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Dec 11, 2012, 08:11 PM
Fremont, WI
That's awesome "V"! Congrats!

I can't wait to see pictures of it completed!

In testing, did you see problems related to lack of v-stab? Did you see improvement when you added it?

Hard to tell, I'm sure, with just hand tossing it.

Can't wait to hear how it goes from here.

Do you have good sloping opportunities? Or will you need to consider other options to get some height?

Also, if you don't mind my asking, how much effect do you have in pitch control? Roll and yaw? Could you get any feel for it with your hand tosses?
Last edited by Anatum; Dec 11, 2012 at 09:26 PM.
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Dec 11, 2012, 09:40 PM
Mongo like wind. Wind Good.
V1VrV2's Avatar
Got to take the Eagle to the slope today. It was blowing about 20 kts or so and a little gusty but lots of soaring seagulls were present today.

Two modes of control were programmed into the radio. The first was patterned after the Japanese birds mentioned earlier that used drag flaps and ailerons for turning and the second was conventional differential ailerons only. Both test scenarios used a vertical fin as back up.

All test flights were short. Not by choice either. The first problem was on launch the plane went skyward into a steep vertical stall but was recovered behind the face of the hill and landed. Added ballast to the nose and launched again. This time the plane went into the wind and used full up trim to keep it from diving too hard. This flight used the drag flap aileron approach and had very poor turn response. Almost Nil. Had to hold full deflection to get it to turn. Hopped over the edge of the slope and landed. I then reprogrammed for conventional ailerons and launched again. The ailerons now were making very good turn response. The elevator was OK but somewhat lacking in response. The vertical tail was somewhat flexible and I could see it bending left or right in response to the plane yawing every so often. The wind shifted direction and I had to land again. All these flights are well under a minute.

I removed 1/2 the ballast added earlier to try and get a better CG then launched it again. This resulted in a steep climb skyward (again) and no response to full down elevator that resulted in a deep stall. tried pulling up but it contacted the ground in a 45 degree dive and shattered the left wing.

The conclusion is that this is a forward swept flying wing. It is unstable in the yaw axis and has a very tight CG tolerance resulting in an unstable pitch axis. If the CG is off a fraction of an inch it destabilizes the pitch stability. I can easily rebuild the wing. The fuselage was unharmed. I don't think I'm going to be persuing this project past this point. I got the impression I would be in for alot of frustration trying to get it stable enough to fly right. If the flight got past the launch phase it seemed to fly like any other plane BUT the pitch stability is a real problem.

Every launch I made always resulted in the immediate pitching up of the plane either on the slope or in calm wind on the soccer field except for the flight where it was nose heavy. That flight resulted in a tendancy to dive the whole time. Maybe if I got the CG EXACTLY PERFECT it would be OK but who knows?

Taking a break for now...
Dec 11, 2012, 10:50 PM
Mongo like wind. Wind Good.
V1VrV2's Avatar
Well, if nothing else, this looked totally cool in flight!

Nothing like flying a Bald Eagle around!

Turbulence and barfbags

Dec 11, 2012, 10:56 PM
Registered User
G-LO's Avatar
Very nice looking bird *

I'd wish that after a brake you would tackle your issue and finally crack that nut
Dec 25, 2012, 07:12 PM
Fremont, WI
Quote:
Originally Posted by V1VrV2
Got to take the Eagle to the slope today. It was blowing about 20 kts or so and a little gusty but lots of soaring seagulls were present today.

Two modes of control were programmed into the radio. The first was patterned after the Japanese birds mentioned earlier that used drag flaps and ailerons for turning and the second was conventional differential ailerons only. Both test scenarios used a vertical fin as back up.

All test flights were short. Not by choice either. The first problem was on launch the plane went skyward into a steep vertical stall but was recovered behind the face of the hill and landed. Added ballast to the nose and launched again. This time the plane went into the wind and used full up trim to keep it from diving too hard. This flight used the drag flap aileron approach and had very poor turn response. Almost Nil. Had to hold full deflection to get it to turn. Hopped over the edge of the slope and landed. I then reprogrammed for conventional ailerons and launched again. The ailerons now were making very good turn response. The elevator was OK but somewhat lacking in response. The vertical tail was somewhat flexible and I could see it bending left or right in response to the plane yawing every so often. The wind shifted direction and I had to land again. All these flights are well under a minute.

I removed 1/2 the ballast added earlier to try and get a better CG then launched it again. This resulted in a steep climb skyward (again) and no response to full down elevator that resulted in a deep stall. tried pulling up but it contacted the ground in a 45 degree dive and shattered the left wing.

The conclusion is that this is a forward swept flying wing. It is unstable in the yaw axis and has a very tight CG tolerance resulting in an unstable pitch axis. If the CG is off a fraction of an inch it destabilizes the pitch stability. I can easily rebuild the wing. The fuselage was unharmed. I don't think I'm going to be persuing this project past this point. I got the impression I would be in for alot of frustration trying to get it stable enough to fly right. If the flight got past the launch phase it seemed to fly like any other plane BUT the pitch stability is a real problem.

Every launch I made always resulted in the immediate pitching up of the plane either on the slope or in calm wind on the soccer field except for the flight where it was nose heavy. That flight resulted in a tendancy to dive the whole time. Maybe if I got the CG EXACTLY PERFECT it would be OK but who knows?

Taking a break for now...
That's a major bummer V!

I hope you get back onto the project and see if you can master it... Would you mind helping with a few questions?

I'm still going to move forward on mine, but would of course like to learn from others if possible. Right now I have a workable hand-tossed non-RC redtail hawk glider (about 17" span). I've been playing with it a lot lately trying to see what is different about it vs yours, and what the strengths may be with each design. I can post photos if anyone's interested, and maybe even a video...

Do you have any decalage between the wing and tail? I do, and have never been able to come up with anything (bird-modelwise) stable without it. If my tail is level, the wing leading edge is higher than the trailing edge by several degrees. The tail I'm using for this model is fanned quite a bit as well. Without that, even with positive decalage the nose of the bird always seems to want to tuck under very hard resulting in a crash. I can't really tell from your photos if you built any in or not...

If that's a factor with your bird, maybe you could shim the rear of the tail and get some stability?

If I toss mine gently, it glides straight ahead. I've hinged the tail, and can deflect both sides for up or down "elevator". Doing so on my model results in predictable stall or dive behavior, so I think/hope it will work when I convert to RC? I can make the glider bank and turn as well, which of course equates to a spiral down with my non-RC version.

On "power" tosses though, I worry that I may have similar issues to yours. It always goes up into a loop... It does stabilize and glide straight after that though.

I do see that the angle I've cut my hinges at is different than yours, and wonder if that may also be why it sounds like you don't have much elevator authority?

The third difference (?) between yours and mine may be the aileron/flaps. I can't see where yours are hinged? How large are they, and how much deflection do you get? If you want to make a left-hand turn, does anything happen with the right wing?

I plan to make my hinged wing surfaces quite large in an effort to try to mimic some of the wing movement I see my birds make. But I do plan to use my tail as an elevator, even though I don't see them do that...
Jun 17, 2017, 10:14 AM
Mongo like wind. Wind Good.
V1VrV2's Avatar
This was an old thread but this project never really died. I did a lot of design changes and finally got this thing flying and fly well it does now.

I have a complete flight report on my blog page which is down quite a ways. Just click on the "continue reading" or "see all pictures in thread" to see the updates that have been made since the last post here. I never gave up, I just kept at it till I got it right!

I am now going to paint the body and add the glass eyes to make it look as close to real as it gets. Real eagles HATE this thing even without the body painted so this will tick them off even more...

I'll post more pictures of it once it has been painted and fully finished.

Cheers!
Last edited by V1VrV2; Jun 17, 2017 at 10:28 AM.
Jun 24, 2017, 12:01 PM
Mongo like wind. Wind Good.
V1VrV2's Avatar
Here's some pictures of the painted version I just finished. I told myself I would not paint it unless it flew successfully. It is basic colors, no fancy airbrushing but someone with talent could make it look even better. The fin was left off for the pictures. It cannot fly without it because of the conventional ailerons.

I hope to get it back flying just as soon as the wind comes back. This time of year in my area the wind craps out or is the wrong direction.

Cheers!
Jun 24, 2017, 07:18 PM
Mongo like wind. Wind Good.
V1VrV2's Avatar

Design your Birds!


I hope this answers some very good questions about "bird design". Not everything is covered but it's a start!


Quote:
Originally Posted by Anatum
That's a major bummer V!

I hope you get back onto the project and see if you can master it... Would you mind helping with a few questions?

I'm still going to move forward on mine, but would of course like to learn from others if possible. Right now I have a workable hand-tossed non-RC redtail hawk glider (about 17" span). I've been playing with it a lot lately trying to see what is different about it vs yours, and what the strengths may be with each design. I can post photos if anyone's interested, and maybe even a video...

Do you have any decalage between the wing and tail? I do, and have never been able to come up with anything (bird-modelwise) stable without it. If my tail is level, the wing leading edge is higher than the trailing edge by several degrees. The tail I'm using for this model is fanned quite a bit as well. Without that, even with positive decalage the nose of the bird always seems to want to tuck under very hard resulting in a crash. I can't really tell from your photos if you built any in or not...

I had this problem as well. Turns out is was more of a problem with what airfoil I used more than any other factor. By "decalage" I am guessing you mean "incidence" between the horizontal stabilizer and the chord line of the wing. I would first suggest if you build a "bird" you MUST think of it as a pure flying wing. Therefore, you must use a reflexed airfoil for that wing. There are many choices. Some are designed for swept wing flying wings and others for Plank (no sweep) flying wings. Pick one appropriate for your project and wing planform. The tail is too short coupled (too close to the CG) to make a reliable source of positive pitch stability so you MUST use a reflexed airfoil.

If that's a factor with your bird, maybe you could shim the rear of the tail and get some stability?

Nope. The tail on the eagle is strictly for show. I could remove it if I wanted to. Birds, however, use it to provide lift as they are balanced with an aft CG. They have very, very good sense of balance and can instantaneously adjust their tail for active dynamic pitch stabilization. Not only that, but they use their tails to trim up their turns as well because they can tilt their tails to vector that upward vector of lift in a turn to adjust yaw.

If I toss mine gently, it glides straight ahead. I've hinged the tail, and can deflect both sides for up or down "elevator". Doing so on my model results in predictable stall or dive behavior, so I think/hope it will work when I convert to RC? I can make the glider bank and turn as well, which of course equates to a spiral down with my non-RC version.

On "power" tosses though, I worry that I may have similar issues to yours. It always goes up into a loop... It does stabilize and glide straight after that though.

Again, you MUST use a reflexed airfoil. See comment above.

I do see that the angle I've cut my hinges at is different than yours, and wonder if that may also be why it sounds like you don't have much elevator authority?

That original version of the eagle used a "V-tail elevator and yes, it had a very poor rate of response to pitch and pretty much nil on yaw.

The third difference (?) between yours and mine may be the aileron/flaps. I can't see where yours are hinged? How large are they, and how much deflection do you get? If you want to make a left-hand turn, does anything happen with the right wing?

Great question! I had to figure this out as well. The ailerons are just that. Ailerons. NO DIFFERENTIAL. Differential is bad Ju-Ju on flying wings as it turns into an elevon effect of adding elevator control in when you don't want or need it. The "flaps" are actually elevons on the eagle. They function only as pitch control devices. I mix in electronically full throw for the elevons for pitch and about 1/2 that mixed to the ailerons as well. I wanted to keep control surfaces off the tail to save weight and besides if you have ever flown a flying wing, they are extremely pitch sensitive to elevator input. If you have an elevator mounted to a rear stabilizer it has an enormous mechanical advantage over the CG and it only takes MINUTE changes to affect any change in pitch. But what knucklehead puts a horizontal stab and elevator on a flying wing anyway? Bird plane guys! Turns out this set up provided way too much pitch authority on the initial flights so I had to tone it down quite a bit. The HS-130 reflexed airfoil is optimized for elevon hinge lines at 75% chord. They look quite large and they are! Danka!

I plan to make my hinged wing surfaces quite large in an effort to try to mimic some of the wing movement I see my birds make. But I do plan to use my tail as an elevator, even though I don't see them do that...

Birds use their tails for pitch as well as wing sweep. They can use either/or. Don't try to exactly emulate the birds as they have dynamic, organic forms controlled by an evolutionary "bird brain". Whatever you design must be capable of both pitch and roll and yaw stability. If it is unstable, it will wallow and dutch roll around the sky. Heck, it might even fly OK for awhile BUT it is only partially under your control. Other birds will think your bird is drunk!

I hated putting a fin/rudder on the eagle. I really did. After fighting low percentages on yaw stability and high adverse yaw at low speed I gave in and put a rudder on my eagle. You know what? It works awesome! If I display the eagle I just remove a set screw on the rudder and detach the ball joint to remove it. My goal was to keep it totally controllable on a slope for landing that has a bit of a nasty rotor. Your design will be governed by what your goals are.
Last edited by V1VrV2; Jun 24, 2017 at 07:26 PM.
Jun 24, 2017, 08:03 PM
Registered User
G-LO's Avatar
AMAZING. ..Look at that detail! Impressive
Jun 24, 2017, 09:04 PM
Registered User
G-LO's Avatar
Thanks for the informative conversation post. I found everything identifiable when putting my bird plane together. I kinda messed up when putting too much weight on the tail just because I "thought" I needed to beef up my tail...also my elevator servos are behind the cg . On that account, I had to add more weight to the nose. I think it's the nicest bird I put together, but there is definitely a need to start all over again...right. It is NO WAY near your skill level V, just a "Frankenstein" bird. Different bird plane pieces put together.

It flew, but it was a handful!! I'm relieved and surprised that I didn't crash the thing! My motor incident was too high and my trailing edge and horizontal stabilizer was probably jacked up just to name a few. ( Pure amateur ). But all things considered, it had a docile flying characteristic with some irregularities. This was my off and on project as well. You have inspired me a little to get back in there in the near future. Thanks
Jun 24, 2017, 10:00 PM
Person of interest
KiwiKid's Avatar
Very interesting thread - birds are tricky things to get flying right and every one is a bit different with it's own challenges.

I have built three over the years and they have been a lot of fun to construct and fly.

The last two are below - Eddie the Eagle is a slope soarer and Connie the Condor is an EPP powered model which also doubles as a sloper. Both of them use the same set up - V-tail (rudder/elevator) with ailerons and drag plates mixed with rudder. They both fly well - just gotta find some time to paint them up.

Here's a vid of Eddie's maiden flight.

Eddie the Eagle (2 min 22 sec)
Jun 25, 2017, 10:31 PM
Mongo like wind. Wind Good.
V1VrV2's Avatar
I LOVE Eddie the Eagle! I bought the plans online and had them sent here to me here in the USA just to see how he was designed. We bird glider guys know Eddie is a long established bird glider and it does fly well!

Thanks for posting the video!

Last edited by V1VrV2; Jun 26, 2017 at 12:31 PM.
Jun 25, 2017, 10:39 PM
Mongo like wind. Wind Good.
V1VrV2's Avatar
I didn't give up and neither should you!

Each tweek and adjustment will make it better. Keep at it.

Tony



Quote:
Originally Posted by G-LO
Thanks for the informative conversation post. I found everything identifiable when putting my bird plane together. I kinda messed up when putting too much weight on the tail just because I "thought" I needed to beef up my tail...also my elevator servos are behind the cg . On that account, I had to add more weight to the nose. I think it's the nicest bird I put together, but there is definitely a need to start all over again...right. It is NO WAY near your skill level V, just a "Frankenstein" bird. Different bird plane pieces put together.

It flew, but it was a handful!! I'm relieved and surprised that I didn't crash the thing! My motor incident was too high and my trailing edge and horizontal stabilizer was probably jacked up just to name a few. ( Pure amateur ). But all things considered, it had a docile flying characteristic with some irregularities. This was my off and on project as well. You have inspired me a little to get back in there in the near future. Thanks


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