a german made hirth 650cc engine offers plenty
of “get up and go” with 65 horsepower.
Model: 87% Pitts Python
Wingspan: 17. 38 ft.
Weight: 300+ lb.
Power: 650cc Hirth
Designer, builder, and pilot greg hayfield paid no mind to naysayers
who called him a “mad fool” for building his giant aerobat.
ailerons, four on the elevators, two on the
rudder, one throttle, one tailwheel, and one
ignition cutout. For the RC, we use two Futaba
2.4GHz R617FS receivers and two 6-volt,
7Ah gel-cell batteries, and a 7-amp multi-strand cable. Dad designed a dual system
bus bar for the servos to run off a full six
volts. you may think that the batteries are a
bit small to be running all this, but the engine
has a built-in alternator, so it produces power
to run and charge the batteries while flying.
Monster Pitts Python
How do you build and fly an 87%
aerobat? Greg Hayfield tells all!
When we first saw Greg Hayfield’s gorgeous 87%-scale Pitts Python fly at the 20th annual Cosford Large Model Association fly-in in Cosford, UK, we couldn’t wait to talk to him and get the scoop on this monster aerobat. Here’s a bit of what we learned; you can go
to ModelAirplaneNews.com for more information on the plane’s design
and construction, as well as the inspections that large-scale models are
subject to in the UK.
How did you get into large-scale modeling?
I blame my father, David Hayfield, for what I’ve gotten myself into over the
years in terms of large models. So, trying to keep something that would
interest the crowd, I thought half-size was the way to go. I designed and
built a 50% Stolp Starduster with a massive (in those days!) 350cc Westlake
engine. I dragged that 12-foot plane around for many years, but the model
was over-engineered and a bit heavy—a bit like flying a house to be honest.
But it was a good learning curve. A few years later, I built a 57% Pitts 11
Super Stinker using more modern materials to keep the weight down.
Unfortunately, I found that kits and ARFs of this size had been produced,
which disheartened me after all the effort scratch-building. So, I thought
to myself: how far would I have to go before they couldn’t find a box large
enough to produce a Chinese copy? So, the 87% Pitts Python was started.
What’s your power choice?
I wanted a flat boxer engine, so I called Hirth and ordered a 650cc, 65hp
powerplant with twin pump carbs, a primary fuel pump, single ignition
system (instead of dual to save weight), tuned exhaust system, and a
reduction drive unit. The engine turns a Powerfin 3-blade, 68-inch, carbon
variable-pitch prop, and the engine mount was created from steel tubes
with rose joint ends to make the final adjustments and alignments easier.
How about the RC gear?
The highest priority is to keep it simple, so there is less chance of things
going wrong. I use Hitec 805BB 25kg servos everywhere: eight on the
Any close calls?
Five minutes into the first flight, the engine decided to seize up solid, so
I was left with a big draggy glider still aloft. Fortunately, with its very low
wing loading, it just floated to our surprise and I brought it around for a
lovely, soft first landing. Back at the workshop with the engine in bits, I
found that the fuel pump had failed and caused the engine to run lean and
seize, so I added new pistons and cylinders with extra cooling ducts fitted
into the cowling. From then on, the test flights went smoothly.
Is it difficult to transport and store?
My caravan met up with an angle grinder to turn the rear of it into a fold
down door with ramps that come out and the rest of it gutted out, except
for a bed at the end to sleep on if I need to, so that’s where the Pitts lives.
It’s dry, covered, and a whole lot cheaper than a purpose-built trailer.
How much time and money do you think you’ve spent on this project?
The model took just over five years to build. The engine and prop alone
cost over £9700. The total was around £ 15,000 [$20,000], not counting
the gear that wasn’t up to my criteria and I didn’t end up using. J
a 68-inch, 3-blade Powerfin propeller (intended for full-scale aircraft) has fully
adjustable blade pitch in flight.