Flying the Bird of Time

[ShaverR6]

Well I went out to maiden my BOT and it didn't go that well. I got three flights in before i had to pack it up. Each flight was very unnerving, the plane was very unstable and i was desperately trying not to crash. I would assume that it was due to the plane being tail heavy, an easy fix. One thing that concerned me was the lack of rudder authority. As soon as one side of the wing caught the wind I could not counter and turn back into the wind, I had to continue the turn caused by the wind. I never had this problem before with my other sailplanes. The rudder tip deflection is currently set up for 2" to the left and 2.5" to the right.
The day ended with me catching a wing tip on the ground and tearing out the wing mount bolt, another easy fix. One good thing about the flights was the spoilers that I added, they worked excellent. :)
Do these flying characteristics sound familiar to anyone else?

[guy mckenzie]

If it's tail heavy you can't really judge anything else....Get the CoG correct first.

[Ollie]

Stall? Tail heavy? Not enough air speed? Too much decalage angle between wing and tail? You need a experinced glider pilot to ground check the adjustments of CG, decalage, servo links and whole airframe before flying.

[ShaverR6]

I like to think i am experienced, i have been flying for over 10 years. :) I balanced the plane as per the instructions but I could definitely tell that it was tail heavy when flying. I will move the CG a few mm forward and try again.
I was more concerned with the rudder deflection and control. The manual did not provide recommended deflection so I simply tried to obtain the maximum deflection possible. Even with the previously stated 2-2.5" travel there doesn't seem to be much control. But Ollie you are right, this lack of control may be due to low airspeed.
Thanks for the input fella's.

[bobby legue]

The BOT does like to fly a little fast for a floater. The best way I can describe it is to fly it about as fast as an eppler 205 wing. It will fly slow and turn but that big wing will take a second to initialize at too slow of speeds. Even an increase of 2 or 3 mph increase will increase rudder authority as well as vastly increase your glide length. (l/d?) A side thought, are your wingtips light and does it balance laterely? If you are getting air blow by through the rudder hinge line performance will suffer. Sometimes greatly. Try tape down the hinge line- always a good idea. Ive turned real dogs into butterflies sealing the hinge lines.
Things for you to ponder,
Bob

[mattJ]

Sounds familiar to me; like when I tried to fly my DayDream tail heavy. I thought I could trim it out to at least fly halfway decent (nope) because I didn't want to add the weight needed to get proper CG. It must be something like that because if they all flew that way nobody would buy them.

If you don't have a Great Planes CG Machine I'd pick one up.

[ShaverR6]

Thanks for the input. I have balanced the wing along the aircrafts centerline, and I consider the outer panels pretty light, I think they were just over 4oz each.
I balance my planes with a homemade jig consisting of a 2x4 with two holes drilled into it. In these holes are placed #2 pencils with their eraser ends pointing up. The erasers are ground down to form a prism which is the resting surface for the wing of the aircraft to be balanced. I will try and re balance for a more forward CG and try and fly tomorrow A.M.

[bobthenuke]

It may help to know just *which* BOT you have as different versions have their own flight characteristics. It's hard to say what your problem is but for a starter I'd think that you should at least have equal rudder deflection in either direction.

As far as the GP balancer goes I have one and they're great, but I think that you did it the smart way and saved $$. ;)

...bob

[ShaverR6]

Hi Bob, this is the Dynaflite kit version. It has been modified to incorporate a three piece wing, spoilers, and carbon tow on top and bottom of the spar with Kevlar wrap.
I know the unequal rudder throw sounds amateurish, but it is due to me trying to gain the absolute max in throw with the end point adjustment in my transmitter without causing the servos to buzz. I have just replaced the rudder pushrod in hopes to free up the movement. The stock metal pushrods did not seem to run very well in their sleeves.

[Ollie]

The stock BOT wing has no wash out. If you use washout you change the average declage. Fix any wash-out or wash-in wing. Use the elevator trim to speed up the airspeed plenty. Change the rudder servo linkage so that the arm at the rudder and the servo arm result with neutral and equal maximum (L or R) throws. Fix any servo or linkage that has ANY backlash!! Be careful with too forward CG because it makes the plane yaw sluggish!!!
Read:
http://www.nesail.com/articles.php?PHPSESSID=193b6722e8c285660739ae1f471 224f7
Trimming Your Model Sailplane by Sherman Knight

And see:
http://polecataero.com/articles/cg-location

[mattJ]

I balance my planes with a homemade jig consisting of a 2x4 with two holes drilled into it. In these holes are placed #2 pencils with their eraser ends pointing up. The erasers are ground down to form a prism which is the resting surface for the wing of the aircraft to be balanced. I will try and re balance for a more forward CG and try and fly tomorrow A.M.


Yeah your homemade balancer sounds a lot nicer than my homemade. I had a board with garden stakes and foam earplugs glued on the ends ;) . Ya know it was real accurate with two of my planes but not even close on two others. I haven't the slightest idea why.

I don't know if it's true with the BOT but my Dynaflite daydream's pushrods are unsupported throughout the length of the fuse and lead to a real mushy/flimsy rudder. I was going to modify that during the build but forgot.

Anyway, good luck. Sounds like you'll get it worked out.

[Stan_in_AR]

I've been flying BoT's off and on since I bought my first kit from Dave Thornburg himself. NONE of my planes have flown as you described. You didn't mention where our CG was but my plans call for 3 5/8" from the leading edge at the root. But you can safely fly at 3 3/4 w/o any trouble, just a little sensitive to the elevator with aft cg.

Assuming CG is correct consider the following:
1. Sand a symmetrical airfoil from TT to tip(no wash out needed)
2. Check for wing warps
3. As others mentioned fly it faster.
4. Where are you measuring the rudder throw at the widest part of the rudder?
5. Have you sealed the rudder hinge line?
6. Are your tips equal distance from the rudder hinge line?

The BoT will not handle like a 100" or smaller sailplane but it is quite respectable in turning performance. My current BoT which weighs 44oz's will come out of a bank with opposite rudder RIGHT NOW.

Just some ideas. It's a great plane.

Stan


Well I went out to maiden my BOT and it didn't go that well. I got three flights in before i had to pack it up. Each flight was very unnerving, the plane was very unstable and i was desperately trying not to crash. I would assume that it was due to the plane being tail heavy, an easy fix. One thing that concerned me was the lack of rudder authority. As soon as one side of the wing caught the wind I could not counter and turn back into the wind, I had to continue the turn caused by the wind. I never had this problem before with my other sailplanes. The rudder tip deflection is currently set up for 2" to the left and 2.5" to the right.
The day ended with me catching a wing tip on the ground and tearing out the wing mount bolt, another easy fix. One good thing about the flights was the spoilers that I added, they worked excellent. :)
Do these flying characteristics sound familiar to anyone else?

[Ollie]

"Each flight was very unnerving, the plane was very unstable and i was desperately trying not to crash."
"I have balanced the wing along the aircrafts centerline, and I consider the outer panels pretty light, I think they were just over 4oz each."
"It has been modified to incorporate a three piece wing, spoilers, and carbon tow on top and bottom of the spar with Kevlar wrap."

You haven't said the wing polyhedral angles numbers. Use stock wing polyhedral angles. One tip panel 4 oz.weight is heavy, in my opinion. Normal tip panel weight is about 2 oz. Too mass at the wing panels makes the sluggish in yaw. Too much reduced polyhedral makes the BOT sluggish in yaw. With good CG position, enough airspeed, no wing warps and good servo links, the BOT will improve yaw response, even with maximum rudder throw 1-3/4" each side.

[Captain Canardly]

Shaaver!
Sounds to me that they have upgraded the print since my last build-'92-2nd
Stan and Ollie have said what I would have, I flew mine with 1/8" washout via sanded symetrical foil, the balance for a single panel, but now that it is 3 may be difficult to see, is about 2 bays inboard of first poly break. Check your tip's balance points individually, and the flatness on a table. you can adjust about 3/16" if you have to with an iron, heating and controling the warpage rate over the full panel.
FLYIN SPEED/ The guys say "fly Faster" but what exactly does that mean in practical terms?
If my OLY 650 could fly from a standstill throw, BOT needs at least a 5 pace run and a javelin throw for minimums. About double the normal "gas bag", When you find "THE STEP", the spot when all the balances are in place, where the best L/D is, the Lady will accelerate a bit , and the flatness of glide rate will increase. The first time I saw this happen, I was expecting to land about a goal line on football field, but was still above crosspole when intersecting that line- quite impressive the first time ya see it!!
I don't remember the dimension from leading edge, for C.G., as I have always used the spar for the C.G. Envelope- from leading edge (spar) to trailing edge with great success!
Johnny
P.S. Shaver!
After seeing your bird on the SEE BIRD Post, can you give us a close-up of your wing /poly joining?- It looked to me like your left side may be causing some greif.
Johnny

[ShaverR6]

I've been flying BoT's off and on since I bought my first kit from Dave Thornburg himself. NONE of my planes have flown as you described. You didn't mention where our CG was but my plans call for 3 5/8" from the leading edge at the root. But you can safely fly at 3 3/4 w/o any trouble, just a little sensitive to the elevator with aft cg.

Assuming CG is correct consider the following:
1. Sand a symmetrical airfoil from TT to tip(no wash out needed)
2. Check for wing warps
3. As others mentioned fly it faster.
4. Where are you measuring the rudder throw at the widest part of the rudder?
5. Have you sealed the rudder hinge line?
6. Are your tips equal distance from the rudder hinge line?

The BoT will not handle like a 100" or smaller sailplane but it is quite respectable in turning performance. My current BoT which weighs 44oz's will come out of a bank with opposite rudder RIGHT NOW.

Just some ideas. It's a great plane.

Stan

Hi Stan,
It is interesting to see that our plans do not provide the same CG location. My plans show a CG range of 3-7/8" to 4-3/16" from the leading edge. I have rebalanced with the CG at 3-7/8".
I followed the instructions and sanded a symmetrical wing tip profile.
I checked the wings for warps before and after covering and it seems pretty true to me.
During my next flights i will try and fly faster. I am perhaps to used to flying my older Dynaflite Daydream which would almost stand still in a slight breeze.
My measurements for rudder throw were made from the furthest point aft on the rudder, or the "widest point" that you mentioned.
The rudder hinge line was not sealed previously, i thought it was a pretty tight gap. I have now sealed it with hinge tape. I hope that it will help out with rudder control, I have a feeling it will.
When I located and drilled the wing mount bolts I made sure that the wing tips were equidistant from the end point of the fuselage, I didn't have the vertical stabilizer mounted at that stage.

Thanks a bunch for your help. As mentioned I am not a complete newbie, but there is always more to learn and I am always grateful for help from others.
Cheers.

[ShaverR6]

You haven't said the wing polyhedral angles numbers. Use stock wing polyhedral angles. One tip panel 4 oz.weight is heavy, in my opinion. Normal tip panel weight is about 2 oz. Too mass at the wing panels makes the sluggish in yaw. Too much reduced polyhedral makes the BOT sluggish in yaw. With good CG position, enough airspeed, no wing warps and good servo links, the BOT will improve yaw response, even with maximum rudder throw 1-3/4" each side.

Hi Ollie.
The polyhedral is not stock. The center dihedral is as per plans, but due to the wing joiner method used (same method as Solo6796: http://www.rcgroups.com/forums/showthread.php?t=269207&page=3) I had to decrease the outer panel polyhedral. I had hoped that this would not affect performance significantly, but perhaps that assumption was wrong.
I believe the outer panel polyhedral is now about 3.5" instead of the 5" per panel as shown in the instructions.
I tried to sand the heck out of my outer wing panels and these are the lowest weight numbers I could get. I think I built the wing too strong in anticipation for rough launches and catching wing tips during landings. And yes, heavier outer panels will increase the inertia of the wing and make direction changes slower.
The rudder is now sealed and has equal throws, hopefully with my new CG location and proper trim I can enjoy this plane as much as you all seem to have.
Thanks again.

[ShaverR6]

Shaaver!
Sounds to me that they have upgraded the print since my last build-'92-2nd
Stan and Ollie have said what I would have, I flew mine with 1/8" washout via sanded symetrical foil, the balance for a single panel, but now that it is 3 may be difficult to see, is about 2 bays inboard of first poly break. Check your tip's balance points individually, and the flatness on a table. you can adjust about 3/16" if you have to with an iron, heating and controling the warpage rate over the full panel.
FLYIN SPEED/ The guys say "fly Faster" but what exactly does that mean in practical terms?
If my OLY 650 could fly from a standstill throw, BOT needs at least a 5 pace run and a javelin throw for minimums. About double the normal "gas bag", When you find "THE STEP", the spot when all the balances are in place, where the best L/D is, the Lady will accelerate a bit , and the flatness of glide rate will increase. The first time I saw this happen, I was expecting to land about a goal line on football field, but was still above crosspole when intersecting that line- quite impressive the first time ya see it!!
I don't remember the dimension from leading edge, for C.G., as I have always used the spar for the C.G. Envelope- from leading edge (spar) to trailing edge with great success!
Johnny
P.S. Shaver!
After seeing your bird on the SEE BIRD Post, can you give us a close-up of your wing /poly joining?- It looked to me like your left side may be causing some greif.
Johnny

Hi Johnny.
I have triple checked the balance of the wing and it doesn't want to drop a wing tip.
From all the feedback from users here it does seem that the Bird of Time needs more speed than other planes. I have to say i find this surprising, I thought that the BOT would be a big time floater that crawls along in light air.
I am looking forward to trimming this plane out further once i can get into the air again, it was too windy this morning. I will use the dive test as mentioned by Ollie. It was interesting, during the first flight i noticed right away that the plane was tail heavy due to the tendency to "tuck in" when i dove to gain airspeed for fear of a stall. That is a scary tendency when you are getting low on altitude!
I took a look at the joint between the let wing tip and the center section, I think what you are seeing is a slight difference in the thickness of the leading edge sheeting. This makes it look like the outer panel has a higher incidence than the center section.
Wen you mentioned the cross bar on the football field you reminded me of one of my flights with a Goldberg Sophisticated Lady with a 0.049 power pod. I was flying on a soccer field with a small crowd of on lookers, i was getting low and was turning into the wind when I suddenly noticed that I was heading straight for the goal post! Luckily I swerved in time to avoid smashing a wing tip and made a smooth landing. :rolleyes:

[Ollie]

Your BOT problem (sluggish in yaw) because of not enough polyhedral in the tip panels!!!!!!!! Increase the polydedral angle tip panels about 5 to 10 degrees!!!

With polyhedral wings, the rudder makes the plane yaw and the polyhedral wing makes the yaw to roll into a turn. With a straight wing (no polyhedral) the rudder makes the plane yaw but it doesn't bank and doesn't turn!

The real problem is your "BOT" sluggish roll and sluggish turn.

[ShaverR6]

Dang it, I was hoping this would not be a problem as i didn't see AJ (solo6796) having any problems with his BOT with reduced tip polyhedral.
With a 35" long tip panel and 3.5" of rise gives 5.7deg polyhedral.
What a heart brake, I just finished covering after a winter of building!
Oh well.

[Stan_in_AR]

The correct poly angle is 8.21*, mine is 8*

What type of wing joiner did you use?

We still haven't solved your "squirrely" behavior. The polyhedral you have wouldn't cause that, but would make the the turning problem.....solution to that would be a larger rudder.

Depending on your wing joiner there is still hope. On my last BoT I used a ply joiner with the "male" sticking out of the root of the tip panel. I came in for a hot landing and forgot to get out of the way of it and broke the tip joiner right at the root. So I decided to use a carbon fiber rod with aluminum tubing for the receivers and micro ballooned them to the shear webbing.

Works great. If your interested in pix's I'll send you some, I'm in process of recovering for this season. stan1936atsbcglobaldotnet





Dang it, I was hoping this would not be a problem as i didn't see AJ (solo6796) having any problems with his BOT with reduced tip polyhedral.
With a 35" long tip panel and 3.5" of rise gives 5.7deg polyhedral.
What a heart brake, I just finished covering after a winter of building!
Oh well.

[Stan_in_AR]

I built my tips out of 4-6oz contest grade balsa and my tips came out at 3.5oz's per with only 5 grams difference in weight.

Stan



"Each flight was very unnerving, the plane was very unstable and i was desperately trying not to crash."
"I have balanced the wing along the aircrafts centerline, and I consider the outer panels pretty light, I think they were just over 4oz each."
"It has been modified to incorporate a three piece wing, spoilers, and carbon tow on top and bottom of the spar with Kevlar wrap."

You haven't said the wing polyhedral angles numbers. Use stock wing polyhedral angles. One tip panel 4 oz.weight is heavy, in my opinion. Normal tip panel weight is about 2 oz. Too mass at the wing panels makes the sluggish in yaw. Too much reduced polyhedral makes the BOT sluggish in yaw. With good CG position, enough airspeed, no wing warps and good servo links, the BOT will improve yaw response, even with maximum rudder throw 1-3/4" each side.

[Ollie]

Stan,
What are the wing tip panel jointers? Dimensions? Material?

[ShaverR6]

The correct poly angle is 8.21*, mine is 8*

What type of wing joiner did you use?

We still haven't solved your "squirrely" behavior. The polyhedral you have wouldn't cause that, but would make the the turning problem.....solution to that would be a larger rudder.

Depending on your wing joiner there is still hope. On my last BoT I used a ply joiner with the "male" sticking out of the root of the tip panel. I came in for a hot landing and forgot to get out of the way of it and broke the tip joiner right at the root. So I decided to use a carbon fiber rod with aluminum tubing for the receivers and micro ballooned them to the shear webbing.

Works great. If your interested in pix's I'll send you some, I'm in process of recovering for this season. stan1936atsbcglobaldotnet

Hi Stan.
See the link at the top of the page for the exact same type of wing joiner method that I used. It was that build thread that I got the idea from.

[Stan_in_AR]

Your first mistake was to permanently epoxy one of the wing wires into the wing. Should you bend that wire with hard landing/launch there is no way to straighten it out.

Your other option is to cut the the permanently mounted wing wire off at the root and put new joiners in aft where yours are currently located. This is was I did when I broke the ply joiner I first used to connect tip to center section. What I used was 9/32 od aluminum tubing for the receiver tubes and 7/32 od aluminum joiner rods. I stuffed 5/32 od carbon rods inside the 7/32od tubes. This is more than strong enough for this plane. Also very light in weight

Now if you don't want to go through all this just use your spoilers as spoilerons to assist your turning.



Hi Stan.
See the link at the top of the page for the exact same type of wing joiner method that I used. It was that build thread that I got the idea from.

[Mr. Kite]

Sounds like it maybe the wind and air of the day more then an the airplane . Try to set up a new airplane on a windy day is imposable .

[Captain Canardly]

Hey Thar Mr. Kite!
Maybe I otta quit talkin', then, huh??
Johnny

[Liberator]

The amount of poly will fix the rudder issue. The squirrly part is almost certainly the cg.
Remember the old saying.
A nose heavy plane flies poorly, a tail heavy plane flies once. :D

[Texas Buzzard]

I have seen the BOT perform in winds of 6 to 10 mph just great.

Things to think about: wing tip wash out, CORRECT CG - (start just a tad nose heavy, that equals stability).

If you have to carry significant up elevator trim for level flight then either the CG or the incedence is wrong.

Keep working. Thornburg designed a great plane in his Bird of Time. He won the World Championships with the BOT.

[Phoebusflyer]

Hey, Shaver, when I flew my BOT last week, I had problems too! I kept adding nose weight to counter what I thought was a heavy tail. Also, on my first launch, the elevator had too much up trim in it and stalled the plane on launch and nosed in. I changed it, but when I launched it next, it responded a little weird to rudder input. Mine had at least as much rudder throw as yours. When it caught a tip on landing, it stripped the servo gear on the rudder. Doesn't look like I'm going to get to fly it again till after Sept. Work and all!!
Did you put cable pushrods in yours? I did and think that contributed to the heavy tail.

[GliderRich]

Hi Shaver,

Just found some pics of your BOT here http://www.rcgroups.com/forums/showthread.php?t=421085&page=3

Love the colour scheme :)

Looking at the wing, you say three piece, do you mean four piece? The polly angle looks waaaaaay too low. Why did you build it that way? I do feel the CG is probably out but the main problem with rudder authority is the almost flat wing. Shame that, as it looks like a real nice covering job. Add some ailerons and it will be fine like that ( I have considered this when I get round to building mine) ;)

[Liberator]

Shaver,

Ummm yeah, your gonna want to do one of two things. Crack the wing open and put in ailerons, or crack the spar and elevate the tips for the corrected poly amount. Ailerons would be less painful.

Years ago my buddy had a Spirit Elite and as an experiment we unhooked the ailerons and flew it as a rudder only. (What can I say...foolish kids) :)

Needless to say rudder only on a wing with little or no poly will make it fly poorly to say the least. You balance may actually be ok, you need to do something about how flat you made that wing!!!

It is cool looking though. I think you did a great job on the plane. :p

[solo6796]

I just looked at the pictures, also. Did you also flatten the center panel dihedral? The one I built had plenty of turning authority at it's normal thermal speed. Any sailplane loses authority if flown too slow. I did reduce the outer panel polyhedral some, but the center dihedral was at least at plan. Yours looks flat. Mine had about 6 degrees in the center and about 7 on the tips.

AJ

[ShaverR6]

I just looked at the pictures, also. Did you also flatten the center panel dihedral? The one I built had plenty of turning authority at it's normal thermal speed. Any sailplane loses authority if flown too slow. I did reduce the outer panel polyhedral some, but the center dihedral was at least at plan. Yours looks flat. Mine had about 6 degrees in the center and about 7 on the tips.

AJ

It may look flat, but the center section is built with the stock amount of dihedral. I will try and post pictures tomorrow showing the wing at the same point of view for comparison. My wing looks pretty darn similar to yours from head on.
Once the weather cooperates, and I have free time I will fly the bird again with the added nose weight and see how she goes.

[ejett]

I just looked at the post regarding elevator travel in my old BOT thread. I think one problem is you have waayyyy more elevator throw than you need. I would suggest that you reduce it some (mechanically at the servo) and try again. I personally don't think your wings are so flat that you can't get it to turn, but it may want to spiral in.

Anyway I think you have so much stabilator throw that the plane is too sensitive to elevator input. I know my plane had probably 2/3 of the throw you have, maybe less. It flew really nice.

EJ

[ShaverR6]

Well I managed to get some flying in this morning. The Bird was re-balanced with the CG further forward. I also sealed the rudder hinge line. Once re-balanced the plane flew much better, no big surprise. As was mentioned, once the flying speed was increased the rudder control was much better, still less than I was hoping for but that is the price to pay for reducing the polyhedral. Anyways, I managed to follow a hawk into a tiny thermal for the longest flight of the day, 2mins :rolleyes: I just couldn't find any significant lift.
I think the plane could use some further CG trimming to improve the glide ratio, another time perhaps. Thanks goes to RomanG for highstart retrieval and picture taking.
Thanks again for the input all.

[Phoebusflyer]

Good looking BOT, Shaver!