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 Post subject: BT-13 habits?
PostPosted: Fri Sep 08, 2017 9:44 am 
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Anybody here got time in one? A friend of mine just purchased one, and wants me to assist with a checkout this weekend.

Anything I should know about -- gotchas?

Thanks,

Dave


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 Post subject: Re: BT-13 habits?
PostPosted: Fri Sep 08, 2017 9:45 am 
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I've read the pilot reports that a googleSearch brings up.


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 Post subject: Re: BT-13 habits?
PostPosted: Fri Sep 08, 2017 9:51 am 
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The only unique thing that I "know" about them is that the flap hangars are mounted to the rear spar which makes up the rear face of the wet-wing fuel tank. I've been told that the forces from flap actuation can tweak the rear spar enough to cause fuel leaks. I think if you are careful to always be well under Vfe everything should be fine.

I have virtually zero first-hand knowledge with BT's (only about 2 hours in one 15 years ago) so I'm no expert by any means. Just passing along the on one BT tidbit I've heard from several people.

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 Post subject: Re: BT-13 habits?
PostPosted: Fri Sep 08, 2017 1:47 pm 
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Thanks. That's the sort of thing I'm looking for.


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 Post subject: Re: BT-13 habits?
PostPosted: Fri Sep 08, 2017 2:01 pm 
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Cross controlling, i.e. tightening up the turn to final will cause it to snap-roll, I know this from experience. The thing about flaps causing fuel leaks is true, caused by lowering the flaps at too high of an airspeed. Easy to land with the wide gear, wheel landings are the easiest. My first takeoff surprised me with the torque, as I had been flying a Cessna 120. Instead of forcing the tail up on takeoff, neutral elevator and let the tail come up, then it's a piece of cake.


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 Post subject: Re: BT-13 habits?
PostPosted: Fri Sep 08, 2017 6:03 pm 
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low level acro will kill you

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 Post subject: Re: BT-13 habits?
PostPosted: Sat Sep 09, 2017 1:53 am 
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Never flown one, or in one.

I like the 13 a lot. I have heard that one of the issues that plagued many a pilot, was the propeller pitch control (2 positions only) and that some people forgot to switch back to the correct setting, thus causing problems and in many cases, crashes on landing.

I would like to hear from someone more experienced in the subject.

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Sooooo, how am I going to know to press 1 or 2, if I do not speak English????


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 Post subject: Re: BT-13 habits?
PostPosted: Sat Sep 09, 2017 8:40 am 
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Mine's a project still, but an old gent warned me that they're nose heavy and the stock brakes can be grabby. If you compile your own set of handling notes eventually I'd really like to see them.

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 Post subject: Re: BT-13 habits?
PostPosted: Sat Sep 09, 2017 12:16 pm 
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Got abt 150 hrs abt 10-15 years ago. Might suggest there's not a significant difference with 20-25 deg flaps vs 30-40 at 70-80, just more drag than anything. We had leaky tanks too so chose to go no more than 20 for that reason.

Not a gotcha, but if you get into a good cruise in calm air, keep it steady and you can feel it get up on another 'step' so to speak along with a few more m's per hr.

Oh, and yes they do seem to vibrate a bit but nothing to worry about.


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 Post subject: Re: BT-13 habits?
PostPosted: Sun Sep 10, 2017 7:49 am 
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Thanks. I appreciate the remarks.

Dave


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 Post subject: Re: BT-13 habits?
PostPosted: Sun Sep 10, 2017 5:42 pm 
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Let us know how you got on please Dave


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 Post subject: Re: BT-13 habits?
PostPosted: Mon Sep 11, 2017 9:12 pm 
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I have about 120 hours in the last four years, primarily in the CAF MN Wing BT, and a few in another BT-13.

I echo the other comments regarding flap deflection and fuel tank leaks. We limit flap deflection to 30 deg for that same reason. And as already mentioned, there is very little reduction in stall speed from 30 deg flaps to 60 deg flaps. One version of the pilots flight operating instructions states 30 deg flap stall speed as 65 mph and 60 deg flap stall speed as 62 mph. Another version of the operating instructions states 65 mph for both flap deflections. I'd imagine there is considerable drag difference between the two settings.

One question I'd ask is, does the BT you're referring to have a constant speed prop installed? Or the original two position style? The MN Wing BT has a constant speed prop on it along with a manifold pressure gauge installed. The original two position prop and instrument configuration did not include a manifold pressure gauge. On the constant speed prop installation, it is possible to overboost the engine. The FAA Type Certificate Data Sheet issued after the war includes a manifold pressure limit of 36.5 in Hg.

The other BT I have flown has the original two position prop and no manifold pressure gauge. My limited experience in that aircraft was that the throttle is just to be "firewalled" on takeoff. The takeoff roll and initial climb at that setting were noticeably shorter, which leads me to believe it was running at a manifold pressure much higher than 36.5. I have subsequently not been advancing fully until I get a bit more time/feedback as to proper operation.

I see no reason to identify the two position prop as causing any issues a constant speed prop installation wouldn't have also caused (i.e forgetting to set proper position). The same is true for either of those configurations.

Of course, it is a tailwheel airplane, and should be flown with the same care as any tailwheel, however, the wide main landing gear stance results in fairly forgiving handling qualities (for a tailwheel).

Tailwheel shimmy seems to be a relatively "common" issue to deal with. The service instructions do cover this. If you run into problems with that, PM me and I will share details regarding MX items to review.

Overall it's a great airplane to fly and has great flying qualities. One other item, there are two different aileron servo tab gain settings which result in noticeable difference in roll control forces. I prefer the configuration with less servo tab gain. I have not found any document describing the different tab gain options, or what scenario it was added for. Might have just been a requested change not found in currently available documentation. I'll dig up some photos of the different servo tab attach point options.

Jordan


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 Post subject: Re: BT-13 habits?
PostPosted: Tue Sep 12, 2017 9:42 am 
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Thanks, Jordan. Good stuff.

Re the prop, I spent the last 2 summers flying the Lysander, which also has a 2-position prop. But it has a MP gauge, because you can definitely over-boost it.

The R-985 has a supercharger as you know, so over-boosting can be an issue. I'd only open the throttle to the stop on a naturally-aspirated engine, or one that has an automatic boost control of some type.

A MP gauge is a simple thing to install, and there will be a plug for it somewhere on the manifold. As a suggestion, I'd recommend installing one, and then use the limits published for the 985 by P and W.

Cheap protection against engine failure.

Dave


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