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Facet Opel

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pylon500

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The Opal is a Hotrod, too much for my abilities to handle. I wouldn’t mind to fly a nimble flying wing, but it would have to remain docile and nimble.
View attachment 98425
this critter without its booms, fins on the wing and a wider airfoil
Hey guys, long time no see!
Ok, getting back into it and spotted this in the Opal update thread, and was tempted to suggest; keep the entire layout, but roll both fins inwards to 45º and use them as ruddervators, no controls on the wing at all.
That said, and looking at the pilot position relative to the wing, it's either fairly heavy, or the pilot (and main wheel) should be moved back a little, maybe 9 inches?
Meanwhile, so many things to update...
Hmm, looks like my little avatar gif has died?
 

Aerowerx

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Hey guys, long time no see!
Ok, getting back into it and spotted this in the Opal update thread, and was tempted to suggest; keep the entire layout, but roll both fins inwards to 45º and use them as ruddervators, no controls on the wing at all.
That said, and looking at the pilot position relative to the wing, it's either fairly heavy, or the pilot (and main wheel) should be moved back a little, maybe 9 inches?
Meanwhile, so many things to update...
Hmm, looks like my little avatar gif has died?
You mean like this: ______/___O___\ ______ ?

Where do you get aileron function?
 

Tiger Tim

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You mean like this: ______/___O___\ ______ ?

Where do you get aileron function?
Picture a plank wing with ailerons out by the tips. Imagine which way they move when you move the stick. Right stick = roll right, left stick = roll left.

Now, imagine drooping those tips down 90° without changing control linkages. Right stick = yaw right, left stick = yaw left. The surfaces now act as rudders.

In theory, there’s some anhedral angle that mixes the correct proportion of yaw input with roll input. I suppose instead of drooped tips you could have inwardly canted fins and control surfaces. I’m not entirely convinced that’s an elegant way to control an airplane but I could well be wrong. That’s the idea of it, at least.
 

Norman

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Now, imagine drooping those tips down 90° without changing control linkages. Right stick = yaw right, left stick = yaw left. The surfaces now act as rudders.

In theory, there’s some anhedral angle that mixes the correct proportion of yaw input with roll input. I suppose instead of drooped tips you could have inwardly canted fins and control surfaces. I’m not entirely convinced that’s an elegant way to control an airplane but I could well be wrong. That’s the idea of it, at least.
Diffuser tips work to add some directional stability and control to aft swept wings becaus the tips are well aft of the CG. For the same reason they won't help on an unswept plank. low AR constant chord planks need a large central vertical stabilizer.
 

pylon500

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You mean like this: ______/___O___\ ______ ?

Where do you get aileron function?
An inverted V tail, when using both rudder surfaces will tend to give you the correct rolling input (as opposed to an upright V tail which will give you adverse ROLL with rudder input), if the two angled tails are on booms and placed out along the wing, the rolling input of the 'rudder' becomes stronger, hence no ailerons needed on the wing.
As for the tips, I'd pretty much stick with the planform used on the Opel, the sweepback will give a feel of stability even without dihedral.
 

Aerowerx

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..... if the two angled tails are on booms and placed out along the wing, the rolling input of the 'rudder' becomes stronger, hence no ailerons needed on the wing.....
Then it is no longer a tailless flying plank wing. A completely new design.
 

Hot Wings

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Then it is no longer a tailless flying plank wing. A completely new design.
Who cares about the taxonomy of plane?
As long as it is easy and cheap to build with the desired flying and storage qualities the goal has been met.
 

pylon500

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Taree Airport Australia
Maybe that's not such a bad thing considering how the original designer lost his life ?
Like some of Rutans aircraft, the Opel was designed for a purpose, it's 'flyability' was secondary, that said, Scott could fly the aircraft well and remember it was a structural failure that brought it down, not it's handling capabilities.

As for;
___/_0_\___
Yes, it's no longer a flying wing, but the image I was commenting on was already not a flying wing.
My comment hence would be; 'For general purpose flying, the Opel could do with some handling improvements.'
But it served it's purpose.
 

pictsidhe

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The official cause of the Opal's demise was a pitch oscillation that overloaded it. That is debated by some. It was reportedly rather twitchy.
 

rotax618

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Evans Head Australia
Why not just decrease the aspect ratio, will increase the pitch stability, and increase the Reynolds Number, would also provide a deeper chord for pilot accomodation.
 

pictsidhe

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Why not just decrease the aspect ratio, will increase the pitch stability, and increase the Reynolds Number, would also provide a deeper chord for pilot accomodation.
Higher induced drag. Unless you also increase wing area, which gives higher parasitic drag. It's already pretty low AR. It may be worth comparing to other planks, like the Fauvel.
I suspect that some taper would help. Sweep definitely would, but that complicates spar design.
It's also possible that the elevator was just too sensitive. One of Mike Arnold's videos has footage of him failing to land after making the elevator lighter with more throw. He then went the other way, making it heavier with less throw, and got great reviews for the handling.
 

nestofdragons

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I recall he had drilled a hole to the spar for an oxygen bottle.
That detail i did not find in my quest about the accident. Many editions are being told. One i heard a loooong time was fuel eating away some structure in wing. Another which i found in recent seach was the heating of a bearing (of the drive shaft of the prop) which was placed in the spar.
 

rotax618

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Evans Head Australia
Like all accident investigations the cause is sometimes an educated guess.
What I can tell you is that I witnessed the Facet Opal fly on 2 occasions and was a friend of Scott’s father. Scott was a very accomplished pilot, he needed to be because the Opal was extremely pitch sensitive, if you want to re-design the Opal so that the average pilot could comfortably fly it you have to engineer some pitch dampening into the design. This can be done by adding a tail boom(s), adding a canard or decreasing the aspect ratio to increase the distance between the neutral point and the elevator hinge. Sweeping the wing is also a solution but it would cease to be a plank.
 

pictsidhe

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Like all accident investigations the cause is sometimes an educated guess.
What I can tell you is that I witnessed the Facet Opal fly on 2 occasions and was a friend of Scott’s father. Scott was a very accomplished pilot, he needed to be because the Opal was extremely pitch sensitive, if you want to re-design the Opal so that the average pilot could comfortably fly it you have to engineer some pitch dampening into the design. This can be done by adding a tail boom(s), adding a canard or decreasing the aspect ratio to increase the distance between the neutral point and the elevator hinge. Sweeping the wing is also a solution but it would cease to be a plank.
Perhaps it just needed an altered control design. There are higher AR planks with smaller root chords out there which aren't a handful to fly.
 

Speedboat100

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There was a report somewhere that said that Scott had added an oxygen bottle behind the spar for the record altitude attempts and had drilled a hole high in the center section of the spar web to carry the oxygen delivery tube to the cockpit and that the failure had emanated from that hole. Seems plausible. The turn was positive Gs so the critical part of that airframe would have been the center of the center section of the spar as it carried through the pod. So the upper part would have failed a weak spot in buckling. Or it could have been flutter or pitch oscillations as mentioned in the report. Funny thing was there is no mention of any pitch instability in any other flying descriptions of this plane. You would think that if he had a difficult airplane to fly it would have been reported in one of the interviews or reports out there. All reports basically are glowing about the things flying characteristics. Really seems like a nice overall concept if it could be kept within limits and control authority. What an easy airframe to create and maintain. Scaled up a bit with a larger engine and some baggage hatches it would be pretty useful. Couple tails on a stick (unjoined for Ross' sake) wouldn't add much to the overall build if pitch was a problem or less trim drag was a goal. The wing could be one piece and a cockpit module, engine module, and tail module could pin onto it. You could build that in most standard garages. Or build it with a three piece wing. Still pretty simple.

Spar ought to be sacred.
 

nestofdragons

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Near Antwerp, Belgium
Perhaps it just needed an altered control design. There are higher AR planks with smaller root chords out there which aren't a handful to fly.
cockpit01.jpg
One item that struck me when seeing the video of the Facet Opal was the steering stick. It reminded me of my early rides in recumbent bikes. I was able to ride a true race-bike (recumbent) and it was a real challenge to keep it on the bike-lane. I went from left to right and back. Very nervous riding.
2020-10-05 ligfiets.jpg
Bike was similar to this one in the picture i took from internet.

Later i had the chance to ride just the same bike, but with a wider steering rod. The previous one had my hands next to each other. This second one had my hands on shoulder distance each each other. All nervous steering was gone. I felt at ease.
Now ... go see the steering stick of the Facet Opal. See how short it is. The slightest movement of the hand gives a deflection of the flight control surfaces. Would simply adding some length to that stick reduce the nervous steering of this tiny beauty?
 
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