Javelin II Pattern airplane with a YS FZ63-S..... the engine call for a 11-9, 12-7 or a 13-5
I have both APC and Zinger Wood with these size props.

Would the 11-9 prop be the best pick?

from what I have read in forums it seems best to stay away from large diameter low pitch props for Pattern flying.

I am new to Pattern and this will be the first 4 stroke engine that I will be running. (I have always used 2 stokes since I began flying)

Aray, I flew my Javelin with YS 63 using 12x7. Depending on what you're used to, it may seem like it's going a bit slow on the uplines, but it will pull indefinitely. I can't recall trying the 11x9, but I think 12x7 is the preferred size. This is a great combination, by the way, and an excellent first pattern model. I presume you fly with the Cape Ann club?

12x8 will work, I diden't like it sice it diden't allow for unlimited uplines on my plane. I like mine with a 13x6 better.

I have a KYosho Majestic 1400 as a winter plane and it's powered by 63FZ. My plane is 2,2kg in weight and I use 30% nitro in my fuel. The main interest for me is to keep the fingers moving during the long Finnish winter and not having to reinvent my F3A flying skills every spring.

I have tested diferent propellers and I find 13x6 APC the best. The other options were 12x7 and 12x8. 13x5 might be ok, but the engine will over rev as it is far more lighter to spin in higher speed. I get good power, rapid acceleration and top RPM around 11200rpm on the ground. In the air the plane performs jus the way I prefer. It brakes pretty well and I can get smooth power transition on low corners without having to throttle up in advance.

I think you should give 13x6 a try, you get the same speed the 12x7 gives but benefit from the 'stronger' performance on uplines.

I just took a look at mine, and it does have a 13x6 on it. Definitely better braking with the bigger disc.

I only plan on using 15% to 20% Nitro Fuel... so I would think a 13-5 would not over rev the YS-63.

I thought for Pattern Flying it is best to have a higher pitch prop?

I read that you can control the speed easier.

With a larger diameter prop the airplane accelerates faster when giving more throttle control versus a smaller size prop with more pitch. Isn't this less desirable?

The dry weight of the Javelin II that I put together came out to exactly 5 3/4 of a pound.

I know someone running a OS 70 Surpass and uses YS 20/20 fuel and runs a 12-6 APC prop on a Javelin II.
he has put a good amount of time on the engine and has not over reved it. we are on sea leval.

5-3/4 lbs is an awesome weight. Mine was 6 lbs 1 oz.

With a YS, you ought not to go below 20% nitro or performance will suffer.

As a general rule, a higher pitch prop will smooth out the acceleration when throttling up, but with a small engine your choice of prop size is constrained by considerations of braking (larger diameter brakes better) and operating on the engine's power curve (a matter of balancing fuel mix, glow plug and prop load). Those who fly higher pitch props (>8) do so on engines with plenty of power in relation to the model AUW, so they can have a big enough diameter for braking and still load the engine with prop pitch. I would not say the YS 63 has enough excess power on the Javelin to justify trading thrust for pitch.

Anyway, the real test is how does it fly, and the flight of the Javelin/YS63/13x6 prop does fly very nicely.

12x6 prop on OS 70 sounds right to me. The OS 70 does not have the power of a YS 63. The someone you're speaking of tells me his OS 70 is "adequate" power for the Javelin. I would say the YS 63 is also adequate, definitely not excess power for this model.

When you fly your plane, you can try whatever prop sizes you want, which is the best way to convince yourself. My recommendation, like the others, is APC 13x6.

Flew a Matrix 40 with SuperTigre 60 in pattern last season with an APC 11x9.
I tried several props but vertical performance was better with this one.
Flew a Venus 40 for awhile also with APC 11x9.

tommy s

Have you tried a 13-5 Zinger Wood Prop on a YS 63? or an APC 13-5 ?

And do the ACP props generaly put out more RPM for a given size? compared to a Zinger Wood prop.

From all my research... I know the YS-63 likes 11,000 RPM plus... better throttle transition... etc...

I never have tried a 13x5 prop on my YS 63, APC or Zinger. I have never tried to push my YS 63 over 11,000. I'm generally happy with anything over 10,000 static, then I know it will be over 11,000 in the air.

There is a world of difference between the razor sharp APC and the very ineffficient, thick-edged, blunt-ended stock Zinger. When I use a Zinger, I re-shape the tips to somewhat resemble the APC (more like a Zinger Pro), and sand down the thickness to get something closer to a feather edge on the tips and TE of the prop. I normally alternate between APC and Zinger depending on whether I want more weight in the nose or less. More weight with APC and TruTurn spinner (heavy backplate), less weight with wood prop & plastic spinner. I have never compared rpm directly between APC and Zinger of same nominal dia-pitch, but I do know I get a few hundred more rpm out of a Zinger between stock and modified.

I have a 63FZ on my Javelin II and swing a 13X6 using YS 20/20 fuel and it has plenty of authority in the air. You will want to bend up a new set of gear legs if you haven't already done so to move the wheels forward an inch or two and give you a bit more ground clearance. The stock gear will clear a 13" prop but it's awful close to the ground.