|Oct 06, 2009, 09:43 PM|
|Oct 06, 2009, 10:06 PM|
Mopar, if I might suggest...
Perhaps you should look at the cause of the break. It appears as though the elevon split around the screws for the control horn. Maybe the screws for the control horn are providing too small of a bite on the elevon.
What I do and suggest trying, is a flat piece of material (I use PVC gutter pipe, but a piece of 1/16 G-10 or C/F would be even better!) that you could splice in the elevon. When glued in with epoxy or jb weld, this gives a very large foot print for the control horn to bond to.
Just my thoughts. Maybe you could talk blanik into making you a nice set of carbon vacuum-bagged elevons??
PS, i picked up one of your super Medusa 28-56-2800 today, so im gonna need some prop recommendations soon
|Oct 06, 2009, 11:16 PM|
I would advise very strongly against anyone using CF heli blades for control surfaces. It's been mentioned before, but no one's tried it, and I'm glad.
500 size heli blades are much heavier than an elevon, even a reinforced one like Mopar is running. Fine for a helicopter, but very bad as a control surface.
The extra weight will increase load on the servos and worse, the risk of flutter! A heavier control surface flutters much more readily than a light one.
Plus, hinging them would be tough. They're hollow, or filled with light foam, and hinges need some meat to bite into for their whole length.
Please don't use heli blades! They're attractive because of their stiffness, but the weight will kill ya!
|Oct 06, 2009, 11:24 PM|
I'm with The Kid on the control horn's footprint being too small. This is one place where the stock hardware comes in handy, as they have nice fat bases.
I am SO GLAD you made it down without carnage!
I'm also so glad you posted it, as I was about to install some just like yours on the elevons for my new bird.
Balsa can be strengthened by dribbling some thin CA into it. You could drill your mounting screw holes, and poke dozens of pin holes in a quarter-sized area in and around where the horn sits. Soak thin CA into the area (no accelerator!) and once it's dry, redrill the screw holes.
This will give you a rock hard base for the control horn to sit on, with no crushing from screws.
|Oct 07, 2009, 12:01 AM|
I've seen that pin trick before adding CA.
A guy who used to own a hobby shop in Washington state and had flown for 20 plus years did it to repair my Ultra stick 60 stabilizer.
***It was sticking out my passenger side window and I rolled the window up till I heard a crack (4-5 years ago)
The wing laying vertical was blocking my view.
He also used some baking soda ...I forget why...I was watching a TRUE master at work.
Also he used a hobby knife to make some slits in outer balsa frame and stuffed in some stuff which looked like CA hinges but were stiffer.
My cost: Pride, a lesson and a gallon of Nitro fuel for him.
Sorry about your elevons. Is the rest of the system o.k.?
You can always make the elevons out of different wood materials heavier than WEAK Balsa....even if it is not the Birch Aircraft plywood (heavy and hard to file your way).
|Oct 07, 2009, 12:13 AM|
The baking soda accelerates CA and turns it to CONCRETE! Insanely hard, and gives it a little volume, too, for filling in cracks like your repair.
I've been playing with elevon materials on my current build, too. Given that something failed either aerodynamically or mechanically between elevon and servo on my last crash, I'm going for super strength, size, and throw.
I built three sets to compare weights and stiffness.
First was balsa covered in 6oz. glass with marine epoxy.
Second was solid basswood.
Third was balsa skinned with 1/64" aircraft ply.
Balsa and ply was lightest, balsa and glass in the middle, and basswood was heaviest.
Balsa and ply was stiffest, basswood was in the middle, and balsa and glass was the most flexy.
So I'm going with the balsa and ply skin, as it's stiffest and lightest in my experience.
I'm sure a glassed, bagged elevon would come out stiffer than my glass, and I'd probably go with that if I had the setup.
|Oct 07, 2009, 12:30 AM|
I've always said that plywood covered balsa is EXTREMELY stiff.
Seems like you did 1/64" on top and bottom.
I do 1/32" just on bottom, so same weight...I also brush it with Epoxy.
(if I am not mistaking)
Moparmyway does multi-angle (Compound angle) filing of elevons to match contour of his wing. That filing is done after the elevons are mounted.
Because of that file job, he cannot just have the balsa thinly skinned with plywood.
|Oct 07, 2009, 12:48 AM|
I have a suggestion that will help with a few problems you currently deal with.
I ran it by you a few months ago, it had to do with Laminar Separation Bubbles http://www.mh-aerotools.de/airfoils/bubbles.htm
Ill call you tomorrow on my lunch break
|Oct 07, 2009, 02:06 AM|
Joined Sep 2009
The reason I said use the Heli blades is they do work very well.
But you do have to get rid of the lead section that is in the baldes, first.
What you do is then remove the amount of balde that you don't need in width.
So if you started with a Trex 500 blade that is 425mm long and 35mm for leading edge to trailing edge. You end up with a blade that is 280mm X 25mm.
Also you need to place a piece of CF rod across the long section that you removed, which will now be your leading edge.
That is just an example, not the exact figures.
So, I disagree with what is above.
Thank You Elvan Wilson II
P.S. Will post some pictures later!
|Oct 07, 2009, 04:12 AM|
Please weigh a heli blade elevon and compare it to a wooden one. You will be surprised at the difference.
There is no getting around aerodynamics. You have to respect physics and play to its rules. And flutter is an aerodynamic, physical problem that is made HUGELY worse by heavy control surfaces.
Are you saying we need to run elevons with a 1" chord????
We'll see how that goes...
Please get a video of one of these flying over 120mph! Get sound, too, so we can hear the buzz!
|Oct 07, 2009, 04:19 AM|
That idea is a great one !!!
That idea of poking holes is a great one !!! How do you add the baking soda, after the CA is applied ??
Everything else is fine, including the 45/90c batts (thats what I carped in my pants over when it happened).
Thanks but I really need some advice from here. Work has me beyond busy, and I had to answer some very pointed questions about that call yesterday (the Home Depot call). Business only while @ work.
I looked, but I didnt see any aileron stock in aluminum
Thanks for every input and idea !!!
Just waiting on boosteds ideas, then repairs will be made. I am leaning on a combo of Kids, Murdnunoc, and / or Gryphons ideas. A re-enforced footprint with larger horn area on a plywood added (lower side) with CA after poke holes, with no less than 5 CA hinges per wing. The 5 that I have on each wing now held on fine while the elevon got destroyed. Seems like it is easy now to see why my HS85MG's were getting hammered in flight !! I tried the heli blades one time, and after seeing the carnage that happens when cutting, and not wanting to rely on the relatively small hinge joint section, I didnt even try to do the install.
|Oct 07, 2009, 04:26 AM|
Than motor kicks ARSE !!!!
Its kv is super high, and a Stryker can only go so fast on a 6x4 sport prop (4s).............so you are limited to 3s for larger props. BEST 3s motor out there (Too bad they are out of business !!)
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