I have been tinkering with my plane that is ready for it's maiden. and i got to thinking about the engine that i put into it (Evo .45 ). My plane is a .40 size "pattern master" (pic below) and it came with an old webra .40 in it. The prop that came with the webra was a 10x6 APC prop. So my question is:

Do you choose the prop based on the engine size, or the type of plane?

I'm a little worried that my Evo .45 is a little too much power for the pattern master, and was wonder if a different prop would help this problem. I'll include The "pattern master" specs.

Pattern Master-

Wing legnth: 60 inches
Fuse legnth: 42 inches
Full weight (no fuel): 6 lbs


Thanks!

P.S. I don't know the CG of this plane but it when i checked it it was half to a full inch forward of the main wing spar. is that good?

The Evo 45/46 is not too much power at all. Until you get into more advanced planes, simply use a prop selection chart to match up to engines. The new engine should take a 11/6 or 7.
The cg should be about 25 to 30% of cord width back from leading edge. The 1" in front of main gear for cg is pretty close; otherwise if it was right on the gear, as soon as you hit the throttle it would drop the tail on the ground and try to lift off before it was ready to fly.
I hope this is not your first plane ??

He said the CG was 1" in front of the main SPAR, which sounds a little nose heavy to me. Try flying it with an 11x6 prop, if the plane won't spin, or doesn't slow down on landings, move the CG back in small increments

This is my second plane.

Bingo told me to check for the CG while the plane is inverted. And i found that the CG is approximetly 2.5 inches behind the "leading edge of the wing". This plane is fairly old and has been given the once over by the orgional owner who knows his stuff and says this plane will be good for someone like me.

To answer the original question -- you chose the prop, based upon the engine/plane combination, plus the intended use. The engine should be kept in its usefull power band & the airframe, in addition to prop pitch & diameter, has a significant effect on engine performance. If you have a small, light, clean airframe you can overrev in-flight, despite an acceptable static RPM -- in that case you could use a smaller diameter "pitchier" prop than you would if the plane was blunt & draggy. In the latter case, an increased diameter & lower pitch prop may enhance airframe & engine performance. If you need vertical, increase the diameter & flatten the pitch. If you want speed, decrease the diameter & increase the pitch (assuming that the plane is clean enough to actually go significantly faster). If you need take-off performance (floats, deep grass, etc.), go with the longer flater prop. If you have long hard runways, you can possibly use a smaller steeper prop, if the ac will support its in-flight characteristics. Altitude & temperature also play a part in prop selection. As engine performance falls with increasing altitude & increasing temp, a flatter prop will probably be needed - with or without increasing diameter, depending on case specifics.

In your case, an 11-6 is probably a good starting compromise for your engine/plane/usage combination. However, there is a substantial degree of trial & error involved & a typical BB ABC .46, like your EVO, can use a wide range of propellers, from a 9-8 to a 12-4, depending upon airframe & in-flight usage. Increasing diameter raises power load faster than increasing pitch. As far as the engine is concerned, too little load will send revs soaring past the usefull range, & possibly into the destructive range and too much load increases piston side-load, increases crankshaft radial thrust loads, & increases cylinder temps & pressures -- all of it bad.


What could be simpler?

The 45 will be fine for the plane.

Prop size is based on engine size AND plane AND intended use. For use as a second plane, the prop I suggest is an APC 11x6 TO START WITH. You will most likely be adjusting the prop dia x pitch later on, depending on what you want to do with the plane.

The balance point is USUALLY 25% - 30% of the MAC. To me, it sounds like the plane MAY be nose heavy. Since an experienced person balanced the plane initially, I would suggest rebalancing the plane using the present CG location (2 1/2" in back of the leading edge), then fly the plane. Readjust your balance point from there. When you readjust your balance, I suggest using 1/8" increments - i.e. move your CG from 2 1/2" to 2 5/8". You do not want to move the CG in large increments, especially since you are a relatively new flyer.

Remember, a nose heavy plane will fly sluggishly, but a tail heavy plane only flies once

The Evo .45 has a lot of power. It pulls my heavy trainer around pretty good with 11x7 props, so your plane should perform even better.

I suggest that you take the baffle out of the muffler. Also, did you remove the weighted flywheel on the .45? If not, replace it with the cheap Evo replacement. Costs around $3 and is much lighter. As for checking the CG, maybe somebody at your club should assist you. Buy some segmented weights at the LHS and separate them in 1, 2, 3, and 4 segments. Drill holes in each one, and take a couple of wood screws to the field. That way, you can add weights easily to the bottom of the fuselage as needed. I did it this way over the weekend and it is a good solution. You can cover the screw hole easily if you need to.

If you are not clear of what MAC means, you can find it by doing a search here on RCU. I don't know any links right now.

Good luck. It looks like you should enjoy the plane and engine.

I just found out that this plane was desgned for .40 size to .49 sized engine so i'm ok there.

I could go to 11 sized props but i would just make it, because the grass on my feild and how low the plane sits. I have already ordered the Evo prop driver. but why wouldn't they put a prop driver on the .45 to begin withm instead of the flywheel. Does it make a difference.

I should finnally be able to get it up tonight if the weather holds.

Righty,

I would go with the 11" prop. A 10" is, in all probability, not only going to allow the engine to over rev, but you are not going to get the power you should from it.

If ground clearance is a concern use larger wheels. When flying from a grass field I like to use
3" - 3 1/4" wheels - makes it easier to get up if the grass is a little long.

the largest wheels i have was 2.75 so i put them on. I don't see why a 10 size prop would over rev. cause i was using 10 size props on my alpha with the same engine with no problems. We'll see tonight when i take it out to the field.

I have a minor problem with APC props on trainers -- while they are superb performers, they are too brittle, & a trainer is going to get a lot of abuse. The old Master Airscrew will be a better bet for this job -- it is much tougher than an APC & will still do an adequate job of towing the model around.

I can use the 11 inch props, but have to taxi and take off with full up elevator. It isn't a problem if I remember that I only have around 1 1/2 inch clearance.

Well I finally got to the field to maiden the pattern master, but no one was there...

So i taxied around for 20 minutes and came in fueled up and switched to the three blade Evo prop that came with the engine, and i let'er rip. A little nose heavy but bingo field found out what the CG for me should be and i was off by about 2 inches. other then that she flew great. i noticed that my rolls were faster and the plane didn't point down coming out of a roll. going from a high wing trainer to a plane like this is noticable different but i feel it suits me better. I forgot how nice trike landings were. all you do is flare when your just off the ground. I think i love this plane. When i'm at the field next time i'll try to take some pics and maybe a little video.

Now i can think about what my third plane will be. but now i'm gonna have to put more hours in at wal-mart. I hate minimum wage!

Righty, aint that the case? You just get another plane. Try it out with your first maiden on it. Then, you think what your next aircraft is!
I do this all the time. My latest has been binge buying. In the last week, I have bought a T-52 (gonna be buggy motor powered and my winter electric with skis), an Omei sailplane, and a new U Can Do 3D 40 and .46 engine. I seem to tend to go overboard with these buying binges. I have thinned out my electric fleet somewhat in order to include more glow power. Theres something about a glow engine
purring as your plane buzzes the field! I kinda like the sound!!

Dave...

Flyinf the pattern master for the first time felt like i was starting over. in a way the controls felt way different, but the same. That makes no sense, but do you get my point.

Righty

I felt that way going from my Lt-40 to my 4 * 40 (very similaiar to your pattern master)then to the H9 Twist. I still have all 3 but I find myself torn between the 4 * and the Twist. I just converted the LT-40 to a taildragger and propped it with an APC 12.25X3.75. Now it's a totally different plane. I do run an APC 11X7 with a Saito 56 on the 4* just cause I like the speed I get. I did by new main gear and 3" wheels to get the ground clearence for a 12 inch prop if I decide to.

I'm allot like LuckyArmpit, my binge buying has me eyeing up a SIG something Extra ARF or a SIG Hog Bipe kit or I just may say the heck with it and get both and build the Bipe over the winter. SOOO MANY PLANES...Not enough money...