Skis for Dummies or Confessions of a Slow Learner

                                                               Skis for Dummies 

                                                                           Or

                                                     Confessions of a Slow Learner

 

Having completed the CH750, flown 130 hours in 6 months, and having builder’s withdrawal, I was getting the itch to build something. Wanting to expand my horizons, I thought it would be great to design and build a set of snow skis and learn how fly skis. I scoured the forums, Bob McDonald was kind enough to send me a copy of his plans. I googled every noun and verb associated with aircraft snow skis I could think of to educate myself on ski design and flying with snow skis. I did find a chapter in the AC 43.13-2b on snow skis as well as a 1947 report by the Canadian government about ski design and setup. I read all of these articles a few times – (slow learner) and applied what I learned to the design of the skis for Sharky. Since I live on an airport that has an asphalt runway, I needed to have wheel penetration skis. And to keep it simple and light, I did not incorporate any type of retraction system.  I thought with high floatation tires and skis, I didn’t need to have a wheel retract system (bad assumption). The area of the skis were designed for “wind blown snow” typical of what would be found on a lake – per the 1947 design study.  I built the skis and was pleased that they weighed only 20 pounds each, refigured the weight and balance, called the FAA to see if I needed to go through a test period, “nope” was the reply – I’m good to go! Great, now what do I do??? I did some touch and go’s, flew around the pattern, did some stalls, steep turns, slow flight; the plane flew same as without skis – what a great airplane! Having never flown with skis, I wanted to start out with a 2-3 inches of snow and work my way up.

I watched the weather and was able to fly with about 4 inches of snow on the local lake. I did call the local law enforcement to make sure there was no ordnances preventing me from landing on the lake – the reply was “in 25 years I’ve never been asked that question!!” So, I figured it was probably ok.  As I came over the trees to experience my first ski landing, it was very difficult to see the snow on a grey cloudy day. I just guessed and managed to flair about 2 feet above the surface, with a kerplop! Into the snow and the resulting tremendous drag, I thought, while I’m still moving I better add power and see if I can get back off the lake. It took some distance, but the nose ski broke free and off we went. I flew around for a few minutes thinking about the first landing and if I should try it again. I came around and did a second and third landing, slowing down to a slow walk on the last landing – trying to get use to the greatly increased drag of the skis and wheels (slow learner, so it takes a few times). After the ice fishermen came out of there shanties and the snowmobilers all stopped to watch, I thought I’d better move on. So that was my first experience on skis; not truly knowing if it was a good or bad experience!!

On my way back to the airport, it was a little turbulent over the bluffs, I heard a CLUNK, then another CLUNK!  OMG – what was that?? Looking down at the skis - Both main skis had dropped down till the front safety cable stopped it – wow!! – the plane is still flying, it did not rip off the gear, in fact, the plane did not change pitch or anything – Awesome airplane! I slowed down and increased angle of attack and CLUNK, CLUNK – up they came. “Need more bungee force and possibly longer aft safety cable” I said to myself – after thanking Mr. Heintz for a Herky airplane.  Over the next week I messed with different lengths of safety cables and more bungee force. Ended up with the original cable lengths and doubled the bungee force.

I thought; now I need more snow. Old man winter was obliging and more snow came, and more snow came. I was hoping for 5 or 6 inches total – instead it was 13 – 14 inches. Way more that I wanted for my “incremental testing”.  A nice day dawned and off I went to gain more experience. This time I picked a different lake with more room (smart move) and it was close to my brothers home in case I balled the up the plane and had to walk (or crawl).  The approach was good, sunshine makes a huge difference in seeing the shadows and snow conditions.  As I touched down the skis went below the snow and there was a huge amount of drag – way more than I experienced on the previous test.  I immediately added full power and after some distance was able to take off. I circled the lake thinking - what just happened ??  I decided I needed to try it again (slow learner).  After three additional landings (really slow learner) I slowed down to a taxi speed, and then tried to accelerate – not reaching flying speed for a longgggggg time. Thank God the lake was more than a mile long. Finally ran over some snowmobile tracks, which was enough to break the nose gear free and I finally got off the snow. Decided that was enough learning for one day.

Flew home thinking about what am I doing???? This is not fun – it is scaring the crap out of me. This is not for me.  I got home, put the plane in the hanger, checked the nose gear and all the skis for damage (all ok) and was thinking about taking them off and hanging them on the shop wall for decoration.  Then I found out about a ski fly-in at a local grass strip scheduled for the next weekend. It would sure be great if I could talk to others to see if what they have experienced is anything like what I’m experiencing.  So I called ahead to see what the runway conditions are like. Well, I was told; after an additional 6 inches of new snow, they were running a snowmobile up and down the runway so it will be “packed snow”.  I thought – well this will work, so I flew over and landed – again a ton of drag, needed almost full power to taxi in the snow to get to a parking spot.  About 30 people looking at me in disbelief – tricycle plane with wheel skis – over a foot of snow - not a great combination…… The snow conditions were 6 – 8 inches of base with an additional 2-3 inches of crust, with another 3-4 inches of loose snow on top.  After I parked – I’m thinking I will never get back out of here. So I went and ate chili and goodies to calm (drown) my fears.

After much discussion with other ski fliers, I learned that wheel penetration skis are nowhere near as good (excess drag) as skis that retract the wheels, and they are nowhere close to straight skis. After watching a number of planes land and take off, I had to agree. I watched one Cub with straight skis take off from his parking spot – across the runway (perpendicular to the runway) and was off the snow just passed the edge of the runway!!  I decided I have some redesigning to do…..  As the afternoon went on – the wind decided to change direction and come out of the north, which did not help my cause – there are trees at the north end of the runway and it is slightly up hill – I’m not going to risk trying to make it over the trees.  So I fired up and managed to break loose and taxi to the other (north) end of the runway. I was breaking through the snow crust, needing almost full power to turn around, and accelerate down the runway, after about 500 feet, I’m thinking maybe eating all that chili was not a good thing. The runway was rough; I was breaking through the crust and not gaining speed. After about 1000 feet, I was really sweating bullets – finally I hit a bump big enough to launch the nose gear and shortly after - lifted off.  Whew!!!! Another learning experience!!!  So I flew home thinking this is not what I call fun. Everyone else was having fun – what do I need to do???? 

 

After additional forum searching and more discussions with successful ski fliers – I have a plan for next year (really slow learner). I will add more area to the ski bottoms – I can add 80% more area to the nose ski and 45% more area to the main skis. I also found out that the successful CH750 ski guys are adding a 2 inch spacer to the nose gear, to increase the angle of attack of the airplane and keep the prop out of the snow.  So my summer project will be changes to the skis and making a spacer. Next winter will be interesting……

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Comment by Rick George on March 29, 2014 at 7:52pm

Thomas,

Conrad Watters also has DATUM skis. I think he is very happy with them. I have the summer to decide if I chuck the skis and buy or build new ones. It will be great to hear about your experiences next winter!

Comment by Thomas Jackson on March 26, 2014 at 4:53pm

Hey Rick great story telling. Your tale really hit home. Last fall I decided to put skis on my 701. After lots of reading and night ski plane dreams I decided on DATUM skis (check out their site). I placed an order with Jean-Marc Auge owner of Datum skis. We communicated back and forth for some time as to the problem of the front ski and me not wanting to go with a smaller tire to fit a ski that would work. The reason for me wanting/needing  the larger diameter tire is prop clearance, even through I had already put in a 2 inch aluminum block spacer. Jean-Marc finally said he would design a ski for the 701 and 750 that would except an larger tire and the work was started. Because of this custom project in the middle of his most busy time of the year I did not receive the skis til February. We here in northern Ilinois were having the worst winter in years so getting to the unheated hanger and doing any meaningful work was slow. I will be testing the skis but with out snow just to get the feel. The skis look great, are retractable with a very simple electrical system. I was able to keep my tundra mains but did change the nose wheel and rim to a 480/400 (16.3 inch diameter) and an aluminum spoke rim both from Leading Edge Airfoils. I had to fabricate a new axle because of the length between the ski supports. Since the snow in this part of the world is pretty much gone, except for the lakes which I don't trust at this time of the year, tests will take place shortly. I watched this winter about a dozen guys/gals in this area having too much fun so next year I will be prepared.

Good luck with your modifications, fly safe.

Comment by Conrad Watters on March 24, 2014 at 4:28pm

I think that there was a typo     i.e.  " snow learner "

Comment by Tim Smart on March 23, 2014 at 11:48pm

GREAT POST and thanks for sharing.  Good luck with your skis, enjoy!

Comment by Rick George on March 21, 2014 at 9:41pm

Hi Conrad,

When you mentioned the 2 inch spacer in a previous conversation, It dawned on me that that is probably a key ingredient to improving my takeoff. I do plan on making one this summer. I tried no flap, full flap and 1/2 flap. 1/2 flap seems to be the best. I did not notice and issues with the cht's, but I was too busy saying my prayers, trying to coax the plane off the snow to pay much attention! I would appreciate knowing the dimensions of the front ski and the total bottom area if it is possible.

Thanks!

Rick

Comment by Conrad Watters on March 21, 2014 at 6:30pm
Rick, epic,
I changed my main tires to 600-6. And front to 500-5. This reduces the width by a couple of inches. With that I have a 2 " spacer to compensate for the reduced diameter of the front tire. It does increase angle of incidence and also prop clearance.
Did you use any flap?
With all that take off effort/work how were your cht readings?
If you are interested, I can measure my front penetration front ski dimensions.
I was surprised as well that the controllability of the ch750 was not noticeably affected by a high angle ski. ( prior to my getting the cables and bungees tuned )
Comment by Bob McDonald on March 21, 2014 at 6:48am

Great read...your a born story teller :>) 

Google "Datum skis" (on Conrad Waters CH750) or "Pierre Girard skis" (on Richard Lauzon's CH801) to see examples of retractable tri gear skis. One is electric actuator the other heavier hydraulic.

Comment by Rick George on March 19, 2014 at 8:53pm

Thanks for the thoughts and positive feedback. It has really been fun - most of the time!! I will continue to experiment and try to learn from others. That is what makes this forum so great. Positive people willing to share! 

Comment by Chris Craver on March 19, 2014 at 2:44pm

Interesting story. I'm glad you are safe and didn't " ball up the plane"! I saw it a the open house last fall ( I missed meeting you somehow ) It's one of my favorite 750's. In fact, a pic of it is my desktop! So many clever little touches.

Thanks for sharing!

Comment by Don Morrisey on March 19, 2014 at 2:01pm

Rick...great story and perseverance.  Having an audience at those moments is tough so my hat is off to you!!

I enjoy your forum posts, always very informative.  Love your paint job and was thinking something along that line myself, so I may shamefully steal it!!

Pretty sure I'm going to go the 912uls route as well...although on a slightly modified CruZer (STOL landing gear).

I have several friends in Quebec who put skis on their planes...one has homemade Federals (so no wheels) and the other has the DatumAir skis with wheels, they both enjoy it a lot.

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