1970s Midwest Clipped Wing Cub conversion
1970s Midwest Clipped Wing Cub conversion
As part of my 1970's vintage haul (3 planes, see http://www.rcgroups.com/forums/showthread.php?t=1741528) I snagged a gear-gutted (except for the engine) Midwest Livewire "T-Craft" clipped wing cub.
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Just finished removing the gas engine and fuel tank and started the conversion.
So far I have the motor mounted (GForce G40 700KV), I used the existing engine mount T-nuts to mount a thick AL plate that is drilled and tapped for 4 10-24 screws, jam-nuts where the screws enter the plate, and just a nut on each side of the motor's normal X-mount. Between bending the screws one at a time and adjusting the nuts I can adjust both the propshaft angle and get the propshaft to exit through the minimal hole in the cowl.
I discovered with the motor and cowl in place the CG is just about perfect without the lead plate that was used when it was a gas plane if I can get the 4S battery all the way forwards.
BTW, the manual says to check the CG with the wing OFF- never saw that before...
I refuse to pull the wing to change the battery (especially as I can transport it with the wing on), and the design of the plane necessitates a side hatch unless I just strap the battery underneath.
So, last night I cut a hatch in the left side of the fuse, I should have good access room under the wing if I tip it up onto the nose.
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I have an RX, still trying to line up a used 100A ESC (on the cheap, I am) and a BEC.
Made huge progress (lol)- put spacers behind the firewall bolts so they don't stick through and poke the battery (when it eventually goes in).
I think just a bit of foam against the firewall and a wooden plank for the battery to lie on will do it, plus something at the rear end to keep it from flopping side-to-side, and some kind of a simple capture system that really just needs to keep it from sliding backwards.
I could get fancy and turn the hatch into the capture system, but I feel better being able to check it's secure and then putting on the hatch.
Since I snapped these pics I have mounted a plank above the ESC that runs up into the nose that the battery will rest on (held in place with the spring), soldered up the ESC and BEC, powered it up and programmed the ESC. The ESC motor leads come out inside the cowl (not shown).
I've got what looks to be the same motor in one of my planes but sold as the 'Firepower 46 sport' by HeadsUpRC. Should there not be a retaining collar fitted to the rear shaft extension? Without a collar the only thing stopping the rotor pulling off the motor in flight is a tiny circlip. The Firepower 46 came with the collar. You only need to fit it if mounting in front of the firewall (as you have done)
This is a photo from HeadsUpRC web site that shows the collar. it's a bad photo (over-exposed) but you can see it next to the cross mount.
Yes, I simply haven't put it on yet. I confirmed that I could put it on with the motor mounted and have it on my 'to do' list.
As a side note I think the bolt-on prop adapter (rotor-end adapter) will also fit my older turnigy sk5055-550 motor as well.
Bit more progress. "GO" fever is going to set in quite soon.
TX and satellite mounted (sat under the servos), ESC, BEC, and fuse servos in place (2 more screws for each to come), also need to wrap the pushrod keepers where they meet the shaft. Battery sets on the 'plank', figured cooling and access was better that way than with a 'deck'.
With the hatch off and wing on I can see the RX LEDs, the SAT LED, and BEC LED.
Motor would not spool up well, changed pwm to 8khz, much better!
Plenty of snot with a battery at storage voltage (4S at 15.20V)
The black piece behind the propeller is a spacer made from the center of another prop.
I had to make a tool that would engage a cooling slot in the motor to hold the motor for prop tightening.
I built a hatch latch from a servo arm, 4-40 screw with a nut embedded in the far side screw well, so the screw will turn the arm. For a bit of drag I trapped a piece of fuel line between the hatch and a double-nut. Needed a handle, wanted to build a small lever, but then realized a beer cap would make a cool knob, when the logo is upright it's latched!
I haven't trimmed down the axles yet, I spaced the larger wheels (much lighter, too!) out, if these wheels work good on grass then I'll move them in and trim the axles, or if I decide to go with 'tundra tires' (sanded profile onto dave brown light-flights, 5 inch, like on my bipe) I'll need all the axle.
In the side view of the motor, the mount isn't bent, the lens is just fwd of the mount by a bit.
Maidened this critter this morning.
I checked the CG with the wing off as per the instructions, was perfect, checked with the wing on and it was in front of the center of the wing by not much, so I added a little weight to the front. Was not necessary, and I had to haul back pretty hard on the stick to keep it in the air. It easily could have gotten out of hand if I'd been too jerky with the stick.
Don't know how I managed to land it with the speed necessary to keep the nose up, but I did. Twice- I needed to judge just how nose-heavy it was.
Pulled the weight, much better, came in way too hot (but successfully) for 2 more landings, I'm used to my Fokker D-VII which practically has airbrakes it has so much drag.
I kept a bunch extra speed (and altitude) on final also because with little power I stalled it (testing at altitude) a few times because the outside wing dragged the nose so damn high, this is the first plane that really needs rudder to turn properly so I don't have a lot of skill at it.
So, is there something not set up right that will cause a horrific skid with no rudder? That just a sign of a smallish rudder?
Another question I need to answer- if the CG is set to spec and it still needs a bunch of up elevator to fly level, that's usually a sign the CG could go a bit rearwards, yes?
Stability seemed good, so I'm not worried to try it (but it will mean adding weight to the tail. Not much, though, it's got a loooong tail).
That kit was designed by Hal deBolt. He had many names on his model aircraft companies through the years, Demeco, DeBolt Model Engineering, and a couple of others. Aparrently Midwest was producing the deBolt line at some point.
Livewire was also one of the names he added to a lot of his planes. I had a Livewire Pursuit and I have a Livewire Trainer on the shelf now.
All the planes by Hal flew pretty well. That plane was designed with a glo engine in mind. The CG would be slightly aft without fuel in the plane. I would question moving the CG aft before doing some testing.
I'd start with checking the decalage. Make sure the wing is in correct relation to the stab and thrustline.
That plane was also before differential aileron throw. Maybe you can increase the upward movement of the ailerons or decrease the downward movement. It might help.
Hope you get it all sorted out OK.
Yes, as I understand it the CG specified tends to be the 'maximum rearward' CG for when you've run out of fuel and need something stable enough to dead-stick it in.
Much of what you mention to check has been set by the previous owner who flew the plane for years. I eyeballed the wing/hstab angles as being the same.
Thrustline was my 'best guess', a little down, and a little right, in my 4 short flights it seemed pretty neutral, and I do have some tests to run to check it out. For example, if I have up elevator for level flight with moderate power and more power causes it to nose down, too much downthrust.
If I get comfortable enough I'll try some dive-tests, trim it for level flight and then dive it, and let the controls go neutral, and see what it does. I need to dig up an old thread on what it means if it dives more, or climbs, as opposed to it stays diving at the same angle.
I do know the previous owner had a gas engine, tank all the way forwards, and a hefty lead weight on the firewall. I do know when I had some weight on the nose it was waaaaay nose heavy.
OK, update, did some testing this morning (several ugly incidents on climbout where turning left after takeoff, nose up high power led to it hanging off the prop and flopping about) where I did some circles under power, and some power-off turns, looks like the small amount of right-thrust I put in is way too much, it climbs in left powered turns, sinks in right powered turns, and is nice an neutral with the power off.
I'll have to get this settled before worrying about anything else.
Got in 2 quick flights as the wind was picking up.
Much improved with neutral L/R thrust, and I tested it with an 11x8 prop in place of the 13x8. The 11x8 makes it fly like a gas plane, I think 12x6 or 12x8 will be the sweet spot, and I'll save the 13x8 for when I'm a bit better.
The gas prop on it was 10x6...
It is still a bit twitchy in pitch, but it's an aerobatic trainer and my DX5e only has a tiny bit of expo (turned on via the secret method).
The Vstab needs a bit of speed to be effective, so it has even more drama on takeoff than my Fokker D-VII as there always seems to be a crosswind and the runway itself has a little side-slope.
I have found it is very easy to get the speed up beyond what I really want, my trainer was draggy and of course the bipe is, this is my first 'clean' plane.
I've gotten the landing speed a bit more under control, but it was starting to get gusty and I didn't want to do a bunch of slow-speed and stall and landing practice.
Runway is a bit rough, and getting to takeoff speed it tends to get pointed one way or the other, nice big transition between tailwheel stops doing squat and rudder starts doing squat. Adding too much power at lower speeds seems to cause it to react poorly to all the prop vortex, so it's tough to get it to accelerate quickly.
When this plane stalls with a bit of power, it rolls rapidly left and right, back and forth.
Took it off a little too quick, and it did that funky dance where it whips back and forth in roll really quickly, it was all kinds of crossed up so I cut power and it drilled in from only 3 feet or so.
Stopped so quick the front of the wing crunched a little, but the battery braces against the firewall so i don't think anything up front moved.
So far, I'm pretty unhappy with this plane, even given the symmetric wing I figured it wouldn't have such a high landing and takeoff speed. Were I ambitious I might make a longer, less-symmetric wing but if I had that kind of time I'd just build the '90s LT-40 kit I have poking around. So, I'll probably see if i can just slap on a trainer wing I have poking about just to see how it flies.
I figured this plane would be the warmup for the bipe, the bipe was pretty easy compared to this one.
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