Hatz Biplane Association

My five gallons gives me an extra thirty minutes of flight... which puts me at two hours with reserve. Here in the auto industry we have a saying.... "the mind can ony process what the backside can endure". You're going to find out two hours is about the limit.
Jeff Moore

Hi Al
That vent line sounds doable. Can you expound on that design a bit. It is plumbed thru the smaller tank to the engine right? Vented from top of aux tank to top of main tank?

Another thought I had was why are all the tanks only 10 gals. or less? Seems to me to be more space than that under the top longerons in front. Is there a reason to keep them small other than weight?.....which you could control just by how much you put in. I do think if they were plumbed straight thru like that the lower tank would need a gage also of some sort.

Hi,
As far as venting the small tank, I have a similar setup in my Cygnet with the main tank (behind my head) feeds the small tank just aft of the firewall above my feet. Fuel goes from small (header) tank to gascolator with a valve at the discharge of the header tank. There is a vent line running from the top of the header tank to the main tank. Foolproof for 20 years.
Al

If you did use it, how are you going to fill it? If the aux tank isn't vented, it's going to take a long time to fill while the air burps it's way up the fuel lines.
Head pressure's not a big deal on a Cub with a little Continental, but it can be with bigger engines. A Luscombe with 65 HP is fine, but with 85 HP is placarded to use carb heat for take off. It will outclimb the fuel.
Again, I'm not opposed to modifications, just understand the ramifications.
Mark

What if the aux tank is plumbed inline with the wing tank and therefore has no filler neck? You'd only need to vent the wing tank. In flight, when the wing fuel gauge reads empty you know how much fuel/time you have left in the aux tank. You'd still have a lowered head pressure when the wing tank was empty, but I don't think that would be an issue considering the fuselage tank in a cub doesn't create a head pressure problem. I'd planned on a fuselage tank of 5 gal. I figured that I'd use this extra 5 gallons as my FAA required reserve. In other words, I'd never (or rarely) use it. Fly till the wing is empty then land. That tank would add an extra 35 or so pounds to the empty weight.

How I designed my header tank. About 7 to 8 gallons

Michael
N838MM

You've talked me into it Mark. I am planning long flights so will need the peace of mind altho the 1 1/2 to 2 hr time frame rules me too. I think I'll go with a fiberglas tank under the glove box ...somewhere between 13 to 15 gals. and valve it to be able to switch from one to the other. Cruising on the little tank and taking off and landing on the wing sounds like a good practice. Another question comes to mind....if the tank is as low as it would be under the top longerons, will it have sufficient pressure to feed the engine without a pump?

You're right about where your mind goes while working ....lots of what ifs....could add tons to the plane easily, making the creature comforts. Me, myself and I have went around more than once to prevent that. And then there is the things you relegate to a time in the future after your flying.....don't know how many of those will get done once I start flying

by the by....this is Mon. Sept the 19th. Hope what happened in Reno, tragic as it was, doesn't shut it down. "they" are talking about it again.

Gaylon

Wise words, Mark.

IMHO, the closest I've ever been to the perfect all around airplane is the RV 4. Short field, slow flight, fast and economical, aerobatic. Sort of a jack of all trades/master of none. I know, this is the Hatz forum, not an RV forum. Just wanted to agree with Mark and say one should figure out what kind of flying you want to do and then build THAT airplane.

If most of your flying is cross country traveling, then by all means incorporate extra fuel. It's what you do most of the time.

My point is simply that if most of your flying is touch and goes, or little Sunday trips to breakfast, don't run up the expense, slow the project down, and add the weight of extra fuel tanks.

Every piece of an airplane is connected to every other piece and even small changes have sometimes major consequences. For an extra few gallons of fuel you have to consider head pressure, valving, lines, quantity indication, C/G, useful load, instrument space, leg room, etc. It's no small thing, but if it make the airplane better for what you do most of time, go for it.

I've just found that guys wildly underestimate the magnitude of work required to make "small" changes, so they wind up making their lives a lot more difficult for something that they really could have lived without.

Mark

M Lightsey wrote:Build the airplane for what you're going to do most of the time.

That sounds like smart advice. I will also say, however, that extra fuel is the one mod I wish I had. I think the perfect situation would be a removable tank that could sit in the front compartment and just attach into the fuel system with a quick disconnect for those rare longer trips. Maybe with just a small transfer pump to add the fuel into the main tank when needed.

Ryan