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#11
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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 |
#12
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Tomahawk 125 hp STC performance?
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 |
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