Just put Evolution 61 on a Seagull Decatlon 40 plane and i am very dissatisfied with the performance. I tried a 11 X prop turning 13,300 RPM and the plane had very little power or speed. I then tried a 12 X 6 prop that was turning 12,600 RPM. It was better but still top speed was slow ans vertical climb was pretty limited. I am assuming this is a prop problem but does anybody have any idea on what to try? thanks

Try an 11-7 1/2 Master Airscrew. Balance the prop and spinner.

FBD.

Mark,


I agree with Dave about the balancing of the prop and the spinner.
About the make of the prop, I do not, however.

Master Airscrew black GFN props, up to 11" diameter, may spin a bit faster than an APC of the same size, or a +.5" Bolly prop. But their thrust and model performance is visibly inferior.

The Scimitar MA is much better, although the RPM will be lower.

The larger 'Four-Stroke' MA props, 12" and larger, are a real burden on the engine, compared with APC props of the same sizes. But they are somewhat more effective.


You did not write the pitch of the 11" prop that you used and the make of both.

I have an older OS .61SF and a 12-6 is not enough for it. I found an APC 12-7 works best. A 13-6 also works well. With a draggy scale plane a small diameter prop is not the way to go.

Many years ago we all ran 11-7 & 11-7 1/2 props on .60s. Today's engines have a lot more power so you do get a lot of rpm, but it may not be translating into useful power unless you have a light, streamlined plane, which a scale Decathlon is not. I see lots of people running 11-7s and 12-6s on .46s and for sure on the .52/.53 engines. i still like an 11-6 on a .46, but the planes do fly well with the larger props.

Thanks for all the info.
1 both props were Master Airscrew K series.
2 the props were a 11 x 6 and a 12 x 6
3 As of yet, I have not mounted th cowling or installed the spinner. I am just using a weight prop nut.
4 Props were balanced using the Dupro finger held balancer

The LHS was out of anything larger than a 12 X 6. I'll have to see if I can bum one from someone at the field tommorrow. I'll let everybody know what happens....thanks

Mark,


The K-Series is Master Airscrew's four-stroke prop.

My experience is that from any performance standpoint, your model will fly better with an APC, or with a Bolly.
The difference is really visible.

The finger balancer is okay at the field...maybe, but you may get more accurate results putting it between 2 glass drinking glasses. I did that for a while before buying the whatever model Dubro balancer. I forgot the model of it. Costs around $25 and is more accurate over finger balancers.

Barry,


The imbalance in any single-cylinder engine is quite large.
Much larger, in fact, than on most props.
It is also unsolvable by any conventional means.


Even if your prop and spinner are balanced to perfection, your model will still shake....

The finger-tip $2-$4 balancer is the most you should ever need to spend.


If you want to read more, please do a search in RCU for engine and prop balancing threads.

Dars, ....you're kidding about all this, right ?

Dave.

Dave,


No, I am not!

Please reminisce on these threads about engine and prop balancing, in which even you took a part.

[link=http://www.rcuniverse.com/forum/m_1133499/anchors_1133499/mpage_1/key_prop%252Cbalance/anchor/tm.htm#1133499]Thread 1[/link].

[link=http://www.rcuniverse.com/forum/m_987339/anchors_987339/mpage_1/key_prop%252Cbalance/anchor/tm.htm#987339]Thread 2[/link].

[link=http://www.rcuniverse.com/forum/m_780489/anchors_780489/mpage_1/key_prop%252Cbalance/anchor/tm.htm#780489]Thread 3[/link].

[link=http://www.rcuniverse.com/forum/m_671471/mpage_2/key_prop%2Cbalance/tm.htm]Thread 4[/link].

[link=http://www.rcuniverse.com/forum/m_1393160/anchors_1393464/mpage_1/anchor/tm.htm#1393464]Post 1[/link].

I have said it all along.

A $20 magnetic/quad roller balancer is a waste of money, as you would not feel its contribution, over the fingertip balancer and not even over balancing the prop on a knife-edge.

This, unless you are running a horizontally opposed piston engine, with a 180 degree crankshaft (simultaneous firing two-stroke, or alternate firing four-stroke). In such engines, the primary vibration is canceled out and only second (and third) order vibration is perceivable. There, you might feel the advantage of a prop balanced on a more elaborate balancing device.

current single cylinder technology and ignition design-produces singles which are glass smooth in actual operation.
My new models -even a 10 lb Funtana equipped with a 25cc single, also my 23 lb EXTRA with 80 single - do not shake-at idle or thru acceleration .
Theory and old info on single cyl unbalance is well known
Some single do shake - and 4 stroke glow engines of large displacement and high compression are among the worst - timing is simply a result of heat/pressure /fuel.
Gasoline setups with well designed and tailored ignition curves ,do wonders for the vibration problem and virtually eliminate the classic 2500-3500 rpm shake or the rough idle.

And now - back to the movie-------------where we find Stanley saying to Oliver ---

I don't know about that part of balancing of the finger balancer vs more accurate ones. I know that the finger balancer leaves a lot of room for errors. Maybe the finger balance range of error is good enough, if you are on the right side of the error range. I would think that getting it balanced better won't hurt anything.

I had a very bad problem with the Evo 3 bladed props and they vibrated landing gear bolts loose after a couple of flights every time, and eventually shook out 3 engine mount bolts from the firewall. Luckily, I found the problem before flying again even though I had to cut a hatch, replace 2 blind nuts, etc to patch up the damage.

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