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Old Sep 04, 2013, 08:28 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
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BBCC 3 -- RTP-to-RC Harrier -- davidterrell80

I am participating in the 3rd Balsa Builders Conversion Contest (BBCC 3) whose thread is located at http://www.rcgroups.com/forums/showthread.php?t=1989790

I have a 2-inch diameter EDF sitting around, from a crashed Skyangel BAE Hawk and wanted to put it to good use. Browsing about the Outerzone site for the oddly interesting, I looked into the "Round the Pole" (RTP) models and found a fascinating plane, begging to become a RC bird...

from Aeromodeller (1996) it's a RTP, profile, semi-scale Harrier!





The original was designed for 20 inch span, I will re-size as needed to accommodate the motor; and, plan on thickening/laminating the fuselage to make a place for electronics and battery.

I may also have to add a channel and play with the thrust vectoring.
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Old Sep 05, 2013, 04:57 AM
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Old_Pilot's Avatar
United States, TN, Memphis
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Thrust Vectoring

David,

Please post lots of pictures and commentary during this build......I can't wait to see how you solve the thrust vectoring problem.

Note, I could never fly this bird...dihedral is all wrong.....

O_P
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Old Sep 05, 2013, 05:12 AM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
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I've always thought the anhedral was simply a design necessity, like the gull wings on a Corsair were meant to keep the gear short (for weight and carrier landings) and the motor high (to allow that big ole' paddle-bladed prop).

In the Harrier, the motor and swiveling exhausts had to be below the wing (so they could point down), the tandem main gear allowed the ducts to point down (like a 4-legged stool), and the wing tips sent down so the outrigger gear could be short and the vents of the little thrusters would be in the same horizontal plane as the CG, avoiding any funky moments being induced during hovering maneuvers.

The anhedral also cancels out the virtual dihedral you get from sweeping a wing back... this thing might need some artificial stabilization to keep it from being a real handful.
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Old Sep 05, 2013, 08:57 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
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The plan, printed 100%, was designed for a 2.5-inch diameter EDF unit... larger than the 2-inch unit in my box. The plan dates from 1996, so I probably have as much power, or more, than the as-planned powerplant.

My doodles, earlier today, conceived of placing the EDF inside a rectangular frame, and fitting the frame into the widened fuselage. The fuse would have to accommodate the battery forward and the ESC, RX & servos aft.

I'll have to redesign the ducting for the smaller diameter EDF.

Hmmm...

I just went and ordered a 64mm EDF combo from Grayson for $40. If I don't use it this time... I will down the road; maybe a Volksjager.
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Old Sep 09, 2013, 05:21 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
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I've been continuing to doodle on the fuselage, considering the benefits of tapering the nose and tail, keeping a 1-inch center section between the forward edge of battery compartment (pilot's seat) and the after edge of the engine compartment.

I received the ducted-fan combo today... It looks forevermore fast.... what am I doing?

I must be nuts to be building a 21 inch span model with anhedral in wing and stab... AND powered by a 2.5-inch, 40 Amp ducted-fan.
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Old Sep 09, 2013, 07:21 PM
UMs & parkflyers... for now.
davidterrell80's Avatar
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I'm going to rework the plane for the smaller EDF. I went and weighed all of the systems components, including an Orange 3-Axis stabilization device.

Then I worked up a weight & balance spreadsheet for just the components, to see if my Mk. 1 Eyeball was in the park. I used 3s 800 & 1000 mAh batteries for the initial calculations. I was pretty darn close (within 0.4 cm) to where I wanted. I tweaked the station locations of the components and now, the systems with the 800 puts the CG about 0.25 cm behind the aircraft CG, and the 1000 mAh would move it to 0.25 cm ahead.

The ESC will be in a good position to shift fore and aft, over the EDF near the CG, so I will make accommodation to make simple moves easy.

Desired GC sta 25.5

Glac 3S 800 82 15.4 1262.8
EDF 52 24 1248
ESC 24 35.5 852
3axis 15 34 510
Vservo 11 38 418
Hservo 11 42 462
RX 7 37 259
VectorServo 11 33 363

Sum 213 5374.8
CG 25.23380282 0.266197183
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Old Sep 10, 2013, 06:11 PM
UMs & parkflyers... for now.
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Started building up the fuselage. Made the sides from 1/16. The fuselage, from the battery bay to the aft end of the electronic bay, will have an inside width of 1.5 inches. I'm using balsa liberally up front to give me some sanding allowance for streamlining The fuse will narrow to 1/2 inch, at the "stinger." I am going to semi-finish the fuselage empty, before cutting hatches for ESC in the turtledeck over the wing, and for servos and electronics, in the side of the aft fuselage.
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Old Sep 14, 2013, 04:54 PM
UMs & parkflyers... for now.
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I'm still piecing the fuselage together, making some design decisions on the fly. The nose is done. The light foam piece filling the nose well will keep the battery from moving forward. I'm now starting to build the light ply box that will frame the EDF unit.
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Old Sep 22, 2013, 07:34 PM
UMs & parkflyers... for now.
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I made some slight progress, over the past few days. I'm continuing to install the ply doublers and bulkheads that will surround the EDF. I'm beginning to consider squaring off the aft end of the EDF "portal"
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Old Sep 23, 2013, 04:26 AM
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As always, you pick an interesting project David! I was stationed at Cherry Point in the 70's when Harriers were still in a shake down process. We had about 3 squadrons of them I think. Whenever they were practicing I would just sit down on the planes I worked on, and watched them. We had a pilot eject at about 100 feet off the deck one time while he was in hover mode, not sure why he did, but that Harrier continued to hover doing a slow circle for about 20 seconds until it slowly plopped down on the deck, and then it started spinning like a top! Fascinating planes all in all, good luck with your project, interesting indeed!
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Old Sep 24, 2013, 09:26 AM
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Quote:
Originally Posted by conrad907 View Post
As always, you pick an interesting project David! I was stationed at Cherry Point in the 70's when Harriers were still in a shake down process. We had about 3 squadrons of them I think. Whenever they were practicing I would just sit down on the planes I worked on, and watched them. We had a pilot eject at about 100 feet off the deck one time while he was in hover mode, not sure why he did, but that Harrier continued to hover doing a slow circle for about 20 seconds until it slowly plopped down on the deck, and then it started spinning like a top! Fascinating planes all in all, good luck with your project, interesting indeed!
How exactly did they manage to get the jet stopped?
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Old Sep 24, 2013, 07:39 PM
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The crash crew trucks arrived with foam cannons which caused the huge Pegasus motor to shut down. Surprisingly, the plane didn't look all that bad when picked up with the crane afterwards, although, I am sure it was cannibalized for parts and never flew again. These were AV-8A Harriers from Hawker Siddley, first run variants that had some issues for a while. Several pilots were killed in early trials by planes flipping over, etc.. Great aircraft though once the bugs were worked out.
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Old Sep 25, 2013, 09:44 AM
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Originally Posted by conrad907 View Post
The crash crew trucks arrived with foam cannons which caused the huge Pegasus motor to shut down. Surprisingly, the plane didn't look all that bad when picked up with the crane afterwards, although, I am sure it was cannibalized for parts and never flew again. These were AV-8A Harriers from Hawker Siddley, first run variants that had some issues for a while. Several pilots were killed in early trials by planes flipping over, etc.. Great aircraft though once the bugs were worked out.
Yeah for awhile, we had this former Marine lady in our Air Force squadron who's fiance was killed when one of those early Harriers flipped over onto its back while hovering...while she was watching. She never did get married either, not to my knowledge. After that, I think she was traumatized.
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Old Sep 26, 2013, 12:02 AM
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Sad story, many do not realize that even stateside and peacetime service takes the lives of many servicemen.

Building profile fuselage planes doesn't really interest me too much, but I have always liked the Harrier and am anxious to see how David's project comes out. It gives me the impression of being a tricky flyer!

Are you going to use gear David, or just grease it in on the grass? Catapult launcher?
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Old Sep 26, 2013, 05:27 AM
UMs & parkflyers... for now.
davidterrell80's Avatar
United States, VA, Herndon
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This "profile" is going to be almost 2-inches thick, to hide the electronics and batteries. My ideal is somewhat similar in concept to the SEMFF VLF (Vertically Laminated Fuselage) planes in that thread.

I'm going to make some plug-in gear. In Flight Test Phase 1, I will do belly landing in the grass. She's only 20-inch span, so hand launching should be fine.
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