How high is "up high" with a turbo?

Quint Van Deman

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Quint Van Deman
Hi all--

I'm weighing options for my next airplane, and I'm basically down to a retractable Saratoga, but am rather unsettled when it comes to whether to go with the turbo model or not. Some of this is easy to sort through. I've read about intercoolers, reaching TBO likelihood differences, etc. Frustratingly, the part I can't figure how is just how high (exactly) folks are talking about when they talk about "better speeds up high" 12k? 15k? 20k? The details particularly matter for sake of a dog that would be a regular passenger...one that's not going to be able to put on the oxygen...

If anyone could help me understand any of the following I'd be tremendously grateful:
1) What is the optimal altitude for cruise performance for a retractable turbo Saratoga? (I'm mainly looking at the SP's from the 80s)
2) At that altitude, what's the book/real cruise speed @ 75%?
3) What's the book/real cruise speed @ 75% @ 10-12k feet? (A pic of the actual POH table would be huge!)

Much appreciated,
-Quint
N7406P (for now!)
 
@Rgbeard can chime in with this, but the summary is that once you get above around 9k the turbo will start to show a noticeable improvement in true airspeed vs. the naturally aspirated engine. For piston turbo engines, anywhere from the mid teens through low flight levels is considered "optimal" depending on the specifics of the engine and turbo system/intercooler design. Some can do fine into the mid 20s.

My personal take - unless you need to fly higher to cross mountains, don't bother with a turbo. There's a significant increase in maintenance cost (and decrease in reliability) that goes with them. Flying without pressurization but with a turbo you're stuck sucking on O2, which is annoying.
 
As high as my Oxygen equipment safely allows.....with canullas....it's 18,000 feet for me, but others will go higher.

The altitude is based on winds and cloud height (I don't go into freezing clouds).....and if they are favorable we go as high as possible.

True airspeed improves with altitude....my V35A TC will true out at 195 kts and 17.5 gph at 18,000 feet.
 
The other problem is that above about 14K, mag arcing can become an issue, causing misfiring. Pressurized mags solve that but I don't know if a turbo Saratoga comes stock with them. Turbo Arrrows don't. Fine wire plugs help.

Also, I have found in the turbo Arrow, that above about 12K the engine would not run smoothly during LOP operations, killing off any efficiency gained by flying above that altitude. Running 50 degrees ROP, the engine sucked fuel like a pig on a cannabis high.
 
True airspeed improves with altitude....my V35A TC will true out at 195 kts and 17.5 gph at 18,000 feet.

TAS improves with altitude until you get to the point where the turbo system starts heating up the induction air so much that your power is decreasing too significantly. Where that "sweet spot" is depends on the aircraft. For the 414, it was something in the high teens/low flight levels, for planes like the Navajo (no intercooler) low to mid teens as about the best.

The other problem is that above about 14K, mag arcing can become an issue, causing misfiring. Pressurized mags solve that but I don't know if a turbo Saratoga comes stock with them. Turbo Arrrows don't. Fine wire plugs help.

Also, I have found in the turbo Arrow, that above about 12K the engine would not run smoothly during LOP operations, killing off any efficiency gained by flying above that altitude. Running 50 degrees ROP, the engine sucked fuel like a pig on a cannabis high.

That depends on how well the engine is tuned and which mags are used. Pressurized mags are made by Slick because their mag design is rather poor. Bendix 1200 series mags don't need to be pressurized, like what the 414 had.

Pressurized mags are a real pain. More stuff to fail.
 
I may have missed it, but what is your mission profile for this aircraft? I mean, if you're only going 2-hour legs or less, I doubt buying a turbo and taking the time to get "up high" into the upper teens is going to be that useful. The time saved, if any, would be minimal, and pretty expensive in terms of fuel burn and overhaul/maintenance expense. If you are running 3+ hour legs, then sure, going up high may be worth it to potentially save a fuel stop you might have to do in a non-turbo bird flying down low. Also, keep in mind that the winds aloft may not be favorable to fly higher depending on direction of travel, so you'll be running it down low anyway.
 
I very much enjoy flying turbos. However, I am getting paid to fly them and therefore am not paying any bills for them (maintenance, fuel, etc.)

What they offer is flexibility on altitude and the ability to get up there comparatively quickly. A non-turbo PA-32 you might not fly above 8000 very often due to the loss in power, speed, and the time it takes to get up higher. Which limits you to about 4000 feet of cruise altitudes (4000-8000 MSL). At 8000 you're going to often be in the clouds and maybe still in the thermal bumps in the summer.

But with a turbo, you just doubled your available cruise altitudes (4000-12000) - and if you're willing to use oxygen, tripled or quadrupled your options. That's useful altitude to open up more options - top weather, get in smooth air, find the best wind.
 
In my experience 16K is the "sweet spot" .., here is why:
-you get a nice TAS boost once you're over 8K to 9K (as Ted said).. I find generally 1-2 knots per 1,000 ft (atmospheric conditions dependent, obviously)
-you're above most typical weather
-there is less traffic (real planes above you, most everyone else under you)
-if you have an issue with cannula / O2 / whatever you aren't guaranteed to die and the safety of 10K-12K is relatively close
-you will be above all the terrain in the continental US
-it's cold enough that even on hot days you'll be nice and cool
-in my experience the engine seems happiest.. visavie vapor / fuel flow / roughness / temps
 
-in my experience the engine seems happiest.. visavie vapor / fuel flow / roughness / temps

What sort of turbo plane experience do you have? SR22 I think?

There's just a big difference all around. A RAM VII 340 or a 421C, especially with winglets, will happily go into the mid 20s just fine, even upper 20s in some cases. A Navajo really maxes out about 14k before you start to feel it. And in the 414 if you weren't above at least 15k you were roasting with inop AC in the summer (until I realized you could leave the windows open during flight if you didn't care about pressurization).
 
What sort of turbo plane experience do you have? SR22 I think?
SR22T and TN.. above 16K you really need that boost pump on, without it you're getting bad vapor lock issues, and even with it you'll find some variations in fuel flow.. even in (what was, at the time, a nearly brand spanking new plane, 2 yrs old, 22T, from the factory).. the 22T would have up to 1 gph fluctuations. The mag is connected to the manifold, so the mag is "at sea level" but the airplane starts to feel "sorta funny" around 17K.. run too close to peak your CHT starts to get up towards 380, it's smooth, but warming up.. start to get too lean (less than 16-ish) and the engine gets a little rough.. there's a 16.3 to around 17.1 sweet spot that you really had to stay in for 2500 and 30 inches

..not to get too tangent-ed here.. but I've been told that could be timing related, however both planes had/have normal 50-75 RPM mag drops on the run ups.. if timing were an issue you'd get a lower mag drop (less than 50 rpm) with the timing being too advanced (at least that's what I've read!)

above at least 15k you were roasting with inop AC in the summer
I'm surprised how hot planes get, even when the OAT is relatively cool, around 9 or 10 C, I'm baking. But 14-16K is usually when I can, in the summer, turn the AC off and not get cooked
 
SR22T and TN.. above 16K you really need that boost pump on, without it you're getting bad vapor lock issues, and even with it you'll find some variations in fuel flow.. even in (what was, at the time, a nearly brand spanking new plane, 2 yrs old, 22T, from the factory).. the 22T would have up to 1 gph fluctuations.

That depends on the fuel system design and not really how old the plane is. I have no time in the SR22, but it's not an issue on Navajos. Continentals are more affected for whatever reason.

My point is, the answer isn't one size fits all.

I'm surprised how hot planes get, even when the OAT is relatively cool, around 9 or 10 C, I'm baking. But 14-16K is usually when I can, in the summer, turn the AC off and not get cooked

It also depends on the airplane. Lots of glass in an SR22, so lots of greenhouse effect. And when you've got a pressurized plane you have a lot less airflow.

The Aztec was great, though. Tons of air leaks.
 
A RAM VII 340 or a 421C, especially with winglets, will happily go into the mid 20s just fine, even upper 20s in some cases.

I agree. I've only had the 421C (no winglets) up to FL220, but it was performing just fine, no problems. I may have had a 340 up there too, again no problems.
 
With my Commander, the sweet spot was 14,000 to 17,000. Especially when traveling NE with favorable winds at altitude. Sometimes 8,000 was all I wanted to do with unfavorable winds. I always had one or two, O2 tanks in the plane on each trip.

On a no-wind basis, 14-17 was about best. Engine ran great up there, climb wasn't too bad, at TAS was decent. It got me above a lot of the scud (so I could usually see the tops....).

It does depend a lot on the aircraft and engine, but don't ignore the other things like wind speed, O2 usage, length of trip (vs how long to climb to altitude), and in areas like the Northeast what ATC will let you have. Out west in the mountains, I'd want the turbo for the additional takeoff, climb,and mountain clearance. Flatlands are a different matter.
 
Of course.. we had planes like the B36 with service ceilings over 40,000 feet.. all it needed was a couple turbos, and other gizmos, plus 145 octane fuel!
 
Of course.. we had planes like the B36 with service ceilings over 40,000 feet.. all it needed was a couple turbos, and other gizmos, plus 145 octane fuel!

B36... bonanza? :)
 
Of course.. we had planes like the B36 with service ceilings over 40,000 feet.. all it needed was a couple turbos, and other gizmos, plus 145 octane fuel!

I've long had a goal to make a piston powered airplane that goes up to FL650. I'd love to do it if I could find someone willing to fund it. :)

Hint: That person is not me.
 
I've long had a goal to make a piston powered airplane that goes up to FL650. I'd love to do it if I could find someone willing to fund it. :)

Hint: That person is not me.
That was a fun little rabbit hole to go down: https://ctipft.com/records-flight-altitude/

From the link above:
"
Altitude records for piston-driven propeller airplanes

Things have come a long way since Clément Ader set the record for getting his Éole propeller plane eight inches off the ground in 1890! As the evolution of piston-driven aircraft gathered speed, so did the records, and the highest altitude recorded in a piston-driven propeller biplane (without a payload) was set in 1938 by Mario Pezzi, who flew his Caproni Ca.161 at an altitude of 56,047 ft.

It was nearly sixty years later that the record was set for the highest flight recorded in a piston-driven propeller monoplane however, when a Grob Strato 2C flew to 60,897 ft in 1995.

But the highest of all the piston-driven propeller airplanes was the record set by the Boeing Condor UAV (unmanned aerial vehicle) during 1988-1989, when it recorded altitudes of 67,028 ft!
"

Highest manned, 60,897
upload_2020-2-4_16-28-54.png

Probably won't fit in a standard T hangar though. Damn
 
^Powered by Conti 550!
 
^ofcourse, it's also cheating by using the gas generator..
 
..and now I feel like some absolutely maniac needs to strap a Pratt Whitney Wasp Major onto a Bonanza.. "lol, nice PT6.. my plane has 3,800 horsepower! do you even lift bro?"
It'd still probably be slower than the PT-6 due to the frontal drag the wasp would create, lol. Not to mention the prop that thing would have to swing, you'd have to put the Bo on stilts!
 
Well now I clearly have a record to beat. Who’s in for the GoFundMe? :D
 
It'd still probably be slower than the PT-6 due to the frontal drag the wasp would create, lol. Not to mention the prop that thing would have to swing, you'd have to put the Bo on stilts!
If I was any good at photo shop I'd take a stab at it
 
Hi all--

I'm weighing options for my next airplane, and I'm basically down to a retractable Saratoga, but am rather unsettled when it comes to whether to go with the turbo model or not. Some of this is easy to sort through. I've read about intercoolers, reaching TBO likelihood differences, etc. Frustratingly, the part I can't figure how is just how high (exactly) folks are talking about when they talk about "better speeds up high" 12k? 15k? 20k? The details particularly matter for sake of a dog that would be a regular passenger...one that's not going to be able to put on the oxygen...

If anyone could help me understand any of the following I'd be tremendously grateful:
1) What is the optimal altitude for cruise performance for a retractable turbo Saratoga? (I'm mainly looking at the SP's from the 80s)
2) At that altitude, what's the book/real cruise speed @ 75%?
3) What's the book/real cruise speed @ 75% @ 10-12k feet? (A pic of the actual POH table would be huge!)

I can't help you on 2 and 3. But...

Any normally aspirated airplane with a constant speed prop will do best around 9,000 feet, presuming you're going to run it at 65%. At that altitude, you've only got about 70% of sea level air pressure available to run the engine with, and if you back off the prop a bit you're probably right around 65%. You're also about as efficient as your engine will run: Lowest pumping losses at WOT, lower friction losses with the lower RPM.

Below 10,000 feet, all else being equal, a turbo airplane will be slightly slower than a normally aspirated one.

Consider also the distance taken for the climb and descent. For example, I figure that in the Mooney it takes me about 8 miles per thousand feet for the climb and descent. You want at least half your flight to be in cruise for maximum efficiency, and thus on a 160-mile leg, I should get there about as fast as an otherwise equivalent turbo bird... But the guy with the turbo will burn more fuel.

To really get a significant speed advantage, you need to get that turbo bird up higher, which means even longer legs. Figure that unless you're regularly doing 250-300 mile legs, you're really just wasting money having a turbo unless you're based at an airport that's well above 0 MSL (I'm talking 5000 minimum).

If you have a dog and/or other passengers that don't want O2 straws up their noses, you're pretty much stuck in the 11-12K zone, where even a normally aspirated plane can make nearly 65% power. In those cases, the turbo isn't going to buy you much except a bigger hole in your wallet.

Also, I have found in the turbo Arrow, that above about 12K the engine would not run smoothly during LOP operations, killing off any efficiency gained by flying above that altitude. Running 50 degrees ROP, the engine sucked fuel like a pig on a cannabis high.

To be fair, the engine that's used in the turbo Arrow (and Mooney M20K and Seneca) is really hard to run LOP at the altitudes where those birds do best. There are various STCs that improve their performance, but LOP is something that eludes them for the most part. That isn't necessarily going to be the case with a PA32 turbo.
 
For work I push a Cessna T182T mainly and it’s a good bird for the mountains of the west. Don’t have to worry as much about DA and a good 15-20 kts faster around 16k feet than a standard 182. But I really don’t go that far, with 400 m/ 2-2 1/2 hours one way probably the max range for any given trip. And most of the time the highest i need to be is 11k. I probably only climb higher and turn on the O2 a couple of times a year. The turbo failed last at 1500 hrs(2000 hr TBO), and took the engine with it. I wouldn’t personally own a turbo unless absolutely necessary.
 
Ive always liked the IO-720 approach to this question. :D

I've actually had a similar idea on that. One of the other projects I wanted to do (but never did) was build a naturally aspirated engine with super high compression (diesel level numbers) with the intent of having lower redline on maximum manifold pressure for takeoff but then not losing so much up high.
 
A flat rated piston engine, hmmm.
 
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I returned from a cross-country trip in a 1981 Turbo Saratoga, this past weekend.

We took it to FL190 across the Sierras, 15,000 across Santa Fe, and 9,000 from Oklahoma to our destination.

The higher altitudes can really help you catch some winds. It's not uncommon to find 210-230kt as a ground track with this airplane at these elevations.

Not all Turbos are the same. Some are maintenance-intensive while others aren't. My experience with the PA-32 Lycoming 540 turbos is that they're in the "NOT" category, while the Arrow, with its Continental is in the high-maintenance category. There are reasons why this is the case, but I don't feel I need to get into those.

If you're West of the Mississippi, and likely to travel in higher areas, it's a necessity. If you're East, it's optional for the most part, but sure doesn't hurt, IMO.
 
IMHO....it's not the turbo that's maintenance intensive....it's the fuel control and waste gate and surrounding "systems" that can require attention. In addition....ham fisted-oblivious operators tend to over heat cylinders.....
 
IMHO....it's not the turbo that's maintenance intensive....it's the fuel control and waste gate and surrounding "systems" that can require attention. In addition....ham fisted-oblivious operators tend to over heat cylinders.....

Correct, the turbo itself is simply a glorified fan and seldom fails between overhauls.
 
Correct, the turbo itself is simply a glorified fan and seldom fails between overhauls.

Depends on the plane and how it's operated.
 
My Rajay 182P is certified in the STC for FL25. Highest I've flown her is 17,500. Around 17K get about 165kts TAS. 12.5 GPH. Best part is flying 4,000+ AGL over mountains and not having to deal with ground waves. High density altitude take-offs are nearly a none event.
 
I returned from a cross-country trip in a 1981 Turbo Saratoga, this past weekend.

We took it to FL190 across the Sierras, 15,000 across Santa Fe, and 9,000 from Oklahoma to our destination.

The higher altitudes can really help you catch some winds. It's not uncommon to find 210-230kt as a ground track with this airplane at these elevations.
If you are flying in mountainous areas, you can also save on distances. My friends flew their Turbo Saratoga to Alpine, WY, a while back. They went IFR direct, 430 nm. I had flown IFR to Alpine in my Arrow, and my service ceiling dictated a route around the mountains, 620 nm along airways. (I was at my service ceiling the entire time, too, thanks to the temperatures that day.) Even without faster ground speeds, having a turbo and a cannula can shave a lot of hours off your flying if you fly in mountainous areas.
 
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