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Old Oct 22, 2012, 10:58 AM
DIY Mania from Taiwan
Taiwan
Joined Aug 2011
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Quote:
Originally Posted by G-LO View Post
The glide IS good* It looks like a pleasure to fly.

Sam, I know I ask this question last year sometime but, can you please take a few pictures of the way you setup your motor in your fuse? You are the ONLY person I know with that setup. The seagull has a very fast climbing rate! I would love to have a bird that flies like yours....

Thanks
Thanks
we are the real RC birds mania like most guys here in the thread
I'll take pics again for you
best regards
Sam
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Old Oct 22, 2012, 11:02 AM
DIY Mania from Taiwan
Taiwan
Joined Aug 2011
1,940 Posts
Quote:
Originally Posted by Joel K. Scholz View Post
Sam, what control surfaces are you using on your Gull. It appears to be elevons only?
Joel:
it's a simple aileron and elevator setup wih 3 servos
regards
Sam
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Old Oct 28, 2012, 02:29 AM
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Pusher version of the Eagle

If anybody is interested, I have built a pusher version of the eagle. It took a few adjustements but it is flying ok now. Yet, I am not happy about the way it glides without power (it sinks the nose). It needs a bit of power to glide. Apparently, it is nose heavy, but if I move the CG back it does not fly as stable ... any ideas ?
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Old Oct 28, 2012, 05:14 AM
DIY Mania from Taiwan
Taiwan
Joined Aug 2011
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Quote:
Originally Posted by rgt52 View Post
If anybody is interested, I have build a pusher version of the eagle. It took a few adjustements but it is flying ok now. Yet, I am not happy about the way it glides without power (it sinks the nose). It needs a bit of power to glide. Apparently, it is nose heavy, but if I move the CG back it does not fly as stable ... any ideas ?
The thrust line may be the cause.
regards
Sam
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Old Oct 28, 2012, 08:27 AM
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It may be very cg sinsetive. Do you move the cg by mm or very small increments? And how much wash are in the wingtips?

More pictures at different angles would be nice. Your bird is beautiful!
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Old Oct 28, 2012, 12:51 PM
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Pusher version of the Eagle

@Sam: I agree with your comment about the thrust line but there is something else involved which I am (hopefully) in the process of correcting now.

When I first flew the bird I noticed a strong tendency to climb. Even with a lot of down elevator it wanted to climb. So, I figured that changing the thrust line (which was initially set to neutral) would fix the problem. In fact it did correct the tendency to climb, but then I discovered the poor gliding ability.
After a closer inspection, today I noticed that it may all be caused by the incorrect installation of the V-tail. In fact, the tail was not perfectly aligned with the wing, thus having an angle of attack such that caused the tail to sink and pull the nose up. I am currently changing the v-tail alignment, I will then reset the thrust line (I will align it wit the center of mass) and I will fly the bird again to see what happens. I will report the results.

@G-LO: I changed the COG gradually, but I guess that my observation was influenced by the v-tail alignment problem as mentioned above. Thank you for the compliment about the looks of the bird. I will post more pictures as soon as I have it reassembled with the tail back in place.
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Old Oct 28, 2012, 07:46 PM
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Quote:
Originally Posted by rgt52 View Post
...
When I first flew the bird I noticed a strong tendency to climb. Even with a lot of down elevator it wanted to climb. So, I figured that changing the thrust line (which was initially set to neutral) would fix the problem. In fact it did correct the tendency to climb, but then I discovered the poor gliding ability.
After a closer inspection, today I noticed that it may all be caused by the incorrect installation of the V-tail. In fact, the tail was not perfectly aligned with the wing, thus having an angle of attack such that caused the tail to sink and pull the nose up. I am currently changing the v-tail alignment, I will then reset the thrust line (I will align it wit the center of mass) and I will fly the bird again to see what happens. I will report the results.
...
I was going to ask if you checked this when I read your post, but see you have already found this problem. My eagle was built with wing and v-tail both at zero incidence with the motor shaft axis. Mine glides like a dream, but has a tendency to climb to the left pretty eagerly when under full power. My motor was a tight fit because I narrowed the beak to look a little more life-like, and that prevented my adding down/right thrust to counter the left climb under power. But I was able to counter it quite effectively by some trial and error mixing of the v-tail surfaces with the throttle stick. The bird will bank and dive with just rudder stick action on the v-tail, so some right rudder mixed proportionally with the throttle stick position does most of the correction. I may have mixed in a very small amount of elevator correction as well, but can't remember that far back.
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Old Oct 29, 2012, 02:18 AM
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Originally Posted by Tom Frank View Post
I was going to ask if you checked this when I read your post, but see you have already found this problem. My eagle was built with wing and v-tail both at zero incidence with the motor shaft axis. Mine glides like a dream, but has a tendency to climb to the left pretty eagerly when under full power. My motor was a tight fit because I narrowed the beak to look a little more life-like, and that prevented my adding down/right thrust to counter the left climb under power. But I was able to counter it quite effectively by some trial and error mixing of the v-tail surfaces with the throttle stick. The bird will bank and dive with just rudder stick action on the v-tail, so some right rudder mixed proportionally with the throttle stick position does most of the correction. I may have mixed in a very small amount of elevator correction as well, but can't remember that far back.
Thank you Tom for your reassuring comment and other useful information provided.

Last night I built a “micro eagle” (see the picture attached) to study/test the glide patterns of this bird and have found the best CG location to be a bit “aft” the spar line while in the plans it shows to be ahead of it. In order to make the pusher version of the eagle I had to extend/expand the tail a bit (maybe 10%), could that cause the CG to move back?
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Old Oct 29, 2012, 08:09 AM
Lee
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I found bird like planes balance like a flying wing more than like a conventional plane. If you calculate the area of the wing and tail combined and balance the plane with the CG back to about 23% of that area on the wing the plane is more stable than if the CG is behind that point. For this reason increasing the size of the tail will move the CG back.

The flat wings behave differently but if built right can still fly good. I think the bird planes are an excellent place for an ultra light flat wing or a wing with a KF airfoil.
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Old Oct 29, 2012, 08:42 AM
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Quote:
Originally Posted by rgt52 View Post
Thank you Tom for your reassuring comment and other useful information provided.

Last night I built a “micro eagle” (see the picture attached) to study/test the glide patterns of this bird and have found the best CG location to be a bit “aft” the spar line while in the plans it shows to be ahead of it. In order to make the pusher version of the eagle I had to extend/expand the tail a bit (maybe 10%), could that cause the CG to move back?
It looks like you also moved the v-tail forward? Changing the v-tail area and it's location (i.e. moment arm) can definitely change the flight characteristics, even though the CG (or more appropriately, center of mass) doesn't change that much due to the very light weight of the tail feathers.

I didn't mention it, but I actually reduced the size of the tail feathers on mine, eliminating some of the curved LE to give them a straighter (and more life-like) look. I also set mine down into the body (keeping the same zero incidence angle with the wing) so they look more realisitic as opposed to being stuck on top body. I posted a number of pics here during my build, along with a maiden flight video link. But the video hosting site I used shut down, so the link no longer works. It was an interesting maiden, with ejection of the flight lipo, followed by a strange and totally unexpected descent of the powerless bird (stable inverted stalls all the way down!).
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Last edited by Tom Frank; Oct 29, 2012 at 08:49 AM. Reason: added build link
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Old Oct 29, 2012, 08:57 AM
Lee
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I have even flown some of my bird designs with elevons rather than ailerons and elevator. If they are tail heavy they don't fly. If they are nose heavy they won't pull up or flair in a glide.
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Old Oct 29, 2012, 02:23 PM
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Pusher version of the Eagle

@Tom & Lee: Thank you both for your valuable comments. I have indeed changed slightly the shape/length of the tail and have mounted it on the body in a more forward position than in the original design. This was done to place the motor & prop right behind the TE of the wing. As suggested, this may have changed the balance point of the bird which seems to be very sensitive in this kind of arrangement as I could verify by playing with the -paper micro eagle- shown in a previous post.
Today, I removed all the electronics and did a few glide tests over an area covered with high grass. The tests showed a good glide rate with the CG located on the spar. I plan to fly the bird again on Wednesday. I will try different CG locations and will report results for anybody interested.
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Old Oct 30, 2012, 04:56 AM
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I could not wait until Wednesday, I had some free time this morning and decided to test the bird again. It was very windy (BAD IDEA) … the only good thing about windy days is the extra lift for the hand launching. Anyways, I balanced the bird just ahead of the spar. It flew OK from my hand, a few clicks here and there, no pitching issues … but … it started banking side to side like crazy, the more wind, the more it was banking. I tried my best to correct the constant left and right banking, but It was impossible … it finally died in a sort of spiral dive.
Fortunately, the damage was not too bad, I just need to rebuild the nose section which is not a big deal … the question is, why is it doing this?
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Old Oct 30, 2012, 10:22 AM
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Humm... did you put enough down & right in the motor to counter the spin of the prop? And was the cg too far back?
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Old Oct 30, 2012, 10:35 AM
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Pusher version of the Eagle

Quote:
Originally Posted by G-LO View Post
Humm... did you put enough down & right in the motor to counter the spin of the prop? And was the cg too far back?
I think that the thrust line was right ... Tail heavy airplanes tend to balloon or have other pitch related instabilities. Yet, this bird was banking side to side like I never saw before. BTW, I did notice this same behavior when playing with the micro paper glider I made (particularly when tested outdoors with some wind).

Now that I think of it, it did remind the sort of side to side movement you get when flying a delta wing at high alpha. However, I do not think that this bird was stalling. Any ideas will be appreciated.
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