Gear Retraction on Take Off

[aldoradave]

Going through the familiarization with the (new to me) N84E and I am now compiling my own check lists, both normal and emergency. Ernie Marin helped a lot with his "generic" list but I am still going to have a lot of questions!

First one is the issue of gear retraction in the case of an engine out right after take off. I am well award of the extreme drag of the gear doors in transit and the reluctance to use them in such a situation.

But N84E has the gear door mod from RT Aerospace and my guess is that it is much less of an issue. It may be that gear retraction should be one of the first acts if airborne. The book on my 73 P337 says it is the last thing.

Your comments are appreciated.

Dave Dillehay

[Ernie Martin]

My gut feeling is that you are right, put the gear up, but I haven't given the matter enough study to comment (even though my first 337 had the mod). Hopefully, others will. Ray Torres, the brilliant engineer (and FAA DEA) who invented these mods, is often reluctant to post on this Board for fear that others may think that he's pushing his products. Perhaps he'll make an exception here and offer his views.

Ernie

[Skymaster337B]

Even with a gear mod the wheels turn flat face into the wind...and must increase drag? Unless there's an owners manual suppliment that says otherwise? As part of the STC there's usually a suppliment that is mandatory to add into the owner's manual. If this STC dosn't have a suppliment then you must, by law, follow the owner's manual which says keep the gear down.

[tropical]

Also consider when the nose gear doors open the drag created along with the nose wheel turning sideways as it retracts.

There is really no need to rapidly retract the gear. Follow the manufacturers recommended guidelines.

[billsheila]

My 1965 has somewhat unclear instructions on this point in the POH or rather "Owners Manual". However when you put all the pieces together, I think the better approach is to leave the gear down until well clear of obstacles or establish a SOP (which I have done) of 1000' AGL before gear movement. Some things to consider:

1) I only have a pump on the front engine, so if I lost the front engine or the pump on the front engine on take-off, gear transit will be slow and manual, not a good time to be trying to pump a handle.
2) The transit time on a skymaster gear overall is pretty long -- there is lots happening down there -- something like 12 to 15 seconds. Again, if you lose climb ability or begin to descend at this moment, these seconds could be very critical and seem very long.
3) The airplane will still climb (not swiftly but still upward motion) with the gear fully extended and operating on one engine.
4) Not always, but generally, things have a greater chance of going wrong when you change something. Said another way, if you are climbing which is the most important thing to have happen right after take-off, don't change anything until you gain a comforting altitude.

When I consider all of the above, my SOP is simply to do nothing but climb (ie no configuration changes) until I reach 1000' AGL. Then I can move flaps (which carries some risk in the skymaster...see other threads re risk of flap cable breakage) and move the gear, and adjust throttles and pitch for cruise climb. In the event something does go wrong before 1000' is reached, then the decision making can proceed from there depending on what has happened.

It drives most twin pilots nuts to see the gear handle not get touched for so long after take-off (in fact many re-current instructors or safety pilots I fly with from time to time often query me on what I am doing, or not doing!!) but I remain convinced the above approach, in a skymaster anyway, is the right one.

[rhurt]

Last month I took off into 300 overcast and did not like the attitude changes from retracting the gear in the clouds on climbout. It was another distraction at a critical time. On the return flight that day, the ceiling was 500 overcast and it felt much better to have the gear retraction done before going IMC.

Obviously I'm willing to accept the risk of losing an engine in IMC on a low ceiling day, and I'm betting the pilot (me) will fail before the engine will while the gear is in transition.

[aldoradave]

My 73 P337 has electro hydraulic power pac and which is not driven by any one engine, and seems to be much faster than the older models. If there was "no change" in SOP then there would seem to be little value in the gear door mod. I will PM Ray Torres on his thoughts and post what I find out.

Dave Dillehay

[skymstr02]

The USAF -1 TO (Flight Manual) has the flight data in the performance charts that show the rate of climb on the rear engine with the gear in transit (doors open) at -240fpm. Notice the minus sign in front of the number.
That means that a trained test pilot could not maintain a positive rate of climb on one engine with the landing gear in transit.

[tropical]

Originally Posted by aldoradave

My 73 P337 has electro hydraulic power pac and which is not driven by any one engine, and seems to be much faster than the older models. If there was "no change" in SOP then there would seem to be little value in the gear door mod. I will PM Ray Torres on his thoughts and post what I find out.

Dave Dillehay

The "value" of the gear door mod is fewer moving parts and elimination of the two big gear doors which do cause a bit of drag during retraction.

Essentially I treat the Skymaster like a single engine plane on take off, once I'm high enough for no landing on the runway the gear comes up.

[billsheila]

Essentially I treat the Skymaster like a single engine plane on take off, once I'm high enough for no landing on the runway the gear comes up.[/quote]

I must be mis-understanding you. Why would you treat the Skymaster like a single engine plane on take off? For me the whole point of owning one and carrying around that extra hulk of steel and aluminum is mostly for this phase of flight, ie it is critically important that it will still climb in the event of a loss of a single engine on take off.

Regarding retraction, the data noted above from the O-2 manual suggests you indeed do have a version of a single engine (ie you are descending) if you put the gear in motion on one engine. No such data is quoted in my manual. The airplane is perfectly happy flying along with its legs hanging out and will apparently still maintain a positive rate of climb at Max Gross on one engine in such configuration. So I am confused as to why you would in effect be suggesting you turn your twin into a single by moving the gear handle. Of course once you have some altitude flying an "engine out" single isn't a big deal for 12-15 seconds of retraction time. But as I said, maybe I am just mis-reading your statement above.

[Roger]

I believe the analogy about being like a single engine aircraft is that in certain configurations and scenerios, the Skymaster with one engine out, climbs like a single with one engine out. This would specifically be hot/high or both, on takeoff, one engine out, and the doors in transit. Get it ?

Just this week my gear breaker popped after takeoff, and it was very apparent that it did. Not because some light blinked or horn beeped. But because it was climbing like a wallowing pig with the doors open. I would never like to experience that with an engine out.

I would think this especially so in those aircraft that have the older style single engine driven hydraulic pump, when that engine goes.

[Mark Hislop]

Why not experiment both ways and see how much reduction in performance you get? Climb up to a safe altitude and level off. Then set one engine to "zero thrust" just like you would do when you are simulating engine out scenarios. Then try climbing with the gear down and locked, and with the gear in transit. It's a safe way to find out, and then you'll know for sure.

Mark

[billsheila]

OK, I am a little thick but I get it now. So Tropical and I are in agreement, I think, except he still wants to see the gear in transit ASAP after becoming airborne does he not? So I gather the logic would be get the plane cleaned up ASAP

Roger, re your incident, presumably your breaker wouldn't have popped if the gear were down and locked right? So why not leave them down and don't risk the possible effects of any configuration changes until you gain some altitude...which was my original point.

I checked my manual again and am embarrassed to say it indeed does contain data on the minus 240 ft/minute effect of in-transit climb impact of retraction (on single engine, rear operating) and quotes minus 110 ft/minute (on single engine, front engine operating). What is not quoted is the drag effect of the gear themselves, ie if left down.

Back to your incident, do you think your plane would climb on single engine, other feathered, gear down and locked...or only a cool day?

I like the suggestion of trying this at altitude and figuring it out that way. In the meantime, I will fly a 336 for the first bit of every flight.

[Roger]

Down and Locked is good. Up and locked is good. In transit blows.

Yes the plane should climb with one engine out and the gear down under most scenerios ( ie.. standard day, or not overloaded, etc.. ) Always check your book and CG to be safe just in case.

My scenerio was classic in that I had set my Props and Throttle for cruise climb and was about 450' off the runway (which was sea level by the way) and I put the gear up. I hadn't flown it in about 3 weeks, and for whatever reason, the breaker popped. I knew almost instantly what was happening becuase it almost stopped climbing, looked out at my shaving mirror on the strut fairing, and saw the open door.

Moved my left knee away from the circuit breaker panel and was happy to see the popped breaker . Happy becuase it seemed like a no-brainer. Worse if you have stuck doors and the breaker is in, because at that point your potential for quick fix deteriorates. Popped the breaker back in, and doors closed immed.

I cycled the gear 3 times when at 2000 feet to make sure everything was working, and didn't have any more problems.

Once it happens to you (gear doors stay open) you won't ask the question "why wait" ever again. Sure you don't look like a fighter pilot, but it's worth the perceived humiliation

[tropical]

Originally Posted by Roger

I believe the analogy about being like a single engine aircraft is that in certain configurations and scenerios, the Skymaster with one engine out, climbs like a single with one engine out. This would specifically be hot/high or both, on takeoff, one engine out, and the doors in transit. Get it ?

Just this week my gear breaker popped after takeoff, and it was very apparent that it did. Not because some light blinked or horn beeped. But because it was climbing like a wallowing pig with the doors open. I would never like to experience that with an engine out.

I would think this especially so in those aircraft that have the older style single engine driven hydraulic pump, when that engine goes.

Your analogy is correct.