Counter rotating multi engine

[Vector4fun]

Hey, ERJ Mech;

Isn't your avitar counter-rotating as well?

 

[Lead Sled]

Nope but like all other Garrets (J31, SA227,B100 ect) both props spin opposite to the "normal" clockwise spin.

I think that that's only true with the Dash 10 powered MU-2s, but I could be mistaked there. I seem to remember something about an extra gear in the gearbox of that particular model 331 that caused the props to rotate "backwards".

Back to the original question. FAA definitions aside, I fully agree with SkyWestCRJPilot's statement that counter-rotating does NOT eliminate the critical engine, it merely makes both engines equally critical. All theories aside, piston powered, twin engine aircraft have two engines because they need two engines. Period. However, under certain, limited conditions, they can manage to remain airborne and controllable on one engine. Keep it above blue-line and the direction the propellors rotate is a mute point. The graveyards are packed with pilots (and their passengers) who either didn't understand or didn't believe that fact.
'Sled

 

[erj-145mech]

Actually, both engines are interchangeable with each other. They are both IO-360-D's, but are bolted to the airframe 180 degrees from each other, so they are counter rotating, or contra rotating, depending on which one you start first, he he. The only difference are the propellers, one tractor, one pusher. The engine accessories are a bit different. The front engine has the only hydraulic pump for the gear and a gear driven alternator. The rear engine has no hydraulic pump and a belt driven alternator off of the prop. Neither engine has a vacuum pump, the gyro's are electric off of an AC inverter (26 v, single phase ac). The rear engine has a fire detection system installed from the factory, with four temperature detectors.

 

[KeroseneSnorter]

Absolutely right. BOTH engines on a piston twin are critical. After an engine failure on a normally-aspirated light twin, what you've got is the same situtation you've got after an engine failure in a '182: You're in a glider. a Baron or Twinkie'll glide quite a ways on one, but you're not going too far.

And here I thought the Critical engine was the one that was still running!!


Some of the light twins do ok on one. The 58 Baron is pretty good on one if you are on the east coast with low altitudes. Got more time on one engine in those things than I care to remember from the old freight days! (shudder...)

 

[ToiletDuck]

Well I now the Seminole can usually climb with two heavy people in it and full of fuel as long as you are below 5k. I just did it this morning

 

[DAS at 10/250]

Nope but like all other Garrets (J31, SA227,B100 ect) both props spin opposite to the "normal" clockwise spin.

WTF?

I don't know what Garrett you're flying but the TPE 331-6-252B spins like every other American made motor.

 

[sky37d]

Actually, both engines are interchangeable with each other. They are both IO-360-D's, but are bolted to the airframe 180 degrees from each other, so they are counter rotating, or contra rotating, depending on which one you start first, he he. The only difference are the propellers, one tractor, one pusher. The engine accessories are a bit different. The front engine has the only hydraulic pump for the gear and a gear driven alternator. The rear engine has no hydraulic pump and a belt driven alternator off of the prop. Neither engine has a vacuum pump, the gyro's are electric off of an AC inverter (26 v, single phase ac). The rear engine has a fire detection system installed from the factory, with four temperature detectors.

On mine, I have hydraulic pumps on both engines, gear driven alternators on both engines, and wet vacuum pumps on both engines. Also, two independent, selectable, regulators. The O-2's were a bit different in those respects.
Good to see another MixMaster on the board

 

[Lead Sled]

I don't know what Garrett you're flying but the TPE 331-6-252B spins like every other American made motor.

I agree, it was my understanding that it was just the -10s and -11s that rotated "backwards". However, there are a lot of combinations and permutations so I'm sure there are others as well.

'Sled

 

[Lrjtcaptain]

The PA31-325 I used to fly had counter roatating
So did the Cheyenne 1 I used to fly.

Ive seen the 400LS with counter rotating but the Mu2 I flew didn't.
Must be a Piper thing.

 

[erj-145mech]

I've worked on a lot of PT-6 powered Cheyennes, (I, II, IIXL, III) and I don't remember any of them being counter rotating? I've never worked on a Garrett powered Piper though.

 

[Lead Sled]

The PA31-325 I used to fly had counter roatating
So did the Cheyenne 1 I used to fly.

I've never flown a Cheyenne I, but the IIs and IIIs that I flew didn't have counter rotating props. Me thinks you might be mistaken - it happens to the best of us. The 400LS had counter rotating props on their big Garretts.

'Sled

 

[KigAir]

Actually, both engines are interchangeable with each other.

Does it perform with one engine out?

 

[Lead Sled]

Well I now the Seminole can usually climb with two heavy people in it and full of fuel as long as you are below 5k. I just did it this morning

There is a big difference between being "usually" able to climb and having "useful" single-engine performance.

Regardless of what the POH says, most propeller-driven light twin engined aircraft really suck when it comes flying on one engine. Several years ago I gave a BFR and instrument check to a guy who had purchased a brand spanking new Seneca II a couple of years earlier. He had taken his original ME training in an Apache and had just flown with his salesman for the Seneca checkout. Evidently, they didn't do much, if any single engine work, on the checkout - "don't want to shock cool those new engines".

During the ground school portion of the BFR he mentioned several times how safe he was now that he had a twin-engined airplane and that his airplane was turbocharged and could fly at 17,000 feet on one engine, etc., etc... It was very obvious that he had been paying very close attention to what his aircraft salesman had been saying. After listening to this for a while I figured that I need to give this guy a reality check.

Long story short, you should have seen his reaction when I pulled an engine back right after takeoff. We were climbing at about what the book said we would, but we weren't getting very high very fast and we were covering a lot of ground while we were doing it. It seems that he had failed to consider the effect of single engine climb gradient. He sure was a "happy camper" when I gave him his engine back. Before that flight was over, he had gained a new understanding and respect for the "real world" performance capabilities of his airplane.

From a training point of view, I really don't think that it makes any difference what twin you train in or use as a time builder. But remember, the single-engine performance in any piston-powered light twin is abysmal. Loss of power is the primary culprit. Remember, normally aspirated aircraft lose power with altitude. An aircraft's climb ability is directly proportional to the amount of "excess" power that it has available vs. what is needed to maintain level flight. For example, if a 200 HP normally aspirated airplane requires 100 HP to maintain level flight it would (at SL, ISA day) have 100 "excess" HP to use for climb. At 10,000' MSL, the engine might only be able to produce 130 HP, leaving it with a 30 HP surplus. This is the reason why turbocharged aircraft perform so well - you would be able to maintain SL power up until you reached the "critical altitude" for the particular engine. In some cases, this can be as high as 18,000' MSL.

This is also why light twins typically perform so poorly on one engine. Take, as an example, a Twin Comanche with two 160 HP engines. If that airplane required, say, 150 HP to maintain level flight it would have 170 "excess" HP to climb with. If it lost an engine, it would have lost 50% of its available power, but with just 10 "excess" HP, it may have lost 95% of its ability to climb. This, of course, will also apply to the Baron and all other light twins. If you only learn one thing from this post, it should be that light twins have two engines because they need two engines.

There are some other operational differences that you should be aware of…

If you're in a single and you loose the engine, the laws of physics dictate what will happen next. Leaving the gear down until you have no more "usable" runway left only makes sense. It will leave the airplane in much better condition should the engine decide to pack it on while you're still over the runway. (By the way, I've had it happen to me once.) I've seen some "hotdoggers" rotate and immediately suck the gear up. A while back, I even heard of a guy who would place the landing gear in the up position as he took the runway. His thinking was that the squat switch would keep the gear from coming up while the airplane was on its takeoff roll and immediately start the retraction process as soon as he broke ground. What a weenie - his practice came to light one morning when he rotated a bit too early and the airplane settled back onto the runway. You don't need a PhD in Physics and Aeronautical Engineering to figure out what happened next. (By the way, these are usually the same guys who immediately pull the throttle back to climb power as soon as the gear is in the wells. Statistically, that's the time when you’re most likely to have an engine come apart.)

Multiengine aircraft are an entirely different matter - you want to get the airplane cleaned up as soon as possible. In the case of most piston twins, their ability to maintain controlled flight depends upon the pilot getting the gear up, the propeller feathered, and the flaps up. Failure to this often results in the airplane being turned into a lawn dart.

I don't want anyone misunderstanding my comments on the need to get gear up on light-twins ASAP. I'm not implying that you need to get the gear cycling the moment the aircraft breaks ground. You don't need to be cocked and on a hair trigger - just get to it as soon as you can get around to it. Sure, there will be situations where you can delay it - if you're based at an airport with a 10,300' long runway and there is no need to be in a rush with the gear. You could takeoff and land most twins 3 times on this runway. However, I believe that on a more typical runway, once the airplane's up and climbing, having the gear out becomes more of a liability than an asset if and when an engine decided to "go south" on you.

We tend to take engine reliability for granted, but I believe that this is a very dangerous thing to do. Most light twins simply won't maintain altitude with a windmilling propeller and/or the gear down. The old Metroliners had a rocket bottle in the tail to buy the flight crew enough time to get the gear up in the wells. Auto-feather systems are on most, if not all, turboprop twins. The manufacturers wouldn't put up with the increased costs and complexity of doing this if there wasn't a true need for it. They put this stuff on the turboprops that have significantly better single-engine performance than piston-twins. It really ought to be on the "little" twins, but no one is willing to pay for it. Like I said, light twins lose up to 90%+ of their climb capability. The figure is probably even higher than that - I've seen several non-turbo'd twins that wouldn't climb out of ground effect and several turbocharged twins that could barely achieve climb rates of 100 fpm or so. But never the less, the point is that twin engine aircraft have two engines because they need two engines and under certain conditions they can maintain controlled flight on one engine IF THE PILOT DOES EVERYTHING RIGHT. You don't have time to dawdle, it has to be done right and right now.

Oh well, enough of that. I really ought it get a life.

'Sled

 

[macfly]

good post sled...

I thought you had to be a military demostration pilot for that hurry up gear procedure.

what a wet noodle.

 

[DC4boy]

My OV-10 has counter rotating props. Does really well on one....