View Full Version : The Pawnee Snowplow

02-06-2004, 11:45 PM
(Long, sorry, a three-beer story)

It all started innocently enought while I was working on the Duchess of York's leaky radiator. (For those uninformed readers, the Duchess is our Glider Club's beloved 1949 Ferguson Tractor, a.k.a. "Fergie". You can recognize her by the "tasteful" nose-art on her cowl, a portrait of her namesake, such as seen on p.2 of the London Tabloids. But I digress.)

It looked like she might be down for repairs for awhile, and it seemed we might have to do some snow plowing around the Gliderport soon. Then I had an epiphany: Our Piper Pawnee towplane was designed for agricultural service. Why not give it a try? With 235 horsepower available, it ought to perform like those big four-wheel drive Steigers that work the big acreages around our parts.

As a simple test of the concept, I hitched the Pawnee up to the ten-ton turf roller we use to smooth out the moguls on the field, using the glider tow hook on the back. It took a little more power to get rolling than I expected, about like a Twin Grob with two up, but once underway the Piper worked just fine.

Rumors that I actually lifted off with the roller in tow were probably embellished at the ensuing "safety" meeting at the Duke of Wellington. What actually happened was that the roller actually "did" lift off, and started to "kite", and I immediately released it. The Pawnee accelerated with alacrity, and lifted off immediately.

The observors on the Liars' Bench mistakenly assumed that I had towed the roller off, but that's an exaggeration. The roller lift-off was probably due to Magnusson effect, whereby a rotating cylinder is able to sustain lift, e.g., a spinning golf ball or a baseball.

While idly thumbing through the Northern Hydraulics Catalog back in the office, I noticed a hydraulic pump with the exact mounting dimensions and drive gear as the standard 211/212 series aircraft vacuum pump. The vacuum pump pad on the back case of the O-540-B2C5 was available, since no gyros are installed. With a couple of hydraulic cylinders tied into the spray gear hard points, we could have ourselves a "jen-you-wine" farm tractor three-point hitch with full live hydraulics for accesories such as the grader blade we already own. Since it really wouldn't be used for flight purposes, no Form 337's, Field Approvals, or STC's would be required.

During the safety meeting that night at The Duke, I proposed the project to those at the table. George immediately saw the possibilities, and an enthusiastic discussion ensued. In the finest traditions of The Skunkworks, sketches were made on the back of cocktail napkins. George kept asking the waitress for another picture, but being from Rural Missouri, he mispernounced it "pitcher." She just kept refilling our beverages.

Before we knew it, George was taking up a collection to fund the project, and soon had the rapt attention of the entire crowd at the bar, Ranchers, Farmers, Bikers, and Glider Bums alike: He attacked the challenge with evangelistic zeal: He shouted, he whispered, he wept. He pounded on the pulpit--I mean bar--and convinced us all that this project would cure warts, athritis, and the heartbreak of psoriasis, and save the American family farms in the bargain.

A "Substantial" sum of cash and the pledge of title to a '74 Harley Davidson were collected. At last! A project worthy of that Internationally renowned handyman, Red Green of the Possum Lodge. Handyman's Corner, here we come.

Now I don't have much experience with hydraulics, but I do occasionally dabble with pneumatic acutators and stuff at work. Recalling that Fluid Dynamics course, and John Reynolds' dictum "Fluids is fluids," how hard could it be?

We quickly obtained the pump, a triple-stack of three-spool valves, and some honkin' big cylinders. Rich fabricated a sturdy adapter to the existing spray gear mounting points, and with a little minor trimming by Dave with his Dremel Tool, everything fit together pretty well.

We learned a lot from the first trial run. Everyone was impressed with the way the propeller sliced through the crusty snowdrifts. Dropping flaps helped mash down the windrows of snow. On the down side, traction on the icy runway was a little dodgy. There was a minor issue with pump rotation and pressure/suction hoses to the hydraulic cylinders, but several layers of yellow duct tape covered that up pretty well. We also discovered that with this setup, hydraulic pressure, and therefore cylinder response, is pretty much a function of engine speed. The ensuing slide into a snowdrift resulted in one of the most thoroughly stuck vehicles since the Duchess of York groundlooped into a barrow pit a couple winters ago.

We were going to remount the propeller backwards and back it out, but Frank had a better idea: Why not winch it out? This worked amazingly well, and with a few thousand feet of cable strung out from our glider winch, it was easy to pull the Pawnee out of the snowdrift from the warmth and comfort of the hangar. The only mishap was when Frank got a little too enthusiastic.

Apparently with a "glider" being winched from the back, the "slow down" signal was difficult to interpret, but the tow release once again saved the day. Frank thinks we can turn this into a profit center with a modest investment in another mile of cable, by winching cars out of the ditch on The Interstate without ever leaving the hangar.

As I said, we learned a lot. First of all, I like working with hydraulic systems a whole lot better than pneumatic ones: It's a whole lot easier to find leaks with a red oil stain than with a vaporous air leak. We also learned that old garden hose that's been sitting out for ten years is not the ideal material for high pressure hydraulic applications, no matter how many wraps of duct tape you apply. On the bright side, that oil slick on the end of Runway 19 Left should help keep the dust down next summer.

The Phase II revisions really helped a lot. It turns out that hydraulic systems with high, but intermittent, loads can benefit from an accumulator system and pressure control valves, to give a little extra boost when needed. A long-time friend of The Club, identified only as "Captain Nemo" donated a genuine aircraft accumulator/regulator system from a Cessna 177RG, which had been the test bed for an unsuccessful attempt to convert the Cessna into an amphibious flying submarine. [My brother-in-law, Dooley, had generously offered the spare hydraulic power pack he keeps on hand for his Swift; I politely declined when he said it ought to work "just as well" in the Pawnee as in the Swift.] Authentic Mil-Spec hydraulic hoses with approved firesleeves and lots of Adel clamps were installed to support the long hose runs.

To aid traction in icy conditions, the hopper and spray booms were brought into play with a good soupy mixture of aqueous calcim chloride to be sprayed while underway. Jerry fabricated a nice set of cable tire chains from discarded winch cable and nicopress sleeves. We were ready to give it a go, and just in time, as there was a nice six-inch layer of power snow, with drifts to boot, on the runways.

The first thirty seconds went pretty well. Unfortunately the dry powder snow quickly obscured the blunt windscreen of the Pawnee. The pitot tube iced over, so airspeed indication was lost, and the wings were icing up.

The "helpful" steeting suggestions on 123.3 from the slackers all warm and snug in the office were difficult to hear on the radio in the freezing cockpit (no heater, due to the Aircare Exhaust System...). Turns out they were were yelling "tree!" and "hole!". I thought they said "gee" and "haw", just like driving mules.

From another Engineering Design Conference, Gary and Eric generously lent their GPS and Datalogger from the LS-4, with each end of the runway preprogrammed. A little duct tape held the nav system securely to the panel for a sort of heads-up display.

George had just finished trimming the wick and refilling the kerosene space heater with surplus Jet-A fuel, so that too was quickly duct taped into place between the rudder pedals, and we were off again, warm and able to navigate.

This time everything went really well for awhile. Dennis claimed to have seen those Big Airport rotary snowplows in operation once, and said the Pawnee Snowplow was almost exactly like that, except that the Rotaries mostly blow the snow up in the air and away from the runway, rather than over the wing and fuselage, and back onto the area just cleared. But that's a small detail. The improved hydraulics worked just as planned, laying out a nice windrow off the edge of the blade.

When we downloaded the GPS trace, it was perfect, too. Straight as a string on the runway courseline, although there were some significant altitude deviations. Hey, towpilots nerver have been any good at holding altitude, even on the runway. Plus or minus 800 feet is pretty good. Never mind those scrapes on the side of the hangar, and the dinged wingtip, they must have been like that before.

The final lurch, of course, dislodged the kerosene heater, and burned through the duct tape. The ensuing fire melted the bottom out ot the fiberglass hopper, but the calcium chloride mixute quickly extinguished the flames. I personally think the resultant black trim on the top of the cowl looks nice, and it cuts the glare. Rich has since repaired the wingtip, and rebuilt the truncated chemical hopper into a convenient cargo hold.

All-in-all, this has been a really successful project by Gliderport standards: There was no DIRECT expenditure of Club funds, and the Prairie didn't catch on fire. Just don't ask me to be the test pilot when we mount the bush hog to the three-point hitch, and route the driveshaft through the pilot's legs.


I was over at [an un-named agstrip] helping a friend with his Pazer, and started admiring the new spray planes. They're huge things called Air Tractors, with the turboprop off of a Kingair, complete with reversible prop to back out of snowdrifts. I've come to love the smell of kerosene in the cockpit.

Frank has found a good used blade and bullring off of a Cat #12 Motorgrader that we can adapt for snowplowing. The Air Tractor ought to work well as a towplane, too. It'll only take some minor modifications to the hangar to get the 60' wings through the 40' hangar door....

We now have a serviceable backup snowplow, but could use a backup towplane. Never fear, while remounting the radiator on the Duchess of York, Ron noticed that she's already equipped with a four-blade prop on and water pump, and has a factory tow hitch. I know where we can get some used C-177RG wings, and ...how hard could it be?


While on one of George's infamous Sunday Supercub breakfast flyouts to a small town out on the prairie, who should we run into but old-friend Craig, the local ag-pilot. He was busy schmoozing the local farmers about the prospects of the new season.

"Hey, how's that Pawnee workin out for ya"? I winked at George and launched into the tale of the Pawnee Snowplow [no, I'm not going to rewind like C.W. McCall in his classic album cut "Classified Ad" or this mess would never end.]

Now Craig operates those Snows, only he prefers to refer them as "Thrushes" to divert snide remarks about "Yellow Snow." But once again I digress.

Craig politely listened to my three cups-a-coffee story, pulling calmly on his pipe. Then responded: "Oh, I did that years ago. That's why they call 'em Snow-Plows".

Uff Da.

12-25-2004, 02:58 AM
i bet i can make this a six pack story. lol jk

12-25-2004, 09:06 PM
If I remember correctly, the girls were always located on page 3, right side with the paper open.

As the ads said when Fergie - The Duchess -had her toes exposed "Life is better in the Sun!"

You had to be there. If you were, you'll understand.


12-26-2004, 08:44 PM
Oops, sorry, Stearman 600, I stand corrected.

But you should see the "nose art" on the Fergie Tractor.

By the way, she may be for sale soon, as sometimes conflicting duties between the Duchess and the Pawnee, now that we've got some snow....

12-27-2004, 10:15 PM
The very best "Nose art" I have ever seen was on the side of an Auster at Little Gransden, Bedfordshire, UK. Without wanting to offend even the gentlest sensibility I will describe this work of art entitled "Shepherd's Delight" as a well, let's just just say a rather buxom little lamb. :-?

01-07-2007, 07:10 PM
Well heck, guess my re-post didn't take: Had to mount up the snow plow on the Pawnee again. At least it was a safe "safety" meeting at The Duke.

Thanks. cubscout

01-07-2007, 07:34 PM

01-07-2007, 10:43 PM

That's about the finest engineering tale I've ever heard. I love it. :D


01-07-2007, 10:49 PM
Murph, hey! Don't start on me, just because I impersonate an engineer sometimes :-?

Thanks. Hope to see you at some cub gatherings this spring/summer. :D

Thanks. cubscout

01-07-2007, 11:59 PM
And Murph, you DID meet that same George down at Ruidoso a coupla years ago: His Supercub is now so nice he doesn't want to get grass stains on the tyres...

But he helped us plough out today.

Thanks. cubscout

01-08-2007, 12:06 AM
Good "chatin" wit ya tnite cubscout, that is the great thing about this site, the people ya meet online and in person don drink over 3 or 4 of them pictures Ye Haw.


01-08-2007, 10:40 AM

I did? He ought to be ashamed for messing up a good usable cub like that. :roll:

Were you there, too?

Raise your Raybans so I can see who you are. 8)

Anyway, being of the rural and somewhat agricultural persuasion, I can certainly appreciate newfound technology and good clean Southern engineering when I see it. :o That Pawnee story is priceless.


01-08-2007, 11:13 AM
That's great cubscout,

The nice thing about being a part of aviation, is that when someone is talking or writing, you can always put yourself there and envision it.
The Pawnee looks pretty Cocky to me. :cheers to ya on that one.


Ruidoso Ron
01-08-2007, 12:59 PM
Cubscout, I've started to fabricate a rig like this for my 150 horse SC. Please let me know if I need to make airspeed adjustments for the change in horsepower or altitude.

01-09-2007, 07:44 PM
Ron, spray mount details are quite different on the Supercub, so the plough mount details would change. I'd think it wouldn't be as rigid as the Pawnee, but at least wingtip clearance on the drifts would be better. And the flaps wouldn't help mash down the windrows on the Supercub. I need to find those pictures....

Of course it wouldn't work very well if you're running a Sorenson belly tank for the aqueous calcium chloride, due to clearance interference with the blade, but the Factory -A hopper should be OK; I might try some magnesium cloride next time, as it works better when it's really cold.

Power and mixture settings will take some experimentation: We're about the same altitude as Ruidoso, so peak EGT +150 rich, or peak RPM and the enrich 'a skosh" should work OK. But we've only got a couple thousand feet to plough out, unlike Ruidoso. Unless of course you were going to help out the folks down at Timberon.

I'd think the 150 or 160 might bog down if you work the hydraulics much, so a 180 would be better. And verify the firewall clearance for the hydraulic pump, too: The one I used is somewhat longer than the 211/212 pumps, and they're pretty tight as it is. And check pump rotation and cylinder cycling direction BEFORE you start ploughing; you DON't want to know how I found this out.... :oops:

And don't forget the tyre chains, unless you've got Warn Hubs, like that experimental that one o' the Bayou Boys is running; I'll bet he had the hubs locked in last week, too!

Keep us posted on your project, eh?

Thanks. cubscout

01-10-2007, 04:59 PM
Murph, yeah we were both there, but not "officially": George didn't realise what he'd walked into, and didn't want to pay the seemingly outrageous camp fee [in retrospect, it would would have been cheap at twice't the price], plus we only had a day or so. And we parked on the ramp, rather than at the east end of the fence.

George's Supercub was up somewhere in Warshinton State for rebuild. He gathered lots of ideas [which was the point], and increased his bill conSIDERABLY, as Clouddancer would say.

Despite the tee-shirts and jeans, we apparently were suspected of being from the Friendly Flying Agency, a lie. Heck, next time I'll show up in a dark suit and skinny tie, and watch the Subercubbers scatter like cockroaches when you turn the light on....

Feel free to share this marvel of engineering mastery with all of your agricultural friends, anRed Green from the Possum Lodge, too.

Thanks. cubscout

01-15-2007, 12:04 PM

I may just submit this to the Smithsonian or at least the Junkyard Wars folks.