Love my P337, want to climb faster

[dan1000]

I love my 1974 T337G (pressurized), and am looking for ways to improve the climb segment of my flights. If any of you are flying on higher horsepower than my Riley-intercooled TSIO-360's (225hp, I believe), I'd love to learn about your experiences in upgrading or operating. The search button has reported that some people are operating TSIO-520-NB's, though there are questions about handing their extra weight.

Why am I interested in climbing faster? The aircraft is fast enough in cruise, but a typical MGTOW climb from sea level to 13,500 ft is about 25 minutes, and to 17,500 feet would increase that to about 33 minutes. This all happens at 120kts in an attempt to hold CHT under 400 degrees. However, it's often ISA+20 here in SoCal, so I'm frequently pouring several GPH of unburned fuel out the exhaust to keep below 400. So that's an *average* climb rate of around 550fpm or a little less if going up to the flight levels.

Doubling that to an average of 1000fpm, while increasing the IAS from 120 to 150kts would cut time-to-climb by 5 - 7 minutes per flight, and would also leave more of the flight occurring at cruise speed rather than climb speed. On a 2 hour flight, this might cut time aloft by 12 minutes, increasing block speed by 10% overall.

Best of all, it seems that safety margins improve with an increase in HP in a number of ways: Reduced take-off runs, massively improved initial climb (therefore much less time spent below the altitude needed to safely maneuver for a landing in event of an emergency after take-off), massively improved single-engine climb performance at all altitudes, and (if cruise speeds are kept the same) much lower percentage output of the engines throughout most of their lives (longevity). And if one does open up those throttles in cruise, perhaps a further 10% reduction in block time might become available, though at a cost of fuel consumption. Still, turning a 2 hour flight into a 1h36 flight can be attractive sometimes.

So: Do any of you have experience with higher HP engines? We've all "read about" and "heard about" such things, but I'd love to hear from someone who is flying a higher-HP Skymaster, to learn how it worked out.

The things that seem most important to me are:

- Is anyone here actually flying Skymasters with engines upgraded from TSIO-360 to something else? Or could perhaps introduce me to someone who is doing so?

- Bigger engines are heavier, and (if pushed) need more fuel. How is the reduction in useful load handled?

- Is anyone actually flying with a MGTOW greater than 4,700 lbs? I'd love to learn how that was accomplished, and how it has worked out. Or are all the wingtips and extensions one reads about basically just a "good idea" that never really came to fruition?

- How has the increased HP helped / hurt the aircraft's usefulness?

- Are there other ways to improve the climb performance (other than by offloading fuel or people)?

I love my P337, and whenever I think about upgrading to a 340A, 414A, or 421C, I remember that the reason I chose a Skymaster is that it's docile, forgiving, safe. I know I can increase performance by changing to a different model. But then I'm into much more recurrent training. Plus, the 400 series isn't going to qualify for BasicMed, which is an issue for me (the 340A would).

Thanks

Dan

[hharney]

Great questions, here are some facts about your ideas

Riley made the 520 converted Skymasters and they were all pressurized cabins. From what I have heard the climb performance is greatly improved and if I remember it was about 30 minutes to FLV 200. But this performance came with a lot of restrictions, because there is only one MOD that provided a GW increase to our birds and that was the Robertson STOL Kit. I am not sure it added anything to the G and H models as their GW was already 4700# and not many Robertson late models were built. So we are stuck with the factory GW. This made the Riley 520's pretty heavy with full fuel. Like 250# useful if I remember.

The other option is the Owen Bell 550's. Those can be STC'd with just changing one engine or both. There are only a handful of conversions out there with this STC and I'm not sure if the conversion is even doable today. But with the cost of the conversion you could have another aircraft that has more performance, more seats, more range etc.

There are a few MOD's that you could do but your trading dollars for quarters.

The Skymaster is a great airplane but it has it's limitations and no matter how much we try to go faster, climb better, land slower, etc it's still just a Skymaster. You need to really look at the mission you have and decide what airplane will fit that mission. It may not be a Skymaster. If you insist on flying a Skymaster, like most of us on this forum, then you just accept the performance you get and keep smiling. They are great planes for what they can do but we can't make them do what they won't do.

[dan1000]

Thank you, Herb. It would be interesting to hear from someone who actually flies one of the higher HP machines (ie: with 520 or 550).

The other interesting engine is the Continental CD-300, which is a jet-A burning 310hp diesel. At "cruise power" (which I take to be 75%), this is claimed to burn 9.7gph per engine, which may mean that the reduced useful load is offset by less need for fuel.

Anyway, I'm likely not enough of a test pilot to be the first one to try that engine out! Still, one can dream.

Dan

[Dan schultz]

Leave the engines what they are.

I had five mission statements prior to choosing the P337.

My eldest daughter is handicapped, needed to have easy access.

Has to fit in my current hangar 30x40 10 foot clearance.

Twin engine for night flying.

Have some altitude capability

Has to fly in and out of 2000’, currently flying club airport.

Operation;

Climb the aircraft at 130-140 mph, burn 27 gph at cruise at appx 75% power

4 200 pounders with full fuel.

If I was at a different airport, I would have a different aircraft.


Great short field performer, excellent ease of access for the handicapped.

Dan
N67S
3OH0

[mshac]

Thank you Herb for your thoughtful and accurate reply. You are a true credit to the Skymaster nation. I hope we meet someday at a future fly-in.

[dan1000]

Thank you, Dan. Sounds like the aircraft fits your needs perfectly. And I acknowledge your stated advice about leaving the engines the way they are.

Engine upgrades such as those done for other 300 and 400 series Cessnas by RAM, or by Jack Riley, are often spoken of on this forum. What is very hard to come by is commentary from someone actually owning and flying an engine-upgraded 337. It would be very welcome, I think, to hear from those owners. There can't be many of them out there, because not too many were modified in those ways. Yet they must be out there somewhere. I hope someone can give a detailed report as a longer-term owner one of these days.

I spent some time conversing with Owen Bell. He asserts that his company's Wingtip mod, along with an MT 3-blade prop, has completed all testing needed to obtain a MGTOW increase to 5400lbs, with one exception. He apparently needs to demonstrate that the aircraft with those modifications still meets the FAA's noise level limitations. He insists that no structural changes, other than the installation of the winglets and prop, are needed.

To me, adding 700lb of MGTOW without beefing anything up -- sounds a bit strange. Nonetheless, my old RAM 414A got a MGTOW increase when they installed the winglets, making it a 414AW. The extra MGTOW allowed extra fuel to be carried in nacelle tanks, providing an extra hour of flight, even with the upgraded RAM engines (310hp -> 335hp).

Owen also insists that installation of a pair of 310hp engines provides 3000fpm of climb, and 302mph (262 knots) of cruise speed at FL250 (presumably full throttle, and presumably in a non-P model, since P's can only go to FL200). I imagine that would become a 230kt cruise at 75% power at FL180 (or thereabouts).

Or I could just step into a 340A, and worry a bit more about recurrent training


Dan

Originally Posted by Dan schultz

Leave the engines what they are.

...

Dan
N67S
3OH0

[n86121]

I have a T337D RSTOL.

To go up FAST I

1, 1/3rd flaps down (more lift, yes more drag but more lift too),
2. 100% power,
3. cowl flaps open
4. About 120 mph indicated - can see horizon and lots of cooling airflow

Give it a try and report back?

[dan1000]

Originally Posted by n86121

I have a T337D RSTOL.

To go up FAST I

1, 1/3rd flaps down (more lift, yes more drag but more lift too),
2. 100% power,
3. cowl flaps open
4. About 120 mph indicated - can see horizon and lots of cooling airflow

Give it a try and report back?

Thanks. Am waiting for the annual to complete, then will give this a try. I will also try it my old way, having had the mechanic apply all the previous advice in this thread.

Dan