Aeronautical Type Question-T-6 Flaps

Jack Cook · **Posted:** Fri Nov 26, 2004 5:49 pm

OK fellows here's a good one for you....
Why do some T-6s have the center flaps secured in the up position??
Our #4 racer has this and the best response I've gotten is that "it's for racing". A good lesson in how to answer a question without really answering it at all. Why do this? Are the remaining 2 flap sections effective enough to do more than make the aircraft pitch? Is landing roll increased? Is this an approved mod for a standard catagory airplane ie just file your 337 and go (our racer is experimental by the way)?

Forgotten Field · **Posted:** Fri Nov 26, 2004 7:36 pm

I was told by a friend who owned BT 13's and T6's that the center flap section on a T6 hangs down slightly on the airplane, due to hydraulic lag, and costs you airspeed. That being said, I do know that if you roll down one turn of BT13 flaps, the plane cruises 3-4 knots faster than a T6, and I think its all due to pitch, washout on the wings, and CG of the aircraft. When I mentioned this to a T6 guy, he said it was due to the flaps on the T6 (maybe the lag the other guy told me about).

As for landing roll, if you are flying the airplane right, it shouldn't cost you more runway. Shouldn't it make you fly a shallower angle of descent (center flap held up) as opposed to a steeper one? If so, then the landing roll shouldn't be affected.

I have to qualify this- I only have 10-12 hours in the back of a T6, and only 2 of those logged.

Stoney · **Posted:** Sat Nov 27, 2004 10:52 am

The USAF had this mod on the "G", it gave more rudder control on landing (center flap blocks air flow to rudder) and had very little effect on full flap stall speed.
As far as I know, it has no effect on max speed.

jcw · **Posted:** Sat Nov 27, 2004 1:03 pm

stoney
bingo... you win... center flap was loked up on the "G" and it does make a good difference in the rudder control as you increase pitch and flare... i have also notied that for short field use, there is about a 100 to 150 foot difference in landing rollout do to the increased drag affect of the center flap if it is working.. also in stall effects if the flap is down the rudder is a little less effective than if it is locked up but as soon as it breaks and the nose drops there is enough air flow that it becomes normal.. remember that the flaps on the BT are fowler flaps and actually produce lift and the flaps on the 6 are split drag flaps and don't produse much if any lift... my 2 cents worth

srpatterson · **Posted:** Sat Nov 27, 2004 4:39 pm

Forgotten Field wrote:

...I do know that if you roll down one turn of BT13 flaps, the plane cruises 3-4 knots faster than a T6,..

Are you saying a 450hp BT13 with fixed gear and one notch of flaps set will cruise 3-4 knots faster than a 600hp T-6 with gear up and no flaps?

Jase · **Posted:** Wed Dec 01, 2004 2:43 pm

Hey FF:

Which BT are you talking about, ours or any other one? Ours will, as you know, out climb a -6, I hadn't heard about adding 2 degrees of flaps to cruise faster than a -6. Technically, you can't roll *any* flaps in at cruise on a BT, as the placarded flap limit speed is 111 MPH.

When ya gonna come pick up the rest of yer stuff?

Regards

Jase

Forgotten Field · **Posted:** Wed Dec 01, 2004 4:28 pm

According to a long time T6 and BT owner friend of mine, the BT with one notch of flaps (VFE be damned) will cruise faster than a T6 (at cruise setting). Of course, this is with a full feathering prop and violating the VFE on the BT. But knowing my friend's capabilities, skills, and penchant for "no BS" (ONLY when it comes to airplanes, out the window with everything else), he is probably only relating what occurred when he flew his airplanes. He flew T6's and BT's for over 30 years, so I would rate his observations pretty high.

Jason, I'll give you call this PM. We've had a funeral and Grandpa is back in the hospital.

Jack Cook · **Posted:** Wed Dec 01, 2004 8:36 pm

FF, A full feathering prop??? BT's had a 2 position prop originally them many were retrofited with a HS constant speed but not a full feathering prop.
I'll never believe a BT could ever out run a 6 except in the 6 driver keeps the gear and flaps down, has full fuel and a back seater. But then again that might be a race.

Jase · **Posted:** Wed Dec 01, 2004 9:01 pm

Jack, dunno bout the full feathering myself. Don't think I've seen one on a single engine before, but then there's lots I haven't seen yet!

As far as our BT, yea, it will outclimb a -6. It's a ringer though, as it's the only BT flying, in Normal Category, with an R-1340. T-6 will outcruise her with the same power settings though.

Jack Cook wrote:

FF, A full feathering prop??? BT's had a 2 position prop originally them many were retrofited with a HS constant speed but not a full feathering prop.
I'll never believe a BT could ever out run a 6 except in the 6 driver keeps the gear and flaps down, has full fuel and a back seater. But then again that might be a race.

HarvardIV · **Joined:** Mon Oct 04, 2004 9:08 pm **Posts:** 1437

My trusty mechanic told me that the securing of the center section flap reduces lift, and affects stall speed. In addition it's a bad idea, because the engineers had specific intentions in mind when the original 3 piece flap was designed.

Jack Cook · **Posted:** Wed Dec 01, 2004 10:21 pm

HVD IV, read postd above by Stoney and JCW. Besides being standard on the T-6G, these guys are long time T-6 pilots. Stoney founded and runs the North American Trainer Assoc and has SNJ-4 N1666T while Jeff got tired of flying everybody elses T-6 so he built and flies his own. I'll takes the experienced word of these 2 over any mechanic. Between the 2 they probably have over 35,000 hours of flying time.

HarvardIV · **Joined:** Mon Oct 04, 2004 9:08 pm **Posts:** 1437

Well, didn't Einstein say that everybody's point of view is true. It's all the same story, but at a different angle.

Chris

Jase · **Posted:** Thu Dec 02, 2004 9:11 am

Um, the flaps on the -6 all reduce lift, they are "drag" flaps, as opposed to "Fowler" flaps which actually add lift up to a certain point.

And by your lights, adding, say, an alternator or a full flow oil filter would be a "bad idea" because the engineers had "specifice intentions in mind"??

Not that I am at all encouraging that we wholesale ignore what the engineers had in mind always, but *sometimes* there is actually a better way that doesn't surface till long after the aircraft is built and out of the design stage.

HarvardIV wrote:

My trusty mechanic told me that the securing of the center section flap reduces lift, and affects stall speed. In addition it's a bad idea, because the engineers had specific intentions in mind when the original 3 piece flap was designed.

bdk · **Joined:** Sun May 02, 2004 1:16 am **Posts:** 11324

Jase wrote:

Um, the flaps on the -6 all reduce lift, they are "drag" flaps, as opposed to "Fowler" flaps which actually add lift up to a certain point.

Hmmmm... Back to Theory of Wing Sections. I didn't know that. :shock:

RobC · **Posted:** Thu Dec 02, 2004 6:03 pm

The first T-6 I checked out in belonged to the late Frank Elliot, and had the center flap wired up. Stoney is of course, correct. It was done to improve ground handling, and also to reduce float on landing, both good qualities to have when you are giving a lot of dual, as Frank did. But I frankly don't recall it handling substantially differently than my own T-6 or others I have flown. Has anyone ever done a side-by-side comparison?

FF, I'll bet your friend meant he picked up 3-4 Kts, by dropping the flaps in the BT. Couldn't possibly have made any more difference than that. Even that seems questionable. I have heard of guys rigging the flaps UP a couple of degrees from neutral to try to pick up a couple of knots. Never know since negligible changes are tough to measure accurately.

Rob Coussens

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Aeronautical Type Question-T-6 Flaps

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