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  #1  
Old 04-06-2020, 06:38 PM
NorthernRV4's Avatar
NorthernRV4 NorthernRV4 is offline
 
Join Date: Mar 2013
Location: Prince Edward Island, Canada
Posts: 143
Default Aerobatic Fuel tank

Good day fellow RV'ers

This winter I've been building the starboard wing and I'm at the point of putting the finishing touches on the tank. Firstly, this tank is getting a flop tube and the standard Van's resistive fuel senders. I'm looking for some tips & advice specifically on mounting the sender in the second rib bay and the anti-hang up guide strap. Van's plans are pretty simplistic and don't show at all any dimensions for mounting the sender.

1. For the sender, do you mount it in a cover plate similar to the end rib to allow for greater access and ease the inserting of the sender/float arm? Or is a simple hole for the sender sufficient?

2. At what vertical position would the sender be mounted in the rear baffle? I would think roughly the same position as mounting it in the end rib would put it.

3. Do you bend the rod to the same dimensions as if it was mounted in the rib? I'd rather not have the tank all sealed up only to find the fuel gauge is way off. I expect some inaccuracy but I'd like it to be as close as possible.

and lastly, in regards to the strap. Did you just fabricate a guide that looks like the diagram provided in the plans? Any specifics here to consider?

Thanks in advance, keep calm and build on!

Starboard fuel tank by James Soutar, on Flickr

Starboard fuel tank by James Soutar, on Flickr
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  #2  
Old 04-07-2020, 03:55 AM
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Dan 57 Dan 57 is offline
 
Join Date: Sep 2018
Location: LSZF
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many questions here, and a long time since I built the tanks... last century...
You might be able to access my build, pictures on https://drive.google.com/drive/folde...BjnALbl5jqrp3x
Pictures #128 onwards detail the tank building (don't use any sloshing compound, not necessary. It is still holding good after all these years, but only thanks to the scuffing I did). Installed the inverted fuel on both sides.

- the hole for the sender was big enough for the float, just a hole did it
- sender was mounted mid-way up, guarantees a linear motion of the float arm
- I remember hooking up the gage to the sender and did a dry calibration, don't remember about the rod though
- yes, the guide was fabricated, main consideration is for the flop tube not to tangle itself in the flap doors (which I guess you will install?)
- don't forget the o-ring on the brass head

Hope that helps, enjoy the build
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  #3  
Old 04-07-2020, 05:50 AM
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NorthernRV4 NorthernRV4 is offline
 
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Location: Prince Edward Island, Canada
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Thanks Dan, your pictures are very helpful. Interestingly I still put the access plate in the end rib in case I ever decide to ditch the flop tube I can go back to a standard pickup. Everyone has their own unique style to their build I guess.

Yes, I still need to fabricate the trap door but I noted from your pictures that you also put a trap door on the middle fuel transfer hole. I hadn't considered that, I'll have to have another look at my plans but it makes sense.

NO slosh! Ever, nope! way too many bad stories with that stuff.

What do you mean about the o-ring on the brass end? My prefab'd flop tube from Vans has one installed already. I assume that's simply to act as a cushion.

How many years has your a/c been flying? Have you ever changed out the Flop tube hose? One thing I realized recently was that if I ever run MOGAS I'm wondering about the compatibility with dreaded ethanol. I'll have to ask around about that one.
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  #4  
Old 04-07-2020, 06:57 AM
MS1095 MS1095 is offline
 
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Location: West Chester, PA
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I made something similar to what was in the plans. I don't think it really matters as long as the anti-hang guide keeps the flop tube from contacting the rib.

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  #5  
Old 04-07-2020, 07:04 AM
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Dan 57 Dan 57 is offline
 
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hadn?t notice the presence of the o-ring, so u all good Jim.

The -4 was in storage for a number of years and has only been flying for like 2 years, AVGAS only, no feedback on the hose.
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  #6  
Old 04-07-2020, 07:07 AM
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emsvitil emsvitil is offline
 
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Ever thought of doing 2 normal fuel pickups with the 3rd being a flop tube?

That way you can have the maximum amount of usable fuel for normal flight.
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  #7  
Old 04-07-2020, 08:25 AM
Freemasm Freemasm is online now
 
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Quote:
Originally Posted by emsvitil View Post
Ever thought of doing 2 normal fuel pickups with the 3rd being a flop tube?

That way you can have the maximum amount of usable fuel for normal flight.
For a gravity fed system, fine. For a system utilizing a pump, not so much. A "vent" (e.g. uncovered fuel pickup) would, vapor lock the fuel system/starve the engine. If this weren't the correct physics, you would ditch the flop tube and just have high and low fuel pick-ups tee'd together. You could get creative with valving applications or a third pump but it's not worth it. IMO, the OP should accept whichever compromise he prefers; range versus inverted flight. Fly safe

Last edited by Freemasm : 04-07-2020 at 08:27 AM. Reason: claity
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  #8  
Old 04-07-2020, 09:43 AM
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NorthernRV4 NorthernRV4 is offline
 
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I was never considering using the flop tube and the standard pickup at the same time. Just have the option of converting if I find I don't like the flop tube.

Thanks gents, I don't know how much time I'll spend inverted. I just want the option, it's more about future proofing to build one tank this way.
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  #9  
Old 04-07-2020, 03:16 PM
007 007 is offline
 
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Location: VanAire, Co
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I'm curious about the statement reference usable fuel in the aerobic tank in an RV4. My tanks are built to plans and all 16 gallons are usable.

Joel
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  #10  
Old 04-07-2020, 05:54 PM
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emsvitil emsvitil is offline
 
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Quote:
Originally Posted by Freemasm View Post
For a gravity fed system, fine. For a system utilizing a pump, not so much. A "vent" (e.g. uncovered fuel pickup) would, vapor lock the fuel system/starve the engine.
Only if the flop tube and normal pickup are T'd together

With a L Aux R fuel valve you wouldn't have that problem
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