|Oct 10, 2012, 08:59 AM|
It looks like the maiden will have to wait, its raining today :-(
On the plus side this gives me time to install the wing struts.
Once I've done a few hand launches to get her trimmed we'll probably aerotow or winch her for the maiden.
Thanks for the correction Bernd, fixed. How did I figure out the stall speed? I used this excellent CG calculator. I've found it to be pretty accurate.
|Oct 11, 2012, 12:15 AM|
It wouldn't be a Cub without the wing struts. I figured the wheel support was a good strong spot to start with...
For the wing mount location I created these hard-points...
Cut a slot...
Glued & mounted. The struts are lightweight aluminum struts available at most hobby stores. The blue tape is there temporary to keep the glue from getting all over...
Now that's looking more Cub-like...
Possible maiden tomorrow, although you've heard that one before.
|Oct 11, 2012, 05:50 PM|
A friend put struts on his 8' telemaster and immediately noticed the extra drag. I had a WACO bipe and flew it for a while then added the flying wires tieing the wing struts etc to make it look more scale. That 1/16" wire created huge drag. Looks great otherwise
|Oct 11, 2012, 11:35 PM|
Thanks guys. If I've not already done so, I should mention this project is not about building a really nice flying sailplane, actually quite the opposite. I'm going for a comical, almost cartoonish look.
Yeah she's extremely short-coupled by design. You're correct, a longer tail moment would no doubt result in a more stable plane.
Again I'm not all that concerned about performance, the struts while semi-functional are there mainly for looks. They're removable though so if they turn out to be a problem its not a big deal to leave them in the workshop.
|Oct 12, 2012, 12:33 AM|
YouTube video, click to watch...
MAIDEN FLIGHT VIDEO
Flight Report (spoiler alert - watch video first)
Well as you can see that didn't go as well as I'd hoped although not a big surprise either, given the deliberately compromised design. Here's my thoughts...
The placement of my ridiculously big wheel sticking way too far out below the fuselage & positioned right at the CG doomed the aerotow. The nose-skid helped but not enough to keep the plane level & stable while towing. A lower profile wheel positioned properly would let her roll smoothly without generating gobs of drag for the poor tow-plane.
Everyone who picks her up is surprised at the weight. She's a heavy bugger, that combined with the short-coupled tail moment makes for some "interesting" flying. I think she'll be manageable if only I can get her in the air & moving along at a good clip.
Watching the alarming angle of attack during the high-start launch, I'm wondering if maybe moving the two-hook location further forward would help. Other factors such as CG & elevator trim may have contributed to the problem too.
The Next Step
After I make the repairs I think I'm going to remove the wheel & nose-skid & just let her slide along on her belly. I'll see if that helps with the ground handling. I may also remove the wing-struts at least until I have a few more test flights under my belt. With the nose-skid gone I can also try moving the tow-hook location forward a little.
Seriously this isn't Serious
While this may come across as a poor excuse for blatantly bad design, my main drive behind this build was to learn about working with foam. This project has in that sense been a success. I'm now confident enough to proceed with some more serious designs. That said I'm not done with this Cub though, at least not yet. I'm pretty sure I can get her flying.
Anyway bring on the theories, suggestions & those inevitable "I told you so's". I have it coming & I welcome it all. Fun Fun.
|Oct 12, 2012, 06:19 AM|
You can make it fly, get to the top of a big slope, wait for a strong wind and with a bit of down trim throw it.
You will have instant airspeed and altitude your odds will be greatly improved.
Great presentation so far.
|Oct 12, 2012, 10:54 AM|
Beautiful job creating the Cub glider. I think it is tail heavy - causing the flick while launching with the high start.
Some weight in the nose should fix it.
Thanks for sharing,
|Oct 13, 2012, 07:54 PM|
I agree, a nice slope would be ideal for test flights however where I live here in Connecticut, all the hills are either covered with trees or urban sprawl. The closest slope soaring spots are hours away.
Paul you're not alone in suggesting she may have been tail heavy. I'm not convinced she was though, as I'm pretty meticulous when it comes to balancing my planes but I can't ignore the possibility. We'll never know for sure as I've re-balanced her now that she's been modified. This time airing on the side of caution I've set the CG further ahead of the neutral point, at 15% static margin (last time was around 8%).
After Further Analysis...
Well I goofed up. I've no clue why I chose to just eye-ball the location for the high-start hook, especially as I'm well aware of the 30° ahead of the CG rule for tow-hooks. Look how far back I had my tow-hook positioned!..
Its no wonder she behaved like she did, I had the tow-hook WAY TO FAR BACK...
So lets simplify things. I lobbed off the nose-skid & "tundra sized" wheel & now we have a nice smooth fuselage to work with. The wing struts are history too...
After re-balancing here's how she sits...
Unfortunately due to the Guppy shaped fuselage the tail is still up in the air & it looks like she'll probably rock forward on her nose again during aerotow. Still though I think its an improvement. At the very least she looks cleaner...
I'm going to concentrate on aerotowing for now. I'll worry about adding a new high-start hook later on.
So anyway, weather permitting, we'll give her another try tomorrow.
|Oct 15, 2012, 05:16 AM|
|Oct 15, 2012, 01:21 PM|
Just throw it when towing instead of the ground start, we do that when the grass is a bit too heigh, even with 3,6 meter gliders after a Funcup.
This gives the tow plane a chance to get airborne.
|Oct 15, 2012, 02:54 PM|
I don't think throwing that would be a good idea, maybe to run with it and let it go gently. If thrown it would take down that cub, it does not have that great of a glide rate, I think it would yank the plane right down once it catches or make it real hard on the plane. If it was a specifically made poly dihedral glider, then ya, throw it, but no offense, that plane sinks quick. Awesome job on the build, not trying to knock you at all, just saying.
Just try the dolly!
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