Inverted Fuel System

Jeff A · #1 02-10-2007, 09:30 PM

Since this is one of my first posts, let me start by saying my father and I started our RV adventure together last September. Since then, we have finished the tail (thanks Mel for your tech advice), and the wings started taking shape the day after Christmas. It has been so much fun. Thanks Dad.

With the wings underway, and the fuel tanks looming in the near future, I had a few questions for anyone who has (or has thought about) installing an inverted fuel system. First, since we will be using float type senders, is it best to mount to sender directly to the tank baffle, or fabricate a "T-408-like" access plate and mod the baffle to accept the new plate? If a new plate is fabricated, how do you keep from interfereing with the angled tank attach bracket? Is it necessary to use a cork gasket? Is the bend angle or length of the float arm any different since the sender is in a different position? The last question I think is...don't laugh...do you only mod one tank or both tanks for the inverted setup? I'm almost postive I've heard someone say they only bothered to mod the left side. Is that right?

I have a pretty good idea about how we can go about this. I guess I'm really asking how everyone else has done this, or is planning to do this. Also, is this all worth it? I wasn't planning on installing an inverted oil system $$$. Is one worthless without the other? I'm sure those questions could probably start a whole new thread. With all that being said, I haven't looked everywhere to see if this question has already been asker/answered; I'm new, so bare with me. Thanks.

Oh, and any of you Dallas area builders/flyers, feel free to stop by and help out.

The garage door is always open if you know what I mean....except when it's really cold.

mark manda · #2 02-10-2007, 10:27 PM

I had a friend tell me that one of the RV Instructors he has flown with said "how long do you think the engine will run if you shut the selector? " almost immediately the guy said. They turned it off and the engine didn't sputter until 20-25 seconds. Meaning or implying, you don't need it for mild acro.

I have heard left tank only too.

We had to shorten the steel braided hose due to interference and then it wouldn't flop over and down all the way so we Pro sealed a big fishing weight on the end of the line near the pick up.

hope that helps. also DanC says he wouldn't bother with inverted fuel without the inverted oil system.

hope that helps.

kens_cockpit · #3 02-11-2007, 04:52 AM

Mickey Coggins has some good pictures of how he installed the float sender when he was planning on using the inverted fuel system. Check out his website at www.rv8.ch I don't have the exact page on that site but you should be able to find it with a bit of searching.

Ken Stanton
RV8QB

pierre smith · #4 02-11-2007, 06:48 AM

Hi Jeff,
Congratulations on a very good choice of airplane! You need to ask yourself just how much inverted flight with negative G's do you really want to do? If you're building a cross-country airplane, you have an excellent one. If it's aerobatics you mainly want, go for oil and fuel systems.

Bear in mind that an inverted oil system is expensive, fairly complicated and adds weight and the firewall-to-engine clearance is tight already, more lines only add to the accessibilty problem.

Furthermore, unless your airplane is operating-room clean when you do inverted stuff, you'll get dirt and sand particles in your eyes and that ain't no fun. Plus anything loose (chocks

) will hit the canopy.

Considering the fact that you can do aileron rolls, four point rolls, loops and Cuban eights, split esses and Immelmans with no negative G's, the inverted system wouldn't be used much anyway. My two cents.

Regards,

jcbarker · #5 02-11-2007, 02:05 PM

In my opinion, if you are going to choose between inverted oil and inverted fuel, I highly recommend you choose inverted oil. The Lycosarus DOES NOT LIKE TO RUN WITHOUT OIL! As most have pointed out, your inverted time is fairly short in the kinds of aerobatics flown with this airplane but long enough to do damage to an engine starved of oil. Besides, if the engine quits, roll upright and wait a few seconds. It'll restart. Finally, I really hated cleaning the oil off the belly of the airplane after flying aero with a non-inverted system. Even when trying to keep all maneuvers positive it still is a mess.

Bill Palmer · #6 02-11-2007, 03:13 PM

Inverted Fuel System Thoughts (Personal Observations/Opinions Only!):

Based on my personal experience, flop tubes are very difficult and time-consuming to install in quick-build wings. Standard-build wings, with Van's outboard capacitive sender plates, are much more builder-friendly with respect to installing flop tubes.

Flop tubes and capacitive-type fuel senders go together. The standard fuel pickups and capacitive or float-type fuel senders go together. Flop tubes and float-type senders don't go together!

Inverted fuel without inverted oil is very dangerous for your Lycoming! Inverted fuel/oil go together!

An inverted oil system adds about 9 pounds firewall forward, and you must find room to install the system. Corollary: Although an inverted oil system is a fairly good air/oil separator, there are much smaller, lighter separators available if that's all you need!

Negative Gs bring all the cockpit dirt and loose stuff to the canopy (if not up your nose!).

Look at your airfoil. It's not optimized for negative-G maneuvers. It's not even close to being symmetrical. That's not to say that RVs cannot be flown negative-G (they certainly can with inverted fuel/oil), but you had better know what you're doing with respect to angle-of-attack (lift margin), inverted maneuvering, and G loading!

I know a very wise, aerobatic-experienced pilot who built inverted fuel/oil into his RV-4. He says he has hardly ever used the inverted capability, and really doesn't use it anymore. His frequent aerobatic maneuvers are all positive-G now. In his opinion, RVs, including their pilots and passengers, simply don't take kindly to inverted, negative-G flight. RVs are great for positive-G maneuvers (as Van designed them to be), but negative-G conditions and maneuvers are another story. This RV-4 pilot is building his new Rocket without inverted systems.

Since they tend to follow fuel movement, flop tubes (plus fuel flapper valves) in each tank might offer improved safety for positive-G slips with a partially-filled, downward tank selected, but, otherwise, they're no better than the standard fuel pickups for positive-G stuff.

I installed flop tubes in my tanks intending to install inverted oil as well, but I now wish I hadn't taken the time (a lot of time!) to do so. I'm skipping the inverted oil system for FWF weight reasons as well as the virtually-always-correct advice of my experienced RV pilot/builder friends. I'm going positive-G only! I suppose it's comforting to know that I have teflon-hose flop tubes and can add an inverted oil system in the future if I ever get the "negative-G" urge, but I doubt that I ever will!

As always, these are just personal thoughts/opinions - - Go Your Own Way!

Best Regards,

Bill Palmer

Mark Cigal · #7 02-11-2007, 05:06 PM

Jeff, I agree with Bill Palmer. I put a flop tube in my left tank thinking I would
also install inverted oil.... well guess what? as you near the end of the project
there are soooo many more things ( $$$$) that you will want instead, and
that will be much more usefull. I"v got over 200 hours on my 8 and have NEVER missed doing any negative G stuff. You should also be aware that it's
reccomended the flop tubes be changed out after so many hours. (can't
remember how many) I for one am NOT looking forward to that. If you use
the float type sending units and install them in the end of each tank they
will be accessble (to fix leaks, change out, etc) without removing the tank
from the wing. THAT is something you do NOT want to do after the paint is
on !!

seward747 · #8 02-11-2007, 05:54 PM

Quote:

Originally Posted by mark manda

I have heard left tank only too.

Anyone know what the reasoning behind this might be?

I've been planning to install the flop in tube in at least one tank, on the premise that it's sure a lot easier to do it during construction, than to wish you had installed it later on down the road. Looking for the downside, other than the extra construction time. Might add a dollar or two in resale value too.

Doug Seward
Seattle area RV-4 wings

N282RV · #9 02-11-2007, 06:23 PM

I installed flop tubes in both tanks, my thoughts are that if the urge arises it will not matter what tank I am on I have inverted capability. I believe this takes some possible error on the pilot (me) out of the equation. I also plan on installing inverted oil. Maybe Ill not fly inverted in the future, Ill be happy when I can tell you if I should or shouldnt have.
BTW the tanks are not as bad to do as you think. Just like the rest of the project it just takes time and patients.

szicree · #10 02-11-2007, 06:26 PM

Quote:

Originally Posted by Bill Palmer

I installed flop tubes in my tanks intending to install inverted oil as well, but I now wish I hadn't taken the time (a lot of time!) to do so. I'm skipping the inverted oil system for FWF weight reasons as well as the virtually-always-correct advice of my experienced RV pilot/builder friends. I'm going positive-G only! I suppose it's comforting to know that I have teflon-hose flop tubes and can add an inverted oil system in the future if I ever get the "negative-G" urge, but I doubt that I ever will!

My situation and feelings exactly.