Author Topic: Tail ski rigging  (Read 120 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.   

Louis

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

Then,

- 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.

Louis

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 »

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

Louis

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.

Louis

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.

Louis

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.