Centre section flop

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English Johnny
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Joined: Wed Mar 08, 2017 2:35 am

Centre section flop

Post by English Johnny » Fri Sep 15, 2017 8:34 am

'Scuse the English spelling. Has anyone built a centre section cut out with a flop?
I'd like some ideas on how to secure the flop for flight using presumably some form of spring catch or sprung bolt please, pics or drawings gratefully received.
English Johnny

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taildrags
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Re: Centre section flop

Post by taildrags » Fri Sep 15, 2017 10:32 am

Johnny; not sure what you're asking. There are many, many Air Campers out there with hinged flops... mine included. Mine uses a section of piano hinge to connect it to the aft face of the rear spar at the cutout, but it creates a bit of a problem because the flop can't really flop all the way forward due to the curvature of the upper surface of the wing. The result is that the hinged section can't rest on anything when it's flopped forward... the hinge takes all of the strain. I've had to replace the piano hinge because the mounting screws pulled through the aluminum of the hinge when the flop was flopped forward either by a gust of wind or by an over-energetic individual. Ever since replacing the hinge, I'm careful to control it when I get in and out and when there is a breeze.

My centersection flop had sliding latches on each side, at the underside of the flop. Nothing more than what you see on windows or cabinet doors... see attachment. However, I have removed them because I found that the flop holds itself down in flight and they were not needed. When I exit the aircraft, I simply lift the flop with my head and it lowers back into place as I climb out. I never have to touch it.
latch.JPG

English Johnny
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Re: Centre section flop

Post by English Johnny » Tue Sep 26, 2017 5:52 am

Hi taildrags
Thanks for your advice, I hadn't considered the flop fouling when opened, thanks for the heads up. I take it you have a ledge around the underside of the cutout for the flop to sit on, if so was this added after fabric or what and is it wood or metal?
Thannks again.

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taildrags
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Re: Centre section flop

Post by taildrags » Tue Sep 26, 2017 10:38 pm

Nope... no ledge around the underside of the flop cutout. The flop when lowered rests with its forward lower edge against the aft face of the cutout in the wing. I added a thin strip of wood to the forward lower edge of the flop to bring the trailing edge of the flop into line with the trailing edges of the wings. Perhaps I'll take a photo... it might help to explain ;o)

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taildrags
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Re: Centre section flop

Post by taildrags » Wed Sep 27, 2017 1:10 pm

Johnny; see photo of my flop in the flopped position ;o) Note that it will not fold forward any more than it is in the picture due to the hinge geometry. Mounting the hinge a bit higher up would remedy this condition but would place the hinge line above the surface of the wing, essentially tripping the airflow over the wing at that point. Since I didn't build the airplane, I didn't pick the way the hinge is installed.

Also in the photo, note the thin strip of wood that I attached to the lower leading edge surface of the flop (in this picture it's at the top since the flop is upside down). Without that strip, the trailing edge of the flop section hung lower than the trailing edges of the wings. Also note the grab handles, which I use every time I get in or out of the airplane, as well as the hole in the aft side of the rear spar. That hole gives me access to a removable link that joins the port and starboard aileron cross-connect cable halves. I have used this several times when I've had to remove the wings from the fuselage for transport.
flop.jpg

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Richard Roller
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Location: Olathe, Ks.

Re: Centre section flop

Post by Richard Roller » Wed Sep 27, 2017 8:42 pm

Johnny. I fly Ken Perkin's Piet N34KP. I thought I'd post a couple of photos of Ken's center section. I'm looking for a photos of the latch's he made, but you can see how his flop folds flat to the top of the wing. He used strap hinges similar to the original hinges used on the ailerons. In the second picture you see the flop partially open. That's how I fly it, that way it clears my head. It also makes a good stall warning indicator. It stands straight up just before the break!
IMG_2797.JPG
IMG_2795.JPG

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taildrags
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Re: Centre section flop

Post by taildrags » Wed Sep 27, 2017 9:59 pm

Well, now that I've seen the strap hinge version compared to my piano hinge version, I like the strap hinge version better. Much simpler, fewer fasteners, it lays flat. Nice!

English Johnny
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Re: Centre section flop

Post by English Johnny » Wed Jan 03, 2018 4:47 am

Hi Taildrags and Richard, sorry for my slow reply but haven't been well for a while and am now about to move so my project is all packed up.
Thanks for the info you've presented, it's most useful and I will apply it all once I am back to building late this year.
I'll post a photo of my progress then also for perusal.
Happy New Year to all.
English Johnny

danoliver
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Location: Cincinnati

Re: Centre section flop

Post by danoliver » Sat Jan 06, 2018 9:53 am

I'm fixin to build my center section and flop as well (American spelling). I was thinking about incorperating magnetic latches like on cabinet doors. Maybe one up top to keep it flopped and one in the hinge joint to hold it down. Might even be able to install under the fabric. Any thoughts?

DHeal
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Joined: Sun Mar 19, 2017 11:32 am

Re: Centre section flop

Post by DHeal » Sat Jan 06, 2018 10:32 am

The latch magnets might negatively influence your Magnetic Compass.

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taildrags
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Re: Centre section flop

Post by taildrags » Sat Jan 06, 2018 11:27 am

If you do incorporate magnetic latches in the flop, just don't install your magnetic compass anywhere near it and make sure you swing your compass after you get everything set in place so you can adjust for any deviation that might result. You'd be surprised how sensitive the compass is.

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Richard Roller
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Location: Olathe, Ks.

Re: Centre section flop

Post by Richard Roller » Mon Feb 12, 2018 4:24 pm

IMG_4101.JPG
The attachment IMG_4108.JPG is no longer available
The attachment IMG_4105.JPG is no longer available
The attachment IMG_4101.JPG is no longer available
I got a chance to take some pictures of Ken's Piet's flop.

at7000ft
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Joined: Mon Mar 06, 2017 3:06 pm

Re: Centre section flop

Post by at7000ft » Tue Feb 13, 2018 9:37 am

I added home made wood and spring latches on either side of my flop with a hole in each butt rib.

https://photos.app.goo.gl/3OnvgddBYcdkiGFp1

Made a hybrid flop, flop and wing cutout in one.

https://photos.app.goo.gl/iylv18lTcjjWT9ow2

RH

Steve D
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Location: Grand Republic of Texas

Re: Centre section flop

Post by Steve D » Tue Feb 13, 2018 8:22 pm

An aerodynamics expert buddy of mine told me that a well done cutout is about as aerodynamic as a flop. He says that the location behind the interference of the cabanes, windshields, heads, gas caps, cables and such makes it less efficient than the rest of the wing.

Mine is probably not very clean, I may someday clean it up, after it flies!

I find the flop going up before the stall to be a great reason to put one on! Cheaper than a stall horn you won't hear or light you won't see. and hard to miss.

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taildrags
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Re: Centre section flop

Post by taildrags » Tue Feb 13, 2018 9:47 pm

Steve; I'll have to take closer notice next time I'm out flying, but my flop does not have latches and I've never seen it budge from the full-down position in any flight configuration. Perhaps I was too busy flying the airplane in a stalled condition to care about looking up at the flop...? I'll see if I remember to do it next time I'm in the practice area. In a power-on stall, it would not seem very likely to want to lift of its own accord but I'm just guessing. In that condition, nose way up high and on the ragged edge, managing attitude by keeping on the rudder pedals lest a wing drop off, I'm only going to give that flop a quick glance since I could fall off into an incipient spin by inattention. Not all *that* curious-!

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Richard Roller
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Location: Olathe, Ks.

Re: Centre section flop

Post by Richard Roller » Fri Feb 16, 2018 10:32 am

About 1:30 into this video you will see me landing in Ken's Piet. You can see the flop jumping up.

https://www.youtube.com/watch?v=HFXw7ARl3dw

Steve D
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Location: Grand Republic of Texas

Re: Centre section flop

Post by Steve D » Fri Feb 16, 2018 10:37 am

WOW, How could you miss that? Thanks.

douwe blumberg
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Re: Centre section flop

Post by douwe blumberg » Fri May 18, 2018 4:22 pm

When my flop unlatched in flight it lifted about two inches and that was it. I remember an article where a guy flew with a cutout and then filled it with a foam filler and compared performance. He reported his plane flew nicer with the filler in place. Your mileage may vary

RobV
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Joined: Wed Aug 08, 2018 6:54 pm

Re: Centre section flop

Post by RobV » Fri Aug 10, 2018 4:30 pm

I wonder if the flop lifting near stall has anything to do with the radiator on Model A powered aircraft vs not having the radiator?

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