Skymaster Forum - P337 Full Robertson/STOL & De-Ice

Some of you have been inquiring about the Horton STOL kit under a separate thread, but I believe the Robertson/STOL will give you MUCH better performace... Our '77 P-model has the full Robertson treatment as well as de-ice boots... boots were installed in 1978 just after the R/STOL was put on ... that's back when Robertson had their facility up in the Seattle area at the Renton Airport and later on at Everett, and costs then weren't as inflated as they are today. Ouch! It just happened that we were fortunate to run across this one, without having to do an expensive add-on afterwards.

Anyway, we've never flown any other Skymasters except for ours and another - and it too had full Robertson but without boots, so I can't give you a comparison to a non-Robertson equipped 337 - other than to say that the Robertson takes a little getting used to. The landing profile using the 'full' Robertson technique is to use a constantly decelerating approach which then requires power to arrest the rate of sink in the final portion from 50' to touch down. Final approach speed is 57 knots, with the touch down performed at 44 knots! With a little practice it becomes a fine art to grease it on with precision. The takeoff's are pretty impressive too. The ground run at 3800 lbs, zero wind, sea-level is something like 365 feet and at full gross, 475 feet to get airborne. For takeoff, the flaps go to 2/3, the nose is lifted at 44 knots, then accelerated to 57 knots over the proverbial 50' obstacle, then flaps retracted to 1/3 as you accelerate to 87 knots, or blueline. With the cuffed leading edge, it does seem the airplane flys just a bit nose low and with perhaps 5 knots faster than Cessna's published TAS in the POH. In my travels I've not seen another R/STOL equipped bird like ours with full de-ice.

With the full Robertson treatment, you get the VG's just aft of the main landing gear and ahead of the rear engine bowel, and in the upsweep of the rear cowl, which by the way are riveted on and they do provide for at least a 150 FPM increase in climb with an engine out situation. These VG's draw high-energy air into the low-pressure 'drag area' of the rear cowl area when you experience the pitch-up with an engine out. Then there are the smooth dorsal fairings that give you greater yaw stability and improved rudder control through the stall; the stall fences at the outboard 2/3 point at the flap-aileron junction gives you complete aileron control, automatic spring-loaded trim that moves the trim wheel when changing flap configuration together with drooping ailerons, and the recontoured/cuffed wing leading edge. And due to the bellcranks and pushrods for the aileron interconnects, you end up with 71.5 gallons of useable fuel per side, instead of 74 gallons.

With AA intercoolers, the RT Aerospace landing gear door deletion kit, and the R/STOL on ours, mountain flying is a cinch, but unless the aircraft is already R/STOL equipped, I would think doing an add-on would be pretty darn pricey.

I understand that a company in Texas purchased the Robertson/STOL STC mods, as the original company is no longer in business.

SkyKing