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Aug 30, 2015, 09:35 PM
I Look, Listen, and Learn
Timbo383's Avatar
Oops totaly forgot about the motor thrust line per cg......was thinking about mounting near the bottom wing like a biplane, but now I know that will most likely not work...one step foward, two steps back. Using slot and tabs for the box end connection to....hopefully.....help with the wing shifting. Center piece is still not coming out like I want. Ok, ok, you were right about it being more difficult than I expected. But no regrets or real disappointments yet, that's part of the fun of building these planes. Took me twelve trys to get my last scratchbuilt plane to finally fly.
Half scale was a somewhat bad idea, should have attempted 2/3 scale. I'm using mostly bamboos instead of carbor fiber because of the small size, so it's not a waste of money if maiden doesn't do well.
Will be posting pics once I get it more put together, right now just the basics done with wing cutting and gluing kfm strips to strengthen it, hide the rods, and to imbed the servos.
Thanks for checking in and giving me info before I make too many mistakes.
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Aug 30, 2015, 11:31 PM
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Quote:
Originally Posted by Timbo383
Thanks for checking in and giving me info before I make too many mistakes.
Glad I could help.
There is no question you can get yours to fly with enough effort. Perseverance will get you there (as the saying goes: "1 percent inspiration, 99 percent perspiration" ).

I'm still waiting for my neighbor to be available to film some loops and rolls of mine
Aug 31, 2015, 06:32 AM
I Look, Listen, and Learn
Timbo383's Avatar
It's the center section that's giving me the most problems. The space is too far in between to make a good looking AND usable motor mount. I was trying to avoid the cage look but now it's become apparent the reason for it. I'm thinking maybe just put motors on the two vertical stabs with differential thrust would look cool, but that's for another time. Still need to conquer this idea first.
Almost done with gluing up the wing bracings. I'll pin it back together and take pics this week (if work and the family allows) it to show you what I have.
Aug 31, 2015, 06:58 AM
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Quote:
Originally Posted by Timbo383
It's the center section that's giving me the most problems. The space is too far in between to make a good looking AND usable motor mount. I was trying to avoid the cage look but now it's become apparent the reason for it. I'm thinking maybe just put motors on the two vertical stabs with differential thrust would look cool, but that's for another time. Still need to conquer this idea first.
Almost done with gluing up the wing bracings. I'll pin it back together and take pics this week (if work and the family allows) it to show you what I have.
You can decrease the space between the wings, but then you get significant interference from the wake of the lower/front wing affecting the rear/top wing. Having a "real" central fuselage with motor at rear or at front is also an approach that's been done (like the Ligeti Stratos), but I'm not sure making that rear fin strong enough to mount the rear wing on is much easier. Also, that puts the weight at the extremities - meaning high pitch inertia and all the drawbacks that come with that.
Having motors at the tips means high roll inertia - also not a great idea. Two motors mounted near the fuselage on stalks (like the Elytron and others) is a very challenging task from a "making the mounts strong enough while keeping it light" perspective.
Two smaller/weaker motors/props will be heavier than one reasonably strong motor/prop (though with two motors you could do some neat differential thrust).
All of the above is essentially why I ended up with the cage approach.
Sep 01, 2015, 08:59 PM
I Look, Listen, and Learn
Timbo383's Avatar
Here's what I have for now......just remember, I'm not college educated so some of the things I did may not make sense. I just do what feels right to me.
The wings are flat, the picture angles just make them look like they have anhedieral...I think that's the right word.
The central fuse is held together by inserting the 4 bamboo sticks horizontally into the foam and cutting a channel diagonally and wire tying all together. Then gorilla gluing over the holes to cover it up. When the fuse is glued to the wings then two more wire ties on the outer ends will keep it all together.....in my theory anyways. Overkill ? Maybe, but it's real firm. Now I just need to figure out better lateral support.
Last edited by Timbo383; Sep 01, 2015 at 09:15 PM.
Sep 01, 2015, 09:21 PM
Careful,.. confident,.. CRASH!
Dukejet's Avatar
Wow Timbo383, That's looking good! your doing a good job bud.....I wonder if using a pusher prop set-up with a hinged motor mount for differential thrust.... ???? Flite test guys have some very simple designs for the mount.
Sep 01, 2015, 11:19 PM
Registered User
Quote:
Originally Posted by Timbo383
Here's what I have for now......just remember, I'm not college educated so some of the things I did may not make sense. I just do what feels right to me.
The wings are flat, the picture angles just make them look like they have anhedieral...I think that's the right word.
The central fuse is held together by inserting the 4 bamboo sticks horizontally into the foam and cutting a channel diagonally and wire tying all together. Then gorilla gluing over the holes to cover it up. When the fuse is glued to the wings then two more wire ties on the outer ends will keep it all together.....in my theory anyways. Overkill ? Maybe, but it's real firm. Now I just need to figure out better lateral support.
VERY, VERY nice adaptation of what I did. I like the motor in the middle because it's protected in a crash, the pitch inertia is lower and the prop disk behind the CG has a stabilizing effect. As long as the thrust line passes through CG (or very nearly so), you're good to go.
You can run two supporting struts in a V from the lower central fuselage for lateral stiffening (similar to what I did) and I think that will probably be enough. If you mount a fairly heavy battery at the nose you will probably be able to get CG right. In the worst case, you could mount the battery on a short boom that extends forward of the nose (I've done this on some planes).
Don't forget to glide test before powered flight. Do it over tall grasses (or similar) so that you don't scuff that beauty's nose.
You also might benefit from beveling the leading edges to reduce drag.
Looking forward to video

By the way: College education or not, anybody can invest the time to read up on how this stuff works and get it done - and you're doing very well as far as I can tell.
Last edited by nuteman; Sep 02, 2015 at 01:59 AM.
Sep 02, 2015, 08:21 AM
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klausi0's Avatar
Timbo if you need some more inspiration you can take a look at my versions of a box wing.
https://www.rcgroups.com/forums/show....php?t=1674533

V2 an V3 were flying very well.

V2
Ringflügel / Ring-Flyer V2 (2 min 17 sec)


V3 is based on Jürgen Be Seapron.
Seapron Box-Wing Maiden (1 min 31 sec)



Klaus
Sep 02, 2015, 08:32 AM
I Look, Listen, and Learn
Timbo383's Avatar
Quote:
Originally Posted by Dukejet
Wow Timbo383, That's looking good! your doing a good job bud.....I wonder if using a pusher prop set-up with a hinged motor mount for differential thrust.... ???? Flite test guys have some very simple designs for the mount.
Thank you, Oooohh, forgot about thrust vectoring motor mounts. HK has them for about $6-$7. Good idea, the mount also pushes the prop more away from the fuse giving me more clearance. Was playing with the idea of making the outer stabilizers into rudders...I know more work and thinking involved....but I just can't stop myself sometimes.
Sep 02, 2015, 08:38 AM
I Look, Listen, and Learn
Timbo383's Avatar
Thankyou Nuteman, I will be rounding off the LE, just wanted to give you an idea what I was attempting by mock fitting the pieces together. I'll post a pic of the v-mount idea I had for lateral support when I get time. Work, the wife and son are taking some of my time away from this for a little while. Maybe a week or two.
Sep 02, 2015, 08:55 AM
Registered User
Quote:
Originally Posted by klausi0
Timbo if you need some more inspiration you can take a look at my versions of a box wing.
https://www.rcgroups.com/forums/show....php?t=1674533

V2 an V3 were flying very well.


Klaus
Hey Klaus,

I like your implementations, and I see your V2 kind of used the v-cage idea I did, but inverted - cool!
I see you're a fan of a centrally mounted motor as well
Sep 02, 2015, 09:46 AM
Laughs at un-boxing videos...
basicguy's Avatar
Nute
Have you considered making the front wing the high wing and the rear the low wing. I can see why it was done on a full size machine but we don't have that worry. Probably would give both wings more 'clean air'

The plane looks like a delta with the center missing with the potential for a lot more interference drag. I am not dissing the design, just thinking aloud.
Sep 02, 2015, 09:54 AM
I Look, Listen, and Learn
Timbo383's Avatar
Ok, now all you guys are just trying to make me crazy with thes unique designs.
When I fly a conventional type plane at the park, people say "that's neat" but when I take one of these unique ones, it's "WOW what is that? That is so Cool!!!" I have a night flying geobat, and my CD12 canard plane...my avatar...and they are so fun to fly. Don't get me wrong, I still like all planes, but the odd ones are a blast to fly.
Sep 02, 2015, 10:05 AM
Registered User
Quote:
Originally Posted by basicguy
Nute
Have you considered making the front wing the high wing and the rear the low wing. I can see why it was done on a full size machine but we don't have that worry. Probably would give both wings more 'clean air'

The plane looks like a delta with the center missing with the potential for a lot more interference drag. I am not dissing the design, just thinking aloud.
I enjoy the discussion, so no worries there

Regarding whether or not the front wing should be above or below: This seems to be hotly debated in the engineering community. Designs like the Elytron, Stratos and others favor the front wing being the lower wing while others have it reversed. And it seems to be that some of the reasons are applicable at any scale.
As I mentioned in one of the posts above, I have a huge gap between the two wings in an attempt to keep the wake from the front wing from interfering with the rear wing.
I fully admit my cage is draggy, but I think it is cool from a structural perspective - and even at the slow speeds this plane flies at, I'm not at all sure that a "full fuse" would be that much less draggy as it would have a lot more skin friction drag.
Regarding whether or not a plain old delta (with similar wing loading, of course) would be less draggy is again not clear. A very low aspect ratio delta has tons of profile/induced drag at even modest AOA.
Whether of not the box design's much reduced wing-tip vortices (which cause drag) offset the added interference drag and weight of the join between wings is again a hotly debated subject in the engineering community.
Finally, as I mentioned in one of the above post, I primarily chose this layout since I've never done it before - I've done at least 4 variations on the delta theme.
Last edited by nuteman; Sep 03, 2015 at 12:07 PM.
Sep 02, 2015, 10:21 AM
Registered User
Just a general note regarding this plane and many of the other large planes I've scratch built: I generally try to build the plane as large as the motor/prop I have on hand can handle and still be hand-launch-able. I regularly fly in 15 knot winds gusting to 20 or 25. I also want the Reynolds number to be as high as it can be even at slow speed - to result in better behavior. I have to land in very rough fields, so I want my landing speed very slow (minimum momentum on touchdown) - which dictates low wing loading. I discuss some of this in the discussion video I did.


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