Single-engine Endurance and Performance
 

A question and then the reason behind it.

In a normally aspirated Skymaster, with 2/3 load, on a day 20 deg F warmer than a standard day, if one engine fails at a cruise altitude of 5,000 feet, can you maintain altitude for an extended period, say, two hours, and what is the performance?

I fly out of Miami, mostly over water. Based on the POH data*, I have been under the impression (and still believe) that, despite the higher temperature, the single-engine aircraft would maintain 5,000 ft altitude without difficulty, at a speed of ~ 110 - 120 MPH (depending on which engine) at 25/25 or a speed in the 90 - 100 MPH range at reduced power (say 24/23).

Someone with Skymaster experience told me otherwise. He thinks that even 25/25 will not maintain altitude, and you have to put the aircraft in a gradual descent (say, 75 ft/min) to maintain 90 - 100 MPH. Meaning that you've got around one hour before you run out of altitude. And he voiced concern, assuming you could keep it airborn longer (for instance, if the load is even smaller), that the engine would run for hours at 25/25 without overheating.

I am hoping to test this using the simulated engine-out procedure, if and when I have such a load without finnicky passengers, but in the interim it would help if you have any opinion or experience on this.

Ernie Martin

______________________
* Where single-engine ceiling is ~ 6,000 ft and there is positive climb rate below that (higher for the rear engine).

My opinion is based on limited single engine work, just enough to know how the aircraft will handle. I have shut down an engine several times but this was for practice and can't say what the loads were exactly but here's a good attempt at remembering.

Out in the mountain states years ago with 2JF dad and I practiced the SE stuff several times. I can remember being at around 10K MSL but don't remember the temperature. I would guess that it was at least standard or maybe less. For load the mains were full, not sure on the aux's but it's a good chance that they were full too. Myself at 200 lbs and dad at 265 lbs. We maintained 10K for some time but it was a little sluggish. The rear was better than the front. I lost a cylinder over Lake Michigan several years ago and pulled the front back to minimal and flew it for about an hour with no problems. I would say that I was at 6500 ft. I did not know what had happened to the engine while in flight but I watched my vitals and limped into the airport. Cylinder separated from the base.

At 5,000 ft and 2/3 load I would estimate that you could maintain altitude. You didn't mention that your experienced source had actual factual info on this or if it was just an opinion based on POH.

The source was basing it on recollections of practices/simulations and conversations he had with others, not on a specific incident.

Ernie

Follow the POH
Feather the engine that doesn't work, because if you feather the engine that was working, you got a lousy glider.
Close the cowl flap doors on the engine that isn't working.
Open the cowl flap doors on the engine that does work.
Go to max throttle, lean for performance. At full load, or pretty close to it, you can maintain altitude, at least at 5K, even on a warm day.
keep in mind, however, that you don't want to do this for very long, and you'll be down to blue line or pretty close to it, which is why it is there.
I was able to maintain altitude for a short period of time, on the front engine, but it was an emergency, and we headed for an airport right smartly.

I forgot
 

you wanted to do it at 25/25, or reduced power.
Not the wise thing to do. POH says max power. Do that, you can stay up.

The issue of power and extended endurance is precisely the question. These engines are not rated for extended operation at full (i.e., take-off) power. If your closest landing is 1 or 2 hours away, you want to go to full cruise power, which is the top of the green band or 25/25. I believe that the engines are designed to operate at this power for extended periods. Can we start with that? Do you all agree or disagree? Then, will it maintain 5,000 ft at 2/3 load on a warm day?

I think this aircraft -- and all twins -- are designed to do that. Am I wrong?

In a single-engine aircraft, you have to promptly find a landing spot if the engine quits. Are we saying that our second engine simply extends briefly (5 - 15 minutes) the time we have to pick a landing spot?

Ernie

Thats max continuous power (25/25), not full power.

On my O-2, I am able to maintain 4K, configured single engine, rear engine operating, near full gross wt.

And what the hell is blue line on a center line thrust airplane?

Come on, people. No more views? I'm seeking your opinion whether or not you ever did this. It's real simple and probably at the core of why you bought a Skymaster. The choices are:

1. Yes, a 2/3 loaded Skymaster on one engine will maintain 5,000 ft even on a hot day. That's what twins are supposed to do.

or

2. No, you will bleed altitude to maintain a safe speed. It's just like a single, where you've got to start looking for a place to put it down as soon as you lose an engine, except here you have more time to look.

Please vote.

Ernie

The best rule of thumb in any multi engine aircraft is once you have lost an engine land as soon as practical.

Thanks, I recognize that. But that's hard to do when you're over water and the nearest airport is one hour away. And the issue is more than academic, because mitigating steps can be taken: if I knew that I can't maintain altitude, then I will fly at higher altitudes* or with lighter loads. Please choose from my earlier memo, do you think it's 1 or 2?

Ernie

_______________
* I now fly at around 5,000 ft, based on prevailing winds, convenience and another factor mentioned on the next sentence, but I'd go to 10,000 ft if I knew that I can't maintain altitude (the extra 5,000 ft would gain me 50 extra minutes aloft if the loss is 100 ft/min). But if there is a fire on board (my third consideration) it would take twice as long to ditch. That is why, in part, this is important: no sense flying higher (a fire/smoke drawback) if the aircraft can maintain 5,000 ft with one engine.

Load your aircraft up and duplicate the circumstances you mention and go out and try it.

No 2 aircraft are the same, nor are two different pilot's abilities.

You're looking for a blanket answer.

It's not easy to find enough people for 2/3 load who are willing to endure this simulation. And I don't seek a blanket answer, just people's opinions until I test it.

Ernie

Bags of sand, bags of concrete mix, free weights, etc. It doesn't have to be people.

You're expecting someone to provide you with an answer when you could go out and prove it to yourself except you don't want to risk it with your airplane. No one here is going out to be your test pilot.

As I said earlier, there are many factors involved in the scenario you have provided, airplane, engines, rigging of the airplane, center of gravity, skill of the pilot, weather conditions, etc.

Tropical, do I sense some problem here? I ask because you seem to find discord with almost everything I say. For the record:

1. I've carried cinder blocks, concrete and lots more on my airplane, and it leaves the interior a mess.

2. I'm not asking anyone to provide with an answer or be my test pilot. Take a moment to read my postings above. I'm seeking only opinions, even from people who haven't tried it.

3. Your flat statement that I don't want to risk it is false. I will do it as soon as I can, something I've said in prior postings. Until then, I was simply hoping to get views that might prompt me to fly lighter or higher.

But, given that the subject seems to trouble you, and to avoid further discord, I will not be posting further replies on this thread. I will let my prior postings speak for themselves and hope that anyone with views on whether our twin can maintain altitude after an engine failure will post them here.

Ernie

Doesn't trouble me at all. Several posters (including me) have already gave you information but you simply won't accept it.

You take a "pollyanna principal" approach to operating the Skymaster as recently exhibited on the thread about flying to Bermuda.

Hoo Rah
 

Load it up, then fly it the way you want. Fill it with sand bags, cement bags (they are readily available). Put in as much or as little fuel as you want. Then take it up to 5K, and shut down an engine. Don't go pansy on us, using the zero thrust thing, shut the engine down. Experiment with the various power settings. Then shut down the other engine. Oh, you might want to fire up the one you shut down first.
See if you can hold altitude at 2300 and 17 inches. Then move up from there.
Do the test pilot stuff your self.
Let us know if how you do. See if the POH can be ignored.
Make a video of all this, too. You can mount a camera so it shows the instrument panel. Looking over the left shoulder.

By the book, it works,

My Vote is YES

Ernie,

My two cents.... Be careful out there. If you are going to start feathering props, start at very light weights and work up from there. And what the heck, you may as well do it over the top of a 4000-5000+ foot runway just in case things do not go quite as planned. I'm just a fan of being conservative. It keeps us safe and keeps our old machines flying. The results would be interesting, however I personally believe the book and assume that is the best case scenario. I figure I would not do as well as the book because my airplane and my skills would not match the airplane and the pilot that Cessna used. Be safe.

Ed

Appreciate the inputs. Hoping to do it late this week. Sorry, but I will do it via the zero-thrust simulation, and yes, on top of a 4000+ runway. I also believe the numbers, adjusted of course for aircraft aging which reduces thrust and increases drag, thus my 2/3 load. Will let you know.

Ernie

Get Real
 

This is supposed to be a valid test.

Do it over the water. See what happens. It's amazing what a little reality dose does to your pucker factor. And the validity of your test.

Just a side note on "zero thrust" settings. Even if you have set the book "zero thrust setting" you are still producing a small amount of thrust.

The airplane will behave differently. Try it with "zero thrust" then go back and feather the engine. It's an eye opener.

I vote YES:

Normally aspirited '76G; FE prop feathered ;4200 +/- weight; summer; 6,500;TAS 115K +/-; 24/24; actual flight from GPT to AWM after losing front engine SE of GWO - continued to AWM. No sweat; opened RE cowl flap 1/2 but don't think it was necessary.

Took a mountain flying course with a United instructor who wrote the book on mountain flying over Leadville, CO; summer; again about 4200lbs at about 11,000 and he asked if it would sink quickly or slowly. Told him I did not kow so he simulated zero thrust and to both our surprises, it mantained altitutde!! We didn't do this long enough for a true test but we both thought it would start down at least 500' per min.

I vote 'Yes.' It's true that the POH numbers were generated on the basis of a new, clean airplane flown by a factory test pilot (and such computer data as was available in the 1960s). But from what I remember when I checked the performance numbers when I started the marine surveys a few years ago, I was comfortable I could get back to dry land on one engine, even with an airplane at near max gross (4200#) - bearing in mind that I'm talking about already being at 700' when the engine craps out.

Even if your airplane is so out of rig or dented that you couldn't maintain, say, 5000,' at max continuous (25/25) the sink rate should be minimal, down to a point where you'd be in ground effect. That would cover a lot of ground (or water).

Regarding the engines, I'd start at the top of the green arc and see what it gave me. If the airplane wasn't holding altitude, I'd let it sink until I wasn't comfortable going any lower and then use it all. A good reason to baby the engines under normal circumstances.

All of this is analogous to the 'driftdown' procedure we used in the airlines on the heavy jets.

Finally, unless you're alone, don't forget about throwing stuff out the cargo door (women and children first?)

Ahab

Have you done it yet, Ernie??

Inquiring minds want to know.

Hoping to do it this weekend.

Ernie

I did this when I went flying in N2131X with the Terrafugia boys who wanted to learn some things about Skymasters and "blown elevators" (as their test pilot referred to it) and as they were toiling with getting the flying car going. In that case we were pretty close to your question, except for the temps, which were right around standard.

Max gross, front engine set for zero thrust. It would fly along all day long at 25/25 on the rear engine at 5000. I have only done a more legit test once when I mistakenly ran the rear engine out of gas. I didn't mess around with gathering data that day, as I was IFR and got it going again in about 20 seconds!

Bill

I did a simulated and brief test on Friday. I conclude, guardedly, that the answer is Yes. I say guardedly because I did it with passengers on board, approaching and slightly overshooting the destination airport, for about 10 minutes. It seemed to maintain altitude with the front engine at 25/25, rear engine at simulated thrust with the adjustment for hotter day, and the front engine temperature seemed to plateau at an acceptable level, without overheating, despite having the cowl flaps only half open.

I say seemed because one cannot say with absolute certainty that I wasn't losing a few feet of altitude or the engine slowly increasing in temperature. It didn't seem that way, but I would have liked to have run the test for, say, 30 minutes, and to do that safely (for me, anyway) I would have to orbit an airport. Couldn't do that with my passengers.

What I can say with reasonable certainty is that any loss of altitude, either because it was undetected or resulting from later having to open more the cowl flaps later for engine cooling, would be minimal (e.g., 25 ft/min would give you over 3 hours of flight from 5,000 feet).

Will be away for over a week without regular Internet access, so there may be a delay in answering any queries.

Ernie

Just the facts man...............
 

Single Engine Trials
Sunday June 6, 2010
C337 N712JF C Model N/A

Main Fuel Tanks - 90%
Occupants - 2 adult male
Misc items in baggage area
Estimate the load to be 50% of gross


Rear Engine Power - Front Engine Feathered
2500 RPM - WOT
5500' MSL - 48 F - 100 FPM - 112 IAS -
6000' MSL - 48 F - 200 FPM - 107 IAS

Front Engine Power - Rear Engine Feathered
2500 RPM - WOT
7000' MSL - 47 F - 200 FPM - 90 IAS

We continued to climb to 7500' MSL and then decided to re-start the rear, would not start. After trying several times I looked over at the AMPS and they were pushing 30. I am not sure why the rear would not turn over. When I engaged the starter it would only move the prop 1/2 a turn and stop. I waited at 7000' MSL until the battery came back to a balanced level and tried it again but no good. It would not turn over out of feather. By this time we have been flying along on the front for about 25 or 30 miles at 7000' MSL. We turned right 90 degrees to a 012 heading for Newman's field and started a descent through a hole in the clouds. The single engine approach was uneventful. Given the front engine was the only engine making power the gear was normal and retracted without using the hand pump. It was a great landing on the turf field at Newman's and taxied up to Larry's hanger with only the front engine. After pulling the cowl on the rear and not seeing any red flags I buttoned her up and jumped in the left seat. Started the front, OK no problem. Voltage and AMPS look fine, started the rear, OK no problem, fired right up like normal.

What happened? Why would I not be able to start the rear in flight? The front started fine. I have the MT props, don't know if this has anything to do with it. Starter is getting compromised maybe? Battery lead is weak? It was really surprising when this happened but a good exercise and everything turned out OK. If anyone has had this happen please let me know your thoughts.

Herb, did you advance the prop lever to the high RPM stop from the feather position on the altitude re-start?

I've caged both of mine at altitude, with sucessful re-starts, but I have the stock McCauleys and unfeathering accumulators.

If you can get the prop out of feather, it should windmill enough that the starter is not necessary for a re-start.

Dave

Weight
 

I'll bet you were 500 pounds under gross. Not a lot more than that.

Hey Herb, it's a Skymaster....you can center the ball with an engine out....might climb a little better!! : - )

Parallax
 

Parallax. It was the camera angle.

Winds, we had a real stiff wind out of the north. Might be some of the reason it looks that way.

Hi fellas! slight re-vector on the thread: searched the whole internet, this and the UK forum, but didn't find an answer: anyone know the engine-out performance degradation with the underbelly cargo pod installed? I'm looking at buying skymaster (there goes the kids' college education $$, which they don't need because the only people making money these days are plumbers and mechanics!). Anyway, I'm fairly comfortable with the SE performance numbers, but can't find the cargo pod penalty. Since I'll be flying out of high pressure alt locations in the mountain west, I'd like to know how bad the SE performance is with the pod installed. Thanks in advance for your knowledge.

Fly Safe!

Cargo Pod Flight Operations
 

Here are the recommendations from my POH 1968 C model. Hope that helps.

Thank you! That is EXACTLY what I was looking for...

I own a '67 Turbo, and we were flying back to Utah from Montana, over the mountains at 16,500' about 7-8 years ago. Fuel probably at about 80% of capacity at that point (using all 4 tanks), 3 adults plus baggae, in winter. I would WAG we were about 400-500 lbs. under 4300 gross.

The rear engine CHT began to creep upwards. There were no corroborating readings, but to be conservative I shut down the rear engine. The plane held 16,500 with no problem at all for half an hour to the nearest decent airport. (Turned out to be only a bad CHT probe.)

Of course, the non-turbo models are vastly different (which is why I don't own one).

Paul

I understand that you want to maintain your operating altitude in the teens because of where you live, but isn't that the only reason to own a turbo?

My question is : is there any advantage in owning a turbo if you don't fly about 10,000 ' ?

Aren't the engines essentially turbo normalized to 210 hp max, so for example you have no increased HP at 5000' on a turbo, vs normally aspirated? It this is true, then there would be no real difference in maintaining altitude / single engine out (outside of that difference as related to density altitude) which of course could be significant depending on the day.

How much manifold pressure are you showing at cruise in the 5000' range on a normal day at 75% (that might answer this).

Any thoughts on this?

thanks/Roger

The idea is that the turbos allow maintenance of sea-level MAP up to the critical altitude. I don't remember off the top what that is, but the POH says full 32" MAP can be maintained by the turbos well above 20K' - you have to manually pull it back an inch for each 1,000' over 20,000 feet becuse of operating limiitations (the 30,000' chart shows maximum 22" MAP). The single engine service ceiling under worst conditions (rear engine off and feathered, 4300 max. gross) and at 20 degrees C is 17,000 feet. Few other light twins can match that, even turbo models.

Ignoring density altitude and per your theoretical situation: at 5,000 you might not have more power and thus staying at 5,000' would seem similar if it's not summer or otherwise hot - the big factors are that you can go higher to clear something even with an engine out - not being limited by the normally-aspirated lower single-engine ceiling, and if you were higher in the first place, you won't drift down to the vastly lower single-engine ceiling of a normally-aspirated model.

Being in the western U.S. definitely means that a turbo is an advantage. But if you live
elsewhere and simply wanting to fly around some mountains like the Appalachians or go west or whatever, what then?

An additional big factor is that you can take off in the heat of the day at just about any airport around. I've calculated density altitude at 6,000+ feet airports and always had plenty of capability and room for takeoff in the peak of summer heat with 4 adults and full fuel.

Claims of higher maintenance from turbos are greatly exaggerated IMO. Both of my engines went past TBO with no turbo problems (I had to once overhaul a turbo controller for $800 but don't consider that very significant and that's a normal maintenance item on a long-term basis). Nor have I experienced any exacerbated maintenance due to turbos. I treat the engines well, cool carefully upon approach and landing, and always run them at low speeds after landing to cool oil in the turbos. I've never had a problem.

I take off at 4450' and climb at 28" MAP / 2600 RPM / 14.5 GPH up to 8,000' or more practically every time I go anywhere, so it would be "28" if I were to quote anything at 5,000 feet.

I realize that normally-aspirated Skymasters work for many, and they are great planes. But beyond just the terrain of where I live and fly, I want to go when and where I want to go. I wouldn't even consider owning a normally-aspirate aircraft except for some specialty like aerobatics, etc. For the same reasons I own a Skymaster with deicing, oxygen, a nice package of IFR/GPS avionics, and have kept myself IFR current for years.

Herb did you ever figure out why your rear engine did not start in flight ? Do you have unfeathering accumulators and if so was the rear one charged to spec ?
I have shut down and feathered the front engine in flight (at 6500 ft) and it re-started no problem. Did not try the rear. Was just reminded of it because am just about to check the pressure in the rear accumulator.
Thanks Herb.