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Old 12-18-2013, 01:22 AM   #1
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Default Some unusual skis

I recently put some floats on one of my foamies, and then tried them out on snow as well. I'm so impressed with how well those floats works as skis that I'm now making a new set that will look pretty much like floats, but will only be for snow . Here are the foam cores with wood longerons glued in place:



Based on my experience with more conventional skis last winter, one of the biggest issues is sinking in too deep if the snow is fluffy, or kinda wet. These ought to be immune to that as they are much wider and much longer. More like a couple of toboggans. Should glide right over foot prints too.

Another issue I noticed last winter was that the sides of flat, thin skis could dig into the snow upon landing if you come in with any significant yaw. These new ones will have nice tall sides which should just slide along instead of digging in.

Finally, these aren't going to pivot at the wheel axle point - they will be fixed front and back. Seems to work just fine with the re-purposed float plane.

More as things progress

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Old 12-18-2013, 03:17 AM   #2
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Some things scale strangely and skis are one of those things. You need increasing area per oz loading as the skis get smaller.

Amphib and floatplane models have always done well on snow.

Sizing skis to "look right" compared to full scale generally leaves you with skis that are too small.
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Old 12-18-2013, 07:38 AM   #3
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Hi DGJ .... just wondering are you going to angle up front ? I'm a little confused as they appear to be tapered sections ?

Nigel

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Old 12-18-2013, 07:53 PM   #4
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Like this:



I'm going to glass the bottom surfaces for durability, then paint.

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Old 12-18-2013, 08:00 PM   #5
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Magic !

Cheers
Nigel

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Old 12-20-2013, 01:10 AM   #6
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Well. I could have them ready to go tomorrow but the weather is not cooperating. Next few day's forecast calls for 50-60 f temps, lots of rain, lots of wind . All the snow is going to disappear...

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Old 12-22-2013, 03:43 AM   #7
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Originally Posted by fhhuber View Post
Some things scale strangely and skis are one of those things. You need increasing area per oz loading as the skis get smaller.

Amphib and floatplane models have always done well on snow.

Sizing skis to "look right" compared to full scale generally leaves you with skis that are too small.
That's because you're not scaling down the snow to match the plane. The same applies to the air density, which is why a lot of 'scale' modelers have to cheat a little.

"Give a man a plane and he'll fly for a day.
Teach a man to build a plane and he'll fly for a lifetime"
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Old 12-23-2013, 11:48 PM   #8
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OK, bring on the snow!



The rear attachment is a wooden plate with velcro on it. I can switch from wheels to skis in a minute or so .

Doesn't look like the weather is going to cooperate till next year though...

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Old 12-24-2013, 01:50 AM   #9
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Looks good!

I think I need a signature.
Larry
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Old 12-31-2013, 12:24 AM   #10
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And a more conventional set of skis (appearance-wise), still more like toboggans:



Snow later this week; can't wait

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Old 12-31-2013, 01:24 AM   #11
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Cool! Hopefully it'll rotate for takeoff. Does the cat approve?
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Old 12-31-2013, 01:51 AM   #12
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Originally Posted by dgjessing View Post
OK, bring on the snow!



The rear attachment is a wooden plate with velcro on it. I can switch from wheels to skis in a minute or so .

Doesn't look like the weather is going to cooperate till next year though...
That does look interesting!

Right now, we've got a half foot plus of snow on the ground around here. Methinks my old 150% scratch built Electrostreak would work well on skis. Personally I'd just buy a set of ski's but have not found any place that makes them.

What is the wingspan, area, and weight of the model?

Let us know how it works on the snow!

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Old 12-31-2013, 12:10 PM   #13
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Just wondering about the cross braces between the 'skis' .. will they snag in snow ?

I have a bunch of alloy V main u/c similar to the float frames here :>



The floats I bought for my Skyartec Cessna but never fitted. I ought to scratch up a model for them.

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Old 12-31-2013, 06:59 PM   #14
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If the cross braces at the top of typical floats were low enough to be snagging, then the nose of the floats would be digging in.
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Old 12-31-2013, 07:04 PM   #15
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Originally Posted by fhhuber View Post
If the cross braces at the top of typical floats were low enough to be snagging, then the nose of the floats would be digging in.
It was just crossing my mind that when I bought my floats and then looked at them rigged ... the cross brace seems low. On water I would expect it to be OK, but on snow - it crossed my mind that snow / ice could build up on them ...

It all depends of course how far the model sinks into the snow ...

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Old 12-31-2013, 07:56 PM   #16
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Just have the cross-braces above the tips of the skis and they won't dig in before the tips.

Generally if the tips can lift above the bumps in the snow you could have the cross-braces almost on the snow.

This is why skis don't scale well... if the tips dig in you're done and as the skis get smaller they tend to dig in more easily.
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Old 01-03-2014, 10:52 PM   #17
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Originally Posted by xmech2k View Post
Cool! Hopefully it'll rotate for takeoff. Does the cat approve?
Rotating for takeoff turns out to be an issue. The cat didn't catch this...

I took both planes out for a quick test today in the 15 degree weather . They both work, but the takeoff run is long, then quickly straight up 'cause you've pulled way back on the stick to make something happen.

I'm going to experiment with tilting the nose(s) up a bit more.

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Old 01-03-2014, 11:35 PM   #18
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Make the rear of the skis able to rise and allow the nose to go up.

On snow you do not need the ski to keep the tail up like you need with floats on water.
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Old 01-04-2014, 01:34 AM   #19
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Originally Posted by fhhuber View Post
Make the rear of the skis able to rise and allow the nose to go up.

On snow you do not need the ski to keep the tail up like you need with floats on water.
+1

I think I need a signature.
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Old 01-06-2014, 01:37 AM   #20
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Default cool skis

I am wanting to set up a pair of unused foam pontoons on a j 3 arf i just finished. Does anyone know how I determine a c.g.? I am cautioned by experienced flyers this will be critical to handling the rig, but they dont know how to determine a new balance point.
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Old 01-06-2014, 02:02 AM   #21
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Here is a great place of info on setting up floats, and to buy floats if you need them.
http://www.wattflyer.com/forums/showthread.php?t=72821
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Old 01-06-2014, 05:24 AM   #22
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RE setting up floats. Keep the SAME CG for the aircraft.

Then the floats should be placed so the model floats with the pontoons level or SLIGHTLY nose-up.
The nose of the floats should extend well forward from the prop on a typical plane such as a Piper Cub or Cessna 152/172 style

The mounting angle of the pontoons should hold the nose of the plane up 2 to 5 deg vs normal level flight cruise attitude (without floats) The goal here is to have the floats very close to level in normal cruise at the higher weight, so the floats will give minimum drag in flight.

Paint/cover the bottom of the floats in WHITE. This will give best reflection from the water so you can judge height from the water better when landing. Misjudging height and resulting late "flair" will flip the airplane as the nose of the floats dig into the water surface.
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Old 01-06-2014, 05:34 AM   #23
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Short sweet and helpful. lovin this hobby. Thanks
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Old 01-06-2014, 04:57 PM   #24
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I have a building jig for skis but they were for bigger nitro planes and the skies are to heavy for electrict . I could build a smallers jig and laminate some very thin veneere and they would be light but strong. I used rubber bands to hold up the nose on each ski and it worked out fine but i dont fly that much in the winter anymore . joe
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Old 03-03-2014, 01:32 AM   #25
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Update Re: the skis shown in post #8, back a way, and the issue with "rotating" for takeoff.

I did indeed modify the mounting angle so the plane was sitting back a bit more (nose higher at rest). This worked, more or less, but the angle of the skies had a pronounced effect on the plane's flight characteristics, and without a significant flare upon landing, landings were dicey because the points of the skis touched down first, which often resulted in an inelegant, violent nose-over.

So this evening I've made a change:



The rear support is .019" (thin) music wire which distorts as shown and allows the tail to settle down. Once the pressure isn't on the skis they fall down and stop level with the fuselage center line. Hopefully this will fix both of the above problems

I think I'll get my last chance of the season to try them out tomorrow or Tuesday.

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