skywagon8a
MEMBER
SE Mass MA6
Not all of them. The IO-550-D in the 185 is 300 hp (minimum). It feels like 310 when compared to the IO-520. The 550-N, -P and -R with the top induction systems are 310 hp.
Engines. A Discussion.
- Thread starter stewartb
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aktango58
FRIEND
18AA
Thank you Pete. I must have been flying the top induction version. Feed them fuel, they take more!
skywagon8a
MEMBER
SE Mass MA6
That's the first clue they have more power. :lol:
Or just a worse BMEP.
mvivion
SPONSOR
Bozeman,MT
Well, not to burst anyone's bubble when it comes to the IO-520 vs IO-550 conversions, the biggest difference is, in fact, the RATING scheme used to certify the respective engines.
The old rating scheme that Continental used with the IO-520 required that the engine make plus or minus 5% of "Rated Power". So, every engine coming off the line, at least theoretically, had to make AT LEAST 285 horsepower.
Now comes the 550, which was certificated under a different requirement: That engine is rated at 300 horsepower, plus 5%, minus ZERO. In other words, every 550 must make at least 300 horsepower.
The Continental Tech Rep who explained this to me then pointed out that you simply cannot have an engine fail that criteria, because if that happens, the factory has to pull a number of engines, not just the one that failed.
So, if all your 300 hp engine has to do is make at least 285 on the stand.....you shoot for "about" 300. If the engine the QC guy pulls only pulls 295 on the dyno, no sweat.
BUT, now, with the minus zero criteria, if that engine pulls 299 on the dyno, that engine and a bunch of others may be rejected.
According to the Tech Rep, the way you deal with that is you build a 300 hp rated engine that actually consistently pulls 310. And, the upper air induction engines, like the N, which are rated for 310....those actually pull about 320, again to prevent failure in quality control.
He also noted that BTW, Lycoming has always applied that tighter rating approach, which I verified when I was at the Lycoming Piston Engine Service School.
Ever notice that Lycoming engines of a certain rated HP often seem to pull harder than most comparably rated Continentals?
I ran 206s on floats, with IO-520s, then one with a 550, and there was no comparison as noted above in the 185 comparison.
But, that's not only a more powerful engine, but a LOT more efficient propeller as well.
You can't legitimately compare two engines running significantly different propellers.
It is, after all, thrust that matters.
MTV
The old rating scheme that Continental used with the IO-520 required that the engine make plus or minus 5% of "Rated Power". So, every engine coming off the line, at least theoretically, had to make AT LEAST 285 horsepower.
Now comes the 550, which was certificated under a different requirement: That engine is rated at 300 horsepower, plus 5%, minus ZERO. In other words, every 550 must make at least 300 horsepower.
The Continental Tech Rep who explained this to me then pointed out that you simply cannot have an engine fail that criteria, because if that happens, the factory has to pull a number of engines, not just the one that failed.
So, if all your 300 hp engine has to do is make at least 285 on the stand.....you shoot for "about" 300. If the engine the QC guy pulls only pulls 295 on the dyno, no sweat.
BUT, now, with the minus zero criteria, if that engine pulls 299 on the dyno, that engine and a bunch of others may be rejected.
According to the Tech Rep, the way you deal with that is you build a 300 hp rated engine that actually consistently pulls 310. And, the upper air induction engines, like the N, which are rated for 310....those actually pull about 320, again to prevent failure in quality control.
He also noted that BTW, Lycoming has always applied that tighter rating approach, which I verified when I was at the Lycoming Piston Engine Service School.
Ever notice that Lycoming engines of a certain rated HP often seem to pull harder than most comparably rated Continentals?
I ran 206s on floats, with IO-520s, then one with a 550, and there was no comparison as noted above in the 185 comparison.
But, that's not only a more powerful engine, but a LOT more efficient propeller as well.
You can't legitimately compare two engines running significantly different propellers.
It is, after all, thrust that matters.
MTV
aktango58
FRIEND
18AA
Mike sort of beat me to the answer, NO.
Horse power the engine makes still must become thrust through the propellor. And as we all know, some propellors work really good at slow speed high power, others are more efficient at speed.
So, the full answer is that it depends:lol:
aflyer
FRIEND
SW Colorado
Went through all this in the '90s, when some of the 180/185 club guys went crazy testing props with a big fish scale. There were some small differences between blade shapes, and even 2 blade vs 3 blade, but the real difference in static thrust came with diameter. The 88" 3-blade McCauley made the most thrust at the time, around 1100 lbs if I remember correctly. This made some intuitive sense to me, since the helicopter blades are the static thrust champions.
Testing for take off distance was a lot harder to do, and would have been more meaningful. The group spent a few days swapping props on hot engines trying eliminate more of the variables, and then gave the whole thing up.
Its still fun to sit with your feet on the cooler and argue about it.
John
Testing for take off distance was a lot harder to do, and would have been more meaningful. The group spent a few days swapping props on hot engines trying eliminate more of the variables, and then gave the whole thing up.
Its still fun to sit with your feet on the cooler and argue about it.
John
Dan Gervae
FRIEND
Upper Peninsula of Michigan
The other very important factor to Pilots besides HP is reliability....we want as much HP as we can get, and still have little to no maintenance....and have it make 1800-2000 hr TBO....because most of us don't have unlimited $$ and we don't have 9 lives...so we want the fan to consistently keep us cool......BUT.....we want more PERFORMANCE!!! we are cursed...lol
mvivion
SPONSOR
Bozeman,MT
Propeller length is in fact a very important factor. The limiting issues are two fold: Prop clearance and prop tip speed. A prop running close to the surface is a FOD magnet, and a tip moving too fast approaches Mach, with associated loss of thrust.
So, ideally, a really long prop, turning at relatively low rpm, is likely ideal. Take a look at the props on a Dash 8, for example. And they’re turning at relatively low rpm....1700 or so?
Problem we have is our engines are optimized for power at relatively higher rpm, and of course our gear isn’t as long.
But there are other factors that prop designers have applied to make new props more efficient. Mostly blade shape.
MTV
So, ideally, a really long prop, turning at relatively low rpm, is likely ideal. Take a look at the props on a Dash 8, for example. And they’re turning at relatively low rpm....1700 or so?
Problem we have is our engines are optimized for power at relatively higher rpm, and of course our gear isn’t as long.
But there are other factors that prop designers have applied to make new props more efficient. Mostly blade shape.
MTV
According to Pponk the popular C401-86" makes identical thrust as the C401-88". I'd love to see a static comparison between an IO-520 and IO-550. Maybe toss in a Yamaha Apex with it's relatively boney prop just to see how they differ. With respect to the big Continentals I know the heavy haulers like the 550 but the STOL guys that I know prefer the 520. I assume the RPM makes a difference? Has anyone dialed up the prop speed on a 550? I know it makes a big difference in my C401's performance. Don't the 520s and 550s use the same props?
In the high powered Cub world the best performing Whirl Wind constant speed STOL prop is not their longest. The 80" blades are wide and have significant twist. A buddy operates in the aerobatic world where they spin their props at 3300 rpm. Whirl Wind, MT, and Hartzell are all used. It's interesting to talk to the aerobatics guys and listen to their opinions about mags and props. The sum of my prop knowledge is that I don't know diddley about props!
In the high powered Cub world the best performing Whirl Wind constant speed STOL prop is not their longest. The 80" blades are wide and have significant twist. A buddy operates in the aerobatic world where they spin their props at 3300 rpm. Whirl Wind, MT, and Hartzell are all used. It's interesting to talk to the aerobatics guys and listen to their opinions about mags and props. The sum of my prop knowledge is that I don't know diddley about props!
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Your on the right track....On the Dash 8-100 (37 seats) I flew in the early 1990’s. Take Off was 1200rpm, Cruise was 900Rpm. Nice and quiet. We took the DC headsets off in cruise. We would speed up the rpm in icing conditions to 1050 to help sling it off. An inevitable imbalance would send a rhythmic vibration though the airframe as the prop de-ice went through four sequential steps over 2 minutes... I loved that airframe.
mvivion
SPONSOR
Bozeman,MT
Static thrust certainly isnt meaningless, but it doesn’t tell the whole story. The fact is, props don’t operate in a static environment.
But I agree, I don’t know diddly about prop dynamics either.
MTV
