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https://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/stiffness-density/basic.html=
So what is Young's modulus for balsa wood?
https://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/stiffness-density/basic.html=
So what is Young's modulus for balsa wood?
Hey, long time no post!In-flight testing is king, is it not?
My Falcon 9 flew fine with the stock fins, but those occasional rougher-than-normal landings is what cracked them *every time*
I would personally go with one step thicker than that.
Because they're not all the way in back, they're not nearly as effective, so I was hoping at least hoping to save some weight.
In-flight testing is king, is it not?
Looking at your fin shape.Hey, long time no post!
That is valuable input.
It does look like the F9 has those swept-back pointy-tipped fins which would seem to have a lot more vulnerability to landing impact. My tail will be more like this:
View attachment 397075
In theory the fins should be subjected to much less landing impact shock. I'm still fiddling around with the final fin shape. Because they're not all the way in back, they're not nearly as effective, so I was hoping at least hoping to save some weight.
Realistically, I could make them 3/32" (which would definitely be plenty strong IMHO) and all it'll cost me is a bit more nose weight, so I probably shouldn't worry about it.
So what is Young's modulus for balsa wood?
Hmm, those diagrams show balsa having a *higher* modulus with the grain than Lexan, but values I've looked up elsewhere show Lexan having 3-4x the modulus.
This website says 3 GPa for balsa, vs. 13-23 GPa for Lexan.
It certainly feels to me like the 3/32" Lexan I have from Home Depot is much stiffer than 3/32" balsa.
All true.I am assuming that the fins are supposed to be invisible. and also assuming that you are not shooting for altitude, so DRAG efficiency isn't a big deal, but CP efficiency IS a big deal.
Constraints are as follows:Note sure how you are picking the root chord length, but figure you have a fixed length in mind.
In OR, squaring off the front, given the same fin root, brings the CP *forward*.That being the case, would a square or rectangular fin shape (take out the delta in front) allow you to use a shorter semi-span for the same CP benefit?
Oh, is that what it's for?Less talking, more doing. Build it lol! You got a motor mount, right?
-Bob
In OR, squaring off the front, given the same fin root, brings the CP *forward*.
.
The real one will look better.Seriously though, looks really cool so far Neil! That eraser tip looks perfect. What is your plan for attaching the fins?
Longer is the best answer I think. I added a few inches to the front, and gained some margin and was still able to reduce the semispan a bit. Small amounts of nose weight should be sufficient to make it all work if it becomes too tail-heavy during construction.Does making the rocket a little bit LONGER (move the nose further forward) throw the “scale-pencil-look” off to much?
I've used a replaceable bamboo skewer mounted between the motor mount and the BT that sticks out 4 or 5" to protect fragile fins at landing.
Great idea, only concern is to round the rear ends or put rubber caps on them.I've used a replaceable bamboo skewer mounted between the motor mount and the BT that sticks out 4 or 5" to protect fragile fins at landing.
Just a thought...
A simple design that could be nice with a good paint job. I started with much more complex rear fins but found it looks way better with the simpler ones. I did this one in white because the unfinished appearance was distracting. Dunno why I found that to be the case here but not elsewhere, but whatever.
View attachment 327580
Here's a good side view (click for giant version):
View attachment 327707
From front to back: PNC55BB, 2" BT55, 1" 5560 transition, 1" 6050 transition, 10" BT50, 1" 5060 transition, 4" BT60, then 24mm motor mount extends another .5". 26" total.
I think you can derive all remaining dimensions from that, including the fins (in combination with the drawing.) Interior structure is not designed, but you don't need my help for that anyway. I'd imagine a BT50 stuffer tube all the way through to the frontmost transition. I'd also imagine you're going to upscale it.
Look forward to seeing it!
Or do you have an ork file you could put up in a post?
Give the man what he wants Neil!
Give the man what he wants Neil!
I think it's meant to be in jest :-DI'm not trying to be demanding here, unlike what you make it sound like
Nytrunner kids everybody, and this time he's mostly kidding Neil. And Neil is well known to give back as good as he gets. Don't sweat it.I'm not trying to be demanding here, unlike what you make it sound like
I'm not trying to be demanding here, unlike what you make it sound like
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