Operation Notice from Bob about Fuel Tanks on Systems with Fuel Pumps

[Battson]

That is an interesting characterization. I've seen that many first timers have issues with the adverse yaw but they sort it out reasonably quickly. Aileron movement requires rudder movement with it. I've never noticed the Bearhawk yawing or dutch rolling in turbulence. It seems sufficiently stable on the yaw axis. (...as well as on the others)

One of things that I love about the Bearhawk is the amount of rudder authority. This is very useful for crosswinds. However, the first time that I came over a tall set of trees and kicked to rudder to slip it, the yawing motion really caught my attention!

This is something we agree on I thoroughly enjoy the huge rudder authority. Slipping and control in crosswinds, just as you say.

Originally posted by Nev View Post
alot of people will initially struggle with the Bearhawks very sensitive rudder.

I don't think we want to overplay the rudder authority. Some don't get it initially, but more often people OK with it. We have a lot of data here, if you know what I mean...

People notice the controls are remarkably powerful, but not shockingly power.
I would not describe the Bearhawk as "short coupled" or "very sensitive" unless you are flying outside the approved CG range.

[kestrel]

This is something we agree on

I thoroughly enjoy the huge rudder authority. Slipping and control in crosswinds, just as you say.

It drives me nuts with some of the other planes I fly that the rudder doesn't do much at low speeds. After learning to fly in a J-3, I expect a rudder to cause yaw/slip! When I fly the C-172 (don't do that often), if you get it slowl, the rudder does very little and I can't get much slip out of it with full rudder. That's probably one of the reasons it won't hold a spin. I wonder of the older square tail ones are better than the newer swept style?

....and what does what I've posted here have to do with Bob's recommendations on fuel selection?

[schu]

If someone wants to explain how changing tanks regularly lowers the risk and offers advantages, compared to using both tanks most of the time, (using a clear substantive argument) that would be helpful.

My bearhawk still isn't flying, but in my 170A the tanks are marked "No Take Off" when below around 1/4 tank. Also, it is placarded to not cruise with the 'both' setting. In fact the POH on a 1959 C172 says this:


172-fuel_orig.png

So, at least with my Cessna, if I use single tank operation and land at an airport with the fuel pump out of service, I can land with 1/3-1/2 a tank on one side instead of having both tanks at the "No takeoff" cutoff. Also, even through zillions of people have been flying them all over on 'both' for decades, there is a remote possibility of a vapor issue that can be resolved by switching to the other tank, which of course is only an option when on single take operation in the first place.

My GPS warns me every 15 minutes to switch tanks which means I am evaluating my fuel situation every 15 minutes of every flight which can catch other issues like a fuel leak.

So, in the case of my cessna (and I suspect there might be carb'd bearhawks in the same boat, but who knows) my argument is that having a completely separate fuel system to switch to in case of an issue, combined with at least one tank well above the 1/4 mark when landing in case I need to find fuel elsewhere, combined with a regular prompting to continually monitor my fuel situation is a reasonable case on why I believe single tank operation is safer than putting it on 'both' and pretty much forgetting about it.

[Battson]

That is a very interesting read.

[Nev]

Heavy wing
When I was test flying my BH I noticed that in level flight the right aileron was reflexed slightly more than the left. Very long story short, it turned out to be the result of a heavy wing. Specifically 2.1 lbs of magnetometer and landing light in the left wing. It also showed up as a 12 lb higher weight on the left wheel at the W&B (a head scratcher), the result of my misplaced effort to minimize conduit runs. At that time we didn't realize the significance.

Steady heading side slip
To fly wings level required a very small right roll input. This generated extra drag on the left aileron with an accompanying left yaw and what is referred to as a steady heading side slip. Very frustrating. With wings level and ball centered, the aircraft would continually turn by a barely perceptible amount. With wings level and a constant heading the ball would be slightly out of center (the steady heading side slip).

The other frustration was that fuel would continually transfer (or draw unevenly) when in the BOTH position, in the direction of the ball.

It took a while to resolve the issue, and finally I was able to fly with the ball centered, wings level, and no accompanying fuel transfer. I mention this because it was my first experience with a persistent uneven fuel burn or transfer between tanks.

[Utah-Jay]

Nev I will ask in a post rather than a comment

What resolved the heavy wing? Can you go into more detail on the conduit run?

[schu]

That is a very interesting read.

Here are two more interesting reads:

Cessna describing the problem:

https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=36949

Cessna's solution:

https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=30276

[Nev]

Nev I will ask in a post rather than a comment

What resolved the heavy wing? Can you go into more detail on the conduit run?

Kev D was a big help with rigging and reducing the heavy wing issue. A lot more info in the thread HERE, including how to raise the aileron hinge line with washers. I think the another solution would be to ensure both wings weighed a similar amount and I plan to explore this further. However I posted it here because it had a direct effect on the fuel system.

[Bcone1381]

Here are two more interesting reads:

Cessna describing the problem:

https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=36949

Cessna's solution:
https://support.cessna.com/custsupt/...df?as_id=30276

Interesting. Thanks for posting Schu!

It looks to me like Cessna designed an escape route for a vapor bubble that might form in the horizontal section of the fuel line. Liquid Fuel has a tough time getting around Vapor Bubbles that reside in a line.