Big Bird Nose Design for Electric Conversion and misc detail notes:

I redesigned the nose of the sky Bench Big Bird XL electric conversion rather than using the drawing supplied in the plans because I wanted a nose that looked like it was designed to fit the spinner and something that look a little more finished. The plans supplied in the kit show the area below the spinner as simply angled back at a 45 degree angle. I wanted something tha FIT FLUSH right up to the spinner, so this is what I came up with: The photos show what the nose looks like before painting.

The nose is exactly 50 mm wide at the nose. This is the same width as the spinner and rest of the fuse until it starts to taper back toward the tail feathers. I cut off exactly 2 inches (what the plans recommend) as measured from what would be the most forward point of the nose if you were building the non-electric version.

The firewall is recessed back 1/16 inch back to provide a small epoxy fillet in front of the firewall for extra strength.

The motor mounting bracket that comes with the motor is not used. The Motor is mounted directly to the firewall rather than using the mounting bracket that came with the motor. I did this because I needed all the shaft length I could get since I used a 3/8 inch firewall that was recessed 1/16 inch back for strength. This gives enough shaft length for the spinner. The firewall/engine mount bolts are 3mm x 8 mm allen head bolts that I purchased in the car section of the hobby store. I liked these because they have a large head and no washer is needed. They also seem to stay put because of the extra friction, but I will probably still use thread locker to make sure they stay put.

The firewall is 3/16 inches thick. Made from bonding 1/16 and 1/8 ply, since I did not have 3/16 and only needed a small piece.

I used 3/8 square bass wood that I cut diagonally to make triangle corner blocks behind the firewall (see photos). You will need these corner blocks because you will sand right through the corners when shaping the nose to the full round shape. The spinner was used as a template to draw a round circle on the firewall. This is used as a guide to sand a perfectly round nose -360 degrees all the way around to be made flush with the spinner.

Used a BB 50 mm Turbo Spinner (from Esprit Models). These spinners have a hole in the middle for air to enter the motor and fuse area and have a built in yoke. A few strategically placed holes are drilled into the firewall for air to flow into the motor. I chose a turbo spinner to eliminate an air scoop. I do not think heat will be a problem anyway because I don’t plan on long engine runs…only 20 to 30 seconds max… just enough to get the sailplane up to about 600-700 feet, then the motor is off for thermal hunting and soaring and then landing. The engine is a Turnigy 3536-1100 and I will turn a 12-6 or 11-6 Aeronaught folding prop. I have bench run this set-up and there should be plenty of power. It has a strong pull, but I have not measured the thrust.

Since the spinner is flush with the bottom of the fuse, the thrust line is 25 mm up from the bottom of the fuse at the nose. I put in 2 degrees right and 2 degrees down thrust. This is what Ray Hayes recommended on his plans for the electric conversion. I won’t know exactly how this will balance out, but it should be OK because the entire area under the wing can be used to slide the battery forward or rearward back from the F-2 fuse former to F-3 fuse former. (inserted note August 1, 2012: Balance was perfect just by moving battery for and aft as mentioned above).

A few other misc notes on my build: I used .06 carbon fiber rods for push rods from CST Composites (they come as a kit) with sheaths, clevis, threaded push rod end and instructions. Nice setup. Very smooth action. Rods cross at back of fuse to avoid sharp bends (see photos). The rods actually start to taper inward at the last former (so new rod holes were drilled in the former), but they intersect behind the former. I used these rods in by 100 in Big Bird (non electric) to eliminate tail weight. I did not have to add any weight in the nose.

Hitec HS 45 HB servos are used on the spoilers. These beautiful little puppies are light (.28 oz.) and come with Karbonite gears. Street price is $16 each. Perfect for spoiler servos on this sailplane. Now these may not be strong enough if you deploy them in a high speed dive, but I will be using them only for landing purposes on final to get the sailplane down on the ground.

I hope this abbreviated build will help others that are building the Big Bird XL or similar kits that want to convert to electric. I build slow and have limited time, so the finished sailplane will take about 2 more months. I will post some final pictures when completed. (Final inserted note: OK it took longer that the 2 more months, but it turned out nice)

Dave

this is really good to see.

thanks for sharing ideas and methodology, it fun to see great craftsmanship, .

I will be looking at the CST pushrods, this will be a useful setup for my next build.

The info on the motor setup is good to see and i am looking forward to hearing how it performs. Its kind of a TLAR except with props, volts, and motor specs.



john s.

Well done...much better than my BB.

After the fact, I discovered that my Multiplex geared inrunner would have fit in the pure glider version of the nose and looked much cleaner....20/20 hindsight.

I did not install spoilers and may add them. Will use the Art Hobby technique to open/close...servo below spoiler, servo arm directly against spoiler opens and a segment of rubber (band) closes when the arm comes down.

Carbon in fuse at rear must extend further back than LE of H stab! How do I know? I made a faster than usual landing and the tail skid (subfin?) hit a small tuft of unmowed grass...fuse broke exactly at H stab LE.

The XL should fly even better than the standard BB. Nice build.

Wayne

yea, I only ran the carbon aft of the LE of the stab along the sides of the fuse and along the bottom, but not the top, but I should have. I hope that will be good enough. I will eventually find out.

DW I use the same motor in my Electra: .Your gonna like it.

Very nice info.

Can you post info. on what carbon fiber material you used in the tail, how you attached it, tips on working with it, etc.?

Also, how are the carbon fiber rod end finished? Do you CA them or?

Thanks,
Harjit

Originally Posted by Harjit

Very nice info.

Can you post info. on what carbon fiber material you used in the tail, how you attached it, tips on working with it, etc.?

Also, how are the carbon fiber rod end finished? Do you CA them or?

Thanks,
Harjit

sure...the carbon fiber in the tail is also from CST Composites (CSTsales.com) as well as the carbon fiber push rods.

The carbon fiber in the tail is 1/2 inch by .07 thick. You simply order some and cut off what you need then I use the black rubber flexible CA by Bob Smith Industries that you can get at most hobby stores. It adheres to the carbon fiber very well. I put some weight on it and let it dry over night. Epoxy can also be used, but the rubberized CA seems to adhere the best.
The carbon fiber pushrods come in various diameters. I have used both .07 and .06 diameter rods and they both work well. the .06 is a little more flexible and easier to bend than the .07 but needs to be mechanically held in place more often (about every 4 or 5 inches) to eliminate any flexing or bowing. You can make these up yourself by purchasing the rods and rod ends at the hobby store, but then you don't get those nice teflon tubing that the rods slide in unless you order the rod kit from CST.

On one end of the carbon fiber rod is a 2-56 threaded end which is CA's ( again using the rubberized CA or you can use medium CA, which I did on a previous sailplane and it has also worked without ever coming loose). But CST now recommends using the rubberized CA. Then on the other end you CA the clevis or in my case I used the DuBro ball link. These rods need to be measured very carefully because once the ends are bonded thats it...they cannot be removed and the only adjustment is on the threaded end, so I try to measure the length so that the clevis that is put on the threaded end is about in the middle of the threads. That leaves me plenty of adjustment room. A steel clevis comes in the carbon rod kit, but I opted to use the DuBro ball link. At any rate the carbon fiber rods work very well because they keep the weight light. And any weight saved in the tail saves 4 times as much in the nose. Go to the CST sales web site and you can get lots of good information. the Carbon fiber in the tail (inside the fuse) will strengthen it. Ray Hayes (designer of this Big Bird kit) says go 3 or 4 inches aft of leading edge of Stab and 1 or 2 inches forward with 1/2 inch carbon fiber if you want extra strength. Hope that helps.

Dave

Originally Posted by Salmon-Run

Well done...much better than my BB.

After the fact, I discovered that my Multiplex geared inrunner would have fit in the pure glider version of the nose and looked much cleaner....20/20 hindsight.

I did not install spoilers and may add them. Will use the Art Hobby technique to open/close...servo below spoiler, servo arm directly against spoiler opens and a segment of rubber (band) closes when the arm comes down.

Carbon in fuse at rear must extend further back than LE of H stab! How do I know? I made a faster than usual landing and the tail skid (subfin?) hit a small tuft of unmowed grass...fuse broke exactly at H stab LE.

The XL should fly even better than the standard BB. Nice build.

Wayne

Wayne, what diameter spinner did you use?

Dave,

Spinner is 45mm.

I need to clarify something. When I opened the fuse to repair the break I discovered I ONLY put the CF strip on the top, NOT the sides and top as the manual instructed (duh). The repair has CF on all four surfaces. I also epoxied 1mm CF rod in the 90 degree joints between the sides and bottom.

My V stab was glued directly to the H stab with no triangular stock. This joint did not break but seemed a little too flexible. During the repair I removed about 2mm of covering at the joints and laid in a section of 1mm CF rod with an epoxy fillet. It is virtually invisible and adds a lot of strength.

If I break it again, it will be somewhere else!

Wayne

PS One more dumb-dumb. One day while preping the BB for flight there was quite a crowd asking all the typical questions. I got it in the air and in response to questions performed loops, inverted flight, etc. On landing I noticed I had not placed the 3M electrical tape at the wing joints....they never moved out a mm!

Originally Posted by Salmon-Run

Dave,

Sp One more dumb-dumb. One day while preping the BB for flight there was quite a crowd asking all the typical questions. I got it in the air and in response to questions performed loops, inverted flight, etc. On landing I noticed I had not placed the 3M electrical tape at the wing joints....they never moved out a mm!

Wow! You are lucky the wings didn't fly off! You must be living right.

I hope my carbon fiber that I put in the fuse does the job. I did not put it on the top because the light ply where the stab sits is not flush with the inside of the top of the fuse, so I skipped that part. I should have built up either the light ply or the balsa to until they were flush and then added CF. Oh well, if I land carefully I should be OK. If it breaks, I will do the repairs correct.

I debated whether to try and narrow the nose a bit down to 45 mm width at the nose, but was afraid it would be too close for the motor to fit without rubbing something. It would have been close, but I didn't want to chance it.

I have now primed and sanded the nose area from the trailing edge of the wing to the nose and its ready for paint. Aft of the TE of the wing will be UltraCote. I like the painted look of the nose for durability and to avoid the difficulty of doing those compound curves. I should be painting this coming week. I will be finishing the tail feathers and covering wings etc within the next few weeks. should be ready to fly by the first of May.

"Wow! You are lucky the wings didn't fly off! You must be living right."

Actually it is near impossible to get a wing panel on/off if they are NOT perfectly aligned with the wing rod and music wire. Any lift component keeps them tight but I don't recommend flying regularly without 'keepers'.

The flat botomed fuse usually allows the landing skid to hit first. This forces the rear fuse and tail feathers upward. It seems to me the CF on the top skin povides the least value (acts as a hinge) and that CF on the sides the most value. I think you will be ok.

Congratulations on stuffing an outrunner in the nose. The only reason I was able to go 45mm was the geared inrunner. Even then, it was a job.

Please post more photos of construction and finish work...would like to see the end result.

Wayne

Hi Dave.
I think you may like this covering material on the bottome of the fuse, between wing LE and front bulkhead on your BB to protect the bottom. It is pliable and somewhat thick translucent plastic with peel away backing (sticky self adhesive).
It costs a lot for what it is - 4.50$ for one foot, delivered to your door - but the payback is in time spent not recovering or fixing holes punched in the bottom of the fuse caused by rough surface landings.

see very bottom of this web page -
http://www.balsabuddies.com/cutouts/Listing.htm

You will really like your BB when your finished. I maidened mine today after being shelved for 2 year. It flys very predicably and with a motor you won't have to walk a mile or so retrieving hight start line like i did

keep going your getting to the end, john s.

John,

just painted the fuse today. Painted from the nose to about 2 inches aft of the wing. the rest of the fuse is covered in Ultracote Lite.

I will say one thing...wet paint has the strongest magnetic force in the world for everything floating in the air. But it really didn't turn out too bad. I used Klass Kote (similar to the old K & B Super Poxy). Used an automotive touch up gun to apply the paint. Very tough when fully cured and is pretty forgiving when painting. Its a 2 part epoxy paint. It is a bit pricey, but for me its worth the effort. I still have 2 planes about 15 years old that were painted with this stuff and they still look great. It is fuel proof if you fly power stuff.

I still figure about 4 more weeks to finish up everything that is left. I will take pictures when finished and post them on this thread.

thanks for the tip on the protective stuff for the bottom of the fuse. I'll check it out.

Your BB XL is Beautiful!

Dave M

Dave,

Looking forward to seeing the paint job. I was a fan of K&B and still have some partial cans. What is your source for the Klass Kote? I am working on a 96" Lanzo Bomber and want to paint trim and then clear coat the old Super Coverite I will be using.

Another source of 'skid tape' is chassis protective sheet by Associated. It is quite thick with self adhesive backing and can be found at LHS specializing in model cars (got mine at AMain). It will conform to gentle curves with a little heat as shown on my ASW 28-18.

Wayne

[QUOTE=Salmon-Run;21118645]Dave,

Looking forward to seeing the paint job. I was a fan of K&B and still have some partial cans. What is your source for the Klass Kote? I am working on a 96" Lanzo Bomber and want to paint trim and then clear coat the old Super Coverite I will be using.

Wayne, go to;
www.Klasskote.com

They have a lot of info on this Klass Kote. Much of the old K & B is compatible with Klass Kote and they tell about it if you go to the web site. The old K & B paint is compatible with their catalyst if you don't have any. I had catalyst 18 years old, but it turns dark and is OK on dark colored paint, but light paint such as white or yellow will turn a little darker. They also sell the thinner (reducer). They have many colors for WWII planes. Check them out. I will CK the stick on stuff to protect the bottom of the fuse.

Dave