Centre section flop

[English Johnny]

'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

[taildrags]

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.

[English Johnny]

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.

[taildrags]

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)

[taildrags]

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.

[Richard Roller]

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!

[taildrags]

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]

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]

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]

The latch magnets might negatively influence your Magnetic Compass.

[taildrags]

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.

[Richard Roller]

The attachment IMG_4108.JPG is no longer available

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I got a chance to take some pictures of Ken's Piet's flop.

[at7000ft]

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]

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.

[taildrags]

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-!

[Richard Roller]

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]

WOW, How could you miss that? Thanks.

[douwe blumberg]

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]

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?