Inverted Fuel System

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.

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.

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

Hmmmmm?

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,

if you are going to choose....

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.

Inverted Fuel Thoughts

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

Inverted fuel

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 !!

Inverted fuel flop tubes

mark manda said:

I have heard left tank only too.

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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

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.

Bill Palmer said:

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!

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My situation and feelings exactly.

Jeff A said:

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.

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Jeff,

We're likely in the same zipcode, would like to stop in and have a look some time.

PM if you want to show off your project....

Dan in Highland Village

In my opinion you need four things to do negative G acro in your RV. Inverted fuel, inverted oil, acro prop, and acro belts. Maybe a parachute too, I wear one but I'm not really sure if I can get out of my seven while it's going fast. I installed flop tubes and all the inverted mods in both tanks my quick build 7. I put the float type senders in the baffle, second bay outboard. I didn't put in a access plate just cut the hole for the sender and installed a doubler. I did have to modify the float rod bend. I fabbed up a quick and dirty mock up of that section of the tank to get it just right. The gauges work fine. It wasn't that bad to do, maybe 10 hours per tank. Probably 15 for the first one and 5 for the second. I have inverted oil as well. That is more money and more work. If you plan to do negative g and inverted flight you really should plan on an acro prop as well, either fixed pitch or counterweighted C/S. Even with inverted oil you will lose oil pressure momentarily on occasion. If you have a regular C/S prop you will over speed the engine in these situations. I'm using a MT 2 bladed composite counterweighted C/S prop which works well. I also have ratcheting 5 point seatbelts to keep my head off the canopy. To me it was all worth it. I like inverted flight and do it often. I also like slow rolls where you will experience -1G. I think the 7 flies inverted just fine and it goes just about as fast upside down as right side up. It will build to redline quickly if you let the nose drop while inverted. I do suggest strongly to have or get experience with an real aerobatic instructor before doing acro in your RV, they are not as forgiving as some acro trainers especially as to how rapidly they will get to redline.

why flop in left?

I'll take a STAB at why people put the flop tube in the left.

They like doing Knife Edges to the left. ? How'd I do?

Just one of many decisions....

Very good advice from everybody....thanks a bunch. This is just one of the decisions I guess we all have to make. I happen to love having the ability to make these decisions. (Experimentals are great!)

Thanks Ken, Mickey's RV-8 website does have very good pictures and info.

Even though I said we don't have plans to install inverted oil right now, I am still leaning slightly towards the inverted fuel on both sides. I have much more time than money, and since the inverted fuel shouldn't cost any more (except for the flop-tubes), I don't mind the extra work and time it takes to install the system. I pretty much agree with Jeremy that if or when the inverted oil system goes in, the inverted fuel is already taken care of. I still dunno.....gotta think on it some more. Thanks for all the advice.

Dan, I'll send you a PM as soon as I can. Love for ya to stop by.

NeilMcLeod said:

... I like inverted flight and do it often. I also like slow rolls where you will experience -1G...

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I love VAF, learning so much as I begin the journey....No negative G's setup and easy on the primer....the list is growing

I still remember like it was yesterday, March of 1986, a Navy kid straddled the canopy rails and synched the "spin belts" extra tight in the back seat of the mighty Thunder Guppy. Ten minutes later we entered the first of 3 inverted spins, a mandatory thing some psychopath came up with. When we entered the crazy vertical outward snapping thing to get into the inverted spin, I promptly formulated on of several "life rules"... I don't do negative G's for fun!

A few years later as a post maintenance check pilot I could attest to the odd things that pop up from floor boards on the dreaded "inverted flight check". It took me a few tries to figure out it was better to write the engine numbers down AFTER I flipped her back up, acro belts would have been nice ...

Good times ...

mark manda said:

I'll take a STAB at why people put the flop tube in the left.

They like doing Knife Edges to the left. ? How'd I do?

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Actually, if you knife-edge to the left, the right fuel is more accessible. The fuel in the right tank is going inboard.