Author Topic: Tail ski rigging  (Read 1585 times)

Paul Dale

Tail ski rigging
« on: February 15, 2018, 10:01:36 PM »
Just trying out fluidyne 3500 wheel skis on our 391B.  Lots of fun of course, we even accidentally landed with the skis up!  I have a question though, the tail ski (beaver model) is rigged with a forward mounted bungee to keep it more or less tracking forward. It really adds to ground turning radius on snow. It can be easily disconnected with the thoughtfully attached carabiner, but I really wonder if it is needed at all. It is on the Wipair install drawings though. Only on foot and a half deep snow so far, but think they are working well and they make me smile.   


Re: Tail ski rigging
« Reply #1 on: February 16, 2018, 05:57:52 AM »
You have the big tailski ?  Yes, you have to put the bungee.  It have a lot of aerodynamic drag in front of the pivot point.  Sometimes it can turn 90 degrees in flight.  Or hit a small bump on the snow or the runway and go 90 degrees.  The clutch can't cope at keeping it straight. 

However, you can put a second carabineer to give some slack.  Just one carabiner and you go from a 300 feet turning radius on the snow to 100 feet.

Remember to push all the way on the control to keep the tail as light as possible to help turning.  With a good push of the engine to make some wind on the stab.

With the 3500 you can make gear configuration mistake.  It won't brake anything.  But passing from wheels to ski on the ground put too much stress on the mechanic.  They are not designed to do that, if i remember well.  On hard surface, like hard snow, it is less stressful.  But on loose snow, passing from wheels to ski put a lot of stress.  This is why i like the AWB because you can go from a configuration to the other on the ground without stressing anything.

With the small tailwheel ski, adjusted with the nose quite up, you can fly it without a bungee.

What i did when i had the 800 was to put a second small wheel at the back of the big tailwheel ski.  A fixed ( not turning one ) so it prevented shimmy when landing on a runway.  Also it did help when landing on snow without the bungee to keep the ski aligned to the front.  The Pilatus ski have an aerodynamic fin to keep the big ski aligned to the direction of flight.  So i would not be the subject of some jokes like with the 295 with the tailskis almost always flying 90 degrees.  I think if you go without the bungee, it would be good to install a fin, and - or a back wheel to keep the big ski straight ahead.

Check list.  Never saw one with the proper first line for amphibious.  It should be :

- Check outside with your eyes for the kind of surface you are landing


- Check that the gear selection is matching this surface

Doesn't have to be written, put you do have to check first outside the windshield before checking the gear.

Because when you take a pilot with some retractable time in it's logbook, he always finish by interpreting "Check Gear" with some kind of this strange phrase:  " Gear down, ok to land" with some mixed result with an amphibious plane.


First photo.  The big ski have so much frontal area, that without a bungee it will turn.  Note the slack of the bungee to make turn easier  ( Landis tailwheel skis)

Second photo.  A second non-turning tailwheel to prevent shimmy, and to have the ski to automatically align itself when touching the snow  ( Aluminium beaver ski )

Third photo, the fin on the Pilatus to keep the ski in line in flight

Fourth photo.  My tailwheel ski would turn side ways when flying without a bungee.  Not really a problem in flight, but i would put the Pilatus fin if i had to fly it without the bungee.  Give some slack in your bungee ( with a second carabiner) and you will be able to leave it on
« Last Edit: February 16, 2018, 06:26:14 AM by Louis »


Re: Tail ski rigging
« Reply #2 on: February 16, 2018, 06:19:17 AM »
By the way, we had all king of problem with the breather tube freezing in winter on flights longer than 3 hours.  With the 391, 295, even the 250.  Does your breathing tube equipped with a hole at the top of it, inside the cowling ?  It can save a day or an engine


Paul Dale

Re: Tail ski rigging
« Reply #3 on: February 16, 2018, 11:15:25 AM »
Yes, it wouldn't pass from skis up to down in the deeper snow, I think the piston angularity is too unfavorable when the skis are pressed to the snow.  When on hard pack or ice it does pass through without complaint, because the first two or three inches of travel are free, and the piston angle gets more favorable.  The drawings indicate not to transfer while moving.  It certainly is handy to leave it on wheels, and then drop the skis for takeoff. My beaver tailski does have the fixed trailing small wheel, i will give it some slack and see how it does.  Thank you Louis for the commentary and advice, it is much appreciated.


Re: Tail ski rigging
« Reply #4 on: February 16, 2018, 12:15:47 PM »
My beaver tailski does have the fixed trailing small wheel

I did not know they were coming with the extra small wheel.  We had to instal it ourselves.  We did not know they were available like that.  On the ground, or on snow, this extra wheel does a marvel to keep the ski straight when you hit some bumps or skidoo track.

The drawings indicate

You have a drawing for the fluidyne 3500?  I am surprised.  I was thinking they were drawing for the AWB by type certificate, and by STC for the penetration fibreglass ones. 

Neil was telling me this morning about the big difference between a 185 installation and a Helio one.  On the 185, the shaft that hold the ski is bolted.  You can shim it so the ski will be flat on the ground.  Most people with  185 don't go all the way to install it properly, and it does work very badly.  When you hit deep snow, or slush, if the skis are not installed flat on the ground, one of the ski will cut his way deeply in the snow.

On the Helio, with the AWB, the cam is very angular.  So it does keep the ski flat.  When you need to adjust it, you remove some pressure on the shock absorber, so the legs widens on the ground, and the skis become more flat to the snow.

We had a 800 on skis, have a 250 , a 391, a 295.  It is incredible how well this plane behave on skis.  We never shushed one up to date.  A lot better than a Beaver with it's hard landing legs.


Paul Dale

Re: Tail ski rigging
« Reply #5 on: February 16, 2018, 09:05:28 PM »
my skis are Federal AWB 3500's,  the Drawings are by the fluidyne corporation, and they are for the AWB installation on Helio. Sorry for the confusion. Just back from a mountain lake, maybe two feet of snow, they float just fine. 

Paul Dale

Re: Tail ski rigging
« Reply #6 on: February 21, 2018, 11:25:36 PM »
Louis, I tried flying without the tail ski bungee attached, much better ground handling, but, sometimes in the air, the rudder felt kind of constrained, or not wanting to return to center easily.  Do you recall anything like that when your tailski was flying sideways?  Now, if  ours was sideways, it must have centered easily on landing, no big scuff marks or grabbing feeling on touchdown, although we were on thin snow cover. We did try an extra carabiner, it helped, but not like unrestrained.   


Re: Tail ski rigging
« Reply #7 on: February 22, 2018, 05:01:14 AM »
but, sometimes in the air, the rudder felt kind of constrained, or not wanting to return to center easily.  Do you recall anything like that when your tailski was flying sideways? 


Which tailski?  You mentioned you have the Beaver one.  Do you really have the big one like on my photo of the 800 ?  We don't fly these one, now.  We all have the Landis fibreglass ones.  Smaller.  Less prone to all kinds of problems.  

But if you have the big one, like you, it was never a problem landing.  The ski with the second tail wheel would realign itself right away.  But i don't think we can fly like that for one hundred landings.  At one point, it will hit a skidoo track sideways and will tear apart the tail wheel assembly.  On a runway, i was able to land two points , put some power, and let the tail wheel touch the ground when almost immobilized.  Never been able to do it on snow, because lack of brakes to help keep the tail up.  So i think that flying the big Beaver tails without the bungee is asking for trouble.  Even if i did it at least twenty times.  I think i was lucky.  If one extra carabiner is not enough, try a second (third) one.  I am sure there was no specific tension specified.  In fact, i am not sure the installation data by type certificate was with the long Beaver ski.  If it was with a shorter ski, the same tension would allow a lot more turning with a small ski than with a long one.  If the ski is long, it is more prone to turn sideways if you hit something hard on the snow.  But it requires a lot less tension on the bungee to keep it straight.  You can have a lot of slack on the bungee and it will work OK to keep the ski from going sideways in flight, or on the ground.  You can even have it ( now i am searching for the right word) you can even have it "lag" ( ? ) Well, i mean having the bungee go down in the middle by one or two inches.  It does not have to be straight and tensioned.  

Then there is the story about what kind of bungee you have.  Too strong or not enough.  Summer or the 100% natural rubber for winter kind. On the suspension of a Supercub, in winter, if you don't have the cold compatible bungee, the suspension becomes very hard.  

My advice is to try with another extra carabiner or more.  Until you can turn the 180 degree on a 75-foot-wide runway.  With full brake on one side, always turning left to have help from the prop wash, and a lot of grimaces with your mouth.  The grimace helps a lot.   

On the snow, if you ever need to turn around in a tight spot, you can lower down one of the wheels.  And keep the right gear on skis.  It will turn  around the left wheel in a very tight radius.  Almost around it.  How do you do that ?  The easy way is to but a manual valve on the hydraulic line of the right ski.  Inside the cockpit.  You can then lower the left wheel.  We equipped one of our Helio like that.  But it can always be done without it.  For some reason, you will see that it takes very little difference of weight inside the plane to have the wheel of one side go down before the other.  Or to go up.  So you pump until you have the left wheel down.  On a going down cycle, or on a going up cycle.  If you want to do it with th electric pump, you just pull the breaker when you have it.

It does help a lot to have the somehow a little bigger cylinders.  The AWB were coming with two sizes of hydraulic cylinder.  The small one takes a lot of force to pump the gear on the ground.  The somehow a little bigger ones ( Maybe just a half inch more diameter ) helps a lot.  

Where do you find to lack some turning radius ?  On ski or on wheels ? ( Snow or runway ? )

I endured for twenty years to have problems turning tight enough.  Until i did just slack the bungee with carabiners.

On snow, never forget to push hard on the control.  So the tailski will jump over the track made by the front ski.  It takes pushing, and power to help the ski go over the front ski track.  

Always planified to turn left when you approach your parking place.

Before stopping for the night, stop five feet before the place you want to park.  Then let the ski cool down.  And then go forward for the last five feet.  It will help prevent the ski from gluing on the snow.

In the morning, have strong boots to be able to kick the ski sideways to destick them from the snow.  Kicking them from left to right, and from right to left, until they feel free.

Never park for the night without a trace in front of you.  Making a large 360 track to come back to park on your trail.  Always park in a direction you are ready to take off.  Never try to go very close to the camp.  If you have a good parking spot at 5 minutes more walking, park there.  5 minutes is very cheap time compared to deslush a plane.  Always have snowshoes for everybody.  Always carry a sleeping bag that you are confident to be able to spend the night with.  For everybody.  With sleeping pads.

If you took some slush on the tailski, and you are going back to a runway, free the tire.  If it is iced up in the ice, it won't turn on the runway and you will destroy it.  In doubt, stop on the runway and go check it.  They can even ignite with taxiing when they don't turn.  ( Been there with a 185 )

Trust nobody about the thickness of the ice on a lake.  Check it yourself.  Charts of minimum thickness can be found.  There is minimum for landing, and minimum for night parking.  And they vary depending on the temperature.

Most of these recommendations come from various experiences/stories and from a book we have in french written by one of our bushpilot.  You can surely find the equivalent in english.


« Last Edit: February 22, 2018, 05:07:45 AM by Louis »

Paul Dale

Re: Tail ski rigging
« Reply #8 on: February 22, 2018, 01:00:13 PM »
Yes Louis, the beaver tail ski.  Our electric pump stops at 2800 psi, and it is is not easy for it to transfer the weight from ski up to ski down on the hardpack snow, and impossible on deeper snow.  The hand pump same thing, I am afraid I would break part of it if I pulled any harder.  So, larger pistons or more pressure seem to be a solution for that. Can you fly the Landis tail ski without a bungee of any kind?   on the Beaver tail ski, I think a solution might be something like the water rudder pull up cable, it would tension up the bungee for landing or takeoff, but free it up on roll out and taxi. My concern on turning radius is just to avoid missing opportunities to stay out of trouble in deep snow. snow that is sloped, and on short runways where turning around might be required. Stopping and disconnecting the linkage solves some of the problems, but not all of them. I really appreciate your knowledge on this, thanks, Paul