I have discovered a relatively deep nick about 2" from the tip on one blade of my prop….I think it can just be filed out but I am waiting for the mechanic to look at it when he gets back to Aberdeen later this week….I had thought myself to be diligent in not doing the run-up on the part of the apron/taxiway known to be subject to loose material….others on this apron have previously suffered deep nicks there….even though it is routinely swept…but my question is: is there a way of achieving a satisfactory mag check and prop cycle without having to sit in one place and suck stones into the prop? Clearly seaplanes manage it whilst on the move….how do others avoid this problem?
If you’re running GAMIs you can do a lean of peak mag check at top of descent on each trip then a very quick mag check before the next take-off. Seaplanes only do a quick check as well before the speed gets away from you. Warbirds do it on the roll to keep the temps low.
Here’s a good article that covers lots of this stuff:
If you have to run up over a gravely surface of one with a lot of stone debris, a running mag check might be warranted if you can’t find a satisfactory location to perform the run up.
I only do one run up per flight day on the first flight of the day as I consider my previous flight as a long run up. I only cycle the prop a single time as I consider it hard on the engine, all I am checking for on a single engine is the RPM change during the cycle to demonstrate to me that the prop governor system is operating.
If you have a fuel injected engine and can run LOP, a better test of the condition of the ignition system is to perform an in flight magneto check prior to descent for landing and eliminate the on ground check as it doesn’t show up very much until things are pretty bad. An engine analyzer will be immensely helpful in determining the faulty plug. A caution if you perform an in-flight magneto check, if one of the magnetos has failed during the flight, you must be prepared for silence and resist the natural urge to immediately restore the switch to the running position. This can cause damage if the fuel builds up in the engine at full throttle and cause a back fire, so it is better to be prepared for this possibility and first retard the throttle to a low setting and then restore the ignition. If all of the EGT indications are substantially higher than normal, a likely cause is a failed magneto. Usually a single weak plug will show up as a high EGT on the affected cylinder. The magneto check will determine L or R. With this information, you can pull into the shop and ask them to replace the #3 bottom plug if you know how your magnetos are wired.
I know it can be like blasphemy to suggest that a thorough run up is not required before takeoff, but if I think propeller damage is even possible, and I am confident with how the engine is running to begin with, a run up might be simply check both mags at idle to make sure that they work at all, cycle the prop once at the lowest power setting which will change pitch, and carb heat just to assure that the engine does not stop, when it is applied. All of the foregoing can be done during taxi, if the taxi environment is not constrained or congested. Or, if lots of runway, at the beginning of the takeoff roll.
Sure, a confident feeling about the condition of the engine resulting from a “proper” run up is nice, but for my experience, scrapping a propeller blade is easy to do with careless run ups, and detecting a genuine engine problem, which might result in an unsafe flight condition is rather hard to do, and quite rare.
Yes, we do quick run ups in floatplanes, but again, keep it brief and lower power, as water spray can be every bit as damaging to a propeller blade as debris from the ground.
Honestly, if I really want to wring out and engine during a run up, I will generally fly the plane to do it. If the engine is not running well enough that I will fly it, then it’s going straight to the mechanic anyway. Yes, on very rare occasions, engines do stop in flight, it is nearly never because of a mag, a plug, propeller pitch, carb heat, or a mixture control having some difficult to detect failing. If they all work at all on the ground, they will work well enough in flight for a cautious circuit. Many was the time when I was hanging around helping with maintenance and diagnosis, that the mechanic would say to me “’Can’t find the problem, let’s take it for a flight and see if we can find it up there”, up to and including a laptop plugged in to a DA-42 a few years back.
Propellers are delicate and expensive…..
Agree. Let’s be honest, we fly to really “bad strips” rather unfrequently (some more some less) so on those few occasions, I just keep any runup action to an absolute minimum.
When in a hurry, I have been known to switch off then back on again the one magneto, then the other, during taxi. The slight drop in rpm is just as clear to observe as during standstill. Remains the need to taxi clear of debris.
And yes, I know one should not take off in a hurry, thanks. Make it “when taking off at less than usual leisure”, ok?
I was lucky as one of my initial PPL instructors had the guts to teach me NOT do do the full runup if on a loose surface. I am fully with Pilot DAR and does it the same way when departing from grass or gravel strips. Passengers do not notice unless they are pilots, in which case they usually think they are going to die when we take off without having tortured the prop with a full run-up or exercised the prop.
The standard mag check is done at fully rich mixture and medium power or so, usually 1800 or 2000 RPM. My understanding is that the ignition system is tested just as well at lower power setting (lower RPM) with the mixture leaned to peak or LOP or whatever is the onset of rough running. So I sometimes use 1500 RPM leaned, which I imagine gives much less risk of prop damage, while still giving a valid mag test.
What confuses some pilots is that carb heat does not reduce RPM when the mixture is well leaned. This is because carb heat enrichens the mixture, and if already lean, this will bring the mixture closer to best power, i.e. increase power. So a check of the carb heat is one part of the engine check that I always do with rich mixture.
Gravel strips ought to look frightening enough by themselves to make people think about prop damage, but I have been told that grass strips can be just as bad, with grass grains always present in the grass and being hard enough to be able to damage the prop just as much as tiny stones from a gravel strip, when they are sucked up during a stand-still run-up. So I consider grass strips to be “bad strips” all of them and preflight accordingly. For the same reason I advance the throttle gradually for take-off, so that full power is not set before the airplane is rolling, so that gravel and grains will be blown back instead of sucked up into the propeller arc. Runway length permitting, of course.
I sometimes just do a quick check of the prop governor during taxi. Pulling the prop lever all the way back (on a single!) will not change anything much during normal taxi, but momentarily adding a little power until the governor “kicks in” will indicate that it works. The minimum governable RPM is between 900 and 1400 RPM with the planes I have flown, lowest in a C177RG, highest in my Piper Dakota.
I fly to grass or gravel strips rather frequently, as do many of my fellow club members. In almost every case the return flight is on the same day. That means that a thorough run-up check has been performed before the beginning of the day’s flying. So if everything worked fine in the morning, I can live with the risk that a subtle fault has suddenly developed a couple hours later, one that will only reveal itself during a full run-up at high RPM.
Interesting. Since my Extra 400 is getting a very expensive prop upgrade and the blades I sent in were really badly nicked, I have been quite concerned about this topic.
Yesterday I flew in a DA42. During the (automated) run up on a very wet runway, I noticed the small vortices that the propeller created on the ground.
The MT props on a DA40 NG (the "chopstick version, not the new ones) make a mini tornado right under the prop hub.
This tornado sucks up anything that’s on the ground at this place and I can imagine within a certain radius.
The water really made this visible and I was pleased to finally understand how this works. Now I know: if the airplane is sitting somehwere with gravel under the prop, I have to push it out of there, period… (how the heck do you do that with an Extra 400? Can’t push on the wings, can’t pull on the (wooden) prop)
And as mentioned by others above, I have been doing “soft” runs ups for the last couple of years. This 2000 RPM torture is nonsense. Much better to GAMI-test in flight…
So what I do on the ground is start around 1600 and lean to max RPM, switch mags and check that EGTs go up across the board and go back to normal when I revert back to 2 mags. Mostly, this can be a 2 x10 seconds exercise.
Based upon the above, I made decided to explain this to my (future) A&P:
1. I make pics of my prop blades before handing over the plane to them, so they know that responsibility for any damage is with them.
2. They may not run the engine more than 1600 RPM on the ground except for take-off during the test flight – if any.
3. If any works require a static run (even 1600), a 2 by 2 square meter area under the prop hub must be thoroughly cleaned of stones etc…
Makes sense?
Makes sense?
Certainly, but making “prescriptions” to shops almost never helps/works. They are either a “good” shop and pay attention anyway or they are a “bad” shop and will not take interest. At the worst, they will be pissed from customers telling them how they should work.
You are right about being “pissed”. I have my plan to get the information to them, and it starts with pics of the 100 hour old prop that looked like it had been machine gunned… Then I will tell them the story of the DA42… Too bad I could not make a video.
But now that we know maybe someone could do it from the outside on a rainy day 
(any UK people here)?
