Performance after failure of engine on takeoff, and SE procedures (was SE T/O Perf)

[hewilson]

Jose's list highlights a question I have had. The single engine rate of climb for the Skymaster under standard conditions varies depending upon the operative engine, the specific model and the publication one reads but would appear to be somewhere between roughly 325 - 375 fpm. I've read though of a number of accidents in which the principle or contributing cause is listed as engine out on takeoff.

Now 300 fpm isn't great but ought to be adequate in good weather and without substantial obstacles at reasonabe density altitude (query "reasonable"). For example I once took off in a C152 at DA approx. 1000 ft. with me (195 lbs at the time), my instructor (approx. 170 lbs) and as I recall, about 20 gals of fuel. Weather was clear but with a near 90 degree crosswind at about 9 (the favored rwy was not available). I noticed that it seemed to take longer than usual to attain rotation velocity and when I did, the plane just did not want to climb. I nearly stalled it immediately off the deck. I pushed it back over, stayed in ground effect and was able to gain enough speed to climb at about 200 fpm which was enough to allow me to turn clear of hills and trees about 1 mile or so ahead. I never quite gained pattern altitude but remained in the pattern and returned safely. Turns out the carb heat was stuck on even though the switch was in the off position and I was not able to get more than about 2250 rpm. Point is, 200 fpm was adequate under those conditions.

I'm assuming therefore that the engine out on TO Skymaster accidents must have occured in poor weather or at high density altitude or have some other contributing factor(s).

Anyone have any insight on that?

Hugh

[Mark Hislop]

Hugh:

The 300 FPM SE climb rate is achieved at Vyse, and more importantly, with a "clean" airframe. With the gear down, you loose at least 100 FPM. If the gear doors are in transit, or stuck open, you will do well to maintain altitude. And if you inadvertantly take off with the rear engine not running, and therefor do not have the prop feathered, the increased drag from the windmilling prop will most definitely cause you to loose climb permormance.

By the way, except for the drag of the gear doors, all of these factors are the same for other light twins. Of course with the other twins, you also have the problem of assymetrical thrust to contend with as well.

Mark

[hewilson]

That answers it I think. Makes more sense now. I didn't realize the SE rate of climb was quoted in the clean configuration. I was assuming that it was with gear still dowm and I hadn't considered the undfeaethered prop. Thanks.

Hugh

[kevin]

Just to clarify, in case anybody else misreads Mark's post, as I did at first, when Mark says you "lose 100 FPM" he means "your climb rate is reduced by 100 FPM". So if you had 375 FPM with the gear up, it would be 275 FPM with the gear down.

I have experimented some with this, and I am not sure the penalty for having the gear remain down is as high as 100 FPM, but there is some penalty. The airplane does climb amazingly well with the gear down though. I experimented with this to determine if, during a best angle, short field departure, I was better off raising the gear, or leaving it down until I had cleared the obstacles. I decided that I was better off leaving the gear down and continuing to climb at 75 MPH (RSTOL) until the obstacles are cleared, then pushing the nose over and raising the gear when I got a bit more speed. If I remember right, this is the Robertson recommended procedure as well.

On the other hand, I am even more pessimistic than Mark about gear doors stuck in transit. I would be very suprised if an airplane with the gear doors stuck in transit (and an engine out) would maintain level flight. My copy of the O-2 flight manual says that the doors extract a 240 FPM climb penalty during transit, at least after a rear engine failure. If you take the performance numbers from a '67 337, the best single engine rate of climb, rear engine feathered, is 335 FPM at sea level on a standard day. I suspect real world performance is 100 FPM less than that, meaning that having the doors stuck open would result in a gradual descent.

This leads to my strong belief that Skymasters built before 1973 which have the hydraulic pump on one engine and have not had the gear door removable mod done should be flown with the gear down during takeoff until a comfortable altitude is reached, maybe 800' or so. Why? If the "wrong" engine (the one with the pump) fails at exactly the wrong time during the gear retraction, I would not want to be trying to hand pump the gear to finish the retraction cycle at the same time I was feathering an engine and dealing with the rest of the emergency. I know, supposedly if you leave the engine unfeathered until the gear comes up the rest of the way, you can deal with it that way. But that would induce a real "sinking feeling" as well, with the prop windmilling and the gear slowly retracting. And I am not completely convinced that the prop would keep windmilling, depending on the situation and the type of engine failure...

Post '72 Skymasters should use positive rate, gear up in my opinion. With the electric hydralic pump, the gear will continue to retract no matter which engine fails.

My opinion only, each pilot should look at the data and make his own decision. Cessna's recommendation is to retract the gear immediately (positive rate, gear up) on all models of 337.

Kevin

[Kevin McDole]

Hugh,

The single engine rate of climb is one factor, but how much runway will a single engine takeoff require? How about to clear a 50 foot obstacle? There's no specs on this. That may in fact be where the danger lies.

[hewilson]

Kevin M.,

That's right. Short field with a long TO roll would be trouble as would low rate of climb and nearby obstacles. During my 200 fpm climb I recounted I was staring at nothing but hills and trees for a while. I was struggling to gain altitude and speed so I didn't want to turn too soon. I started about a 20 degree turn at about 400' agl maintaining about 65 kias and it worked out OK. In retrospect though I probably had plenty of room to get up to 800' agl before I turned. But those hillsides looked pretty imposing at the time.

Kevin webmaster,

When you say "post '73" is that inclusive of '73 or truely post '73 only?



hugh

[kevin]

You're right Hugh, I should have written "post '72". I mean 73 and later.

Kevin

[SkyKing]

Our '77 P337 has the RT Aerospace 'No Doors' deletion kit... this coupled with the improved takeoff/climb performance with the full Robertson STOL kit is the way to go. There's no penalty for the clam shell doors, as they are removed from the equation.

SkyKing

[Frank Benvin]

1967 337B

My rule of thumb is not to touch the gear until I reach 500 Feet AGL

Frank

[WebMaster]

If you are single engine, and operate the gear, opening the doors, you will experience a negative rate of climb. On one accident, as I remember it, the pilot cycled the gear shortly after takeoff, and the resulting negative rate of climb caused the accident. I think, have to look, that it is not just diminished by 250 FPM, that it is actually -250 FPM, for the 10-12 seconds to cycle.
Also, take note, that in 69, it was possible to get gear pumps on both engines. Mine has that, as does Jenny Stack's plane. It doesn't make anything work faster, just gives you the ability to cycle the gear with either engine running.
Of course, taking off with one engine not working is always a root cause. Another thought, however, is that these are reported accidents, and I know that in the Cessna ads of the time, they did get one off the ground with one engine feathered.

Which brings up an interesting point. If you can't get the engine started, how can you feather it?

[Dale Campbell]

I have a 337H model with main gear doors removed. Three years ago while flying with my flight instructor. He pulled my front engine to idle on take off at 300 feet AGL. I had just raised gear, still had 1/3 flaps down. I quickly dropped the nose to maintain 90 kts. It was a 80 degree day & the airport was 600 feet above sea level. I had 100 gal of fuel on board. My son-inlaw in the back seat who weighs 165 pounds, I weigh 170 pounds & my flight instructor weighs 265 pounds. I made a slow turn to the left to go down wind and could not gain a inch of altitude until I was mid field. Than it started to climb slowly. I managed to gain 90 feet before turning base. I know the front engine was creating drag at idle. If it was a real engine out I would have feathered the prop on dead engine. I was impressed with performance under the conditions of high tempature and high payload. Try that in a single engine aircraft.

[Bob Cook]

I rather doubt the gear doors contribute much drag other than during transition. It certainly will not assist in climb other than the weight reduction.

If it were an important as one is led to believe then why did Cessna put them on in the first place?

Since there is superficial drag with the wheels down why not transition the gear at during cruise transition at 1k ft?

You can reduce drag by obtaining a wing removal kit ;>)

Bob

[Jerry De Santis]

Dale, for the very reason you describe is why I do not rotate until blue line is achieved. I fly P337G and blue line is 100 MPH, Loss an engine and keep on trucking. I believe Bob Cook also rotates at blue line. Am I correct Bob?
Jerry

[Ernie Martin]

Jerry:

Why rotate at 100 MPH? Let me play devil's advocate for a moment on an approach which may accomplish what you're trying to achieve, but (I think) earlier and safer.

In my normally aspirated 337G I rotate around 80 MPH. I then remain at 20-30 ft altitude or so, within ground effect, until I reach blue line of 100 MPH. I do a quick check of engine gauges just before getting to 100 and at 100 I start my climb.

My objective is to minimize rolling friction from the tires. I believe I get to the 100 MPH point earlier in the runway than if I had been rolling through the last 20 MPH of increased speed. Thus, when I hit 100 MPH I've got more runway left, than if I had rolled all the way to 100 MPH. Also, notice I'm airborne at 80 MPH, so if there's a problem with controls, I'd rather find out at 80 than at 100.

In short, I agree completely with getting to blue line quickly, to protect against an engine failure. Why not do it really quick?

Just food for thought and perhaps the start of a healthy debate.

Ernie

[Mark Hislop]

Ernie:

I too rotate at 80. Why make those little wheels rotate any faster than they already are? The aircraft accelerates so quickly that I don't think there is any reason to keep it on the ground until reaching blue line.

After takeoff, I climb at 120 mph (top of the white arc) until 400-500 AGL. I raise the gear and retract the flaps, then I reduce power to 75% (top of the green arcs for MP and RPM), and continue climbing at 130 mph. This airspeed allows me to see over the nose, keeps the engines cool, and gives me 500 to 750 fpm climb. The extra margin above blue line also gives me some time to react to any problems and still make sure I stay ahead of the power curve.

Mark