Single-engine Endurance and Performance

[JeffAxel]

Hey Herb, it's a Skymaster....you can center the ball with an engine out....might climb a little better!! : - )

[WebMaster]

Parallax. It was the camera angle.

[hharney]

Winds, we had a real stiff wind out of the north. Might be some of the reason it looks that way.

[Learjetter]

Hi fellas! slight re-vector on the thread: searched the whole internet, this and the UK forum, but didn't find an answer: anyone know the engine-out performance degradation with the underbelly cargo pod installed? I'm looking at buying skymaster (there goes the kids' college education $$, which they don't need because the only people making money these days are plumbers and mechanics!). Anyway, I'm fairly comfortable with the SE performance numbers, but can't find the cargo pod penalty. Since I'll be flying out of high pressure alt locations in the mountain west, I'd like to know how bad the SE performance is with the pod installed. Thanks in advance for your knowledge.

Fly Safe!

[hharney]

Here are the recommendations from my POH 1968 C model. Hope that helps.

[Learjetter]

Thank you! That is EXACTLY what I was looking for...

[Paul Sharp]

I own a '67 Turbo, and we were flying back to Utah from Montana, over the mountains at 16,500' about 7-8 years ago. Fuel probably at about 80% of capacity at that point (using all 4 tanks), 3 adults plus baggae, in winter. I would WAG we were about 400-500 lbs. under 4300 gross.

The rear engine CHT began to creep upwards. There were no corroborating readings, but to be conservative I shut down the rear engine. The plane held 16,500 with no problem at all for half an hour to the nearest decent airport. (Turned out to be only a bad CHT probe.)

Of course, the non-turbo models are vastly different (which is why I don't own one).

[Roger]

Paul

I understand that you want to maintain your operating altitude in the teens because of where you live, but isn't that the only reason to own a turbo?

My question is : is there any advantage in owning a turbo if you don't fly about 10,000 ' ?

Aren't the engines essentially turbo normalized to 210 hp max, so for example you have no increased HP at 5000' on a turbo, vs normally aspirated? It this is true, then there would be no real difference in maintaining altitude / single engine out (outside of that difference as related to density altitude) which of course could be significant depending on the day.

How much manifold pressure are you showing at cruise in the 5000' range on a normal day at 75% (that might answer this).

Any thoughts on this?

thanks/Roger

[Paul Sharp]

The idea is that the turbos allow maintenance of sea-level MAP up to the critical altitude. I don't remember off the top what that is, but the POH says full 32" MAP can be maintained by the turbos well above 20K' - you have to manually pull it back an inch for each 1,000' over 20,000 feet becuse of operating limiitations (the 30,000' chart shows maximum 22" MAP). The single engine service ceiling under worst conditions (rear engine off and feathered, 4300 max. gross) and at 20 degrees C is 17,000 feet. Few other light twins can match that, even turbo models.

Ignoring density altitude and per your theoretical situation: at 5,000 you might not have more power and thus staying at 5,000' would seem similar if it's not summer or otherwise hot - the big factors are that you can go higher to clear something even with an engine out - not being limited by the normally-aspirated lower single-engine ceiling, and if you were higher in the first place, you won't drift down to the vastly lower single-engine ceiling of a normally-aspirated model.

Being in the western U.S. definitely means that a turbo is an advantage. But if you live
elsewhere and simply wanting to fly around some mountains like the Appalachians or go west or whatever, what then?

An additional big factor is that you can take off in the heat of the day at just about any airport around. I've calculated density altitude at 6,000+ feet airports and always had plenty of capability and room for takeoff in the peak of summer heat with 4 adults and full fuel.

Claims of higher maintenance from turbos are greatly exaggerated IMO. Both of my engines went past TBO with no turbo problems (I had to once overhaul a turbo controller for $800 but don't consider that very significant and that's a normal maintenance item on a long-term basis). Nor have I experienced any exacerbated maintenance due to turbos. I treat the engines well, cool carefully upon approach and landing, and always run them at low speeds after landing to cool oil in the turbos. I've never had a problem.

I take off at 4450' and climb at 28" MAP / 2600 RPM / 14.5 GPH up to 8,000' or more practically every time I go anywhere, so it would be "28" if I were to quote anything at 5,000 feet.

I realize that normally-aspirated Skymasters work for many, and they are great planes. But beyond just the terrain of where I live and fly, I want to go when and where I want to go. I wouldn't even consider owning a normally-aspirate aircraft except for some specialty like aerobatics, etc. For the same reasons I own a Skymaster with deicing, oxygen, a nice package of IFR/GPS avionics, and have kept myself IFR current for years.

[JamesC]

Herb did you ever figure out why your rear engine did not start in flight ? Do you have unfeathering accumulators and if so was the rear one charged to spec ?
I have shut down and feathered the front engine in flight (at 6500 ft) and it re-started no problem. Did not try the rear. Was just reminded of it because am just about to check the pressure in the rear accumulator.
Thanks Herb.

[hharney]

James, it was a bad starter adaptor. No accumulators on my bird. With a new starter adaptor it works fine. Those are expensive units, more for you because of the turbo scavenge pump. They are like 5 grand!