Propeller powered bicycle....awesome!

Jimigunne · #1 04-27-2009, 10:11 AM

I have a PK80 2-stoke motorbike, but I am planning my next powered bike. There is a video on Youtube of a guy who took a weedwacker engine, and attached a large RC airplane prop to the shaft.
I can't post a link, but look up "bicycle with weed wacker engine and propeller" This is cool beyond words! My next project is going to be a 4-stroke engine....I have a Cub Cadet CC4105 BENT-SHAFT weed-wacker which I could use for the project. Problem is this guy used what I guess was a straight-shaft weed wacker and put a 1.5:1 edger converter (45deg. angle) onto the end of the cut-down shaft. If I am understanding correctly, he has the prop geared up to turn 50% faster that the engine shaft. So I am thinking that if I just take the trimmer head off my weed wacker and attach a similar prop, it might not generate enough thrust, as it is only spinning at engine speed. So to be sure my installation will work well, I would need to know what RPM that 17.5 in prop is turning, as well as the pitch of the prop he used. I think also I would put a cage around the prop for safety...imagine what could happen if someone with long hair rode on it and leaned back a bit too far!

YouTube - Bicycle with weed wacker engine and propeller

Bikeguy Joe · #2 04-27-2009, 04:09 PM

If anything, you want to use a reduction, not a multiplyer for the prop, or just run it right off the shaft of the engine.

Bigger slower turning props are more efficient and will push your bike better.

Cabinfever1977 · #3 04-27-2009, 04:21 PM

like a windmill,there props arent turning fast and there big too.seems to work.

a_dam · #4 04-27-2009, 10:07 PM

I could see the benefits of a prop drive. Simplicity, no extra tire wear, no clutches or chains to worry about. But I would have to think that the efficiency is horrible. I'd be surprised if you get 15 mph on level ground with no wind running a 70cc wide open.
I could be wrong. I'd love to see it (ride it) in person. But I wouldn't put too much faith in a YouTube video!

Edit:

I guess even with a prop, you'd want a clutch in there somewhere. And you'd have to have a pull start (more parts).

Jimigunne · #5 05-03-2009, 05:56 AM

I have located a prop on ebay (although only a wooden one), a 20x8, to use. The shaft on weedeater should not be too difficult to cut down from the engine end, but there is a plastic spline that has to be knocked out of the cut-off engine end-piece, and re-inserted into the shortened end.

The original plastic tank is not suitable, as the filler neck will be oriented horizontally. So I will
use a much larger.5 gallon motor bike tank, the same one my PK80 kits has.

Most weedeaters are about 30 CC (this one is 26CC), so its' legal in Texas.

Once built and proven, I will add a prop shroud. Lots of people will be looking at this bike! I will use two bike wheel rims, and join them with a strip of hardware cloth about 4 in. wide. Some sort of hub (for the prop shroud) big enough to go around the shaft behind the prop will have to be engineered.

It is very easy to remove the on-shaft throttle, and use a standard bike shifting cable instead. Could use the standard PK80-type throttle/kill switch mechanism on the handlebar.

Can you imagine how long a little 26 CC engine would run on a .5 gal tank? And you just pull into any gas station to refill. Most, if not all, weedeaters have an integral centrifugal clutch, (this one does, as the spool stops turning at idle). So if you stop, the prop should stop, too.
The idea is to mount the engine on the rack over the rear wheel with pull-handle facing up.
Since it would be directly behind the seat, I don't think one could start it without dismounting.

I will probably just temporarily wire or tie-wrap the weed-eater with unmodified shaft length to the left side of the bike (like the guy in the youtube video) until problems (if any) with prop type and RPM are worked out. That way the weedeater isn't ruined for its original use.

A mount for the engine/prop can be made out of Home Depot steel perforated bracket material.
It should also be possible to engineer a muffler to increase power and quiet it down.

The big unknowns still to be worked out are what kind of thrust it will provide, and what will be the prop speed/load on engine.

frictiondrive · #6 05-07-2009, 06:57 PM

About 15 years ago I built an RC car using a 33cc weed wacker engine and airplane prop mounted to a much shortened shaft and inner flex springy thingy. My engine had a centrifugal clutch as well. It was so powerful, the car was uncontrolable and not worth the trouble, so I took the rig off the car and rigged it to my bicycles front handle bars and off me and it went! Neighbors thought I was nuts, but the thing would go about 10/20 mph. Problem was the prop wash blowing smokey exhaust all over me, so the best bet would be to put all that behind you!!! The other thing is the noise and the chance of someone coming in contact with the spinning blade. I even mounted two blade on the shaft end with the blade being rotated 90° to each other for more thrust. Good luck!

Cris

Jimigunne · #7 05-08-2009, 08:40 AM

Just wondering what size prop did you use? I noticed on my weedeater, that it does not take much extra drag to bog the engine down. If the four strings are only a couple of inches longer than
supposed to to be, its making that wizzing sound from the cutter hard, and the wide-open throttle RPM drops down a lot.

frictiondrive · #8 05-08-2009, 12:10 PM

Jimigunne,
I don't remember, but they were a good 12 to 14 inches in lenght. At the hobby shop I just asked for the biggest ones they had. A 3 blade prop would have been even better! I don't think the engine revved all that high under load, at least at a standstill. After you get up to speed, it may have less resistance and spin faster....don't know. The air turbulence/wash behind the prop's was like being in a wind tunnel!

Cris

captainrichhill · #9 05-08-2009, 02:19 PM

DANGER! DANGER! DANGER, Wil Robinson!!! Do you really want to have a spinning prop on any public property? That looks like a lawsuit and at the very least, a ticket from the POPO.

Jimigunne · #10 05-09-2009, 04:33 AM

Sure, it would be a danger to the public to ride up to the grocery store where the public is around.
So once the design is worked out, I will replace with some sort of composite prop that doesn't break, and construct a circular "cage", sort of like you find on air boats, but smaller. Hardware cloth, with two circular hoops of some sort, would be ideal.