Quiet! Master Craftsman at Work
Building a Stewart S-51
Builder: Owen Smith
Well, if you haven't been in the hangar in the last oh, say, eight months, then you might have missed Owen's S51 that has been taking shape in the #2 hangar. This man can build an airplane. The quality is outstanding and the attention to detail is bordering on art. We've all been watching as this beauty takes shape. We've all cheered him on and watched in amazement as, little by little, you see the replica's shape emerge from the otherwise pile of parts. Take a look below for an in depth look at the construction of this wonderful aircraft.
by Owen Smith
The Stewart 51 is an aluminum P51 replica at 70% scale. It comes as a kit with most of the metal forming, fitting and trimming already done. Most of the rivet lines are pilot drilled, then the airframe is assembled and pop-riveted together. The builder must generally take everything apart and reassemble it with structural rivets, install all the systems, etc.
Pictures 1 and 2 show the start of this process. Here the fuselage and wings are stripped down to the skeleton and installed in simple holding fixtures. The S51 uses wet wings. The main tanks (70 gal) are in the inboard part of the wing aft of the main spar. I installed auxiliary tanks in the outboard part of the wing forward of the main spar.
Picture 3 shows one of these tanks in pressure test. I leak tested each tank surface with water as they were put on and before the surrounding structure was closed. This made it relatively easy to find and repair leaks. The final tests with air were anticlimactic. Everything passed on the first try.
Picture 4 shows the fuselage with most of the skins installed and the scoop and radiator attached. The scoop comes preformed, but the builder must do the trimming and fitting, install the radiator and the electrically actuated air outlet door.
Picture 6 shows the wings being mated. The wing halves bolt together at the root, just like the real P51. The missing sections of skin form the top of the main fuel tanks. It's easier to install the mating fittings before these are riveted on and sealed.
Pictures 8 and 9 show the cowling installation. The cowling comes mostly formed, but the builder must fit and trim it. Generally, the installation is done working aft from the spinner backing plate to the firewall. About one third of the total fuselage length is forward of the firewall. The empty CG of the completed aircraft is about even with the forward edge of the windscreen.
Picture 10 shows the first fitting of the engine and propeller gearbox. The engine is derived from a big block Chevy V8. The PSRU is a spur gear unit, like in the real P51. We use a prop from a Cessna Conquest. The intake manifold shown is popular with boat racers because the long runners give excellent low to mid range torque. We had to chop 2 inches out of it to get it to fit. Oh well, so much for the long runners!
Pictures 12 and 13 show the partially assembled engine with the gear driven accessory case. The reverse rotation engine is based on a tall deck Donovan aluminum block. It has 4.5" bore and stoke, giving 573 CI displacement. The compression ratio is 9.2:1, so 92 octane pump gas can be used. It should make nearly 600 hp at maximum (4750) rpm, normally aspirated. The accessory case is a spur gear unit which drives the alternator, dual Bendix magnetos, duel sprint car style water pumps, dual dry sum oil pumps, a sprint car mechanical fuel pump, a vacuum pump and the propeller governor. There is also provision for driving a Vortec centrifugal supercharger through a sub-gearbox. We use Airflow Performance mechanical fuel injection.
Picture 14 shows the uplock assembly in the right wheel well. The gear retraction (tailwheel too) is electro-hydraulic. The landing gear, custom made wheels, retraction mechanism and Matco brakes are supplied with the kit.
Picture 15 shows some of the equipment installed under the seats aft of the main spar and just ahead of the radiator. You can see the insulated stainless steel coolant lines which run from the firewall to the radiator. The plenum box and air ducts are associated with the cabin heat and ventilation system. The system is just like you find in automobiles. We use a GM aluminum heater core, which is installed at the bottom of the plenum. The aluminum radiator is visible at the bottom. This comes with the kit.
Picture 16 shows the cockpit and mostly complete instrument panel. The landing gear selector lever is on the lower left, as in the real P51. Environmental controls (heat, air and defrost) are installed in the top of the landing gear selector console. Above that you see the regulator and pressure gauge for a constant flow oxygen system which is installed permanently in the aircraft, and above that the P51 style throttle quadrant. The circuit breaker box is not visible on the left. One of the rear rudder petals is visible in the lower right corner. The S51 is a 2 seat tandem aircraft. The rear passenger's legs extend along the sides of the pilot's front seat, as in a Cub.
Picture 17 was taken while the usable fuel capacity was being determined. It turned out just short of 100 gallons. The airframe is complete except for the dorsal fin and rudder. When it finally flies, we expect to see a top speed slightly greater than 300 mph in level flight, about 4000 fpm climb and a service ceiling of about 29000 ft. These figures are for the normally aspirated engine. I won't mention what the fuel flow is for all of this. It ought to be a big hit at the gas pump.