Yaw stability

[kestrel]

A small increase in yaw stability would absolutely get my vote and in my opinion would not detract from the ability to side-slip, should it actually be desired.

Sure would be fun if there were a way for us to swap rides for a couple of flights and see where the planes differ and where pilot preferences differ.

[Nev]

My guess would be that the planes wouldn't be much different although there is a possibility that mine might have additional cowling area due to the prop spacer supplied by Hartzell. Any increase in cowling area being forward of the CG will counter yaw stability.This was something I didn't know about until well after the aircraft was completed. But yaw comments seem to be common on the forum so I guess it's prevalent, particularly amongst those of us relatively new to tail wheels and older type designs.

I've become used to mine now (200+ hours and 900+ landings), but it took a while, and I'd still prefer to have a small increase in yaw stability. It would also help adverse yaw. The main problem is the effect that flying with the ball not centred has on the fuel system, particularly when operating with a lower fuel quantity. When the ball is not centred, the sight gauges will often indicate more fuel in one tank when actually that tank has the same (or less) fuel, but simply has more fuel against the sight gauge. Obviously this can have serious consequences if one is not aware of the cause.

[kestrel]

particularly amongst those of us relatively new to tail wheels and older type designs.

There is a definite difference. I find that most modern designs don't enough authority vs stability for a good slip at slow speeds.

I've become used to mine now (200+ hours and 900+ landings)

The main problem is the effect that flying with the ball not centred has on the fuel system, particularly when operating with a lower fuel quantity. When the ball is not centred, the sight gauges will often indicate more fuel in one tank when actually that tank has the same (or less) fuel, but simply has more fuel against the sight gauge. Obviously this can have serious consequences if one is not aware of the cause.

That is an issue, but for my own feeling, even a moderate improvement in yaw stability won't make much difference, Unless the air is smooth, I find that the sight tubes confirm that I have fuel and a very rough estimate of how much. ...not more than that.

I've read of some people putting restrictors in their sight tubes with very small holes. This won't help if there is a systematic slip, but I would think could help quite a bit with the turbulence problem.

[kestrel]

Just in case any of what I've posted here was misunderstood. I was deliberate when I used the words "pilot preferences". Two pilots might have identical airplanes, missions and skills and still have different preferences.

[alaskabearhawk]

I've read of some people putting restrictors in their sight tubes with very small holes. This won't help if there is a systematic slip, but I would think could help quite a bit with the turbulence problem.

I put restrictors in my sight tubes more as a safety measure than a readability issue. If the sight gauge gets somehow compromised (i.e. leaks!) I don't want to have an open fuel line above me in the cockpit.

[Bissetg]

Interesting thread.

Nev and I flew a 4A together before our kits were completed. He nearly made me sick (I kid you not). Sitting in the back was fun for a few minutes ?.

Nev is a very accomplished and experienced aviator, but from a very different background to me.

I think Kestrel has hit the nail on the head. If you’re used to aircraft that require foot input then you will go huh and adapt to the Bearhawk quickly. If you’re from a yaw dampened background then it might be a little while longer before you go huh and adapt.

One of the things that I didn’t enjoy in the Maule M5 was the lack of rudder authority. The Bearhawk has plenty.

Personally, I think once you’ve adapted you’ll appreciate the control authority for X wind landings atc.

[Mark Goldberg]

Grant's comments are correct from what I have seen over the years. On a slightly different subject - adverse yaw - the perception of the pilot was 100% based on their flying experience. A pilot who did not have to use his feet much previously often felt the adverse yaw was difficult to get used to. A pilot who came out of an Aeronca, Stinson, or PA18 says "what adverse yaw?" Mark

[kestrel]

My primary training and first solo (on my 16th) was in a 65 hp J-3. My evaluation of the Bearhawk is that it has a lot of adverse yaw, but... meh... That's what the rudder is for. When I bought my Bearhawk, I flew it about 0.5 hrs and did one landing with the seller. The next morning I climbed into it and flew it from FL to NH in one day. I didn't once notice or think about the adverse yaw. At that time nearly all of my recent experience had been in a C-172 and an RV-4. My life experiences give me one perspective on it. Others have different experiences and preferences and thus, different perspectives.

[AKKen07]

I’m loving this conversation. Now 30 hours into my Bearhawk training I’m finding myself pretty comfortable. Having a bit of time in stubby tailwheel planes (Pacer, Maule) helped. The adverse yaw to me seems a bit more than the Citabria I have flown and am most used to and so was pretty easy to get used to. But, initially, while on skis, the yaw stability was downright confounding. It’s better on wheels but still the least stable plane with the most authoritative rudder that I’ve flown.

[Richard E]

My guess would be that the planes wouldn't be much different although there is a possibility that mine might have additional cowling area due to the prop spacer supplied by Hartzell. Any increase in cowling area being forward of the CG will counter yaw stability. This was something I didn't know about until well after the aircraft was completed. But yaw comments seem to be common on the forum so I guess it's prevalent, particularly amongst those of us relatively new to tail wheels and older type designs.

I've become used to mine now (200+ hours and 900+ landings), but it took a while, and I'd still prefer to have a small increase in yaw stability. It would also help adverse yaw. The main problem is the effect that flying with the ball not centred has on the fuel system, particularly when operating with a lower fuel quantity. When the ball is not centred, the sight gauges will often indicate more fuel in one tank when actually that tank has the same (or less) fuel, but simply has more fuel against the sight gauge. Obviously this can have serious consequences if one is not aware of the cause.

Nev, You comment upon the affects on fuel flow whilst flying with the ball out of centre. When I was flying my first few hours in the Bearhawk I was still very new to using those rudder pedals and the affects of flying out of balance. I was in the 1000ft circuit about mid downwind, still out of balance from the climb and turn from crosswind, when the engine spluttered and all but died. Heading straight down toward the runway we made a very short approach and thankfully safely landed. The engine was still spluttering, but after a few seconds on the ground it came right and we taxied back to the hangar to investigate.

The facts were that ZK-RJE is a Model B 4Place with an IO540 engine. We had about 15litres (4 galls) in each tank. We were on Left tank only. We had completed a handful of circuits and I was struggling to keep the aircraft in balance having only flown tri-cycle Cessnas previously. We intended a couple more circuits before filling up. Back in the hangar the engine ran sweetly and no problems were discovered with fuel flow, pumps, air intakes, electrics or anything else.

Learnings for me:

• Flying in balance is absolutely essential, especially when fuel levels are low.
• For ZK-RJE flying on BOTH is preferable to allow fuel flow from either tank, especially when low on fuel.
• Keep that ball in the centre.

Never had a problem since.

[Bissetg]

What rudder pedal springs are folks going with these days? I’ve beefed mine up to C-141 but I’m considering something a little heavier.

[Nev]

Just a data point, my original springs measured 4.2 lbs tension on the fish scale, and the C141's measure 7.2 lbs.

[SpruceForest]

Stick-fixed versus stick-free stability... some of the friction in any mechanically-coupled control system is likely a contributor to stability, but too much is unpleasant. Could be worse - I've flown aircraft that were happy to swap ends in cruise flight but for the AFCS system... 'I have the controls' meant hands on stick and thrust and feet physically on the pedals. Light and responsive is a good thing, right?

[DBeaulieu]

Why not add an adjustable friction adjustment to the rudder cable versus swapping springs...seems relatively easy to implement. Standby for sketch of the idea.
Disclaimer: I have strange ideas working alone in the garage sometimes

[jaredyates]

Might not be nice to have friction for the takeoff or the landing.

[DBeaulieu]

jaredyates Thinking the friction would be added/used as necessary for cruise conditions, T/O, approach and landing phases - friction off

[jaredyates]

Hmmm... Sounds like something easy to mess up from the pilot's perspective.

[Bissetg]

I’ve just re read this entire thread.

My take on this is that there isn’t a yaw stability issue at all. The “yaw” issue relates to over controlling with rudder. The rudder is very powerful by design but due to the aerodynamic horn gives little tactile feedback or resistance to pedal inputs compared to for instance Cessnas.

I think the reason that pilots often don’t fly the Bearhawk in balance from the get go is that they can’t relate the very light rudder pedal pressure input to the significant control deflection so they over control sending the ball all over the place and us grabbing at cross tubes to stop getting thrown out sideways.

There are several references in this thread about increasing the strength of the rudder pedal springs, I think that is where the answer lies in fine tuning this handling trait.

As we have already discussed at length, it’s not hard to adapt to but it’s a bit unnerving for other pilots who aren’t used to it and that is the real reason I would make any change. Watching experienced pilots have the ball bounce from one side of the court to the other can be entertaining but mostly is irritating and frustrating.

[Nev]

I resemble that !

[Nev]

Something I need to clarify - when I first started this thread in Dec 2021, I was part way into flight testing, and having an issue with yaw stability, which was resolved at that time. Since then I've still found the BH to be very sensitive in yaw, and although I got used it, it's still particularly noticeable when other experienced pilots fly with me. It manifests as the ball being chased about continuously.

I've used the terms yaw stability and yaw sensitivity somewhat interchangeably, but they're really two different things.

What Grant and I have been exploring recently is the yaw sensitivity. With the help of Mark (aka Helidesigner) we've made some progress by changing to slightly stronger rudder springs. (Thanks to those who suggested this change earlier on!)

Baby steps, but all in the right direction.

[Helidesigner]

There is no taw stability problem with the Bearhawk. There can be a slight dutch roll mode that develops in turbulence given the right combinations of rudder springs, prop size, tires, and rudder cable friction. It is easily countered with control movements. I prefer a plane with stiffer yaw stability on cross country trips. That is why I have the small ventral fin. I find the yaw sensitivity force required about right. Increasing the yaw stability will reduce the rudder sensitivity a little.

[Battson]

My take on this is that there isn’t a yaw stability issue at all. The “yaw” issue relates to over controlling with rudder. The rudder is very powerful by design but due to the aerodynamic horn gives little tactile feedback or resistance to pedal inputs compared to for instance Cessnas.

I think the reason that pilots often don’t fly the Bearhawk in balance from the get go is that they can’t relate the very light rudder pedal pressure input to the significant control deflection so they over control sending the ball all over the place and us grabbing at cross tubes to stop getting thrown out sideways.

There are several references in this thread about increasing the strength of the rudder pedal springs, I think that is where the answer lies in fine tuning this handling trait.

As we have already discussed at length, it’s not hard to adapt to but it’s a bit unnerving for other pilots who aren’t used to it and that is the real reason I would make any change. Watching experienced pilots have the ball bounce from one side of the court to the other can be entertaining but mostly is irritating and frustrating.

Well summarised. I totally agree - the design is stable but sensitive on the pedals (and elevator, which I have come to enjoy - and I wish the aileron were lighter to match, especially in a dive).

Flying Graeme's Patrol about 6 years ago, the larger springs made a remarkable difference. Its as simple as that, if you like more feedback then install larger springs. I haven't bothered.

There's no design issue causing instability, and no need for complex do-dads unless the builder so wishes (which many often do!)

Alun has changed the rudder design to give more feedback, and is probably flying any day now. I would be interested to see how that feels, but personally I wouldn't change from the original design because I like it.