Part 103 Sky Scout?

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Captain Trunk
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Joined: Fri Jul 31, 2020 2:23 pm

Part 103 Sky Scout?

Post by Captain Trunk »

Greetings to all,

I have looked, but being new, may have overlooked some of the answers to my many questions. I would sincerely appreciate any input on any of these ideas.

I need a part 103 compliant aircraft, oops meant to say vehicle. From reading multiple sources, mostly copies of a series of 1933 Mechanics Illustrated articles and plans for the AirCamper and SkyScout, it appears a SkyScout could be built with an empty weight under 254 pounds.

* Weights from 1933 article (153#).
Fuselage sans covering 43#
Wings sans covering 90#
Empennage sans covering 9 3/4#, we'll call it 10#
Landing gear including both wheels and tires 5# per side
* Weights from Aircraft Spruce (52#)
Hirth 33 (30hp) w/ reduction drive 40# (electric start adds 5#)
Wooden fixed pitch or carbon fiber ground adjustable prop 12#
* Weights from discussion group on SuperCub web site
(I estimated 400 square feet of fabric will be needed)
(for reference 400 sq ft of medium weight polyfil is 8 1/3#)
(With 6 crosscoats of silver 17 1/2#)
With 4 coats of white over 6 coats of silver 22 1/2#, we'll call it 23#

153+52+23=228 pounds

That leaves 26 pounds for struts, cable and hardware (negligible unusable fuel, no engine oil in a two stroke), is this do-able?

I have seen the RaggWing UltraPiet plans briefly, but I'd rater build a new copy of a classic. I know that the cg will be seriously affected by the 200-400 pound weight difference between a 30 hp Model T engine and 30 hp aircooled two stroke, to keep the same lines would shortening the fuselage a bit (along with moving the engine forward be practical? Would moving the fuel tank to the nose, as many do with an aircooled engine, make the cg situation better or worse?

Thank you
PPL 1980, CPL 1982, ATP 1987. Soloed in a PA-28. PA-32, PA-31, BE-18, DC-3/C-47, C-46, C-54, G-21, 28-5ACF, BE-99, DC-6/C-118, CL-215/415, EMB-110, EMB-120 (1982-2018). Stroke, rehab, no medical, no pilot licence = Chotia Woodhopper.

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Richard Roller
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Joined: Mon May 22, 2017 11:14 am
Location: Olathe, Ks.

Re: Part 103 Sky Scout?

Post by Richard Roller »

Up front, my experience is with the model A powered Air Camper. The airplanes have a tendency to be tail heavy, especially with today's "heavier" pilots. The Piet I fly has had its engine moved forward 7 inches because of the
c.g. I'm not sure you could get a proper c.g. with the
Hirth engine. The only Sky Scouts I'm personally aware of have model A engines in them. You would need to do some serious figuring first. You might want to look at the West Coast Pietenpol site, there are several Sky Scout builds pictured there.

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Captain Trunk
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Re: Part 103 Sky Scout?

Post by Captain Trunk »

Roger Mann, when he built his 103 compliant UltraPiet, started with the original AirCamper plans. His fuselage is shortened by one bay. He shortened the wing's chord from 60 to 54 inches - which also decreased it's depth - and went from 32 ribs to 25. He used slightly larger cap strip - 3/4 x 3/4 vs 3/4 x 5/8 - and increased the rib spacing from 10," 11" and 12" to 12" and 15". The resulting 248# (Kawasaki 440 powered) Ultra is 14" shorter and has 15" less wingspan than a Scout.

The single cockpit is roughly in the place of the AC's passengers cockpit (I don't have AirCamper plans) moving 175 pounds of useless ballast :) forward to balance the loss of all that cast iron up front. In the 1933 article I am using, Mr. Pietenpol said that he reduced the fuselage length on the Scout and that the AirCamper's wing is overbuilt.
'
The Hirth 33 is nine pounds lighter than a 440 (the 440 has 7 more hp and 2 cylinders, but only a single ignition) so one could logically build a 239 pound UltraPiet. I'd just rather build off the "original" plans -- not that I won't have to modify it to solve the CG issue. Unless someone sees something that I am missing, I think it's possible.

Guess it's time for some proof of concept scale models.
Last edited by Captain Trunk on Sun Aug 02, 2020 7:37 pm, edited 2 times in total.
PPL 1980, CPL 1982, ATP 1987. Soloed in a PA-28. PA-32, PA-31, BE-18, DC-3/C-47, C-46, C-54, G-21, 28-5ACF, BE-99, DC-6/C-118, CL-215/415, EMB-110, EMB-120 (1982-2018). Stroke, rehab, no medical, no pilot licence = Chotia Woodhopper.

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Richard Roller
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Location: Olathe, Ks.

Re: Part 103 Sky Scout?

Post by Richard Roller »

Sounds cool. Good luck!

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taildrags
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Joined: Tue Mar 07, 2017 10:39 pm

Re: Part 103 Sky Scout?

Post by taildrags »

Hey, Cap'n Trunk- in the Air Camper, the passenger is positioned just about on the CG, which is between 25 and 33% of wing chord. Sits directly under the wing. The pilot sits slightly under the trailing edge of the wing... some more under it, some less, depending on whether they've shifted the wing aft or not, or by how much. The point is, I've run all sorts of what-ifs with the W&B spreadsheet and I can put as large a passenger as I want to in the airplane and it doesn't affect the CG much at all. Same goes for the fuel... if you put it up in the wing centersection, it won't matter what it weighs because it won't shift the CG. So now take those two elements -fuel and pilot- and examine them. Under part 103, you're limited to 5 gallons of fuel. If you run autogas at about 6.2 lbs per gallon, that's 31 lbs of weight that you might as well chisel in stone unless you want less fuel than that aboard. If you fly on avgas exclusively (about 6 lbs per gallon), you can pick up a pound that you can use somewhere else but the idea is going to be to put the fuel as far forward as you can to help offset the light weight of the 2-stroke engine. Just aft of the firewall will most likely be as far forward as you can get it, or want to.

Looking at the pilot's weight, if it's at or near the CG, it's not going to help you or hurt you so you're going to have to make everything else work for you. If it were me, I think I'd start by connecting with someone who owns and flies a Sky Scout and see if they'll share their W&B info as well as dimensions of their airplane, then start "unbuilding" it and then "rebuilding" it -in a spreadsheet- the way your proposed ultralight will be constructed. Take out everything in the panel that you possibly can. Take away the weight and moment arm of their inline-4 iron engine and plug back in the weight and moment arm of your 2-stroke with redux and prop. Take away the weight and moment arm of their fuel tank and plug back in the weight and moment arm of your 5-gallon tank. Then seat an imaginary pilot in the seat and run the numbers to see where the CG falls and you'll know what you've got to work on. Engine mount extension? Lighter empennage and tail feathers? You'll at least know how near or far you are from your objective. Sounds interesting!

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 engine

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Captain Trunk
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Re: Part 103 Sky Scout?

Post by Captain Trunk »

Greeting Misters Roller and Taildrags,

Thank you for your input and ideas.

Those original 1933 drawings put the 5.5 gallon fuel tank between the wing spars, right across the CG. I imagine both it and the AC were designed so that fuel and passenger load affected weight but not moment. But the Model T engine weighs about 200# (Model T website says exactly 184 without ignition box and cooling system, and you have to fabricate an oil pan), just a bit more than your 75 horses. But I need to stay light or stay on the ground. I could in theory lose weight in the rear to compensate for less weight up front with a 40# powerplant.

I want to keep the aesthetics without compromising the engineering, to that end I took cardboard and duct-tape and constructed a mock-up of the cockpit that showed I could accept a ten percent reduction in the size of the airframe and move the seat back location as far forward as station 42. Since I seem to be getting older rather than younger, I figured a half door would be a better option than the flop anyway. (As an aside, Mr. Mann said that his half door is an effective stall warning device. Secured with a piano hinge, when left open it lifts from vertical once airborne, but as the aircraft approaches a stall it flops down abruptly just as before the wing stalls - level and sans buffeting.)

My current thought is a metal "mailbox" type 1188 cubic inch (5gal mogas at 100F per API) fuel tank right behind the fire wall (depth and length somewhat dependent on placement of pilot) with a Cub style float in the cap. I have seen these done well matching the fuselage curvature offsetting some of it's weight by eliminating stringers, polyester and paint. From an engineering point of view I would prefer a half door in front of rather than behind the rear cabane strut.

Opinions and or input are most decidedly welcome.

John
PPL 1980, CPL 1982, ATP 1987. Soloed in a PA-28. PA-32, PA-31, BE-18, DC-3/C-47, C-46, C-54, G-21, 28-5ACF, BE-99, DC-6/C-118, CL-215/415, EMB-110, EMB-120 (1982-2018). Stroke, rehab, no medical, no pilot licence = Chotia Woodhopper.

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Captain Trunk
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Joined: Fri Jul 31, 2020 2:23 pm

Re: Part 103 Sky Scout?

Post by Captain Trunk »

Quick modeling results, weighing 200 or so pounds less than Mr. Pietenpol's Model T powered original, I shortened the SkyScout model about six inches (almost five behind the firewall). In the wing I spaced the ribs a bit further apart, decreased the chord three inches while retaining the same airfoil and used fewer ribs, shortening the wing span about two feet. The pilots seat is between the vertical cabane struts. Just about where the passenger seat is in the AirCamper. The Hirth 33 is mounted well forward to maintain proportions and the lift struts maintain their trademark rake. I'm sure I have left something out of the equation (a cowling, flight control cables and pulleys, and instrumentation for instance) but I'm at 207 pounds with a decent CG.

fuselage, covered in poly fiber, six cross coats, less all metal pieces, 46 pounds
three wing sections, covered in poly fiber, six cross coats, less all metal pieces, 52 pounds
empennage, covered in poly fiber, six cross coats, less all metal pieces, 15 pounds
landing gear, 10 pounds
metal struts and hardware, 18 pounds
Hirth 33, mount, carbon fiber propeller, less aluminum cowling, 56 pounds.
PPL 1980, CPL 1982, ATP 1987. Soloed in a PA-28. PA-32, PA-31, BE-18, DC-3/C-47, C-46, C-54, G-21, 28-5ACF, BE-99, DC-6/C-118, CL-215/415, EMB-110, EMB-120 (1982-2018). Stroke, rehab, no medical, no pilot licence = Chotia Woodhopper.

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taildrags
Posts: 372
Joined: Tue Mar 07, 2017 10:39 pm

Re: Part 103 Sky Scout?

Post by taildrags »

Cap't Trunk: there have been various tests and comparisons of latex house paint on aircraft fabric and there is a possibility of saving some weight by going that route. Rick Holland and Kirk Huizenga ran some documented tests and I began some tests of my own but didn't get to the actual endurance part (although I still have the test pieces and could still put them out in the weather to continue my tests). You can read those accounts on my website, here- http://www.flysquirrel.net/piets/paint/paint.html . If you even save a couple of pounds, it might be useful... and will certainly cost less than conventional aircraft fabric finishes.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power
Poly-Fiber system

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