Twin Commander

General Category => Airframe => Twin Commander Piston => Topic started by: JimC on April 02, 2022, 12:56:10 pm

Title: Turbos...yes or no?
Post by: JimC on April 02, 2022, 12:56:10 pm
Here's my question for those more experienced than me...turbos or no? I fly out of Santa Fe. DAs are typically over 8000 in the summer. For a typical trip, I'd be 500 under gross. If I need to leave at gross, I could adjust my time of day to depart with a DA closer to 7000. After I leave my home field, MOST trips will head downhill.

Published rate of climb for a 500B at 6000lbs, 7000' and 75 degF is about 110 ft/min.
Published rate of climb for a 500B at 6750lbs, 7000' and 75 degF is negative.

Turbos or no?

I think it's a slam dunk YES, but I'm interested in hearing from others with more NA commander time.
Title: Re: Turbos...yes or no?
Post by: kent4142 on July 01, 2022, 08:38:13 pm
There is no question yes for turbos - anywhere out west.  You not only live at a high altitude home field.  Any where west, north or east have mountains.  Not to mention the need to climb for weather.

All that to say it is easy to spend other people's money - but IMHO turbos are not that expensive, for a big improvement in safety and performance.
Title: Re: Turbos...yes or no?
Post by: Badger on July 05, 2022, 01:17:27 pm
Excellent discussion.  For me, living in the flat lands (East Texas), I can adjust GW when I fly out West where you live, so, although the extra thrust would be very nice (always!), I can get out there and back without turbos.  I have flown into Santa Fe, Sedona, Telluride (carefully) with no real problems.  However, if I were living out there and flying Max GW on each takeoff, I would definitely consider the turbos.

Where will you get them?

Title: Re: Turbos...yes or no?
Post by: Bruce Byerly on July 05, 2022, 10:46:49 pm
According to more than a couple of my favorite Commander people, turbos are one of the best ways to ruin the simple beauty of a 500.  I’ve pretty much subscribed to that theory. Of course if I had to cross the Sierra Nevadas everyday, and had to have a 500, I may have a different opinion but I’ve never had any use for them nor have the operators I’ve known including those out west. Except for Hoover, I suppose he needed them.  From what I’ve seen, turbos on a Shrike are not some highly engineered deal you can buy anywhere and have Mr. good wrench put on. I’ve definitely seen them try to kill people with the added complexity, lines, heat, reduced maintainability, and poor support that you expect to find nowadays. Sucking oxygen at 16,000’ worrying about a backyard turbo install just doesn’t appeal to me anymore.

Imho, if you’re gonna have turbos, you might as well have pressurization i.e. an Aerostar.  Or a 421. Or better yet, an 840!

Title: Re: Turbos...yes or no?
Post by: JimC on July 29, 2022, 09:56:44 am
I now have about 100 hrs of flying a NA 500 in the mountains and at sea level. I'm happy with my decision.

I'm very rarely at gross weight, and have yet to do a gross weight takeoff at over 4,000' DA. AT gross weight above 6,000 you need to consider that you're flying a single with a good glide ratio - in other words, if you lose an engine you're going down. It's just a question of where.

I've taken off several times at DAs over 10,000' and weights that are about as low as you get - single pilot & partial fuel. The plane does well and climbs away easily. That's obviously not very practical, but I can do a lot of my missions at 600-800 lbs under gross. I don't know how many 10,000'+ takeoffs I have left this summer (our temps are already dropping) but I'm sure I'll find one or two opportunities and slowly raise the weight I'm comfortable with.
Title: Re: Turbos...yes or no?
Post by: appleseed on August 02, 2022, 12:40:45 am
Ive been meaning to add comments ever since this interesting thread was started. I agree with Bruce , Badger, and JimC - there is a fairly narrow range of missions that would benefit from turbos.  And the performance and cost penalties are significant.

If your mission is to fly above turbulence in the west in the middle of the day, or imc above 10-14,000 MEAs, or takeoff with a full load and DAs above 7,000 - yes turbos can give you margin above what an NA Shrike offers. But, unless you are only flying by yourself, or carrying boxes, those are really jobs for 421 or Turbo-Commander.

The mission that JimC talked about seems like the one case where turbos might be justified on a non-pressurized twin - back country ops with some payload, and terrain and DAs of 8,9, and 10,000.

Once you get used to the performance of twin turbine aircraft (in thrust we trust) with their ability on one engine to easily exceed most climb gradients and carry a splash of ice at most of the MEAs in the US, it is a big strategic adaptation flying piston twins. Theyre still much better than singles (in luck we trust), which have roughly have an engine out descent rate equal to the engine out climb rate of a 690. Pretty much all NA piston twins have a S/E climb rate somewhere between just barely climbing and shallow descent (depending on weight and DA). Adding turbos shifts the polar just slightly so that you can maybe just barely climb, but hopefully at least maintain altitude in the hot high heavy corner of the charts.

With such marginal performance it is even more important than turbine twins to be fully proficient in emergency procedures. Most turboprops have some form of autofeather (and even rudder boost). In a piston twin, most of your performance is recovered by a correctly executed eng fail procedure that includes gear and flaps up and correct engine feathered. But, there is still as much as 200 fpm of climb (or reduced negative climb) to be achieved with correct technique (or squandered).

Imagine yourself cruising along in smooth summer morning air at 10,500 (DA 12,000) above an 8,000 western plateau. Your single engine service ceiling is only 7,500. Could you make it to your 4,500 drift down airport 30 miles away?

Maybe, but only if you:
establish zero sideslip. Use your yawstring. If not installed, bank 3-6 degrees into good engine. 50-75fpm.

Close cowl flap on dead engine and correctly set cowl flap on good engine 25-50 fpm.

Correctly lean good engine for maximum cooling without giving up power. 50-100 fpm.

Fly best performance speed - at higher altitudes and reduced power, it is lower than blueline. In smooth air experiment with speed to find min sink and fly that speed -0/+5 kt. 25 fpm

Thats enough for tonight. While Im a Commander newbie, I do have some experiences to share later regarding turbo vs non turbo performance and maintenance in GA aircraft. As well as alternative solutions for high altitude ops.
Title: Re: Turbos...yes or no?
Post by: JimC on August 03, 2022, 09:16:10 am
The one thing I'd add: Ignore maximum cooling. I did some tests during my initial in the commander and I think one cowl flap is about 60-70 fpm - it might even be more. Over a 10 minute stretch to an airport that's 600-700 feet. Remember our true engine redline is 450. We keep them lower (I try to use 380, even in climb) for long term health. If I need to make a field, I won't hesitate to close it down and run at 450 (or 480 if that's what it takes.)

I'd rather drag six trashed cylinders to a runway than put six good cylinders into the dirt. The nasty twist to that decision is that insurance pays for the latter but not the former.
Title: Re: Turbos...yes or no?
Post by: appleseed on August 04, 2022, 01:23:43 am
There is an interesting variety of ways to control the waste gate on turbocharged airplanes. And of course a wide range of engineering quality for the whole installation. For the purposes of this discussion I would break them down into three levels.

The minimum engineering modification with stock 8 to 8.7 to compression ratio pistons and simple wastegate (often manually controlled). These can retain pretty good performance (the higher induction temp means you need to boost manifold pressure by a few inches to maintain HP). They only weigh 25-50lbs per engine. And theoretically these simple wastegate controllers are easier to maintain and troubleshoot. The downside is that the installation is often under engineered, resulting in heat or vibration or cracking problems under the cowling. They are also more demanding of the pilot. There is a lot more potential for overboost, and with the stock pistons, there is less detonation margin. If timing is off, or the ignition system is not maintained, or injector plugged, or plenty of fuel is not provided these installations are much more susceptible to accelerated wearing out of or plain wrecking of cylinders. With a reduced detonation margin, the "redbox" of potential detonation is much larger.

Next, the still under engineered factory planes (and some of the better stc'd ones) that were widely marketed in the late 60s and 70s. These airplanes still had simple wastegate controllers but compression ratio reduced to maintain detonation margin and manifold boosted up around 36-41" to maintain power. They were more tolerant of sub-optimal maintenance or pilot technique but performance and efficiency sucked. Kind of like the recalled vw diesels with compression ratio dialed down. Over the years I worked for operators that had in the fleet both turbo and NA versions of the same plane. Bonanza, Arrow, and 310/340. I was a young consumer of aviation marketing magazines in the 70s when manufacturers were racing to come out with turbo versions of everything in their lineup. They planes were pimped as a big jump in performance with impressive speed and altitude potential. I was pretty stumped when I actually flew them. In every case the NA plane easily outperformed the turbo at any altitude that didn't require oxygen. Full throttle and S/E performance was better up to 5,000', and cruise performance was better up to 10,000'. Whenever you did a two ship mission, the turbo would take off first and land second and burn 20% more fuel. Generally though you didn't have to fuss with the mixture for takeoff and climb, so the workload could be lower.

Eventually the quality was brought up to the fully engineered systems like the ones on a 404/421, Chieftan, Columbia 400 and others that I am not as familiar with. These still had the lower compression pistons, so fuel efficiency was reduced, but they got sophisticated waste gate controllers, tuned induction, intercoolers and they were boosted up to provide horsepower above what any NA plane could produce. Often a bitch to work on though and 25-40% more expensive to run per mile than the NA version.

But this all pretty academic right? Is there anywhere to buy a turbo kit for a 500?  It seems like turbo'd airplanes do come up for sale. What level of quality is the turbo installation? The better ones, like Chieftan level should up the performance but at a significant weight and cost and fuel burn penalty.

As long we are fantasizing, the fadec Lycoming that Cape Air is running in their Tecnam 2012s would be an awesome Shrike engine if they ever get it sorted out.

In a less fantastic world I would rather have the plane that Ted designed for this mission 60 years ago than an aftermarket turbo install. IGSO 540s seem to be considered unmaintainable in the Commander community, but I saw a lot of T-bones and several Queen Airs at OSH, and some of them had the big supercharged motors.

But all of those options are well beyond my means. I can only afford the approach that JimC describes - keep the weight down and be realistic about your options.

Maybe eventually I will be able to afford some new blueprinted engines. I believe ported and polished and flow matched E1B5's will produce 300hp on the dyno. Supposedly there are engine builders who, if you ask tactfully, will install 9.0-1 or even 9.5 pistons while they have your new cylinders off for rework. You would be giving up some of your detonation margins, same as the first turbo example described,  but fuel efficiency is improved if you can safely operate lean. Finally, if you had a good relationship with a shop (or you were your own shop) you could swap governers for ones that would let you turn 2700 rpms. Then you would have a plane with expensive (to buy, not to run) 325ish hp engines with no weight penalty or complexity, that would outperform a turbo shrike on one engine up to 7500' and out cruise  it up to 12,000'.