Frostypaw's Snow Tractor "Sitka"

I am presently working on a budget build with on hand components I have and decided to enter this tractor in the build-off.  The main challenge is making it resemble a tractor, but I am thinking of using a tractor hood for the front as both decorum and as a superstructure where the drivers legs will go (Think old iron Bolens/Wheelhorse hoods).  
For those not aware the basic principle of this machine is based off of old Soviet and Scandinavian snowmobiles called aerosleds or in native tongue aerosani.   It will be a quad ski platform with movement provided by the airscrew.  I was going to finish the skis this weekend but my plasma cutter went kaput.  I will use this machine still in a tractor format towing light ice sledges for ice fishing since I do not own a snowmobile.  Design and construction of the propeller coming soooooon...... hint its just a 2x4  .





Honda Powered!

HolyMoly! That's one interesting build! I love that prop, maybe double up on it and really get some pulling power!

I dunno T-Dub, the engine is already strained a bit with the current prop.  If only I had a 20 HP Briggs oppy, that'd make a nice aircra... err...propeller engine!

Here is how I designed and built the propeller.  The one constraint I had was horsepower.  Too big a prop and you severely load the engine down (moving massive quantities of air takes HP!) and decreases the RPM which decreases thrust.  I used several online calculators to arrive with a 38" diameter prop with a 10" pitch (like a bolt thread pitch except our "thread" is length through air per revolution of propeller) for my 5hp Honda.  I won't go into specifics unless asked so hopefully these pictures will suffice for general understanding of propeller construction.  It was done mostly with hand tools so it took longer than anticipated to build, but so far it has exceeded my expectations.


Billet 2x4, this the most knot free piece I could find, which ain't sayin much.


Prop planform is cut-out.  Also seen is the master template for the prop which you can easily draw by hand.


Carving out the airfoil side of the prop with chisel and handsaw.

It was then sanded and urethaned twice for element protection.  From WOT tests, I'm arriving at a ballpark figure around 100-120lbs of static thrust which is probably plenty for my light duty tractor.  Estimated top speed is around 35mph   .  Should be a nice frozen river runner too!

frostypaws wrote:

Billet 2x4

Hahahahahaha!!!!! That's funny right there!

I'm morbidly curious to see if that thing's gonna shake like a fat hula girl (sorry for the visual). Do you have a means of balancing that prop? I gotta give you props (pun intended) for hand-fabbing that thing though! If nothing else, this is certainly the most unique build I have seen in a long time. Good luck!

Looks like a good amount of pitch on the prop. Looked flatter in the other pic.

This is going to be an interesting build.

It doesn't vibrate too much, but it does put quite a load on the engine (just listen to the idle knock from the aero load).  I finally was able to upload a video of the props performance. It's surprising to note the test stand was inching forward oh so slightly!

AWESOME!!!!     

  impressive!

Did you balance the prop? Will be fun to follow this build, Good Luck   

Thunderdivine wrote:

Did you balance the prop? Will be fun to follow this build, Good Luck   

Very crudely... I used a small 1/4" bolt on center and some graphite powder as a dry lube. Was off balance a little, but was able to knife a little wood out the left side. I think it was good 'nuff lol.

This is a very interesting build..Ill be keeping an eye on it.

frostypaws wrote:

Thunderdivine wrote:

Did you balance the prop? Will be fun to follow this build, Good Luck   

Very crudely... I used a small 1/4" bolt on center and some graphite powder as a dry lube.  Was off balance a little, but was able to knife a little wood out the left side. I think it was good 'nuff lol.

Oh it's pretty important for safety issues. If it dont shake to bad id leave it, but if it's real noticeable id drill a hole and add tiny lead balls until perfect   

I would HATE to see that prop come apart. Are you going to install a cage around the prop?

just don't stand in-plane with the props rotation lol



Despite a lot of myths out there, props are pretty forgiving. during ww1, it was common practice to simply saw off a bit of the ends of wooden props to rough balance them. The load produced on the prop by the air helps to dampen the vibration some. The most common failure point in a prop is the hub... the torque of the motor tends to tear the bolts through the wood. On this "BILLET" pine board, I'd suggest 2 large metal plates, like washers, to sandwich the wood with. A good wood hardener might help close the grain as well

I am very impressed, reminds me of the ice boats I saw as a kid. I was curious about how you plan to stop?

tree brakes
lol

I always wanted to do that. Pretty cool. It sounds good in the video. I don't really like being the guy that says this (you already know, you've been told by other people, and I don't like being told sometimes myself). But be careful with that stuff, you could get hurt real bad real quick. Seems to me as long as no one is standing where the pieces might fly out if it should break apart, everyone should be ok. I see small propellors for sale at swap meets sometimes and always thought about putting one on a lawn mower engine. Good luck on your build. I'm not trying to be a wise guy on the safety stuff, just saying.

Thank you gentlemen, I appreciate your concerns.  During the design phase of this project I did realize the dangers concerning this contraption.  As far as caging the prop, there will be a simple brush guard located on the sides of the engine tower to protect the prop.  Braking will be permitted by a scraper type brake that will be hybridized for both snow and ice.  

My main concern is keeping weight down.  So far I am looking at a conservative chassis weight ~140-150lbs total (w/o driver) even with wood which is far more than I expected.  It might end up having poor acceleration, but I designed the engine tower to accommodate "upgrades".  Sent the plasma for repairs so it will be another week till I can work on the skis.  Next up is finishing steering, controls and lastly skis.





A quick&dirty MSPaint job to kinda convey the look I'm going for.  Trying to make it look like a tractor but not like an air propelled box  .

Man thats awesome i like how your using wood.

HAHA! Its alive! Well kinda, steering is really uncontrollable at high speed.  Once I hit about 20mph any correction ends up in sideways snow drifting lol.  Maybe deeper undercuts on the skis might help   Still have lots to do like ski reinforcement, throttle, scraper brake and possibly skinning it with a thin veneer plywood.  

Handling is really weird, it's like a hybrid between a wheeled vehicle and a hovercraft.  But it's a hoot to drive  .

cross between a snowmobile, airboat, tractor, and a go kart maybe lol. Looks fun as hell to drive!

Not that I doubted this thing was gonna run or anything... but....


IT LIVES!

Would changing the thrust angle help steering? More downforce on the steer skis. The pics look like the prop is at a slight upward angle.

The engine should be mounted 3 degrees to one side, to zero out the torque (paddle) effect of the prop. That should help on turning.

And nice work it Ruuuns, now safety measures can be put into account