WWI Replica Safety

[j ferguson]

Originally Posted by Machinbird

The most probable reason for a mush instead of a stall (but not the only reason) is mis-rigging of the elevator. If the elevator stop results in a decrease of elevator up travel by as little as a degree from optimum, this kind of thing can result. When I rebuilt my Luscombe, I noticed that there were two elevator up travels in the type certificate and mine was set for the lower one. After two turns of a spin, it would fall out of the spin and accelerate. I set the higher up travel and the spin would then do 2 turns of flopping around and settle into a stable (semi-flat) spin which was still easily recovered. The difference between elevator travels was something like 1.2 degrees. Not really very much when you are trying to read angles. Things like stabilizer incidence and wing incidence as well as cg location can factor into things here. Set those things as accurately as possible, then wear a parachute on your test flights so you are ready for a surprise.
Sid

Sid, I find this a very sobering observation. A difference of 1.2 degrees would be something like 1/4 inch travel at the elevator's trailing edge. This doesn't seem like enough to provoke a detectable difference in flight.

A builder might hope that the inevitable small tolerance excursions on his project would cancel each other. One might also hope that the rigging geometry has been confirmed by flight-testing in the original planes AND you know what it is.

But connecting flight characteristics with where to alter the rigging geometry looks very challenging if you don't have someone around who is really sharp on this stuff. You also need to know what flight-tests to try in order to detect adjustment issues. Who would think that a quarter inch of elevator deflection could have a consistently demonstrable effect such as you report?

I suspect that there are designs which are more forgiving of small rigging variations than others.

It would be good to know what you are confronting when you decide what to build and decide for yourself if what you want requires unusually knowledgeable flight testing.

[Flysafe]

Rigging of surfaces, flight control stops and flight control systems require absolutely meticulous attention to detail AND must be inspected by an independent person following installation or modification.

Mis-rigged flight controls have killed or seriously injured many people in aircraft.

With WWI aircraft the flight characteristics can be unique to start with so changing rigging from plans requires careful and knowledgeable expertise to determine what should be changed and by how much.

Flight control stops on WWI aircraft require careful positioning. Not enough travel is a problem, but too much travel can find you with a rudder hard over and insufficient force/authority to recover.

[joepilot]

Joe, FlySafe, et. all,

Outstanding Thread Joe - thank you! Great advice and opinions and thoughts. This thread is soooo needed by novice builder like me. I thank all who have contributed, please continue as it all applies to safety of flying replicas. So much has been brought to my attention that I had never considered. Every subject has affected my "chair flying" and building. Please keep this info coming and I especially appreciate the less-than-expert questions as I have a lot of "dumb" questions to ask.

Joe this is an awesome Thread you created. Good luck on those "high-lift" devices call floats!?

C'ya
Joepilot

PS I know this Thread and the information presented will save lives as it has definitely made me aware of shortcomings. I thank each one who has spoken here. Please keep the posts coming.

[Joe Perkel]

Originally Posted by joepilot

Joe this is an awesome Thread you created. Good luck on those "high-lift" devices call floats!?

C'ya
Joepilot

PS I know this Thread and the information presented will save lives as it has definitely made me aware of shortcomings. I thank each one who has spoken here. Please keep the posts coming.

Thanks Joe!

So much has been brought to my attention that I had never considered. Every subject has affected my "chair flying" and building

I'm finding this to be the case as well. My long delay in starting, has it's advantages.

Good luck on those "high-lift" devices call floats!

I'm having second thoughts on the floats. My reasoning being that I can't seem to re-produce the original thrust with modern power and still remain within the constraints of the original design.

Preparing a post regarding this for the Sopwith Baby thread.

Rob,

Did you notice in the 1918 Handbook the passage regarding required thrust and predicted performance? I have not had a chance to get back to it since spotting it, but there were some formulas.

[Blue Max Aviation DR1]

Originally Posted by Flysafe

Sid, the issue of the mechanism used to steer a tailwheel during taxi (brakes or rudder) is in my opinion not an influencing factor in the decision making process.

A low speed taxi event is a far lower risk than a groundloop during landing.

I have several thousand hours of tailwheel time in all shapes and sizes and having operated with both the lockable and unlockable variety I can attest to the safety enhancement that the locking version provides.

With respect to the scenario you describe of a brake failure, let's examine the risks. First, steerable tailwheel or not you have a stopping problem. Second, in all your flying how many brake failures have you had? Third, with only a few exceptions aircraft are built with a separate master cylinder for each wheel assembly, so the likelihood of a complete brake failure is low. Fourth, how often do we run into crosswinds on landing - almost all the time. Lastly, a single brake failure with a locking tailwheel offers improved directional control - it wants to stay straight to start with.

When you look at the whole package, for WWI replica aircraft, the lockable tailwheel offers the best safety enhancement value overall.

The final decision is a personal one and I respect that 10 pilots in a room will give you 20 opinions. My comments are only offered from the perspective of my knowledge and experience, based on 34 years flying, 18,000+ hours, lots of tailwheel time and 20+ years flying many WWI replicas. But it is still just one mans opinion. As the wiley old Chief Pilot said; "opinions are like a**holes, everyone has one".

The classic example of lockable v.s. unlocked tailwheels can be found in the Harvard MK2 and Harvard MK4. The 2 was always in danger of groundlooping if you weren't careful. The 4 was a pleasure.
One should also factor in crosswinds on taxiing. The DeHaviland Otter did not have a steerable tail wheel on the first models, and - with the huge cross-section - was impossible to taxi with a sideload. The steerable electric tailwheel made it a charmer. With a locked tailwheel you can taxi in a straight line. I realize these are not small - light aircraft. But "small" sometimes magnifies the problems.

[Flysafe]

Here are some pictures of the GWFM 1 1/2 Strutter lockable tailwheel.

1. Tailwheel in Locked Position

Tailwheel Lock.jpg

2. Tailwheel lock/unlock lever

Tailwheel Lpck Lever 2.jpg

3. Tailwheel in Unlocked Position

Tailwheel Unlocked.jpg

[Machinbird]

Thanks for the pictures Flysafe. It appears you started with a Scott tailwheel. The spring on the pawl tells me that in event of cable failure, the tailwheel will lock the first time it goes through center. The detent on the handle is for unlocked, isn't it? Looks simple and effective.
Sid

[Nick]

Have been learning lots from this forum, and slowly adding a few of the suggestions to my pre-flight checklist.
Think I’ll now add to the list: Maximum Crosswind component 1 knot.
This is the Snipe plough shear tail skid with limited steering



Actually I would hope once the stick is hard back it would help keep it straight. The Tiger Moth leaves a fair old furrow with a relatively flat shoe, hate to think what this will do.

Nick

[Flysafe]

Sid, you are cprrect. We started with a Scott 3200 tailwheel. If the cable fails the wheel will lock as it pass through the center point. The forward position (no cable tension) is locked and the rear detent position (tight cable) is unlocked.

A very simple and effective system that we have populated onto other aircrft with different tailwheel types also.

[Blue Max Aviation DR1]

Originally Posted by Machinbird

Thanks for the pictures Flysafe. It appears you started with a Scott tailwheel. The spring on the pawl tells me that in event of cable failure, the tailwheel will lock the first time it goes through center. The detent on the handle is for unlocked, isn't it? Looks simple and effective.
Sid

Billy Bishop's mother told him to keep it low and slow and level in the turns.