HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Nov 12, 2006, 01:29 AM
Registered User
Spokane, WA
Joined Nov 2004
11 Posts
Question
Bird of Time Scratch Build

I am gearing up to scratch build a bird of time. I want to make a few minor changes to the bird to try an incorporate some more modern ideas into the design. I'm not trying to make this ship into something its not, I just want to bring it a little more up to date. Anyway I want to run my ideas by you all and see what you think.

First off I'm going to build the wing as a three piece (two outside wing panels and a center section) instead of a two piece. I also am going to use the airfoils off of Mark Drela's Allegro-lite and I'm going to cap the spars with CF out to 4 bays pass the polyhedral breaks.

For the fuselage I think I'm going to lengthen the tail moment by about 1.5" and the nose by 1". I plan on fiberglassing the fuse for some extra strength. Which actually brings me to my first question. What weight and how many layers of glass do you think I should use on the fuse?

My last modification is I'm going to make a built up rudder instead of the solid one to try and save some weight. I'll probably change the bearing system on the flying stab so its a little more durable too.

So thats the plan. Any comments or recommendations you can give me will be greatly appreciated.
The-Jessman is offline Find More Posts by The-Jessman
Reply With Quote
Sign up now
to remove ads between posts
Old Nov 12, 2006, 01:55 PM
Genie Builder
greyhound flyer's Avatar
Portland, Oregon, United States
Joined Aug 2004
264 Posts
Some suggestions...

Here's a nice thread in the sailplane talk forum about scratchbuilding a BOT:
http://www.rcgroups.com/forums/showt...ight=bird+time

For the spar, make sure you wrap it with kevlar thread or biased (wetted-out) 1.4 oz glass--keeps the carbon caps from delaminating.

The best way to build a wooden and glass fuselage (The Genie fuse):
http://genie.rchomepage.com/FILE%200...NSTRUCTION.pdf

Built-up rudder is definitely the way to go. Use the lightest wood you can get ahold of. Monokote is hard to work with but does yield a strong structure for the rudder and stabs. For the stab drive mechanism, check out Harley's tubing/wire sizes. They work very well on the Genies and are quite light.

--Byron.


Quote:
Originally Posted by The-Jessman
I am gearing up to scratch build a bird of time. I want to make a few minor changes to the bird to try an incorporate some more modern ideas into the design. I'm not trying to make this ship into something its not, I just want to bring it a little more up to date. Anyway I want to run my ideas by you all and see what you think.

First off I'm going to build the wing as a three piece (two outside wing panels and a center section) instead of a two piece. I also am going to use the airfoils off of Mark Drela's Allegro-lite and I'm going to cap the spars with CF out to 4 bays pass the polyhedral breaks.

For the fuselage I think I'm going to lengthen the tail moment by about 1.5" and the nose by 1". I plan on fiberglassing the fuse for some extra strength. Which actually brings me to my first question. What weight and how many layers of glass do you think I should use on the fuse?

My last modification is I'm going to make a built up rudder instead of the solid one to try and save some weight. I'll probably change the bearing system on the flying stab so its a little more durable too.

So thats the plan. Any comments or recommendations you can give me will be greatly appreciated.
greyhound flyer is offline Find More Posts by greyhound flyer
Reply With Quote
Old Nov 12, 2006, 02:25 PM
Hot Dawg Glider Pilot
schrederman's Avatar
United States, TX, Weatherford
Joined Nov 2002
7,845 Posts
I scratched one out and and found it to be a rewarding build. I made it stock dimensions, used the stock airfoil, and still had a killer BoT. I used CF tow laminated in the spar and made it thicker the closer to center it was. I didn't break it but kept it hanging out as I built the first panel. Then I propped it up and built the second panel on to it, keeping the CF in tact. It was bullet proof. There's a picture of it on the houstonhawks.org page under "How the Hawk came about".

Enjoy... and post your build as you go... we're all interested...

Jack Womack
schrederman is offline Find More Posts by schrederman
Reply With Quote
Old Nov 13, 2006, 01:58 AM
Registered User
TLyttle's Avatar
Keremeos, BC Canada
Joined Mar 2004
2,639 Posts
As far as the tailfeathers are concerned, The Old Buzzard Himself recommended that the sheet used should be the lightest, punkiest stuff you can find, so clearly weight was a consideration. I ain't sure, but I think he was driving for consistent, thick sections there.

I saw Thornburg and crew at Belgium in '79, and that model wasn't giving away much to anybody. The Dassels were there to open everyone's eyes to the future, but the BoT did well for what we found out was Old Technology. The BoT and the South African "Yellow Bird" were about the last of the polyhedral ships in the WCs.

That considered, I suppose there is a little bit of updating to do to the BoT, but I have yet to see a BoT that didn't tax the abilities of its pilot; it always seems to be capable of more...
TLyttle is offline Find More Posts by TLyttle
Reply With Quote
Old Nov 13, 2006, 04:47 AM
The original Flying Pigs Sqd.
Up&Away's Avatar
Netanya, Israel
Joined Aug 2002
10,091 Posts
What airfoil does the BoT use? Is it the same as Dynaflite's ARF foil?
Up&Away is online now Find More Posts by Up&Away
Reply With Quote
Old Nov 13, 2006, 08:00 AM
Hot Dawg Glider Pilot
schrederman's Avatar
United States, TX, Weatherford
Joined Nov 2002
7,845 Posts
I believe the most recent kit used the Eppler 205... if I remember correctly.

Jack
schrederman is offline Find More Posts by schrederman
Reply With Quote
Old Nov 13, 2006, 08:55 AM
Registered User
Punta Gorda, FL
Joined Apr 2002
4,952 Posts
"First off I'm going to build the wing as a three piece (two outside wing panels and a center section) instead of a two piece."

Understand the wing spar under bending loads. At the tip, the bending load is zero and at the center of the wing is maximum bending load. At the jointer between tip panel and root panel has a bending load only less than 25% than maximum bending at center. It is important to taper the carbon spar caps for low cost and weight! Please don't over kill the strength at the two jointers or over kill the spar caps in the tip panels.

Also, understand the spruce spar caps. The top spar cap is under compression and has a strength of 5610 PSI. The bottom spar cap is under tension and has a strength of about 14,000 PSI. Is is better to use hard balsa for the bottom spar cap rather than spruce. Better yet, taper the spruce and balsa caps to near zero at the tip.
Ollie is offline Find More Posts by Ollie
Last edited by Ollie; Nov 13, 2006 at 09:02 AM.
Reply With Quote
Old Nov 13, 2006, 01:45 PM
Registered User
Los Angeles, CA
Joined Jun 2004
200 Posts
From what I've heard...

Dynaflights airfoil is not the original airfoil.

Soaring Specialties sells a laser-cut set from DT's plans, see here:
http://www.soaringspecialties.com/botribkit.shtml

enjoy.
johnsocj is offline Find More Posts by johnsocj
Reply With Quote
Old Nov 13, 2006, 05:03 PM
The original Flying Pigs Sqd.
Up&Away's Avatar
Netanya, Israel
Joined Aug 2002
10,091 Posts
Dynaflite mentions somewhere a "Clark Y variant". I may be very wrong (I often am) but isn't Clark Y often used for "work-horses" not thermal birds?
Up&Away is online now Find More Posts by Up&Away
Reply With Quote
Old Nov 13, 2006, 05:57 PM
Registered User
Spokane, WA
Joined Nov 2004
11 Posts
greyhound flyer -
I plan on wrapping the spar with kevlar thread just for the reason you described.

Thanks for the link on the wood and glass fuse build. That has answered a lot of questions I had about glassing the fuse.

Ollie -
I'll probably take your recommendation and use hard balsa for the bottom spar cap. I want to get good strength without building in any unnecessary weight. What would you recommend for a root panel to tip panel joining system? I was thinking of using 3/16 carbon fiber rod going into brass tubes in the root panels. I was going to use small rare-earth magnets to hold the panels together.

Up&Away -
In the instructions I think Thornburg says the airfoil in a modified Clary Y with a raised entry point (Phillips entry). I may be wrong though as I don't have the instructions in front of me.


I am still in the preliminary stages of this build so it will probably be at least a couple weeks for anything really gets going. I'll try to post my progress as I go for all those who are interested though.
The-Jessman is offline Find More Posts by The-Jessman
Reply With Quote
Old Nov 13, 2006, 08:01 PM
Hope is not a strategy
quietman's Avatar
LoCal
Joined Jun 2003
79 Posts
great project, I love the BOT, nothing looks quite like one in the air.

At the first F3J worlds in England the team from Greece flew them.

They all broke on tow or hit the ground after a couple of minutes.

But we all loved watching them and they certainly had fun.

which is the point...

John Roe
www.roenation.com
quietman is offline Find More Posts by quietman
Reply With Quote
Old Nov 13, 2006, 08:24 PM
4 wheels move a body; 2 a soul
Saratoga, Ca
Joined Feb 2004
1,462 Posts
I agree w/John, nothing much out there looks as pretty as a BOT in the air.
Or on the ground for that matter. Lots or work but certainly worth the effort.
Hey John, you still yak fishing?
Walter
(Malibu XFactor)
glderguy is offline Find More Posts by glderguy
Reply With Quote
Old Nov 13, 2006, 09:18 PM
Registered User
Punta Gorda, FL
Joined Apr 2002
4,952 Posts
Jess,
See:
http://www.charlesriverrc.org/articl...rengthcalc.htm
&
http://www.charlesriverrc.org/articl...mproofwing.htm

Simple tape holds the panels together better than magnets. KISS

Calculate the maximum bending moment for the jointers. Be careful of carbon rods in brass tubing. Burrs on the edge of brass tubing can nick the carbon rod. It is better to use soft aluminum tubing rather brass tubing. It is important to wrap the spar with kevlar in the area of the jointer. The kevlar keeps the jointers from prying apart the spars.
Ollie is offline Find More Posts by Ollie
Reply With Quote
Old Nov 14, 2006, 08:12 AM
Registered User
John Gallagher's Avatar
Lindenwold, NJ, USA
Joined Dec 2000
3,193 Posts
Quote:
Originally Posted by johnsocj
From what I've heard...

Dynaflights airfoil is not the original airfoil.

Soaring Specialties sells a laser-cut set from DT's plans, see here:
http://www.soaringspecialties.com/botribkit.shtml

enjoy.
I'm pretty sure that the ARF airfoil is a selig 3021 and the kit airfoil is close to the original. You gotta remember that Dave designed the original airfoil using the that-looks-about-right method of design. Mark Drela would know for sure, but the 3021 is probably a step up from the original. The original airfoil was noteworthy in it's time because it was thinner than on most gliders available then.
John Gallagher is offline Find More Posts by John Gallagher
Last edited by John Gallagher; Nov 14, 2006 at 08:19 AM.
Reply With Quote
Old Nov 14, 2006, 12:46 PM
Registered User
Spokane, WA
Joined Nov 2004
11 Posts
Quote:
Originally Posted by Ollie
Jess,
See:
http://www.charlesriverrc.org/articl...rengthcalc.htm
&
http://www.charlesriverrc.org/articl...mproofwing.htm

Simple tape holds the panels together better than magnets. KISS

Calculate the maximum bending moment for the jointers. Be careful of carbon rods in brass tubing. Burrs on the edge of brass tubing can nick the carbon rod. It is better to use soft aluminum tubing rather brass tubing. It is important to wrap the spar with kevlar in the area of the jointer. The kevlar keeps the jointers from prying apart the spars.
Hmm, didn't think about the brass nicking the carbon, I'll see if I can find some aluminum tubing. Thanks for the heads up.
The-Jessman is offline Find More Posts by The-Jessman
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Bird of Time (BoT) - Build Urbanarmitage Thermal 66 Jan 08, 2011 02:10 PM
Question Who'll build me a Bird of Time Wing? michaeljt Sailplane Talk 8 Mar 09, 2010 09:20 PM
Build Log Bird of Time ARF build with ailerons/flaps/spoilers tjcooper Electric Sailplanes 23 Jan 13, 2009 05:59 PM
Bird of Time build question CalT Thermal 16 Jul 12, 2005 05:57 AM
New scratch-built Bird of Time schrederman Thermal 26 Sep 08, 2003 09:23 PM