Building a Nieuport 11...

[wyoranch]

Frank,
I am not a taildragger pilot (therefore I am not a real pilot) so I am sure I will get beat up over this question, but is the issue on T/O the fact that the tail wheel does not have enough authority till the rudder does or is it the issue of the rudder not having enough bite by itself? Please be gentle with your answer, while I have a boatload of time in a lot of aircraft, I only have 5 hours total of taildragger time of which include only 2 takeoffs and two landings.
Rick
P.S. your video scared the stuffing out of me and I was 1500 miles from the airplane..... lol

[Frank Giger]

Heck, I need to write this out so I can fully understand it!

The problem is the wheel and the rudder are fighting each other.

So with the wheel down on the pavement, it's sticking the plane in one direction and has a lot of authority, and does NOT want to give. So to maintain directional stability, the rudder has to be neutral. But the wheel needs that authority, as the rudder can't work until it gets enough air flow hitting it.

On grass this wouldn't be an issue, as the tail wheel could literally slide as one applied rudder. Heck, the mains can slide on the grass, giving one extra help - but on pavement that's not going to happen.

When the wheel comes up, it's the rudder's job to keep the plane straight - and it needs to be applied just right and Right Now. The problem, of course, it that it's binary in nature and instantaneous. We're people, though, so we can learn the skill. In a Champ on pavement I can do it without thinking; but then again, a Champ has springs on the tail wheel (more on that later).

Part of that is managing the acceleration to take off speed, of which I've done a poor job. The first flight I was too hesitant in accelerating the throttle and danced around the transition to flight, which put me up and over to the right edge of the runway. This last flight I did it waaayyy too quickly, and you saw the results. So it's clearly a smooth, constant acceleration using the throttle that is required (one of the Dawn Patrol guys guesstimated that it's about three or four seconds from idle to full).

With the wheel and rudder directly connected, right now there's no middle ground between them. What one does, so does the other. Heck, the control horns for both are pretty much the same size, so I don't get a break there, either.

So what I need is for the rudder to be able to be applied while the wheel does its thing. Enter in springs. It allows the rudder (which is directly connected to the pedal) to be moved and the tail wheel to keep doing what it's doing with much less pressure on it, giving one a grace period between the two. Now the rudder and wheel will be compromising with each other rather than at an impasse.

Or so I hope. One of the things not listed in the specs of the compression springs is the amount of tension required to compress them. Too much and it might as well be a direct connection. Too loose and it might make landings a bit more interesting than they should be.

Oh, and on the types of springs - there are two. First is the typical tension spring, like one finds on a screen door, with all the coils touching each other. The spring wants to be short and so pulls back when load is put on it. The problem with them is that they can stretch over time and lose their tension. The second is a compression spring, which wants to be long; its coils are spread apart, and resist being pulled together. They hold their strength longer than tension springs, and perform better at failure (or so I've read, though that may be propaganda put forth by Big Spring).

To be honest I wasn't scared in the least during the flight - I was actually more concerned on the landing! Part of that is the speed at which event were happening, but I could immediately see I had airspeed and acres of room to get her in the air and pointed the right way on my side, provided I didn't do anything sudden. That and the alternative of chopping the throttle and attempting to land on a rough unpaved slope down from the runway seemed ripe for disaster.

I invested almost all of my flying time doing touch-and-goes in a Champ - up, around, land, down to taxi speed, up, around, etc., knowing that they would be the critical skills required when the plane was built (and I became a pilot specifically to build and fly this aircraft). Yes, I did a bit of sight seeing and other stuff (loads of slow flight, ground reference maneuvers, etc.) because that's just fun! Indeed, I haven't bobbled a landing like the one in the video in a long time - I guess the observer rule counts when a camera is rolling - but I've also done my share of them and know how to work through a bounce (and when to hang it up and just go around).

[edit]

What makes these planes in particular sort of, well, particular is the short wheel base and the actual footprints of the wheels. The mains are only an inch and a quarter wide (each), and the tail wheel is two inches wide - the tail wheel has almost as much friction on the ground as the two mains combined! I may actually replace the tail wheel with a thinner one in the hopes of reducing it's grab.

[wyoranch]

So the geometry between the rudder and the tailwheel are the same? I would thing that even with springs you would want exponentially more rudder movement than tailwheel (sorry if that is obvious to all of you).
Rick
P.S. I will stop hijacking this thread. I am just fascinated with all that goes into the plane AFTER it is built. I have never given much thught to that part of it.

[Frank Giger]

One does want more rudder than wheel, but there's only so much one can design without getting crazy. Make the tail wheel horn longer and you'll get less movement of the wheel versus the rudder, but in my case they'd still be linked - the turn would be of a lesser degree, but I need more than that - I need the tail wheel cable to give and not turn at all when I apply rudder (at least initially).

You are correct that most build threads stop at the inspection, which always kind of irked me. In Dick Stark's books the build part is interesting only in the amusing stuff that happens around building - the real entertainment is in the flying of the aircraft.

That's one of the reasons I keep adding to this monster - to show that getting the pink slip, much like getting the little plastic pilot's card - just means that you now have a license to expand on the "recreation and education" part of building and flying the aircraft.

I'm probably the perfect guy for it, as I seem to have more than my fair share of glitches and things to work through than most. Heck, my carefully thought out (and written down) program, based on AC 90-89B, Amateur-Built Aircraft and Ultralight Flight Testing Handbook is in tatters at this point, as it was just too ambitious. Who knows, though, once I get through Step One: Take Off of the active part of flight things might progress more quickly than what I laid out.

[pittsdriver3]

Frank, I like to set up my tailwheels with a slight amount of slack in the springs. That allows the rudder to move a bit before turning the tailwheel. I also like the compression springs much better that tension. This also helps when you lift the tail off as again you are using more rudder for steering even with the tailwheel on the ground and you will get far less of a swing as the tail comes up. Don

[Frank Giger]

Yep, gonna put some slack in them as well.

[Frank Giger]

Springs on tail wheel!

I thought for a second that I might just be able to stick the compression spring on there and have it a little slack, but it was too much - the tail wheel didn't move at all!



So I measured back seven inches from the thimble end of the cable, whipped out my Harbor Freight dremel type tool, stuck a cutting wheel on it and cut them. Digging through my pile o' parts, I found two - and just two - nicopress sleeves of the right size. So only one try with the go-no gauge on each.

The springs came with one long chain, so I cut it roughly in half and started dinking around with the correct lengths - I want a little slack between the wheel and rudder, with the rudder getting the play.



I tested it out, and it looks like I get a little left rudder when the wheel cable snugs up; this is what I wanted. Taping the extra chain up (I don't want to trim it just yet), I went around the hangars at fast walking speed and I think this is just what I needed.

We'll see on the next attempt!*

I worked a bit on the left brake drum, slowly taking down some of it on about a quarter of the way around on the belt sander. It's much, much closer to round now and isn't making a thumping noise as the high spot goes through the brake band. I was getting a little anxious with shaving tiny amounts off and thinking of being more aggressive, so I stopped work. The brakes behaved much better on the taxi run as well, so I'm at the 90% solution there. I just didn't want to ruin the drum because I was getting tired of putting it on the plane, spinning the wheel, marking the drum, taking it off, running it on the sander, putting it on the plane....

The right drum runs pretty true but has a little squeak at the end when it's full stop. I think that just may be that everything is new. I'll look at it next time.

The last thing I did was trial fit my antenna extension, which is just a coax cable with fittings on both ends that go the handheld on one end and the rubber duck on the other. I put it on a fuselage tube just behind the seat, inverted to where it points downwards. I reckon it'll work much better than laying sideways in the seat next to me.

* I've made a rule for myself - I won't fly immediately after performing maintenance. That gives me a chance to look at what I've done with fresh eyes the next time around.

[pittsdriver3]

Frank, That looks like a little too much slack. You want maybe 1/2" droop in the steering. Works well on RV's , Pitts, Supercub, Stinson and 140. Don

[Frank Giger]

The slack is taken up when my feet are on the pedals, as I elected not to put springs on the forward parts of the pedals; I should have made that clearer in my writing!

Good eye, though!

[Frank Giger]

I had a special visitor the other day, yet another friend from Florida!

The day he flew up it was too late for flying my Bebe, so I put him to work doing a bit of tinkering on some minor things.



Part of being ground crew is bearing witness when things go wrong and helping diagnose it. Note the leather combing around the cockpit, particularly the bit by his left shoulder; it figures pretty large into the tale of Test Flight #3.

The next day we were out at the airfield bright and early - CAVU with zero gusting to one winds - and we did the pre-flight and I taxied her out for a nice showy takeoff.

Initially it was straight forward, and the addition of the springs and chains to the tail wheel seemed to be just the trick I needed to keep stability. I applied left rudder, relaxed it a bit, and put in a little more.

Only I was stomping the left rudder cable and Jack Nothing was happening. At flying speed. And she was flying. To the right. Ghaaaa! I rolled the aircraft to the left, throttle to the stops, and brought her over the runway, leveling out the wings with the right rudder and ailerons.

A quick check and the rudder was responding left and right as it normally does.

"Um, I got a problem with my left rudder," I say over the radio.
"Roger," OG says over the handheld he has, "Copy you've got a problem with your rudder."

The initial plan was for me to shoot some go-arounds, floating the runway to find the perfect landing speeds without actually landing. But with a control issue, all that was out of the window - I needed to get her down.

Lining up was no problem, though I was a bit high and a bit fast. I two bounced her, realized I was just asking for trouble in trying to make a bad approach into a good one and went around. The rudder was responsive throughout, so I was cautiously optimistic that I was in jeopardy but not danger (if that makes sense).

I landed okay, but as I finished up with all three wheels on the ground and began to slow the left rudder stopped responding again. It was like the pedal wouldn't go down. The aircraft did a little half circle right at taxi speed; not enough to cause damage to aircraft, but enough to bugger up my bicycle wheel and flatten the tire.

Oh, hell, that's why I have spares. I taxied it back on a flat tire and a slightly warped wheel.

I started at the front of the left rudder control system. My rudder stop nut was loose and turning freely in my fingers. Nut out and thrown against the hangar wall with some bad words. The cable guide bushing at the front was back fully in the mount for it. I moved it forward, wondering if that might have caused the binding.

OG leans over the aircraft and says "Hey, what's that in the fuselage?"

I look back and see something black right against the left control cable for the tail wheel at the bushing that guides it over the fuselage tubing. I fetch my grabber tool and with OG guiding me, snatch it up.



It's a piece of pipe insulation foam, the type I used to form the combing around the cockpit. I had put a small piece of it on the long piece that goes all the way around to give the combing a better silhouette.



I must have knocked it out of the combing when I got in the aircraft and mucked about with the shoulder straps. It fell in exactly the wrong place to where it would sometimes pick up into the cable at that bushing, binding it - but when the rudder went the other way would pop out enough to allow free movement.

Another flight that day was out. Much to sort out.

I felt kind of bad that OG came all the way from Florida to see the plane fly and it turned out to be all screwy, but he knew it that I'm still very early on in the test flight program and handled it with grace.

Since it was a loss of a flight control system due to mechanical reasons, I self reported to NASA about it. I didn't violate any FAR's or anything, but the program is there to build a database of f--kups.

So this morning I went out to the airfield with the intention of just covering the spare wheel and dancing around the airplane, but was shocked to see there were absolutely no winds. Hmmmm, I worked off all the gigs from the last flight, might as well get back on the horse that threw me.

This was an easy video to make: