Heinkel He 8-31 (oz8117)


Heinkel He 8-31 (oz8117) by Ed Westwood 1995 - plan thumbnail

About this Plan

Heinkel He 8-31. Radio control scale model floatplane, for electric power.

Quote: "At last, a micro-sized Sport Scale Float Plane for a quiet day at the lake. Heinkel He 8-31 by Ed Westwood.

A Stand Off Seale Electric Seaplane. Back in the 20's and early 30's, Ernst Heinkel and his associates designed a series of low-winged, very large span, monoplanes exclusively for water use. The more noted were the He 4,5, 8, 12 and 58; all radial powered. The end of the series culminated with the He 31, an 800 hp Packard powered test bed.

Two noticeable features of all these ships were the extensive use of the float-wing strut combination which helped carry the wing loads and a distinctive TE cut-out which took the place of the 'no step' sign since it hadn't yet been invented. (Editor's Note: The distinctive wing trailing edge cut-out was not used on the original prototype model and, therefore, is not shown in the construction photos; however this cut-out is shown on the plans and depicts the correct wing shape.)

RCM carried the 40 size HM-II (oz5261) a Danish He 8, in its June 1978 issue. Several of these ships show up each July, at the NW Scale Seaplane Championships held at the Pine Hollow reservoir in Oregon.

I chose the He 31 for an electric since the geared 035 could be cowled in for lower drag and finding a 1/4 scale radial is nigh impossible. The ship was sized to keep the wing loading below 16 oz /sq ft. Thus, the 40 inch span. Most of these ships were either camouflage or gray but I kept the red paint scheme of the arctic exploration HMII's for visibility. Should the builder desire to make his ship resemble the He 8, a nine cylinder Jaguar will need to be simulated.

CONSTRUCTION Fuselage: This is typical free flight construction: two sides built right over the wax paper covered plans. The sides are then lined up and assembled. The battery bottom plate installed and then the motor in its mount. The Cannon rudder and elevator servos are cut in the rear of the battery plate and the receiver battery configured to fit just aft of F-2, the wing attachment bulk head. The entire radio and motor system should be installed and tested before the fuselage is covered. That way should any problems be detected, they can be resolved more easily. Remember not to sheet the bottom of the nose until the forward hold-down holes are drilled.

Wing: My prototype wing was constructed with internal slide-through spars, but the final design uses four balsa 1/8 spars with thin webs between. Make a rib pattern out of plywood and cut one rib to check for spar fit. Adjust the pattern as necessary and then cut out the remaining ribs. Note that the ailerons are built right into the wing and cut loose later.

The Riblett semi-symmetrical airfoil was selected for its soft stall and low pitch sensitivity. The airfoil, however, has its down side and that is construction. My suggestion is to split the wing rib along the dotted line and build the top of the wing first, then add the bottom rib sections and finish it up. I used individual aileron servos. With hindsight, one servo and its associated linkages or 1/2A throttle cable would have served just as well.

Whichever way you choose to proceed, remember to make the appropriate cut-outs in the ribs to accommodate either the cable or wires. As you proceed, keep in mind the fact that this ship should only weigh 2.5 lbs ready to fly, and all material should be selected with that in inind. Now, position the wing on the fuselage and drill through F-2 into the wing LE, then the rear hold-down holes are drilled through the TE. Tap the fuselage blocks for the 10-24 nylon screws. Now the bottom of the nose can be covered..."

Update 23/1/2023: Replaced the article with a clearer copy, thanks to AugustaWest.

Update 11/7/2023: Replaced this plan with a clearer copy, thanks to theshadow.

Supplementary file notes

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Heinkel He 8-31 (oz8117) by Ed Westwood 1995 - model pic


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