SeanB

SeanB

Well Known Member
I'm considering installing trap doors in both my tanks, and don't plan to use flop tubes. Will have floats as well.

Anyone have any thoughts/input on this idea? Am I wasting my time with this idea for a little extra fuel in positive G maneuvers?

Thanks,
 
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I put them in, cause I wanted to have max fuel in the inner bay during low fuel scenarios (and it was very easy to do during assembly). Not flying yet.

Bevan
RV7A wiring
 
SeanB said:
I'm considering installing trap doors in both my tanks, and don't plan to use flop tubes. Will have floats as well.

Anyone have any thoughts/input on this idea? Am I wasting my time with this idea for a little extra fuel in positive G maneuvers?

Thanks,
Click to expand...

Yikes! How long and hard of a "g" pull are you planning to execute?:eek:
 
another question

Thanks for the responses. Bevan...did you also cover the other large hole in the center of the same rib?
 
What if

Tom,

I'm just planning way ahead, and don't have aerobatics training/knowledge...yet.

What happens if: I do a sustained sharp turn to the left and the fuel selector is on the left tank with say,less than half a tank? It will be a positive G manuever, but the fuel will go outboard. Wouldn't the trap door help?

I guess without experience, I don't know what is expected in this situation and would like to build in some extra capability.

Am I way off base?

Thanks again!
 
X-wind

Hi.

As long as you're flying coordinated turns, the fuel won't go anywhere.

BUT... when landing in X-wind, you will always want to fly the last portion of final and touchdown with a low wing. In those cirumstances you want as much fuel as possible in the inboard chamber and trapdoors will help you there.

Also, when sideslipping to loose energy, (on final for example) the trapdoors will prevent fuel from flowing towards the lowest side of the tank.

Of course you can always select the high wing (the wing which will be downwind) during landing.

But I say to install them during construction.
 
Very good

Alf,

I hadn't considered some of your points regarding slips and and crosswind situations for these trap doors. That alone has convinced me to install them in both tanks.

Thanks so much for the great advice.

Best regards,
 
SeanB said:
Alf,

I hadn't considered some of your points regarding slips and and crosswind situations for these trap doors. That alone has convinced me to install them in both tanks.

Thanks so much for the great advice.

Best regards,
Click to expand...

I have a lot of respect for Alf, please don't forget that...but with more than 1200 hours on my -8, much of it Acro, lots of it with slips and skids for crosswinds, I have never had an issue with fuel feed. No trap doors. Never even considered them along the way. Not sure how many others have them or not (without flop tubes), but I have not heard of this concern before. it would be interesting to hear from anyone who has experienced a fuel feed problem under these conditions with standard tanks.

It's good to consider all the possible pitfalls of the stock design, but then again, it's nice to not have to build something that you don't need.

Paul
 
Well, not exactly the same thing, but I once did some photo shoots out of my old C172 and wanted to fly straight while tipping the airplane for the shoot so ended up uncoordinated. Wasn't particularly thinking about the tanks at the time, but after about 5 minutes of flying this way my engine quit because I was selected for the low wing at the time. I don't know if a trap door arrangement would have made a lot of difference (I had half-full tanks at the time).

My two cents of experience. I don't fly any acro.

greg
 
SeanB said:
Alf,

I hadn't considered some of your points regarding slips and and crosswind situations for these trap doors. That alone has convinced me to install them in both tanks.

Thanks so much for the great advice.

Best regards,
Click to expand...

Sean,

I commend you on your inquisitiveness and willingness to experiment. Before considering any fuel tank modifications, I would talk to Van’s and ask them about their design testing parameters. Present them with your questions. You may discover that the modifications are not necessary. It is impossible to design a system that will protect one from all human blunders to include low fuel level flight and sustained uncoordinated flight. Below, I copied a previous post of mine just to illustrate that a fuel tank modification is serious business.

**********

This topic brings me back 30 years ago when I briefly worked for Cessna Aircraft in Wichita. One of my projects was to conduct unusable fuel quantity tests for the Cessna 404 Titan. The engineers wanted a tank design to reflect about 5 gallons unusable fuel. We had a mock-up tank of the existing prototype installation on the floor of the hangar. The objective was to come up with a published figure to place in the POH.

According to certification requirements, it required 35 separate flight parameters to test the unusable fuel quantity. Many of these flights had to be repeated. We flew in a variety of pitch attitudes, angle of bank, and coordinated and uncoordinated flight.

For example, we would put just enough fuel into one tank to get us out to the practice area and perform the stated maneuver. The maneuver could be a 1/2 ball skid, level flight, 15 degree bank turn. We would maintain that attitude until the engine coughed. Switch back to the good tank. Return to the field, empty the tank, and measure the results.

If the results didn't meet the target figure, we would walk over to the mock up, look at the tank baffling and lightening holes, make funny airplane gestures with our hands analyzing the problem, then tell the technicians to move this or that, or make a another hole here or there.

We go drink coffee for a couple of hours, they would make the mods to the tank. Then we would go flight test again. This process, for a certified aircraft was very laborious and costly.

*********
I wish you the best of luck in your design.

Regards
 
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SeanB said:
I'm considering installing trap doors in both my tanks......Anyone have any thoughts/input on this idea?.......
Click to expand...
Not really required but I made a pair of trap doors just because I could. The additional cost is next to nothing and since I was in the neighborhood anyway, felt 1/2 or 1 hour of additional labor an insignificant investment in construction time. When you build an RV, you get to pick your own battles, like everybody else does.

e0rda8.jpg
 
Well......

I appreciate all the responses, everyone. It seems there are as many opinions on this as other popular topics.

A previous call to Van's (Gus) indicated they are not useful unless planning negative Gs and using a flop tube.

I guess I'll ask Van's again, maybe get a different answer, then make a decision. I'm still leaning toward installing these.

Thanks again!
 
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