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Sherpa
by Budd Davisson, courtesy of www.airbum.com

Once in a while you have an experience that so opens your eyes you suddenly realize how little you know about certain segments of aviation. And its exciting! It's damned exciting to suddenly be soaking up raw knowledge in the form of equally raw experiences which add so much to your understanding that the effect is immeasurable.

I just had one of those experiences and it kept me awake for days designing airplanes in my dreams. What has me so fired up?

I just flew the Sherpa! You know...that humungous bush bird which showed up at Oshkosh last year and looks like a Super Cub on steroids. It's the one with a severe foot condition.

More than just flying it, I was forcefully inserted into the world of hard core bush flying for which the Sherpa was designed. When I returned home I babbled on like an idiot about the experience for hours but found my tales were split and focused on two different subjects: The first was the Sherpa itself, but I found it did no good to speak of the airplane without putting it in context. It does no good to talk about a bush or utility airplane without truly understanding the world in which it lives because very few of us really know what that world consists of. We may think we know about bush flying but believe me, we don't.

I learned how little I knew about bush flying and what it demanded as soon as I walked up to the Sherpa's birthplace and company headquarters; Byron Root's hangar complex, which was located mid-field on his private strip in the suburbs of Portland, Oregon. There was maybe 350 feet of runway extending past the hangars in both directions with tall trees at one end while the last 100 feet at the other end dropped off at a steep angle before disappearing entirely at a small cliff. The surface snaked through the trees, bucking, twisting and turning as it went, and had water standing in the low spots. And this was their main airport!

Byron has been building super bush planes as a side line (he's actually a real estate developer) for years because that's what he and his friends do. They jump into their airplanes and disappear into the Oregon wilderness hunting and fishing in places which have never seen a road. That means landing where you possibly can which in turn means accepting runway lengths and surfaces which are an accident of nature, not the result of planning or preparation. Both the pilot and the airplane have to be able to handle what nature hands out. The only absolute known in those situations is that there will never be enough runway and what there is will be really rough. As I found out, sometimes it is rough beyond the imagination.

In all his years bouncing in and out of river beds and canyons, Byron learned from experience what it takes in terms of the hardware to both get in and not break. More than once he's had to walk many, many miles for help after landing somewhere and having the airplane break. In conversations with him certain subjects continually resurface and those are what formed the seeds for the Sherpa development.

His list of "musts" for a serious bush plane include:
Lots of power
Lots of wing
Lots of flap
Lots and lots of structural durability

He arrived at these through continually flying airplanes deemed to be bush planes and finding what doesn't work and what breaks.

For instance, he doesn't like spring gear and aluminium airplanes because the gear throws up rocks which tear up the tail and the gear is too easily eaten by hidden rocks and holes. He prefers rag and tube because it is less likely to suffer unflyable damage (duct tape is great stuff!) and is easier to repair and beef up.

In his continual upgrading of his own Super Cub, he kept breaking parts and beefing them up, changing and evolving the airplane until today it boasts a six cylinder, 0-540 Lycoming and what is essentially a redesigned, beefed up fuselage.

He and his friends take their flying so seriously they've enlisted the aid of a radar gun to evaluate aircraft slow speed performance. Using the radar gun they determined that many of the much vaunted short field airplanes, like the Helio Courier, may be able to fly really slowly across the airport, but when it comes time to land on an extremely short strip, they have to come in 5-7 knots faster because they have to put the nose down to see the end of the runway.

As I was to find out myself, the ability to see the exact spot you want to hit is paramount to short, rough field work. And you have to use both words together, "short" and "rough" because that's what defines most bush strips for the airplanes that utilize them on a regular basis.

A few hours after hooking up with Byron we were somewhere out in the eastern Oregon wilderness which looks surprisingly like a desert, but after drenching rains, it was all mud. We were sitting on top a small mesa with the engine idling and out in front of me, maybe 250 feet away, was a distinct semi-ditch where an old stock road had eroded into sharp edges. Half way to the ditch was a narrow swale I'd have to ride through. The entire undulating surface was low sage brush and mud. Lots of mud.

Byron was sitting in the back seat with no control stick and no throttle. He had no way to correct if I screwed up. The best he could do was scream into the intercom. I was going to have to get off on what was in front of me and then come back around and land on what was behind me. The 150 feet or so behind me started at a sheer cliff, went up hill for 30 or 40 feet, and then plateaued with the ditch at the far end. We had about 400-500 feet of runway, mud for a braking surface, and very little wind on the nose to help.

Was I nervous? Surprisingly, no, I wasn't. I'd seen Byron make three approaches and landings and for some reason, the airplane gave me so much confidence I wasn't worried. Byron must have felt the same way because I was the first person outside his company to occupy the sole pilot seat and he was turning me loose in what I thought was a marginal situation. Later I was to find that wasn't the case. 500 feet wasn't even close to being marginal.

Byron's voice was somewhere in the back of the Bose headsets (which are an absolute necessity!) but I wasn't hearing it. As the throttle went in, I was listening to my own voice inside my head coaching me as if I was a student. With 400 horses streaming out of the IO-720 Lycoming and over the tail, I just held on and tried to hold the tail wheel just barely out of the mud.

There is no way you can imagine what it feels like to be bounding over rocks and sage brush and down into a swale, while hanging on to a raging bull. My mind was speaking to my right hand, asking it to keep gently applying back pressure, while willing the airplane off the ground and away from the awful beating we were taking.

The big tires soaked up an amazing amount of what I knew were airplane destroying impacts, then we bounced once and were airborne. I held that attitude for a second, letting the airplane accelerate until it felt as solid as it had at cruise, before banking steeply around as we came out over the yawning edge of a small canyon. As I banked I glanced at the airspeed for the first time. 55 knots! I thumbed the electric trim on the stick forward for a second and grinned. At that speed the airplane felt absolutely stone solid.

The confidence the Sherpa gave in that situation was truly awe-inspiring. I don't ever remember an airplane that felt that good that slow or that early in a flight It just seemed so right that I immediately felt comfortable, which is not the way I usually feel before even making the first landing. I'm not one of those super pilots who are good in every airplane and this airplane couldn't have been further removed from my usual mount, a Pitts Special, if it tried. Here I was, 55 knots, 100 feet over a desolate wilderness in a 30 degree bank in a machine that weighed nearly two and a half times what my Pitts does and I felt good about it. Really good. That says something for the airplane.

I stayed low and bent it around in a tight pattern heading for the other end of our so-called runway, which was nothing more than a piece of raw wilderness. I punched the rest of the flaps out (40, slotted-Fowlers) and trimmed for 50 knots as I turned final.

The vertical edge of the mesa and the short, up-hill ramp which was my intended touch down spot was well up in the windshield. It was as if the airplane had no nose the visibility was so good. Also, the airplane was so speed stable, I found cross checking the airspeed was a waste of time. As long as I didn't move the nose, the needle stayed stuck in one place. I trimmed it back to 45 knots, licked my lips and visually fixated on my landing stop.

Not once in my entire life have I ever been in that type of situation, one which demanded the airplane hit exactly where I wanted and for which the consequences of failure were so great. Land short and we'd be a jumbled pile of junk on the edge of the mesa (or so I thought at the time) and the multi-million dollar investment of Byron Root and his partner Glen Gordon would be gone. Land long and I'd go slithering through the mud into the road/ditch unable to stop (or so I thought at the time).

I flew an abbreviated final but it took only a few seconds to realize the airplane absolutely followed the throttle, what little I was using of it. We weren't grinding along nose high, with the power screaming to keep us in the air. Rather, we were simply in what would have been a steep glide but we were using just a little power to flatten it out and overcome the drag.

At 45 knots everything is happening in slow motion and it seemed as if I had all day to gently move the power in and out to draw a straight line to my landing spot. Then, suddenly we were there and the spot loomed large in the windshield. I gently brought the nose up and eased the power off (Byron had demonstrated it needed just a bit of power to flair). We flopped into the mud with me sucking the stick into my gut and the airplane had nearly stopped rolling before it dawned on me to get on the brakes.

I let out the breath I had taken on downwind and grinned about as wide as I believe I have ever grinned. What an absolute, positive, unqualified blast! I looked ahead at the road/ditch I was worried about and realized I had more distance left to takeoff than I had the first time. We hadn't used much over 150 feet on landing and I didn't know what I was doing! That says a lot for the airplane.

I made a bunch more take-offs and landings on top that mesa before trading places with Byron so he could show me how the airplane really flew.

I was feeling like a bush pilot until we dropped down into a canyon and started buzzing along right over a serpentine river 1,000 feet below the rim. We did our eagle routine and twisted and turned right along with the river. As we did, Byron was pointing out gravel bars and small spaces along the bank they used as landing spots while fishing. That's when I knew I was no bush pilot and why Byron was so willing to let me flop around in the mud on top the mesa...the spots he was pointing out weren't large enough or smooth enough to orchestrate a crash, much less a landing. At least that's what I thought.

Just to prove a point, Byron pointed out a small speck of gravel sticking out of the water and said that was a good spot for steelhead fishing. He ran out all the flaps, pulled up over a rock ledge sticking out of the side of the canyon, floated around in a tight turn and dropped down close to the surface of the water. From the back seat, I never saw the gravel bar until our big baloney tires crunched onto it at the edge of the water. We bounded along over the incredibly rough surface for less than half the length of the gravel bar. I paced off our landing roll as 110 feet. We were two people, 85 gallons of gas, 65 F and 3,500 ft MSL. I had trouble pacing off the distance because the surface was comprised entirely of water-worn rocks the size of cantaloupes and I was afraid I was going to break an ankle!

This was the kind of surface that, according to Byron, eats stock Super Cub structure and it was easy to see why. Even with fat tires, the Cub's structure just wasn't designed for those kinds of loads, especially around the tail post.

Byron also says fully loaded to 4,750 pounds (2,200 pounds usable) the airplane will still get into or out of anywhere you'd dream of putting a Super Cub and loaded to lower weights can go places you wouldn't dare take a stock Super Cub. In most situations it will even out fly his big engine Cub.

Undoubtedly the most impressive part about the airplane is the ease with which a pilot could learn to handle it in the bush environment. The controls are very normal feeling, meaning neither light nor heavy and the airplane responds surprisingly quickly for an airplane that size. They have a number of aerodynamic changes in the works to be completed before certification which include a longer tail moment to take care of the reduced tail efficiency at full flap extension and a larger wing with more flap. Their aerodynamicist says they will trim another 6 knots off the stall speed with the new wing. Considering they have radared the airplane as flying 34 mph (power-on), a 6 knot speed reduction would make the airplane even easier to get in and out. In fact it would be the next best thing to a helicopter, which it is already. Byron says their goal is an airplane that can get off in less than 100 feet, zero wind with 500 pounds on board. As it is, with a ten mph wind they can do that in 72 feet!

It's this last point, the comparing of the airplane's utility with that of a helicopter, that continually bounced through my mind during the day. With the possible exception of landing on roof tops and tennis courts, the Sherpa could do probably 80% of what a helicopter does with a fraction of the purchase and maintenance cost and with much less chance of equipment breakage in the field.

When we were enroute back to home base I noticed a curious change had taken place in my mind. I found myself thinking like I used to when flying a Super Cub on skis after a major snow storm. In that situation, with skis and lots of snow, everything flat is a runway. You can land everywhere. On the way back with the Sherpa, I'd look down and see a small flat spot and think, "...we can land in that easy..." It was a very comforting feeling.

And when I saw a small remote town without a runway, I realized it didn't need a runway for emergency medivac situations. There were a dozen flat spots within city limits where the Sherpa could land with no sweat. A football field becomes an airport...literally!

The Sherpa is also faster than all but the most exotic choppers. We were showing 120 knots, which at that altitude and temperature was a shade over 140 knots true. Incidentally, while we were cruising along at altitude, the visibility in all directions was amazing. The nose is way, way down and the glass doors let you look straight down. Byron said the fish and wild life boys who were evaluating the airplane would go for the standard 29 x 11 x 10 tires because they wouldn't block as much of their view. He also said they were working on a curtain/shade for over the pilot's head because he is out in the Plexiglas and gets pretty hot.

Ignoring the airplane's ability to work in the bush, I'd be very surprised if government agencies, both ours and other country's, didn't jump on this bird as one which could replace helicopters and other fixed wing airplanes for a lot of use where ultra-short runways aren't even a factor. At 45 knots it is slow enough to do bird counts, pipeline patrol, border surveillance and on and on. It is also an airplane almost anyone can fly easily since its ground handling is so benign.

I think these guys are really onto something!


Sherpa Tech Specs

Structurally the Sherpa is a rag and tube fuselage and metal wings (airfoil 43015A Modified) with 120 gallon (to be increased to 180 gallon!) fuel tanks. But this is a serious tube fuselage...the longerons, for instance, top and bottom are 1 1/4 "x .058". Everything about the airplane is built tough to take a beating.

The landing gear, besides being massive, utilizes a shock absorber along with the bungees to dampen rebound. This shock is not an air/oil oleo because that wouldn't let the gear come back to rest quickly enough after hitting a rock. The gear might still be partial extended when it hit the next one. The Sherpa shock uses urethane washers which have a more immediate response.

The elevator trim is electric utilizing dual screw jacks and the flap motor looks big enough to move a house. It takes about 9 seconds for extension and ten to retract them.

The Lycoming IO-720 engine is an enigma to most of us because most of our knowledge of it comes from its use in the Commache 400. There it had a less than enviable reputation largely because it was tightly cowled and prone to over heating. The Sherpa team has utilized the experience of numerous Piper Brave ag operators in the area which swear by the engine. They say they go to 2,000 hr TBO will few problems. While we were flying the airplane, in ten hot-starts, it never hesitated.

They have gone through a number of propellers and have yet to finalize the selection. The four-blade they had on the airplane during our evaluation wasn't putting out as much thrust as their earlier Hartzell three-blade had.

Some foreign governments have expressed an interest in a turbine installation, but no one at Sherpa is wild about the idea. Besides doubling the cost of the airplane, they say its not going to improve its performance enough to justify the cost except possibly on floats.

The tires can be either the standard 29 inch, aircraft versions or the baloney skin tundra tires like we flew. Those are actually four-wheel truck tires with the tread ground off mounted on 15 inch aluminum, one-ton Chevy truck rims. They say they have been flying that type of tire for nearly 15 years with little or no problems. The brakes are two, three-spot calipers on each wheel.

The tailwheel is a standard 500 x 5 main gear unit and the tailwheel assembly is something that is undergoing continual revision. Because of the airplane's weight and the surfaces they intend to work off of, nothing commercial has stood up so they've left a lot of tailwheels up in the canyons. Presently they are testing their own assembly which utilizes a CNC'd 7075 pivot with a 4130 weldment fork.

The airplane is currently configured for a 1-2-2 seating arrangement but the seats are actually wide enough for three across in a tight squeeze. The single front seat will be changed to a side by side arrangement for those who want it along with a sliding, side opening door in the rear of the fuselage for passengers, cargo or litter cases. Knowing what little I know about bush flying at this point, I'd rather have the single pilot seat so both sides of the nose are visible on landing.

The floors are a honeycomb sandwich and production airplanes will have a multi-use track system which would allow easy removal or repositioning of seats as well as cargo tie down. The cargo space aft of the pilot's seat will accept the equivalent of five 55 gallon drums. Useful load is just short of 2,200 pounds!

It's some kind of hoss!

Wing Span 42.6' (present wing)
Wing Area 258 (to be increased)
Fuel Capcity 121 Gal (180 in production)
Empty Weight 2585 lbs (includes survival gear, tools, etc)
Gross Weight 4750 lbs
Useful Load 2165 lbs

Performance
Takeoff roll (3,000 lbs., 0 mph wind) 135'
Landing roll (3,000 lbs., 0 mph wind) 145'
Takeoff roll (3,000 lbs., 10 mph wind) 72
Landing roll (3,000 lbs., 10 mph wind) 77'
Takeoff roll (4,750 lbs., 0 mph wind) 396'
Landing roll (4,750 lbs., 0 mph wind) 282'
Takeoff roll (4,750 lbs., 10 mph wind) 272
Landing roll (4,750 lbs., 10 mph wind) 191'
Cruise speed, 75% 160 mph
Fuel burn, 75% 20.1 gph
Economy cruise 15.5 gph