"Corky Scott" wrote in message
...
On Sat, 27 Mar 2004 13:39:39 -0700, "Bill Daniels"
wrote:



Thanks for the nice reply. Now I have another question that, while it =
is about engineering, also relates to a market opportunity. First a bit
=
of background - forgive me if you already know all this.

I fly gliders which are most often hauled into the air by a tow plane. =
Now glider tugs belong to the same engineering category as tractors used
=
for tractor pull competitions - brute force and not much sophistication.
=
For spark ignition, air cooled engines, glider towing is brutal work - =
red line temps followed by rapid chill down five or six times an hour.
=20

Sometimes, the tug is asked to tow a 1300 pound glider into a mountain =
wave at 15,000 feet which can really tax the engine's cooling capacity =
as well as high altitude performance. =20

A Piper Pawnee with a 260 HP Lycoming O-540 has enough power for the job
=
but, without some VERY careful operating techniques, overhauls come up =
often. Fuel consumption on a Lyc O-540 runs over 20 GPH. All this =
makes glider tows far more expensive than they should be. A Pawnee with
=
a standard 2-blade prop is also noisy enough to prompt airport neighbor =
complaints.

A glider tug tows at about 65 knots and speeds above that are =
unimportant. The power package needs to produce maximum thrust for the =
HP at that airspeed. This fact suggests that a large, slow turning prop
=
or perhaps a ducted fan could do the same job with much less horsepower =
- and noise. =20

A 160 - 200 HP Deltahawk looks like a perfect match for the job if it =
were matched to the correct prop. Would you please comment on this =
application?

Bill Daniels

Bill, I have a question for you: Why is the O-540 overheating? You
are climbing using full rich aren't you? If you are, then the engine
should not be overheating. Full rich for takeoff and climb is called
for so that the overly rich mixture burns slow enough to allow the
Peak Pressure Point to occur around 16 degrees past top dead center.
As long as the timing of the magnetos is properly set and the mixture
valve is working properly, it would be nearly impossible for the
engine to overheat. It does use a lot of fuel with that setting
though.

You might be interested in the Ford powered Pawnee developed by Dave
Sharples in Australia. It's been running for about six years now
since they installed it to replace the O-540. Swings the same prop at
the same rpm but uses a lot less fuel. The engine took a long time
for them to sort out, but once they got it running the way they
thought it should, they've bascally forgotten about it, other than
routine oil changes and spark plug changes.

They developed it strictly for glider tug duty. They were very much
hoping to reduce the overhaul costs for the Lycoming.

They managed to do that.

Corky Scott

As I obliquely mentioned, you need to be VERY careful with the Lyc's
operating procedures. Running rich of best power is one of them.
Unfortunately, that cuts climb performance which can lead to other dangers
such as taking the glider out of gliding range of the runway during the
initial climb. It also washes oil from the cylinder walls accelerating
cylinder wear, fouls plugs and contaminates the oil among other bad things.

In addition to running rich, there is a cool-down protocol after the glider
releases. All of this helps engine life at the cost of fuel consumption and
the number of revenue tows per hour. Mess up the engine operating protocol
just once and the life of the engine is compromised.

Economically, glider towing teeters on the brink of being a big money loser.
Profits are very elusive and disaster is always close. If an operator is
smart enough to make money at it, he's probably smart enough to get
seriously rich doing something else.

Yes, I am aware of Sharples Ford powered tug. I think it's an all-round
great idea. I just wish the FAA would open a loophole in the regs to
permit that kind of experimenting here. Unfortunately, the FAA considers a
glider tug a "for-hire" commercial operation and damn near enforces Part 135
regs.

The Deltahawk seems to have even more advantages than Sharples Ford plus it
will be certificated which will satisfy the Feds.

Bill Daniels