P337 Full Robertson/STOL & De-Ice

[SkyKing]

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

[mikezen]

Hi !
I posted a question today about re-installing de-icing boots on a P337 that had them removed why R/STOL was installed.
Is it legal and do you know a shop who does it ?
Thanks for your answer

[mshac]

Originally Posted by mikezen

Hi !
I posted a question today about re-installing de-icing boots on a P337 that had them removed why R/STOL was installed.
Is it legal and do you know a shop who does it ?
Thanks for your answer

SKYKING has been banned here for over a decade. Plus, IIRC, he sold his P-model and bought a P210.

[chrisb]

No idea, but I'm currently deep in the restoration of a Riley P337H that has a Robertson STOL kit and De-Ice boots. If you need anything feel free to drop me a line. Wings are currently in storage at my other place but I can go take photos if required.

[mikezen]

Thanks for your answer !
Yes, I would be interested in some photos, especially the end of the boots and the negative leading edge camber areas.
Take your time, no emergency !
Do you know if the boots are same size then original P337 ones ?
Could you also mesure the boots dimensions for me, please, including the horizontal stabilizer boot ? I will compare with the original ones.
About certification, do you know if the boots are part of the field certification or are they parts of the R/STOL STC ?
If your Riley is a Super Skyrocket, the useful load is rather low : does it have a gross weight increase to 5120 lbs ?
Thanks for your answers

[cbxmike]

So, I just purchased my 2nd Skymaster. Yes, I’m a glutton for punishment and weird planes. This one is a 1977 P with full De-ice and a partial Robertson STOL (Cuffs only), with three bladed MT props, and the gear door mod. There are VG’s on the fuselage behind the mains in two areas as well. We are moving to a grass strip that’s not the greatest (yet) and my question is rear prop damage? These Skymasters seem to have an oddly decent short field performance for a light twin, but will my rear prop take a beating over time? Mostly grass with some dirt and light shale type rocks in isolated spots. My last Skymaster took a small bolt through the rear prop after another mechanic did some work and before I could do a thorough inspection. It damaged a rear blade pretty good, so I’m a bit worried about heavy use on grass strips. Any insight, guidence or differing techniques would be great. Mike.