This is the little brother to the Badger, just for fun and kicking around.
I've never had a 2m plane before, the loss in performance was too much to take when trying to thermal, and we never have 2m contests around here. Now that I have built one, it's a neat size, strong enough to winch and see at a distance, small enough to handlaunch. On the other hand, the amount of work to build a 2m is exactly the same as a open class plane, and the cost is only marginally less.
This plane is based on the Levoe Super Vee 2m fuselage, which weighs 6.9 ounces! I don't like canopy fuses any more, you can see a carbon strip at the rear edge of the canopy opening to allow dork landings. The fiberglass cracked on the very first test flight, thus the carbon strip.
Wing
The SA 7035 airfoil was used full span for the wing, and the intent was to get a fast plane at lighter wing loadings. Flaps at 22% and ailerons at 22% increasing to 26% at the tip were used. A 1/2" diameter carbon rod is used for the joiner. 3/8" was too small, and 1/2" is overkill. The joiner rod is straight with dihedral built into the wing tubes, so wing rotation will not be a problem. Dihedral has been reduced to 4 degrees so that it will roll better on the slope. You can see the triangular CF layup under the paint. A spar section with 0.020" X 0.5" CF cap strips runs from the root rib to 18" of the span. This spar holds the joiner tube, there is no support rib for the outboard end of the joiner tube. We shall see if this system will hold up to the normal abuse of my landings.
The planform layout based on the Emerald, with a minor acknowledgement to Mr. Reynolds at the tip. Wing root chord is a whopping 9". Knuckle hinges made from microballoon mix were fitted to the flaps. Skin hinges and Mylar gap seals on the ailerons close up the flipper thingies.
The paint job was done on the Mylar. It's winter here in Calgary, and the house did not come with a paint booth. Rather than wait for good weather, I painted the Mylars in the back of the truck, with a portable heater for warmth. There was so much dust and dirt in the air as the paint dried, that the wing is covered with specks of detritus. Through the magic of JPEG, the wings look great in the pictures.
Fuselage and Tail
As mentioned earlier, the fuselage is from a 2m Super Vee. CF pushrods in Teflon tubes were CA'd in place for the full length. No other changes to normal practices. A CF arrow shaft was added crossways at the CG, and a short dowel can be slipped in as a finger peg. Typical hand launches are over 50 feet high, but pretty hard on the shoulder. I should get lots of spot landing practice in the yard this way.
The tail area was calculated using the formulas from the DJ Aerotech website. I used a tail moment coefficient of 0.395 (same as the Badger), and then converted it to a 110 degree V-tail. So far the test flights show that it's OK, but thermal turns will need to be carefully observed for correct tail area. The V tails are built up balsa and CF, covered with Ultracote and are removable using a bolt and sleeve across the tailboom. Elevators are 30% of chord.
This plane balanced out nose heavy with everything laid out as usual. Things were shifted a bit and a 270 MAH battery balances the plane with no nose weight. Full flying weight is 35.6 ounces with no major strength concessions.
Radio Gear
I should buy stock in Hitec RCD. Servos are HS-80MG on the ailerons, HS-85MG on the flaps and HS-80 on the V-tail. A slim line Futaba receiver is Velcro'd to the tray, and a 4 cell 1/2 AA 225 MAH battery pack powers it up.
Specs
Airfoil - SA 7035 all the way, no washout. You bet it's touchy.
Span - 78.5"
Weight - 35.6 ounces
Area -595 sq. in.
A/R - 10.4, basically a pig.
Test Flights
December 23, 1999
Ok, the tail area is too small, the lack of dihedral and small tail resulted in some interesting low level handling problems (i.e. spun in). I have rebuilt the tail with 5% more area, all in the ruddervators. Handling seems to have improved (i.e. no crashes yet). This is the <joy> of designing and building your own planes, sometimes you get a "do over".
Observation - I was out to test fly on the slope at -15 Celsius, and one of the ailerons servos started to creep upwards. After about 3 minutes, the deflection was full up and nothing could reset it. When back inside, I replaced the gear train and re-lubed the moving parts. It appears that the grease had become wet (and frozen), resulting in a binding of the feedback pot and then the servo neutral shifted. I've never had that happen before.
December 29, 1999
Last flight of the century for me, the wind is 12-15 mph at the radio tower hill. No ballast, the CG is set at dead neutral, and the plane is ripping the slope. V-tail response is really off, rudder input causes significant positive pitch change and the V-tail program does not have enough to compensate. Later that afternoon, a C-mix was programmed in for the ruddervators to add more down elevator. Rolls are non-axial, inverted flight and outside loops (with a TD Plane?) are smooth enough. Slowing this plane down using camber is marginal, although high bank turns are stable as long as the speed is up. I love guys who say " this plane really slows down and floats without a tip stall, buy boy does it move out when cruising." Their concept of moving must be a lot different, this plane really moves and CANNOT fly slowly, even accounting for relative perception of plane size. In fact, none of my floaters can fly fast, unless the L/D goes to zilch.
The wind is picking up to over 25 kph steady and I'm a little worried about the landing zone rotor. At least the flaps are effective, so dive it in and pull out at 10 feet with the flaps, the plane stalls into a pancake flop in the tall grass. I'm not going to try that again.
February 8, 2000
A lull in winter and it's off to the slope again. The wind is barely noticeable and 100% overcast as a cold front moves in from the north. It doesn't look like there is enough lift, but might as well try anyway. The first few minutes are spent adjusting the V-Tail differential, which was off in previous flights. Flight times are only a minute or so before land or walk, the lift is extremely smooth and steady. I realize this a unique opportunity to observe the minimum sink of the plane at various speeds and camber settings. Crank on some camber and watch the plane float or sink, vary the speed, I can now see that there is too much camber for the best minimum sink rate. The lift is so marginal that any changes are obvious. Now try a few thermal turns, and does the sink rate ever go up! Trying various combinations of camber, turn diameter and turn rate and you can see changes in minimum sink. This was a really good learning experience for me, I spent an hour throwing the plane and seeing how long it would stay up, trying to smooth out my flying. A great way to test relative performance too, next time I will have to bring two planes for comparison.
April 2000
All of the flying so far has been on the slope to get the plane trimmed, now it's time to try out the winch and thermalling. On the new winch, the full speed launches are incredible, almost too much speed to get a consistent launch profile. However, the thermal handling at distance is extremely poor. I have no trouble close up where every twitch is observable, but at distance the plane will not stay in a nice thermal turn and proceeds into a series of borderline stall turns. After much thinking, and having already increased the tail area, I decide to put in some more dihedral. The joiner tube and spar prevents any adjustment of the center dihedral, so a poly break was put in at the aileron/flap junction. The servos were not removed in this operation!
Next week at the field, the plane handles much better and can now be flown at the limits of visibility. High speed launching proves to be the undoing, as the tip folds during an incredible pullout for the zoom. I like to launch hard, but no TD plane could be expected to survive the last series of zooms off the new winch with mono line. A big CF Band Aid was applied to the wing and the plane is flying again but it's starting to look like a beater. It did survive a stuck solenoid on the Rahm winch.
With all these changes, it is time to build another one, incorporating all of the design evolution. This time it will be a one piece wing to save weight, and a rolled tube fuselage will save a few ounces too.
The one piece wing was finished a year ago,
but other things delayed the remainder of the plane. The break was good because it gave me some time to think
about what should be changed in this iteration. I was quite happy with the performance of the wing but the
fuselage was way too heavy for a TD design.
A major rethink on the fuselage resulted in this:
Painting continues to be my nemesis, this time it was so cold in the garage that the epoxy paint just gelled instead of the solvent evaporating, resulting in lots of streaks and orange peeling. Too bad. The pod is built up from 1/32” plywood covered with 3 oz. satin FG and Uni-CF reinforcement. A nosecone was fitted from braided FG. The boom is hand rolled from 4 layers of Uni-CF and bias FG, with a 5/8” inside diameter CF tube for the wing brace. Extremely rigid in both flex and twist, minimal cross section as well. Servos are a friction fit with the fuselage sides and the AA battery pack is in-line. A HLG type tail layout with a 34” tail moment will slow the landing control response, but should improve the thermalling. Overall weight of the fuselage and tail is 6.5 oz. Total weight is 32.3 oz. with 18.3 in the wing!
Learning from the last wing, this one has the normal 5.5 degrees of dihedral, although the spiral stability coefficient is still marginal. Calculations from the full size Badger result in the tiny fin, 23 sq. in. but it works fine. You can even do wingovers on the slope! The plane has plenty of yaw damping, it appears that rudder power is really the limiting factor.
I tossed it around in the yard for a few minutes. Throw
it, two thermal turns and a hand catch to avoid landing in the snow. At 3-4 oz.
lighter than before, the landing approach is very slow and predictable. Complete
trimming has taken less than an hour on the slope in perfect conditions
(although -4 C) since the program was loaded from the last 2m Badger. The
float is vastly improved and the slower elevator response has allowed a slightly
rearward CG. Without the V-tail, no problems setting the rudder coupling
and aileron differential. Off to the winch to do a stress test on the one piece
wing once the snow clears.
Launch on the winch is a little squirrelly, probably due to flexing of the stab. The height is quite good so long as the speed is reasonable, no mono on the winch this time. Thermalling is steady, lots of tail damping but control response is very muted. This will help a lot when trying to fly a 2 meter at distance. The thermal turns are steady enough to hand toss it and climb out without too much effort. Everybody thinks it looks like an overgrown handlaunch in the air, except it will come back from a long downwind run.
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