Bird of Time Tail

[mr_wood]

Hi,

I am building a BOT kit. I am used to designing and building HLG's and DLG's. I have looked at the tail construction and a little concerned about the brass arm that is connected to the horizontal tail. I am used to building light especially at the tail end so I don't need useless weight at the front to balance. It really pains me to add a lump of brass to the tail - does anyone have any better ideas for operating or arranging the Horizontal Tail ?

Thanks
Tim,

[SoCalGliderFlyr]

I wouldn't use the original design to drive the stabilator. It's a pain to get right. Just the sort of fiddly thing Dave loves though. Use the conventional inverted 'L' design. Yes you can have the piviot in the back and the drive pin in the front. And you can sweap the long drive arm forward a bit to make it all fit in the V-Stab area.

[ejett]

My Dynaflite kit supplied Aluminum tubing instead of brass. I'm not sure how much weight that was supposed to save, but I built new stabs and replaced the original pivot hardware with even heavier brass tubing arrangement. It sure straightened out my wobbly stab problem. I did not add any nose weight to counterbalance my now heavier tail and it flys fine. In fact, though unrelated to the change, I think I still need to pull some nose weight out of it.

Here is a link to a sketch provide to me by BMatthews on the modification to the horizontal stab support tubes.

http://www.rcgroups.com/forums/attachment.php?attachmentid=357255

EJ

[SoCalGliderFlyr]

A little research always helps. Here is the original linkage and the redesigned RCM linkage. I'm not sure who redesigned it. Keep thinking it was Dave. Then it could have been a collaboration between Dave and Paul Plecan the RCM plans drafter.

[SoCalGliderFlyr]

I wouldn't use aluminum tubing for anything. It will corrode and lock up on the steel stab wires.

[ejett]

You could always redesign the stabs as horizontals with elevators like Ray Hayes' Bird series. I personally like the flying stabs on the planes I have with them. (Aquilas, BoT, Alcyone, Pitchmoth,
Chuperosa and eventually Gnome 3m)

EJ

[SoCalGliderFlyr]

That's what Dave did to one he used in 1979 for the world team trials. Very small elevator too.

[SoCalGliderFlyr]

I also found Dave's typed instructions. Interesting read.

[BMatthews]

My Bird uses the arrangement in that second sketch with square brass tubing for the upright. With a bit of care the nylon bellcrank method will offer a lot less play and neutral deadband than the cable option.

Hints for the nylong option. The horns are made for use with 1/16 wire. You want to preserve the nice fit so DO NOT use a Z bend that has to turn the corner and will bruise the nylon. Use an L bend with a wire keeper that is presoldered on to keep it in place (SoCal, you had a nice sketch of wire keepers that solder to the main wire I believe). For the upright use an L of wire that pins the upright and horn and then bind the L to the side of the upright with thread and seal the thread with some CA glue.

DO NOT solder around the nylon horn. The heat will damage it and make the hole bigger.

Done with a bit of attention to the details like this I think you'll be very impressed with the low amount of free play.

After 2 bad experiences with 90's and a T tail S curve I won't ever use cable in plastic type rods for elevators again. There's far too much slop between the cable and the plastic. It won't show up with a fairly straight run but for a strong angled curve like the 90 or an S you'll see a lot of deadband. And on a high performace glider that's the kiss of death.

[SoCalGliderFlyr]

Most aileron bell cranks have a sleeve or bushing in the center for the nylon to ride on. They are intended to be bolted to a piece of ply wood so the bushing is a bit over size for the bold and thus any music wire. You could drill the bell crank out to the next size brass tubing then use a tubing in tubing bearing arrangement.

The L bend and wire keeper is an old U-control design.

http://www.rcgroups.com/forums/attachment.php?attachmentid=388387&stc=1

(Hey Bruce! What's the path to the image files so I can call them out directly?)

[BMatthews]

Right click over the image>properties>highlight path>CtlC to copy then paste between the image code in the square brackets.

But you still need to keep track of where the image is or have a gallery set up someplace on the web and keep a notepad list of the pathnames for quick use.

[SoCalGliderFlyr]

Rennlist.com just established a means for a user to check which images they have uploaded. Interesting.

[SoCalGliderFlyr]

I get the same link as the above posting. I know the name of the file as you can do a Save As to see it. On some sites it's a directory off of the main called uploads or downloads. Must be a path here.

[rubberduck]

hello,
i normaly build my own ... :confused:
(sorry my bad school-english...)
look at the image, i think you will see it

:rolleyes: :)

[SoCalGliderFlyr]

You can also turn it around with the pivot in the back. Almost a must for a swept tail like on the BoT. Or swept stabilators. Or both.

[BMatthews]

SoCal, if you look at the BoT tail again I think you'll find that Ducky's version would put the fixed pivot closer to the magic 25% point that is considered ideal. Certainly the original with the rear pivot that Dave used and as shown in the cable or link rod sketches puts the main pivot back at around the 50-50 area point. The leading edge may be swept back a bit but the trailing edge curve forward with a vengeance.

While mine has never had a flutter problem I attribute that moe due to care in avoiding any slop in the controls than to good design. If I finally get around to making another Bird I think I'd use Ducky's version with the moving link at the rear. The only catch is that I'd have to redesign the stab a bit so the main spar somehow connects with the front rod more effectively..... Hmmmmm.... Maybe Dave's way is best afterall..... It's a compromise for sure but it's a compromise that seems to work.

[rubberduck]

At the most horizontal tails the pivot is at approximately 30 per cent, so that the pressure does not become so high on tail by starting with rubber or winch.
If you take the pivot in the back of the tail, position it at 40 percent and the rudder at 5 percent in the front. That is also a good solution.


juergen, bonn

[Esprit2]

Has anyone considered actuating the tail like the Sagitta? Build the push-pull cable into the tail, curving up into the stationary portion of the vertical stab. Pivot the stab where you wish, and drive the other end up and down with the cable. The only down-side I ever noticed with Sagittas is that the free end of the cable may move around a bit when the stabilizer is removed. Getting the stab-rod back through the eye adds a few seconds to set-up time, but no big deal.

Regards,
Tim

[SoCalGliderFlyr]

Tim, The original BoT was designed that way. I think it's doable on small planes using spiral wraped acoustic guitar strings. These have to be run in tubing that fits the OD of the string. You solder the ends to stiffen. Leave only what you need to connect to the control surface free of the guide tube.