Gear Retraction on Take Off

[JeffAxel]

My POH for a '77 T337G says the penalty for gear down amd locked, doors closed is the loss of 110fpm climb on one engine. The plane will climb on either engine with the gear down amd locked with the doors closed. It will just maintain altitude with the gear in transit if everything goes right. The aforementioned -240fpm is what my POH says as well as the penalty for gear in transit. I am sure loosing the big main gear doors helps some as far as drag goes, does any of the paperwork that comes with the STC say what the difference is?? That would be useful information.

[Ernie Martin]

Two thoughts.

1. I don't think any of us should assume the POH climb rates to be realistic for our aircraft. Those numbers, squeezed to the max by Cessna, are for brand new aircraft, with perfectly smooth (and waxed) skin, perfectly tuned engines, perfect-pitch props, etc. Ours don't fly that good. I assume 100 - 200 fpm penalty for age, plus the adjustments for temperature, pressure density, etc., and I try to fly below max load, so if an engine fails I can get close to the POH numbers.

2. Of the added drag introduced by the gear in transit, I don't know the proportion of the big doors (the ones removed by the STC), but if you've seen a gear retraction test up close, you know it's big. My guess 2/3 of the in-transit added drag is due to the big doors.

Ernie

[aldoradave]

OK guys, it seems I'll have to do it myself! Tomorrow I will give it the big test and report back as soon as I safely land. I'll go up to 10,000 msl with gear down, retard the rear engine to zero thrust, pop the front to full boogie then record my rate of climb. At 10,500 I'll cycle the gear up and note what happens.

Given that there are so many differences in our birds, this is the only rational way to do it anyway. I'll post my results as soon as I can.

[JeffAxel]

Ernie,
No argument from me on either of your points. Don't make assumptions is a good point. In my case, I also don't fly at gross wt. too often, and so also hope for book numbers. But out of curiosity, when I bought the plane, I took it up with an instructor to see what it would do. I was pleasantly surprised, but we were pretty close to gross wt., and the plane did climb at 100-150fpm with the gear down on the rear engine. Later, when I lost the rear engine on a go around in instrument conditions, it climbed out at 350fpm on the front engine, probably 250lbs under gross on a cool day. Turns out the fuel was set up way rich on the rear engine and it choked when I gave it power, came back when I leaned the mixture, thankfully. Made me a Skymaster believer though! Fuel set up is better now too. I am still not sure what the best course of action is with the gear though. I usually leave it alone until all set for cruise climb, then retract it. When I asked about this at Recurrent Training Center, they made the argument that getting the gear up resulted in better climb, and altitude is your friend, and so had no problem with positive rate gear up. They weren't unhappy if you waited either. I guess to each his own. I can wait to pull up the gear myself....

[billsheila]

What are the settings for zero thrust on a NA Skymaster. My instructor dug these up a few years back and I recall keeping a copy, but now can't find it. In my 1965 Owner's Manual, there is no data given.

Thanks to anyone who can help.

[Ernie Martin]

Dave, when you do the test, please note weight (how close to max load) and weather conditions (temperature). Also check carefully the specs for zero thrust, because temperature enters into the mix. Anxious to see what you get.

Ernie

[hharney]

Originally Posted by JeffAxel

I am sure loosing the big main gear doors helps some as far as drag goes, does any of the paperwork that comes with the STC say what the difference is?? That would be useful information.

RT Areospace did not provide any new numbers for the gear door removal......fly it by the book!

[Roger]

If the self test is going to start at 10,000' at near gross, with the rear out, and doors open I believe we may have to wait a few days for him to get to 10,500'

[Ernie Martin]

Good point, Roger, since the single-engine ceiling is around 6,000 ft (more with the front out, less with the rear out).

Ernie

[aldoradave]

Originally Posted by Roger

If the self test is going to start at 10,000' at near gross, with the rear out, and doors open I believe we may have to wait a few days for him to get to 10,500'

Dear Roger,

Please note that N84E is a P337 and should have no problem getting from 10,000 msl to 10,500 with rear engine out. If it does I have bought the wrong airplane. My guess is that with the gear door mod it will be easier with the gear retracted.

Dave Dillehay

[RAY TORRES]

Hi Guys:

Normally I stay away from commenting here, but since the topic is my gear door mod I figured its time to clarify somnme things.

With regards to the RTAero gear door STC. The STC does not provide any procedural changes as to when to raise the gear or any changes in rates of climb/performance for before/after mod.

When we did this STC there was no doubt in our minds that the majority of the gear drag came from the large clamshell doors, and I think the modification has proved that out. I don't feel the wobbling or drag that I use to when cycling the gear before the mod. In addition, the modification removed 2 actuators and 4 hydraulic lines with no change in cruise or cabin noise.

As with most STCs, the FAA only requires that we show that the modified aircraft meets a minimum performance standard. In other words, you could modify the aircraft, and get approval for an STC where the aircraft performs worse or has no change from before being modified.

The FAA requirements to show improved performance figures is extremely cost prohibitive, thats why you won't find performance figure changes for most of your stol kits or other performance enhancing modifications. Normally you'll just get a general statement that the modification "improves" slow flight, rates of climb etc. The other side to this is the liability implications for the modifier when someone tries to fly to new performance figures and eats the trees at the end of the runway. Try to get hard numbers for any of the STC's out there and see what you get.

Getting back to the gear door mod. We did have to demonstrate to the FAA that the modified aircraft had positive rates of climb at 5000 feet and gross weight. We did a series of flights with front/rear and both engines in varying directions and averaged the results, and if my memory serves me right we averaged to around 100 fpm on the rear and about 60 on the front. But that was with an old tired airplane, performance will also be different depending on airframe and engine condition.

When you raise the gear is basically up to you. I raise my gear when I have positive rate and can't make the end of the runway. I do it even sooner if I'm taking off over water. But everyone is different and has to determine what is best for them. The "What ifs" are way too many to say one procedure is better than the other.

By the way, I blew a hydraulic hose the other day and had to sweat getting the gear down, luckily I had enough fluid to get it down and locked. But now I'm thinking that maybe the best solution is to just leave the gear down.

Best regards to all and thanks for supporting our mods.

Ray Torres

[aldoradave]

Dear Ray,

Thanks for stepping in. I own a scuba diving company in Cozumel and frequently look into associated web sites and threads--with the firm conviction that it is not my place to be posting. But sometimes I do and thank goodness you do as well.

Your post is much appreciated by me and most likely others. It was not possible for me to fly yesterday but I still intend to on Friday. MY plot is to take my P337 to 10,000 msl and try both engines out(zero thrust) one at a time of course, with gear down and then note rate of climb both before, during, and then after gear retraction. I do have your gear door mod, as well as Horton STOL.

The reason I pick 10,000 ft msl is that I frequently fly out of Mammoth Lakes CA and routine 10,000 ft density altitudes. So I really want to know what to do when the poop hits the prop!

If you or anyone else could give me a procedure that may be better than what I have in mind--that would be of benefit to everyone.

Thanks


Dave Dillehay

[hharney]

Originally Posted by billsheila

What are the settings for zero thrust on a NA Skymaster. My instructor dug these up a few years back and I recall keeping a copy, but now can't find it. In my 1965 Owner's Manual, there is no data given.

Thanks to anyone who can help.

Here are the numbers from my 1968 model. Should be close to yours.

[billsheila]

This page is not in my manual, so must be something they added between '65 and '68

Really appreciate you sending it along.

Bill