beachbrada

My Feedback: (17)

Im running a 16x6 on my Saito 125 and I cant get it over 9000 RPMs, the highest so far has been about 8700. I know that if I go with a lesser pitch or smaller diameter I will get better RPM's, but I dont want anything less than a 6 pitch. So what kind of gain or loss in performance would I see with something like a 15x6 or 15x7?

RCKen

My Feedback: (9)

That RPM sounds about right for that engine. I wouldn't spend too much time trying to get as many RPM's as you think it should get. If you are basing that goal on what the manufacturer claims then I wouldn't worry about it, as real life never matches what they "say" it can do. The 8,700 you are getting is right about what they engine should put out. Base your prop selection on what you need the plane to do, not *****g out the engine. 4-strokes aren't designed for high RPM's, if that's what you are aiming for get a 2-stroke.

Ken

CGRetired

My Feedback: (1)

That is especially true for four strokes engines. They are capable of more torque and don't need the RPM as two strokes do to get into the upper end of the power curve.

I have three OS 1.20 AX engines, all two strokes, and they run very well at about 9000 RPM and a 15-10 prop. The performance I get out of these engines is exactly what I expected (actually more), and I would never try to get more RPM out of them.

Just remember that noise does not necessarily equate to power, but can create some serious problems with that engine. If you can get them to perform as you want them to perform, at a lower RPM, then be exceptionally happy with how long those engines will last.

CGr.

Jetdesign

My Feedback: (8)

I just got a YS 110 four stroke, and that only gets about 9400 with a 16x6 and it's supercharged. I wouldn't expect much more than you are getting.

beachbrada

My Feedback: (17)

I knew before I posted I was going to get a reply like this, lol, but to be honest Ive heard in other threads that 8700 RPMs is about right but I still wanted to post my question to see what the difference in performance would be by changing to a smaller diameter prop with an equal or higher pitch. The whole reason why Im asking this question is because when I fly around at half throttle it seems like there is no power at all especially for this plane which only calls for a Saito 100. Half throttle will allow me to creep around as long as I dont point the nose up. Full throttle is more than enough power it just seems weird to me how big of a difference there is between full throttle and half. Ive also been wondering if weight is a factor, this plane is supposed to be close to 7 lbs but with the larger engine Im close to 8 lbs. It has 693 sq in wing area, so how does that factor in? Even with the extra weight she has a very slow stall speed.
I see you pulled the trigger on engine choice, how do you like the YS 110? I put a iron bay regulator on my Saito 125 to help with the carb flooding and boy was it a good investment. My transitions are so smooth and quick, it also incorporates a one way check valve on the exhaust line to help pressurize the tank. It does a really good job since everytime I take off the fuel line it hisses from all the built up pressure.

Jetdesign

My Feedback: (8)

I think you want more pitch. That will give you more speed at lower throttle and leave you with some power 'in reserve'. The beauty of a four stroke (from what I've learned so far) is that you will have the mid-range torque to accelerate a heavier loaded prop in the mid-throttle range. This is why I just got my first four stroke. My experience is that a large pitch on a two stroke takes longer to get up to desired RPM due to the lack of torque, but they have the ability to spin those props fast at high throttle. A four stroke might lose some top end RPM with the same prop, but spool it up to desired RPM almost instantaneously. This is the #1 sought after performance benefit of four strokes: throttle response (and of course there are other benefits).

"Pattern props" have very large pitches - 10" and more. I asked why this was, and found it is to allow the plane to fly at a decent speed at low to mid throttle, thus leaving plenty of power in reserve for vertical maneuvers (NOT hovering).

I don't know what the prop range is for your engine - is a 15x10 within range? If not, try a 15x8. There are lot of people who go with large diameter and shallow pitch props, but what the experts (Troy Newman, for one) are saying is that this ONLY benefits hovering; nothing else. It is really nice to have plenty of flying speed between 1/3 and 1/2 throttle (though not too low or it's hard to slow down for landing). This gives you more than half of your throttle travel in reserve. Am I repeating myself?[&:] Time to go

MikeL

My Feedback: (3)

8lbs seems really heavy for that AW Edge. Your engine isn't more than a few ounces off of the recommended engines. That's part of your weight gain, but not all of it.

Different airframes fly differently on different props. Buy a slightly smaller prop and see what it does. You do want to keep that engine under 10k RPM, though. Keep in mind that it's probably not completely broken in yet, and should get a hair stronger.

Your question about the throttle has to do with the RPM not being linear with the throttle position. If your radio has a multi-point mix, you can create a throttle curve. Tach out your high and low, and then depending on how many mid-points you have you can use the radio to make your throttle stick match your RPM curve.

mandtra

My Feedback: (29)

are you sure your throttle is set up correctly, and even? if not that may explain why your power curve is not even as it should be.

mandtra

My Feedback: (29)

I run a 17X4W apc on my Saito 125 with 30% Heli fuel on a Sig mayhem 3D at just over 8lbs and it will pull straight up out of sight

Gray Beard

My Feedback: (-1)

A rule of thumb is: a smaller prop and a bigger pitch= more speed and less torque. I like my planes to fly slower with more pulling power so I run a longer prop with a smaller pitch. I also have a number of different props for my engines and I test props until I find the prop that will fly the plane the way I want it to. There is no such thing as the perfect prop for an engine/plane combo until you discover it. As long as the engine doesn't over rev and the plane fly's the way you want it who cares about size or pitch?? I use a 16X6 or a 16X4 on my YS 1.10 in my HOTs, the 4 pitch works better for me but there isn't a huge difference, the plane is so over powered sometimes it's had to tell the difference. [8D]

KWJ48

There is also a difference between wood vs. composite prop also. The wood is typically lighter, and will give you a faster spool up.

Jetdesign

My Feedback: (8)

My Venus is close to 9lbs and a 15x8 (break in prop) has been pretty good for that plane. Unlimited vertical, 90mph on the radar, and totally floats around when I want it to. Now I've got more power though and will be switching to 16x8. 16x6 seems to be the common prop for my 8lb-ish Yak, or 17x4w for 3D, with both the Saito 125 and YS110.

Oh yeah this was about throttle response. Sorry I forgot[&:]

Gray Beard

My Feedback: (-1)

Joe, don't forget the 16X4W!! Just for grins!

Jetdesign

My Feedback: (8)

That's what I meant. 17x4w for the 120 2s, 16x4w for 110-125 4s.

beachbrada

My Feedback: (17)

You said you have more power now so you'll be switching to a 16x8, are you talking about your YS 110 having more power than the OS 120 AX? If so, whats the YS 110 hp rating, because the OS 120 is rated at 3.1 hp. My Saito 125 is only rated at 2.2 hp.

Jetdesign

My Feedback: (8)

Sorry Beach, it's past my bed time now that school's back in session! I meant the 120AX now has more power (broken in) and will be switching to a 16x8. The YS is rated at 2.2hp I think. It will most likely be swinging a 16x6 since that's what I saw in the best video of my plane.

Nighty-night[sm=sleeping.gif]

beachbrada

My Feedback: (17)

no problem, that makes more sense. When do you plan on having your plane finished?

Jetdesign

My Feedback: (8)

Engine comes today, fuel tank and stuff tomorrow, and I'm missing a few small parts for the control setup. I'm not flying again until May and am in no big hurry anymore to finish. There's a chance it will be done this weekend or next, but who knows? I obviously haven't flown the YS yet, but there is a video of my plane with the YS anda 16x6 and it is everything I could ever want and more

Let us know what you end up changing. I don't know anything about the throttle curves and am curious how it works out. IMO you've got one of the nicest planes out there with a good engine and I'm hoping to see you happy with it

I've got a 5" pitch on my Venus 40 and it sounds a lot like your issue-barely enough to keep the plane flying at half throttle, but a good amount of power at WOT. Maybe I should try an 11x6.

beachbrada

My Feedback: (17)

Which engine is coming in? Do you have a link to that video you saw. I have been trying to find videos of your plane.

Jetdesign

My Feedback: (8)

[link=http://www.rcmodelaviator.com/Videos/Yak69_YS110.wmv]Here is a link[/link] to the original plane that my plane is derived from - identical plane with different covering - with a YS FZ110-s which is the engine that's coming in today. This is with a 16x6 prop.

[link=http://www.rcmodelaviator.com/Videos/QQ-Yak69.wmv]Same plane w/ 120AX[/link] but not yet broken in.

[link=http://www.youtube.com/watch?v=VMjvEqeKhwQ]Here is a link[/link] of same plane with a Saito 125, but important to note a different prop.

[link=http://www.youtube.com/watch?v=IuIxoqMWzE4]This is the only video of my actual plane which is a copy of the one above[/link] I've been able to find; it's got a 120AX (two stroke).

Edited to better show that I don't 'pretend' to own a QQ plane. I thought I made that clear with the use of proper grammar.

MikeL

My Feedback: (3)

You didn't buy a QQ Yak. You chose to buy a cheap unlicensed knock-off, which makes you a party to stealing from someone who has done a lot for this hobby. Don't pretend that you have a QQ Yak.

Jetdesign

My Feedback: (8)

Point is show a plane in the same weight and engine size category as the OP, with different the 3 leading engine choices and different prop selection.

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My apologies for being a beginner, making an inexperienced decision on an airframe, and having it tarnish other people's threads with drama. [&o]

Gray Beard

My Feedback: (-1)

HAHAHAHAHAHAHA, this is getting fun now. Shame on you Joe.