Lawn Boy/specs/education

[WHY]

Mentioned on earlier thread here that I was considering using a Lawn Boy mower engine as a pre-rotor engine on my tractor, mounting it down in the turtle deck and using a centrifugal clutch to drive a shaft up to the bendix.

Well since then I have had some encouraging information about the engine, it seems that I am certainly not the first to think of this, another person here on the forum has already tried it and although he eventually went another route, his experiment was very encouraging. He ran the Dura-Force engine to a small transmission near the rotor head and drove the transmission with a v belt (poly V I think) was able to get about 180 on the rotor before the clutch in the transmission began to slip. My guess is that this was due to the fact that the engine was getting into it's power curve at about this point and the clutch could not hold the power. The blades were 24 ft. in length.

This would seem to hold the prospect of better than 200 rpm if a drive system is used that will handle the power. My preference is to use a centrifugal clutch with a cog belt drive but so far have not been able to locate such a clutch but will be contacting Comet manufacturing after the holidays for info.

The encouraging feature that I have found so far is that both the "F" series engine and the "Dura-Force" engine are 141 cc but the "F" series is rated at about 3 1/2 hp at around 3300 to 3500 RPM !!!!!!!!! and this is a two stroke engine. The only way I can think the Dura-Force can be rated at 6.5 hp is they are cranking up the RPM. Even if this is the case I doubt they are going very high because of mower blade safety so I think it is possible that this engine or the "F" series engine may really make a fine pre-rotor engine ( or a spin up engine for a towed glider ????)

Don't know how world wide the Lawn Boy mower was sold, but there may be a good supply of these engines around although I don't think they will be considered very much by those flying pusher style gyro's since other power sources are more easily used due to engine location.

Again would like to here from any small engine mechanics who are experienced with these engines or anyone else that have used them a lot or anyone with some solid engine specs like hp at what rpm's.

Tony

[Friendly]

Tony,
I remember the Lawnboy offered a 6 hp model. My grandfather used them to cut large lots. He did not believe in riding lawn mowers.
I have wanted to examine the plastic recoil starter for the Lawnboy engine. It engaged the flywheel teeth from the bottom of the flywheel and spun in and out like the Bendix drive on most eclectic starters. I always thought it could be adapted on a large scale to hand start the rotors of the ultralight gyros and tall mast.

[WHY]

Hi Mark

I think it would work , BUT, I am afraid that as you started to get some rpm you would not be able to keep up the "yanking" speed to get more rpm.

Tony

[Arnie Madsen]

Hi Tony
As I read this thread (and your other one) I was wondering if a chain saw engine would work for you. They already have the centrifugal clutch built in , can be run sideways or upside down , they are designed to be as light as possible , and are well built for long term use and abuse.

I took a quick look at some specs and the 76.5cc STIHL model MS 460 produces 6.0 hp and weighs 14.6 pounds ....weight is for the powerhead with chain & bar removed which is what you would be using. Here is the link to all their engine specs & weights:

http://www.stihlusa.com/chainsaws/comparison.html


Probably the gearing down would be an issue ... they rev pretty high although there are gearsets made by the factory used for earth drills (for tree planting) that reduce the rpm to 190 but the engines are too small for you. I enclosed the link so you can take a look.

http://www.stihlusa.com/augersdrills/BT121.html

Arnie
Bell 47 G2

ps: I have used Stihl saws for years and they seem to produce decent torque and power even at mid-range rpm and up.

[WHY]

Hi Arnie

I had looked at chain saws for some time, and if I were to choose one it would be the Stihl. There are two problems that I encountered with a chain saw, first was that they are so special build that it is difficult to eliminate the blower housing for a custom made one and then have some way to mount it. secondly the chain drive centrifugal clutch has the sprocket on the in side which mandates a chain drive and finally the sprocket would require a custom rework since the sprocket does not match any "standard" pitch chains. But as far as power and reliability, they sure have it.

Tony

[WHY]

Arnie

I looked at the Stihl site and looked up some specs on the "cut off " saws, they are belt drive, would you know what kind of belt????

Tony

[dinoa]

How about using the chain after grinding off the cutting tips.

Dino

[Arnie Madsen]

Arnie

I looked at the Stihl site and looked up some specs on the "cut off " saws, they are belt drive, would you know what kind of belt????

Tony

No , I know they have them but couldnt find them when I wanted to. Will look again later and let you know if I find.

Also , I now understand when you mentioned about mounting a chain saw engine , as I look closer they are mounted on rubber isolators and hard to find a good mounting area without going metal on metal etc. (vibration problems ?) Even when not running as a prerotator they would absorb your flying airframe vibrations which is not good.

I noticed that the newer Stihl's mount the chain drive gear on the outside of the centrifugal clutch . It is like a spline mount and the gear can be changed in 30 seconds . I was surprised how much "slop" there is in the spline set-up but was told it compensates for any mis-alignment and has been trouble free so far.

I was also told that the quick change gear was designed for a variety of attachments ( like maybe the cog belt) . I dont know for sure.

I read on the link for the ground auger attachment that Stihl used a double gearset of 47-1 to bring rpm down to 190 so that tells me such attachments are out there and light weight.

Anyway , if I come across more I will let you know. In the meantime I find your ideas interesting .... besides I had one of the old cast aluminium Lawn Boy mowers years ago. Smoothest running 2 stroke in the world. Cut grass perfect. I think it had to do with the aerodynamic vortex created by the cast body that pulled the grass straight up and cut it cleanly. Something like that. Very Light too.

Arnie
Bell 47 G2

[Arnie Madsen]

How about using the chain after grinding off the cutting tips.

Dino

Might work Dino. If you could find a larger (say 10") receiving sprocket. Trouble is they are not a true chain drive to start with. On a saw the drive part of the chain is more like a set of inverted triangles (wish I had a picture) that run in slots on the drive gear. I do know of people who have used this for remote control model drives with success . Something like a proper gear or belt like Tony mentioned would probably be best.

greetings from canada
Arnie Madsen
Bell 47 G2
...................................

ps: the RC model used a Husqvarna chain saw engine . Had about a 4 foot rotor span , copied the Bell 47 helicopter , and when it flew from a distance it looked like the real thing. Even had the wop wop sound. I thought of building one .... thus the blend of helicopter and chain saw engines for me.... I was going to use tail rotors from a Bell 206 but could not figure out how to adapt light duty servos to the control system .... I'm no good with electronics or radio stuff ....

[BUD ONEAL]

Check out the gas powered 12 foot reach pruning saw. Small light weight and has a drive installed from the factory. Designed to run upside down also. Mine has a 25cc engine,is a "poulan Pro" The shaft is about 2' long. I'm sure that it could be made to fit.

[WHY]

Hi Arnie

Hey, thanks for the research on the Stihl saws, that quick change sprocket idea makes me think that someone at Stihl is using some good sense. I would not be suprised that this quick change sprocket idea is for a v-belt or cog belt sprocket that may be available. They may have done this to allow the "power head" to be used in either a chain saw or a concrete/cut-off saw or other application 'REAL SMART THINKING".

Now if the power head can be purchased by itself ( expensive i'm sure but very possible) and custom blower housing made with some for of mounting, then we have a WINNER.

So often on other chainsaw models, other important parts of the engine (ignition assembly, carbureation, ect.) were incorporated into the blower housing along with the fuel tank(no problem) to such a point they become a major issue to do the change over.

Tony

[WHY]

While this is about the Stihl bran of engines I think I will still put it under the "pre-rotor" category.

Just learned a "little" more about the Stihl cut-off saw and the engines available in it. The TS700 and the TS800 use a 98 cc engine that makes 6.7 hp at abouot 9800 rpm and it has "V-belt" drive on the output (with a centrigugal clutch, I think), Sooooo this is another good possibility, specially if it can be purchased as a "power head only" uses a recoil rope start. It will certainally be of top quality, the price may be a little scary though. One would only have to make a blower housing and some form of mounting system.

Tony