Questions about gear speed and flying fixed gear

[BBerson]

A normal master circuit would have a solenoid master relay similar to this instead of a circuit breaker: Master Relay - Battery Solenoid | Aircraft Spruce

Rated at 80 Amps or 60 Amps continuous from the data sheet.
It is not a circuit breaker.

 

[rv7charlie]

That is correct; the master contactor should be next to the battery to make the airframe completely 'cold' for emergencies. Still doesn't resolve the issue of putting the engine on the same bus as the airframe, though. You don't want any airframe issue to auto-stop the engine, regardless of severity. Then there's that muscle memory thing again...

 

[TXFlyGuy]

Those looking to improve their T-51s will want to assure they are no longer using the original shoulder harness attachment scheme that was a significant factor in the death of a builder/pilot in NZ in a very survivable crash. My own opinion is that Titan's "fix" isn't much better than their first design.
More here:Full Accident Report - T-51 Fatal Crash, NZ

This accident has been discussed at length here, and on other forums. The general thinking now is the pilot had a myocardial event prior to the crash. This was a very survivable accident. Had he flown the plane all the way through the crash, it would have made a difference...assuming he was not already dead.
Regarding the restraint system, I will guess that 80% of T-51's have not addressed that issue.

 

[TXFlyGuy]

Out of how many flying examples?

Minimum = 45
Maximum = 90

 

[Dan Thomas]

This accident has been discussed at length here, and on other forums. The general thinking now is the pilot had a myocardial event prior to the crash. This was a very survivable accident. Had he flown the plane all the way through the crash, it would have made a difference...assuming he was not already dead.
Regarding the restraint system, I will guess that 80% of T-51's have not addressed that issue.

Most accidents are loss-of-control accidents. Pilots fail to fly the airplane. They stall and spin in. They mess up the landing. Sometimes the engine quits soon after takeoff and the options are all bleak: pick a building to hit. In almost all cases one had better have secure restraints. Even ditching can kill if the restraints can't handle the deceleration forces. The reasons that shoulder harnesses were finally mandated were the head injuries that could have been prevented just by keeping the head away from the instrument panel.

Lost a friend that way. He had the shoulder harness and didn't use it.

 

[Marc Zeitlin]

Minimum = 45
Maximum = 90

Thanks. And this is where statistical analysis comes into play (something that no one ever wants to consider, because it makes stuff look as dangerous as it actually is, rather than just sweeping failures under the rug and hand waving about successes).

Everyone is always talking about the things that DIDN'T fail. But a success is almost meaningless from the standpoint of failure analysis - if a system has a 1% failure rate in 100 hours, then 99 out of 100 of the people you talk to are going to tell you that their system works fine - no issues, in the 100 hours they've flown their plane. But a 1% failure rate is miserable, particularly when you're talking about a catastrophic failure (and I use the word "catastrophic" here in the FMEA/SSA sense, not in the hyperbolic sense). So the only response that's meaningful out of those 100 is the one failure. And here we are.

Now, if you make some assumptions about how to calculate the upper bounds on failures, we can see (using the binomial method) that with one failure in 100 units, the upper bound on failure rate, with a 95% confidence level, is 4.65%. That means that in 95% of the populations of 100 units, no more than 4.65% of the units in that population will fail. If there is one failure in 50 units, the upper bound is 9.1%.

These, to be extremely blunt, are freaking miserable failure rates, and no one in their right mind should get into a plane that has an upper bound of 4.65%, much less 9.1%, on a catastrophic failure probability.

No matter how much one likes the visuals of the design.

Now, since you were discussing total electrical failures, IF one can redesign the electrical system so that it's not susceptible to the type of failure that occurred, then the failure RATE will decrease substantially and the plane can be made safe to fly.

Jim and I have not been able to find a schematic from Titan for a "stock" T-51 electrical system. Whether the system in his plane is "per Titan's specs" or was made up by the builder, we don't know. But it's clearly brain damaged either way, as everyone has stated. And we're going to address that with a modified system based on AEC's Z-19 or Z-101 schematic, which I suggested to Jim after my visit, and which (not coincidentally) Billski also recommends. Once that's done, we may or may not address more of the landing gear mechanical design, depending upon Jim's wishes.

 

[Vigilant1]

This accident has been discussed at length here, and on other forums. The general thinking now is the pilot had a myocardial event prior to the crash. This was a very survivable accident. general thinking now is that

This was a very survivable accident. Had he flown the plane all the way through the crash, it would have made a difference...assuming he was not already dead.
Regarding the restraint system, I will guess that 80% of T-51's have not addressed that issue.

The CAA report:
https://www.aviation.govt.nz/assets/publications/fatal-accident-reports/ZK-SMF-Fatal.pdf

This was a very survivable accident.

The CAA agrees with you on that. It definitely should have been survivable. Folks can look at the report, see the failed shoulder harness attachment points, see the CAA recommendation, and decide for themselves if the harness setup as originally designed by Titan belongs in any airplane. Then, see if their "fix" is a good one.

 

[pantdino]

I find this thread interesting. As usual there are thoughtful comments and others with arms flailing in the air. As stated above, one breaker on the main buss is a terrible idea.

Questions for Pantdino, what serial number is your kit? Also, I seem to remember that you bought this plane complete and flying. What engine did it have originally? Finally, what gear do you have, the standard gear or the 3 inch upgrade? Also what retract pump configuration and plumbing do you have? There is more than one.

If I were building from an unmolested kit I would use 5052 hard lines, AN fittings, and Stratoflex hoses at the retract cylinders, like most general aviation A/C use. The cost would be minimal in the scope of the build.

The overcenter downlock requires correct adjustment to work properly. Once CORRECTLY adjusted it should not need any more attention. There is also that spring loaded downlock that connects to the gear selector lever via a cable to release it.

Sorry, I didn't answer your other questions. It is kit #15, but that is not very useful because when the Titan factory upgraded the plane to the LS3 engine they did extensive mods- like replacing all the skins forward of the cockpit with thicker sheet and welding in additional triangulation bracing in the frame. It has the 3" gear and the builder changed from the original gear hydraulic system to the newer one while he still had it.

 

[pantdino]

Those looking to improve their T-51s will want to assure they are no longer using the original shoulder harness attachment scheme that was a significant factor in the death of a builder/pilot in NZ in a very survivable crash. My own opinion is that Titan's "fix" isn't much better than their first design.
More here:Full Accident Report - T-51 Fatal Crash, NZ

This is another problem. I agree that just attaching the harness to a lower bar will NOT make it a lot stronger. But looking inside the airplane there are no "big, thick, strong things" to attach to. You'd have to run cables back to multiple frame members and hope their collective strength would be enough to hold in a crash.
And the cables from the pilot's frame would run thru the back seat space, making it basically useless.

 

[Vigilant1]

This is another problem. I agree that just attaching the harness to a lower bar will NOT make it a lot stronger. But looking inside the airplane there are no "big, thick, strong things" to attach to. You'd have to run cables back to multiple frame members and hope their collective strength would be enough to hold in a crash.
And the cables from the pilot's frame would run thru the back seat space, making it basically useless.

This is how Vans does it on the RV-8. Stout triangulated tube frame. The RVs are aluminum, with the tubular T-51 frame I'd think it even easier to find a good way to attach a frame like that to some substantial structure.


It is better than the alternative. If this T-51 picture below is any indication, the straps need to be higher than the existing seat back to get them above the pilot's clavicle (and reduce chances of spinal compression from the harness in a frontal deceleration).


Does the pilot's seat back on Lady Elaine look like this one (about as high as the canopy rail)? IMO, nobody tall enough to see over the glare shield should be using straps with that attach point. A higher seat back would also be a help for other reasons.

 

[Dan Thomas]

It is better than the alternative. If this T-51 picture below is any indication, the straps need to be higher than the existing seat back to get them above the pilot's clavicle (and reduce chances of spinal compression from the harness in a frontal deceleration).
View attachment 123902

Definitely bad geometry there.



From https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_21-34.pdf Page 26. Some other good stuff in that AC.

 

[BoKu]

Redacted; already addressed. I should have read further up in the thread.

 

[pantdino]

This is how Vans does it on the RV-8. Stout triangulated tube frame. The RVs are aluminum, with the tubular T-51 frame I'd think it even easier to find a good way to attach a frame like that to some substantial structure.
View attachment 123901

It is better than the alternative. If this T-51 picture below is any indication, the straps need to be higher than the existing seat back to get them above the pilot's clavicle (and reduce chances of spinal compression from the harness in a frontal deceleration).
View attachment 123902

Does the pilot's seat back on Lady Elaine look like this one (about as high as the canopy rail)? IMO, nobody tall enough to see over the glare shield should be using straps with that attach point. A higher seat back would also be a help for other reasons.

Yes, that's where the top of the seat frame is. The "upper extension" was probably a way of raising the attach point a little at the expense of structural weakness. Unfortunately there is nothing high enough to attach the harness to to give a reasonable level. You'd have to build triangulated structures on the frame behind the seats, one for pilot and one for passenger, with extensions up to provide attach points.

IMO T-51s should always be flown with a helmet, just like the P-51

 

[Vigilant1]

You'd have to build triangulated structures on the frame behind the seats, one for pilot and one for passenger, with extensions up to provide attach points.

I think that's a good plan. And either extend the seat back up to the frame top or attach a "headrest" on that new frame, between the strap attach points, to keep the pilot's head from bashing into that new frame during a crash/tumble, etc. That RV-8 setup looks great.

IMO T-51s should always be flown with a helmet, just like the P-51

A helmet is fine but it's no substitute for a proper harness. A head inside a helmet contacting a hard object provides about 1” of deceleration/"stroke" distance. A good restraint provides inches of "stroke" distance (so much lower G loading) AND stops the motion of the occupant using the stout clavicle rather than that tender noggin on the end of a fragile stalk.

 

[wsimpso1]

This is the Titan design. I'm only a "I had college physics and work on cars" level guy, but common sense and real world experience would suggest that mount is going to withstand any serious level of force in the direction it is being applied. No, there is no triangulation to surrounding structures.
The only good thing about it is, as Marc texted me, if something fails it's going to be that easily replaceable thing rather than the spar. But unfortunately if it bends you end up with a gear failure, which causes non-trivial damage to the aircraft.

The structure for the gear actuator only has to be strong enough to safely operate the gear. That means a FOS of 1.5 over the worst actuation loads. Anybody competent in the design of sheet metal stuff ought to be able to do it pretty easily. Once you have that much strength, stop there. If someone puts it on the ground too hard or too sideways, the ideal result is the gear parts bend, not break, and do not tear up the spar it is attached to. Designed to near min weights to carry the design loads is a good thing...

 

[wsimpso1]

It may very well withstand "normal" actuation forces, but it is a masive chunk of metal to accomodate these modest loads. In other words, its a very inelegant solution. That whole mess could probably be replaced with a few small webs of .032 2024 sheet and some rivets and do the job. If you are an airplane designer and you throw a bunch of mass at a solution because you are too lazy to do it right, that's just bad engineering. Simple as that.

Since this and the electrical scheme are "Titan designs", I have to wonder how many other corners were cut...

Classic job of design the stuff to carry all of the nominal loads with a FOS of 1.5 or more, and stop there. I too like the idea of a couple pieces carefully designed of sheet metal will make it sturdy to actuation and landing loads, but bendable under overload to save the spar. And it can probably be lighter than what is in there now.

 

[wsimpso1]

Thanks. And this is where statistical analysis comes into play (something that no one ever wants to consider, because it makes stuff look as dangerous as it actually is, rather than just sweeping failures under the rug and hand waving about successes).

Everyone is always talking about the things that DIDN'T fail. But a success is almost meaningless from the standpoint of failure analysis - if a system has a 1% failure rate in 100 hours, then 99 out of 100 of the people you talk to are going to tell you that their system works fine - no issues, in the 100 hours they've flown their plane. But a 1% failure rate is miserable, particularly when you're talking about a catastrophic failure (and I use the word "catastrophic" here in the FMEA/SSA sense, not in the hyperbolic sense). So the only response that's meaningful out of those 100 is the one failure. And here we are.

Now, if you make some assumptions about how to calculate the upper bounds on failures, we can see (using the binomial method) that with one failure in 100 units, the upper bound on failure rate, with a 95% confidence level, is 4.65%. That means that in 95% of the populations of 100 units, no more than 4.65% of the units in that population will fail. If there is one failure in 50 units, the upper bound is 9.1%.

These, to be extremely blunt, are freaking miserable failure rates, and no one in their right mind should get into a plane that has an upper bound of 4.65%, much less 9.1%, on a catastrophic failure probability.

No matter how much one likes the visuals of the design.

Now, since you were discussing total electrical failures, IF one can redesign the electrical system so that it's not susceptible to the type of failure that occurred, then the failure RATE will decrease substantially and the plane can be made safe to fly.

Jim and I have not been able to find a schematic from Titan for a "stock" T-51 electrical system. Whether the system in his plane is "per Titan's specs" or was made up by the builder, we don't know. But it's clearly brain damaged either way, as everyone has stated. And we're going to address that with a modified system based on AEC's Z-19 or Z-101 schematic, which I suggested to Jim after my visit, and which (not coincidentally) Billski also recommends. Once that's done, we may or may not address more of the landing gear mechanical design, depending upon Jim's wishes.

This statistically trained guy thinks so too. Marc knows what he is talking about. A rethink of the electrical system seems essential to me in any airplane schemed out like this one.

After that, a modest rethink of the gear actuation system can probably result in a suitably sturdy gear without noticeable weight gains.

With good help on the engineering, both will be quite doable and pretty straightforward. The rest of the T-51 community might do well to pay attention to what goes on here.

Billski

 

[TXFlyGuy]

Regarding the T-51 seat frame, and the aircraft in general, it underwent extensive G-Load testing for certification in the UK.
The seat was tested with loads up to 15 G's. It held up fine.
The wings were loaded up to 12.3 G's, before the skins started to wrinkle.
This was done at a GW of 1650 lbs.
Other testing was performed, but I do not have the data now. They used static weights, forklifts, etc., to put the loads on the airframe.
The above info was provided not only by Titan Aircraft, but by their European sales rep.

I know that these numbers are not "state of the art" in today's aircraft.

We estimate that my plane impacted with 14 G's. The pilot walked away. Without a scratch. And, he had removed my custom seat cushions, so he was sitting on the bare metal seat. My seats are not from Titan, but custom made being much taller.

 

[Vigilant1]

We estimate that my plane impacted with 14 G's. The pilot walked away. Without a scratch.

Just to be clear, a plane hits the ground at a particular velocity and it is possible to compute a rough average deceleration rate for the plane if it slid intact for a distance. But everything in a plane decelerates at varying rates (thus differing "G forces") once deformation, shifting, stretching, rotation, colliding, etc begins. Peak deceleration rates and duration are important. The peak load on a seat frame in a crash could be a LOT higher than we can deduce from the occupant's weight and the aircraft hulk's average deceleration.