Maintenance and Pilots on the ball.
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Hey Jaba, I think you touched on something worth noting when you say,
Quote: " typically on a dusty old C172 "
I have worked on aircraft that live central Aus, and the dry climate does play a part in the longevity of such, think Arizona. I picked up a 182 from central Aus, not internally primed (typical and maybe a little unique for Australia more so than other places due to saving a couple grand when ordering from the factory in the 70's-80's, but that's another story) and it was like a coke can inside, absolutely pristine, now it lives on the coast any surface not inhibited was quickly corroding.
Jas24, Typically when you file a blade, personally I come from a minimalist point of view, it is difficult to know how much material has been removed, and considering most of the damage is toward the tip where the centrifugal forces are at most play, has the most effect on balance, and will very quickly go out of balance, yes we do dynamically balance props, but sending a fixed pitch to the shop allows them to measure at incremental stages the remaining chord and statically balance also, along with check blade angles etc.
You would think blade angles wouldn't change much but it is not uncommon to find when trouble shooting an imbalance a blade out by more than half a degree at the tip which is significant.
Whilst a blanket change to AD/Prop/1 to Service/Overhaul in accordance with the manufacturers Data (i.e. 6Yr) may seem counter productive at times, I think the incorporation of a geographically guiding covenant would be appropriate.
Ultra, Solid.
Quote: " typically on a dusty old C172 "
I have worked on aircraft that live central Aus, and the dry climate does play a part in the longevity of such, think Arizona. I picked up a 182 from central Aus, not internally primed (typical and maybe a little unique for Australia more so than other places due to saving a couple grand when ordering from the factory in the 70's-80's, but that's another story) and it was like a coke can inside, absolutely pristine, now it lives on the coast any surface not inhibited was quickly corroding.
Jas24, Typically when you file a blade, personally I come from a minimalist point of view, it is difficult to know how much material has been removed, and considering most of the damage is toward the tip where the centrifugal forces are at most play, has the most effect on balance, and will very quickly go out of balance, yes we do dynamically balance props, but sending a fixed pitch to the shop allows them to measure at incremental stages the remaining chord and statically balance also, along with check blade angles etc.
You would think blade angles wouldn't change much but it is not uncommon to find when trouble shooting an imbalance a blade out by more than half a degree at the tip which is significant.
Whilst a blanket change to AD/Prop/1 to Service/Overhaul in accordance with the manufacturers Data (i.e. 6Yr) may seem counter productive at times, I think the incorporation of a geographically guiding covenant would be appropriate.
Ultra, Solid.
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On props and pilot maintenance....
Do whatever it takes to not put chips in the prop in the first place, whilst there is bad luck it is still possible to operate over gravel large and small with a high horsepower engine and low prop clearance and not get significant dings.
Run ups can be brief and on the run into wind, this high power static run up stuff is a little last century.
Wash your prop.
Bug guts can contain acids aside from a range of chemicals likely still unknown to science, dirt contains salts none of which rammed into a porous sand blasted LE at near sonic speeds is going to help prevent internal corrosion. Detergents used for washing it need to be chosen wisely with regard to PH and corrosive qualities. At the risk of making a recommendation CT18 from Chemtec seems pretty good and the fact millions of truck owners swear by might be worth something.
After washing and when dry, really dry, wipe some 50w oil along the LE, it will help seal it and slow the progression of contaminants into the grain structure of the blade.
This tip is not legal, but past to me from an older wiser seaplane driver, use a hard smooth surface instrument, side of leatherman, shaft of a large screw driver etc to rub the rough porous sand (or water) blasted LE this will put a smooth worked finish to the LE. Seems to me this blending of the surface grain leaves the LE a little more tolerant to ingression of contaminants.
Little of the above is relevant to employed pilots as the general rule is turn key and go, maintenance cost are someone else's concern. But aircraft owners who pay there own bills might garner something.
Do whatever it takes to not put chips in the prop in the first place, whilst there is bad luck it is still possible to operate over gravel large and small with a high horsepower engine and low prop clearance and not get significant dings.
Run ups can be brief and on the run into wind, this high power static run up stuff is a little last century.
Wash your prop.
Bug guts can contain acids aside from a range of chemicals likely still unknown to science, dirt contains salts none of which rammed into a porous sand blasted LE at near sonic speeds is going to help prevent internal corrosion. Detergents used for washing it need to be chosen wisely with regard to PH and corrosive qualities. At the risk of making a recommendation CT18 from Chemtec seems pretty good and the fact millions of truck owners swear by might be worth something.
After washing and when dry, really dry, wipe some 50w oil along the LE, it will help seal it and slow the progression of contaminants into the grain structure of the blade.
This tip is not legal, but past to me from an older wiser seaplane driver, use a hard smooth surface instrument, side of leatherman, shaft of a large screw driver etc to rub the rough porous sand (or water) blasted LE this will put a smooth worked finish to the LE. Seems to me this blending of the surface grain leaves the LE a little more tolerant to ingression of contaminants.
Little of the above is relevant to employed pilots as the general rule is turn key and go, maintenance cost are someone else's concern. But aircraft owners who pay there own bills might garner something.
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All excellent advice Youngmic. Here is another prop saving tip that was passed on to me by the operator of a fleet of GA aircraft that operates into many unpaved strips.
Before starting the engine select full coarse on the prop and be careful not to let the engine rev much on start up. With practice you can start without exceeding 1,000 revs. When you want to move off slowly increase the revs till the aircraft is rolling. You will notice that with full coarse selected the aircraft will move off 200 to 300 RPM less than with full fine selected. This achieves 2 things. First it is less inclined to suck rocks into the prop arc and secondly when the odd one does come through the slower moving prop incurs considerably less damage.
The rest is common sense. Many bush strips have a concrete pad for the flying doctor . Use it for your run ups. If one is not available do the mag checks at a fast taxi. On take off start the roll full coarse and once past the speed of a fast jog go to full fine (not TOO fast) and bring up full power. If you forget to go full fine the aircraft will tell you. It wont go any faster than 15 to 20 knots.
If the strip is a real bad one(Light bauxite stones or just graded strips are bad. Ones not touched since the last rain are better as the dry mud glues the stones down to some degree) consider not doing the mag check. What's more dangerous? The unlikely possibility of having to fly on one mag or the high chance of picking up a stone and inflicting unknown damage on the prop. I know this sounds a little complicated when you read it but in practice it is quite simple to do. Once we adopted this method prop damage was greatly reduced and I can't remember when we last had a bad rock chunk taken out of our prop.
Before starting the engine select full coarse on the prop and be careful not to let the engine rev much on start up. With practice you can start without exceeding 1,000 revs. When you want to move off slowly increase the revs till the aircraft is rolling. You will notice that with full coarse selected the aircraft will move off 200 to 300 RPM less than with full fine selected. This achieves 2 things. First it is less inclined to suck rocks into the prop arc and secondly when the odd one does come through the slower moving prop incurs considerably less damage.
The rest is common sense. Many bush strips have a concrete pad for the flying doctor . Use it for your run ups. If one is not available do the mag checks at a fast taxi. On take off start the roll full coarse and once past the speed of a fast jog go to full fine (not TOO fast) and bring up full power. If you forget to go full fine the aircraft will tell you. It wont go any faster than 15 to 20 knots.
If the strip is a real bad one(Light bauxite stones or just graded strips are bad. Ones not touched since the last rain are better as the dry mud glues the stones down to some degree) consider not doing the mag check. What's more dangerous? The unlikely possibility of having to fly on one mag or the high chance of picking up a stone and inflicting unknown damage on the prop. I know this sounds a little complicated when you read it but in practice it is quite simple to do. Once we adopted this method prop damage was greatly reduced and I can't remember when we last had a bad rock chunk taken out of our prop.
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I'd be careful suggesting people skip the mag step altogether rutan, you can check for both ignition systems at any rpm, check it @ 1200 if you must, but at least check it!.
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In practice that's what we do but I make the point that the aircraft will fly quite safely on one mag but shed 6" off one prop blade and
. I've seen young inexperienced pilots do things that would horrify their boss/LAME. eg parked in loose gravel and sand meticulously doing mag and prop checks sending dust,sand ,stones and tumbleweeds from Blackstone Range or similar place almost to Alice Springs.
. I've seen young inexperienced pilots do things that would horrify their boss/LAME. eg parked in loose gravel and sand meticulously doing mag and prop checks sending dust,sand ,stones and tumbleweeds from Blackstone Range or similar place almost to Alice Springs.
And tell us what is the risk of taking off, having not tested a CSU's operation at 1,700 RPM.
Pregnancy of all local maidens? Chooks not laying?
What are the problems that the test identifies, and what are the probabilities and consequences of those outcomes, if a CSU fails to reduce in RPM during a 'standard' check?
Pregnancy of all local maidens? Chooks not laying?
What are the problems that the test identifies, and what are the probabilities and consequences of those outcomes, if a CSU fails to reduce in RPM during a 'standard' check?
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Eddie the whole point of the exercise is to keep the prop revs as low as possible to prevent stone damage. You'll quickly discover if the governor is working or not as you add power. Try it one day.
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Before starting the engine select full coarse on the prop and be careful not to let the engine rev much on start up
But given an aircraft needs exactly the same amount of thrust to move, it would likely follow that the same aerodynamic flow forces are in play. As such tip vortices and the surrounding frontal low pressure area might be much the same. In fact with a higher AoA what might occur is a greater amount of thrust at the tip and with it perhaps a stronger likelihood for a ground vortex to be created closer to the tip. As opposed to the finer pitch setting which may well have negligible AoA at the tip. If you watch those ground vortexes, once established they seem to like to settle about a 1/4 way up from the tip.
The difference only being a higher blade AoA and slower RPM, of course the slower RPM will have a significant mitigating effect on the size/depth of the dent. Assuming you can reach governing speed off idle, I seem to recall some types being shut down in course pitch to try and achieve this.
To my thinking the key to it is never let a stone sucking vortex even form from ground to prop as once it forms it will start picking up stones.
I liken the whole exercise to a bit like standing on a meat ants nest in thongs, it's no problem as long as you keep moving.
Interesting thought anyway.
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Did the AD under discussion include fixed pitch props? I had assumed it was about constant speed props, although a 172 was mentioned and obviously they normally have fixed pitch props. Can someone explain the AD to a non-ozzie?
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To my thinking the key to it is never let a stone sucking vortex even form from ground to prop as once it forms it will start picking up stones.
An interesting test for people with time on their hands would be to spread flour or similar in front of the prop and observe where vortices form at the revs needed to start the aircraft rolling both at full fine and full coarse. Any takers?
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An interesting test for people with time on their hands would be to spread flour or similar in front of the prop and observe where vortices form at the revs needed to start the aircraft rolling both at full fine and full coarse. Any takers?
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OK, I gotta ask, is it common for your engine to spool up to 1800 RPM when you start it?
However in 45 years in and around aviation I have seen some, shall we say, 'interesting' start ups.
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Just read about another story today.
This is Why I keep telling people to invest in a good engine monitor and an Advanced Pilot Seminars engine class. This guy should too.
Maybe the mag timing is off? 
Ya kidding me! No doubt and it is advanced what's worse!
This is Why I keep telling people to invest in a good engine monitor and an Advanced Pilot Seminars engine class. This guy should too.
So, I get the plane home from annual and the EGT gauges (single point) no longer line up at idle or even take off where they used too. The right one reads off the chart low, whatever that means, and the left one reads higher. On top of that the right engine CHT(single point) is reading higher than normal quickly showing 400 degrees on climb and that is unusual. Also the right oil temp is noticeably higher than normal usually a tad over 150; now 190-200. LOP at 12k I still cannot get the CHT below 400 when it's usually 350 easy. Then I noticed on the mag checks there was hardly any drop when switching mags; this is unusual; I usually get at least a 50-75 rpm drop off. So finally I ask another mechanic and suggested maybe the mag timing was off. Comments?
Ya kidding me! No doubt and it is advanced what's worse!
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Thought I would share another one.
With a class coming up in November this is timely. This fellow is a lovely B737 pilot with a gorgeous RV8 (LAME Maintained). And a real student of the science. Well done sir!
With a class coming up in November this is timely. This fellow is a lovely B737 pilot with a gorgeous RV8 (LAME Maintained). And a real student of the science. Well done sir!
Gday David,
I've now installed the Dynon EMS D10 into my RV8 and it is fantastic. The engine has been running roughly, but still (just) passing the 1800 RPM mag check*. With the engine monitor and the knowledge from the course to really use it, I could fly without being terrified by the rough running because I could easily see the cause, and after landing I was able to ask my LAME to replace the lower plug on the number 3 cylinder to fix the problem.
Last month I flew with my LAME mate from America in his RV7 who is a true believer of the 50 ROP technique. After hearing me out, he let me run the engine as lean of peak. One of the CHTs was higher than he liked and he was about to shove the mixture in to fix it. I persuaded him to let me lean it out a fraction more, and when the CHTs all dropped 10 degrees you should have seen his jaw drop. He promised me he'll be going to do the course at Ada.
Love the knowledge to use the D10 - it's like having little windows in all the cylinders.
Keep up the good work. I'm trying my best to spread the word about you guys.
Cheers,
Rob
* I also get that a mag check isn't as good as a higher power in-flight check
I've now installed the Dynon EMS D10 into my RV8 and it is fantastic. The engine has been running roughly, but still (just) passing the 1800 RPM mag check*. With the engine monitor and the knowledge from the course to really use it, I could fly without being terrified by the rough running because I could easily see the cause, and after landing I was able to ask my LAME to replace the lower plug on the number 3 cylinder to fix the problem.
Last month I flew with my LAME mate from America in his RV7 who is a true believer of the 50 ROP technique. After hearing me out, he let me run the engine as lean of peak. One of the CHTs was higher than he liked and he was about to shove the mixture in to fix it. I persuaded him to let me lean it out a fraction more, and when the CHTs all dropped 10 degrees you should have seen his jaw drop. He promised me he'll be going to do the course at Ada.
Love the knowledge to use the D10 - it's like having little windows in all the cylinders.
Keep up the good work. I'm trying my best to spread the word about you guys.
Cheers,
Rob
* I also get that a mag check isn't as good as a higher power in-flight check
When you live....
Adelaide - money very well spent.
Someone asked me if I was the
that started this thread off - but I failed at the first test....
Someone asked me if I was the
very smart guy, who randomly visits this forum and has a large pressurised twin
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The knowledge gained from understanding the chemistry and physics of piston engines is not only for the balanced injector multi probe fraternity it is a huge benefit to any pilot regardless if you never fly a machine equipped to operate LOP.
Here is the why.
A few years back I was in a position (briefly) to oversee a mixed bag of pilots flying piston SEA. One of these pilots was good enough to point out to me that he was unable successfully lean the IO-520 C210 as he had in the past (the company was a 50 ROP operation).
I jumped in and went for a ride, the single EGT and CHT was all it had, after take off and leveled it quickly became apparent that full rich equaled 75 ROP.
Somewhat concerning and leading to the next question where the hell was it during full power, fuel flow looked fine and it leaned smooth enough for a standard set up in cruise, so likely no blocked injector. With the engine as cool as I could get it a brief full power setup and very quick lean to have a look.
Just as I hoped I wouldn't see but did, at full power it was running 75 ROP too.
Back at the engineer facility I pointed out FF seems right but this EGT indication is worrying (note Fuel Flow is a pressure indication not fuel flow).
They changed out the probe, still no joy, they checked the FCU and all in speck and checked all the injectors too. At this point they were happy to shrug their shoulders happy to see it fly away. After I showed some persistence they did set FF's at the max permissible and this resulted in a positive change, now it was 85 ROP at full power and full rich.
I was still not happy, clearly this engine was talking its just that we weren't listening properly.
The engineering company brought in the big guns, a major aircraft and engine rebuild shop, they were keen to play down the significance of an EGT reading if everything else checked out.
Feeling very unsupported I decided to give TCM tech support in the US a call. I now felt supported they backed me up stating at the absolute minimum 150 ROP should be achievable and if we aint see'n it then keep looking and don't worry about setting a FF above red line.
The company in turn brought in a very wise local CAR 35 fellow hoping he would douse the fire and cure me of my troublesome thoughts, then I could release the aircraft back to service. Fortunately he was a well read and wise fellow and stood by what TCM and I had been saying, there is a problem.
In the end they set a smidge over red line fuel flow, they could not get past the fact the red line was a legal limit that could get them in the poo for willfully ignoring.
In the end I think I saw 125 ROP at take off power, far from ideal, but the best I could push for.
Without the knowledge gained through JD and et al that poor old engine would have been climbed out under power, often in stinking hot OAT's running just a tad outside of the optimum detonation mixture setting. And given the natural spread of inter-cylinder mixture maldistribution no doubt some cylinders were smack bang at best detonation.
Sadly not many seemed to care.
Here is the why.
A few years back I was in a position (briefly) to oversee a mixed bag of pilots flying piston SEA. One of these pilots was good enough to point out to me that he was unable successfully lean the IO-520 C210 as he had in the past (the company was a 50 ROP operation).
I jumped in and went for a ride, the single EGT and CHT was all it had, after take off and leveled it quickly became apparent that full rich equaled 75 ROP.
Somewhat concerning and leading to the next question where the hell was it during full power, fuel flow looked fine and it leaned smooth enough for a standard set up in cruise, so likely no blocked injector. With the engine as cool as I could get it a brief full power setup and very quick lean to have a look.
Just as I hoped I wouldn't see but did, at full power it was running 75 ROP too.
Back at the engineer facility I pointed out FF seems right but this EGT indication is worrying (note Fuel Flow is a pressure indication not fuel flow).
They changed out the probe, still no joy, they checked the FCU and all in speck and checked all the injectors too. At this point they were happy to shrug their shoulders happy to see it fly away. After I showed some persistence they did set FF's at the max permissible and this resulted in a positive change, now it was 85 ROP at full power and full rich.
I was still not happy, clearly this engine was talking its just that we weren't listening properly.
The engineering company brought in the big guns, a major aircraft and engine rebuild shop, they were keen to play down the significance of an EGT reading if everything else checked out.
Feeling very unsupported I decided to give TCM tech support in the US a call. I now felt supported they backed me up stating at the absolute minimum 150 ROP should be achievable and if we aint see'n it then keep looking and don't worry about setting a FF above red line.
The company in turn brought in a very wise local CAR 35 fellow hoping he would douse the fire and cure me of my troublesome thoughts, then I could release the aircraft back to service. Fortunately he was a well read and wise fellow and stood by what TCM and I had been saying, there is a problem.
In the end they set a smidge over red line fuel flow, they could not get past the fact the red line was a legal limit that could get them in the poo for willfully ignoring.
In the end I think I saw 125 ROP at take off power, far from ideal, but the best I could push for.
Without the knowledge gained through JD and et al that poor old engine would have been climbed out under power, often in stinking hot OAT's running just a tad outside of the optimum detonation mixture setting. And given the natural spread of inter-cylinder mixture maldistribution no doubt some cylinders were smack bang at best detonation.
Sadly not many seemed to care.