Single-engine Endurance and Performance

[Ernie Martin]

Hoping to do it this weekend.

Ernie

[billsheila]

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

[Ernie Martin]

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

[hharney]

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.

[skymstr02]

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

[WebMaster]

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

[JeffAxel]

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