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Pitch vs Vertical Perfomance & Downline Braking.

Old 03-05-2010, 12:54 AM
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Rendegade
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Default Pitch vs Vertical Perfomance & Downline Braking.

Okay guys, I'm having a small breakdown here trying to get my head around pitch, downline braking, and vertical performance.

I have my 140 powered ship currently swinging a 17x12, and I'm getting overspeeding on the downlines. Some searching on the subject revealed that a few people have suggested the 17x13 to give better downline braking, and a little better vertical.

I'm cool with that, and will give it a try this weekend, BUT!

In shuffling through the IMAC threads, everyone is swinging larger diameter, lower pitch props and saying their downline braking is great.

I've got a CAP 232 with an OS 160FX swinging an 18x6 on it (as suggested by every man and his dog on FG) and I can't help but feel that it's all wrong. I think a 17x10 would be better, but this is counter intuitive to what the IMAC boys believe.

I guess my question, is who's right, and why?
Old 03-05-2010, 01:08 AM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Decreasing pitch (no change to diameter) will increase downline braking, AND reduce top speed, and increase noise. IF the engine was "overpropped" and lacked sufficient torque to maintain RPM in vertical uplines, the speed in uplines might increase.

Increasing diameter (no change in pitch) will increase downline braking, AND likely reduce top speed, and likely increase noise (unless the RPM really drops off due to the engine becoming very overpropped). Speed in uplines might increase (if the engine has enough torque to maintain RPM in an upline).

In general, IMAC planes tend to use larger diameter lower pitched props to overcome the greater drag of the IMAC style planes. Pattern planes and the pattern style of flying generally benefit from more pitch. If you want to do upline snaps, especially with a draggy plane, you will want to use the larger diameter / lower pitch prop which will generate more thrust, at the expense of top end speed.

Regards,

Dave

Old 03-05-2010, 01:11 AM
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Rendegade
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Ahh, ok so everyone's right, airframe dependant.

I'll stick with what I'm doing then!
Old 03-05-2010, 04:01 AM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Dear Rendegade;

I suggest you to test APC 18x10, after switch from 17x12 I do not came back. 17x13 was too much propeller for 140RX in my opinion but if you plane is very light it can work. I use only 15% nitro.

Best Regards. Alfonso.
Old 03-05-2010, 12:01 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Rendegade

I fully agree on the 18*10. I use the 18.1*10 APC on my integral. Its better than the 17*12 as used before.

Regards

Werner
Old 03-05-2010, 05:09 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

One thing to check is whether your low speed needle is too lean. A lean low end needle will cause the engine to stay pretty well wound up on a downline, so you may want to try richening it a bit at a time to see how far you can go before you don't like the rest of the low to mid-range response (especially when throttling back up).
Old 03-06-2010, 01:35 AM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.


ORIGINAL: Rendegade

Okay guys, I'm having a small breakdown here trying to get my head around pitch, downline braking, and vertical performance.

I have my 140 powered ship currently swinging a 17x12, and I'm getting overspeeding on the downlines. Some searching on the subject revealed that a few people have suggested the 17x13 to give better downline braking, and a little better vertical.

I'm cool with that, and will give it a try this weekend, BUT!

In shuffling through the IMAC threads, everyone is swinging larger diameter, lower pitch props and saying their downline braking is great.

I've got a CAP 232 with an OS 160FX swinging an 18x6 on it (as suggested by every man and his dog on FG) and I can't help but feel that it's all wrong. I think a 17x10 would be better, but this is counter intuitive to what the IMAC boys believe.

I guess my question, is who's right, and why?
The 17x13 will not break better than the 17x12. Higher pitches generally don'tbreak as well as lower pitches. Diameter is king however due to larger disc area. Better breaking can be had from an 18.1x10. You have both larger diameter and lower pitch, both working together to lower speed everywhere.

Depending on how clean the airframe is, the 17x13 will tend to pick up lots of speed in horizontal flight and throttle management becomes very important. Your timing could be changed. With the 18.1x10, the plane is slowed down a bunch so that might be a little easier to control.

MattK
Old 03-06-2010, 04:49 AM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Well, this weekend, I failed badly because I did too many things at once.

My biggest downfall was going to a tx-tray. I felt very awkward, and spent the flight worrying about the tray breaking, or the radio slipping out, or some other nonsense, and just couldn't get in the groove, and had a less than neat landing. I don't think I'm cut out for trays.

That said the 17x13 gave me a bit more speed, uplines were fairly good (considering the aircraft is long, low and light!) and the braking felt a little better, that said I attibute this more to the lower prop speed I was getting at idle.

I think the pipe's a bit long too.


If I can find an 18x10 I'll give it a go.
Old 03-13-2010, 07:39 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Try and stick with the tray. You'll get used to it and never go back to "thumbing" it!! Pinch 'em instead! I suggest extending the sticks as far out as they'll go and tightening the stick tension. See your manual on how to do this. I have the biggest sticks that JR sells on my 9303 and love them. Just go to the JR site and they are in there but a few pages in. Hope this helps.

Cheers

MJ
Old 03-14-2010, 07:53 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

I stole Quique's method, which is a strap, and two hooks on the base of the tx that connect to your belt buckle, and then I can pinch or thumb depending on how I feel. I already have the sticks as far out as I can, and this method feels quite natural, as the tx is angled slightly down. My main issue with the tray was the feeling that the radio was too far away, and the overriding fear that the tray will suddenly fall apart and I'd lose my TX!
Old 03-15-2010, 04:12 AM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

I'm using the 18x10 on my RX.1.40.anything under 1/4 throttle is like using an airbreak.You have to keep the power on much longer during manouvers.The only down side was that the prop hub is far bigger than normal, thus is too large for your average F3A spinner back plate.Just remove the spinner and try it out. It'll get you there.As mentioned, it's like throwning out a parachute compared to the 17x12/13.
Old 03-15-2010, 06:39 AM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Just so we're all on the same page the APC 18X10 and 18.1X10W are two totally different props.

The 18X10 has a huge stepped hub (44mm OD ) and chord tapers in fairly much a straight line to the tip and whether it performs well or not, it is WAY too ugly to put on any plane. Also the standard prop driver on the 1.40RX (34mm OD) and DZ170 (30mm OD) is too small to engage the full rear surface of the hub (28mm ID/ 44mm OD) and raises a safety issue.

The 18.1X10W is the more traditional pattern prop blade shape we expect from APC and has a "normal" sized hub. I can't comment on the in flight performance of either yet but it just looks better.

Old 03-15-2010, 12:19 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.


ORIGINAL: bjr_93tz

Just so we're all on the same page the APC 18X10 and 18.1X10W are two totally different props.

The 18X10 has a huge stepped hub (44mm OD ) and chord tapers in fairly much a straight line to the tip and whether it performs well or not, it is WAY too ugly to put on any plane. Also the standard prop driver on the 1.40RX (34mm OD) and DZ170 (30mm OD) is too small to engage the full rear surface of the hub (28mm ID/ 44mm OD) and raises a safety issue.

The 18.1X10W is the more traditional pattern prop blade shape we expect from APC and has a ''normal'' sized hub. I can't comment on the in flight performance of either yet but it just looks better.
The 18x10 actually does perform well and has good braking, but is a bit loud, but yes, it is a bit ugly for a pattern plane (not to mention quite heavy).

AND...to complicate things further....there are actually 18.1x10, 18.1x10W, 18.1x10.1, and 18x10PN. I never ran these props extensively on glow, but used them a fair bit on higher KV electric setups (running the same RPM as glow would), and my preference was for the 18.1x10.

Regards,

Dave Lockhart
Team Horizon, Castle, Tech-Aero
Old 03-15-2010, 03:55 PM
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Jeff Boyd 2
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

I was running the 18.1 x 10W on an piped OS160 in a Integral. It was good but seemed a bit too much prop for it, and I am SURE it would be too much for a 140RX. I now use a 18.1 x 10 cut down to 17 1/2" (is that now a 17.5.1 x 10?? ). The motor sounds a lot happier on this prop, and it's quiet . . I would like to try it on a 140RX (if I was still flying with one) . . I think it would be sweet !

Cheers, JB
Old 03-15-2010, 04:18 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.


ORIGINAL: Jeff Boyd 2

I was running the 18.1 x 10W on an piped OS160 in a Integral. It was good but seemed a bit too much prop for it, and I am SURE it would be too much for a 140RX. I now use a 18.1 x 10 cut down to 17 1/2'' (is that now a 17.5.1 x 10?? ). The motor sounds a lot happier on this prop, and it's quiet . . I would like to try it on a 140RX (if I was still flying with one) . . I think it would be sweet !

Cheers, JB
I don't know what the wide blade buys you. In my experience it buys nothing and actually may hurt performance unless the engine is strong
The webra 160 had no problem swinging this one but I had no improvement anywhere in the flight envelope.

I changed the 18.1x10 by lengthening the tips. The modified prop was a 19x10 and it barely tamed the webra 160...but again to what end? There was virtually no improvement anywhere in the flight envelope. Expectation was at least a slower downline but in practice that didn't pan out

MattK
Old 03-15-2010, 06:29 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Just had a quick read of the rules, is variable pitch for IC and Electric allowed again providing it's not automatic?

This would allow the use of throttle and pitch curves as used by the heli guys, ang give us IC users "active" braking...

Just another thing to spend money on
Old 03-15-2010, 08:13 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Prettner used it. Tony Frakowiak used it, Steve Helms used it.

I had thought that it might be a better way to get a more useable power curve from a smaller capacity engine.
Old 03-15-2010, 09:02 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

Yeah, variable pitch used to be OK, then it was banned but I can't see in the rules that it's still banned today.

Maybe with electrics and the larger 4-strokes having more than enough power and downline braking there's no clear advantage to it any more so it's been opened up to allow those who like to fiddle?
Old 03-17-2010, 12:52 PM
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Default RE: Pitch vs Vertical Perfomance & Downline Braking.

I think I remember reading that variable pitch was only banned if it automatically changed pitch. If the pitch was controlled by the transmitter, it was still allowed.

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