# Mike Patey - Scrappy's Wing

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#### ScaleBirdsScott

##### Well-Known Member
Sometimes it feels like Scrappy has become a bush plane built more like a fighter jet. But looking at what the rock crawler and high end custom vehicle guys are doing this all feels about on par.

I can't speak much to the aerodynamics of his whole doubleslat-comboflap super system; it's not my realm. But so far I'll believe his claims as plausible unless we see otherwise. The tolerances, fit, finish, etc all seem good in any case. I would like to see this level of machined-to-perfection more common in the future. Hand fitting and lots of adjustment is a pain.

I'm not a huge fan of the sheer amount of tiny lightening holes in all of those machined ribs. It seems like a throwback to the airship days. Certainly there's gotta be better ways to go than that strategy of cutting dozens and dozens of little holes in every possible location? Like going with thinner webs? It just looks excessive. And feel like crack propagation could be an issue if any one hole isn't perfect.

Luckily, having bored a lot of holes with a mill now, I have more confidence in machine interpolated holes than most drilled holes as far as quality of finish.

Definitely makes me think about what the options are for precision machining rib components and spar elements. Certainly some benefit to everything fitting dead on first time. For the wing I'm working on I've been going about replacing a lot of groups of basic parts with single machined components that are cut on a VMC and have all the holes and locating features cut to within a few thou. Parts end up stronger, straighter, things move smoother. Mike is showing a lot of the potential here and I'm definitely taking notes even when I already have a plan.

#### Andy_RR

##### Well-Known Member
I think he's done an amazing thing and is truly with the spirit of experimental aviation. I hope it works well enough to demonstrate during flight test. He's put a lot of design and analysis effort in it, no doubt. The management of the centre of pressure/lift and pitching moment is very cool too.

I question how much he's relying on the SW flow simulation for such a thing. I'd be wanting to corellate the flow analysis in another package at least. A lot of manufacturing effort hinging on these results!

The structural analysis must have been a bit of a headache too!

Most disappointing thing is him reverting to aluminium for his ribs rather than moulding ribs and mechanical devices in carbon.

But nevertheless, it's fantastic and I'm looking forward to see the test results!

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#### Hephaestus

##### Well-Known Member
Yeah I'm surprised there's not a scale proof of concept. Clearly he can fly rc...

The ribs actually make me sad - I mean you're taking a 20lb slab of aluminum and milling away 19. That's got to be a 100k+$wing #### rbarnes ##### Well-Known Member The ribs actually make me sad - I mean you're taking a 20lb slab of aluminum and milling away 19. That's got to be a 100k+$ wing
He's got to keep everything up to par with that spaceship panel.

#### ScaleBirdsScott

##### Well-Known Member
I can't imagine it being cost effective and accurate for what he's doing where each rib is so unique to try and embed so much mechanical systems into a carbon wing/rib system. Embedding all of those mechanical tracks and linkages and hinge points into a composite rib seems messy and prone to having to make multiple passes.

When you have a CNC mill that can machine metal and you're using aluminum ribs and fuel tanks and integrating all these mechanisms it makes a lot of sense to just stick to aluminum. Clearly if he felt composite structure would have been a better approach they have the experience and means to have gone that way.

#### Andy_RR

##### Well-Known Member
Once you have the CNC capability, which he clearly has, to make those ribs isn't that much of a deal. Not cheap, but not nearly as expensive as you might imagine. The aluminium swarf all goes in the recycling bin so not such a big deal either. It's also worth a bit so will get recycled.

Aluminium is more that twice the weight and not nearly as stiff though. With some imagination you could integrate some of the mechanical elements from aluminium inside a moulded CF rib.

#### bmcj

##### Well-Known Member
HBA Supporter
The guy's amazing!
All I know for sure is that if you are doing a video and have the name “Scrappy” painted on the side, you should really try to make sure that the work table doesn’t hide the letter “S” in the name.

#### edwisch

##### Well-Known Member
Most impressive! Seemingly unlimited re$ource$ of every kind, including computation, CAD/CAM, time. He's obviously got some help along the way...

#### Island_flyer

##### Member
Very fascinating. It seems like more design and engineering for the leading edge than the trailing edge. I would have expected triple-slotted Fowler flaps for the trailing edge. But it looks like he's got it all figured out. Eager to see it fly and learn more about the numbers. One of many ways to measure versatility in an airplane is to compare maximum speed to stall speed. A Cessna 150 is almost exactly 2.5:1. Some aircraft designs offer 4:1. A Helio Courier is almost 5:1 (depending on model). Scrappy's? I'm curious about the actual numbers from the flight tests. Undoubtedly it will be a high ratio.

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#### Lendo

##### Well-Known Member
Impressed with the design, but can't see where this Rib sits in the wing, as I can't see any accommodation for the Spar, also part of the mechanism protrudes through the upper skin. I guess the proof is in the testing.
George

#### trimtab

##### Well-Known Member
Mike is exhausting to be around when he's in the groove, frankly. But he gets stuff done. He has help for the CAD and CFD (in-house, with the biz).

There are papers dating as far back as the 40's for every major element of the flow design he has. It's all legit. Most of it has been executed in some form or another as well with varying levels of success. I think it's great to see a human dynamo pull it all together in a single flash of light to see here it can all go. Personally, without knowing the actual weights involved, I can't see what numbers he is likely trying to achieve. The flying landing gear struts could very well provide a few hundred pounds of lift in the slipstream, for example. The slotted design could very well provide attachment for a few to several more degrees of AoA, leading to a linear-ish increase in the Clmax. But in the end, if one is looking to fly super slow, and land anywhere, there might be better tools for that. If one wants to do so while flying 150 kts, it might prove harder but some helicopters will do that. So I think this is more of a release of productive energy for Patey, in a new and interesting way. I look at it as 'interesting art' at the very least, and an example of the art of the possible.

I like the mention by Island Flyer about speed ratios. It's a pretty fundamentally conserved characteristic of conventionally designed airplanes, with wing loading and power loading characteristics forming the groupings for the ratios from a J3 through biz jets. My only estimation on Scrappy is that it seems to genuinely be trying to get to150 kts cruise while landing at around 25 kts. If I was going to spend that much cash on something, I think I'd want to do a whole lot better than that.

When you have VMC in house, you do think differently in terms of how to execute a project. It's no different than having any other capable tool...spectrum analyzers, lasers, etc. Mike is the kind of guy that would stay up for days at a time if he acquired a new capable tool and had a mission to match to it. I suspect that the CFD package he has is directly making it possible to get a lot of things from inside his head to reality in a new way, and he's probably pretty thrilled by that.

For those interested, Openfoam is monstrously capable. It's free. Give it a whirl.

##### New Member
Impressed with the design, but can't see where this Rib sits in the wing, as I can't see any accommodation for the Spar, also part of the mechanism protrudes through the upper skin. I guess the proof is in the testing.
George
Spars shown in the video from 2:18 to 3:00 minute mark. Mechanism for the slats goes through the front spar.

#### Rhino

##### Well-Known Member
Or it could just be a matter of, "After Draco, what next?" That's a hard act to follow.

#### TFF

##### Well-Known Member
You have to remember that this thing is meant to be able to take off at 4000 lbs if he wanted too. He is building the thing to the dream loading everyone wishes for. Yes it can takeoff at 2000 lbs and go straight up, that mission one. Next it’s to pretend it’s a C5 and carry anything he wants. It’s not meant to be dainty.

#### ScaleBirdsScott

##### Well-Known Member
One thing I do want to comment on for this video is that even this apparently "short" video did give me a good sense of what is trying to happen with the airflow using slats. Even though as mentioned I'm definitely not super into aerodynamic theories and am in no way formally educated on any of it. But the idea of slats creating enough air velocity over 'top' of wing that it essentially forces enough entrained airmass to be pulled down around the 'top/back' of the wing at high AOA that it prevents the wing forming a pocket of air from that which is flowing around the trailing edge of the wing. It suddenly was very intuitive from his explanation and images exactly how the slat could help. And that's something that while I've heard things explained by engineers in the past, never really would understand in quite the same way. Always just a bunch of terms that don't connect to intuition. Patey because he's as far as I know not a formal traditional engineer, has the right knack for absorbing this information and being able to re-explain it quite well.

#### D Hillberg

##### Well-Known Member
Once you have the CNC capability, which he clearly has, to make those ribs isn't that much of a deal. Not cheap, but not nearly as expensive as you might imagine. The aluminium swarf all goes in the recycling bin so not such a big deal either. It's also worth a bit so will get recycled.

Aluminium is more that twice the weight and not nearly as stiff though. With some imagination you could integrate some of the mechanical elements from aluminium inside a moulded CF rib.
CF and metallic structures don't mix well. With the fuel and all that monkey motion for slats/flaps.
His material of choice is the right pick.
Molds for the CF would delay the build and add a cost beyond his disposable income.

for spot landing and 150 kts I'd go helicopter

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#### paraplane

##### Well-Known Member
I don't think a lot of the fund to build Scrappy came from backers. In one of his videos he explains much of his wealth came from his design firm on a project that was a water purification system. I think it was a system to make grey water or black water potable with an emphasis on high volume and to be available to developing countries.

#### trimtab

##### Well-Known Member
for spot landing and 150 kts I'd go helicopter
Precisely.

The pitch moment balance motivation is pretty well covered in the Wren 460 design.

For the mechanical design of the deployment, there are a lot of similarities to other slat deployment designs.

For examples of multislotted concept, here are examples Links and files).

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#### cirrus232

##### New Member
I'm tempted to call this an extensible double slotted chord/airfoil with a double slotted flap -- when all is fully extended. The slats are used differently than the traditional way. He seems to understand all that and is using them to get his 'cp' where he wants it. It is very creative!, and I did not see this coming. To me, this cements his slot in aviation history .... no pun intended.