WWI Replica Safety

[Machinbird]

Joe, Udo's picture is no longer online, it was originally on the DR-1 thread and used Mercedes drum brake parts. I found a posting by Von Writter that was fairly similar in concept (except for the cone bearings) so I'll post that. You could probably make the back plate from flat stock if you wished. I also found an older DVII replica and I'll post a picture of that as well.
Sid

[Maxim08]

machinbird,
The photo on the right appears to be of a 1930's era Bendix wheel.
They have a cast alloy inner structure with integral brake drum. The exterior skins are riveted and structural. These are increasingly rare.
The GWFM D VII uses a pair of these with 30" x 5" tires. The wheels we use were original equipment on the N3N before they changed to Stearman wheels and tires.
Regards,
John

[Joe Perkel]

Originally Posted by Machinbird

Joe, Udo's picture is no longer online, it was originally on the DR-1 thread and used Mercedes drum brake parts. I found a posting by Von Writter that was fairly similar in concept (except for the cone bearings) so I'll post that. You could probably make the back plate from flat stock if you wished. I also found an older DVII replica and I'll post a picture of that as well.
Sid

Ah yes, now I see! For a moment there, I had a bit of trouble visualizing this. Now I know what to look for.

Thanks Sid!

[Machinbird]

Flysafe has made a very strong case that directional control is more positive and pleasant with a lockable tail wheel than with a steerable tail wheel and his observations should not be discounted.
I am still not sure I want to go that route. Why? Because I have had a brake (cable) failure in a taildragger while taxiing in close confines and what saved the day was my steerable tail wheel. With a lockable tail wheel, you are dependent on brakes for directional control at low speeds. With a steerable tail wheel, you still have options.
I have flown Cessna 170s which have steerable tail wheels and are heavier than my proposed build, a Fokker D.VII and have had no problems. Some of the problems people have had with steerable tail wheels are maintenance issues. If you look at the design of the Maule tail wheel, you will see that a properly functioning Maule tail wheel will not disconnect until it reaches 40 degrees of deflection from straight ahead. This article has information on overhaul and Rigging of the Maule tail wheel. http://www.bowersflybaby.com/tech/Maule_Tailwheel.pdf and also has important installation geometry information on tailwheels in general. If your properly rigged and maintained Maule tailwheel disconnects because of side loads, you are already in a ground loop.
The Scott tail wheel is similar in operation, but is perhaps less supportable and more complex to maintain. For such a simple looking systems, many of the interrelationships of the components are complex so it pays to fully understand them before blithely installing a tail wheel on your aircraft.
Perhaps the best solution to directional control problems on narrow (and highly crowned) paved runways is to avoid them unless everything is in your favor.
With a steerable tail wheel, if you touch the tail down with a strongly deflected rudder, you will probably get a kick from the tail wheel so you may want to ease the tail down on landing to lessen the severity of that kick. Not a big deal if you are anticipating it.

Flysafe has made a few other significant observations and we’ll see if we can add positively to them in some later discussions.
Sid

[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 tax 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; "opnions are like a**holes, everyone has one".

[Machinbird]

Originally Posted by RobW

I would say differential brakes and a steerable tail wheel are the things you are suggesting.

However, I will bet that that tail skid does wonders for keeping the aircraft straight on a grass strip as long as you maintain full back stick to keep it digging in.

As for what could the pilot do to promptly increase the rudder (and elevator)effectiveness... a little burst of power would help a lot, though it takes a bit of practice to know how much and when. Since this was a rotary... it may even be easier due to the blip switch and the need to keep that engine turning through the roll out.

Bald Eagle, what do you think?

Rob,
You were the first to answer the second question I asked at the beginning of the directional control discussion. For that you get a big attaboy.
It is such a simple thing, but a burst of power when you are having control problems can often quickly stabilize the situation and save the day. A good thing to have in your bag of tricks.
The following tale involves a more modern aircraft and a different axis but should be illustrative:
I was a newly minted pilot and I had checked out the club Cessna 150 from the FBO where it had just undergone maintenance involving tail removal and re-installation. I checked out that the control motions were in the proper direction prior to flying and launched. On my first landing approach with full flaps, I was flaring the aircraft above the runway, still nose low, when the elevator hit the stops! I reflexively gave the aircraft a burst of power and got the nose up enough to land it. I checked the elevator and found that the elevator bellcrank had been mounted upside down. I had lots of down elevator and very little up elevator.
I don't know if a burst of power would have lessened the swerve in the Dr.I that we saw in the video, but that was about the only option left at that point.
Sid

[RobW]

Sid,
Whew... you hadn't said anything so I was begining to think I was off the mark.

My one and only serious ground loop was in a '48 Cessna 170. I was landing on a runway that was on top of a hill. Next to the runway on the right side were a bunch of hangars.

There was a pretty good crosswind blowing... and I was getting pretty confident in my 170. Two of my kids were asleep in the back.

The approach sucked... should have given up at that point. It was gusty... plus being on top of a hill, there were lots of down drafts to deal with too as you got close to the runway. As I crossed the threshold everything magically came together and I put the main wheels down in a wheel landing and began my roll out... yoke forward... The plane was slowing down nicely.. tracking right down the middle of the runway...

Remember those hangars I mentioned... well at about this time I passed the last one and suddenly was smacked broadside by that crosswind I'd been fighting all the way to the ground.

The tail swung around faster than you can imagine. I stomped on the left rudder... all the way to the stop. all that did was stop the swerve... I was now about to exit the runway at a 45 degree angle.

I could tell that I stopped the swerve because one of the runway lights was directly in front of me and only getting bigger...

I was adding brake now, only a little, and was getting nowhere... had to make a decision... continue with what I was doing, or figure out something else.

It was clear to my right so I eased up on the rudder a bit, let the plane turn into the wind where it wanted to go anyway, stopped the turn, and brought the plane to a stop just off the runway... exactly in a tie down spot.

Kids still sleeping... I pulled the mixture, let the engine die... and had a long think about what just happened.

Hmmm... hangars masked the wind from the runway... should have quit the approach when I was having difficulty getting it stablized, a little power might have been helpful... wow that tail came around fast... yes, the ailerons were into the wind... suprised that the downwind wing didn't come up... maybe it did, didn't notice... kids snoring away in the back... heart going 90gazillion mph...

As I was thinking about all the stuff I looked in the parking space to my right... there sat a Luscombe with a banged up wing tip... hmmm I wonder what happened to him...

rob

[Machinbird]

Rob,
Thanks for the great story. About all you can hope to do in these situations is be mentally ready for things like the return of the cross wind when the blanking effect of the hangars stops. Predicting these things takes experience and experience isn't always cheap. Just keep flying the airplane all the way and you will get the best possible result.
I have to apologize for being slow in addressing the front part of the discussion.
I also owe Joe Perkel an attaboy for answering the first question.
Best wishes to all,
Sid

[j ferguson]

lost one brake on the 210 on rollllllllll-ouuuuut at Oshkosh for the airshow. got stopped for the turnout in front of the tower to be directed to the north tie-down. had to do a 270 degree turn to turn north. this didn't faze the ground guys a bit - I still wonder why. Nose wheel steering was enough for gradual turns plus power bursts (when no-one behind us). You ought to try leaving your foot off one of the brakes to see what it's like - not nearly the disaster you'd think - in easy conditions.

Cranking in full deflection with rudder and nose-wheel steering while touching the toe-brake with the other foot is a little tricky, but if you pay attention it works - somewhat.

Back at PWK we found one brake used lightly did help while there was rudder, but not slower, I got it to the shop with power bursts and nosewheel steering

[RFC Pilot]

Originally Posted by Jeff Brooks

I read a story about a guy in Long Island who built a Fokker DVII and he let a friend who is an experienced pilot do the inital flights. On landing, the plane swerved off to the right as weight was applied to the wheels. It turns out that the bungee cords were tighter on one side than the other. That pilot had the opportunity to talk to an old timer who explained that on preflight, they used to sit on the wing and measure how far the wing drooped. Then they repeated the check on the other side, trying to determine if both wings dipped down to the same level. Now that is in my preflight.

Not sure if someone mentioned this already (too many pages to look through), but that is actually something we do at the Museum when we redo the bungies. We rock it by the wings a few times, to settle them, then check a couple of things.

1) Are the cords laying right.

2) Are the wings level.

3) Is the gear on each side compressed the same with it is sitting on the ground.

and

4) by pushing down on the wing tip, does the suspension give the same amount one each side.