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Old Jan 31, 2009, 10:07 AM
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Springfield, VA
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Build Log
Sport Aerobatic Biplane--Cutting Edge

Yes, it does say “Build Log” but it’s almost an “As Built Log”…I have 3 projects I was brave enough to put on the web but think I must have a mild case of model ADD because I start thinking about new projects until it becomes too much to ignore—so another one gets started. All of them eventually get finished, but just not in the same order as they got started This is especially so when I reach the covering stage—I just hate to cover and too often that gives me that extra “incentive” to start something else…so to avoid another part way effort I vowed not to post this one until it was far enough along that I was sure I would finish it in a reasonable amount of time…
But enough on that, back to the Cutting Edge. This is a sport aerobatic biplane that was designed in 1991 and published in 1992. It looked so sharp I had to order the plans, and it is one of several I have in a stack—and one of several that finally called to me so loudly I had to build it. With a 64” wingspan it qualifies as a Giant model, hence the posting here (although I did consider Glow to Electric Conversions—but that is really more for ARFs). The original was an all wood, fully sheeted model with lots of plywood doublers. That added up to a 12 pound behemoth designed for a 1.08 2-cycle fuel gulper. I am now basically all electric, so felt compelled to see what I could do to lighten it up. So here is my composite version (balsa, a little ply, Depron, foam, and paper) (what—you thought composite meant it had to be carbon fiber or Kevlar, or boron? Then you don’t know what the definition of composite is, so go look that up in your Funk & Wagnel’s [those of you in my generation will know the reference ). But I do have some carbon fiber tubes in the bottom wing, so not all outside the accepted meaning.

For the best description, let me just use the designer notes:

Brian Reed’s notes that came with the plans for the Cutting Edge:

I was quite pleased to receive your letter expressing your interest in knowing more about my Cutting Edge biplane design. The plans and instructions do a pretty good job of guiding you though construction so what follows is some background and design details to help you understand my design goals and the aircraft’s unique abilities. While I’m pretty well versed in aero-theory and such, I tend to be more ‘style’ motivated in my designing. And, while I’m sure there are optimum numbers for everything, if all designers used these numbers, all aircraft would look the same so, I put creative originality ahead of numerical perfection.

The Cutting Edge started out as Tricksy, a .28 powered, 36” span biplane I designed for a friend in 1987 while stationed at Hunter Army Airfield in Savannah, GA. This little airplane was capable of some very unique maneuvers and had a roll rate that had to be seen to be believed! Even so, it was quite easy to handle and I let anyone that wanted to try it do so…aileron rates on low of course. I’m not sure if it’s still around (note this was written in 1992) or not as I gave it to the gentleman I’d designed it for when I left Savannah.
In the spring of ’92 it was again time for a new airplane and I decided to draw up plans for a quarter scale Sukhoi SU-26. Space limitations killed that idea (wouldn’t fit in my station wagon) but a biplane only needed a 60” span to get into the “Big” meets so I again turned to Tricksy. Let’s start with the wings first s they’re what makes a biplane work.
The 64” span was chosen as a compromise between what I needed (60” minimum) and the rib spacing I wanted. One less rib bay per side and the span would have been only 56”. I considered reversed stagger (bottom wing ahead of the top) too, at first, as I wanted to mount retracts in the bottom wing, ahead of the CG. This was scrapped, though, because it put the top wing’s mounting pylon back into the canopy area. Top wing sweep is used for stability: it adds “effective” dihedral without some of the crosswind problems of actual dihedral. Actually, 42 degrees total sweep is more than is necessary, but more looks better, has less drag, and quickens up the roll response. A general rule for biplane wing separation is one chord width. This keeps the tip and TE vortices from interfering with each other and the tail. Actual air compression doesn’t occur until near-supersonic speeds so it’s not even a factor.
Proper wing incidence is very important to biplane design and, while quite simple, can also cause headaches. Think of it this way: it’s okay to have the airfoil centerlines parallel or slightly apart (LEs aimed away from each other) but try to keep the centerlines from converging ahead of the aircraft (LEs slanted towards each other). This can lead to erratic flight and a pitching oscillation that may or may not be recoverable. Consider washout, also, when setting wing incidence angles. IE: The bottom wing’s incidence at zero and the top wing’s center section positive with the tips washed out to zero.
The plans show both wings set at zero degrees and the Edge flies fine that way. I’ve shimmed the original’s top wing slightly positive, though, and gained some straight line stability. Here’s why: in straight and level flight with the bottom wing at zero and the top wing slightly positive (1 - 1 1/2 degrees), most of the work is being done by the top wing. In other words, most of the aircraft’s weight is being carried by half of the available wing area, doubling the effective wing loading and increasing straight line stability and resistance to crosswinds and turbulence. As up elevator is applied the bottom wing starts working, going positive, relative to the airflow. The wing loading is halved and maneuvering is crisp and predictable.
“Ahh! that’s fine, but what about inverted flight?” you ask. The same rules apply except it takes some extra down elevator to hold inverted flight. But, when you fly the Edge, you’ll notice that it takes very little down elevator to stay level, inverted. This is due to the airfoil selection which I’ll explain next.
I designed a semi-symmetrical airfoil especially for this airplane. It’s dual cambered (top Max Camber Point at 33%, bottom MCP at 29%) for good lift and excellent performance both upright and inverted. Here’s how it works--right side up it behaves just like any other semi-symmetrical section producing good lift and a proportionate amount of drag. Turn it upside down, though, and things change. Since the airfoil’s bottom MCP is ahead of the top’s, the aircraft is now “more” tail-heavy than when upright, increasing the effectiveness of the elevators so you’ll need less down input to maintain level, inverted flight. And, since the bottom MCP is closer to the wing’s LE, the LE’s shape is more equal top and bottom (actually a 7/8” ellipse) giving an increased flying (angle of attack) range. This means nice, tight inverted maneuvers without unexpected stalling.
CG is easy too. Locate the bottom wing’s MCP and mark it. Then, locate the top wing’s center section and tip MCPs, average them together and mark that. Now just average the top and bottom marks and you’ve got it. I’m sure there are all kinds of formulas and “crossed line” drawings for finding correct CGs, but this method works on just about any wing-and-tail aircraft (deltas and flying wings being two of the exceptions). That’s about it for wings. Pretty simple, huh!
Vertical and horizontal tail areas were chosen as what looked right to balance the design visually. The bigger the aircraft, the less area (% wise) you can get away with, but you can still get carried away.
Tail incidence is easy too, but still needs careful attention. The horizontal stabilizer can be set at zero degrees on just about any smaller aircraft but, as models get larger we start to see the effects of downwash created by the wings producing lift. Air deflected off of the bottom of the wings moves back and down over the tail causing the airplane’s nose to pitch up. To counter this, we set the tail’s incidence slightly positive (LE up 1 - 2 degrees) placing it inline (parallel) to the relative airflow (washing down off the wings). Here’s where I cheated a little bit. I set the tail incidence to zero and tapered the elevator so that its bottom is parallel to the stab with the top tapering down to meet it. I think it’s easier to build it to zero, and cheat a little bit like this, than to have to mess around with degrees and fractions, getting confused and messing it up.
On to the fuselage. Length and shape were chosen for what looked right and what I needed to fit the radio and engine installation. Nose and tail moments were also an artistic decision but the general rules still apply--short nose and tail makes for a snappy airplane, longer ones give it more stability and smoother, more graceful maneuvers. With the Cutting Edge I tried to strike a balance. The long nose makes it look fast (which it is!) and the relatively short tail keeps the aerobatics coming.
The canopy design is similar to one I’ve seen on some pylon racers. I chose it for its simplicity (can be cut from a flat sheet of clear butyrate) and “mean” looking presence that adds to the Edge’s fast look.
The top wing mounting pylon is of built-up construction and incorporates a rather thick, symmetrical airfoil section for low drag (no cabane struts) and enhanced knife edge capabilities--hence the name. It uses 1/8” ply ribs, 1/4” spruce spars, heavy balsa leading and trailing edges and is fully sheeted. The airfoil’s thickness also lends some lateral support to the top wing but don’t even consider flying this one without the wing struts! The pylon’s forward slant (sweep) was also just for looks and I even added a trim stripe to enhance the effect.
In flight, the pylon does a couple of things. Straight and level flight is quite fast with excellent directional stability. Knife-edge flight is also very easy with knife turn-arounds and consecutive knife loops coming with practice. One negative aspect of the pylon is that it adds proverse roll with the application of rudder. This is because it’s only producing lift on one side of the fuselage centerline at positive angles of attack (yaw). My transmitter allows me to mix in some adverse aileron correction with rudder, allowing me to fly around “sharp” indefinitely.
Half-throttle knife edge flight is also possible and if you get it too slow, it’ll start “bucking”, stalling the pylon. This will continue until you add power or become mesmerized and crash.
For power, I’m using an OS 1.08 with the stock muffler. I use APC 14x8 props and a 24 oz tank is good for about 15 minutes. Torque rolls and hovering flight on take off are always attention grabbers but it’s not completely vertical. A little more power wouldn’t hurt, but I wouldn’t go over about a 1.5ci 2-stroke. The aircraft is traveling at over 100mph now! Larger models have a VNE (Velocity Never Exceed) just like their full sized counterparts and too much speed can lead to destructive flutter and the loss of an airplane and/or other personal property. More is better--to a point!
Well, there it is! And remember, you asked for it.
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Old Jan 31, 2009, 10:20 AM
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Build description starts...

So a good place to start—tail feathers. The original was solid 3/8” sheet for both the vertical and horizontal—I changed that to a ¼” sq framework with 2mm depron sheeting for the vertical to give it a solid look, and 1/16” balsa sheeting for the bottom of the horizontal with depron top sheeting. The balsa was to give it a bit more strength and rigidity given its size. This was then covered with silkspan applied with water based polyurethane to try and give it a bit of ding resistance (have to say balsa does stand up better to normal handling—anyway, I will try to be careful when moving it around).
Since I was doing framing I moved on to the fuselage, I did think about using 3/16” square but decided for a model this large the ¼” was the better choice. Again, the original was 3/16” and 1/8” sheet with 1/8” ply doublers, ¼” ply motor bulkheads and landing gear mounts. I framed it up, used some ¼” balsa sheet inserts without ply doubling, sheeted the inside with 1/16” balsa, and used 1/8” ply for the motor mount bulkhead and the landing gear plate. The way I figured I could get away with this was lots of balsa triangle reinforcement . This gave me support for the Great Planes motor mount, and reinforcement for the landing gear plate and wing mounting plates. Standard Dubro landing gear, perhaps not the lightest but not so bad at 5.2 ounces with axles, and it also didn’t cost an arm and a leg. Also a Dubro tailwheel setup, light wheels, and foam based wheel pants finished it off—after the depron sheeting and silkspan/WBPU, of course. And I couldn’t resist putting in some bamboo cross braces, learned from my Antic Bipe construction. It was unbelievable how stiff that fuselage became with all the bamboo braces. My concern was finding bamboo small enough to use—turned out not to be a problem as 1/8” skewers split easily and straight, and then easily split again using just an X-acto knife. I will remember this easy source of small diameter braces for future models.
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Old Jan 31, 2009, 10:23 AM
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Previous post rest of pictures

More tail group and fuselage pictures...
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Old Jan 31, 2009, 10:26 AM
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And more pictures...

Gee, had more of these than I thought....
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Old Jan 31, 2009, 10:39 AM
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I got the fuse so far and then moved on to the wings, since I would need them to ensure alignment was in order. The wings are the best and worst of a biplane. The best because the wings are always my favorite part to build and a bipe has 2 of them, and the worst part because a bipe has 2 of them! But at least for this one it’s building 2 different wings.
I started with the bottom wing. The original had 3/32 ribs, spruce spars, and was completely sheeted with 3/32” balsa. I substituted 6mm depron for most of the ribs (keeping 3/32” balsa and 1/8” ply for the key ribs—center section and the interplane strut mounts), balsa spars, and what I considered critical for strength, carbon tubes. These are ¼” diameter tubes connected in the center with brass tubing held by the ply ribs. Center section was also sheeted with 3/32 balsa for strength and durability (taking wing on and off). Depron took the place of the balsa sheeting, and a single high torque servo with torque rods gives the motivation for the ailerons. I didn’t want to do a servo per aileron because I didn’t want to have 4 aileron servos to task the BEC, in addition to the elevator and rudder. Besides, the set of torque tubes is lighter than an additional servo and attendant hardware—and the control is positive enough for me. A nice constant chord, single size rib design that gives a little over 5 sq feet of lifting area for the bottom wing alone.
The top wing is certainly unique with all that sweep, and I was a bit concerned about getting the ribs just right. So I ordered a set of foam cores, and then proceeded to cut a set of ribs, 8 per side, for the wing. I was able to use the core as a pattern for the balsa ribs needed. I used balsa spars again but no tubes, instead I installed 6mm depron shear webs to add some strength. Besides, the top wing will be tied to the bottom wing with interwing struts, which alleviates some of the need for additional top wing oomph. With a 1/8” thick center ply plate holding the wing halves together, as well as providing mounting block support/attachment (again with lots of balsa triangle reinforcement), I am confident the wing has enough strength. Besides, the depron sheeting will also add some strength, especially for torsion and bending loads—just don’t want to stand on it or hit it with something
Wingtips were just depron layers with a balsa “center” (not center of the depron stack, but mounted on the rib centerline), sanded to shape. The balsa was to give a bit of edge bump resistance as well as an outline for sanding purposes. Then it was just a matter of sanding and shaping until I was satisfied.
Of course there were some minor dings, but the thing to remember with white depron is spackle is your friend The lightweight white spackle goes on great, sands super, and blends great. It allows me to fill in the porous look of the sanded wingtips, allowing the silkspan layer to go down much smoother.
Of course, for this model, the top wing is mounted onto a pylon. While parts of the top wing were drying/setting up, I built that. The original was a ply/spruce/thick balsa sheeting construct that I think would support my weight. I changed it to balsa, keeping only the top rib ply (due to need to put in blind nuts) and 1/16” sheeting instead of the original 3/32” sheeting. I thought about also doing a depron layer, to give it the same basic appearance as the rest of the model, but decided it wasn’t worth the effort, and I would just save the (small) weight of the depron/glue/silkspan. Once I had the pylon frame done, that allowed me to mark the top wing plate for the hold down bolts and the servo cutout. The plate was carefully positioned to match the wing rib centerline so that I would not have to do anything fancy for the mounting blocks—just cut them to size and thickness and glue in place. Off the model I set the wing to 0 degrees, with the idea I would set the wing to +1 degree when I was in final assembly in accordance with Brian Reed’s recommendation (see his notes in post 1). Anyway, 8-32 bolts hold the wing in place, and the aileron servo cable feeds through the pylon without a lot of hassle. The bolts are accessed through small holes in the covering, going through the film/silkspan/depron to allow the allen wrench to be inserted.
Covering. First was the silkspan. I did each wing half in one piece (36” wide sheets). I first tried placing the silkspan on and wetting it to let it pre-shrink and dry in place before using the WBPU. That was a mistake—it just wrinkled very badly and didn’t seem to gain me anything. So then I put it down using a 50/50 mix of WBPU/water. It went down well enough but when it was dry had more wrinkles than I expected. Experimentation showed the problem was using the 50/50 mix. When I applied the bottom sheets, I used straight WBPU, and also brushed it chordwise. The result was almost totally wrinkle free. This meant very little sanding was needed to have a really nice smooth surface, the base for the next layer—plastic film.
Why plastic film? Well, couple of reasons. First, I did think about painting the model, since it would have a silkspan base that would be an option. But it’s winter time, so outdoor painting is out, and besides, that would mean primer, sanding, primer, sanding, painting, sanding, etc—no thanks. It would also mean extra work to get the balsa and depron to show equally. But the silkspan alone was not quite enough, being a bit wavy in appearance and also not doing much to hide the balsa. I also did some samples weighed them, and in order to get the opacity of the covering I used, a paint job would actually have added more weight. The covering I used was white Towerkote as the base. I was initially going to use Microlite/Nelson litefilm since it’s .6oz a square yard versus the 1.8oz of the Towerkote—but the opacity is really bad. It doesn’t hide the balsa at all, and I did want the model to look somewhat decent. So I decided to just accept the extra 3 or so ounces it would add using the heavier, more opaque coating. I went with Towerkote to keep the cost down—it's going to take 3+ rolls to do the entire model. Towerkote is also a low temp film, a consideration for the depron. The opacity is very good, not perfect, but you don’t readily see a difference. This was also a consideration in my decision not to put a depron layer on the pylon—I would just let the film hide the balsa and be the color match. (Note: I forgot to weigh the top wing before covering and didn’t think of it until I had it ¾ done, but the bottom wing I did weigh first—the Towerkote and trim so far has added 4 oz. Since the top and bottom wings are about the same area I expect about the same amount of weight can be attributed to the covering. By the way, the wing weights right now are 1 lb 7.2oz for the bottom, and 1 lb 8.1 oz for the top--with servos. I also forgot to weigh the tail surfaces before covering—final weights were 3.3oz for the vertical and 5.6oz for the horizontal).
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Old Jan 31, 2009, 10:43 AM
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More pics of wing builds...

Next set that goes with previous post description....
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Old Jan 31, 2009, 10:47 AM
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Top wing build pics

Again, more than I thought I had....
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Old Jan 31, 2009, 10:50 AM
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And even more top wing pics!!!

Well, I guess pics are good...
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Old Jan 31, 2009, 10:53 AM
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Pylon pics...

Build pics for pylon....
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Old Jan 31, 2009, 11:02 AM
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So back to the fuselage. The reference line is the top of the fuseelage square, all assembly uses this line as the reference. The plans call for 0 degrees for the stab and bottom wing, 0 for the motor, and +1-1 ½ degrees for the top wing. In putting in the mounting plates for the bottom wing, I used my building board as a flat plate, and a ruler, triangle, and Robart incidence meter to ensure the wing was square to the fuse, and not tilted in yaw or pitch (actually, the meter shows just the slightest amount greater than zero, but it’s positive relative to the fuse and the same on each end of the wing—good enough for me). As the stab mounts directly to the fuse square, that puts it at 0 degrees, and the motor plate I also squared up in both axes—so it’s at 0-0 as well. The original model had a rear deck with a standard balsa former-keel design that is then fully sheeted. I decided to do a turtle deck, using Depron instead of balsa, as this is a non-load bearing section. I also decided not to bother with a clear canopy (the original model did not have one either, although the plans indicate using clear acetate as an option), just will go ahead and use black monokote to simulate the canopy. The entire deck assembly is only 1.5 oz, and matches the original design shape almost exactly (minor mods, of course, due to my decreasing the fuselage width from the original). As shown in the photos, I used 6mm Depron for a keel, on a 3mm Depron base, with 6mm formers. This was then sheeted with 2mm Depron, the forward section sanded for the canopy shape, and Depron sheeting wrapped around the front (the original design also used flat sheeting to form the canopy section, no compound curves--translated to the foam copy very well). I used Sumo polyurethane glue for the sheeting (it dries white, unlike Gorilla glue--although I think there is a new version of Gorilla glue that also dries white?), as it gave me a bit more time to adjust the sheeting and get it positioned before using masking tape to hold it down. The expanding nature of polyurethane glue was also helpful, filling in minor gaps, especially at the sheeting/former interface. Otherwise, I have been using foam safe CYA (and some Titebond), which works pretty well, although it has on occasion taken several minutes to set. The turtle deck base, being 3mm Depron, almost exactly matches the 1/8" balsa floor for the stab.
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Old Jan 31, 2009, 11:52 AM
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When I started I was thinking a fuselage hatch, in order to access electronics/etc., but then realized there is nothing back here that would require top access--everything can be reached through the bottom wing mount. So that saved some effort and unneeded complication--but it also highlighted the potential need for a top side forward hatch to give me easy access to the ESC (because of the planned plywood battery floor). More on that later…

With the turtle deck taped in place, I added the tail group surrogate and foam blanks for the tail group fillets. This is a standard technique I always use for my models, as it gives perfectly shaped and fitted fillets for the vertical and horizontal stabs. The pictures pretty well tell the story.
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Old Jan 31, 2009, 11:56 AM
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I then installed the rudder/elevator servo mounts. I bounced back and forth between hardwood rails and plywood with cutouts and opted for the plywood approach, because it is easier (to me) to more securely mount (more triangular balsa J). I put the servos as far back as I could, and still be able to access them and the pushrods. I just used nyrod pushrods--easy to install, light weight, and I had them available. The servos are Hobbico/Tower Hobbies CS-TS 35 metal gear servos.

With my lipo pack in hand, I started having concerns about meeting the specified CG. Doing a preliminary estimate indicated a strong likelihood I was going to be horribly nose heavy, at least if I wanted reasonably easy access to the battery power pack through a lower forward fuselage hatch. The power pack could always be moved back enough, of course, to balance the model without adding weight, but if it had to go too far back it would not be reachable through a forward hatch, making change out a lot more difficult. It was time to get the fuselage far enough along that I could determine about where the battery pack would have to be--and how much, if any, tail weight I would need to allow a forward hatch to be useable.

This basically meant pretty much getting the fuselage done--installing motor mount and motor/electronics, mounting the pylon, gluing in the tail, mounting the wings, and then seeing where I had to put the battery pack to get the needed CG.

For the motor mount, I decided to use a Great Planes aluminum motor mount as I didn't want to hassle with making and fitting one, figuring that whatever additional weight I might have due to using a commercial mount would be more than offset by the convenience (but I might have to change my mind if the CG becomes an issue). It is also a quality item in my opinion. The 1/8" ply mounting plate was attached to the fuse with Sumo glue and again reinforced on the back with triangular balsa. The motor is a Scorpion 4025-12, a 2000W capable motor weighing about 12.3 oz, that will swing a 16 inch (either a 16-10 or 16-8 APC Electric) prop when using a 6S lipo pack--that should be plenty of motivation for an expected 8 pound model. The ESC is a CC HV-85, with a CC BEC to provide rx/servo power. Once I had the motor mount squared away, I roughed out the cowl, using 3/4” pink insulation foam as a base (better texture than Styrofoam and easier to shape and sand), with Depron as needed. I wanted to do this now instead of later, as moving the fuselage around while shaping the cowl lends itself to hangar rash. This allowed me to avoid dinging the tail group, which would surely have happened if I had installed it before doing the cowl. The pictures show the base plate of a 3” spinner, this gave me a pattern to sand to. However, the flying spinner will be either 2 1/4” or 2 1/2”, leaving an open ring around the spinner for cooling air to enter. I figured this was much easier than doing scoops, although to increase air flow to the battery I may yet have a scoop--still thinking about that one. It’s a 5000mAh/20C battery and I don’t expect amp draw to be more than 60 amps (and then only at full power), so I don’t expect battery cooling to be an issue…

The tail wheel bracket is a Dubro mount, but I didn’t like the tail wheel wire, so I made up my own. I went from the 1/8” Dubro tail wheel wire to 3/32”, and used some leftover aileron plastic torque rod tubing as a bushing in the Dubo mount--it fit perfectly. The picture shows the new tail wheel wire as compared to the old one. The 90 degree bend will insert into the rudder and was located to allow the rudder control horn to fit over it. A side benefit is I now don’t need to drill out the tail wheel I am planning to use--it fits 3/32” wire.
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Old Jan 31, 2009, 11:58 AM
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Dive, dive, dive....

Sorry, couldn't resist Walking into my work area and seeing it sitting there, my first thought was it looks like a submarine....
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Old Jan 31, 2009, 12:09 PM
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It really IS an airplane...

I then installed the pylon. The original model had 1/4" top sheeting, and I thought about it for quite some time before deciding to use 1/8" sheeting. Partly a weight saving measure, but mostly I didn't think the extra thickness was that critical to the strength of the model. I am relying on the lesser vibration of an electric, as well as (once again) more triangular balsa. The 1/8” balsa was topped with a layer of 3mm Depron to give a uniform color base as well as to give more material to sand when rounding the fuse. I also used 1/8” balsa on the fuse bottom, the first few inches, to provide some rigidity to the front of the fuselage and to provide the attachment point for a bottom hatch. I went ahead and covered the pylon with Towerkote before gluing in place, no sense making the covering task any harder than it already was (which, to tell the truth, really isn’t that hard, I just don’t like doing it)…and of course the pylon had to be installed to allow the top wing to be put in place for the balance check.

This basically left installation of the tail group and sheeting the fuselage as the only major tasks to do before I could see where my battery pack was going to be. Since I still had a few internal fuselage requirements (final battery tray position, hatch) I wasn’t ready to install the tail. It would make the fuselage assembly unwieldly to handle as well as increase the hangar rash quota. So I weighed the stabs and used a weight to represent them. With the landing gear in place, using the rest of the spinner to represent the smaller flying spinner and prop, wings mounted and lead weight representing the tail group, I set the model up for balancing….while not exact (after all, no fuselage film covering, no wheel pants, no hatch, sanding not done), this was enough to tell me what I was trying to find out--was I really way nose heavy?

Anyway, as it sits the model is 7 lbs 2 oz, so I think I will make under 8 lbs easy. However, that is without the 27oz 6s battery pack. But to ramble a bit, the original model power plant was 26.5 oz (OS 1.08 w/ muffler) with a 24 oz fuel tank which, counting the tank, would be about 22 oz, for a total of about 48.5 oz. My motor is 12.5 oz, the speed control 4 oz, and the battery pack 27, for a total of 43.5 oz. And of course the original model at 12 lbs was without fuel--so I will go ahead and say I made my 8 lb model weight (empty, compared to the original's 12 lbs), while my RTF weight will be about 9.5 lbs, compared to the original's RTF weight of 13.4 lbs--a nice savings in weight....
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Last edited by pmisuinas; May 16, 2013 at 06:54 AM. Reason: typos
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Old Jan 31, 2009, 12:12 PM
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Springfield, VA
Joined Feb 2000
1,192 Posts
And the answer is....

No tail weight will be needed With the model assembled as shown in previous post, I was able to set the battery pack so it would balance and still be easily accessible/removable from a front hatch. Still a bit to add, of course, so final battery position will change, but not so much that it will change the results. I have to say I was very pleasantly surprised with this result--I was sure I was going to have to add a couple of ounces of lead to the tail to give me a battery placement I could live with....
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