Engine/Drivetrain

I will be using two engines for this Hovercraft, The Lift engine will be a 10.5 hp vertical shaft, and the Thrust engine will be around a 47hp 2 stroke from a snowmobile engine.
Snowmobile engines have lots of vibration, I will be isolating this vibration using 1 1/2 inch pipe with a washer welded in 3/8 of a inch from the bottom. A 3/4 inch washer is then placed above and below the washer to isolate the vibration. Please no comments on my welding skill.
I cut the tops of the pipe on a slant so that I could have access to the washer. This will also make it easier to get at the nuts when installed.
This is a dry fit on the hovercraft, notice the 1X4 under the legs, these will be installed to add strength. The same size 1X4 will be placed on the bottom of the craft and threaded rod will sandwich the mount/foam/1X4's together.
This is the bottom of the craft, I missed some pictures here but you can see the engine mounts on the bottom. What I did here was using a router, counter sunk a pine 1X4 into the foam, then counter sunk a larger piece of 1/4 inch ply to act as a big washer. These pieces were then epoxied in place and the bottom of the craft was fiberglass using 6 oz cloth.
A different angle, *** Universal Hovercraft says not to fiberglass the bottom in their plans, but if you talk with them they tell you to fiberglass the bottom. I figure it will add about 10 lb. and will protect the bottom from sticks etc. But more important will stop the foam from soaking up things like gas or oil. Do not make the mistake I am making here, fiberglass your hull before you add the cockpit on top. *****
These are the washers for the engine mount to reduce vibration. I cut my own using a sharpened pipe in a hydraulic press, a large vise would work too. The rubber I used was from a old mudflap that I found lying around.
Hey look at that , Got my thrust engine today, Rotax 503. Recoil start. I would like to have a electric start but on this engine the starter turns the clutch. I will just have to start it the old fashioned way.
The following set of pictures are the making of a 4 groove 3v wood pulley for the driven pulley of the air drive. This picture just shows the wood being epoxied and prepared for turning. I used clean pine 1X 6 and 1X8 laminated together to produce the blank for the pulley. This shows that blank in clamps
Here we have the wood blank all laminated together, you can see the excess epoxy that has been squeezed out during clamping. The dimensions of this blank at this time is roughly 13 inch square and consists of 4 layers.
Using a compass I drew a 12 inch circle and roughed out a cut. This picture shows me attaching the face plate of the lathe to the wood blank.(Yes it is home made,my lathe is rather old).
Here I have put the blank in the lathe and started turning the blank so that it is 12 inch circle. This lathe could only turn 10 inch stock, so I had to put spacers in to turn a blank this size.
The first thing that I did was to make sure that this face was square to the sides and that the blank was taken down to the pulley size of 10.8 inches. I then cut a circle on the face to accept a roller chain sprocket. The sprocket will be inlayed into this face so that the pulley will be perfectly centered.
Here you can see the sprocket and the bushing in place. This is the first side. After I Finnish cutting the 3V grooves I will do the same thing on the other side. The pulley will be installed between 2 roller chain sprockets. Universal Hovercraft sells these wood pulley's, they machine a tapered hole in the center to accept a P1 bushing. I am unable to machine to that precision so I will just bolt the pulley between 2 roller chain sprockets.

In order to cut a 3V groove I had to sacrifice a old wood chisel. I carefully grinder the chisel to a 3V shape on a grinder. (Careful to go slow and not ruin the chisels temper). The 3V shape was just taken from the cast pulley that I will be using on the engine itself. Universal sells aluminum pulleys that have a taper to them for snowmobile engines. I used a cast pulley instead, I believe it is only a couple of LB's heavier than the aluminum.
Here I have started to cut the grooves. I first marked the blank by just transposing the grooves from the cast pulley to the wooden blank. I also added welded a guide for the knife to follow. This will assure that the groove is square.

Here you can see me just lightly pressing the knife into the blank using the guide.
All the grooves have been cut. I can not stress the importance of going slow and not letting the knife catch. Mine did. on the third groove the knife caught a flaw in the wood or something and remove more wood than I wanted. You can not see it in the picture. My plans are to repair this with epoxy and carry on.
Just another picture of the grooves. I also rounded the edges of the pulley.

This just shows that I turned the pulley around to cut the inlay for the second roller chain sprocket.

I then cut the center hole. This is just a pilot hole but I will be cutting a 1 inch hole for the drive shaft. As expected I did not cut a perfect square center hole but that is ok because the pulley must center perfect to the roller chain sprockets.
I will be giving the pulley 3 coats of epoxy. this picture is after one.


Well I did not like the first design for a engine mount so I re-did it . The pulley is now between two pillow blocks which will distribute the forces more evenly.
Picture showing additional supports

The dimensions of the top of the engine mount is 11 X 18.
All painted up and ready to install. I will be installing the muffler as you see it. It will vent into the thrust prop. update I have changed this muffler setup
Top view showing the shape, along with the tabs to mount the supports for the thrust duct.
This picture shows the mount on the craft. If you look close you can see the vibration washers under the mount.
A top view of the mount.I use carriage bolts so that there is nothing to catch on the bottom of the craft. I will also be drilling a hole in the bolt to put in a cotter pin just in case the nut loosens.
This is the drivetrain complete. You can see the wooden pulley centered with two sprockets and bushings. I have yet to attach the duct supports, the prop in the picture is just pushed on. It will be attached with a roller chain sprocket as well once it is balanced.
Here is the engine that I will be using for lift. It is a 10.5 Briggs. My first choice would have been a 10 hp Tecumseh, because it uses a different oiling system and is rated to be installed at a greater pitch, which is important because of the lift duct being on a tilt. Briggs recommends not operating over 15 degrees, my duct is at 20 degrees. I guess we will see if this motor runs at 20.
Here are my plans for the front engine mount.(one square = one inch). The mount will be placed in the duct and will be attached to the side walls. It will be made of 1 inch aluminum tube and aluminum plate welded together. The side walls of the duct will be re-enforced with some pieces of hardwood, and foam will be sprayed around the entire duct so that it will keep its form. Sorry about the quality of the picture.
Well I cut all the aluminum to length and called in a favor to have it welded up. This is what the mount looks like.
This picture shows the rivets I used to hold the mount together before I sent it out, also the mounting brackets for the side wall of the duct.
This is the wood I will be using to re-enforce the duct wall. It is actually the ends of the fan that I had cut off.
I used some old steel and welded some nuts to it. This will also be used to re-enforce the duct wall.
This top view shows all the pieces epoxied and bolted together, all in all I am pleased with how it all turned out. When I mount this permanently, I will use some tire tube between the engine mount and the duct wall just to make a good seal and perhaps remove some engine vibration.
There you have it. Engine all mounted up. I will now do all the engine connections and Finnish off the foam. I will be glad to cover up all that ugly foam, sure looks like shit. If you want to see the pictures of how I made the front cover, go to the cockpit section of the web site.
This picture shows the front engine assembly in place. I will remove it for painting.
Well Here I am about to install the lift engine, I tilted the craft to level to make it somewhat easier. A lot of work went into preparing the engine and lift fan before this picture was taken. The lift fan was covered with glass and then smoothed/balanced and painted. etc.
I have put a Finnish coat of paint on the duct only so that I can just cover the whole engine when I paint the rest of the craft. I made a huge mistake before this picture. Make sure you wash off the wax that cures on the fiber glass before you paint, In my case the paint did not stick, I had to remove all of it and re-do it. You will also notice on the engine that the stock muffler and a home made deflector is in place.
I ran the engine and noticed that it damaged the duct wall, sort of a blister, it is caused by the heat of the muffler.
I removed the stock muffler and installed a extension and elbow so that I could install a different muffler.
Side view, you can see that the exhaust is now pointing down through the duct, you can also see the damage to the side of the duct. I am not happy with how sensitive the duct wall is to heat, I think I should have put more glass down on the duct.
Safety first/ This is the guard that I created, basically two circles and some supports. I will add some mesh around the sides to stop hands from going in the duct. the guard is made of 1/2 inch emt, it is fairly light a couple of pounds and can be easily bent around anything round, I used a oil barrel and a brake drum to bend these.
Just another view, Time for the thrust engine.
This picture shows the engine compartment. I have cut holes in the cabin walls for exhaust and air intake.
Well this is the Gas pipe leading to the muffler, not all that pretty but it should work. update do not do your exhaust this way, check out the skunk works section.*
This is the lift guard all finished, I used plastic quick connects to attach chicken wire to the frame.(not sure exactly what gauge the wire is but it is fairly strong)
here you can see that I painted the drive pulley, really just wanted to keep the rust off of it, yellow was the can of paint that was closest. You can also see the filter that I put on the carb, it is just a sock that I made from a shop vac filter , just wrapped it and used elastics to close the end and secure it to the carb. I also started the fuel connections, you can see a plate that I used to mount the primer pump. Primer pump is important for winter starts
These are the fuel connections, you can see the fuel line feed into the vacuum pump and then to the carb. The carb has 4 connections or lines running from it. 1)fuel to reservoir,2) fuel input past carb for priming, 3) & 4) are venting tubes that just lead down to nothing. This engine has oil injection, the feed goes into the nipple with the yellow covering at the front of the engine. I do not have the throttle cable hooked up but it is one cable that splits to two at the engine, this cable will lever the throttle and the oil injection lever at the front of the engine. Electrical lines are visible and labeled with tape, I have not figured out how to run the lights yet.
I needed to balance the driven pulley, this took a little time using the methods you can see in the prop section, this picture shows the lead inserts that will be epoxied into the pulley.
And all installed, I used four 3V 360 belts. I could have used a combined belt but I thought that separate belts might be more forgiving to my home made upper pulley. update Do not use separate belts, they will break and go through your duct. I learned this the hard way.
This is the rear guard, made of 1/2 inch EMT, it is not hard to make these bends just use the forms that you used for the thrust duct support. I tack welded and then brased (not sure of the spelling )the connections
putting on the wire
These are the connectors used
Here you can see the guards in place.
side view

mailto:bruce.einarson@mts.net