Quote "The idle is as low as it will go. when on the ground at idle it will barely move."

Just curious, what rpm is your idle. If you are on grass your plane should not move at all at idle. But if you fly off concrete, it'll almost take off at idle. Are you landing on grass or a hard runway?

I don't have a tach yet.. one of those things that gets put aside for new planes. My first test flights were on cement and unless you gave it a bit of a push to get it rolling the idle would not get you rolling, and no there is no excessive friction in the wheels.. It is just a very smooth low idle motor. Something interesting I just learned today from an old hand at R/C said that for every 2000 feet in elevation you need another inch or foot? of pitch to compensate for air density. I am fairly happy with the results of testing different props. I tried a low pitch 12 inch prop today (since we were on cement this time)(ground clearence) It was like having massive airbrakes on a glider. It means having small amounts of throttle on landing. ( which I prefer ) Seemed to make it a bit easier for the father inlaw to set up his apporaches this way. After he learnes a bit more about airspeed control, I am planning on switching it back to a 11X6 to make it more of a challenge to set up his approach.

FW

What was the pitch on the 12 inch prop? Just wondering. Thanks...

I went with the 12X4 like you had suggested. was a bugger to find. had to dig in the bottom of a discount box at the LHS! lol guess not to many people have gone to this extreme, but in my case the curiousity definately killed the cat. dune skinned him too Thanks AQ

Cheers,

FW

BTW on a full scale story. Was sitting right seat today in a Pilatus PC-12. we did a zero pitch (2.4 torque) in other words zero thrust practice decent to landing from FL 160. about 15 miles from the airport (5588 in Alt). goes to show even a 10,000 pound airplane glides pretty far with no drag from the prop.

Seems to me that I can make my trainer float the whole length of the runway also. My instructor has been teaching me how to use the elevator to scrub off speed and put the wheels on the runway. I don't know how many times he's taken control of the plane to power up and make me come around for another pass. Practice, Practice, Practice. You say you're not a newbie but even the old timers at our field need a little coaching from our instructors once in a while. Even our instructors, for that matter, need a little coaching from time to time.

I, too, consider myself a novice at prop selection (and many other realms!)

Just finished a 79" Spacewalker and started with the YS91 recommended prop - 14 x 10 (as I remember)

Couldn't get it landed. Let the masters try it....couldn't get it landed (properly)....

Finally, last weekend I came equipted with a battery of different size props. Each flight, a different size prop, different manufacturer.

Finally found that the 14 x 6 was the key. Boy, what a difference in how it slowed on final! The wooden Zinger and Master Airscrew slowed much better than the agressive APC.

From a ten (10), to an eight (8), to a six (6) pitch made a big difference in the breaking aspects of the plane. APC to Zinger added to the joy.

It is gratifying to read the suggestions of all of you knowledgeable guys, wish you were all in my club...

I agree crash. Many times it seams people just accept a way a plane flies and chalk it up to "you have to land it this way" or "you don't know how to land it" sometimes palying with different parameters makes a HUGE difference. I am pretty happy now with what I have learned, and I am sure it will make a difference in my modeling in the future. or as my other half say's. "oh great! more excuses for you to stay out at the field longer" *laugh*

Cheers,

FW

I can't believe how much change prop pitch makes. Props are relatively cheap too, depending upon size, which i find amazing that something that cheap can change the whole flight characteristics of an R/C airplane.

Hey Fourthwind - You are right on for experimenting with props. I have had a Goldberg Extra 300 for years and used to run a 14X10 prop on a YS 120. It always tended to float and made for long approaches and roll-outs. I figured it was just a clean plane and left it at that. Finally I did a little research and decided to try less pitch (but more diameter to not over rev the engine). The difference was amazing. It is still forgiving on landings but can make a much steeper approach. It also made for better vertical and more realistic speeds at full throttle. Beginners and experienced pilots can all benefit by experimenting with props.

If I increase pitch will I get more pulling power(more vertical) and less speed in level flight ?

If I lower the pitch less vertical and more speed in level flight ?

What would be the effect if I increase pitch only , lets say a 10X6 to a 10X7 ?

What would be the effect if I change Prop length only, let's say a 10X6 to a 11x6

What about both, a 10x6 to a 11x7 ?

Thanks
Jim

I think you got backwards Jim, more pitch gives you top end speed with sluggish vertical or static thrust. Less pitch and bigger diameter would work on the opposite fashion.

funny no one mentioned a 3 blade prop makes a ton of difference on an Alpha like 2 different planes.

I got a Phoenix Classic trainer a while ago with an O.S 46AX on it. The motor has an 11x8 Master Airscrew prop on it. From what I can gather this thing is going to be incredibly fast ?

I am yet to even fly it so dont want it to be a monster just yet.

I live in the second windiest city in the southern hemisphere (Trees grow sideways!!) and I am guessing he has this sort of size prop so the plane will actually fly into a decent headwind perhaps?

After all I guess I dont have to fly flat out the whole time

I have an APC 11x6 here but cant get the spinner to fit over the blades on the prop without warping the spinner (It's a plastic spinner).
Is it ok to shave a little bit off the prop slots in the spinner cone to fit the prop or will that lead to problems with the spinner? I use a chicken stick to start the plane.

11x8 seems like a lot of pitch for a 46 engine. 11x6 would likely be better. Trim the spinner so it does not touch the prop; if it touches it will cause the prop to break. Keep the slots as close as possible to the same size.

Thanks Carrellh.
Woke up late this morning and the wind was really gusty. So grabbed the plane swearing and muttering under my breath about sleeping in and went out to the field. A lot of the guys were packing up and leaving as I got there, but three guys hung around and helped me out heaps. Tuned the 46AX for me as it used to run 15% nitro and I had bought a bottle of 10% by accident. In very little time after a range check etc my unofficial flight instructor Norm said he would take it up and trim it out for me, but the club buddy lead was nowhere to be found. So he took it up and got the TX trims sorted (non-computer radio) for me and bought her in for a landing. His first impression was it was very quick and I then mentioned the 11x8. So yeh I will be dropping the pitch back to an 11x5 as I have one of those and might grab a couple of props at the end of the week to play around with at a later stage.

But will keep the 11x8 in the toolbox for later anyway

All in all was awesome to see my plane fly at least. Bit disappointed I didnt get any stick time, but the wind had picked up to a pretty nasty pace and not constant wind it was really turbulent. So better to wait til next weekend and I will be sure to get to bed at a decent time so I can wake up at 5am instead of 10am [&o]

Hi!
A 11x8 prop is way way too much pitch for a .46 twostroke engine. It's for a.61 two stroke!

When you fly a .45-.46 powered trainer airplane and most low winged sport airplanes an 11x5 or an 11x6 APC, RAM or Graupner cam-prop is what you should use. In a fast, small, Q-500 type airplane a 9x7,9x8 or 10x6, 10x7 APC could be used.

Regards!
Jan K
Sweden

Thanks for the info. I did notice in the destruction manual for this motor that it recommends a range of 11x6-11x8 in the prop selection. But I agree and so does my instructor who flew it today that that prop makes for hot landings. So I have a spare 11x5 sitting here I will put on for my first flight next weekend.

Thanks again

APC 12-4 -- it will give you entirely adequate airspeed, better climb than the 11-6 & slow you down very well. As you already said, the 12-6 is too big -- much too big. Whatever you use, you want to reduce the pitch, but reducing the pitch means increasing the diameter to keep the correct engine load . Assuming that the engine is idling as slowly as is reliable, you want to cut the propeller idle-speed discharge velocity, but maintain the correct load on the engine. ----- APC 12-4.

Thanks for the info. I will grab a 12x4 as soon as my hobby shop can order one in.

Will the 11x5 be ok as far as engine load goes?

Don't want to over-rev the engine and kick a leg out of bed or anything stupid. I wont be flying at full throttle, but tuning at full throttle could cause hassles?

Want to go out this weekend and get a good days learning in. And the hobby shop only has monstrous 12x6+ sized props.

On a side note I cant wait to get my Dave Brown fuel pump and Great Planes filling can setup. Filling the tank with a squeeze bottle is no fun at all.

11-5 is good -- better than the 11-6

A couple rolls of pennies or a railroad spike will stop the plane from floating, and doesn't cost too much either

Actually,
--Tack streamers on to up the drag, not like a trainer needs to go 75mph anyway
--Shim / washer the rear of the wing 1-2mm to get a more neg inc to gain drag & offset the abundance of lift. I had to do this to a 6' glider I put a pair of Norvel074 on, so much speed was a pain to stop from climbing without shimming the wing, all landings had to deadstick
--Flywheel a small prop with a big spinner, or even a fenderwasher or 2 on the propnut for flywheel, made my 4stroke sound like a Harley.... ok, not just like a harley, but I used personal bias listening to think of it that way.
--Put actual flaps on: split flaps & a $9 servo