Long range flight with rear engine only

[Kevin McDonnell]

Someone had to bring up this heresy ....

Just get a set of Gami balanced injectors and run LOP. Apart from installing bigger tanks, this is the easiest way to increase your range. You'll get 15% or better decrease in fuel burn.

Let the flames begin ....

[Ernie Martin]

No, no flaming. You do have a point.

I happen to believe, as others above, that 2 engines running at lower power levels and properly leaned for economy per the POH will give more range than one engine. But you can certainly extend the range even more by leaning further and operating lean of peak (LOP), if you have the proper equipment and conditions.

There's another thread on this message board about operating LOP at http://www.337skymaster.org/messages...&threadid=1208 but here's an excerpt from there on what you need:

"Those who are technically astute (you don't have to be an engineer or a mechanic, just someone who is technically inclined and understands the subject), who have installed GAMI injectors for smooth operation across all cylinders at LOP, who have cylinder-by-cylinder engine management/monitoring equipment, who are willing to to give a bit more attention to engine management in flight, and whose engine is no longer under warranty can run LOP at cruise."

Of course the cost of the GAMIs and the engine monitoring equipment, if you don't have it, is substantial.

Ernie

[Nick Bailey]

I'd have to say with my recent experience running single engine that the skymaster will not hold altitude at 65% power and full gross, even at SL. Lighter, maybe but not full gross. From a safety standpoint, I agree with Kevin that the single engine operation offers too many potential problems. A recent experiment with extreme leaning ( Gami jectors) I was able to get about 130 knots with each engine using just over 7.5 GPH. Don't know if that is better than single engine, but will let the rocket scientists do the math.

[Jim Rainer]

This has been an interesting thread to keep up with. One comment: there have been numerous "won't hold altitude" comments - what altitude?? I had the front engine of my normally aspirated 337G feather itself (governor blew a seal ) over Greenwood, MS and after the dust settled, I held 6,000', lost about 20K didn't change the rear engine setting (FT and 2400 rpm) and flew on to Memphis - about 100 n mi. I cracked the rear cowl flaps but didn't need to and this in the summertime. Medium load of fuel and folks.

When taking a mountain flying course in the middle of the summer my instructor and I were over Leadville, CO at 12,000 and he wanted to see how well it'd hold altitude, if at all. We reduced the front engine to zero thrust and held the 12,000' with about a 20K loss. Two people, 2/3 fuel (148 gallons when full) and HOT. The change in angle of attack in each case was minor.

The airplane in question (fly to Africa) is a turbo model. I believe it'll hold any altitude below at least 10,000 without a struggle. I've done no testing but my gut says a normally aspirated 337 will go further on the rear engine alone than on both (but I probably wouldn't push one thay way!)

[proto]

Our aircraft is still in maintenance (due to a change of the de-ice boots)

I promise that I'll check the numbers with just one engine running at altitude. It seams that this test will be a subject of interest !!

Thanks to be patient.

PROTO

[Walter Atkinson]

Gentlemen:

The answer is in the science. There are two things required to achieve max range.

1) Attain the best L/D airspeed (someone said that's 100 knots in a Skymaster. I cannot confirm that, but suspect that's very close.)

2) Set the mixture to BSFC (min). This will be at a mixture of about 15dF LOP at the very low power setting required by having two engines running and at 100 knots. With one engine running BSFC(min) will be 20-25dF LOP since the single engine will be putting out more power.

BOTH of these actions will result in max range AND max efficiency.

Personally, I would choose to attempt this with both engines running and I'll be quite surprised if the single engine scenario were better. Running on only the rear engine is likely to alter the angle of attack at the slow airspeed to a less efficient drag condition. Testing would be necessarly at the expected flight weights.

[walt]

I have a pair of tip tanks. $3000.00 if interested.
Jaws83@optonline .net
631-757-7567
Walt Simendinger

[Paul Sharp]

I did a precautionary shutdown of my rear engine coming back to SLC from Montana one day. Full load of fuel, 3 passengers plus luggage. Of course I had burned off about an hour of fuel before I saw the engine CHT start to rise.

My plane is a 1967T model. I was at 16,500 feet at the time. After getting over the mountains, I let it down to about 10,000. It held just fine and I feel quite confident that I could have neld the higher altitude had there been a reason. This was in November if I remember correctly.

Anyway it was an NBD (no big deal), and I could have started up the engine again had there been a need. I flew on in to Idaho Falls, did some checking, and found that it was just a bad gage. Fired 'em both up and went on our way home.

[proto]

Dear Walter

you're talking physics. Very good. I am sorry, our T337 is still not ready - SO WE MAKE ESTIMATIONS !

I just tell you that a Conti - Engine takes a minimum fuel of about 4 gal / hour in IDLE (NO THRUST). If you fly with one engine, you save this amount of fuel at least!!

There is no problem to maintain this bird in the air with one engine. I think, we can even fly with 14 gal/hour (LOP) with one engine at FL 120. Speed > 120 KTAS..

In that cas we can fly nearly 1200 nm without a ferry tank and reserve, since we have the 4 tanks. This distance will be ok for our mission.

What do you think ?

PROTO

[KyleTownsend]

I don't know if this is a true story, or a tall tale, but it was presented as a true story:

A fellow was ferrying a skymaster back from Europe on the North Atlantic route. He feathered the front engine and was cruising only on the rear.

There was a low overcast over the atlantic, and he was flying very low to stay under it.

As he was approaching Greenland (I think), he felt a huge shudder through the whole airframe and heard a loud noise. But he could see nothing wrong. He continued on and landed.

Upon inspecting the airplane after landing, he found that the tip of one blade on the front prop had been bent backwards.

Pilots in the area advised him that he probably clipped a large ice ridge that had developed some distance south of their location.

Talk about close calls!

[Walter Atkinson]

Proto:

**There is no problem to maintain this bird in the air with one engine. I think, we can even fly with 14 gal/hour (LOP) with one engine at FL 120. Speed > 120 KTAS..**

If that's true, then the question is, "will it fly on two engines at the same TAS on less than 7 gph each when LOP?"

That answers the question.

[OSCARDEUCE]

I'll try to contact one of the pilots who ferried the O2's across the pacific. As was stated they did it on 2 engines at lower power settings. If there was an advantage to single engine cruise, I'm sure they would have used it. GMAS's data showed they was an efficiency advantage with both engines over the theoretical SE cruise. None of the FACS I've talked with flew SE to lengthen their patrol times or time over target. The military fleww the wings off these birds and I trust and use the procedures they did. Personally, my O2-A is a dog on one engine.

[WebMaster]

The 0-2's ferry flights are more analagous to what Proto wants to do than simply shutting down one engine and flying on one. In his initial post, he says he intends to install a ferry tank. Everything I have read indicates that you can take off at 30% over gross, with out a special permit. Now, take the average skymaster at 4400, add 30% and you are at 5720. Make it 20%, and you are at 5280. If I was going to go a long ways over water, I'd want all the fuel on board that I could get away with. In other words, I'd be at 5720. If the average usefull load is 1500, that means you could carry 2800 of people and fuel, or 2600 of fuel. To get to the point where you have burned off enough fuel to get down to normal max takeoff, you will have flown for a while. Quite a while. I don't think a normal, or turbo, skymaster can hold altitude at 20% over gross. Maybe 10%, but I doubt that too.
So, my initial premise was that for a long time, he's going to have to run with 2 engines. It would make sense to me to have them leaned out as much as possible. I would also, no science here, just an opinion, think that 2 engines running at reduced power, could generate more thrust than one engine running at some reduced power setting.

There are a lot of opinions, we'll just have to see what happens when proto gets the bird in the air.

Good luck.

[Walter Atkinson]

Larry:

** It would make sense to me to have them leaned out as much as possible.**

No, you want BSFC(min) for max engine efficiency. That would be at about 15-20 LOP at the reduced power you would want for best L/D for the airframe. That will give you max range. Leaning further will actually decrease the range as the engine will be less efficient. BSFC => Brake Specific Fuel Consumption => pounds of fuel required to produce one HP per hour => efficiency. You want to be producing the most HP per pound of fuel possible.

Max range is found at BSFC(min) and best L/D airspeed.

[proto]

Hi Larry

Additional tanks are expensif, they take to much space (hangar etc.) and in Europe is a hassle with the authorities to get a permit - even with a STC. If you have to ditch your aircraft with a full aux-tank (interior), there is dead-penalty - so forget it!

So we try to fly with one engine shut down for max. endurance - (I know, you are all waiting for the results) - and then we will see.

I bet with one engine we can go 10% or more farther !

Proto

PS. End of the week I am in Lakeland ( Sun n' Fun) - is there any C337 people around ??