Turbos altitude advantage
 

Often, turbos are lauded as having the advantage of being able to climb out of IMC or into tailwinds (among a few other things). I'm curious to know from those experienced/knowledgeable what magnitude of altitude increases are commonly sought for these scenarios, and at what climb rate. Obviously it varies, but as a neophyte, I'm wondering if they're talking about 4k ft climbs, 10k ft climbs, more? ... and from what altitudes to start? I guess I'm looking for anecdotes where the above advantage has been taken.

Here's the points that I would make and remember I don't have any time in a turbo Skymaster. I have been on a couple trips in P models but no time in a straight turbo. Saying that I do have a lot of experience in a Normal Aspirated Skymaster. I also have several hundred hours in turbo charged multi engine airplanes that are non pressurized.

Flying the normal aspirated Skymaster is just fine for 95% of my missions. Mission is the key word here. Identify the true mission that you expect to have and that will dictate the selection. I plan for 700 - 1000 FPM climbs up to flight level 100 at 120 - 140 MPH IAS. Beyond that and it's realistically 300 - 500 FPM up to about flight level 130. At flight level 130 it's time to don the mask so I really don't go there.

Saying that I learned to fly my normal aspirated Skymaster in the mountains of Idaho and the northwest states. Out there you depart at 4,000 ft and cruise at 12,000 to 16,000 ft to clear the mountains and weather. That's where I cut my teeth and didn't know any different. Now I'm a flatlander and the need to go above 10,000 ft is non-existent. Out in the west I didn't really think about it much, I had O2 on board but I was young and didn't really use it all that much. For the most part we would fly 12,000 ft on average or lower. But my record for my bird is 21,500 ft. With 2 adults and 2 younger ones on board, the performance held the altitude just fine. But for the most part in the normal aspirated birds flight level 160 is about as high as you want with full seats and fuel. I've maintained 12,000 ft on one engine with a light load.

Performances for the turbo model are going to be very similar until you continue beyond 10,000 ft. Manifold pressure will maintain and not disappear like the normal aspirated does. You will burn more fuel but that's because you still have HP being generated. Maybe some of the turbo drivers can chime in with some realistic performance numbers.

The problem I see is you still have to don the mask. Not a big deal if it's just you and your favorite co-pilot but when you get the family in there or passengers it gets complicated. Not the best or easiest procedure to take care of. Sure you can fly around at flight level 140 or 160 and get away with causing too much problem with the passengers but you the pilot better have the O2 on. Speed is better with turbos but along with that comes more fuel burn. I think having the right mission that requires higher altitudes the P model makes things simpler and convenient. But if I was still out west, flying the mountains and I found the right straight turbo I would not hesitate to make it fit my mission. Turbos aren't a must out there but they really do make a better platform for that environment.

The earlier straight turbos have the one piece entrance door but you also have a baggage door. I like my baggage door. The two piece door on the late model is really nice but I would miss my baggage door. For the right plane and condition I might give up my baggage door. If you go P model then you don't plan for a baggage door. End of subject. Cessna only made 11 Turbo model H aircraft (1979-1980) and most of those are owned by Air Scan. Those are nice birds, rarest out there.

So what's the mission?

Excellent points Herb.
I would add that if you fly above mountains or above clouds with ice or above weather you would not want to be in then it helps to know your single engine service ceiling for 'what if', especially if you are near max gross.
I have attached the single engine service ceiling for the P337H - if someone could post for the non-turbo'd Skymaster it could give you a basis for comparison.
Also have attached numbers for single engine rate of climb because if eg. you are taking off from Sedona airport at +20 degC, can you climb if an engine fails in a non-turbo?
One thing these tables do not include is density altitude. i.e. if you lose an engine at near max gross on a very hot and very humid day, can you even maintain eg. 6000' in a non-turbo?
These guys had a turbo but did not follow the POH and push up the MP into takeoff power ( http://generalaviationnews.com/2012/...l-it-cost-you/ ) i.e. 37"/2800". She left it at the top of the green arc i.e. 33" and crashed. What is the max MP on the non-turbo version? And it goes down 1" for every 1000 ft in a non-turbo.
Food for thought...
Also attached the both engines rate of climb for comparison.

Thanks for some thoughtful and informative replies gentlemen. So far as the "mission" goes, again I'm a neophyte so I've had trouble with that term. Perhaps I think that means the occasional trip from CT to [pick your destination within 3 hours, Skymaster time]. Maybe the occasional grass strip (which I've read these aircraft are comfortable with). 2-4 adults and light luggage. Don't forget the dog (@45#). I'll never knowingly put myself and pax into harm, and am willing to advise them that the trains are a lovely ride, but sometimes you find yourself in a surprise, TAFs be damned.

So may I ask, have you found yourself in the scenario described, where you were cruising along and suddenly needed to climb over nasty weather--be it 337 or other a/c? What increase in altitude did it require and from what original?

RSTOL Turbo 337
 

Good afternoon,

I've had a Robertson STOL turbo for decades. I transitioned in a non-turbo ages ago. What I recall of the non-turbo was that once you got a bit hot and heavy, it took quite awhile to get from 7,000 to 9000. I wasn't looking for a turbo per se, but in retrospect it was the right choice.

With the RSTOL the unofficial trick is to leave 1/3 (full wing) flaps down and pull it BACK to 120 mph. That way I can still see over the schnozz. VX is 70mph, and vy 85mph, but I like to see where I am going, AND give the engines a little more cooling airflow. With 1/3 flaps, full power and 120 mph, 2,000 fpm can readily done. It bogeys up.

There are a few advantages with turbos

1) You can climb from anything to anything with almost constant climb rate. Even on the east coast, in summer it's nice to quickly pop above 10k convection layers common around
Wash DC.

2. Ballpark, one picks up around 10 mphs per 5,000ft climbed. So whatever your power setting gives you at sea level, at 10,000 add about 20 mph, etc.

3) Advice from a T210 pilot who used to fly Aspen CO all year, including winter. When I asked him what was most important in icing, his boots, his heated prop? He replied turbo's because icing is always just a few thousand feet thick, so you can always climb out of it quickly. After that he said heated prop, which the REAR prop is always, as it is right in line with rear turbo exhaust. Keeps from icing and gives that famous Skymaster blaaaaat sound, as rear prop chops exhaust.

4) At higher altitudes (even low teens) the turbos make the aircraft quite fast.

5) Single-engine service ceiling for my turbo no-pressurized is 16,800 ft !

6) For just spooling around down low, low power scenic cruise, the turbos are just along for the ride.

Ok, I've been in the 337 market for several months now. I have seen Ps, Ts and normally aspirated aircraft come and go. My A&P guy says the I.O. 360 was not designed to be turbocharged, and that will result in much faster engine wear. Resolve?

JB,

I'm by no means an expert here but have copious amounts of reading on the subject behind me. It seems that at the hand of a well trained and disciplined pilot, tbo and greater is just as achievable in a turbo. Some have argued more so, under those conditions. But was your previous owner in that category? Therein ...

But that really stands to reason, right? After all, what is the turbo that is rarely boosted past 30"? ... Warmer air at eternal sea level. More maintenance given the additional parts, yet still the owners who switched almost never, in my reading, bemoan the expense. Some old logic that may ring true still:http://www.avweb.com/news/maint/182808-1.html

Many TSIO 360's go past TBO as we know. Also they make them better now eg. my SFRM TBO is 1600 hrs.
Engine management planning however as we know should be in the pre-descent checklist so that you can plan ahead and then ahead some more so that the standard 1" per min MP reductions can happen etc. The other thing is not shutting down for 5 mins until after touchdown to reduce coking. As we know sometimes ATC mismanages the flow and leaves you too high - luckily the Skymaster has plenty of drag with the gear out (140 KIAS ext'n but 130 KIAS I have been told is much easier on the gear, so I do that - means sometimes you have to pull up slightly, start extension, continue descent) and also the 1st notch of flaps is 165 KIAS which is really useful. My acft has speedbrakes- useful sometimes esp in long descents from the high teens in winter. All this to say that even though it is 'just' a Skymaster, with the TSIO's you still need to manage power and speeds really much like a bigger twin, though not to the same extent as in a geared engine environment. All really doable (ideally) with practice and good checklists that you stick to. You always have to fly the plane and not just be along for the ride, but perhaps just moreso with TSIO engines.

One more thing - nowadays most of us have EDM 760's or 960's. They tell you what the CHT cooling rate is and it gives you an alarm if > 50 deg/min. If you are foolish enough to think you can descend at 195 KIAS and impress your friends then at least the monitor will let you know you are being very unkind to your engine. Much better to not let things get cold under the cowling. Also in winter in descent you can freeze the air/oil separator can that the TSIO's have or the breather tube and end up pressurizing the case, then blowing the seal, which has caused engine failures in many different types of acft. In acft that fly in colder conditions you often see this can and the breathing tubes insulated, with holes drilled or notches cut before the cowling interface to let liquid water out and minimize the chance of this happening. Keeping things nice and toasty with slower descent rates and proper engine management still however remains safe and smart.
So with the TSIO 360's, if you have the right engine monitoring equipment it is easier to ensure that the engines remain much more durable and dependable than in the olden days.

Single engine service ceiling numbers are attached for a 1971 (non-turbo) Skymaster. Just to illustrate as an example, today it is +70 deg F at Sedona airport (4830 ‘ asl) and say an engine fails at max gross after take off. In a turbo model you will be climbing at ~ 240 fpm. According to the attached table, in the 1971 model you will have to descend. Obviously those who fly the non-turbos already know this. This also implies that say it is 80 deg F and humid, you will be lucky to maintain even 4000 feet at max power if an engine fails. Anecdotes re turbo vs non-turbo are entertaining, but the only anecdote that really matters is the one that you got yourself into when those Swiss cheese holes line up.
So like anything in flying you have to weigh the pros and cons (for turbos cons include the weight, the cost of maintenance/repair/overhaul, you have to be more careful with MP settings and treat them right, and it’s another thing that can fail in flight), and make your choice. Personally I chose turbo for all the reasons in the P337H tables attached earlier.

Yikes ... sure hope that's a typo.

Fixed it thanks for your feedback.

Hmm...+70C is about +158F...and here I thought Texas was hot! :eek:

:D

I have a 1969 T337D with a Robertson kit and I have to say I totally agree with N86121. The airplane is just amazing. Climbs without hesitation up to 19000 ft, which is the highest I've taken it so far to get over the Rockies. Lifts 850 lbs with full fuel. And the engine out service ceiling is 19k ft on the rear engine, 16k ft on the front. So I can lose an engine over the Sierras and basically coast into Livermore where I am based. Every once in a while I look around for other airplanes and keep coming back to the T skymaster. In the west I would not want a non turbo airplane. A P model might be nice though....

Some great info here. Though I am largely a flatlander (here in the northeast our tallest hurdle is 6288ft, and a standout at that), as my opener mentioned I have put some stock in the discussions various and wide about climbing above IMC conditions. I'm not especially stoked about the extra cost of maintenance, but our weather here is (in)famously unpredictable. Guess I'm pretty much sold on the idea of a turbo at this point. I'd still love to hear any anecdotes from those who've found themselves with a sudden need to climb above weather.