening the boom do to the plane.
the tail is currently to long for a single she at of foam to stretch the fusalage. A foam boom?
How would y'all do this?
I think of an octagon starting larger in front the tapering but. I'm not sure how strong this would be I must test
i suppose it depends on the design and plane parameters, but generally pushers are placed near plane axis.
you could browse the forum or watch the Flitetest build youtube vids for reference on foam boom,
much easier to understand watching than explaining in words.
GL.
 

Ron B

Posted a thousand or more times
#9
try a triangular foam boom as they are lighter than a square one. if the foam board isn't long enough then join them with a smaller triangle inside so both pieces get a good glue point like in the nose of the mini Guini.
it depends on the size of the push rods but usually pushers are tail heavy so mounting the servo farther forward will help cut down on tail weight.