Turbo vs NA

[macaman]

I fly a '68 T337C between Salt Lake and California at 14 and 15,000 feet and usually get 165 knots (195 mph) True Airspeed at 65% power. The book shows 20 gph for these power settings but I find I need 23-25 gph to get 50-100 degrees rich of peak.

The book shows a possible true airspeed of 220 mph (190 knots) at 25,000 feet at 22.7 gph. The numbers may be easier for the later Turbo models with more than the 210 hp engines I have but you'll still be in the flight levels cruising at 75% power to get that number.

I really enjoy having the turbos with density altitudes that can top 10,000 feet at my 4,500 foot elevation runway in the mountains, especially to out climb the Sierra Nevadas but if I were flying in lower terrain most of the time I'd definitely lean toward the normally aspirated model. We have a Hawk XP (210 hp Cessna 172) that does just fine on VFR days cruising up to 12,000 feet where it sips 7-8 gph for 110 knots or high speed cruise of 130 knots on 12 gph at 8,000'.

I guess the big thing is that you can't just set it and forget it with power on the Turbo models, you become a true manager of the engines and on working with ATC to be able to cool the engines slowly on approach but if done correctly, the turbos will treat you right.

Good luck and if you would like, I can e-mail you the performance section of my owners manual. Just private message me your e-mail address to see them.

[hharney]

Dan

I was great to meet you at Batavia during the SOAPA event. Hope you can join us in the future. You must have the itch to stay with the benefits of a Skymaster if you are contemplating the scenario above. I have been flying my current normal aspirated Skymaster since 1985. I was based in Idaho for the first 15 years and now reside in the flatlands. Here is my opinion on your questions.

First and foremost I always ask, What's the mission? Sometimes that is hard to determine because it can always change down the road. Specifically your main question is Turbos or Non? I learned to fly in the mountains without turbos but if I had turbos I can see that it could have some advantages. Remember, turbos will increase some maintenance costs. If you fly and manage the engines correctly you should be able to achieve TBO and beyond. I have seen P model flyers go way beyond TBO because they are the only pilot and they fly smart.

When looking for a Skymaster I would be more inclined to look for an aircraft that has been treated right than just a specific model. The aircraft has to be priced right, configured right (avionics, mods, engine times), mid to low total time and corrosion free. You mentioned in your message above that you don't plan to fly much IFR and didn't know if boots would be a good idea. Remember, the Skymaster is not certified for flight in icing. Therefore boots are not a go or no go requirement for flight into icing conditions. If the right aircraft had boots and my mission was frequent flights in IFR conditions then boots would be a bonus. But having boots is another maintenance burden.

As far as performance Skymasters just don't really have the ability to be the fast twin engine cruiser that everyone wants. It is slow and uses a lot of fuel but it is safer than most and flies so stable. It is strong and like you we love them. So you deal with the cons to appreciate the pros. My Twin Comanche will pass the Skymaster with an extra 5 to 10 knots and burns 3 to 5 gallons less each hour. I just don't feel as comfortable in the TwinCo as I do in the Skymaster. I don't like the fact that I have to pour myself to get in the TwinCo off the wing, I don't like the fact that I can't see nothing under me and I don't like the limited power on one engine in the TwinCo. But there are a lot of TwinCo pilots out there that just love their airplane and they spend huge dollars in upgrades to make their Comanches look brand new with all the new technology.

Bottom line, if you can find the right turbo model out there go for it. i don't think you will be disappointed. The turbos are more rare so the task of finding one might be a little harder than say a normal aspirated model where there are more to choose from. All the straight turbo models will be mostly late 60's vintage. Nothing wrong with that but it will be really rare to find a straight turbo with an air stair door if that is what you want. Something else that is really important is the Pre-Buy inspection. I highly recommend that you use a qualified, referred, mechanic that knows the airplane but is NOT the sellers current mechanic. Too many times I see a mechanic hired for a Pre-Buy that is the sellers good buddy. I just think you need a good non-biased inspection. Remember the inspection isn't the deal breaker, it's the ammunition to negotiate the best price. Most anything can be repaired so knowing what the aircraft needs is the deciding factor. Good luck.

[Walter Atkinson]

A big advantage to the turbo is the ability to run it at very high power settings LOP with cool CHTs and low ICPs. In these scenarios, the engines last a long time and are quite efficient in fuel burn while resulting in higher TAS.

If the turbocharged engines are operated according to the POH, engine life is shorter due to higher CHTs and ICPs. If one appropriately runs them richer ROP to offset this negative issue, range will suffer and the cost of the extra fuel will be significantly more.

I recognize that few SkyMaster owners operate their engines in this optimal manner, but the scientific facts are compelling. Few Baron owners are operating ROP any more and fewer and fewer Twin Cessna owners are doing so. Almost zero turboCirrus, or turbo Bonanzas are operated ROP any more.

In an aircraft where cooling the rear engine has been a challenge, it remains a mystery to me why the advantages of optimal mixture management have not caught on. The turbo SkyMasters are the perfect airplanes to be operated this way.

[Ernie Martin]

Walter is right, Dan, and despite some early resistance to operating lean of peak ("LOP"), it's a good solution in many instances, especially considering the $6 per gallon we are now paying for fuel.

Make sure, however, that you understand the landscape. Do a Search on this Message Board for "lean of peak" and read the postings. Briefly, you want to have "balanced" injectors (read: GAMI injectors), engine monitoring with cylinder-by-cylinder EGT/CHT readings, the willingness and ability to understand and manage the leaning process, and preferably an engine no longer under warranty from an overhauler which prohibits LOP.

Ernie

[Walter Atkinson]

Originally Posted by Ernie Martin

Make sure, however, that you understand the landscape. Do a Search on this Message Board for "lean of peak" and read the postings. Briefly, you want to have "balanced" injectors (read: GAMI injectors), engine monitoring with cylinder-by-cylinder EGT/CHT readings, the willingness and ability to understand and manage the leaning process, and preferably an engine no longer under warranty from an overhauler which prohibits LOP.

Understanding is always a good thing. Your engine is SUPPOSED to come with balanced F:A ratios as that is how it was designed. Unfortunately, many don't, hence the business opportunity for a company to produce an STC'd product that addresses that deficiency. No matter whether you operate ROP or LOP, the F:A ratios should be balanced for the engine to be a conforming engine. (a conforming engine is one which complies with the engineering design and the appropriate set-up.)

While engine monitors are very good ideas for a variety of reasons (I considered them mandatory), leaning isn't one of them. If you have balanced F:A ratios and the engine runs smoothly LOP, you do not need an engine monitor to properly or safely operate any engine LOP. If that were the case, literally hundreds of millions of flight hours of LOP mixture operation could not have been successfully accomplished. Those who have a thorough understanding of the issues appreciate that they need an engine monitor MUCH more when they operate ROP. There is no mixture setting that needs an engine monitor more than the mixture historically recommended by the OEMs. Go figure?

IMO, any overhauler who prohibits LOP operation should be asked why. It could be that the engine is not properly delivered (if it can't run smoothly LOP it is not a conforming engine), or the builder is poorly educated. In either case, I want to know what they know and don't know before buying their product. There are some shops which build very good engines who are truly clueless on how to operate them properly. If they deliver an engine that CANNOT be operated smoothly LOP, it is not a conforming engine. Period. For the money I spend on an overhaul, I darned sure expect it to be a conforming engine no matter how I plan to set the mixture.

YMMV.

[Ernie Martin]

I am a supporter of LOP operations under the right circumstances, but I stand by my views.

Let's look at Walter's points.

1. Balanced Injectors. Many (most?) engines -- even new ones -- don't have balanced injectors and don't operate smoothly at LOP without GAMI injectors. We are in agreement here, except that Walter seems to suggest that a conforming engine (new or overhauled) has to have balanced injectors and operate smoothly at LOP. In theory perhaps. In practice, forget it. You almost certainly will have to buy GAMIs.

2. Engine Monitor. Walter views these monitors as a) mandatory, but not to operate LOP, and b) more necessary for ROP operation. I'm baffled by the latter point, in part because I've never heard it before and because it seems to run counter to what airplane manufacturers have historically done (i.e., they tell you to run ROP and they don't equip their aircraft with an engine monitor). But on point a) every article I have read in support of LOP clearly indicates a need for an engine monitor. As an example, take the one in the July 2009 issue of AOPA Pilot magazine at www.gami.com/articles/frugalflyer.php. Here is an excerpt: Electronic engine monitors that show cylinder head and exhaust gas temperatures for every cylinder are necessary for safe LOP operations. Here's another: GAMI showed that with precise fuel/air metering systems and graphical engine monitors high-compression and turbocharged piston aircraft engines could run safely and reliably LOP. In the article, engine overhaulers specifically point to LOP without engine monitors leading to engine damage. In the recent May 2011 issue of the same magazine, in the dogfight article on LOP vs. ROP, it's stated that those engine rebuilders who now accept LOP operation require both balanced injectors and engine monitors.

3. Overhauled Engine Under Warranty. Walter believes that overhaulers should deliver engines with balanced injectors (my response in point 1) and should not object to LOP operation. I would like that too. But the reality is different: many (most?) engine overhaulers will not honor their warranty if you deviate from the POH, which for Skymasters means ROP operation.

So, at the risk of being repetitive, LOP is a good choice if you have "balanced" injectors (read: GAMI injectors), engine monitoring with cylinder-by-cylinder EGT/CHT readings, the willingness and ability to understand and manage the leaning process, and preferably an engine no longer under warranty from an overhauler which prohibits LOP.

Ernie

[Walter Atkinson]

Ernie:

These conversations are very beneficial. Let's look at some of these issues with a little more depth.

Originally Posted by Ernie Martin

1. Balanced Injectors. Many (most?) engines -- even new ones -- don't have balanced injectors and don't operate smoothly at LOP without GAMI injectors. We are in agreement here, except that Walter seems to suggest that a conforming engine (new or overhauled) has to have balanced injectors and operate smoothly at LOP. In theory perhaps. In practice, forget it. You almost certainly will have to buy GAMIs.

By definition, a conforming engine is one that conforms to the design. They are designed to have balance F:A ratios. As you so correctly state, they usually don't. That makes them mostly NONconforming engines. If they were, they would run like they were designed to run--across the entire mixture spectrum. As you also correctly state, "forget it!"

Originally Posted by Ernie Martin

2. Engine Monitor. Walter views these monitors as a) mandatory, but not to operate LOP, and b) more necessary for ROP operation. I'm baffled by the latter point, in part because I've never heard it before and because it seems to run counter to what airplane manufacturers have historically done (i.e., they tell you to run ROP and they don't equip their aircraft with an engine monitor). But on point a) every article I have read in support of LOP clearly indicates a need for an engine monitor. As an example, take the one in the July 2009 issue of AOPA Pilot magazine at www.gami.com/articles/frugalflyer.php. Here is an excerpt: Electronic engine monitors that show cylinder head and exhaust gas temperatures for every cylinder are necessary for safe LOP operations. Here's another: GAMI showed that with precise fuel/air metering systems and graphical engine monitors high-compression and turbocharged piston aircraft engines could run safely and reliably LOP. In the article, engine overhaulers specifically point to LOP without engine monitors leading to engine damage. In the recent May 2011 issue of the same magazine, in the dogfight article on LOP vs. ROP, it's stated that those engine rebuilders who now accept LOP operation require both balanced injectors and engine monitors.

This is a major misunderstanding by quite a few folks.

Consider this ONE condition:
You do NOT have an engine monitor. You run ROP. You have a conforming engine that has balanced F:A ratios. One injector partially plugs and the fuel to that cylinder is reduced. That puts that cylinder not as rich as you assume it is by your leaning. That cylinder is running hotter and quite possibly in the most detonation-prone mixture possible and you do not know it. The HP curve is very flat ROP so the engine does not run rough to let you know you have a problem. Your next takeoff makes this worse as that cylinder is run near best power during takeoff and detonates.

Now, consider the same situation--no engine monitor, but you run LOP. As soon as the injector partially plugs, one cylinder becomes leaner just like before. BUT, this time the partially plugged injector results in that cylinder putting out less HP than the rest (due to the slope of the HP curve LOP). Due to this, the engine runs rough and you immediately know you have a problem that needs addressing BECAUSE, a conforming engine will run smoothly LOP. Because it has begun to run rough, you know something is not right.

So, if you run ROP as a matter of routine WITHOUT and engine monitor you should run LOP occasionally to be certain it will run smoothly and everything is still conforming. If your engine is not conforming, you will not know.

If you run LOP as a matter of routine, the absence of an engine monitor is not nearly as critical.

Remember, the engine manufacturers and OEMs wrote those POHs before engine monitors were invented. They should be re-written, but I wouldn't hold my breath.

Since the most detonation-prone mixture is 50dF ROP and that's where the OEM has recommended operating in many cases, you can't do ANYTHING worse, ROP or LOP than do what they recommended. That's a fact of science which is confirmed by all data from every source.

The concept that you need an engine monitor to operate LOP more than ROP is simply wrong. We routinely operated Twin Beeches, DC-6s, DC-7s, and many others LOP since the 1930s and had no engine monitors. We did that with a single CHT, no EGT at all.

All of that said, I will not make an IMC flight without a working engine monitor--no matter how the mixture is set. I've seen too many "saves" through the use of monitors.

Originally Posted by Ernie Martin

So, at the risk of being repetitive, LOP is a good choice if you have "balanced" injectors (read: GAMI injectors), engine monitoring with cylinder-by-cylinder EGT/CHT readings, the willingness and ability to understand and manage the leaning process, and preferably an engine no longer under warranty from an overhauler which prohibits LOP.

We don't disagree all that much. I would simply "refine" your position to include proper understanding of WHY engine monitors are important--and it's not for leaning. It's for saving you money, your engine, and maybe saving your butt. And, you need it MORE if you operate ROP.

The only issue is the last one. TCM and Lycoming both support LOP ops. TCM has since the early 80s. Lycoming came around last year.

They did realize that they were delivering nonconforming engines and to keep their tech support lines from ringing off the hook, they suggested running ROP so their engines would run smoothly.

I don't have a SkyMaster POH handy, but I'll bet the engineering charts are in them that do show the LOP side of the mixture chart. Cessna has been including those charts in most model's POHs for a long, long time.

Ernie, thank you for the good conversation.