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Thread: Cessna 185 IO-520 or IO-550

  1. #1
    Steve Pierce's Avatar
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    Cessna 185 IO-520 or IO-550

    I have a friend interested in a Cessna 185 that is a little past TBO on the orginal IO-520. We were discussing if it would be time to upgrade to the IO-550 or get a remanufactured IO-520 with the heavier case. I know several people here have C180/185s and wondered about pros and cons of either engine.
    Steve Pierce

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    Cubus Maximus's Avatar
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    the general impression I get from the 185 cognoscenti around this neck of the woods is to stick with the 520.

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    520

    Steve,

    I know several guys that have "upgraded" to the 550 that wish they had a 520 back in Cessna spray planes. I have never had much trouble with the 520s and since I backed down to 2700 for takeoff the prop hub/case/cylinder cracking has all but went away. They still seem to be a 12-1400 hr. engine but we run them hard.

    Dave

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    I pulled my hi-time IO-520 and put an IO-550 in. No regrets. The IO-550 gives me 10-15mph more at the same fuel flow, is about the same weight, and is an updated engine. It's worth the $2000 to upgrade. I also went to a 3 blade McCaulley 401 prop. Take off is head and shoulders above what I had before. The engine/prop combination is like flying a turbine, it is that smooth. The big thing with the IO550 was the autolean. Use the same manual setup as the 520. Also the IO-550D for the Cessna has tapered fins on the barrel. The engine will run hotter and you have to pay attention to the cowl flap position and cylinder head temps. Motor mount will be the same. I used an Atlee-Dodge seaplane mount and there are no problems. Also Continental has been very good at answering my questions. Switch.

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    mvivion's Avatar
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    Steve,

    I haven't flown a 550 in a 185, but we switched to 550's in several 206's. I think the 550 got a bad reputation early cause people were running them too hard, didn't understand hp rating or leaning on these engines. Also, the auto lean feature is a bad idea on these low level airplanes, so as da man said, stick with the stock manual system. Continental also changed the design of the cylinders several years ago, and that pretty much eliminated a lot of the cylinder problems.

    I ran a 550 in a 206, almost always at 3800 pounds on floats for 1400 hours, and never touched a cylinder. Loaned the plane to the wrong pilot, who put 20 hours on it, and had to change a cylinder. He didn't understand or care about setting power, or leaning, and refused to read the book.

    This is a continuous rated 300 hp engine, at 2700 rpm, whereas the 520 is a continuous rated 285 hp engine, with 300 hp permissable for 5 minutes. Percent horsepower settings for power and leaning are based on the CONTINUOUS power rating, not the full power setting. So people who are used to 520's get in the airplane now has a 550 and push up 24 square, as usual. Except that's way up there in percent power, like 80 percent. Read the book--leaning is prohibited at these very high power settings. Point is, though, you don't NEED those very high power settings to do everything the 520 did, and more.

    These engines, since they are rated by the NEWER rating standards, actually put out more power at takeoff setting than ANY 520, AND they have much more torque. Finally, they are much smoother.

    I'd certainly recommend a 550 to anyone who will take the time to read the operators' information on the engine and learn to run it. If this is a customer who NEVER will listen to advice or read a manual, may not be the best, but those types will screw up a 520 as well, so....

    Also, this engine, at relatively low power settings, runs lean of peak so nice you can't even believe it. I ran the one in the 206 all the time at 13.2 gph or so in cruise.

    MTV

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    375handh's Avatar
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    Cubus Maximus:

    Cognoscenti. Such a great word, but you so rarely get to use it.

    Kinda like "gargantuan" in Kill Bill 2.

    375HandH

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    Cubus Maximus's Avatar
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    or even "Bloviate"

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    A couple of other things I forgot to mention. In talking with the Continental rep, I asked for the dyno test results of my factory reman. He said no but stated the IO-520 generally dynos between 287-295hp. The IO-550 will generally dyno between 309-316 hp. And this accounts for the increase in torque on the 550. Also Continental was short on cores when I got my reman. ALL PARTS except the starter housing were new manufacture. I would strongly suggest a factory reman.

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    mvivion's Avatar
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    The difference Charles notes relates to what I mentioned: The engines were rated under two different rating standards. The old standard permitted the manufacturer to put an engine out the door that made more than rated hp, or some less, I believe 5%, but may have been a bit different. The newer rating standards, under which the 550 is rated, require +5% and -0%. In other words, a 300 hp rated engine MUST make at least 300 hp.

    With the 520, it was "acceptable" to push a brand new one out the door that made only 290 hp on the dyno, or maybe a little less. With the 550, every one has to make AT LEAST rated power, so they actually build in a little extra ooomph, just to be sure it passes. If a test engine fails, that whole batch of engines has to be torn down, and rebuilt. That's per Lycoming, at least, and I was told the same by Continental reps.

    So, they build the 550's to put out 305 or 310. That way if one is a tad lame, it'll still make 300.

    I really do think the intial teething problems with the 550 are fixed. The ones I've run are great engines.

    I don't know if there's an IO 550 N conversion for the 185, but that is the sweetest of the 550's, and if I were doing a 206, I'd use the N. It has a much better balanced induction system.

    MTV

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    io520 or 550

    i redid mine last year and went with replacing the 520. mainly due to cost(about 12 grand cheaper) went with a factory reman and a mac 401 86 incher, runs great but seems to run a little hot if you are not real carefull with the mixture, with a ramp temp of 100 down here most of them probably would run a little hot, about the same speed but climbs and takes off great

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    io520 or 550

    i redid mine last year and went with replacing the 520. mainly due to cost(about 12 grand cheaper) went with a factory reman and a mac 401 86 incher, runs great but seems to run a little hot if you are not real carefull with the mixture, with a ramp temp of 100 down here most of them probably would run a little hot, about the same speed but climbs and takes off great

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    T.J.'s Avatar
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    delete

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    Quote Originally Posted by mvivion
    These engines, since they are rated by the NEWER rating standards, actually put out more power at takeoff setting than ANY 520, AND they have much more torque.
    Of course the 550 has more torque. HP=Torque X RPM. For (approximately) the same HP, if the RPM is lower, the Torque must be higher. That's just arithmetic, not a characteristic of the engine independent of it's horsepower.

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    Quote Originally Posted by T.J.
    Mike:
    Would you happen to know how the factory built in the little extra "ooomph" to make sure it makes 300 HP?
    By increasing displacement.

    550 puts out 300 HP at 2700RPM, 520 puts out 285 at 2700 RPM, that's about 5% more power.

    550cid is about 5% larger than 520cid,

    5% more displacement gives you 5% more power.

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    HP=Torque*RPM/5252.113
    JimC

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    mvivion's Avatar
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    TJ,

    There are lots of ways to put a little more soup in an engine. aalexander pointed out the salient point in the 550--as every hot rodder knows, there's no replacement for displacement when it comes to making power. Displacement isn't the ONLY way to make more power, though. Camshaft lift and duration can make a huge difference in torque, as well as horsepower.

    As to the rating standards, Lycoming has used the "new" rating standards voluntarily for many, many years. This is why most Lycoming engines of comparable hp to most older Continentals always seem to actually make a little more power.

    Induction design, valve size and design, fuel flows, displacement, cam lift and duration, etc--remember--these guys are designing a NEW engine, so it's pretty easy to build in a few extra hp to make certain you meet the standards.



    This same story was given to me by Lycoming at the Piston Engine Service School, where I asked the question directly, and also from a Continental rep, who confirmed that the 550 is the first engine that Continental has certified under the more restrictive standard.

    MTV

  17. #17
    cpthazard's Avatar
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    I just had a fun four days on a 185 with a Cont IO-550, the starter adapter failed ......did I mention this beautiful airplane sits on amphib Aerocets. But we're on cement here in the desert not on the water. After unhooking all the usual things and hooking a chain fall from a bigger chain between beams in the hanger ceiling it was a simple matter to rotate the engine down to gain access to the rear of the engine, remove the old starter adapter and install the newly rebuilt yellow tagged unit. Just once I'd like to see the gentleman that designed some of this stuff come out to the shop and get his hands dirty~and smashed~and twisted..... Luckily?, I'm too fat to get up inside to hold onto the mount attach bolts, the removal of those plus the re-installation are the stuff of nightmares. TT on a factory new engine was 1089 hrs.

    The owner of this airplane would happily engage in verbal jousting with anyone that prefers the 520 over the 550, he's convinced that it's the best thing that ever happened for float flying.

    I believe for me and my sanity I'll just stick with my ol'stuporcub.

    db

  18. #18
    mvivion's Avatar
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    More torque, more power are always good in the float environment--in fact it's not a bad idea in the high density altitude environment, or for that matter--well, let's see--anywhere.

    The manufacturers really do make these things convenient to service, don't they .

    MTV

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    Quote Originally Posted by mvivion
    More torque, more power are always good in the float environment
    Mike,

    Can you explain how torque, by itself, is advantageous?

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    mvivion's Avatar
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    In a floatplane, that first few seconds of acceleration is where the engine is pulling hard, with little forward movement. Torque, as opposed to horsepower, is what gets you up on the step just a bit quicker because of this. It allows the engine to pull a big prop to max rpm at basically static, and with the blades pitched steeper while doing so, therefore generating more thrust early in the takeoff run.

    With a wheel plane, the airplane starts accelerating relatively quickly, and therefore torque isn't quite as noticeable when changed on wheels.

    Floats is a great place to test things like propellers and engines, cause it's a demanding environment. Skis also.

    MTV

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    Quote Originally Posted by mvivion
    In a floatplane, that first few seconds of acceleration is where the engine is pulling hard, with little forward movement. Torque, as opposed to horsepower, is what gets you up on the step just a bit quicker because of this.
    OK, so if we accept this premise, then you would agree that if you installed a powerplant on your 206 (for example) which produces twice the torque produced by an IO550, then your 206 would get up on the step much faster?

  22. #22
    Gordon Misch's Avatar
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    Mike, at a given prop speed and configuration, torque and power are identical in their effect. The horsepower the engine produces is equal to torque (foot lb) times RPM divided by 33,000. The horsepower actually acting on the aircraft is the propeller thrust (lb) times the speed of the plane (ft/sec) divided by 550. The physical principal is that 1 horsepower is defined as 550 ft-lb/sec, which is equal to 33,000 ft-lb/min.

    The portion of the engine horsepower that is converted to thrust will of course vary with the propeller, cowling configuration, airplane speed, air density, etc, etc. Thrust is a direct result of accelerating the air (Newton's second law), and (simplified) is the average prop blast velocity multiplied by the air density multiplied by the volume of air moved per second.

    Bottom line though, again, is that for a given engine speed horsepower and torque are directly proportional to each other, so an increase on one results in a proportionate increase in the other. For a given RPM, to distinguish between power and torque in terms of the airplane's performance is not meaningful.
    Gordon

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    mvivion's Avatar
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    12 Geezer,

    I can introduce you to a LOT of hot rod and motorcycle guys who would prove you dead wrong that torque and horsepower are directly correlated.

    You are missing the point that I was trying to make:

    The prop CONFIGURATION is going to be different in an engine with more torque. The prop blades are going to be able to go to a steeper pitch more quickly on an engine with more torque. Horsepower kinda comes along, generally, but torque is what permits that big prop to bite right away.

    This only makes a difference for maybe five or eight seconds, who knows? After that, torque is less of a factor.

    But the point is, in a floatplane, that time in the hole, coming up onto the step is where TORQUE is very important. Granted, horsepower doesn't hurt, cause generally big horsepower brings with it big torque, but not always.

    Again, its getting that prop pitch to STEEP quick, and delivering that thrust that makes the difference, and torque, not horsepower, does that best.

    And, yes, if you got twice the torque, you'd get up on step quicker. How much?? Who knows. If you doubled the torque, I'm betting horsepower would also change substantially as well, though.

    Nevertheless, for just this little short period of time, torque rules. And its over quick.

    Fly a Soloy converted 206 sometime. Granted, lots of horsepower, but the thing never hits the step. It sets you back in the seat on floats, and just goes from plow to flight.

    MTV

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    T.J.'s Avatar
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    mvivion's Avatar
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    TJ,

    Sorry, didn't understand your initial question.

    The 550 was designed from the outset to the stricter horsepower rating standards. It was designed as a ~ 308 to 310 hp engine, to make absolutely certain that every example turns out AT LEAST 300 hp on the dyno.

    The 520, on the other hand, was designed as a 285 hp engine, with a five minute limit at 300, but was rated, as I recall, at minus 5 % to plus 3%, or I may have that backards. Point is, every one of those engines only had to make somewhere around 290 hp to meet the certification standard as a ~ 300 hp engine.

    I'm sure the reason Continental went to 550 cubes was largely to make certain they could make 300 hp consistently. Also, they wanted to run the engine at lower rpm, for noise, which required more of something from the git go.

    They are similar engines, but not that similar. Particularly the IO 550 N is a very different engine, with a balanced intake manifold.

    In this regard, note that Lycoming has used the later horsepower rating standard for many years. Their comparable engine, normally aspirated--is the IO-540--a 300 hp engine as well. For years, I wondered why the IO 540's seemed to make more power than the IO-520 Continentals, even though they were both RATED as 300 hp engines.

    Lycoming long ago decided that at least 540 ci was the minimum it took to make 300 hp to the rating standard they were using. Those engines all come out the factory door making just a little more power than 300. And so do the 550 Continentals.

    MTV

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    Quote Originally Posted by mvivion
    And, yes, if you got twice the torque, you'd get up on step quicker. How much?? Who knows. If you doubled the torque, I'm betting horsepower would also change substantially as well, though.

    Nevertheless, for just this little short period of time, torque rules. And its over quick.
    OK, torque rules, and is the sole determining factor of how fast a plane gets op on the step.

    A 550 at 2700 rpm is producing about 583 ft-lb of torque.


    I'll give you a powerplant which more than doubles that torque. It's a 5 hp Briggs & Stratton lawnmower engine with a 150:1 gear reduction unit attatched. This setup will produce 1270 ft-lb of torque.

    So with the 5hp engine with gear reduction unit installed in your 206, it should get up on the step *much* quicker than with the IO 550, right? The torque is what determines how fast it gets up on the step and we're more than doubled the torque.

    Agree or disagree? If not, why not?

    edit: Just to clarify, I'm not positing this merely to make a frivolous argument, there is a point to this, so indulge me for a moment if you will.

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    Steve Pierce's Avatar
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    I talked to Ken at Lycon on Friday and it appears that the IO-550 is about $2K more than an IO-520 and there is a $2K core charge to upgrade. Also the original crank is non-VAR so I think that is a big chunk of change unless you go with a factory reman or new. Thanks for the input. Hadn't figured on extra speed at the same fuel flow but that makes sense after comparing to a 180 hp SC compared to a 150/160. I guess the decision has to be made as to weather more power, speed and fuel economy is worth the extra cash. Thanks again.
    Steve Pierce

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    mvivion's Avatar
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    aalexander,

    Well, your argument is frivolous, though I think I know where you're going.

    I did not imply that horsepower is irrelevant. My point was that with engines rated for similar horsepower (the IO 520 compared to the IO 550 IS the topic of this discussion, remember?) , the one with more torque will get up on step just a bit quicker. Not orders of magnitude, mind you...

    I'm comparing apples with apples. You're talking bananas there with max torque lawn mower engines, Dude. And, my point was that the torque really only makes a difference for a very short time.

    MTV

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    Well, let me throw in my 2 cents worth and stir mango's into this fruit salad.

    Back in the days when I was flying turboprops (mango's) some had torque gages, some had HP gages and some had % power gages. They were all the same gage, just with different markings. We were always told that - for example - 100% power = 875hp = 1240 lbs torque. So I always thought torque and horsepower were BOTH expressions of the amount of working force you could get out of an engine.

    I can see where gearing has a dramatic effect, but if assume that you could somehow mathematically account for that.

    This is an interesting discussion and I always learn from SOMETHING from MTV's postings.

    John Scott

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    Quote Originally Posted by Longwinglover
    Back in the days when I was flying turboprops (mango's) some had torque gages, some had HP gages and some had % power gages. They were all the same gage, just with different markings. We were always told that - for example - 100% power = 875hp = 1240 lbs torque. So I always thought torque and horsepower were BOTH expressions of the amount of working force you could get out of an engine.

    No they definitely are not the same. not by any stretch of the imagination. The airplane I fly has torquemeters. We have a high cruise power setting we use when heavy and a low cruise setting we use when lighter. The high cruise setting, is more power than the low cruise setting. however the torque meters read Higher on the low cruise setting. Torque is not the same as power.

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    Quote Originally Posted by mvivion
    aalexander,

    Well, your argument is frivolous, though I think I know where you're going.

    I did not imply that horsepower is irrelevant. My point was that with engines rated for similar horsepower (the IO 520 compared to the IO 550 IS the topic of this discussion, remember?) , the one with more torque will get up on step just a bit quicker. Not orders of magnitude, mind you...

    I'm comparing apples with apples. You're talking bananas there with max torque lawn mower engines, Dude. And, my point was that the torque really only makes a difference for a very short time.

    MTV


    No. Michael, it is not frivolous, not in the least. Sometimes it's easier to understand a concept if you examine the extreme example, and that's what I've done. I don't have the time right now to explain myself further, but I'll come back with I do. For now, the description 12 geezer gave is just about perfect. if you find your self in disagreement with that, it's because you're understanding of the physics is not up to par. I don't say that to belittle you in any way.

  32. #32
    180Marty's Avatar
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    While this is a little different example, it helps me understand hp and torque. Back in the early 80's I was hauling a load of cattle out of Idaho with a Peterbilt with a 445 hp 2 cycle Detroit Diesel. I looked in the mirror and a Kenworth is right on my bumper around Soda Springs so I comment that he must be empty and he says no, he weighs the same as me and also that he has a 450 hp Cat engine. When we get to the hill east of town, where he can pass, he smokes on past me and out of sight. While rated at the basically the same HP, the Cat had more torque or pulling power, thus my being passed.
    Marty

  33. #33
    mvivion's Avatar
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    aalexander,

    Maybe I don't understand the physics.

    As I noted earlier, however, the flaw in 12Geezer's argument is that a higher TORQUE engine will permit the propeller blades to run at a steeper angle for a little while, making more thrust--again for a little while. As the airplane accelerates, the blades change pitch angles, etc.

    My point was precisely that more torque will permit operation for a bit at a different blade angle, or prop configuration, producing more thrust.

    Then again, maybe I don't understand the physics.

    But, I'll tell you also that a C-90 Continental on the front of a J-3 will out pull an O-200 getting onto the step. Been there, done that. Why does a 90 hp rated engine actually get going quicker than a 100 hp engine? I've heard this same observation from others, by the way. The only theory I've heard that explains it is, if I understood the argument correctly, the C-90 has a different cam, which makes more torque.

    Fill me in when you have time.

    MTV

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    See, I told you I always learned something!

    John Scott

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    Let me put some numbers in this discussion. When I was doing my homework as to doing an upgrade or not, I talked to PPonk at the Airmen's Show here in Anchorage. The IO-520 with the 2 blade McCaulley turning at 2850rpm pulls about 920ft/lbs of torque at t/o. Also the prop tips exceed the speed of sound at that rpm. When the prop tips exceed the speed of sound, efficiency is lost-torque in other words. The McCaulley 401 prop(88 inches) pulls about 1075ft/lbs and this is at 2700rpm on the IO-550, without exceeding the speed of sound.

  36. #36
    mvivion's Avatar
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    Thanks, Charles. I hadn't heard any specific numbers, but the point is, the 550 pulls a good bit harder than the 520.

    That may not be a big deal on wheels.

    I like the 550 for a lot of other reasons as well, though.

    Steve, he can run the 520 LOP with good injectors, and get the fuel flows down as well. Don't let him do so till it's good and broken in, though.

    I really like the way the 550 runs LOP. I've spoken to Continental on LOP ops, and they say they're fine, unlike Lycoming.

    MTV

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    My take on the 550/520 debate is this: For a given constant speed propeller (operating at it's designed RPM), if the engine used produces more torque...it will produce more thrust. With in limits, that torque is translated into inches (or millimeters) of pitch. The propeller accelerates a tube of air, this "tube" having roughly the same diameter as the prop's diameter. Propellers produce thrust by adding momentum, M=mass*velocity. You can add mass (more air) in two ways: diameter and pitch. We are of course limited in diameter because of the noise concerns, tip speed-compressibility limitations and ground clearance. That leaves pitch. Make more pitch at any given RPM, you make more thrust. And again, more available torque from the engine translates into more pitch. The 550 on a engine dyno clearly produces more torque than the 520 in the range of RPM's that we are talking about.

    Lastly...just as a clarification. Thrust is measured in pounds or Newtons. Not ft-lbs, not ft/lb or any other set of units. Torque produced by an engine is measure in ft-lbs or Newton-Meters. There is a lot of mis-information in the aviation world about this.

    Bill

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    Bill,
    Your synopsis is correct. I have Dyno tested many race engines, primarily drag race and oval track. The torque curve is important when describing the capability to move an object given the same transmission device. If the propeller was the same for both engines, the engine with the flatter torque curve would accelerate the plane the quickest. This is caused by the higher torque value being available at a lower engine rpm. If the engine has more torque the propeller pitch will be greater at a given rpm. This produces greater thrust, which the airplane uses to accelerate. Now rpm being equal, the engine produces a torque value, which negates the affect of the torque curve. The only time that the torque curve is important is in variable engine rpm, such as with a fixed pitch prop. A constant speed prop is similar in operation to the slipper clutch used in Top Fuel drag racing. A Top Fuel engine is designed to operate within a very narrow speed range. The clutch is slipped to keep the engine in this engine speed range. There are many nuances to this subject, but the overall situation is, given the same propeller, with variable pitch, the engine that will allow the most pitch at a given rpm will produce the most thrust. More torque will produce more thrust. BTW, a dyno does not measure horsepower, it measures torque and rpm and then calculates horsepower from the formula previously stated. There are correction factors used to adjust the "Observed Torque" values. The intake air being different than standard, a correction factor is applied. While it is easy to control temperature and humidity, controlling barometric pressure is not at all easy. The Dyno that I worked with had a controlled environment for temperature and humidity, not barometric pressure. This eliminated the need for correction of temperature and humidity. We found that the correction factor for temperature and humidity was not as repeatable as the correction factor for pressure. Therefore we eliminated this factor.

  40. #40

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    Jan 2005
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    My 2 cents, if this plane is used for float operations, put the biggest baddest motor in it you can. No one has ever had too much power in any at gross loaded float plane on a hot humid no wind summer day.

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