Auto conversion ideas

[Dan Thomas]

If you read the FAR 33.37 is states "or have an ignition system of equivalent in-flight reliability." With the reliability being subjective for the FAA to decide. Remeber, by LAW (or AD) you have to rebuild a tractor mag every 500 hours. Who is replacing an car alternator that often? Reliability?

Three things you get wrong right away:

1. There is no law or AD that mandates magneto overhaul every 500 hours. These are manufacturer recommendations, not laws, and while Champion/Slick is 500, TCM/Bendix is 400 hours.

2. Alternators on aircraft engines do not last anywhere near as long as in cars, and there is a completely understandable reason for that. The alternator in both cars and airplanes is geared or belted at a ratio to have it reach its redline RPM at the engine's redline. This protects it from overspeed damage or failure, while having it spin fast enough at idle to generate useful output.
A. The car's engine cruises at around a third of its redline RPM. My Hyundai and Ford ranger both cruise at about 2100 on the highway, and their redlines are both around 6500.
B. BUT the airplane's engine typically cruises at around 2500 RPM, and redlines at around 2700. So that alternator is running at 93% of its redline RPM, far higher than the car's 30% of redline.

Why does that matter? Because the carbon-block field brushes that run on the rotor's slip rings to bring the power to the field coil in the rotor are wearing faster at higher RPMs. It's as simple as that. Cessna, for instance, recommends a 500-hour inspection interval on those brushes. I did that on all our aircraft; at 500 the brushes were about a third gone, and at the next inspection, 1000 hours, 2/3 gone, I replaced them. If the airplane uses more power, as the 172SP did with its glass panel, the brushes were mostly gone by 600 or 700 hours. More current causes more electrical erosion.

And so, alternators on auto conversions will also have much shorter lives than they did in the car. If there is no redundancy for EI and EFI power supply, you're in trouble pretty quick. Those auto conversions won't be cruising at 2100 RPM. I cruised the Subaru EJ22 at 4600 RPM, in the Glastar I installed it. Redline was 5600. Its alternator was then at 82% of its redline.

On POA we read constantly of alternator failures, and it's mostly due to running alternators to failure. No preventive maintenance. No brush checks.

pfarber: If you read 33.75 it gives guidance that I bet almost no one designing a car motor package ever read. While (to me at least) its all common sense, being in EAB land means that you can legally ignore all the common sense and do whatever you want.... and give the nay-sayers of auto conversions more fodder to blather on about.

You'd be surprised at the stuff auto designing engineers go through. No automaker wants a reputation of many their cars sitting broken down at the side of the highway.

Yes, go ahead and do what you want with your experimental, but it's all on you, then. Not on anyone else at all.

Even though a newly overhauled certificated engine has significant 'infant mortality'.... so much for those properly designed and freshly rebuilt motors done by trained professionals.

3. Significant mortality of overhauled certified engines? Where do you get your numbers? Please post the source. Ron Wanttaja has actual numbers on that, and he posted this chart in Post #42 of this thread:


One also has to remember that a Lycoming or Continental in a homebuilt has often been "rebuilt" or at least opened up by the homebuilder, often without any reference to the overhaul manual for the engine. They often use the wrong sealants (RTV being a common mistake), over- or under-torque hardware, and do not maintain proper tolerances, and the engine fails. That's supposed to be Lyc's or Continental's fault?
Then add in the improperly designed fuel systems that fail. Those aren't included in that chart, which lists only mechanical failures of the engine itself.

Understand that chart. It's not saying that 58% of traditional engines are failing by 400 hours. It's saying that those that DO fail are failing at the rates shown. And not many fail. This is in homebuilts, too, not certified aircraft maintained by certified professionals.

I bought many Lycoming factory overhauls in my time as a director of aircraft maintenance for a flight school (and flew them as an instructor, and also as the test pilot after installation. Not one of them ever failed me. None, in about 35,000 total hours of operation to TBO). Your assertions of high infant mortality are just made-up baseless accusations. If it was actually true, all the aircraft engine manufacturers would have been sued out of existence long ago.

Edit: Re the SDS stuff, yes, it's good stuff. But like all electronic fuel injection and ignition, it relies completely on electrical power from sources outside itself; the alternator and battery, and if one wants reasonable reliability, one needs redundancy, such as a second alternator and battery. Lycoming's certified iE2 engines are fully EI and EFI, and have a built-in redundant alternator and would also require a separate battery. FAR33.37.

Magnetos and carbs or mechanical fuel injection need no electrical supply, which is why we still see them on brand-new airplanes. Cheaper, no extra weight or complexity of redundant systems. They just need to be maintained properly, and the SDS stuff will be no different. Ignore it or its electrical supply, and it will eventually cause problems. In any aircraft (or car), electrical problems make up about 90% of engine problems.

SDS has some dandy stuff to improve the legacy engines. O-ring seals in rocker covers instead of gaskets. O-rings in induction flanges instead of gaskets. Other such stuff. Lycoming has no incentive to change it, because the recertification costs might never be recovered. Their volumes are too low. But it's great stuff for the homebuilder.

 

[flyingron]

The Casale Vdrives aren't light (75pounds dry or so). Add that to the weight of whatever engine (small blocks run about 500lbs without accessories) you're putting it on, and you'll likely find it is of diminishing returns.

 

[moparrob66]

Okay thanks! Ive seen pics, they look like lightweight aluminum but they have to be beefy enough tolerate big v-8 ski boat shenanigans. Im considering multiple v belt pulleys, like 5-6 belts. They wont transmit as much torsional vibration as a big toothed belt. They would run cooler than the wide toothed belt, and if one fails, you probably have a few seconds to throttle back before they all fail. Isnt there a helicopter that uses this arrangement? A simple switch triggered by the could activate a warning light indicating trouble with one of the belts, and a ir pulley temp sensor could be an indicator of belt slippage. Still seems easier than resolving the torsional vibration dilemma.

 

[Dan Thomas]

Okay thanks! Ive seen pics, they look like lightweight aluminum but they have to be beefy enough tolerate big v-8 ski boat shenanigans. Im considering multiple v belt pulleys, like 5-6 belts. They wont transmit as much torsional vibration as a big toothed belt. They would run cooler than the wide toothed belt, and if one fails, you probably have a few seconds to throttle back before they all fail. Isnt there a helicopter that uses this arrangement? A simple switch triggered by the could activate a warning light indicating trouble with one of the belts, and a ir pulley temp sensor could be an indicator of belt slippage. Still seems easier than resolving the torsional vibration dilemma.

You will need a set of matched belts. They're cut from the same tube, adjacent to each other. That way, they're as close a possible to the same length. Differing lengths create problems, not least the shortest being the tightest and transmitting the most power and burning out, and the longest jumping around because the pulley ratios are messed up for it, and sometimes just coming right off and fouling all the others. If a belt breaks it can fall into the space between the pulleys and lift the whole works off.

They won't run cooler than the timing belts. There is friction as the belt enters and wedges in the pulley groove, and more friction when it pulls out. That makes heat, and that's the reason why V-belts are less efficient than timing belts.

The Robinson helicopters use V-belts between the engine and transmission. Here is the R22 setup:



And the Schweitzer (Hughes) 269:



Note the rod between the drive pulley shaft and the driven shaft; that takes the bending loads off the crankshaft.

 

[moparrob66]

Good info! I'll have a lot of testing to do before any flight. Ben Haas seemed to have a good set up with his alloy small block ford- powered Zenith 801.

 

[Kenny Phillips]

Rotax has entered the chat. They are snowmobile engines with a reduction gear and are certified for certain aircraft. So it's not that PSRUs fail, or auto engines are bad, but poorly designed PSRUs and engine conversations fail. There is absolutely nothing special about an airplane motor or car motor... they do the exact same thing, and both can be very reliable as long as the installer has the competency to make it work.

The Rotax boxers aren't "snowmobile" engines. They are aircraft engines.

 

[pfarber]

Three things you get wrong right away:

1. There is no law or AD that mandates magneto overhaul every 500 hours. These are manufacturer recommendations, not laws, and while Champion/Slick is 500, TCM/Bendix is 400 hours.

2. Alternators on aircraft engines do not last anywhere near as long as in cars, and there is a completely understandable reason for that. The alternator in both cars and airplanes is geared or belted at a ratio to have it reach its redline RPM at the engine's redline. This protects it from overspeed damage or failure, while having it spin fast enough at idle to generate useful output.
A. The car's engine cruises at around a third of its redline RPM. My Hyundai and Ford ranger both cruise at about 2100 on the highway, and their redlines are both around 6500.
B. BUT the airplane's engine typically cruises at around 2500 RPM, and redlines at around 2700. So that alternator is running at 93% of its redline RPM, far higher than the car's 30% of redline.

Why does that matter? Because the carbon-block field brushes that run on the rotor's slip rings to bring the power to the field coil in the rotor are wearing faster at higher RPMs. It's as simple as that. Cessna, for instance, recommends a 500-hour inspection interval on those brushes. I did that on all our aircraft; at 500 the brushes were about a third gone, and at the next inspection, 1000 hours, 2/3 gone, I replaced them. If the airplane uses more power, as the 172SP did with its glass panel, the brushes were mostly gone by 600 or 700 hours. More current causes more electrical erosion.

And so, alternators on auto conversions will also have much shorter lives than they did in the car. If there is no redundancy for EI and EFI power supply, you're in trouble pretty quick. Those auto conversions won't be cruising at 2100 RPM. I cruised the Subaru EJ22 at 4600 RPM, in the Glastar I installed it. Redline was 5600. Its alternator was then at 82% of its redline.

On POA we read constantly of alternator failures, and it's mostly due to running alternators to failure. No preventive maintenance. No brush checks.

pfarber: If you read 33.75 it gives guidance that I bet almost no one designing a car motor package ever read. While (to me at least) its all common sense, being in EAB land means that you can legally ignore all the common sense and do whatever you want.... and give the nay-sayers of auto conversions more fodder to blather on about.

You'd be surprised at the stuff auto designing engineers go through. No automaker wants a reputation of many their cars sitting broken down at the side of the highway.

Yes, go ahead and do what you want with your experimental, but it's all on you, then. Not on anyone else at all.

3. Significant mortality of overhauled certified engines? Where do you get your numbers? Please post the source. Ron Wanttaja has actual numbers on that, and he posted this chart in Post #42 of this thread:
View attachment 132131

One also has to remember that a Lycoming or Continental in a homebuilt has often been "rebuilt" or at least opened up by the homebuilder, often without any reference to the overhaul manual for the engine. They often use the wrong sealants (RTV being a common mistake), over- or under-torque hardware, and do not maintain proper tolerances, and the engine fails. That's supposed to be Lyc's or Continental's fault?
Then add in the improperly designed fuel systems that fail. Those aren't included in that chart, which lists only mechanical failures of the engine itself.

Understand that chart. It's not saying that 58% of traditional engines are failing by 400 hours. It's saying that those that DO fail are failing at the rates shown. And not many fail. This is in homebuilts, too, not certified aircraft maintained by certified professionals.

I bought many Lycoming factory overhauls in my time as a director of aircraft maintenance for a flight school (and flew them as an instructor, and also as the test pilot after installation. Not one of them ever failed me. None, in about 35,000 total hours of operation to TBO). Your assertions of high infant mortality are just made-up baseless accusations. If it was actually true, all the aircraft engine manufacturers would have been sued out of existence long ago.

Edit: Re the SDS stuff, yes, it's good stuff. But like all electronic fuel injection and ignition, it relies completely on electrical power from sources outside itself; the alternator and battery, and if one wants reasonable reliability, one needs redundancy, such as a second alternator and battery. Lycoming's certified iE2 engines are fully EI and EFI, and have a built-in redundant alternator and would also require a separate battery. FAR33.37.

Magnetos and carbs or mechanical fuel injection need no electrical supply, which is why we still see them on brand-new airplanes. Cheaper, no extra weight or complexity of redundant systems. They just need to be maintained properly, and the SDS stuff will be no different. Ignore it or its electrical supply, and it will eventually cause problems. In any aircraft (or car), electrical problems make up about 90% of engine problems.

SDS has some dandy stuff to improve the legacy engines. O-ring seals in rocker covers instead of gaskets. O-rings in induction flanges instead of gaskets. Other such stuff. Lycoming has no incentive to change it, because the recertification costs might never be recovered. Their volumes are too low. But it's great stuff for the homebuilder.

Strike one:
At least one AD (I don't care to find more... but you know they exist)
AD 78-09-07 R3 was superseded by AD 96-12-07 was Superseded by AD 2005-12-06. AD 78-09-07 R3 & AD 96-12-07 required the repetitive inspection of the Impulse couplings installed on the magnetos at 500 hour intervals and the possible replacement of riveted impulse couplings with Snap ring couplings. AD 2005-12-06 superseded the older AD’s and removed the requirement for the 500 hour inspection of any Bendix series magneto installed on any engine except those installed on Lycoming AEIO-540, HIO-540, IO-540, 0-540, and TIO-540 series engines. So that it does not apply to any Bendix magneto installed on an O-300 or C145 engine. Read the AD’s and service bulletins.

Strike two:
Car alternators run at the or near the exact same RPMs as an airplane motor. At cruise speed on a highway, what is the normal RPM for 70mph for a 4 or 5 cly engine? My v6 is just shy of 2000rpm at 70mph.... whats the cruise RPM of a typical GA? About 2000rpm. Isn't Cessna famous for using car alternators? Like right off the shelf production Ford 60A alternators? Like from AutoZone? I'd dying to hear more about these carbon brushes you are infatuated about.

Strike three:
there is no comparison to be made concerning a certificated airplane engine rebuilt to new specs by an approved FAA manufacturer or repair station and Joe Q. Public in his garage. You are comparing a boiled hot dog to a 5 star Michelin restaurant and are surprised that one is better than the other.

I'll agree that the monkey turning the wrench is way more a problem for E/AB than infant mortality of a certificated motor... but the fact that even PoA is filled with 'how do I break in my motor' shows that both are still more of an art than a science.

 

[tspear]

Strike two:
Car alternators run at the or near the exact same RPMs as an airplane motor. At cruise speed on a highway, what is the normal RPM for 70mph for a 4 or 5 cly engine? My v6 is just shy of 2000rpm at 70mph.... whats the cruise RPM of a typical GA? About 2000rpm. Isn't Cessna famous for using car alternators? Like right off the shelf production Ford 60A alternators? Like from AutoZone? I'd dying to hear more about these carbon brushes you are infatuated about.

Alternators do not run at a one for one speed of the engine. They are geared to spin faster to generate a more stable field. From what I have seen posted by a number of people, is the alternator gearing is based on the max engine speed. e.g. Assume the max speed of the alternator is 27K RPM. Above this number, you have the potential for failure. Therefore, if the max speed of your engine is 5400 RPM, you might have a 1 to 5 ratio on the gearing. So, when cruising at 2000 RPM on the highway, the alternator is only spinning round 37% (2000/5400) of max capacity. Now look at your airplane engine, it has a max speed of 2700 RPM. Therefore to hit the maximum speed of the alternator, you would have a gear ratio of 1 to 10. Now cruise at 2500 RPM this would give you the alternator running at 92% (2500/2700) of maximum RPM. The higher the RPM, the faster the brushes wear out. This is a primary reason why the same alternators used in planes and cars have differences in longevity.

Tim

 

[Capt. Geoffrey Thorpe]

Compare the size of the pulley on the crankshaft.

 

[Dan Thomas]

Strike one:
At least one AD (I don't care to find more... but you know they exist)
AD 78-09-07 R3 was superseded by AD 96-12-07 was Superseded by AD 2005-12-06. AD 78-09-07 R3 & AD 96-12-07 required the repetitive inspection of the Impulse couplings installed on the magnetos at 500 hour intervals

Note that the ADs demand 500-hour inspection or replacement of the impulse coupling. It does not demand a magneto overhaul. There is a MAJOR difference between inspection or parts replacement and overhaul. Major. English matters here.

Strike two:
Car alternators run at the or near the exact same RPMs as an airplane motor. At cruise speed on a highway, what is the normal RPM for 70mph for a 4 or 5 cly engine? My v6 is just shy of 2000rpm at 70mph.... whats the cruise RPM of a typical GA? About 2000rpm. Isn't Cessna famous for using car alternators? Like right off the shelf production Ford 60A alternators? Like from AutoZone? I'd dying to hear more about these carbon brushes you are infatuated about.

TSpear and Capt. Thorpe made it clear, as I did in my answer to you on the subject of alternator drive ratios. I have explained this brush-wear factor many times on POA and most people understand it.

Strike three:
there is no comparison to be made concerning a certificated airplane engine rebuilt to new specs by an approved FAA manufacturer or repair station and Joe Q. Public in his garage. You are comparing a boiled hot dog to a 5 star Michelin restaurant and are surprised that one is better than the other.

I'll agree that the monkey turning the wrench is way more a problem for E/AB than infant mortality of a certificated motor... but the fact that even PoA is filled with 'how do I break in my motor' shows that both are still more of an art than a science.

Well, that's obvious, isn't it? I was making the point that a Lyc or Continental in a homebuilt was very possibly opened or overhauled by the homebuilder, in an effort to save money, of course, and if he didn't follow the overhaul instructions, he's much more likely to have trouble with that engine.

Many POAers, you included, do not seem to know that the internet has a wealth of answers for them. The Lycoming Direct Drive engine overhaul manual: http://www.monticellofc.org/aircraft/Lycoming-OH-Manual 2002 ed.pdf

That's a free version. It's not fully up-to-date. If you want a fully updated version, you buy it from Lycoming: https://www.lycoming.com/sites/default/files/attachments/SL-L114BJ_Technical_Publications.pdf.pdf

Break-In prodedure? https://www.lycoming.com/sites/defa...gine%20Break-In%20and%20Oil%20Consumption.pdf

Lycoming also publishes FREE engine operator's manuals. Just Google "Lycoming O-360 Operator's Manual" for instance and it will pop up. Lots of good info. Here's the 360: https://www.lycoming.com/content/op...O-360-IO-360-AIO-360-HIO-360-TIO-360-60297-12

There are not-free manuals available for magnetos and alternators and such. Fooling with this stuff as an amateur is foolish, especially magnetos. What is your life worth? Less than the cost of the manual?

Continental has its M-O manual that covers a lot of stuff. It's not an overhaul manual. There are free Continental O/H manuals, not updated, on the 'net. A great education. There is no excuse to be ignorant. https://pceonline.com/wp-content/uploads/2017/04/M-0standardpractice2017-01-15.pdf

 

[moparrob66]

Robinson helicopters seem to have success with multiple v belts. I'd either need double the belts with double the horsepower or half the lifespan. With a properly designed psru, belts and pulleys could be inspected and changed easily and frequently.

 

[Bell206]

Robinson helicopters seem to have success with multiple v belts. I'd either need double the belts with double the horsepower or half the lifespan.

FYI: No comparison between a Robinson and a direct drive reduction unit you are looking for. Completely different dynamics and operation outside the use of multiple belts. About as black and white as you can get.

 

[pfarber]

Alternators do not run at a one for one speed of the engine. They are geared to spin faster to generate a more stable field. From what I have seen posted by a number of people, is the alternator gearing is based on the max engine speed. e.g. Assume the max speed of the alternator is 27K RPM. Above this number, you have the potential for failure. Therefore, if the max speed of your engine is 5400 RPM, you might have a 1 to 5 ratio on the gearing. So, when cruising at 2000 RPM on the highway, the alternator is only spinning round 37% (2000/5400) of max capacity. Now look at your airplane engine, it has a max speed of 2700 RPM. Therefore to hit the maximum speed of the alternator, you would have a gear ratio of 1 to 10. Now cruise at 2500 RPM this would give you the alternator running at 92% (2500/2700) of maximum RPM. The higher the RPM, the faster the brushes wear out. This is a primary reason why the same alternators used in planes and cars have differences in longevity.

Tim

You are correct that the pulley's do create a greater than 1:1 ratio. But airplane engines also run higher ratios.

You kinda made the point... an alternator has to spin fast to induce the current in the windings.

Here's a photo of an O-320 alternator pulley. Are you seriously gonna tell me that alternator is spining at the same or SLOWER speed than the engine RPM?

Please be more accurate. From what I can fine a Cessna stock alt. pully ratio is 3.8:1, at full RPM you're turning over 8000 rpms.

Also you're blow out a rectifier long before you kill a bearing on a properly set up alternator.

 

[moparrob66]

Okay i'm sure they are different. 160-180hp under constant-ish load vs 200-300-400hp under varying loads. But isnt the Robinson helicopter turning a much larger rotor AND tail rotor and demanding more torque on the belts than a proportionately sized propeller?


Looking at the Helio Courier and its GO-480, it is reported by those who have flown them that it's 300ish horsepower and appropriately matched propellor performs better than the later models with direct drive 350hp and 400hp Lycomings. Gears CAUSE increased torque, and RPMs ALLOW an increase in horsepower. This difference in performance has to be due to the propeller speed reduction units on the GO engines vs the IO engines.

 

[Bell206]

But isnt the Robinson helicopter turning a much larger rotor AND tail rotor and demanding more torque on the belts than a proportionately sized propeller?

Sure. But as I mentioned, there are substantial differences in why/how those belts are used vs your need/use. For one, Robbies use belts so they can start the engine by reducing the belt tension to allow slippage between the lower (engine) sheave and the upper (transmission) sheave. Only when the engine is running and stabilized does the pilot engage clutch actuator via a switch which moves the upper sheave (pulley) to tension the belts and start driving the rotors. Yours would be a direct drive couple, with the belts in constant tension which has a much different operational affect than with the helicopter belt system. Regardless, those belts/clutch are still known to be the weak link in the drive system and tend to not handle abuse over a long period. So not really a good example to base your design on.

 

[Dan Thomas]

You are correct that the pulley's do create a greater than 1:1 ratio. But airplane engines also run higher ratios.
You kinda made the point... an alternator has to spin fast to induce the current in the windings.
Here's a photo of an O-320 alternator pulley. Are you seriously gonna tell me that alternator is spining at the same or SLOWER speed than the engine RPM?
Please be more accurate. From what I can fine a Cessna stock alt. pully ratio is 3.8:1, at full RPM you're turning over 8000 rpms.
Also you're blow out a rectifier long before you kill a bearing on a properly set up alternator.

Oh, dear. We have a problem. Just what is it that you did not understand about this, in post #81?

Alternators on aircraft engines do not last anywhere near as long as in cars, and there is a completely understandable reason for that. The alternator in both cars and airplanes is geared or belted at a ratio to have it reach its redline RPM at the engine's redline. This protects it from overspeed damage or failure, while having it spin fast enough at idle to generate useful output.
A. The car's engine cruises at around a third of its redline RPM. My Hyundai and Ford ranger both cruise at about 2100 on the highway, and their redlines are both around 6500.
B. BUT the airplane's engine typically cruises at around 2500 RPM, and redlines at around 2700. So that alternator is running at 93% of its redline RPM, far higher than the car's 30% of redline.

I bolded the important part: The alternator is ratio'd to the engine so that both reach their redlines at the same time. That way, we get good power at idle, but don't "blow out a rectifier or kill a bearing" at those redline RPMs. Rectifiers, for one thing, do not care about RPM. The bearings in these alternators are also designed for speeds well above redline. Their failure is usually due to corrosion or overtightening of the belt, both of those being maintenance problems, not alternator problems.

It is very simple math. And it means that since the aircraft engine is operating near redline in cruise, so is the alternator, and its brush wear is higher than in the car's alternator due to that. Moreover, I had alternators with many thousands of hours on them, with only brush replacements. Some of those alternators were taken off the runout engine cores and installed on the new engines, repeatedly. Some might have had 8000 or 10,000 hours on them, on those bearings and rectifiers and everything, all at near-redline RPM. What usually finally failed them was the depth of wear on the slip rings, too deep to clean up anymore. And those slip rings last a lot longer than they do in a car, because they're not subjected to the dusty conditions so many cars are often in. How many airplanes are taking off in blinding dust storms, or right behind another airplane on a gravel runway? And how dusty is it at altitude? It's not.

Have you even had an alternator apart? Do you know how it works, in conjunction with the regulator? Do you know what the regulator does and how it does it? These are all important things that mechanics need to know for intelligent troubleshooting.

 

[Dan Thomas]

Gears CAUSE increased torque, and RPMs ALLOW an increase in horsepower. This difference in performance has to be due to the propeller speed reduction units on the GO engines vs the IO engines.

There's much more to the story than that. The Helio used a geared engine so it could swing a larger propeller while staying subsonic. Larger propellers are far more efficient in takeoff and climb; if we take it to its extreme, we see that the Robinson R22 uses 124 HP to swing a 25-foot rotor that lifts the 1370-pound gross weight machine. No six-foot propeller would ever do that.

The Helio's forerunner was the Helioplane, and this is Wiki's description of it:

The demonstrator for the Courier's concept, "Helioplane #1", was converted by the then-local Wiggins Airways firm from a Piper PA-17 Vagabond Trainer, one of the so-named "short-wing Pipers" in production following World War II. Only the cabin area of the PA-17's original airframe remained unmodified, with the fuselage lengthened by four feet (1.2 meters), given a taller fin-rudder unit, clipped the Vagabond's stock 29 ft-3 inch (8.92 meter) wingspan down to only some 28.5 feet (8.7 meters), fitted the shortened wings with full-span leading-edge slats, long-span wing flaps that forced the ailerons to be much diminished in their span - only occupying the two outermost rib bays inboard of the wingtip; and a longer-travel main landing gear of a taller design, not unlike that of the 1930s-origin Fieseler Fi 156 German military short take-off and landing (STOL) pioneer aircraft. The powerplant for the demonstrator was switched to the Continental C85 boxer-four cylinder air-cooled engine, upgraded with fuel-injection, and uniquely equipped with a multi-belt speed reduction unit to drive its Aeroproducts nine-foot (2.75 meter) diameter, variable-pitch two-blade propeller, which contributed greatly to the amazing STOL flight characteristics of the demonstrator aircraft.

Look at that last sentence. That little C-85 swung a nine-foot, variable-pitch propeller. That's a 50% larger diameter and a disc area 2.25 times larger. Makes a BIG difference.
The Helioplane:



You can see the redrive behind the prop.

 

[moparrob66]

Thats incredible! I knew the Helio prototype started out as a vagabond but I didnt realize it had a wildly modified C-85. Very impressive!

 

[Daleandee]

Thats incredible! I knew the Helio prototype started out as a vagabond but I didnt realize it had a wildly modified C-85. Very impressive!

Dan knows stuff ...

 

[moparrob66]

Reading about how 85 horsepower turns a 9' propeller with apparent success has me wondering how many GA aircraft are fitted with a less than optimal prop.

 

[mondtster]

Reading about how 85 horsepower turns a 9' propeller with apparent success has me wondering how many GA aircraft are fitted with a less than optimal prop.

That generally only happens when the owner thinks they know more than the manufacturer.

 

[moparrob66]

Would static thrust be a better way to quantify engine/propeller performance? I'd love to see a H295 vs H250 vs H700 comparison in static thrust.

 

[Dan Thomas]

Reading about how 85 horsepower turns a 9' propeller with apparent success has me wondering how many GA aircraft are fitted with a less than optimal prop.

Every airplane is a collection of compromises. The average consumer-grade spam can is an all-metal trike with a fixed-pitch prop, directly driven by the engine. There are reasons for all of that:

All-metal can be tied down outside. It stands the weather better. But it tends to be heavier than a rag-and-tube machine.

The fixed-pitch prop is simple and stout and its manufacturing and maintenance costs are far lower than any C/S or variable-pitch prop. There is no prop control to fuss with, no governor. But the range of performance gets limited. You have only second gear, sort of.

Direct-drive avoids more cost and complexity and failure points. But now the propeller has to be shorter to let the engine spin up to some RPM where HP is reasonable, and we lose the efficiency of the long prop. Shorter props are cheaper, too. There have been numerous geared engines, but they've had their drawbacks and have not been particularly popular with pilots or owners. They cost a lot more to overhaul. The advantages of gearing have to be major, or it makes no sense.

The trike is much easier to handle than the taildragger. So it's popular. Imagine a nine-foot prop on a 172. Now the gear legs have to lift that airplane another 18 inches or more above the pavement, at least twice as high as it is now, so they get a lot longer and heavier and the ground stability of the airplane becomes terrible. Too tall. Hard to get in and out. Heavy. The four forces the prop makes that cause hassles especially on takeoff are much bigger: Torque reaction drives the left wheel harder onto the surface and creates more drag, pulling the nose left; Gyroscopic precession pulls the nose right when you raise it; Asymmetric thrust is higher on the right side in the climb, pulling the nose left; and P-factor, the swirling propstream, strikes the left side of the vertical fin, forcing tail right/nose left.

It all makes the airplane much more expensive and harder to fly, and most pilots don't like to work too hard or borrow too much money. So Cessna and Piper and others don't do this.

A 185 with a seaplane prop, 86" diameter, a bit over seven feet, is bad enough. You need a bootful of right rudder on takeoff, and if there's a crosswind from the left, things can get exciting. Unlike the trike, raising the taildragger's tail makes precession pull the nose left, so all four forces are piling on to the left.

The manufacturers have found that cheaper, easy-to-fly airplanes have generally sold better and have kept their pilots out of trouble more often. So marketing and liability concerns dictate what we see out there.

 

[Dan Thomas]

Would static thrust be a better way to quantify engine/propeller performance? I'd love to see a H295 vs H250 vs H700 comparison in static thrust.

Good static numbers can be achieved with a low-pitched prop, but the airplane might not even take off as the AoA of the propeller blades drops to nothing before flying speed is reached. So static numbers are untrustworthy.

 

[Capt. Geoffrey Thorpe]

Reading about how 85 horsepower turns a 9' propeller with apparent success has me wondering how many GA aircraft are fitted with a less than optimal prop.

All of them. (Depending on your definition of "optimal")

 

[Dan Thomas]

All of them. (Depending on your definition of "optimal")

Yup. How many new airplanes are fitted with an optimal price tag?

 

[moparrob66]

Now Im curious about how much of an improvement is made by only adding a constant speed prop? Werent there some Beech Sierra/Musketeer etc that were made with same airframe and horsepower but some fixed and others constant speed? I'd love to build a test stand to work on this but im better off using data gathered by someone else. I know sone 172s have STCs for the 180hp O-360 and some have fixed pitch while others are CS.

 

[Dana]

Would static thrust be a better way to quantify engine/propeller performance? I'd love to see a H295 vs H250 vs H700 comparison in static thrust.

No, because the propeller is or should be optimized for operation at some nonzero airspeed. A helicopter rotor would make a huge static thrust, but it wouldn't do a very good job of pulling an airplane forward at 150 knots.

Now Im curious about how much of an improvement is made by only adding a constant speed prop?

Constant speed props start to make sense when you need good performance over a wide range of airspeeds, i.e. climb and cruise. Otherwise they're usually not worth the added cost, weight, and complexity.

 

[pfarber]

Oh, dear. We have a problem. Just what is it that you did not understand about this, in post #81?

I bolded the important part: The alternator is ratio'd to the engine so that both reach their redlines at the same time. That way, we get good power at idle, but don't "blow out a rectifier or kill a bearing" at those redline RPMs. Rectifiers, for one thing, do not care about RPM. The bearings in these alternators are also designed for speeds well above redline. Their failure is usually due to corrosion or overtightening of the belt, both of those being maintenance problems, not alternator problems.

It is very simple math. And it means that since the aircraft engine is operating near redline in cruise, so is the alternator, and its brush wear is higher than in the car's alternator due to that. Moreover, I had alternators with many thousands of hours on them, with only brush replacements. Some of those alternators were taken off the runout engine cores and installed on the new engines, repeatedly. Some might have had 8000 or 10,000 hours on them, on those bearings and rectifiers and everything, all at near-redline RPM. What usually finally failed them was the depth of wear on the slip rings, too deep to clean up anymore. And those slip rings last a lot longer than they do in a car, because they're not subjected to the dusty conditions so many cars are often in. How many airplanes are taking off in blinding dust storms, or right behind another airplane on a gravel runway? And how dusty is it at altitude? It's not.

Have you even had an alternator apart? Do you know how it works, in conjunction with the regulator? Do you know what the regulator does and how it does it? These are all important things that mechanics need to know for intelligent troubleshooting.

You are moving the goalposts. Is it bearings going bad or brushes wearing out? Car alternators turn JUST AS FAST as AIRPLANE ONES. They have to in order to make rated output. MAX RPM is not an issue. As long as the alt is spinning at its min rated output speed (usually less than 2k rpm) the voltage/amps are regulated at rated output.

Alternator brush wear is not a thing to worry about, nor are bearings wearing out unless you have the belt tensioned wrong.

You are just killing electrons with tired old wives tales. Because MECHANICAL alternator issues are rare. You'll blow a rectifier long before you wear out a bearing or a brush.

Since you have nothing new to add, and are simply bouncing from one old wives tale to antoher, and I have debunked everything you have said, unless you have some FACTS or numbers and not old wives tales, I'm gonna say this horse is dead.

 

[pfarber]

I'll add this tidbit to prove my point more-er. Here's a Cessna SB calling for alt's to be replaced due to brush wear. WHY? The brushes were made with the wrong material that didn't have the proper wear characteristics,.

SB06-24-03

You may thing 'but that proves you're wrong! NO. It proves that unless there is a massive issue (like the parts being made wrong) alt's don't have a significant issue with mechanical wear in normal use.

Popping a VR or rectifier or mis-tensioning a belt will kill an alt quick.. but that's not what were talking about.

 

[Dan Thomas]

You are moving the goalposts. Is it bearings going bad or brushes wearing out? Car alternators turn JUST AS FAST as AIRPLANE ONES. They have to in order to make rated output. MAX RPM is not an issue. As long as the alt is spinning at its min rated output speed (usually less than 2k rpm) the voltage/amps are regulated at rated output.

Again, car alternators spend most of their life at much lower RPM than they do in an airplane, because the car's engine cruises at a far lower percentage of redline than the airplane's engine. The belt/gear ratios and cruising vs. redline RPMs PROVE that. I will not argue such obvious stuff anymore with you.

Alternator brush wear is not a thing to worry about, nor are bearings wearing out unless you have the belt tensioned wrong.

Once more: I ask you where you get your "knowledge." What are your aviation credentials? Are you a pilot of any sort? What sort? Do you have any aircraft mechanic's training at all? Any certifications? I have asked for this info five or six times now, because what you keep saying is wrong.

You are just killing electrons with tired old wives tales. Because MECHANICAL alternator issues are rare. You'll blow a rectifier long before you wear out a bearing or a brush.

Funny, that. I replaced an awful lot of worn brushes, but NEVER replaced rectifier assemblies, or even an alternator with a failed rectifier. How many failed rectifiers have you replaced, or even encountered? Were they aircraft alternators? I have replaced alternator bearings maybe twice, at the most. They live a long time.

This is part of a Cessna inspection checklist:

That note 7 there, for alternator brushes and slip rings:

Do you see alternator bearings or rectifiers mentioned there? I don't. They are not a problem. Cessna is concerned with the alternator's security of mounting, its external condition, and the condition of its wiring, and with its brushes.

Since you have nothing new to add, and are simply bouncing from one old wives tale to antoher, and I have debunked everything you have said, unless you have some FACTS or numbers and not old wives tales, I'm gonna say this horse is dead.

You have debunked nothing. Claiming to have done so is not proof of debunking. It's called gaslighting.

I will say nothing more on this. You believe as you wish. Just don't go confusing other people.

 

[mondtster]

Now Im curious about how much of an improvement is made by only adding a constant speed prop? Werent there some Beech Sierra/Musketeer etc that were made with same airframe and horsepower but some fixed and others constant speed? I'd love to build a test stand to work on this but im better off using data gathered by someone else. I know sone 172s have STCs for the 180hp O-360 and some have fixed pitch while others are CS.

Where are you hoping to gain performance? Climb or cruise or somewhere else?

While my last comment may have been a bit abstract, my point and experience remains constant. What I have seen almost universally is that when people try repitching a fixed pitch prop to get more cruise speed (and keeping everything else constant) is that takeoff performance will suffer and the cruise speed will remain the same but fuel consumption increases. It’s almost like OEMs tested things and came up with the best compromise for the airplane to start with…

The Cherokee 235 and Cherokee 6 260 were sold with both fixed and constant speed propeller options. You might consult Piper’s documentation for both to see what, if any performance differences they relayed to the pilots via the flight manuals.

 

[Daleandee]

What I have seen almost universally is that when people try repitching a fixed pitch prop to get more cruise speed (and keeping everything else constant) is that takeoff performance will suffer and the cruise speed will remain the same but fuel consumption increases.

This has been proven with fixed pitch props on several versions of the experimental plane that I fly. Some builders have said a xxxxx prop gives me a slightly higher cruise and then admit that the rate of climb "is not quite as good as before" thereby reinforcing that fact that TANSTAAFL. I don't doubt that some FP props may have a bit more efficiency than others but among the leaders of the pack those differences are likely pretty small ...

 

[Dan Thomas]

It’s almost like OEMs tested things and came up with the best compromise for the airplane to start with…

They did. Most type-certified airplanes with fixed-pitch props have the prop designed and pitched to allow the engine to reach redline RPM in level straight flight at full throttle at sea level on a standard day. This actually tends to be accurate even several thousand feet up on cold or hot days, too. As the atmosphere's density decreases with altitude and temperature, the engine produces less HP but the drag on the prop and airframe are also less, so the redline RPM at full throttle still works for level flight.

So a prop with higher pitch means that the engine will never be able to produce its max power except in a shallow dive, and what good is that? A prop pitched lower means that the throttle will have to be pulled way back for cruise to keep the engine within redline, so you mush along.

If one wants better performance, a constant-speed prop is necessary.

 

[pfarber]

Where are you hoping to gain performance? Climb or cruise or somewhere else?

While my last comment may have been a bit abstract, my point and experience remains constant. What I have seen almost universally is that when people try repitching a fixed pitch prop to get more cruise speed (and keeping everything else constant) is that takeoff performance will suffer and the cruise speed will remain the same but fuel consumption increases. It’s almost like OEMs tested things and came up with the best compromise for the airplane to start with…

The Cherokee 235 and Cherokee 6 260 were sold with both fixed and constant speed propeller options. You might consult Piper’s documentation for both to see what, if any performance differences they relayed to the pilots via the flight manuals.

Wanna know what the piper PA-28-140/150/160/180/235 service manual says about alternator brushes and slip rings? Answer: NOTHING. hahahahaha



So that must mean that either there are no brushes? That they never wear? But that cannot be an oversight as the hydraulic motor has a specific entry for brushes:


Note 19 is to inspect every 100 hours if used in training.

So in Piper land alt brushes never wear out? Or (as any MX should realize) that GA SMs/POH are a laughable mess.

I haven't seen anything that points to all these brush failures that are claimed to happening. Alternator brushes wearing out is just a thing. Please present SOME sort of evidence to disprove that which is not empirical are second hand.

 

[Bell206]

Wanna know what the piper PA-28-140/150/160/180/235 service manual says about alternator brushes and slip rings? Answer: NOTHING. hahahahaha

Well... thats because the alternator, vacuum pump, mags, etc. are considered components of the engine or a standalone item. And in most cases, those inspection requirements and intervals are only found in the component maintenance manual and not the airframe mx manual. So the 500hr alternator brush inspection, 500hr mag inspection, 500hr vac pump vane inspection are not listed in the Piper inspection program. And this is the reason it is missed or not required during an annual just like you missed it.

Don't know what you do in the aviation industry, but its obviously not mx related or only in a very limited capacity as shown by your posts. So I guess the joke is on you... again. ha ha.

 

[Dan Thomas]

Wanna know what the piper PA-28-140/150/160/180/235 service manual says about alternator brushes and slip rings? Answer: NOTHING. hahahahaha

If you look again at that inspection checklist, you'll see that engine overhaul is listed. But the manual doesn't tell you how to overhaul the engine. You use the engine overhaul manual for that. Similarly, Piper expects you to inspect the alternator in accordance with the alternator manufacturer's manuals. Cessna put the brush inspection in the checklist likely because so many alternators were being run to failure.

On page 4C1 of that Piper manual I see this:

So that must mean that either there are no brushes? That they never wear? But that cannot be an oversight as the hydraulic motor has a specific entry for brushes:

See above. Piper mentions pump brushes and so does Cessna, in the inspection checklists for their airplanes. That's another item that typically gets run until it fails.

Aircraft inspection costs money, so many owners want it done quick and dirty. They're more concerned with having that signature in the logs than in having the machinery safe and reliable. That is, until it quits on them in a bad place and time. So many of us have to learn stuff the hard way.

From the Hartzell Alternator Owner's manual:



Hartzell is the current owner of some of the popular alternator designs using in light aircraft, including Pipers. https://hartzell.aero/wp-content/uploads/2014/12/ES1031-Alt-Owners-Man-Rev-New.pdf

 

[pfarber]

moving the goal posts again did we???? I showed that there is no requirement for the brush inspection as per the Piper inspection schedule.

"Cessna put the brush inspection in the checklist likely because so many alternators were being run to failure." So not only were the goal posts moved, now comes pure conjecture. Please keep moving the posts, I want to see how wacky it can get.

the 4C1 paragraph is for (wait for it) BENCH TESTING THE ALTERNATOR. HAHHAHA

So yes, I will agree that if you alternator is not alternating the current, then by all means troubleshot IAW the SM. I also agree with putting air in tires when air is missing, changing lamps when lamps are burnt out and other common sense items.

DId you see that goal post move?

'Cessna has a SM inspection item to check brushes'
Me Piper doesn't care about brushes, and I post the inspection items.

the goal post is picked up, moved 200 yards away and then a post about how BENCH CHECKING a broken alt. is the same thing as a scheduled inspection per the SM.

If anything else at least two people are reading the manuals lol

Its also hilarious that Piper is telling you directly that the brushes are just not a big issue, yet (as I have said) the rectifiers are easily blowed up.

 

[Dan Thomas]

moving the goal posts again did we???? I showed that there is no requirement for the brush inspection as per the Piper inspection schedule.

"Cessna put the brush inspection in the checklist likely because so many alternators were being run to failure." So not only were the goal posts moved, now comes pure conjecture. Please keep moving the posts, I want to see how wacky it can get.

the 4C1 paragraph is for (wait for it) BENCH TESTING THE ALTERNATOR. HAHHAHA

So yes, I will agree that if you alternator is not alternating the current, then by all means troubleshot IAW the SM. I also agree with putting air in tires when air is missing, changing lamps when lamps are burnt out and other common sense items.

DId you see that goal post move?

'Cessna has a SM inspection item to check brushes'
Me Piper doesn't care about brushes, and I post the inspection items.

the goal post is picked up, moved 200 yards away and then a post about how BENCH CHECKING a broken alt. is the same thing as a scheduled inspection per the SM.

If anything else at least two people are reading the manuals lol

Its also hilarious that Piper is telling you directly that the brushes are just not a big issue, yet (as I have said) the rectifiers are easily blowed up.


View attachment 133504

Once again: What are your credentials and experience? I don' t believe you have either of them.

 

[Bell206]

moving the goal posts again did we???? I showed that there is no requirement for the brush inspection as per the Piper inspection schedule.

Even the Part 43 Appx D regulatory reference does not require a brush inspection. So what’s your point again?

However, any experienced and knowledgeable mechanic… will recommend to an owner, additional checks they know will protect the owner’s investment and decrease the chances of failures, regardless if the OEM or even the FAA think they are not important.

Its about as basic as basic gets when maintaining an aircraft. Unfortunately, there are aircraft owners who think like you and prefer to be reactive when it comes to maintaining their aircraft vs being proactive. It is what it is.