Alex's Fiberglass Bird of Prey - RC Groups
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Jun 17, 2008, 07:26 PM
Engineer for Christ
IBCrazy's Avatar
Build Log

Alex's Fiberglass Bird of Prey

I had told myself I wasn't going to build one of these because I had too much to build already. But when I was asked by Kevin Von Speedmiester and Triple Digit Don to build them a fiberglassed Bird of Prey, I felt honored. So I figured I'd build a few of them including one for myself

So here is the plan:

Build a Bird of Prey that can take the speeds Kevin and Don want to fly and make it capable of holding a 4S LiPo.

The specs on the original Bird:

Wing: EPP 30" X 7.25" tapered to 3"
Wing sweep: Tips 3" ahead of root
Airfoil: NACA 0014
Nose: 8" EPP
Elevon: 1" balsa

Since I can't leave well enough alone, here are my specs:

Wing: Fiberglassed 2# EPS 29.5" X 9" tapered to 4.75"
Wing sweep: Tips 2.5" in front of root
Airfoil: MH30 - 7% (Low Reynolds#)
Nose: 12: balsa sheeted foam
Elevon: 1" live hinge

Handling should be similar, except mine will be more rigid in flight and hopefully faster too. Estimated AUW on this is somewhere around 22-28 oz.
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Jun 17, 2008, 07:37 PM
Engineer for Christ
IBCrazy's Avatar

Wings Done!

I cut the wings out Sunday evening, and finished applying the fiberglass today. I used 2 oz glass and West System Epoxy and applied it free hand (ie no vac bag). The wings still need either a skim coat of epoxy and paint or covering. They are quite stiff. Definitely stiffer than carbon fiber rods.

I already have the motor I'm planning on using. It's a GBX 9N10P 4 turn WYE (2625kv).

Now on to the fuselage.

Jun 17, 2008, 09:14 PM
Engineer for Christ
IBCrazy's Avatar
The fuselage is complete except for the nose peice and chambers. I will have to cut the battery, rec, and ESC chambers after the plane's assembly to get the COG correct.

The construction is balsa sheeted foam 24 X 2". This will comfortably fit a 4S LiPo (although I only plan on using 3S). This will be very rigid and will not flex at all.
Jun 17, 2008, 10:17 PM
Speed Freak
Spid's Avatar
Nice Alex!! Looks great.

I've got my BOP repaired and glassed using the "ritewing method" in addition to adding 2 carbon flats inserted on edge running from about the wing root to wing tip running parallel to the TE (looks like a "V"). I just have to finish covering it and it will be ready for the weekend.

The center carbon tube failed, so that along with the balsa elevons cracking was the snap sound we heard. I replaced the broken tube with a solid carbon rod. I'm really glad I covered it as the damage was very minimal.

Sorry or the hijack, just wanted to let ya know. Looking forward to seeing yours fly!
Jun 18, 2008, 07:29 AM
Engineer for Christ
IBCrazy's Avatar
Hijack?? No. Your Bird was the inspiration for this. I couldn't believe the speed and stability... until the structural failure. The structure on this one WILL NOT FAIL! The wing will be able to take no less than 8 lbs when supported at the tips.

By the way, Kevin, yours and Dons will be ready by tonight. I need to make a stabilizer for them. Warning: this will be a rocket! I think you'll understand why I scratch build once you fly it
Jun 18, 2008, 06:25 PM
Engineer for Christ
IBCrazy's Avatar

Wing strength test

The Epoxy on the wings dried last night so I could do a wing stress test today. I placed the wing between two tool boxes and place 10 lbs of weight on the wings. The wing flexed 3/4" I don't think this one is going to fail in flight no matter what maneuvers it makes.

The wing weighs in at 7 oz It might be heavy, but it's strong and fast
Jun 18, 2008, 06:31 PM
Engineer for Christ
IBCrazy's Avatar

Don's and Kevin's planes ready

I finished up Don's and Kevin's airframes. The final coat of Epoxy is drying right now. The airframe weight is coming in at 9 oz for the fuselage, wing and stabilizer.

It is now up to those guys to set it up with electronics. You guys will have to decide how you want to mount the wing. I'm probably going to use blind nuts and 1/4" nylon bolts to hold mine on.

You guys can pick them up anytime or I can bring them to Sagamore on Sunday (assuming the weather is good).
Jun 18, 2008, 06:46 PM
Indoor Free Flight Modeler

Looks good! I will grab mine at Sagamore.


Jun 18, 2008, 06:59 PM
Speed Freak
Spid's Avatar
Ditto. Nice job Alex and Thanks a bunch!!

Originally Posted by The Don

Looks good! I will grab mine at Sagamore.


Jun 20, 2008, 09:19 PM
Engineer for Christ
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A twist in design

I finally finished building my tail and fuselage. I fiberglassed my fuselage to add some strength. However, I decided to change a few things from my original idea. Sure I want this thing fast, but speed alone will not satisfiy me. I am going to thrust vector mine. My tail is made from Coroplast with a flute removed for movement. The motor is mounted to the tail. This is the same set up as my Menace. However, this one will be faster! Also I plan on adding winglets so I can fly knife edge. This also requires a longer nose to counter act the tail weight so my nose peice is 20" long, instead of 14".

Unfortunately, this is going to be very heavy. Right now the airplane alone weighs almost 14 oz without any electronics I need to add 4 servos (HS-81MGs), battery, motor, ESC and reciever. My electronics will weigh another 14 oz. So this one is going to be around 30 oz

The hinges are live hinges cut into the bottom of the wings. These are very stiff and will not vibrate in flight. I cut mine 13 X 1.5". Don and Kevin will probably opt for 10X1" or so.
Jun 21, 2008, 11:05 PM
Engineer for Christ
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Ready for flight

I finished the Bird of Prey so it's ready for Sagamore. I'm not sure how the thrust vectoring is going to do. I'm sure it won't beat the Menace.

Final specs:

AUW: 26 oz (4 oz lighter than I expected )
Wingspan: 34:
Wing area: 240 square inches
Airfoil: MH30 - 7%
Servos: HS-81 MG
Motor: 9N10P modified GoBrushless GBX triple 4 turn WYE (2625kv)
ESC: DonsRC Pentium 60 Amp
COG: 1/4" in front of Leading Edge
Jun 22, 2008, 07:39 PM
Engineer for Christ
IBCrazy's Avatar

New Fuselage

The original Bird had the COG too far forward. I could hardly control it so I had to make a new fuselage to move the COG back some. The new COG will be right at the leading edge of the wing where it meets the fuselage. I haven't painted it yet. I shortened the plane to 26" long, but it still will thrust vector.

Jun 23, 2008, 02:35 PM
Registered User
critterhunter's Avatar
My "Ka-Tock" Klingon battle cruiser will eat that flying garbage truck alive.

By the way, that aint what I'm calling this thing. Don't even know if it's a word in Klingon. Probably means "desert tray" or something. Have to search online for a Klingon dictionary to name it. (Man, I'm never getting some ever again, am I?)
Jun 24, 2008, 09:11 AM
Engineer for Christ
IBCrazy's Avatar

Maiden Flight Success

I took the new Bird of Prey out for it's maiden today and luck was not with me. All of the first 4 attempts resulted in a nose down crash. Thankfully the ground was soft and I fiberglassed the fuselage. On the first throw my trims were way off and my tail had some port side vectoring causing a spin right out of my hand which plunged the nose in. The second wreck was launch error. I threw the plane with a twist of my wrist and couldn't get it upright in time to recover. On the third attempt the plane flew for a minute or so before it began an unintentional flat spin and wouldn't recover. Attempt #4 I had the plane up and going long enough to realize it was VERY tail heavy and I stalled it on landing. I found the nose embedded 3" in the mud and it was sticking up right like a bright neon sign.

Attempt #5 had it up and going great with 3/4 oz of lead in the nose. I was able to open it up and really let it run. A very smooth ride. Every movement was fluid and deliberate. I made several thrust vectored flat spins. It is no Menace SpinMaster, but it spins fairly quickly at 2 revolutions per second. I'm considering removable winglets for it to fly knife edge. I'd guess my top speed to be about 105 or so. Not as fast as my Diablo, but surely no slow poke either.

I am really impressed with the 9N10P 4 turn motor. Although it is excessively noisy at less than half throttle, it cleans up and runs smooth once it gets going. The motor runs very cool and so does the ESC. It also has an unmistakably unique sound to it. I think I will build another one of these motors for the Lunatic.
Jun 24, 2008, 09:27 AM
Speed Freak
Spid's Avatar
Congrats Alex. Glad you got it sorted out.

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