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To Flop or not to Flop

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Daniel S.

Well Known Member
Guys,
I'm kind of torn here. I know -7s are a bit of a slug when is comes to inverted flight.... But I'd like to have the flexability of minor negetive G's. There are so many pros & cons here that my head is kind of spinning. I do plan on puting additional access panels in the rear tank baffle. So, replacement of a single flop shouldnt be too bad... BUT is it worth it? What is the typical life span of the Van's flop tube before getting "stiff" etc. As a side note, I'd only be putting in one flop tube (left tank)... And now the million dollar question.... Is it really worth it?

Thanks for your oppinions!!!
 
A bunch of questions - what kind of aerobatics do you want to do? What do you mean by "minor negative G"? Do you mean momentary or sustained -1G flight? Or do you want to do inverted turns or pushes (outside loops, push vertical, etc) at greater than -1G? Are you simply wanting to cover momentary negative G exposure as for level rolls and cubans? Do you have inverted oil? If no inverted oil, there's absolutely no reason to install a flop tube unless you plan on adding inverted oil later. Do you have fuel injection? The engine will keep running for a few seconds of inverted time with FI without flop tube...sufficient for the very brief negative G exposure of a level rolls and cubans. And especially with a metal prop, having the engine quite for 2-3 seconds doesn't hurt anything. You need to be more concerned about the oil (loss) issue than the fuel issue if you're only wanting coverage for a few seconds. A couple seconds of oil pressure loss is no big deal. Happens with inverted oil systems anyway. If you want to sustain negative G, you'll need inverted oil, a flop tube, and either FI or a pressure carb. You might also search here for Ron Schreck's half-Raven oil system w/ accumulator. No flop tube (FI). Works very well for very brief negative G acro.
 
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The only down side of the flop is the cost. If there is even a hint that one day you might want one, you should absolutely install one during building. It is not easy to install one later. Further, your next owner might want it too.
Replacing an existing flop tube can be done in place wings on through the access plate. You would have to remove the tank to install a new one and have to change fuel wing root routing later as well. Best to install now once.

Inverted oil install after flying is no harder than before flying so that can always wait until needed.
 
Yeah, My engine will be fuel injected & I plan on a inverted oil system at some point (Maybe from the get-go) depending on my budget adjustments. Maybe, the wife will like hanging upside-down for a while ;). May be -1 or -2 G outside loops etc. I guess I'll go ahead and flop the left tank. Mike brings up a good point that I like... (options). I didn't know there would be different outter-tank routing.

Honestly, How long do these things last in 100LL? Is it an annual replacement item, Bi-annual, five years? I don't ever plan on sell my plane unless I lose my medical or something horrible like that. I'm building this thing to last the rest of my life :D... So options are good.
 
What do you mean Slug while inverted? I haven't heard that one before..

Regarding your original question. One thing to note is that you should also consider what type of senders you are going to use.

For example, a flop tube with float senders requires you to relocate the float by modifying the tank baffle and introduces some complexity. Capacitive senders don't require any modification for Flop Tubes.

Thx
 
I am interested in this also, I thought I read one post of a FI engine running up to 5 or 10 seconds inverted with no flop tube? That would be fine for me.
 
Flop Tube Service Life Expectancy

Guys,
Thank you for your input!. Here is the skinny I couldn't find any info on the service life of the Van's flop tubes so I contacted them. Below is the info I recieved back. Knowing this, I'm putting this item on the 36 month replacement list. Yep, It's probably overkill but if you know me, you know how I operate with this project :cool:

"We do not have any actual testing data on this but we believe a service life of five to eight years is reasonable."

Sterling

Chad. Thanks for the info also, I already have the capacitive senders! Wow! Sounds like it would have been a PITA if I had gone with the floats! glad I went with the the plte senders :)

As far as being a slug inverted, I've heard it from a few locals. I have not experienced this first hand so please don't quote me, it's just hear-say ;). It make perfect sense that it would be a bit of a slug for sustained inverted flight. If we had a perfectly flat / fully symetrical wing, a -7 would fly inverted no problem. But we do have some dihedral in the wing so this alone will have aerodynamic forces working against you while inverted. You'll have to have a nose-high attitude (high angle of attack & lower AS) and you'll be fighting the "self-righting" roll-over correction tendencies of the dihedral. All said, What the heck do I know? I just makes sense to me. :)
 
RVs inverted

RVs have different inverted flight characteristics than those other acro birds because of the differential ailerons. Might even call them slugs. When turning inverted, much more rudder (opposite) is required because of the increased drag on the down wing. Also shows up with vertical rolls. I can't do a decent inverted wing wag or stay aligned going into an acro box, but I still have fun trying.
Bill McLean
RV-4 Slider
Lower Alabama (LA)
 
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