Model Engine Maker

Supporting => Engine Ancillaries => Topic started by: cfellows on August 23, 2012, 09:35:24 PM

Title: Making Model Engine (flywheel) Propellers
Post by: cfellows on August 23, 2012, 09:35:24 PM
I've built several model aircraft type engines and felt that a propeller would be more suitable than a flywheel.  However, I also like the way a flywheel improves the low speed running of model engines.  The solution to me seemed to be a heavy propeller, one that looked suitable for an aircraft engine but was still heavy enough for the flywheel affect.

Finding such a propeller in the hobby market is near impossible for obvious reasons... model airplane builders want as light a propeller as can be found which pretty much obviates using something like steel.  So, in each case, I've made my own.

On earlier models, I used cad to draw a propeller template, printed it out, and glued it to a piece of metal with scotch spray on contact cement.

(http://s192.photobucket.com/albums/z195/cffellows/17304b66.jpg)

This works reasonably well, but there are a couple of problems.  First of all, when cutting the propeller out of steel and also when grinding it to shape later on, it gets hot.  This causes the paper template to come loose.  It also makes it impossible to dip the piece in water to cool it off.  So, on this latest propeller, I decided to scribe the outline directly onto the metal.

Perhaps the most important part of making a multibladed propeller is symmetry.  All the blades should be identical, not only for appearances sake, but also for balance.  So, I made a template of one side of one blade of a propeller.

(http://s192.photobucket.com/albums/z195/cffellows/ec965a4a.jpg)

It's made from steel stock about .1" thick, an inch wide and 4 or 5 inches long.  It has a scribed line, on both sides, that define the centerline of the propeller  blade.  The curved part of the template should be a smooth curve, and on this propeller, not much metal needed to be removed.  The curve only sweeps in about 1/8".  The overall width of the propeller blade at it's wides point is 1/2"

I then drilled a hole at what will be the center of the finished propeller.

(http://s192.photobucket.com/albums/z195/cffellows/20a6760c.jpg)

Okay, I drilled two holes, but the bottom one was a mistake!

I used a carpenter square to layout the two perpendicular axes of the propeller, which, by they way, will have 4 blades.

(http://s192.photobucket.com/albums/z195/cffellows/1c30aa4b.jpg)

(http://s192.photobucket.com/albums/z195/cffellows/e5f98c89.jpg)

(http://s192.photobucket.com/albums/z195/cffellows/8ab1fb30.jpg)

I drill a hole at the intersection of the two perpendicular axes so I can use a screw to line up the template with the propeller blank.

(http://s192.photobucket.com/albums/z195/cffellows/d949cabd.jpg)

The template is first used to draw one side of all propeller blades.  Then the template is flipped over and the other side is drawn for all 4 blades.

(http://s192.photobucket.com/albums/z195/cffellows/44f76531.jpg)

After all the lines are scribed, I used my bandsaw to cut the propeller out then used my belt grinder to grind up to the scribed lines.  The next task, and I don't have any pictures of this part, is to mill out the waist at the bottom of each blade above the hub.  This was pretty simple process, using a rotary table to index the blade and mill out the waist at the bottom of each blade.

Next, I clamped each blade in turn into my bench vise and used a crescent wrench to put about 15 degees of twist in each blade.

(http://s192.photobucket.com/albums/z195/cffellows/80f6c92c.jpg)

The last step is grinding the leading and trailing edges of each blade.  Using a belt grinder, this is not a particularly difficult task since not a lot of metal needs to be removed.  Here is an end shot of one of the blades toget an idea of the blade profile.  Again, you don't need to remove a lot metal.  It just needs to look like a propeller, not behave like one.

(http://s192.photobucket.com/albums/z195/cffellows/b96b5300.jpg)

Here is a picture of my latest, finished propeller.

(http://s192.photobucket.com/albums/z195/cffellows/a4929780.jpg)

Chuck
Title: Re: Making Model Engine (flywheel) Propellers
Post by: tel on August 23, 2012, 09:42:05 PM
good idea Chuck - that's a method I will tuck away for future reference.
Title: Re: Making Model Engine (flywheel) Propellers
Post by: vcutajar on August 23, 2012, 10:06:39 PM
Thanks Chuck for the writeup.  It was always a mystery how people do these things and you have shed some light (actually a lot) on the subject.

Vince
Title: Re: Making Model Engine (flywheel) Propellers
Post by: zeeprogrammer on August 23, 2012, 11:11:26 PM
Very good write up Chuck.

As a side note...it takes me back to childhood. I can't help imagining a P-51 sitting behind it.
Title: Re: Making Model Engine (flywheel) Propellers
Post by: Don1966 on August 24, 2012, 01:03:11 AM
Thanks Chuck, great write up as usual and a learning curve to boot. Love the propeller.

Don
Title: Re: Making Model Engine (flywheel) Propellers
Post by: gbritnell on August 24, 2012, 01:37:02 AM
Hi Chuck,
I'm glad you did it first. I have been contemplating doing the same thing for my radial as the composite prop I have on it now just doesn't have enough mass. The reason I didn't want to tackle it was because I didn't want to have to grind all that material away from the blades.
gbritnell
Title: Re: Making Model Engine (flywheel) Propellers
Post by: cfellows on August 24, 2012, 08:31:05 PM
Very good write up Chuck.

As a side note...it takes me back to childhood. I can't help imagining a P-51 sitting behind it.

Ah, yes, the P-51.  One of my other great loves.  Maybe a model V-12 Merlin one day, if I live long enough!

Chuck
Title: Re: Making Model Engine (flywheel) Propellers
Post by: cfellows on August 24, 2012, 08:36:17 PM
Hi Chuck,
I'm glad you did it first. I have been contemplating doing the same thing for my radial as the composite prop I have on it now just doesn't have enough mass. The reason I didn't want to tackle it was because I didn't want to have to grind all that material away from the blades.
gbritnell

George, there isn't nearly as much metal removal required as you might think.  If you're just after the mass, you can get by pretty much with token metal removal and it'll still look pretty nice.  And my propeller actually does move some air, but it doesn't move nearly as much as a finely tuned propeller.  Of course, your engine would require quite a bit bigger propeller.  Mine is about 7" from tip to tip.

Word of caution, if you do make a steel propeller, and you use your belt grinder for shaping, wear a cap and a face shield.  That steel dust gets in your scalp and facial pores and will drive you crazy from itching and stinging!  That happened to me on the last propeller I made so I took precautions this time.

Chuck
Title: Re: Making Model Engine (flywheel) Propellers
Post by: RonGinger on August 24, 2012, 10:40:03 PM
I would be very worried about running a model engine with a prop like this. With a flywheel the engines are very safe, but a prop like that would sure give a finger a mighty whack. I know the edge was not made sharp, but it would still be a heck of a whack. I would never want to see one running at a show where kids could get near it.

Why not just make a bit heavier, or larger diameter, flywheel if you want to better load the motor.
Title: Re: Making Model Engine (flywheel) Propellers
Post by: rleete on August 24, 2012, 10:44:37 PM
I doubt it would have enough impact to do more than deliver a sharp whack.  Air engines have ery little torque.  Maybe painful, but I highly doubt it would do any lasting damage.

Chuck, how do you attach the prop to the engine, and how do you insure it rotates true, and doesn't wobble?
Title: Re: Making Model Engine (flywheel) Propellers
Post by: cfellows on August 25, 2012, 01:38:14 AM
I doubt it would have enough impact to do more than deliver a sharp whack.  Air engines have ery little torque.  Maybe painful, but I highly doubt it would do any lasting damage.

Chuck, how do you attach the prop to the engine, and how do you insure it rotates true, and doesn't wobble?

Prop is bolted to a brass hub that is attached to the crankshaft with a setscrew.

This is my third aircraft engine with a steel prop.  I mostly I just run the engines at an idle and I never display the engines at shows or run them around children.  I'm well aware of the dangers and treat the engines with the respect they deserve.

Chuck
Title: Re: Making Model Engine (flywheel) Propellers
Post by: DaveH on August 26, 2012, 12:03:14 AM
Chuck,
I think that is very nice.  :)

Nicely shown as well  :)
 :cheers:
DaveH
Title: Re: Making Model Engine (flywheel) Propellers
Post by: swilliams on August 26, 2012, 02:08:12 AM
Very creative Chuck

Steve
Title: Re: Making Model Engine (flywheel) Propellers
Post by: V 45 on August 30, 2012, 12:31:43 AM
A great idea that you brought to light/ life !!! Excellent  :ThumbsUp:
Title: Re: Making Model Engine (flywheel) Propellers
Post by: Mel Larsen on August 30, 2012, 12:48:46 AM
I started building Chuck's 4 cyl. opposed engine a while back.  I will probably finish it this winter.  I plan on putting a propeller like the chuck has shown here, but I think I will weld a ring on the outside diameter of the prop. just for safety.
Mel
Title: Re: Making Model Engine (flywheel) Propellers
Post by: steamer on August 30, 2012, 11:01:49 AM
Nicely done Chuck!   4 blades is in keeping!   

Dave