skywagon8a
MEMBER
SE Mass MA6
Yes, he was one of them. I had several flights in different programs with this same FAA pilot and got to know him quite well. Definitely a 50%er.
PA-12 outperformed by identical PA-12 on floats
- Thread starter squirrelhunter44
- Start date
skywagon8a
MEMBER
SE Mass MA6
I've had the IO-520 @ 2850 max of 300 hp, intercooled TSIO-520 @ 2700 max of 310 hp and the IO-550 @ 2700 minimum of 300 hp all in the same 185. The IO-550 is clearly the better of the three. Pulls better from the start, climbs better and cruises faster. On top of that it is smoother and quieter. The turbo will clearly perform at much higher altitudes but overall is an inferior engine.
mvivion
SPONSOR
Bozeman,MT
Stewart,
The problem is that the IO 520 and the IO 550 were certified to different standards. Essentially, the 520 only had to make 300 hp plus zero, minus 5 %. So, legally, an IO 520 can make a maximum of 285 hp, and be acceptable.
The IO 550, on the other hand has to make 300 hp, plus 5 %, minus zero. That engine HAS to make full rated power of 300 hp when it comes off the line or it's not airworthy. This is the same certification standard that Lycoming has followed for decades. According to a Continental tech rep I talked to, the IO 550s all make over 300 hp out of the factory, since one test engine that makes 299 hp causes a whole batch to fail.
There is no question in my mind that, while the 520 and the 550 are both rated for 300 hp, the 550 pulls harder. By the same token, a Lycoming 540 is almost always stronger than a Continental IO 520, though they're both rated for 300 hp.
And, equipped with the right prop, either engine pulls harder at 2700.
MTV
Did you take off a brand new IO-520 when you put the 550 on? If not you weren't comparing apples to apples. Not unlike pireps when guys remove a worn out beater 320 and put a fresh 360 on their Cubs.
My own 0-520 pulls harder with the prop governor dialed up. There is absolutely no question about that in my own plane using a C401-86" Mac.
I have several friends who've had rebuilds of their IO-520s that came with dyno reports. All ranged between 320 and 330hp at 2850.
In Cubs we've all accepted long, flat props are key to short performance. Why is it different with an 86" prop on a Skywagon or Stationair? Why would running it coarser at lower rpm be beneficial if power at the flange is equal?
My own 0-520 pulls harder with the prop governor dialed up. There is absolutely no question about that in my own plane using a C401-86" Mac.
I have several friends who've had rebuilds of their IO-520s that came with dyno reports. All ranged between 320 and 330hp at 2850.
In Cubs we've all accepted long, flat props are key to short performance. Why is it different with an 86" prop on a Skywagon or Stationair? Why would running it coarser at lower rpm be beneficial if power at the flange is equal?
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skywagon8a
MEMBER
SE Mass MA6
This thread has moved way beyond the original question about a PA-12.
Long SLOW turning props are the most efficient for moving large volumes of air. In fact a single bladed prop is more efficient than the more common two blade due to the lack of disturbed air from the other blade. When you turn that LONG prop at high rpms, the tip speeds get up into the high mach number range where there is a high drag rise and trans-sonic inefficiency. If you wish to extract 320-330 hp at 2850 rpm you would be more likely to achieve this objective with less diameter and noise. By reducing the diameter and the tip speed you would be producing thrust with the whole prop blade. The high tip drag is absorbing your extra power. Also the airfoil and plan-form of the prop blades contribute to these differences. It is a science beyond the scope of this thread.
Long SLOW turning props are the most efficient for moving large volumes of air. In fact a single bladed prop is more efficient than the more common two blade due to the lack of disturbed air from the other blade. When you turn that LONG prop at high rpms, the tip speeds get up into the high mach number range where there is a high drag rise and trans-sonic inefficiency. If you wish to extract 320-330 hp at 2850 rpm you would be more likely to achieve this objective with less diameter and noise. By reducing the diameter and the tip speed you would be producing thrust with the whole prop blade. The high tip drag is absorbing your extra power. Also the airfoil and plan-form of the prop blades contribute to these differences. It is a science beyond the scope of this thread.
Takeoff performance has little to do with efficiency.
I've had the opportunity to play with prop speeds and temperatures to reduce the supersonic tip speed drag. My experience regarding performance is not consistent with the graphs that seem focused on noise. Fly at a DA of several thousand feet below sea level on a short strip with tall obstacles. Dial the prop speed down to fit the speeds on the Pponk tip speed calculator. Note the crossing height relative to obstacles. Repeat without reducing prop speed. Note the improved clearance over obstacles. More noise? Absolutely. In sub-zero temps at sea level the noise coming from a plane operating on a creek bottom is deafening. I say cover your ears because I'll take the improved performance over the trees every time.
I've had the opportunity to play with prop speeds and temperatures to reduce the supersonic tip speed drag. My experience regarding performance is not consistent with the graphs that seem focused on noise. Fly at a DA of several thousand feet below sea level on a short strip with tall obstacles. Dial the prop speed down to fit the speeds on the Pponk tip speed calculator. Note the crossing height relative to obstacles. Repeat without reducing prop speed. Note the improved clearance over obstacles. More noise? Absolutely. In sub-zero temps at sea level the noise coming from a plane operating on a creek bottom is deafening. I say cover your ears because I'll take the improved performance over the trees every time.
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mvivion
SPONSOR
Bozeman,MT
Stewart,
Dyno runs on rebuilt airplanes are often done without the engine driving accessories and no exhaust system to speak of. Everything I posted before was direct from Continental, after I asked a tech rep why a "300 HP" IO-550 seems to make more power than a "300 HP" IO-520, and at a lower prop rpm. His answer was simply that the IO-550 in fact makes more power out of the factory.
There's no question that there are rebuilders who tweak their engines a bit, and probably do achieve a bit more power than the factory typically does.
But, if you don't believe that a 550 makes more power than a 520, ask any 206 driver who's gone from a 520 to a 550. I've flown three of them, and there's no doubt in my mind.
MTV
squirrelhunter44
Registered User
Prince George
I can bring it back to the original PA12 question. So when my boss bought the doggy PA12 he was told it was a 160hp O-320. I'm suspicious that it actually is a 150hp , based on engine data plates and the lack of information in the logbook about any 160hp upgrades. How much difference can 10hp make?
One other thing I've noticed, the doggy Cub really doesn't seem to like much of an aft CG where as the other performs great wherever you are loaded.
JimParker256
Registered User
Farmersville, TX
Oh, man... Ten HP can be an incredible upgrade... A few years ago, I owned a Grumman Traveler (150 HP 4-seat predecessor of the 180 HP Tiger). In our Texas summers, it was a dog when it came to climbing... Didn't help that I'm a "larger than average" guy, and so is my son who flew with me a good bit, but we would see about 450 fpm at "best climb" airspeed – even less at cruise climb.
So during a particularly good annual inspection (that's one where your IA finds nothing wrong!), I decided to go ahead and spring for the high-compression upgrade (STC) that converted the engine to exactly the configuration of the O-320 160 HP models.
From the very first flight, I noticed a HUGE difference in the rate of climb. I picked up at least 250 fpm - with the only difference in the plane being the 10 added HP. My static RPM was about 150-200 rpm higher than before, but the most surprising thing to me was that I was burning almost 1 GPH less fuel at the same airspeeds. I almost didn't believe it myself, but when I added up all the fuel used before the upgrade, divided by the total hours flown, I was averaging 8.0 GPH for that block of almost 100 hours. After the upgrade, I flew the plane another 75 hours, and the average fuel burn was 7.1 GPH for that block of hours. I didn't change the way I flew - cruise climb to altitude, and use the same cruise speeds (same RPM setting).
I think the fuel savings came in two areas:
1) Faster climb meant less time climbing to altitude at full power.
2) The higher compression engine was just more efficient at cruise power (2500 rpm or roughly 65% power).
The "Grumman Guru" who recommended and performed the upgrade for me said I would have seen even better results if I has also switched from the original McCauley prop to a Sensenich prop that was significantly more efficient than the Mac... But since my prop only had 106 hours on it since new, I couldn't bring myself to spend the money for a different one...
So, yeah, if one of the airplanes had a "stock" 150 HP engine, and the other one was 160 HP, I would expect the 160 HP plane to accelerate faster, get out of the water sooner, and climb and cruise much better than the other one!
So during a particularly good annual inspection (that's one where your IA finds nothing wrong!), I decided to go ahead and spring for the high-compression upgrade (STC) that converted the engine to exactly the configuration of the O-320 160 HP models.
From the very first flight, I noticed a HUGE difference in the rate of climb. I picked up at least 250 fpm - with the only difference in the plane being the 10 added HP. My static RPM was about 150-200 rpm higher than before, but the most surprising thing to me was that I was burning almost 1 GPH less fuel at the same airspeeds. I almost didn't believe it myself, but when I added up all the fuel used before the upgrade, divided by the total hours flown, I was averaging 8.0 GPH for that block of almost 100 hours. After the upgrade, I flew the plane another 75 hours, and the average fuel burn was 7.1 GPH for that block of hours. I didn't change the way I flew - cruise climb to altitude, and use the same cruise speeds (same RPM setting).
I think the fuel savings came in two areas:
1) Faster climb meant less time climbing to altitude at full power.
2) The higher compression engine was just more efficient at cruise power (2500 rpm or roughly 65% power).
The "Grumman Guru" who recommended and performed the upgrade for me said I would have seen even better results if I has also switched from the original McCauley prop to a Sensenich prop that was significantly more efficient than the Mac... But since my prop only had 106 hours on it since new, I couldn't bring myself to spend the money for a different one...
So, yeah, if one of the airplanes had a "stock" 150 HP engine, and the other one was 160 HP, I would expect the 160 HP plane to accelerate faster, get out of the water sooner, and climb and cruise much better than the other one!
supercrow
FRIEND
Smith Pond near Millinocket, Me
I agree; major difference, just like between the 85 and 90 continental. The 160 is much more powerful and burns less fuel.
TurboBeaver
Registered User
Northern Maine
Of course you could easily find that if you switched engines in the planes the one that was the best may still be ?
As looking identical, and truely being identical are two entirely different things. Having flown lots of different "Cruisers" on floats, there are VAST differences in them . We had a 180 hp /12 at Bristol Bay Lodge in 1980 that would take off between
the two docks that at that time were 200 ft apart, I had a buddy that had a 180 hp Cruiser on the same floats that wouldn't get out of its own way and commonly went 1000' with two people and half tanks. Weight, wing rigging, prop, float rigging, engine mounts, and don't go by a data plate there are o360's with 165 hp ( wore out ones) and others that are modified to 220hp ( Mark Bills) so a data tag won't tell you the whole story, neither will the log book.
There are hundreds of 0320's with both 160 and 170hp HC pistons in them but no mention of that in the log books.
There will be a darn good reason WHY it outperforms the other one and it could be the engine but it might not be.
A good place to start is which one will fly the slowest???
As looking identical, and truely being identical are two entirely different things. Having flown lots of different "Cruisers" on floats, there are VAST differences in them . We had a 180 hp /12 at Bristol Bay Lodge in 1980 that would take off between
the two docks that at that time were 200 ft apart, I had a buddy that had a 180 hp Cruiser on the same floats that wouldn't get out of its own way and commonly went 1000' with two people and half tanks. Weight, wing rigging, prop, float rigging, engine mounts, and don't go by a data plate there are o360's with 165 hp ( wore out ones) and others that are modified to 220hp ( Mark Bills) so a data tag won't tell you the whole story, neither will the log book.
There are hundreds of 0320's with both 160 and 170hp HC pistons in them but no mention of that in the log books.
There will be a darn good reason WHY it outperforms the other one and it could be the engine but it might not be.
A good place to start is which one will fly the slowest???
JimParker256
Registered User
Farmersville, TX
One other MAJOR source of difference could be the propeller.
When my Grumman was in the shop for the high-compression update (150 to 160 HP) described above, there was an almost identical Traveler also in the shop because the owner had complained about lack of power, slow climb and cruise, etc., though it would develop full static RPM. I wasn't paying much attention to that plane, since I was helping with the (owner-assisted) annual. But eventually, these two airplanes wound up sitting nose-to-nose, and at least part of the reason for the performance differences became instantly obvious to me. Both planes had the same McCauley cruise prop installed (same diameter and pitch), but you would never have known it by just looking at them. My prop's was almost twice as wide (chord-wise) as the other one...
I commented on the "skinny" prop to Dave (the Grumman Guru), who told me that he saw props like this fairly often. Apparently, over the years that prop had been "dressed" so many times that it looked like a toothpic compared to mine. He also put a micrometer on my prop and the skinny prop, and the skinny one was only 2/3 the thickness mine was... Dave told me that the owners of those "heavily worn" props often do NOT want to send the prop to a prop shop, because they know the shop will condemn the prop on sight. Dave had actually installed a "known good" prop (from his personal stock), and test-flown the plane with both the old and the new prop, within an hour of each other. With the skinny prop, it was at least 10 knots below book cruise numbers, and climbed very slowly. With the "known good" prop, on the other hand, it flew with "book" level performance. Clearly, the skinny prop was the issue.
But even after all that, the airplane's owner refused to replace his "perfectly good prop" to address the performance issues – insisting there had to be something else that could be done. Dave even offered to sell him that "known good" prop at a REALLY decent price (like 1/3 the cost of a new on), and the guy refused. Eventually, he came and flew his airplane back home, still complaining about the lack of performance.
When my Grumman was in the shop for the high-compression update (150 to 160 HP) described above, there was an almost identical Traveler also in the shop because the owner had complained about lack of power, slow climb and cruise, etc., though it would develop full static RPM. I wasn't paying much attention to that plane, since I was helping with the (owner-assisted) annual. But eventually, these two airplanes wound up sitting nose-to-nose, and at least part of the reason for the performance differences became instantly obvious to me. Both planes had the same McCauley cruise prop installed (same diameter and pitch), but you would never have known it by just looking at them. My prop's was almost twice as wide (chord-wise) as the other one...
I commented on the "skinny" prop to Dave (the Grumman Guru), who told me that he saw props like this fairly often. Apparently, over the years that prop had been "dressed" so many times that it looked like a toothpic compared to mine. He also put a micrometer on my prop and the skinny prop, and the skinny one was only 2/3 the thickness mine was... Dave told me that the owners of those "heavily worn" props often do NOT want to send the prop to a prop shop, because they know the shop will condemn the prop on sight. Dave had actually installed a "known good" prop (from his personal stock), and test-flown the plane with both the old and the new prop, within an hour of each other. With the skinny prop, it was at least 10 knots below book cruise numbers, and climbed very slowly. With the "known good" prop, on the other hand, it flew with "book" level performance. Clearly, the skinny prop was the issue.
But even after all that, the airplane's owner refused to replace his "perfectly good prop" to address the performance issues – insisting there had to be something else that could be done. Dave even offered to sell him that "known good" prop at a REALLY decent price (like 1/3 the cost of a new on), and the guy refused. Eventually, he came and flew his airplane back home, still complaining about the lack of performance.
reliableflyer
Registered User
Seldovia, Alaska
The long mount makes for a forward CG. The short mount moves the CG aft and will fly at a slower speed..
when the CG is further forward the tail needs to develop more lift in a downward direction to compensate for the forward CG. The wing then needs to fly the additional weight that the tail is generating in a downward direction. The short mount is STC'd and should have a tag on it. It will also show on the distance the engine is from the firewall. The PA 12 tends to have a forward CG issue.
when the CG is further forward the tail needs to develop more lift in a downward direction to compensate for the forward CG. The wing then needs to fly the additional weight that the tail is generating in a downward direction. The short mount is STC'd and should have a tag on it. It will also show on the distance the engine is from the firewall. The PA 12 tends to have a forward CG issue.
cruiser
Registered User
South Glens Falls, NY
from the EDO drawing. Thanks for the help Pete.
Attachments
Why not use a dial indicator and measure the cam lift at the rockers or valve springs?
squirrelhunter44
Registered User
Prince George
Is 4 years late better than never? We believe we have discovered the issue with the "Doggy" PA12 from back when the original post was made. Had to change a cylinder on the poor performer and it was confirmed by the engine shop that it was a 150hp engine, not the 160hp we had been told.
A lot has changed in the last 4 years though, doggy PA12 was sold, the good one is a pile of metal and fabric now after an engine out forced approach. Everyone was ok.
This turned out to be a very educational and informative thread though.
A lot has changed in the last 4 years though, doggy PA12 was sold, the good one is a pile of metal and fabric now after an engine out forced approach. Everyone was ok.
This turned out to be a very educational and informative thread though.
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