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  #1  
Old 06-16-2017, 01:50 PM
jthocker's Avatar
jthocker jthocker is offline
 
Join Date: Jan 2005
Location: Cincinnati, Ohio
Posts: 1,059
Default Inverted Flop tubes

A data point for anyone considering fuel tank flop tubes.

Decided to see how long my engine would run while inverted and on the NON inverted tank.

I have a flop tube in the right tank and a standard pickup in the left. From "experience" I've noticed I can fly for quite some time inverted and on the wrong tank!

Today, I decided to find out just how long! With only 4 gallons in the left tank and the left tank selected, I rolled inverted and started a timer. At 25 seconds I rolled upright and at the 30 second mark the engine stumbled for about 2 to 3 seconds then it smoothly regained power.

Hope this will convince guys to bite the bullet and install that inverted oil system. There is absolutely no need to put in a flop tube unless you intend to fly inverted for more than 20 seconds.
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  #2  
Old 06-16-2017, 07:06 PM
merlin3 merlin3 is offline
 
Join Date: Jul 2014
Location: ohio
Posts: 201
Default

Awesome news! I just need fuel injection as well : (
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  #3  
Old 06-16-2017, 07:31 PM
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scrollF4 scrollF4 is offline
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Default

Quote:
Originally Posted by merlin3 View Post
Awesome news! I just need fuel injection as well : (
....and a zero/negative G oil system?
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  #4  
Old 06-16-2017, 09:06 PM
KatanaPilot KatanaPilot is offline
 
Join Date: Feb 2015
Location: Locust Grove, GA
Posts: 850
Default 12 hours too late

Completed the retrofit of the QB left tank with a flop tube on our RV-7A project just before noon today.

Already converted the O-360 to IO and have the Christen inverted oil system ready to install.

Good to know we will be able to fly inverted for more than 20 seconds. Thanks for the test flight
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  #5  
Old 06-17-2017, 12:59 AM
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CubedRoot CubedRoot is offline
 
Join Date: Sep 2013
Location: Ooltewah, TN.
Posts: 585
Default

I just received my wing kit, and I ordered a flop tube, but also two normal pickup assemblies as well.

I am still going back and forth on whether I want to install a flop tube. I am not sure I will be going inverted for more than 30 seconds, and I plan on doing a simple inverted oil system (probably one of the accumulators) so that's only going to give me about 30 seconds of engine oil pressure anyways.

I am not a big fan of putting the fuel pickup in the inner bay and attaching it to the tank baffle. It won't be easy to service if I ever need to get at it.

I am also considering installing a set of capacitive senders (already got the kit) in addition to the normal pickups so the above may be a mute point.
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  #6  
Old 06-17-2017, 04:22 AM
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ronschreck ronschreck is offline
 
Join Date: Mar 2006
Location: Gilbert, AZ
Posts: 1,722
Default

Quote:
Originally Posted by CubedRoot View Post
I just received my wing kit, and I ordered a flop tube, but also two normal pickup assemblies as well.

I am still going back and forth on whether I want to install a flop tube. I am not sure I will be going inverted for more than 30 seconds, and I plan on doing a simple inverted oil system (probably one of the accumulators) so that's only going to give me about 30 seconds of engine oil pressure anyways.

I am not a big fan of putting the fuel pickup in the inner bay and attaching it to the tank baffle. It won't be easy to service if I ever need to get at it.

I am also considering installing a set of capacitive senders (already got the kit) in addition to the normal pickups so the above may be a mute point.
I have the same results as Jon when flying inverted. I get about twenty seconds of engine run when inverted using the tank with the normal fuel pickup. I flew with only an oil accumulator for awhile and found that my 1.5 quart accumulator only gives me about 7 seconds of oil pressure. If you want 30 seconds you had best go with a full Raven or Christen system. I think installing both float and capacitive senders is a bit of overkill. If you have a flow measuring system (red cube) that will be your best indicator. Only a suggestion. You do what you want. I do have a flop tube and full inverted oil so I can fly inverted to my heart's content. My heart runs out of contentment after about 20 seconds these days.

Note: If you are doing competitive aerobatics there are no maneuvers in the Primary or Sportsman sequences that require more than about 4 seconds of inverted flight.
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  #7  
Old 06-17-2017, 04:28 AM
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WillyEyeBall WillyEyeBall is offline
 
Join Date: Jan 2007
Location: Daleville, AL
Posts: 361
Thumbs up occassional sputter

Have a flop tube in one tank, and Jon is correct that you can get extended flight time inverted on the wrong tank. However, there are certain maneuvers, such as a Cuban 8, with several seconds inverted and negative Gs that might give you a short engine stumble. Typically, I can go through the Sportsman sequences on the wrong tank and not get a stumble. With the Intermediate sequence, which has a Cuban 8 without the half roll, and pushed to inverted level flight- BIG STUMBLE. Still not a big deal. Engine completely stopped only twice so far. Still looking to see more RVs come join the fun of competition.
Bill McLean
RV-4 slider
lower AL
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