Facet Opel

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autoreply

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I can see a lot of advantages to a design arrangement like this for an aircraft with the same goals as the Facet Opal.
Keeping the same low aspect ratio while enlarging the root chord allows more of the fuselage to be buried within the wing, which can provide a much-needed increase in cockpit room for improved pilot comfort, while also lowering wing-fuselage interference drag.
A taper ratio of about 0.5-0.7 seems about right.
Mounting the vertical fins/rudders further outboard on the wing has the advantage of a greater lever arm, thus allowing a reduction of vertical stabilizer area, and associated drag.
Putting the fins all the way out at the tip (IOW, installing proper winglets) might be even better, providing an even longer lever arm, though this gets you away from the jump twist concept, thus requiring a different control surface arrangement.

Your thoughts?
Keep winglets/tipfins, make it aesthetically pleasing and it sounds like a winner.

Make sure to study:
https://www.akaflieg.uni-karlsruhe.de/project/ak-x/
 

EzyBuildWing

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Isn't Dean Winton rebuilding the old Opal Facet? I seem to remember reading that you could donate to help the re-build? Anyone know anything?
Time to re-invent Scotty's Plank by taking it into the hi-tech 21st Century ......twin-electric, and carbon-fiber ....it'll turn heads!
For simplicity, brushed Saietta Axial DC motor is simplest, cheapest, smoothest, most reliable, most efficient, lightest and by far the easiest to wire. Google it.
Check out "Carbon fiber cricri size smallest airplane project" on Youtube.... it's the new wave!
Gotta move with the times and catch the wave!
 

lr27

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Wave, schmave. The air don't care. Doesn't matter if it's fashionable or slick, matters if it works. And in that case, batteries are the bottleneck. There are a lot of electric motors that are good enough already. The Saietta I saw on Amazon is kind of heavy for the power, actually. At least compared to brushless motors I've seen.
 

Victor Bravo

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The significant advantage of electrics in this case is that you could have four electric motors on the trailing edge of the wing, with smaller propellers, and this would allow a shorter snd lighter landing gear.

The smaller propellers would allow the thrustline to be directly on the wing chord or vertical CG, eliminating power pitch-over.

Spacing the motor weight along the span (and the batteries along with them if possible) would create lower bending moments on the spar, allowing a lighter weight spar and wing structure.

Motors and propellers outboard of the tires would eliminate rock and dirt damage to the prop on takeoff/landing.

Propellers outboard of the fuselage would eliminate most of the "dirty" fuselage air into the propeller, thick boundary layers, etc. More thrust from the same propeller.

All of those positives might very well balance out the advantage of one larger diameter propeller.
 

Hot Wings

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All of those positives might very well balance out the advantage of one larger diameter propeller.
You forgot/overlooked a few advantages if using electric distributed units. However for anything but a part 103, with it's arbitrary limitations, the advantages haven't added up to a real overall advantage. This is using my personal set of priorities so others may come to a different conclusion. Add in a sustainer ICE and the balance tips to the good - again using my personal parameters.

For most builders simply using a longer gear, possibly with a kneeling feature similar to the EZs for easy entry, seems to be a better path?

Thrust angle/offset relative to the CG doesn't degrade performance much. The angle needed is such that the Sin is still very close to zero and the Cos is still very close to 1.

If using multiple units 4 is the sweet spot. To replace a 60" prop with 4 smaller units of = disc area yields 4 30" props. For the same tip speed a 60" prop @ 2700 rpm the 30" prop would spin @ 5400 rpm - well matched to OTS brushless RC motors. Not a direct equivalence, but it demonstrates the trend.
 

Victor Bravo

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How much shorter do you want to go?
Shorter as in one wheel at the bottom of the fuselage like a sailplane, making a significant reduction in aircraft weight, complexity, build time, etc.

As in using an existing landing gear retract mechanism from a wrecked sailplane.

As in using the entire forward fuselage, cockpit, canopy, seat, instrument panel, landing gear, and control stick from a wrecked sailplane, saving half the build time, and leaving the builder to basically hot wire one large wing section and find a way to bolt that to the spar attach pins built into the sailplane :)
 
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Tiger Tim

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using the entire forward fuselage, cockpit, canopy, seat, instrument panel, landing gear, and control stick from a wrecked sailplane, saving half the build time, and leaving the builder to basically hot wire one large wing section and find a way to bolt thata to thespar attach pins built into the sailplane :)
Fair point. I'm not ready to go electric yet, does your plan come in jet?
 

Hot Wings

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As in using the entire forward fuselage, cockpit, canopy, seat, instrument panel, landing gear, and control stick from a wrecked sailplane,
I'm not in the loop for this kind of salvage. Is this really a practical option - other then using an L-13 :whistle: fuselage? If this were a realistic option, it could be a good one. The typical glider has shoulder mount wings rather than the mid wing of the Opal, which would move the engine mounts/thrust line up a little bit.
 

Norman

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The smaller propellers would allow the thrustline to be directly on the wing chord or vertical CG, eliminating power pitch-over.
Putting the propellers on the trailing edge of the wing results in significant conversion of hp to noise and vibration. You can lose as much as 15% of your horse power. Keep the hub as far away from the TE as possible. Considering that the center of drag and the CG are both pretty close to the top skin of the wing and that the prop is most efficient when it's perpendicular to the free stream it should be easy to see that the least bad placement of a pusher prop is above the wing, angled down to point at the CG at an angle opposite to the best lift to drag angle.

Spacing the motor weight along the span (and the batteries along with them if possible) would create lower bending moments on the spar, allowing a lighter weight spar and wing structure.
At such low aspect ratios the skin become is a bigger contributor to wing weight than the spar.
 
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lr27

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If you're going to use a bunch of electrics on the wing, why do they have to be pushers?
 

Norman

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why do they have to be pushers?
They don't have to but if you put them up front you'll need bigger tail fins and a more forward CG because any thrust producer acts like an empenage. Pushers increase power on stability (both in pitch and yaw), tractors decrease it.
 

EzyBuildWing

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They don't have to but if you put them up front you'll need bigger tail fins and a more forward CG because any thrust producer acts like an empenage. Pushers increase power on stability (both in pitch and yaw), tractors decrease it.
Problems solved: Youtube this vid: "Silent 2 Electro Promo" check it out! Let's start building!
 

lr27

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They don't have to but if you put them up front you'll need bigger tail fins and a more forward CG because any thrust producer acts like an empenage. Pushers increase power on stability (both in pitch and yaw), tractors decrease it.
I was thinking of mounting them just in front of the wing, but I guess if the pilot is in the same geometric plane, that's not such a great idea.
 

Victor Bravo

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Then I amend my idea to mean that the electric motors could be close to the trailing edge (instead of way under the wing or above it) which would keep the power pitch issues as low as possible without screwing anything else up. As Norman said, if this means the propellers should not be exactly on the waterline for the trailing edge then they would go up or down the least amount necessary to avoid the noise/vibration problems.
 

lr27

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Then I amend my idea to mean that the electric motors could be close to the trailing edge (instead of way under the wing or above it) which would keep the power pitch issues as low as possible without screwing anything else up. As Norman said, if this means the propellers should not be exactly on the waterline for the trailing edge then they would go up or down the least amount necessary to avoid the noise/vibration problems.
Electric motors can be very small and light for the power. You could put one on a strut up top and two under the wings. Somewhere, I've seen an aircraft with the motors on two struts, much like with a Cri Cri, except some distance behind the wing. Putting props in clear air means more thrust for the power, and less noise.
 
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