Different Main Landing Gear

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gseiter
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Joined: Wed Jan 31, 2018 10:46 am

Different Main Landing Gear

Post by gseiter » Sun Jul 28, 2019 9:10 pm

I was looking at the plane on the back of the most recent BPA magazine. It appears to have a J3 landing gear. I'm looking for feedback as to why or why not use this gear. There are several sources of gear legs and other parts. I just ordered a copy of the W & B book so I hope to be able to sort through all the gear location considerations. If my cyphering is correct the axle on a J3 gear will be 2" forward of the axle on the plans.

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taildrags
Posts: 274
Joined: Tue Mar 07, 2017 10:39 pm

Re: Different Main Landing Gear

Post by taildrags » Sun Jul 28, 2019 10:49 pm

gseiter-

Others may chime in here with other background information, but in fact a fellow named John W. Grega developed an adaptation of the Pietenpol Air Camper in the early 1960s that utilized a number of subassemblies and parts from the J-3 Cub into his GN-1 Aircamper. The upper mounting points for the gear legs of a Cub are spaced differently from those of a Pietenpol, so the fuselage framing of a Pietenpol is not designed to transfer the landing loads of the J-3 gear directly to the airframe. The GN-1 is framed differently in order to use the adapted Cub gear and if you intend to use that landing gear, you should study the GN-1 framing plans to see how it differs from that of the Pietenpol.

You may also notice that the airplane in the photo on the back of the latest BPA Newsletter has the landing gear mounted to the fuselage in a way that matches neither the Pietenpol nor the Grega. The Grega retains the forward mounting point for the gear on the fuselage but moves the aft mounting point forward, away from where the aft lift strut attaches. The airplane in the photo, Andrew Carter's Aircamper 19-3452 from Australia, has the gear mounted with the aft point retained but the forward point moved aft. This may have been done to change the landing attitude or the CG, but I don't know the actual reason why it was done so take care if you decide to consider this adaptation, as it is not trivial.

Note also that his airplane appears to also have small side doors for the cockpits, another adaptation that requires structural modifications to transfer the loads through different paths in the airframe than the original was designed for, and should not be undertaken without structural analysis. Knowing Australian aircraft certification requirements, 19-3452 surely must have had such analysis performed in order to gain certification by their authorities. The centersection cabanes appear to have been lengthened a bit from stock to raise the wing in order to make entry and exit from the cockpits easier, and the lovely (to my eye) "deHavilland style" humped fuel tank is another evident modification that provides a nice fuel increase over stock. Flying in Australia where airfields are fewer and farther between than in the states, Andrew may have wanted the increased fuel volume. Lastly, the Subaru EA-81 engine that he used in his airplane is water-cooled, but rather than mounting the radiator up at the top like the original Model A-powered Pietenpols had it, he chose to install the radiator underslung, and that's the radiator that is visible in the dark hump under the nose. The Subaru EA-81 (1.78L, 8.7:1 compression ratio) was originally rated at 73 HP at 4800 RPM, about the same output as my A75 Continental (2.8L, 6.3:1 compression ratio) but turning twice as fast, which requires a reduction drive to keep the prop tip speed subsonic where it is most efficient. I can hand-prop my engine and have no electrical system, while the Subaru has an electric starter, electrical system, and full electronic engine control module and ignition.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

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taildrags
Posts: 274
Joined: Tue Mar 07, 2017 10:39 pm

Re: Different Main Landing Gear

Post by taildrags » Sun Jul 28, 2019 10:52 pm

gseiter-

Others may chime in here with other background information, but in fact a fellow named John W. Grega developed an adaptation of the Pietenpol Air Camper in the early 1960s that utilized a number of subassemblies and parts from the J-3 Cub into his GN-1 Aircamper. The upper mounting points for the gear legs of a Cub are spaced differently from those of a Pietenpol, so the fuselage framing of a Pietenpol is not designed to transfer the landing loads of the J-3 gear directly to the airframe. The GN-1 is framed differently in order to use the adapted Cub gear and if you intend to use that landing gear, you should study the GN-1 framing plans to see how it differs from that of the Pietenpol.

You may also notice that the airplane in the photo on the back of the latest BPA Newsletter has the landing gear mounted to the fuselage in a way that matches neither the Pietenpol nor the Grega. The Grega retains the forward mounting point for the gear on the fuselage but moves the aft mounting point forward, away from where the aft lift strut attaches. The airplane in the photo, Andrew Carter's Aircamper 19-3452 from Australia, has the gear mounted with the aft point retained but the forward point moved aft. This may have been done to change the landing attitude or the CG, but I don't know the actual reason why it was done so take care if you decide to consider this adaptation, as it is not trivial.

Note also that his airplane appears to also have small side doors for the cockpits, another adaptation that requires structural modifications to transfer the loads through different paths in the airframe than the original was designed for, and should not be undertaken without structural analysis. Knowing Australian aircraft certification requirements, 19-3452 surely must have had such analysis performed in order to gain certification by their authorities. The centersection cabanes appear to have been lengthened a bit from stock to raise the wing in order to make entry and exit from the cockpits easier, and the lovely (to my eye) "deHavilland style" humped fuel tank is another evident modification that provides a nice fuel increase over stock. Flying in Australia where airfields are fewer and farther between than in the states, Andrew may have wanted the increased fuel volume. Lastly, the Subaru EA-81 engine that he used in his airplane is water-cooled, but rather than mounting the radiator up at the top like the original Model A-powered Pietenpols had it, he chose to install the radiator underslung, and that's the radiator that is visible in the dark hump under the nose. The Subaru EA-81 (1.78L, 8.7:1 compression ratio) was originally rated at 73 HP at 4800 RPM, about the same output as my A75 Continental (2.8L, 6.3:1 compression ratio) but turning twice as fast, which requires a reduction drive to keep the prop tip speed subsonic where it is most efficient. I can hand-prop my engine and have no electrical system, while the Subaru has an electric starter, electrical system, and full electronic engine control module and ignition.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

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