Mustang Fever

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I've been thinking about this for some time, starting with the first successful flight of my 55AX powered Arrow. I want a smaller version that I can fly just about anywhere, but particularly off the snow at a ball field complex near my home, and a pond over at a club buddy's house.

I'm shrinking the plans down 50%, so the wingspan will be around 22 inches, wing area something less than 200 square inches. I'm shooting for a wing loading of under 20 oz per square foot, so I'm basically just "halving" all the materials: 1/16 where the plans call for 1/8, etc., except when it doesn't divide out even, then I go up to the nearest 1/32. I'll be using an Astro 020 brushless on a 3 cell 2100 LiPo for power. Past projects of similar size using that motor with a 5.5x4.5 APC prop have been literal rocket ships.

Cutting ribs, now. (1/16 balsa) Don't have any 1/16 ply, so the ply #1 and #3 ribs will have to wait. Going to use 1/4x1/8 spruce for the upper and lower spars, and 1/32 sheet for the LE, TE and cap strips. I just ordered a 48" length of carbon fiber tube, .188 OD, from dragonplate.com I'm not going to make the wing panels removable, though.

Mustang Fever

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Did a little framing today after cutting all the ribs I could. Here's the stackup of the full size material thicknesses, and the half pint:

Ribs: 3/32 vs 1/16
Spars: 1/2x1/8 vs 1/4x1/8
Sheeting/capstrips: 3/32 vs 1/16
Trailing edge stick: 1/4 square vs 1/8 square.

I like this design. It's easy and builds quickly, flies marvelous, and even the full size one doesn't take up much room. Like Laddie says, "versatile and compact"

Mustang Fever

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The right wing panel partially constructed- waiting on some 1/16 ply to do the three inboard ribs, but the sheeting and most of the cap strips are in place.

Did the hull sides from 3/32 balsa, the upper reinforcement is 1/4 triangle and the chine pieces are 1/8 square spruce. The design calls for balsa in that area, but as my big one was a little tender on the bottom, I decided to beef it just a little.

Mustang Fever

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Did a little more on the hull last night. Made the bulkheads from 1/16 balsa, except for F-9, it's 1/8 light ply. (The big one has a 1/8 ply F-9, too, but I was afraid to go down to 1/16 as the piece is so small I'm afraid I'd break it during the assembly process.)

Starting planning for the servo bay and the battery installation. The servos will go upside down as shown, with the battery in the very bottom. I'm going to completely assemble this bird before I put the bottom (1/16 ply) on, so that I can position the battery wherever necessary to get the CG.

Mustang Fever

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A little more progress. Soon as I figure out where to put the receiver and how to route the servo leads to it, I'll stick the other side of the hull on. The area above the 1/8 ply servo tray is a removable hatch, defined by the 1/8 square rails you can see just above the tray. There's a double, upper bulkhead at both ends so it can be cut free after the hull is sanded.

Mustang Fever

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Got everything figured out, so I stuck the left side on.

The ESC is going to go between bulkheads 4 & 5, below the servos and above the battery, where I can get at it if it dies. It will be accessible through the same piece of removable bottom that provides access to the battery. When operating as a flying boat, that piece of bottom will be sealed with tape. The power leads from the battery and the ESC will come up through that big round hole in the servo tray aft of bulkhead 4, so they can be plugged and unplugged when the hatch is removed. I'll probably put the little Rx arming switch in that area, too.

The Rx fits best between bulkheads 5 & 6, and the leads from the servos and the ESC can reach it without extensions. One of the Futaba 6EX attennae will run out through a tube in the side and reside in the starboard wing panel, the other directly aft, to give the required 90 degree separation.

Tomorrow I'll start the pylon (fin) and maybe get it installed. Still trying to figure out how to do the pod for the motor. It doesn't have to be square, like the glow birds' are, so I'm leaning towards making a paper or balsa tube for it.

Strykaas

I cannot imagine you are not retired Too much free time

Mustang Fever

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I thought I told you that I was. From the National Guard in 1999, and from my civilian career in 2000.

I did some more on this puppy this afternoon, between sessions flying the Blade mCX around the basement, tormenting the cat.

Never thought about this before, but sheeting a long, flat surface with balsa requires some stiffening under the sheeting joints, or they start to look like they do on my big Arrow. [&o]
Pics show that, and the bracing around F-9 in the tail section.

Mustang Fever

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#2 of the 5 major subassemblies got built today. (Wing panels, hull, pylon, pod) This is a really easy build.

Mustang Fever

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Finally got to a HS in the Detroit area, looking for 1/16 ply. None to be had, so I had to settle for 3/32 ply for ribs W1 and W3. Here's the RH panel, awaiting the elevon hinge blocks and the upper sheeting.

Mustang Fever

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Completed right wing panel, sans elevon.

Mustang Fever

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Now that one wing panel and the hull are framed up, it's possible to do some more accurate calculations of wing area and wing loading.

Actual wing area will come in around 217 square inches, or 1.51 square feet. If all up weight is kept at 24 oz., the wing loading will be a very respectable 16.5 oz/square foot.

Item Weight
HS 81 (3) 1.98
Astro 020/w ESC 3
1200 battery 3.7
Wire 1
Hull (est) 10
Wing (est) 5

Total 24.68

The hull/wing estimates are based on the current weights of 3 oz for the hull and 1oz for one wing panel. The pylon is too light to measure.

The Astro 020 will produce 19,600 rpm spinning a 6x4 APC "E" prop, which should be good for about 75 mph and a pound and a half of static thrust.

Should be pretty peppy. The only unknown at this point is whether the 3.7 oz battery will be enough to balance it. I might have to go heavier.

Mustang Fever

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Only the pod left to construct, then this beauty can get put together. Weight right now (according to my highly accurate trigger pull scale) is a touch under six ounces. I'm really hoping to beat my target weight.

Mustang Fever

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Here you see it with the lower fin glued on, and all the electrics installed except the battery & motor. Weight (including the motor) is at 13oz, so it's coming along close to target.

The ESC ended up nearer to the stern than optimal, mostly so as to keep the motor wire length as short as possible and avoid going to heavier wire. The battery wire extensions are 12 gauge, so the voltage drop will be minimal.

Mustang Fever

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This approach to constructing the motor pod, or nacelle, required two weeks of mostly subconscious thought. It occurred to me yesterday that I could make a box with pieces of balsa triangle in the corners, much like the full size design, only I could make it fit the motor as tightly as possible, and then round off the front of it to match the spinner.

I used 1/2 inch balsa triangle stock, pushed together over a piece of 1/16 balsa sheet. The motor fits into this very nicely, and doesn't overhang the sides. By gluing a piece of 1/4" triangle stock upside down on the centerline below and above the motor, I can round off the forward section to match the spinner, leaving the top and bottom flat where the box glues to the top of the pylon and where the upper fin glues on top of the box. I eliminated the former that normally goes inside the box and glues against the square spruce stick assembly, as I need the space for the wiring. I'll make a 1-1/4" OD ply motor mount that will glue against the front of the nacelle.

Mustang Fever

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Here's the upper nacelle piece in place. I'll wire the motor tomorrow, and then glue 1/16 balsa sides on the nacelle before gluing the upper in place.

Mustang Fever

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Got the motor wired and test run, and finished the nacelle.

Mustang Fever

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This is gonna be it for a few days. Going out of town for family Thanksgiving. When I return, the wings will get glued on.

Mustang Fever

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Wings glued on, and all the control surfaces made. She's sanded and ready to cover.

beenie

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Dave,
Your build is looking good. Should be neat little airplane. I built something similar this summer for a .074, although it was not a scaled down Arrow. I will be curious to read the flight report to see if the good flight characteristics scale down. Mine was a handfull in the first few flights due to a bit of an aft cg. Things calmed down with a little nose weight.
http://www.rcuniverse.com/forum/m_77...tm.htm#7867974
Ben

Mustang Fever

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Ben:

That's a cool plane. I think the general consensus is that 15% is way tail heavy for a delta that has its fuel tank behind the engine.

beenie

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Well, the cg difference between a full tank and an empty one was not very much. However, 15% was a little tail heavy. I have a video of it in an inverted flat spin/ tumble type maneuver during the test flights. I'll have to upload them when I get some time. Since your plane is just a scaled down version of a very well proven plane, I doubt you will have any of those problems.
ben

Mustang Fever

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Yeah, I ended up balancing my big one at 16" forward of the CG, as recommended by a guy in the UK who flew one at that. I finally moved it aft a bit, to 15 + 3/4, and it handles really well at that. Before I balance the little one, I'll fill the tank on the big one, find the location, then use half of that. Should work OK. I built a big one three years ago that was destroyed on its first flight because the recommended CG on the plans is wrong. It was kinda spectacular.

I made the same kind of first landing you did with my big one- bounced off the water cause I was going too fast, nailed the throttle, and did a faceplant. Had to repair the left wing. The trick on deltas, for me anyway, is to make a low lap to get slowed down (you'll be amazed how well they fly at slow speeds if you haven't tried it yet) then when it's coming towards me about 100 yards out, chop the throttle and when it gets close to touching, haul the nose up, and I mean up. About 40-45 degrees. All it will do is slow down and settle into the water. It won't balloon and stall the way a conventional wing will.

beenie

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Dave
i have had deltas before that would land like you are describng, with the nose way up and the speed very slow. The Dart doesn't fly like that. When it gets to a certain speed it instantly transitions to a spin, sometimes flat. I have only put one flight on it since I moved the CG up and it shows more promise in slow flight. I put the test flight videos on my youtube page
http://www.youtube.com/watch?v=JalyugknC9c
http://www.youtube.com/watch?v=jOUbJ6_RotQ

Do you know what %MAC 15 3/4" works out to on the arrow?

Mustang Fever

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This is strange: 0% [:-]

The root chord I determined by extending the LE and the TE (of the elevon) to the centerline: 31 inches
The tip chord was straightforward: 5.5"
MAC: 18.25

When I layout an 18.25" line between LE and TE(of the elevon) and then measure forward 15 and 3/4 inches from the TE of the wing less the elevon, it falls right on the LE, so 0% of MAC.