Embarrassing Question - What Prop?

[ctdahle]

I can't remember what prop I was using on my Four Star. It's engine is an OS 46 FX.

I have a buch of 11X7's in a box here, but I can't beleive that I used a prop that pitchy. Does an 11X5 seem right?

On the other hand, I have a bunch of 10X6's and 9X5's.

Thoughts, suggestions, snide remarks?

[jetmex]

Chris, I've had good luck with an 11-5 on 40-46 size engines. Gives you a little more pull, but not quite as much speed as a 10-6. I flew and 11-5 on my first Goldberg Cub and it was just right for that airplane.

I think 11-7 is a little much for a .46, but you'll probably find a thousand people out there who swear it works just fine for them.........

[ctdahle]

Thanks Jaime, I'm going to try an 11X5. We finished up the repairs on the Four Star this morning and we'll give it a try as soon as I put some stick time on the Kadet. I've been flying the Cutie in the park, but since there is no runway there, I've gotten really sloppy. Hope I can remember how to hit a runway.

[EJB]

Make that an APC 11X5 prop.

[ctdahle]

I like APC props, but I have Master Airscrews coming out my ears. Last time I bought props, Master Airscrews must have been on sale. I was probably trying to build up to the free shipping minimum at Tower.

The Four-Star is now ready to go except that I find I have a bad flight battery. It will only keep my loaded meter in the green for about 20 minutes. Not surprising though, it's dated May 1999. I'm going to cycle it twice and see if it comes back up, but I'm getting ready to order new TX and RX packs. I generally replace packs every 2 years unless they have had very little use, and I was at the end of a two year cycle when I started having kids.

I've got one radio boxed up to send in for tuning and cleaning and when it comes back I'll send the other. They are over due too.

[Britbrat]

I just noticed this -- Chris, what is yiour altitude above sea level? I seem to recall that you are somewhere around 5,000 or 6,000 ft -true?

If so, an 11-7 will be like an anchor on that engine.

An APC 11-5 is what you will probably do best with. If that ain't so good, try an APC 12-4 if you have ground clearance.

If your airspeed is too low with either of those, then a 10-6 will fix the problem, but the loss of disc area will hurt somewhat.

[ctdahle]

Hmm, I'm at 8000 feet. My theory has always been that I needed a bit MORE pitch because I need to keep up the airspeed, but I'm not adverse to trying a flatter prop.

As I was sorting through stuff this morning I found that I had several 11-5's that were a bit dinged up, suggesting that I did use them on the .46.

The Four Star is going to stay grounded for a while yet. I went out and flew the Kadet this morning again and so far I can't land worth a darn. I kept it on the runway and I didn't break anything but out of 15 landings, I only put it on the stripe twice. My take-offs were pretty squirrelly too. If I don't improve pretty darn quick, I'm thinking of installing a nose wheel.

[HB]

Just to mention it, I've actually shortened the diameter of props before.

The way that I've done it is to mount the prop on a rigid shaft protruding from a base, (1/4" ply) and to mount the base on my band saw table and just rotate the prop thru the blade to trim both ends. The less play in the mounting set-up the better.

If you like aerobatic flying tehn propwash is important and a wider blade and or higher pitch will throw more air.
You can make fine diameter adjustments on the prop to maximize engine performance.

Also if ground clearance is an issue you can use a bulky prop and trim it to the desired ground clearance/engine performance.

An 11/7 might be fine cut back to an 10.5/7

[HB]

Also some motors run/idle better under a little bit of a load.

[HB]

Anybody that doesn't have a bandsaw could use a drill press with a drum sanding attachment on it or could even use a portable belt sander clamped to a table.

One should take care to use a stable section of the belt with the belt sander setup.

I don't bother balancing my props.

I think that as long as a prop is symmetrical in material and dimension that balancing is unnecessary.

Air resistance on the prop seems more of an even load issue than very slight weight inequalities.

I had a friend who would be dripping ca on his props and or sanding surface
I really don't see an superior effect from doing this.

But he seems like an expert ;D

He sure "knows" alot of "stuff ".

[HB]

I've used the band saw and then just lightly hand sanded some roundness onto the ends.

The drum sanding attachment on a drill press would probably work best.

The reason for this is that a bandsaw blade is more apt to bind whereas a drum sanders "cut" angle of attack is more flexible due to the radius of the cutting surface.

[HB]

You could actually "point" the tips of you props by clamping the prop to an secondarwy base and so you could offset the agzis point also

[HB]

But that would require 2 agzis points i.e one for each end wiz both symmetrically even from the actual prop agzis point

[HB]

Drill three holes in a straight line on your secondary base using care to make certain that the outside holes are even distance to the center.
Mount your prop to the center hole with the base tight but able to rotate.

Then rotate the secondary base in relation to the prop and you have 2 even axis points. One for each end.

Tighten secondary base to prop before cuting prop.

[ctdahle]

I usually cut down diameter by finding a good rough surfaced rock. Then I start the engine and run it up to about 1/3 throttle. Then I carefully push the rock against the edge of the prop disc and grind off the excess until I get the diameter I want...Kidding...

Actually, I have a jig made up with a series of holes in it, measured from the edge in 1/4 inch increments. I put a dowel in the hole that matches the diameter I want. I shear off most of the excess with tin snips and then finish with the sanding block.

Be aware that when you cut down a prop, you are also changing the pitch, for example, if you cut down a 9X6 to 8 inches, the altered prop will be more like an 8X7 than a stock 8x6.

[Britbrat]

ctdahle said:

Be aware that when you cut down a prop, you are also changing the pitch, for example, if you cut down a 9X6 to 8 inches, the altered prop will be more like an 8X7 than a stock 8x6.

You got that right.

At 8,000 ft (wow), power will be a problem, that's why I'm interested in minimizing the load.

While some engines will lug better than others, they ain't lugging much at 8,000'. You are going to need to maximize the output which means RPM & the best-fit compromise prop to keep the engine in the power band.

Fortunately, the 4* doesn't have a bulky nose, so a smaller dia "pitchier" prop will probably work reasonably well.

I'm pretty sure that an 11-5 will drag it around OK, but if not, a 10-6 could give you the necessary air speed to stay aloft in the stuff that you call air up there. It won't be a rocket getting off the ground though.

[ctdahle]

Well, it ain't gonna hover, but it actually performed pretty well before. The big problem is that EVERYTHING lands really fast up here.

I'm pretty sure that I will be safe with an 11-5 to start and then I'll try the 11-6.

[katria]

Hi
While some engines will lug better than others, they ain't lugging much at 8,000'. You are going to need to maximize the output which means RPM & the best-fit compromise prop to keep the engine in the power band.

[brianw517]

Always balance your props; your motor's will thank you and it's a safety issue also.