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07 Nov 2012,
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(Created 09 Jun 2009)
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Here's more vintage Stan Mott/Bob Cumberford brilliance; this appeared on page 57 of the
January 1958 issue of Road & Track:
(09 Jun 09)
[I hope Stan and Bob will forgive me for reformatting the illustration;
it was a vertical half-page in R&T and I've strung it out horizontally here.]
[For a HUGE (1.5Mb) image, click HERE.]
[For a HUGE (1.5Mb) image, click HERE.
This was a two-page spread and I chose NOT to dummy up the gutter;
nor to try to compensaiet for the differing xerographic copy backgrounds.]
The fake Continental engine is made of fiberglass and can be used for storage. Cooling air for the P&W engine is scooped by the top shrouds and the hot air exits at the bottom of the fuselage.
There has been a wonderfu1 increase in the number of scaled-down military classics in the past few years: 3/4-size Fokkers, 2/3-size Mustangs, 5/8-size Hawker Hurricanes. We even offered our own suggestion for a 4/10-size B-17E in the March 1972 issue of Air Progress ("Hey, Buddy - Wanna Build a B-17?").
But why must all aircraft always be scaled down? Aside from one or two World War-I fighter replicas that have been built to original plans; people rarely make an interesting airplane in its original size. Of course, there was the Convair janitor interviewed years ago by Bob and Ray who was building a B-36 in his basement, but he was taking home pieces of the real thing in his lunchpail, which is not at all in the spirit of homebuilding, and he never did get the FAA to let him fly it...
Why, too, must all the repllca aicraft be military models? There are some exceptional civilian aircraft worthy of a homebuilder's attention and efforts. For instance, what could be more worthy than the good old Taylor-cum-Piper Cub? Thlnk of it! A scaled up J-3! What could be more fun to build and easier to fly?
How many times have you heard the J-3 held up as the standard to which all other aircraft should aspire with respect to handling? How many times have you heard its praises sung by the oldest, boldest aviators? Think of all the pilot reports that end by comparing the subject aircraft to a J-3. If a Howard, or a Stinson, "handles just like a big Cub," doesn't it stand to reason that a genuine big Cub wouJd handle even more like a big Cub?
Of course it would. So, here are the schematic plans for the ultimate in a true family homebuilt, the J-3³ -- King Kong Cub.
The choice of size was easy. If you accept that a normal J-3 is not quite wide enough for one person, it follows that a twice-1arger version is still only about on-and-a-half people wide - not a great improvement. But when you get to thrice-sizing, ah, there you!ve got something. There is plenty of room for two comfortable side-by-side seats, with a nice little aisle between them for the hostess to use when she's serving coffee, and for the passengers to use on the way to the rest room. Triple-sized, the J-3 fuselage is amply high for strolling about, and yet the overall airframe is not unreasonably large - the span is only 10 feet more than a DC-3.
Sure, it's big ... maybe too big for one man to build by himself, but what a wonderful group project! An airplane that would occupy an entire EAA chapter for months, even years, and yet could be flown anyone in that chapter.
Even better, it could be flown with every chapter member in the airplane. Try that w1th a Baby Ace!
When you increaae the linear dimensions, areas go up by the square, so that the wing area is nine times as great as the standard airplane's. Sixteen-hundred-plus square feet of area is like a small house, so we've decided that the wing construction should be a little different from the normal J-3's. By using plywood to cover the wing, you elminate expensive (in this size, very expensive) drag-bracing w1res and gain a splendid walkway, which is a nice place to hold chapter meetings when the weather is good.
Since we don't want to lose that good old Cub fee1, the wing loading must remain just as it is on the normal airplane, around 6.8 pounds per square foot. This g1ves us a maximum permissible gross weight of 10,924.2 pounds. For simplicity, we can round it off to 10,900 - just under 5½ tons, wel1 within the FAA's 12,500-pound limit for light planes. To put the wing performance into proportion, recall that the L-1049 Lockheed Constellation, with a wing about the same size, carried 85 pounds per foot.
Of course, the Connie had Fow1er flaps and other fancy devices that you don't need with a USA J5B airfoil, but its weight defeats it when real grassroots flying is to be done. Our J-3³ will get off at fu1l gross and charge over a 50-foot obstacle in only 375ft.
Naturally, you've got to have quite a bit of power to handle an airplane nine times heavier than a J-3, even if al1 you want to do is maintain the standard power loading of 18.8 pounds per horsepower. And that presented us wlth a rea1 prob1em. There just aren't too many good engines in the 600-hp class (9x65hp =585). Rare old Ranger V-12's would fit inside the cowling, of course. But where would you find one? The answer, it seemed at first, was to look to the most modern and efficient powerplants available, the miniature turboprops that give such exce11ent service in a wide variety of military and business aircraft. The Garrett/AiResearch TPE-331, with 610 hp for takeoff recommended itself, but it dld suffer a big drawback - aside from the price - that you'll understand when you think about airplanes like the Turbo Beaver and the Pilatus Turbo Porter; the engine is too light for a classic airplane; it has to be mounted too far forward. We were p!anning to compensate for that with extremely heavy dummy cylinders on the sides of the cowl (remember; we wanted to preserve the classic lines for you), when the EAA came up with a magnificent solution, as it so often does.
It was a 1939 J-3 that appeared at the 1972 Oshkosh Fly-In, a genuine stock Piper with a radial engine! To be sure, the Lenape Papoose was only a three-cylinder radial, and it had only 50 bhp, but the principle was established: a chunkety radial engine sound is legitimate for a J-3.
You can take your choice of powerplants, but we chose the P&W R-1340 with a s1ight lowering of the thrust line to fit it all inside the cowling. There are literally hundreds of them around, they don't cost too much and you could make use of most of the power section of a T-6. Of course that skimpy littlc Hamilton Standard metal prop wou1d have to go, to be replaced by a nice fixed-pitch wooden one, but that shouldn't bother you. Props like that were good enough for the first Spitfires, after all. And wood is fatigue proof. NASA used to have some 35-foot 5-inch metal props in their full-scale wlnd tunnet at Langley, but they changed to wood 30-odd years ago {remember that this was written in 1973}, and haven!t had a moment's trouble since. Of course, you'd have to have another gear box to keep the prop under 1100 revs.
A stock 1946 J-3, brand-new, very clean, wlth a well-tuned Contlnental C-65 pushed to its limits could manage a maximum speed of 83 mph and a 73 mph cruise. Its rate of climb was 450 fpm, and it could go as far as 200 miles in no-wind, no-reserve-fuel conditions. Our airplane should be somewhat better. With a top speed of 105, we look for a cruise speed around 95mph, with a slight edge on power, we're looking for 750-fpm inital climb, and we think we'd hold on to that rate pretty well. But the big Cub won't have much more ceiling than a little one. At around 12,000 feet, you may as well level off and enjoy the fresh air. One place we lose performance is in stall speed. A stock J-3 lets go at 38 mph, the J-3³ just under 45. That's not bad, and if you had to hang on longer, you cou1d open up the throttle a bit. We've cut down on fuel capacity, proportionate1y, in order to hold the range to not much more than 200 mires, just like a normal Cub.
Tires for an airplane like this could be a prob1em. Most big, big airplane tires are high-pressure, rather narrow jobs, not meant for the rigors of grassfield work. There is an answer, though: Goodyear!s big baggy Terratires, a group of low-ground pressure terrestrial vehicle wear (closely related to the original Alrwheels). You might have some troub1e getting the size you want without earthmover treads, but there is a Trai1-Rib design that looks just right. And they weigh only about 170 pounds apiece.
Brakes, of course, have to be cranky mechanical1y-unsound types, operated by little buttons under your hee1s. Best bet here is to get some old Ford car brakes and convert them to hydraulic operation, using cylinders carefully chosen to reduce mechanlca1 advantage and give you true J-3 stopping power - practically nil.
And in order to savor the c1assic feel of the airplane, you're going to want to be as cramped and uncomfortable in the pilot's seat of the big J-3 as you were in the little one. Mount the seat too close to the pedals and leave out all adjustment, so things will seem perfectly familiar.
Since you wouldn't want to forego the pleasure of reaching up and behind you to crank trim, we!ve moved the pi1ot's position up into the windshield area. True, you get a most un-Piperlike view, but you can still grapple backwards for trim, and that's what counts.
Oh, yes; the entire airplane will still be fabric-covered, even the p1ywood-paneled wing surfaces. Grade A cotton would be the most authentic, but in view of the incredible job covering this much surface is going to be, we recommend Ceconite covering. There is no need to discuss the color of the finish: Cub Yellow, with a black stripe.
Since this will be primarily a local-flying airplane, not much attention need be paid to baggage accommodation. There's a fair amount of room under the gas tank. Suitcases can be put against the firewall for trips to Oshkosh or local fly-ins. A couple of light tents, a few ropes and other equipment could be stuffed into the wings from within the cabin. After all, the wings are more than 2 feet thick.
Construction is fairly straightforward, with no surprises and no problems beyond those associated with handling very large, heavy chunks of material. The wing spars is not quite as big a problem as you might think. As a simple, strut-braced airplane, the Cub has no need of continuous spars, tip to tip, and although a half-wing panel is about as big as the largest ordinary homebuilt's entire wing, an enthusiastic and ingenious group can manage. Getting a piece of aircraft-grade Sitka spruce big enough for a solid spar might be a problem, but you could make a ply-web, four-flange spar with laminated flanges. That way, the pieces of wood are not so heavy.
And if the whole wing daunts you too much, there's a practical solution. You can leave out the inner bay: 10 feet, 1½ inches on each side of the wing, cutting the span down to a mere 85' feet 4½ inches - a triple-size clipped-wing Cub. You'd have a fine "little" aerobatic machine.
The fuselage construction is probably simpler than a regu1ar J-3's. The tubes are bigger, the joints are easier to see, and the welding, if it takes longer, is still less difficult. The same is true of the welded-up tailfeathers. Everything is easier to handle when it is big enough to see and get hold of. We've suggested putting a few more ribs in to keep fabric spans down, but you could do some ply covering here too, in which case you'd stick to standard spacing.
When you get to thinking about it, you can see how much easier it is to build a big airplane than a small one. You're working with hefty chunks of stock, substantial pieces a man can really get a grasp on. You can use a whole range of tools you've already got around the house: pipe wrenches, big hammers, large screwdrivers - things you've never considered for aircraft work before. You may have to sell your station wagon and buy a moderate-size truck to carry parts in, but you'll need the truck, anyway, to tow the rig out to the airport. And, it'll be handy for hauling in the lumber you'll need for the extension to your house.
You'll farm out some jobs. For instance, only a sail loft is likely to have the space and the proper sewing machines for running up a set of coveriag bags, and since they'll be totally familiar with Dacron materials, they're your best bet anyway. And they probably won't charge much more than three times the cost of a 1946 Cub.
Ah! yes, costs. A 1946 J-3 could be had for: $2,195. Today, a good one is likely to go for $3,000 {again, this was written in 1973}. So, if 12 members of your EAA chapter each invested in a Cub, there would be a total outlay of $36,000, you'd face a monthly tiedown cost of maybe $180 to $240, you'd use more than 50 gallons of fuel an hour if you all flew at once, and all you'd have would be a flock of commonplace airplanes.
That $36,000 should be far more than you'll need to spend on a King Kong Cub, even if you buy a freshly-overhauled P&W (and remember these engines go 2,000 hours between overhauls), and any airport operator will pay you to tie down at his field (provided your ropes are strong - can you imagine what th1s airplane would do if it got loose, just for the attraction. At Oshkosh, you will be able to sell rides all dayc long.
After all, it's just about the perfect airplane. It combines classic lightplane design with classic airline-engine reliabi1ity, strength with simplicity. It's an airplane that the whole gang can enjoy together. Best of all, it'll fly just like a ...
[25 Aug & 02 Sep 09 pictures by S. Berliner, III - all rights reserved (but why?)]
(26 Mar 2012)
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