Thu Nov 15, 2007 10:30 am
There are quite a few variables that you guys are overlooking where ag aircraft selection for modern operations are concerned.
The only reason for a guy to move back to a round motor I see is less volume overall due to ground rigging, chemigation, fertigation, and genetic alteration. The down sides are too great.
Number one is that most of us run real hard for two months or so a year, make it or break it. 200 hours a month for a round motor requires a mechanic performing unscheduled maintenance in the middle of the night (unless you do night work then it's oposite) or worse, missing out on work during the day.
Number two - fuel - yeah they may only burn 35 gph instead of 45-55 gph but it costs more per gallon, in some cases as much as $.45.
Number three - fuel - it BURNS more easily. I don't like the prospect of crashing in a Low Lead burner at all. Jet-A is way more friendly when shit starts flying apart.
Number four - fuel - If neccessary you can burn number one kero or home heating oil, and even though I wouldn't due to dye build up on the t-wheel causing imbalance, red farm fuel. 100LL can also be burnt in the PT-6 for short periods. You can burn auto in the radials as well but there are differing opinions on that just as the variable fuels in the turbines.
Number five - aircraft size in a modern world - Due to the decrease in our use overall we are ferrying further and further all the time. A 600 is only going to haul 350-380 gallons. Where a 500 gallon airplane will haul 450-480. That difference could mean fewer ferries at as much as 25 miles one way for me personally. the extra load with the round motor negates the lesser fuel burn of it. This is an isue that will only get worse with new containment regulations. Guys aren't going to want to build $40,000 pads at every dirt strip for a little work so they'll start ferrying from home.
Garretts - The new AD for less than -10 or -11 (I believe) engines makes many of them more expensive to operate. Basically Honeywell (after a couple of uncontained catastrophic failures) realized that ag and jump operators are starting them up and flying 20 - 50 loads without a shutdown. So they abbreviated the cycle count formula which made many of the wheels timed out instantly and made the cost per hour go up.
They are loud as hell on the ground which makes it hard to operate at certain strips near people and makes it hard to talk to customers/ fieldmen without getting out. Ingestion of objects (birds) even with an intake screen is a problem and has caused failures. Ingestion of corrosive chemicals such as liquid fertilizers and Cotton Quick is a problem due to the fact that there is no filtration.
I have also personally witnessed some wierd "voodoo" on Garretts where they run and run with no problems for a while then a chip light comes on and then you can't saxrifice enough chickens to fix them. I have seen a -10 on and off an airplane three times in 125 hours with over $50k spent EACH time!
Overall for ag they weren't meant for this application, they were meant to be APU's. Strated up and run at constant power for long periods in a concrete environment. The MU-2, Aero Commander, King Air profile works for this; roll off a shiny floor, taxi out and take off on pavement, fly at FL 220 for three hours, land FOD-free on pavement, taxi in, shutdown, and push back in to the shiny floored hangar to get buffed on. Not start up and take off on dirt, dust, rocks 50 times a day, while ingesting fertilizer dust/ liquid chemicals while dodging birds.
Fuel burn is less which is a benefit in these expensive fuel times.
Walter's - never flown one by the way, just operated next to a couple. Seemingly good on the surface as far as maintenance. The cost of these has gone up over the years so they aren't as good of a deal as they used to be when they were trying to certify the D's. I lived in Deland, FL when Turbine Design was working on them in 1995 on Cat's, Thrush's, 301, etc. and the price kept going up and then they couldn't get certified at all.
On the certified engines front they seem to pull a bit less than compareable H.P. due to the prop. This has been fixed a bit by the three blade instead of the five. They are fast though once you get them going. In the certified world you HAVE to send the engine back to Europe to O/H and once they got your shit thousands of miles away you gonna argue when they say it ain't what it was supposed to be. On the non-certified front South African John at Dimech turbines in Deland can do the work fairly reasonably.
They also seemed to lose power faster than PT-6's when hot or high. Of course they have a hot/high model for more money but then you are getting close to the price of a PT-6.
I also have heard rumors of an AD but I'm sure a64 knows more than me on that.
PT-6's - EXPENSIVE - But damn they do it. With the filtration systems that the ag aircraft manufacturers have come up with they are a freakin' horse. There aren't many ag operators that will argue with the efficiency of a 500 gallon PT-6 powered ag plane. VESATILE, you can haul a 50 acre load 15 miles on one job and not lose your ass, then turn around and get 1,500 acres of work done in a reasonable fashion time wise. When it comes to dry work 65 cubes gets the work done reasonably fast even when ferrying. Don't get me wrong I've flown them all and bigger CAN be better BUT when the phone stops ringing the -34 500 gallon airplane won't eat you at the bank. Fuel burn a bit higher but they will do it to it. I'm not saying this is good but I'll give you the numbers on mine (it is the only affordable way to start into the business in a turbine) mine has 14,500 hours on it, more than most fly in a lifetime, NEVER BEEN OVERHAULED, hot sectioned every 700-1000 hours (last one cost me $8,000 dollars after 1150 hours, next one will be @ $40-50,000 though), ONE gearbox inspection at about 8,000 hours (probably $25-35,000). That's it. Now it is going to nickle and dime me if I'm not careful but there are two guys that rode the equity out of it and made an ass-load of money. Assuming that it has averaged $750/hr gross over it's lifetime it has grossed $10,875,000. That's almost 11 million dollars for about $500,000 in engine maintenance costs over 28 years. Here again though I don't bullsh*t myself about what I have, I know that I bought low up front, it will cost more along the way, and I'll need a little luck for a few more years until I can get on my feet and trade up.
Other notes; I have 8,000 hours of PT-6 time having flown almost all from -20 through -67. Almost 3,000 hours of Garrett time -1 through -11. Only about 1200 hours of round engine time.
NONE of them have ever quit me.....yet.
The most important thing in ag aircraft selection is that it fit's the individual operator's situation but it has got to be something special to go BACK to radials.