Tomahawk 125 hp STC performance?

"Peter Dohm" wrote

That confirms what I have long suspected: I could only justify it to
operate from a higher altitude airport--which is just not in the cards.

I wouldn't think that would be the only justification.

If your are going to operate at a lower airport, that will see some high
density altitudes, due to high temperatures, for one.

If you are going to operate close (or slightly over) to gross, would be
another.

If you plan to go into and out of airports that might be a little short, or
have high obstructions at the end of the runways, as another.

If you want to do cross countries often, that involving climbing to
relatively high altitudes, it would be nice to have better climb.

If you combine two or three (or more) of the above, it would be a slam dunk
reason to go with the more HP engine!
--
Jim in NC

Peter Dohm wrote:

"Kyle Boatright" wrote in message
. ..
/snip/

Anyway, I just ran the numbers and you should expect to burn 7 gph at 75%,
/snip/
That confirms what I have long suspected: I could only justify it to
operate from a higher altitude airport--which is just not in the cards.

Peter


Peter,

I used to maintain a fleet of 152's (virtually the same engine) that we
converted to 125hp. As a maintenance decision, we did it simply to
reduce lead fouling problems in the spark plugs, a BIG issue in the
original configuration. How did it work out? Great. Why did it work?
The kit merely installs higher compression pistons. This causes a
more efficient burn, and more complete combustion.

All the folks who assume this mod will increase your fuel burn are
incorrect. It really makes a more efficient powerplant, so you are able
to realize a small HP increase at no noticeable fuel penalty. In fact,
the POH supplement that comes with the STC simply states that the
performance of the modified aircraft is guaranteed to meet, or exceed
the original figures. You couldn't make such a simple statement if fuel
burns had to be recalculated at any given power setting.

There must be some sort of compromise, though, right? Yeah, in the 152
at least, the kit also comes with modified (improved) engine baffling,
and warns about monitoring CHT's during hot or high climbs, as well as
the importance of correct mag timing. In other words, detonation
becomes more of a danger, if your not paying attention.

In the many thousands of hours of training fleet operations that I saw,
not once did we find evidence of harmful detonation. What we did see,
on about 50% of the fleet, was a noticeable reduction in compressions
around the 1500 hour mark. Removing the cylinders revealed compression
rings as soft as butter. You could almost twist them into a pretzel! A
quick hone, and new rings, sent the engines off to a succesful
completion of their run (typically 3000-3500 hours).

Mind you, these were trainers, flown by pilots who had no idea how to
properly care for the engine. All they knew was throttle in, go up.
Throttle out, go down. As an owner, I would expect you to get as much
service life out of a modified engine, maybe even more, than an
unmodified one.

Happy Flying!
Scott Skylane