WWI Replica Safety

[Flysafe]

Make the tailwheel lockable. Any of the larger full-size replicas such as the DVII, SE5A, Strutter or N28 benefit from having the ability to lock the tailwheel for landing and takeoff. I have flown all those aircraft with both locking and non-locking tailwheels and can state that I would never build a WWI replica without a locking tailwheel. A much better directional control device than a steerable tailwheel.

[Machinbird]

Flysafe, I know that the heavier tail draggers tend to have lockable instead of steerable tail wheels. The steerable tail wheels are locked to the rudder (with springs intervening) until you develop enough force to disconnect them. I presume you are concerned about a steerable tail wheel unlocking at an inopportune moment. For an aircraft such as a Dr.1, I would think that the ability to control the aircraft directionally (ie. steerable tailwheel) with the tail down would be an important control asset.
Could you discuss the pros and cons of the lockable/steerable tailwheel systems? I'm interested in your thoughts.
Sid

[Joe Perkel]

Originally Posted by Flysafe

Make the tailwheel lockable. Any of the larger full-size replicas such as the DVII, SE5A, Strutter or N28 benefit from having the ability to lock the tailwheel for landing and takeoff. I have flown all those aircraft with both locking and non-locking tailwheels and can state that I would never build a WWI replica without a locking tailwheel. A much better directional control device than a steerable tailwheel.

More valuable than any other form of data. Thank you for this input, it will be committed to memory.

[Flysafe]

Sid, while a lockable tailwheel is "locked" it does not remove all directional control. What it does is provide a strong resistance to turning moments.

The problem with WWI replicas is in many cases we fly them on narrow pavement runways, not grass fields that they were designed for. The critical element then becomes remaining within the confines of the runway laterally. Many of the WWI aircraft have flat, slab-sided fuselages that act like a large wether vane, and, with any crosswind the aircraft will turn in to wind. While each WWI airccraft is different, they all share a common problem of not having much leeway before a slight directional control problem becomes a runway excursion and/or ground loop with damage and potentially injuries.The problem is compunded by less than ideal rudder effectiveness, particularly with the tail down. Add in narrow undercarriage width and the recipe for disaster is complete.

The locked tailwheel still allows good yaw control, but like a keel on a boat it provides directional control stability and resists forces that try and push you out of runway alignment.

The problem with steerable tailwheels on these aircraft is that the rudder/spring/tailwheel relationship can get complex with the spring action affecting the rudder input vs. tailwheel movement. Couple this with the changing rudder effectiveness and it is not uncommon to get into yaw oscillations due to pilot input being out of synch with aircraft movement and rudder inputs. I have personally witnessed very experienced taildragger pilots, and, had issues myself with yaw control on the runway with the steerable tailwheel types. The final element with the steerable tailwheel is the "break point" where it swivels completely. There is no ability for a pilot to precisely predict and control this point and when you get the beginnings of a runway excursion you can quickly reach the "break point" and the real ground loop starts.

Getting used to steering the aircraft while taxying with brakes only is easy. I am far more concerned about preventing a runway excursion and/or a ground loop than the ability to steer with the tailwheel.

None of the GWFM aircraft had lockable tailwheels years ago. We tested the DVII first and realized that it was a huge ssafety of flight improvement and have been building/modifying aircraft with them ever since.

The two triplanes and 85% SE5A do not have locking tailwheels due to their short fuselage lengths, low tail down speeds and powerful rudders. That being said, there would be a benefit to modifying these aircraft to have locking tailwheels, but there are some engineering issues to resolve firts.

I would personally build any WWI replica with a locking tailwheel.

[Jim Bruton]

Makes me feel better about using the tailskid...

[Flysafe]

Jim, tailskids are excellent for directional control augmentation - on grass. I have no personal experience with tailskids, but intuitively I have to think that the skid will not provide any resistance to sideways motion on pavement.

The skid will also wear rapidly on pavement.

If you are only going to operate off grass, I agree use a skid!

[Flysafe]

With respect to Triplanes and strong crosswinds; the big challenge I find is not the directional control during the initial part of the landing with the tail up. There is plenty of rudder and aileron authority. As you slow down I find the rudder authority is still excellent. The problem is aileron authority. Because the DRI has only a single set of ailerons and a very narrow wingspan the ability to stop the upwind wing from lifting is very limited.

The two GWFM triplanes have different aileron styles and the "blue/green" DRI has much better aileron authority.

In gusty winds the triplanes can get very sporting and I have regularly been close or have run out of aileron authority. One of the axe handles on the red GWFM triplane bears witness to a strong gust that exceeded aileron authority. The wing dragged on the axe handle and wore it down. And yes it was me, and with a lot of hard work and luck I did not ground loop or damage the aircraft other than the sanding job on the axe handle.

There are some ways to make this betteron the DRI; use the larger more effective ailerons and make sure that when you are sitting in the cockpit that full aileron movement is achived before the stick hits your inner thigh. It is common to see full stick movement be impeded by pilot appendages.

I have flown all kinds of taildraggers for over 30 years. everything from Cubs to DC-3's and WWI replicas are the most challenging aircraft I have flown in crosswinds. As I was told years ago, you don't stop flying them until they are tied down.

[Machinbird]

Jim,
Just from empirical evidence, I don't think a tail skid will give much sideways resistance to movement on grass/dirt either. I've seen a couple of videos of the Kingsbury Dr.1 ground looping on their dirt strip. I think all the skid really does for you on grass/dirt is act as a brake to help slow you through the twitchy speed range quickly. Yes, steerable tail skids seem to offer some degree of directional control, but probably not that much. There really isn't that much on a skid to resist sideways motion. Just like a car steering tire slipping on ice, doesn't matter what direction you point the wheel until you release the brake.
Do you have a big enough field to operate from so that you can always land into the wind?
Sid

[Maxim08]

Machinbird,
If you look at the later style D VII tail skid, you will note that the steel shoe on the bottom is designed to dig into the ground slightly with a pronounced 'keel'.
This would add reactive directional control and a litle drag (remember that the D VII skid has a central pivot that allows some rotation.) I have seen pictures of skids that look decidedly like anchor flukes that I would assume are for more drag and shorter roll outs.
Regards,
John

[Joe Perkel]

I will ask again.....


-What has been done regarding brakes on WWI replicas?

-To clarify what I'm thinking,... what can be done to hide the mechanism if using fabric covered spoked wheels?

-Any known examples of clever arrangements,..pics,...etc ?