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Prop Pitch

Chrysopelea

Active Member
I got to fly a friend's RV12, and noticed it was a bit smoother.

I've been reading up here everything I can about prop pitch, and static and WOT RPM's. Static, I got 5000 RPM, haven't checked the WOT R's in the air, but the plane performs wonderfully.

After noticing my friend's plane being a tad smoother riding than mine, I got the necessary tools and checked my prop pitch.

I found one blade (pick a side) to be one degree off from the other.

From what I've read, this is enough to make a difference you can feel, so I plan to adjust my prop until both blades read exactly the same.

I'm hoping this will help make my plane run as smoothly as my friend's.

It's not like my plane shakes, although throughout the RPM range there are certain speeds that I can feel the engine doesn't like, but a quick twist on the Vernier solves that.

Any tips for when I tackle this?

I'm planning on matching the blade with more pitch (my meter reads 60 and 61 degrees, but I didn't level the pane, so those are just the degree numbers I got) so I hope to get 61/61.

The most important thing is to make sure both blades have the exact same pitch.

Even though I'm planning on only moving one blade, I should still loosen the entire hub evenly, so I can get a proper re-torque on the hub after I've made the adjustment, correc?.
 
.2 degree difference is enough to be felt if the prop is otherwise well balanced, so 1 degree difference should be considered huge.

A good procedure is to always zero your digital level relative to the cockpit side rail. then it will never matter what surface the airplane is sitting on when you do an adjustment.... the number you read will always be relative to the longitudinal center line / water line of the airplane.
Measure each blade with them in the exact same rotational position. I.E., measure carefully from a point on the ground or use a level across the prop hub.
What are you using for a tool to repeatably attach a level / protractor to the prop blades. If you are using the tool sold by Van's on the back side (when the prop is horizontal) of the right side blade as most do, then increasing the pitch of a blade requires reducing the degree value. So if you want slightly more pitch you would make both read 60.
When I make adjustments I try and leave the center two bolts a little tighter than the outer four so that the blades aren't sloppy in the hub.
Sometimes as you are tightening the outboard bolts a blade rotates a minute amount and changes the value by .1. You can counter this by re-loosening the bolt slightly and tighten the opposite side most of the way, and then finish to final torque using the standard cross pattern. Not sure if that makes sense or not.

There is some variation in how smooth the Sensenich props run, even if the blades are pitched perfectly.
The only way to know for sure if it is really good is to have the dynamic balance checked once you have the pitch here you are happy with the pitch setting. Occasionally they are pretty good right out of the box but my experience is that most of the time it can be improved somewhat, and probably 50% of the time it can be improved an amount that is very noticeable. But don't spend $700 to have it done. You should be able to get it done for $150-$200. Finding someone that has previously done Rotax engines is a plus.
 
Mike, I think I'm right behind you for a different reason. My blades are within .1 degree of each other, but I think I need a bit more pitch. On the trip to Oshkosh I was half an hour behind a friend flying at the same altitude and airspeed. I was at 7500', WOT turning just under 5400 RPM. He was at 7500', not quite WOT turning about 5100 RPM. My fuel burn is considerably higher as well, of course. When we landed at the same airport, I put in 15.7 gallons and he put in less than 12. Part of that difference would be his HACman mixture control, but not all of it. I need to check and see what my static RPM is, I haven't had it past about 4100 RPM on the ground since I bought it.
 
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Mike, I think I'm right behind you for a different reason. My blades are within .1 degree of each other, but I think I need a bit more pitch. On the trip to Oshkosh I was half an hour behind a friend flying at the same altitude and airspeed. I was at 7500', WOT turning just under 5400 RPM. He was at 7500', not quite WOT turning about 5100 RPM. My fuel burn is considerably higher as well, of course. When we landed at the same airport, I put in 17.5 gallons and he put in less than 12. Part of that difference would be his HACman mixture control, but not all of it. I need to check and see what my static RPM is, I haven't had it past about 4100 RPM on the ground since I bought it.

My prediction is that you are actually slightly over pitched already, based on how I adjust RV-12's.

If you increase the pitch even more your take-off and climb performance will begin to suffer.
 
That could be, I'll let you know what I find out what the static RPM is. I do know the previous owner was making efforts to see if he could get a little more speed out of it. He may have pitched the prop a little more aggressively, I don't know. However, I'm trying to figure out how that would cause me to run a couple of hundred RPM higher in cruise than my buddy with an RV-12 flying at the same speed.

I just looked again at a D180 screen shot from the trip. 7500', OAT 18C, DA 9690, 22.3" MAP. The TAS was 119 knots, 5380 RPM and burning close to 7 GPH. The EGT was 1152/1102. It sure looks to me like it could use a little more pitch and a leaner mixture, but I could well be wrong. Its happened before, just ask my wife. :)
 
Here is an article I copied and pasted from another website, but it has made its rounds. It's worth reading and may help you. Good general info.

"" Understanding the Ground Adjustable Prop
Keeping it simple and effective for the common setup.

Let's discuss prop pitch and how it affects flight characteristics. It can help flight characteristics or it can hinder. I'm often asked; What's the correct prop pitch for a specific plane? There is no single answer as many props are available to us today for Rotax engines and for different fuselages. There are, however, some commonalities and that is where we are headed in this article.
Certain principles do apply in either the 2 stroke or 4 stroke engines, although the numbers will be different as with most ground adjustable props. This article won't get into all the designs, blade twists, angles, thrusts, shaft powers, etc...etc. Whoa, just thinking about it puts my brain in a tail-spin. We are going to keep it simple and easy to follow. I am going to use the Rotax 912ULS as an example.
First let's pick a few numbers to keep in the back of our minds for later. We are going to shoot for certain idle rpm, so let's pick 1700 +/- rpm and 5600-5650 rpm for wide open throttle (WOT), flat and level at your average cruise altitude. It wouldn't make sense to set a prop for sea level when you are at 9,000' msl all the time. Why 5600- 5650 rpm as a target? Through a lot of testing this was found to be the BEST BALANCE point for climb, cruise, engine temps and fuel consumption. The "continuous run" rpm Rotax recommends for the Rotax 912ULS is 5500 and that rpm can be flown all the time if you chose to do so. Another good reason would be if you were to break a cable or had a throttle control failure. One carb would probably go wide open, as it's supposed to do and then you could advance your throttle and have the other carb go wide open. You could then fly to wherever you needed for a safe landing area; shut down and land. Anything over 5500 rpm (i.e. 5600-5800 rpm) would limit you to a 5 minute run time under normal flight situations for longevity of the engine, but in an emergency the engine can truly run for much longer times without fear of damage. A prop manufacturer will usually have some instructions for their prop and sometimes a suggested starting point for pitch depending on the engine. Another often asked question is “What should my static rpm be”? There is no specific or accurate answer for everyone's engine and prop. The static won't mean much if you only want to fine tune your existing setup. Static is more important for the first run owners or for new prop installation. The static rpm setting is just to get you in the ballpark and then you will need to fine tune it for your specific aircraft and needs while flying WOT at your average altitude. So in keeping it simple, you will want to set the pitch on most props to achieve a target with a beginning static (ground run) WOT rpm of around 4800-5000 rpm, but your static rpm may be slightly different depending on what you wanted for a final in flight WOT rpm outcome and different props can run different static rpms from one to another. The factors here are long vs shorter blades, two vs three blades and stiff vs flexible blades.
(Note: These next figures are general and yours may vary slightly) To do this properly, you will need to go fly at your average cruise altitude and fly flat and level at WOT for at least 1 minute. Now if your WOT rpm at this time is 5500 rpm and up to 5650 rpm you're probably set up fairly well for your engine, temperatures and fuel economy. If you are up at 5700+ rpm then you may want to land and add a little pitch (about .25-.75 degrees) back into the prop pitch, which will make it more coarse.
If you already have your prop setup is only turning 5200 rpm WOT flat and level you need to flatten or reduce the pitch approximately 1.5-2 degrees to achieve 5600-5650 rpm. Now you may have some special circumstance like a float equipped aircraft (heavy aircraft) that needs a little better climb, lots of high DA takeoffs or lots of tight short fields where better climb is more important so a climb pitch of 5650-5725 rpm WOT might be warranted. We need to tune our props for the type of flying that we do.

What else does my prop pitch do for me?

Setting the prop pitch excessively coarse (i.e. 5000-5300 rpm WOT) causes excessive stress on engine components and gearbox which may necessitate early maintenance and has been known to crack crankcases. Having the pitch too coarse will cause higher engine (CHT, EGT) and oil temperatures, excessive fuel consumption, poor climb and decreased cruise speed. Your engine doesn't have the horse power and torque to turn an excessively pitched prop. All piston engines have their limits and the props all have limits, too. So if your engine temps are up and your WOT engine rpm is below 5500 rpm try unloading the engine by reducing the prop pitch. If you have a prop that is too flat then it may climb well, but have a loss in cruise speed and of course engine temps and fuel are affected again.
Your exact numbers may vary some, but you now have a general idea on what to look for and how it may affect your flying and engine. We'll keep this discussion on the root topic of ground adjustable props. Special circumstance rpm settings and in flight adjustable props will warrant discussion in a future article.
One last parting comment: If adjusting prop pitch sounds complicated, it isn't; it usually will only take 30-40 minutes, a couple of wrenches, a prop protractor and/or a level. So take the time to fine tune, your engine will say thank you in improved performance. ""


p.s.
A plane does not need to be leveled to set a prop pitch. Just put a level on the blade out to your right side and level it to the ground with a 12" torpedo level. Then measure in from the tip of a blade 8"-8.5" inward and put a mark on each blade so your protractor is in the same place for each blade. Then put the prop protractor on the back side of that blade and take a reading. Determine how much you want to add or reduce the pitch and then loosen the securing bolts on the hub and turn it to that setting. Repeat for each blade. This way will ensure you can get a minimum of .1 degree of accuracy and depending on the protractor may be better.
 
Here is an article I copied and pasted from another website, but it has made its rounds. It's worth reading and may help you. Good general info.

"" Understanding the Ground Adjustable Prop
Keeping it simple and effective for the common setup.

Let's discuss prop pitch and how it affects flight characteristics.
Excellent article, thanks for posting.
With Rotax 912 ULS and a Neuform 3-blade prop (standard day), .25 degrees pitch change equates to how many RPM (approximately)?
 
Plaincode clinomitor on cell phone

I have used this set my prop and it is easy to use and very accurate
I use it on my Samsung Ck it out.
 
p.s.
A plane does not need to be leveled to set a prop pitch.

I agree, but there can be times when it is valuable to know what the blade pitch value is relative to some part of the airplane so that regardless of the pitch attitude of the airplane you can reset the propeller pitch to a specific value.
Such as if the propeller is removed for some reason, or if you seasonally re-pitch to different values. If you know the pitch value relative to the side rail of the airplane, you will not have to remember to check it before the propeller is removed, and the ground attitude of the airplane will never matter (variability from different tire pressures, empty vs full fuel tank, re-pitching during a trip with a lot of baggage in the airplane, etc.)

I keep it recorded in the airframe logbook and regardless what ever happens or where the airplane is located, it is easy to get back to the exact same pitch value.
 
This is a sanity check for my personal, and slightly altered method of measuring prop pitch. The above article, as well as most all documentation that I have seen, use the rear flat surface of the prop blade on the right side. This surface is slanted forward at the bottom, and requires holding the level against the surface with a magnetic based level, or rubber bands. I have been using the left blade. The flat surface on the left blade slants "bottom to the rear" and makes it much easier to position the level with repeated accuracy. So. my question is, why do all documented procedures call for fitting the level to the right blade? Am I making a mistake by using the more convenient left blade?

Thanks....Tom
 
VANS PROP PITCH BRACKET

I used Vans Prop Pitch Bracket. Unit hangs nicely off the trailing edge of the blade and is a very repeatable setup. Took only 30 minutes to get my blades within 0.1 degree of each other. Very easy and precise.

rups9z.png


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20fz1g9.png
 
OK, I just checked my pitch, using the method in the pics in the previous post, measuring from the backside of the prop.

Also, I measured a little further in towards the center, at the edge of the inner paint stripe.

My blades are over 2.5 degrees off from each other!!!

No wonder my friend's 12 felt smoother than mine!

I pulled my spinner, and I think I have one of the bad hubs, as the serial number went something like xxxx RB, so I think I have one of the "B" hubs that Sensenich is replacing, or machining .008" from, anodizing black, and sending back.

The plane has 160 hours on it.

For now, I think I'm going to set the blades to their proper pitch and watch and see if anything moves.

Is the "B" hub a mandatory send-in/replace/get fixed item, or is it a "send it in if you have creeping blades" item?
 
2.5 degrees is a lot. You might want to check it again, following the procedure from the start to make sure you got it right. When I find something like that I like to re-check a couple of times so I know it's not a measurement error.

I also have one of the hubs covered by the Sensenich SB or AD (I forget which it is at the moment). I asked them about it. The guy who responded said to watch the pitch setting over time. if it changes, send the hub in. If it doesn't change, keep flying until/unless it's convenient to send it in. Apparently not all of the affected hubs will have problems. He said turnaround is quick, said they have hubs on the shelf to send back. That was the state as of early this year. But if you have that much difference, it could possibly be a sign that your hub is bad. If that's the case I'd be a little concerned about fretting between the hub and blade root.
 
I reset the blades late yesterday.

I kind of split the numbers.

I was getting around 5000 static, so I added a degree to one and removed a degree from the other, but got both blades reading exactly the same on the gauge, hoping that will be OK.

I know the blades are very close to each other now, so I hope things run more smoothly.
 
I thought I?d add this? I reset my prop to 71.4 per Van?s spec. Pic is taken early this morning.

119 IAS, 125 TAS @ 2200 MSL / 77F, 4.9 GPH. Climb is still 1000 FPM. This is economy cruise setting of 5150 RPM. Retirement is good?
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1zpo849.png
 
Is that with or without wheel pants? Agree retirement is good - especially when an RV12 is part of the plan! My total time is very similar - 145. Also bought flying but at only 25 hrs.

Jack
 
Limitations markings

I thought I?d add this? I reset my prop to 71.4 per Van?s spec. Pic is taken early this morning.

119 IAS, 125 TAS @ 2200 MSL / 77F, 4.9 GPH. Climb is still 1000 FPM. This is economy cruise setting of 5150 RPM. Retirement is good?
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1zpo849.png

Has the normal operating speed range upper limit of 45 - 108 kts and VNE of 136 kts for the RV12 been amended or have the ranges on your display been incorrectly set up or?
 
MPH?

Has the normal operating speed range upper limit of 45 - 108 kts and VNE of 136 kts for the RV12 been amended or have the ranges on your display been incorrectly set up or?

Considering the ground speed is in MPH in Piper J3's photo, could the IAS and TAS be in MPH too? That'd make sense regarding colors of speed ranges.
 
Considering the ground speed is in MPH in Piper J3's photo, could the IAS and TAS be in MPH too? That'd make sense regarding colors of speed ranges.

Correct, I have EFIS set for MPH. Range markings are Van's RV-12 software for the D-180.
 
Flew yesterday for the first time in a month and a half!

I still remember how to fly, that's a good thing.

Static runup got me around 4950-5000, and performance was great. In the air, firewalled, I got 122 true air speed knots, 120 at 3/4 throttle, so I pretty much nailed it! YES!!!

The best part is the plane runs smoother than butter now. Such a huge difference I really couldn't believe it, especially at idle and low rpm's. High rpm's it was silky smooth as well. HUGE improvement.

I plan to put checking my prop pitch on my post-flight checklist, at least after one flight nothing has moved.

I'll admit I torqued the outer (blade) bolts to 21lbs/sq ft instead of 20, and I hope the blades stay put.

I do NOT want to have to take my plane back to a mechanic. So far, after my annual, I've found 2 dents, and one big giant scratch across my windscreen, and greasy finger and palm prints all over both inside and outside the plane. It's a total mess that's going to take a few hours for me to clean and get back to the clean, pristine point it was when I took it in.

My plane also needed the doublers added to the bottom of the wing spar root rivets as they were showing signs of movement. Apparently this is a known issue, because Van's knew about it, and sells a double kit that's easy to install that addresses the issue. My A&P said it would take him an extra 3 hours to install, but my friend and I had to remove, and reinstall the wings for the mechanic as he's never done this on any 12.

My engine number also fell under the service bulletin of NEEDING the carb floats changed, even though they were checked last year and found to be good per my log book, so that was another extra cost to my annual.

My ELT battery was dead, and so replaced, another extra cost.

Anticipating the bill, I have no idea what it will be, hoping it will be reasonable.

Regardless, I am so happy to be back taking my lessons, every Monday and Friday.

Hoping to find time to finish my ground school as well. I'm 2/3 through my course, but stumped on the sectional charts and maps part without some tutoring and/or reading of some books.
 
Flew yesterday for the first time in a month and a half!

I still remember how to fly, that's a good thing.

Static runup got me around 4950-5000, and performance was great. In the air, firewalled, I got 122 true air speed knots, 120 at 3/4 throttle, so I pretty much nailed it! YES!!!

The best part is the plane runs smoother than butter now. Such a huge difference I really couldn't believe it, especially at idle and low rpm's. High rpm's it was silky smooth as well. HUGE improvement.

I plan to put checking my prop pitch on my post-flight checklist, at least after one flight nothing has moved.

I'll admit I torqued the outer (blade) bolts to 21lbs/sq ft instead of 20, and I hope the blades stay put.

Glad to hear about your performance and vibration improvement. You missed one important statistic that would be most helpful to the rest of us. What was your WOT (wide open throttle) RPM?? That will be great information. Enjoy the fruits of your effort..........Tom
 
I will report back on Monday with my WOT RPM's.

They were right in the ballpark from what I've read here, I just forget the actual number.

I did a quick runup on the ground, just enough to know it wasn't way out of whack. Static R's were around 4950-5000.

Climbing out was lower than I thought it should be, (around 4800 I think if i remember correctly) but it was hot, we were full of fuel, two guys, climbing at 75.

Monday I'll take the time to write the data down.

This last flight was more of a shakedown flight. Just got it back from the annual, adjusted the prop, wanted to just make sure it was all still in the ballpark.
 
If I remember correctly, those are the RPM's I got at WOT flying flat and level, 5500 or 5600. True airspeed was 120-125, right around there.

Usually the RPM's are at or around 5000-5100 for normal cruising at cruise throttle settings.

I'm still taking lessons, and from what I've read, the engine actually prefers higher RPM's. I know I'd like to fly a little faster, but for my lessons my instructor likes it around 5 to 51.

Tomorrow I'll note my RPM's and report.
 
4800 RPM climbing at full throttle is hard on the engine. I looked in the POH but could not find the minimum full throttle climb RPM, but believe it should be between 5100 and 5200 RPM at 75 knots. Scott?
 
Ideally, at wide open throttle setting, during straight and level flight, you should be indicating 5600-5650 RPM, at your typical cruise altitude.
That provides the best "balance" for climb and cruise.
An exception for that may be for high altitude airport operators.
 
4800 RPM climbing at full throttle is hard on the engine. I looked in the POH but could not find the minimum full throttle climb RPM, but believe it should be between 5100 and 5200 RPM at 75 knots. Scott?

Rotax's recommended Climb RPM is = or > 5200 RPM. That can probably be possible on a lower speed / higher drag airplane, but with the RV-12, the prop setting that most owners typically end up with that just isn't possible.

4800 would be excessively slow though. If actually climbing at Vy (75 kts), the typical prop pitch setting will result in an RPM in the 5050-5100 range.
 
Ideally, at wide open throttle setting, during straight and level flight, you should be indicating 5600-5650 RPM, at your typical cruise altitude.
That provides the best "balance" for climb and cruise.
An exception for that may be for high altitude airport operators.

And the other exception is density altitude.

This time of year the density altitude can easily be 3000-4000 ft higher than pressure altitude. Something to keep in mind as it will have an influence on engine power and propeller thrust.
 
OK, I took another lesson today, and took notes of my RPM's, and then forgot to bring the data home.

I have an excuse though, I found a coolant leak, and so for the next hour and a half we were removing the cowling and finding and fixing the leak (basically, an ill-placed clamp, placed on the bend of the metal tube portion instead of directly behind the bulge in the metal tube) which really didn't take anything, just moving a clamp and twisting the tubing a little.

BUT, I remember I think.

4960 static on the ground, and I think 5640 flying WOT at 127 knots True Airspeed are the numbers I believe.

Again, smooth as silk, and no pitch movement after the lesson.
 
And the other exception is density altitude.

This time of year the density altitude can easily be 3000-4000 ft higher than pressure altitude. Something to keep in mind as it will have an influence on engine power and propeller thrust.

Scott, the PAP makes no mention of adjusting for DA when setting the pitch for the desired static RPM. Would it be a factor? I checked yesterday and, as you predicted, found my static RPM at full throttle was a bit low -- like 4700, if I recall correctly. The field elevation is 1050, but DA this time if year can be over 3000 on a hot day. Should I do the check & adjustment early or late when it's cooler, or does it matter?
 
The PAP check is to confirm that the pitch setting is in the ball park. It is not meant as an absolute for every one (though it will probably be fine for a lot of people that aren't interested in fussing with the pitch setting). Particularly for a first flight when most people new to the airplane have no idea what to be looking for.

RV-12 pilots may (and many do) make small adjustments from that value to tailor performance to fit how they fly the airplane. Some even do it seasonally if their local temps swing between extremes of hot and cold.

I.E., if someone flys out of primarily higher altitude airports in the mountains and isn't as concerned about all out cruise speed because the never venture very far (particularly into the flat lands) they will probably want a pitch setting that is a bit flatter than average, and vice versa for someone that flys mostly from low altitude airports in the flat lands parts of the country.

My comment about density altitude was meant to convey that even if you use in flight performance (like rpm value at WOT at 6500') if you simply use 6500 indicated (pressure) altitude, the result you get can be quite different between a cold winter day at that altitude and a hot summer day at that altitude.
 
I called Vans and they sent me the tool, it was like $8 and they sent it quickly (if you're talking about the prop pitch tool that they sell).
 
After adjusting the pitch, I cannot describe to you just how much smoother my plane is running! What a huge difference.

Gained some performance too!
 
. . . "I remember I think.

4960 static on the ground, and I think 5640 flying WOT at 127 knots True Airspeed are the numbers I believe.

Again, smooth as silk, and no pitch movement after the lesson." . . .

. . . "After adjusting the [prop] pitch, I cannot describe to you just how much smoother my plane is running! What a huge difference.

Gained some performance too!" . . .
I think you've nailed it.
Besides a good carb synch and prop balance, trimming the ground adjustable propeller to 5600-5650 RPM, at wide open throttle setting and the desired average cruise altitude (DA) . . that is the key.

Glad it is where you want it now.
 
I feel like I nailed it as well.

From all the data I've gathered here, and the performance of the plane, and numbers all matching what others say is the "sweet spot'', plus, I got 127 TAS knots, so I'm really happy with the new blade settings.

Now if they'll just stay put!

I'm checking prop pitch after every flight as part of my post flight check.

On my last PRE-flight check, I noticed my coolant level was a little lower than normal. I marked the level on the expansion bottle.

After the flight, there were drips on the ground, and the level was 1/4" lower than my mark, so I knew i had a leak.

A very nice friend and I took the cowling off and quickly located the leak. The clamp for the tube exiting the head was Not placed just in front of the bulge in the metal tubing, it was too far forward and actually up in the bent area of the metal tube. Simply sliding the clamp back into it's proper position fixed the issue, and I also placed a regular hose clamp on the extra rubber behind the oem clamp for extra insurance. Not too tight so as to bite into the hosing, just enough to add some extra insurance.

Mechanic said this wasn't too rare of an occurance, and he'd seen it before. Total coolant loss was only a cup or 2 after an hour lesson.

This is I'm sure why a good pre-flight check is so important!

Plane's back together now and ready for my next lesson.
 
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I posted on here somewhere else a recent failure of the rubber coolant line between the header tank and the overflow bottle - about 250 hours of use. Its going to happen with rubber hoses so the suggestion to do a good inspection every time the cowl is removed for oil changes is a good one. (unfortunately, you don't need to change the oil that often in a Rotax using MOGAS)
 
I feel like I nailed it as well.

From all the data I've gathered here, and the performance of the plane, and numbers all matching what others say is the "sweet spot'', plus, I got 127 TAS knots, so I'm really happy with the new blade settings.

That?s a very fast airplane.

Van?s performance numbers are

Top Speed 135 mph
Cruise (7500? @ 5500 rpm) 131 mph
Cruise (7500? @ 5000 rpm) 116 mph

Van?s numbers must be TAS because altitude is given. So it looks like the 12 tops out at 135 mph at 7500? WOT.

Your 127 knots TAS is 146 mph. Somehow you?re cruising speed is about 10 mph over top speed. Just say?n?.
 
127 is fast. I'd want to run a GPS course to see how close the airspeed calibration is. I don't think it's impossible by any means, though.

I have some tweaking to do on mine, but it's not unusual to see 123 kt TAS at 5500-7500 MSL. I know there's a little more to be had with some more aerodynamic cleanup. Given the minor speed gains, I'm much more interested in cutting the fuel burn at 115 or 120 kt than I am in trying to wring out another couple knots of top speed. Those two goals just happen to coincide.
 
That?s a very fast airplane. Van?s performance numbers are
Top Speed 135 mph
Cruise (7500? @ 5500 rpm) 131 mph
Cruise (7500? @ 5000 rpm) 116 mph

I suspect that Van's numbers are for an RV-12 without wheel pants, since they are an optional kit item.
 
I moved this from an older duplicate thread. Before the switch to the 12 I flew my 9A with a CS prop. I'm still trying to adjust to one prop pitch and not flying by manifold pressure.

I have been reading up here on 12 prop pitch and it almost looks like there is no one "right" pitch setting and you adjust to personal preference and climate. I set my pitch slightly coarser than Van's and I have acceptable climb and cruise but probably not optimum. Flight at about 4000' density altitude solo today I could not use full throttle and had to keep pulling power to stay below redline. At about 5500 I saw about 124 TAS. 5500 rpm at about 9000 DA earlier was 117 with a lot less throttle. Do I need more pitch so I can run wide open at 5500 (or 5700 as some have suggested) at cross country altitudes? If I do that rpm will be way low for take off performance and low flights. Where is the sweet spot for the engine to run for a cross country, set by rpm, throttle or manifold pressure? Should you run at lower altitude and rpm under a higher load or higher altitude and rpm with a lower power setting?
 
Where is the sweet spot for the engine to run for a cross country, set by rpm, throttle or manifold pressure? Should you run at lower altitude and rpm under a higher load or higher altitude and rpm with a lower power setting?

It depends on what altitudes you want to be optimized for.
That is the price we pay for using a fixed pitch prop. It can only be set for absolute optimal performance for specific conditions. And even then, if you set it for absolute optimal cruise for some specific range of altitude, you may be compromising take-off / climb performance more than you would be willing to.

This is why all of the threads on prop pitch have many different values posted, because not everyone flys their RV-12 the same.
 
Having too much pitch can also cause our hot-running ROTAX 912 ULS engines to run even hotter -- not a good thing. Think of it as trying to quickly accelerate up a steep hill from a low speed in your stick-shift car in fifth gear -- excessive engine heat and combustion pressure, pre-ignition, detonation, etc. The RPM numbers suggested by Van's, Rotax-Owner.com, etc seek a balance of aircraft climb/cruise performance while not over-taxing the engine.
 
Just to follow up on my experience. Scott was right, of course.

I was seeing pretty high fuel consumption in cruise, and when I checked it my static RPM was 4700. I took two degrees of pitch out and the static RPM was too high, around 5250 or so. I put one degree back in and the blades measure within .05 degrees of each other. I haven't had a calm enough day to check the static RPM again yet, but I can report that there are some definite changes.

First off, the rate of climb after takeoff is remarkably better. It was almost scary on the first takeoff, in fact. It would climb well before, but now it's like a big yellow kite. I am also seeing substantially lower fuel burn in cruise. I haven't taken any long trips or had time to do detailed analysis. On the short trip I did take I noticed I used less throttle and was burning about 1GPH less at 5400-5500 RPM than I would have expected before.
 
Just to follow up on my experience. Scott was right, of course.

I was seeing pretty high fuel consumption in cruise, and when I checked it my static RPM was 4700. I took two degrees of pitch out and the static RPM was too high, around 5250 or so. I put one degree back in and the blades measure within .05 degrees of each other. I haven't had a calm enough day to check the static RPM again yet, but I can report that there are some definite changes.

First off, the rate of climb after takeoff is remarkably better. It was almost scary on the first takeoff, in fact. It would climb well before, but now it's like a big yellow kite. I am also seeing substantially lower fuel burn in cruise. I haven't taken any long trips or had time to do detailed analysis. On the short trip I did take I noticed I used less throttle and was burning about 1GPH less at 5400-5500 RPM than I would have expected before.

Very interesting....my experience so far the same. Think as soon as I get mine back from the paint shop I'll d-pitch a degree as I have can't spinner up past 5300 in cruise.
 
A two degree change is huge. My experience is that you should be working in tenths of a degree once you are anywhere near the ball park. Mine's about 5050 static. I find that is a good compromise between climb and cruise with climb favored slightly. My WOT cruise is a little over 5500 RPM and 117KTAS. I usually cruise at 5100 and about 113 KTAS.
 
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