why using high pitch prop on pattern ?
 

Hi,
Can you explaine why pattern flyers prefer using high pitch props ? for example 17x10 and not 19x6 etc ?

Thanks,

RE: why using high pitch prop on pattern ?
 

Noise requirement for one. The other is to have the best all around prop for performance, constant speed and handling of most wind conditions. In my case, I am currently using a 20.5"X14" RASA carbon fiber prop.

RE: why using high pitch prop on pattern ?
 

For me the answer is multi-fold.  For one thing, ground clearance!  But I think we've grown accustomed to long gear legs for the electrics that are swinging 21" props.    The main reason is speed/torque.  The motors (YS) produce a TON of usable torque.  You can load them up and they'll just keep pulling.  So when you say 19x6 vs 17x10... I was running a 19x10!  So i'd need a 22" prop to get down to a low pitch.  

Lastly and maybe most important, is noise.  Prop noise is a major contributor to the noise output, and with strict noise limits, prop size is a critical factor in making the noise requirements.  Too big a prop at too high an RPM will put you over the Db limit in a hurry. So the mantra is high load, lower RPM, lower diameter.

RE: why using high pitch prop on pattern ?
 

Also RPM of motors. Many times, and especially with electrics, the RPMs are quite low (5-6000 RPM) so you need more pitch for the same airspeed.

RE: why using high pitch prop on pattern ?
 

I have been flying 1.20 size pattern planes for 2 seasons now. I started with a 10 pitch on a 2-stroke and moved to a 12 pitch on a 4-stroke YS, and now am flying a 12 pitch on an electric motor. I like the higher pitch as it gives a pretty good ground speed at lower throttle, leaving plenty of reserve for verticals to maintain constant speed.

I am trying to learn about prop stalls though; seems that when I enter the higher pitch props into the motor calculators, it warns of a loss of thrust due to the prop stalling. It makes sense since a prop is basically a rotating wing and higher pitch is a high angle of attack, and there's only so much AOA a wing can handle before it stalls. Once I get a little more settled this season I might start experimenting with the calculator and props to see if I can see or feel what it's talking about.

RE: why using high pitch prop on pattern ?
 

Thrust doesn't seem to be our problem, our models are very light compared to IMAC planes for example, thus we don't need big dia'/low pitch.<div>More to the point though, because F3A is flown out at such a distance 150-175m it just takes so damned long to fly across if the pitch is to small.</div><div>And we have a time limit to complete the sequence.</div><div>
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RE: why using high pitch prop on pattern ?
 

Aside from the excellent technical explanations given, that is a fine practical explanation I would not have considered!

RE: why using high pitch prop on pattern ?
 

That's true for FAI-F3A only.

The only time limit AMA classes have is in start-up...3 minutes to become airborne

RE: why using high pitch prop on pattern ?
 

No problem for my Focus II. Covers a lot of ground very quickly!

RE: why using high pitch prop on pattern ?
 

I am a Pattern flyer also flying IMAC and also prefer higher pitch props on gas engines. (DA 100L - Menz 26x12 at 7,000 ft ASL) for lower noise and constant flying speed. I also think it improves penetration at high altitudes, say compared to a 27x10. But my Extra 260 QB is a 75cc 32% weighing 22lbs. So I agree with the above on the question of weight.

I also tend to think that Pattern pilots tend to know how to trim planes better than the average IMAC flyer, without a Pattern background. ie the benchmark is how a Pattern plane flies.

RE: why using high pitch prop on pattern ?
 

For smaller diameter props, say less than 22", a 12" pitch seems to be a magical pitch for best all around performance compromise (thrust/speed, penetration, noise). Not sure that holds for larger diameter props too but it may. According to Rodney Tanner is seems to

Many (but not all) IMAC planes nowadays are wing loaded about the same as the better pattern planes and actually perform at least as well on the available power. IMAC designs often need more work to fly in a pattern-like manner but that's doable too. Patternlike performance is mainly had by longer tail moments, as much as 1/3 longer for pattern models, which make a model really groove. A tail moment that is only 2 X MAC or less sported by almost all IMAC planes will not groove as well as one that is 3 X MAC sported by most pattern planes

RE: why using high pitch prop on pattern ?
 

I flew my FUNTANA 140S with a Hacker C50-14XL and a 22 x 10 APC (Perfect 3D prop) in a pattern contest... and I swear, I heard one of the judges yawn during an upwind pass!!

lol

RE: why using high pitch prop on pattern ?
 

My perception is that a 12 pitch prop helps there. I heard that Quique Somanzini used to fly a 26x12 on the early DA100s. Could be just coincidence.

Thanks Matt. That's it in a nutshell. The Andrew Jesky (notable Pattern pilot and designer) AJ Slick IMAC/3D designs are getting closer to that. Looking at the videos, the AJ Slicks seem to have a definite Pattern groove in IMAC precision maneuvers.
Pretty sure an AJ Slick will be my next IMAC plane.

Sorry to get off topic.

RE: why using high pitch prop on pattern ?
 

I totally agree. I've ended up, almost across the board with at least 2" more pitch than everyone else on my smaller 2m Imac style aircraft. I find the extra prop speed tends to give me a more linear throttle response, less noise, and due to a higher speed a more "groovy" plane.