WWI Replica Safety

Mad Mac · 19 March 2009, 10:45 PM

Quote:

Originally Posted by Flysafe

make sure 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.

drrivah · 20 March 2009, 02:43 AM

Flysafe-
Could you say a few words about the mechanism of the tailwheel lock, and if locks are inherent in tailweel design. Can a lock be retrofitted to, for example,
the steerable Scott tailwheel commonly used on homebuilts?

A diagram or photo would be welcome.

Great topic, BTW.

-pete

Flysafe · 20 March 2009, 04:36 AM

Pete, sorry I don't have any pictures/diagrams and will not be back out to the museum for a few days due to that nasty impediment - a day job!

There are a limited number of lockable tailwheels that are available to purchase. Ours were retrofitted on both Scott and Maule tailwheels.

The mechanism is a lever in the cockpit, on the left side, behind the throttle quadrant, that connects a cable to the locking mechanism on the tailwheel. The forward lever position is locked. Pull the lever back and to the right into a detent and the tailwheel is unlocked.

The cable pulls a lever/spring mechanism on the tailwheel that locks/unlocks the swivel mechanism. When the tailwheel is unlocked the pulling action lifts the lever and works against the spring to unlock the tailwheel.

The first "mod" on the DVII was done was taken from concept, through design, build and test in about two days by one of the very gifted mechanical types at the GWFM.

The last item in the before takeoff check as you position on the runway is "Tailwheel Locked". Last item before landing - "Tailwheel Locked". Neither is a critical flight safety item - you can land/takeoff without the tailwheel locked.

Machinbird · 20 March 2009, 06:02 AM

Quote:

Originally Posted by 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 ?

Joe, If I recall, UDO posted pictures of a small drum brake with spoke attachments along the rim and an extension to form the opposite side spoke attachment. The majority of the mechanism was inside the drum, and the mechanism was anchored to the axle. I'll look around and see if I can find a picture tomorrow when I'm not at work. The profile of the wheel brake assembly was pretty much the same as the original, and the non-rotating part of the brake was not obtrusive.
Sid

Machinbird · 20 March 2009, 06:34 AM

Quote:

Originally Posted by 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.

Flysafe.
First, Thank you for your thorough description of the Lockable Tailwheel and its operation.

That was an area I have had no experience in.
It seems we have two directional control problems we are trying to address. Oscillatory problems caused by late pilot control inputs actually driving the directional oscillation and maximum cross wind control limits.
If I understand the gist of your explanation, the lockable tailwheel is extremely effective in damping down oscillatory directional control problems.
By the same logic, wouldn't a locked tailwheel slightly decrease rudder effectiveness in the case of cross wind induced directional control problems such as we saw in the Dr.1 video?
Related to the subject of directional control:
I have always used a two step process in directional control.
1 Actively zero the yaw rate continuously.
2 Make a second small yaw correction in the direction I desire to correct to and then, zero that yaw rate.
I haven't had problems with oscillatory directional control since I was a student.

I've enjoyed the diversity of viewpoints on the subject of directional control. It has been very beneficial to me.
Sid

Flysafe · 20 March 2009, 08:25 AM

Sid, while technically there is a point to a discussion of addressing two issues, they cannot be descirbed or dealt with in isolation. In some ways which came first the chicken or the egg.

The lockable tailwheel is a directional control stabilization device. However, it cannot correct a bad landing event, it will only assist in maintaining the direction you are travelling.

I personally have not noticed any problem with diminished rudder effectiveness with a locking tailwheel. The rudder still imparts the same amount of force, but the locking tailwheel is acting like a keel.

As far as the DRI video on this thread, I believe that a tailwheel lock would have been beneficial in keeping the aircraft straight. I also believe that lack of aileron effectiveness was a major contributor to the event. As discussed earlier this is a significant problem with the triplane.

I am a firm believer in using the wheel landing technique with WWI replicas, especially in strong crosswinds and/or on narrow paved runways. On grass with light crosswinds a three point landing works very well. The problem is that while directional control is enhanced by the wheel landing it will become problematic in a strong crosswind when transitioning from tail up to tail down. This is not unique to WWI replicas, I used to see it when flying Beech 18's. I find the it becomes critical with the DRI to keep the tail up as long as possible, use ailerons effectively to keep the wing down and when you feel the tail get heavy make a conscious, positive movement to tail down, while maximizing into wind aileron and keeping the aircraft straight with rudder.

The DRI can be a handful at this point - lack of aileron effectiveness, the need to maintain full aileron into wind, stick back to keep the tail firmly down and the critical problem; no forward visibility to monitor yaw. To quote a former Chief Pilot, who was flying commercially the year the Hindenburg crashed, "You are busier than a one-legged ass kicker".

Having flown seven different WWI replicas as well as the same replicas with varying mods to them I can truthfully say that each is different and each has their bad habits. All of them share one common theme - they are challenging to land especially in crosswinds and a healthy respect for your limits and their limits is required.

j ferguson · 20 March 2009, 09:10 AM

During the period when I was transitioning from being certain I didn't know what I was doing to supposing I did, I made 3 attempts to get the 120 on the ground in a crosswind that was beyond my skill-level. I ultimately conceded defeat and flew to a nearby field whose runway was into the wind, landed there, tied it down, and cadged a ride back to where the car was.

But would this work with a replica? Sure, physically, but there is a big difference between a C-120 and what you guys are building and flying, and that's the "attractive nuisance" effect. I suspect the need to get it home is more driven by necessity than it is for the rest of us. You can tie a 120 down and return a few days later and expect to find it as you left it. But a Dr-I?

Here is where one of you should tell me I'm being unrealistic.

If you base your replica at a field with one runway, wouldn't it be a good idea to visit a nearby field with a runway at 90 degrees from yours or even better with 2 runways and cut a deal with someone who has a hangar there to borrow the space if you get stuck there? I can't imagine that it would be that hard to find someone who would welcome a call to come and let you put your DR-1 in his hangar while he ties his 172 outside. But clearly you would need to try this idea on for size before needing it.

Is this impractical?

John

Flysafe · 20 March 2009, 11:17 AM

John, great discusssion. Knowing when to say no and divert is important. Knowing where possible diversion fields are and the runway orientation is more critical. The key is having a plan. When you set off somewhere know the diversion options enroute and at destination before you get airborne.

On the surface parking a WWI replica seems problematic, but usually is not. After 20 years I have found that because the aircraft are so unusual that when you divert people are always willing to help. Worst case scenario is a cockpit cover and tie it down outside overnight and solve the problem the next day.

Over the years I have a number of diversion experiences for weather and mechanical faults. The most recent being last summer. The biggest challenge is not diverting and parking the aircraft, it is getting back home or to your car. Over the years my experiences has left me with stories that would make a great comedy routine, including a car, train, subway adventure that ahd people wodering who are these whackos in flying suits on the subway.

One key point, never let your concern about parking an aircraft or gettting home cloud your thought processes on diverting. Set weather limits and stick to them. Far better to land safely somewhere else and find/pay for hangar space and be late getting home, than bending an airplane and or yourself trying to avoid the cost/embarassment of a diversion.

Machinbird · 20 March 2009, 12:25 PM

Quote:

Originally Posted by Flysafe

John, great discusssion. Knowing when to say no and divert is important. Knowing where possible diversion fields are and the runway orientation is more critical. The key is having a plan. When you set off somewhere know the diversion options enroute and at destination before you get airborne.

On the surface parking a WWI replica seems problematic, but usually is not. After 20 years I have found that because the aircraft are so unusual that when you divert people are always willing to help. Worst case scenario is a cockpit cover and tie it down outside overnight and solve the problem the next day.

Over the years I have a number of diversion experiences for weather and mechanical faults. The most recent being last summer. The biggest challenge is not diverting and parking the aircraft, it is getting back home or to your car. Over the years my experiences has left me with stories that would make a great comedy routine, including a car, train, subway adventure that ahd people wodering who are these whackos in flying suits on the subway.

One key point, never let your concern about parking an aircraft or gettting home cloud your thought processes on diverting. Set weather limits and stick to them. Far better to land safely somewhere else and find/pay for hangar space and be late getting home, than bending an airplane and or yourself trying to avoid the cost/embarassment of a diversion.

Amen Brother.
Its even more amusing when you divert somewhere wearing nothing but an orange rubber survival suit, you left your wallet behind, and the people don't even speak the same language.

Sid

Joe Perkel · 20 March 2009, 08:25 PM

Quote:

Originally Posted by Machinbird

Joe, If I recall, UDO posted pictures of a small drum brake with spoke attachments along the rim and an extension to form the opposite side spoke attachment. The majority of the mechanism was inside the drum, and the mechanism was anchored to the axle. I'll look around and see if I can find a picture tomorrow when I'm not at work. The profile of the wheel brake assembly was pretty much the same as the original, and the non-rotating part of the brake was not obtrusive.
Sid

Thanks Sid, that would be interesting and very worthwhile to see.

Equally interesting if you think about it for a moment,... is the varying degrees of authenticity mixed in with modernization, that is possible with WWI replicas, while still maintaining that overall historical panache.

For my part, differential braking and a lockable free tail wheel for the land version of my craft seems mandatory in view of the operational limitations of a small paved field. The floats are of course a different animal, and allow for systems and operational simplification in exchange for logistical difficulties.

A very productive discussion!