Facet Opel

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Jay Kempf

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Most of the specs I have read are for 10 sq meters of wing and the picture I took this from is bigger than that. Someone must have gotten the scale way wrong.

So for 10 square meters and say aspect ratio of 4.125 ish that would be a root chord of approximately 2.42 meters or 6.15 feet or 73-74 ish inches? The drawing is no where near this. Span would therefore be something like 21-22 feet?
 

Head in the clouds

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I think some of the engineers around here are going to want to have a word with the owner about galvanized metal, and those triangular holes in the rear spar. There are people here whose knowledge might have helped prevent the crash of this aircraft years ago, and I suspect they will be more than happy to provide that type of guidance and assistance this time around.
Yes, that was my first reaction, it's rather bizarre ...

I thought Dean had a reasonably good understanding of structures so I'm surprised to see this. If the folded galvanised sheet was being used just as a mold to form up a GRP repair to the spar then there wouldn't have been any need to cut the 'lightening holes', so I presume it's meant to stay there, and I wonder why the holes are the shape and orientation that they are. It'd make more sense if they alternated upright and inverted, forming some sort of a truss, but would still be better if they were circular and flanged. By making them that shape it looks like the web will buckle just above the lower chord. But more to the point - why commercial grade galvanised sheet in such a critical application?

I used to have Dean's contact details somewhere, I'll try and dig them out and see if I can find out a bit more.

Regarding the size of Scott and the Opal, it's been a while but from memory Scott was about 5' 10" and slim build, quite narrow in the shoulders and even so he was a snug fit in the Opal cockpit. I think the Opal span was about 22ft and the chord about 4'6".
 

Jay Kempf

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4'6" is tiny but that jives with a 22ft wingspan and 10 square meters. If you go back take a tape measure for chrissakes :)
 

autoreply

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I think some of the engineers around here are going to want to have a word with the owner about galvanized metal, and those triangular holes in the rear spar. There are people here whose knowledge might have helped prevent the crash of this aircraft years ago, and I suspect they will be more than happy to provide that type of guidance and assistance this time around.
Gives me the willies too, it looks like this has some serious structural issues.

@ Cheapracer; I often use paper with 5 mm lines (top/down, left/right) as reference in pictures. Works like a charm and you could (lots of effort) rebuild a full model from a few pictures.
 

cheapracer

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I had no personal need to take measurements and I have them available via the engineering student who has done the lot previously, I have asked her to send them to me and will post them when they arrive.

I thought Dean had a reasonably good understanding of structures so I'm surprised to see this.
Dean didn't do them, they were suggested and made up by Howie Hughes apparently and they are certainly a part of the structure.

The plane is being rebuilt primarily to go into a museum although it was suggested that the final World Record for distance might be undertaken that Scott was preparing for, Sydney to Perth was mentioned (non-stop) - 2000 miles / 3300 kms.

According to others who also knew him, Scott wasn't as tall as you remember. I'll look through some other pictures to see if I can get a human size reference ...
 

Head in the clouds

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Dean didn't do them, they were suggested and made up by Howie Hughes apparently and they are certainly a part of the structure.

The plane is being rebuilt primarily to go into a museum although it was suggested that the final World Record for distance might be undertaken that Scott was preparing for, Sydney to Perth was mentioned (non-stop) - 2000 miles / 3300 kms.
Although Howie (we're talking about Howard Hughes, owner of the Australian Lightwing Company) isn't particularly a structures man himself (he has always had his structural engineering overseen by aeronautical engineers - Bill Whitney primarily), I'm sure he certainly wouldn't have suggested and/or supplied a bit of garden shed tin for a spar centre-section repair if he thought it was ever intended to fly again.

I do recall that the original moves for a restoration of the wreck was to be able to put it on display at the Temora aviation museum. At the time there were also moves, recently revived, to have Scott added to a 'hall of fame' to coincide with the delivery of the display.

So perhaps, and I certainly hope so, Howie's contribution was based on the intention to make it strong enough to hang from the roof on static display. It certainly wouldn't be airworthy the way the photos you posted show it, not even if it was strut braced, let alone as a cantilevered wing.

As for Scott's height, you may well be right, but I'd be fairly close I think. He was certainly a fair bit taller than me, but then most people are ... on one occasion he jumped out of one of his early Sapphires having flown it to Kooralbyn and I took it for a fly but I had to use a lot of backrest cushions to reach the pedals, as well as one or two under me. And that was after using the couple of inches pedal adjustment that was available.
 

flyvulcan

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I met Scott just the once way back in the early '80s when I visited his factory just outside Bankstown Airport in Sydney. It's been a long time, but my fuzzy recollection is that he wasn't super tall. I would have said less than 5'10" but I could be wrong...

I recall that I was distracted from him by the (around half) scale Spitfire that was hanging in the roof of his factory. It was a project he was working on at the time. Being a warbird fan, the Spitfire attracted most of my attention but Scott was very passionate about his desire to see the Spitfire finished after he had completed the project he was working on at the time (I cannot recall what it was, possibly the Ultrabat).
 

DangerZone

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It does look a bit unconventional but without knowing a lot more about the structure than can be determined from the photos we can't make any good evaluations. That area could be an uncompleted torsion box/motor mount between the wing halves and all of the bending loads go through the main spar?
Actually, from my understanding Victor Bravo was talking about two different things, galvanized metal and triangular holes.

The triangular holes are obvious but the galvanization process has also an inverse reaction than the one in industrial application of coatings. When a high speed shaft passes through/around another conductive metal in a fluid (air is fluid, with moisture it has some similar properties to water) it creates small electric charges which act on the surface of the surrounding metal at an electronic level. Simply speaking, when turning it fills and depletes the electrons of the metal atoms and slowly but thoroughly corrodes/eats through the metal at a microscopic/nanoscopic level. For more than a hundred years ships&boats (and some aircraft) used zinc protectors for propeller use so that galvanic currents would 'eat' the zinc instead of the prop, shaft and/or surrounding metal. The metal deterioration is not visible to the naked eye but CAN be visible on the zinc protector because after some time it starts to look like something was biting it with tiny/small teeth. In a closed environment like the rear of the aircraft where the engine and shaft are located, with thermal and moisture fluctuations and shaft spinning through metal, it might be smart to see IF some galvanic protection would be needed so the metal structural part would not deteriorate and fail in the future. Thus the problem could be invisible and so would the surface of some metals be, not all of them look 'eaten' on the outside as zinc. Some might have microscopic holes and one could break a metal part that was once stiff - with bare hands. This can happen in some cases more than in others (most aircraft usually change parts and install new ones regularly so this is rarely visible) but many high rpm engines could usually have this effect more present than the slow turning machines.

Even with good grounds/wirings this effect is present so it could be worth looking into, just in case.
 

cheapracer

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So perhaps, and I certainly hope so, Howie's contribution was based on the intention to make it strong enough to hang from the roof on static display.
Probably, but that doesn't explain the lightening triangles of which I would like to make this statement, in 1903 when the Wright Brothers first flew ... oh look, a squirrel, where's my stick, tee hee hee .....
 

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Head in the clouds

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Probably, but that doesn't explain the lightening triangles ...
Yes, I considered that, and concluded that perhaps they might have been to make it look more authentic on display, if that part was visible through the engine cowling, but it's rather less likely than that it was/is perhaps supposed to fly like that, which gives me the runs ...

On further examination of your posted photo I'm coming to the conclusion that spar centre section is actually a piece of C15010 or C15012 roof purlin which at least is made from 450MPa steel but the lightening holes ... the presence of the zinc ... well I wouldn't be getting in it anyway.

I wonder how the purlin is joined into the rest of the original spar.

I also see he has used a piece of similar galvanised steel sheet to blank off a wing rib in the centre bay. Why would you do that when you might use aly sheet which would be much lighter - if you intended to fly it, that is.
 

Victor Bravo

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OK, I understand now. Those are galvanized "home improvement store" construction purlins and metal stud pieces... to cobble the airplane back together... to put it on display. That explains the silly triangles, I remember seeing them in home improvement store metal studs now.

Disregard my previous comment about the engineering, they are clearly putting it in a museum instead of flying it. That is as it should be. The Facet Opal should be considered an important historic aircraft, somewhat of a minor "national treasure" to the homebuilt aircraft movement in Australia. It will serve a far more important purpose inspiring new builders and wannabee pilots being on display than it ever could as a flying aircraft.

For the pride and bragging rights of the Aussie homebuilt and aviation community, somebody should make an identical copy of the aircraft... identical... and finish setting the records that Mr. Winton was going after. But the original should be on display as an educational and inspirational thing IMHO.
 

cheapracer

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Confirmed and my scaling was pretty darn close ...

Sorry for the late reply. The measurements you're after are:


Span no wingtips: 2440mm
Span w/ wingtips: 2930mm
Total span: 6600mm
Chord length: 1610mm
Aileron chord length: 320mm
Fuselage length fwd of leading edge: 1210mm

 
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Retroflyer_S

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The magazine article says ~22' span and ~6' chord, or ~120 SF wing area when the fuselage is deducted.

The article also says ~100 knot cruise speed, which is considerably less than the video said. This on nominally ~40 hp and ~242 lb. empty weight. With pilot and normal fuel aboard, this suggests something like 4 lbs/SF wing loading.

Sexy little plane!

However, compare apples vs. oranges and go on YouTube for Davis DA-11, which reportedly cruises ~120 knots on ~20 hp, with ~162 lb. empty weight, at more than 100 miles per gallon. The DA-11 has fixed gear and is not aerodynamically refined. But, it easily could be with simple wing root fairings, contoured wing and fin tips, etc. which would surely improve its performance.

Still, you can't help wondering what would happen if a DA-11 got the Kent Paser or Lopresti, treatment, increased it's chord length 25%, retracted the gear, and bolted on the 40hp version of the engine to match Facet Opel power.

Facet Opel was a STOL plane, presumably because it accelerated to takeoff speed pretty quickly, coupled with low wing loading for a low stall and takeoff speed. With significantly less weight, and assuming the same thrust and somewhat increased wing area, a plane like DA-11 might be competitive.

Back to Facet Opel: The original was reportedly pretty expensive, with lots of carbon fiber and composites. How much weight penalty if done with marine grade plywood? Alex Strojnik said that stiffness to weight ratio being vital, a plywood plane would rival aerospace composites in weight, but at a fraction of the cost. Thoughts?
So it was 242 lbs empty and 10 m2...fuel 20-25 kg and pilot 75-80 kg makes it then 204-214 kg loaded. So the wing loading was around 21 kg/m2 ( AR was 4 ).

How about using Duramold instead of veneer/plywood..as the D doesn't warp or shrink...and it weights 50% less than aluminum but is 70% stronger at the same time.

Using carbon would be 30% more weight but then double or triple the strenght....and cost and effort.

Engine was Rotax 447; http://www.rotaxservice.com/documents/447info.pdf ( seems to have 5.3 gal/h consumption at peak rpms ).
 
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danmoser

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It good to see that this old thread is still alive, and that the Facet Opal itself is being revived.
Earlier in the thread, Hans and others had suggested some interesting design modifications, and I'd be interested to explore that further.

I especially liked the idea of maintaining a relatively straight trailing edge, but mildly tapering and sweeping the planform while keeping the low aspect ratio (~4) for light weight & high speed cruise.
The FO's pod & plank arrangement does have the appeal of simplicity, but I generally do not like full-span elevons or inboard elevator pitch controls.
This type of pitch control via variable airfoil reflex has the double disadvantage of having the lowest CL capable airfoil section on landing, and the least pitch-stable airfoil at high cruise speeds.
"Pancaking" your landings is a common issue with plank wing piloting.
And I seem to recall reading that Scott Winton reported that the FO had extreme pitch sensitivity at high speed .. please correct me if I'm wrong about that.

With the more typical arrangement of outboard elevons on a swept wing, pitch control is accomplished via variable twist, which enables slower landing speeds and a more stable fast cruise than the plank.
The third option for pitch control is via variable CG, IOW, weight shift. Somewhat familiar to us hang glider pilots. ;)

Nickel & Wohlfahrt briefly mentioned the advantages of a "jump twist" wing design in section 7.6 of their book.
JumpTwistModel.jpg

This is similar to the "Wild Wing" RC model racer layout.
WildWing.jpg

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?
 
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