prop advice needed
08-04-2003, 02:21 AM
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prop advice needed
Thanbks to the great advice I received at this site I'm now able to get me H9 J3 Cub safely off the ground. It flies great but the problem is that it's a real floater. I have an OS .46 FX in it and have it idled down pretty slow. I am trying to make approaches as low as possible but have to keep clear of trees. Right now I have an APC 11x6 prop on it. Will changing prop size help as a brake effect. Any suggestions? Also have a CG Ultimate ready to get into the air. It has a ST,75 for power. I'm not into extreme aerobatics ie: (not able) but would like just all round good performance. Any suggestions on prop size would be appreciated. Thanks.
08-04-2003, 02:51 AM
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Different props,
Check out this link to Tower Hobbies spec sheet of your engine.
It lists quite a few prop sizes you can try. Basically, you want to reduce the prop's pitch, say to a 11x5, or even a 12x4. With the decrease in pitch, you'll lose some overall top speed but will have greater vertical pull. When you throttle down for a landing, the lesser pitch will also slow you down. Look at all the props the .46FX can use:
http://www2.towerhobbies.com/cgi-bin...=++&search3=Go
Just experiment and see what works best for you. Get a good tachometer and keep an eye on your top RPM's. Don't exceed the recommended range. You can also use the tach to set your idle and make sure it is as low as you think it is. Good luck.
Jesse
It lists quite a few prop sizes you can try. Basically, you want to reduce the prop's pitch, say to a 11x5, or even a 12x4. With the decrease in pitch, you'll lose some overall top speed but will have greater vertical pull. When you throttle down for a landing, the lesser pitch will also slow you down. Look at all the props the .46FX can use:
http://www2.towerhobbies.com/cgi-bin...=++&search3=Go
Just experiment and see what works best for you. Get a good tachometer and keep an eye on your top RPM's. Don't exceed the recommended range. You can also use the tach to set your idle and make sure it is as low as you think it is. Good luck.
Jesse
08-04-2003, 03:14 AM
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prop advice needed
Try an APC 11.5x4...That ought to do the trick pretty good. Will really add to the braking effect. It's a wider blade, with less pitch...You might want to try a 12x4 and a 12.25x3.75 as well and see which one you like the most.
08-04-2003, 04:02 AM
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prop advice needed
Any cub will float if you handle it wrong. Coming from flying a full scale one I can tell you what I see on the field.
Even tho I'm new I see a LOT of people that try to fly an approach or loose altitude nose down. Ever watch a full scale plane land? They don't nose over to loose altitude.
The way to loose altitude and speed at once is idle down AND keep the nose up a bit.
The reason the cub floats is if you point it the slightest at the ground it picks up speed - even the slightest speed will give that wing enough lift to float.
Bleed off airspeed in an approach by idling down, keep the nose up enough not to loose altitude - when you do that you loose speed. After you slow down you can start dropping the nose down a bit to start loosing altitude.
It's just like a full scale, you don't point it at the ground and idle down and expect to keep the same speed and loose altitude.
Even tho I'm new I see a LOT of people that try to fly an approach or loose altitude nose down. Ever watch a full scale plane land? They don't nose over to loose altitude.
The way to loose altitude and speed at once is idle down AND keep the nose up a bit.
The reason the cub floats is if you point it the slightest at the ground it picks up speed - even the slightest speed will give that wing enough lift to float.
Bleed off airspeed in an approach by idling down, keep the nose up enough not to loose altitude - when you do that you loose speed. After you slow down you can start dropping the nose down a bit to start loosing altitude.
It's just like a full scale, you don't point it at the ground and idle down and expect to keep the same speed and loose altitude.
08-04-2003, 06:09 AM
#5
prop advice needed
Norm if you are trying the prop thing and of course slowing the airplane down for approach and still not getting an adequate rate of descent to meet the parameters of your field there is an old rigging trick that will improve things.
Simply unscrewing both aileron pushrod clevis' equally two or three turns so that both aileron trailing edges are 'reflexed' up a bit. In other words the aileron edges are not inline with the rest of the wings trailing edge but up a few degrees. This will increase takeoff distance almost imperceptibly and increase the aircrafts speed in level flight very slightly for any given power setting but will yield a higher sink rate at any given approach speed to make things easier.
Just a thought.
John
Simply unscrewing both aileron pushrod clevis' equally two or three turns so that both aileron trailing edges are 'reflexed' up a bit. In other words the aileron edges are not inline with the rest of the wings trailing edge but up a few degrees. This will increase takeoff distance almost imperceptibly and increase the aircrafts speed in level flight very slightly for any given power setting but will yield a higher sink rate at any given approach speed to make things easier.
Just a thought.
John
08-04-2003, 10:28 AM
#6
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prop advice needed
John,
I usually agree with your advice, but not in this case. First time to the field with my Cub it drove me nuts. Getting it off the ground was TOUGH, which just isn't right for a Cub, they usually leap off and require a bit of down as soon as they break ground.
This one acted tail heavy when it broke ground, wallowed around a few feet off the ground, etc.
After a couple of attempts I started taking a serious look at things and found the ailerons reflexed up just a bit. Not sure how I'd managed that but....
Once I took it out, the Cub's take off performance improved dramatically. And it flys just like a Cub.
Norm,
As others have said, try the larger diameter props. Larger diameter WILL slow down your approaches. Smaller pitch slows down overall speed, but the diameter will act as a brake.
Dennis-
I usually agree with your advice, but not in this case. First time to the field with my Cub it drove me nuts. Getting it off the ground was TOUGH, which just isn't right for a Cub, they usually leap off and require a bit of down as soon as they break ground.
This one acted tail heavy when it broke ground, wallowed around a few feet off the ground, etc.
After a couple of attempts I started taking a serious look at things and found the ailerons reflexed up just a bit. Not sure how I'd managed that but....
Once I took it out, the Cub's take off performance improved dramatically. And it flys just like a Cub.
Norm,
As others have said, try the larger diameter props. Larger diameter WILL slow down your approaches. Smaller pitch slows down overall speed, but the diameter will act as a brake.
Dennis-
08-05-2003, 04:37 AM
#8
prop advice needed
I have a few OS 46 engines (2FX and 2SF) and on the planes I wan't to slow down I use the 12x4 APC, One plane I have glides better than a Kadet (Known to glide forever) It is a Ultrasport 40+ with a YS 63FZ on the nose and this thing just does not want to come down, How I get this one to land is get a long approach to bleed off the speed a little and actually have to fly it right onto the ground and as soon as the main wheels touch it starts slowing because of the drag and a little up and it puts the tailwheel down. First flight with it really surprised me but I did dead stick it that first flight about 50 feet up and circled 3/4 the way around the field, That's when I knew landing this one was going to be a little work, Been doing good so far, I would try the 12x4 on your plane and do what Borzak suggests and you should have better luck with your landings.
Dauntae
Dauntae
08-05-2003, 11:46 AM
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prop advice needed
Being poverty-stricken, I was limited to a ocuple engines and manipulated prop sizes to get a plane to handle the way I needed it to. My Goldberg Cub used an Enya .40SS (bushing) engine and 11x5 prop. My brother's Cub had a K&B .61 with a 12x4, I think - maybe a 13x4. It's an issue getting 'em down out of the sky if you have an engine that doesn't have a really slow idle speed.......
