Big Pistons Forever
19th Oct 2012, 01:17
Kind of slow on the boards so I thought I would stir the pot :E
My first (of many) votes
Teaching the RUNUP:
I think the flight training industry in general does a very poor job of teaching how to do a proper runup. It seems to be often mindlessly performed by rote with little or no understanding of what the engine/systems are actually telling you. Things that I think should be included, but hardly ever are:
1) Pick a runup spot that doesn't have the prop over loose gravel with the airplane not unnecessarily blocking other traffic and with the prop wash not going to blast somebody/something, even if this means the aircraft will not be exactly into the wind
2) Start by setting the POH recommended RPM. I have seen several instances where some other RPM setting is used because somebody thought their number was "better". After the engine is stabilized at the runup RPM setting ask yourself do the gauge indications make sense. By that I mean is the oil temp and pressure correlating with the conditions. If it is a cool day and the first flight I would expect to see low oil temp and high oil pressure and conversely on a hot day with an airplane that has just flown higher oil temp and lower oil pressure would be expected. If I saw for example a cold engine that had bottom of the green oil pressure the flight would be over right there. I also want to see some correlation between battery condition and charge rate. If the engine was a bit slower slower turning over at start than normal then I would expect to see a fairly high rate of charge on ammeter. No charge with a weak battery or a high rate of charge with a strong battery are red flags.
3) The characteristics of the RPM drop when the mags are cycled tells you a lot about the health of the engine ignition system. A properly set up engine should have both mags show a 75 to 100 RPM drop. A larger drop indicates that side is not delivering the power it should be (usually as a result of worn spark plug(s) ). If the drop is within limits this is not a show stopper but it should be mentioned to maintainance. A big difference in drops or a mag with a very low drop is indicative of poor mag timing and again should be discussed with maintainance as if left this condition could result in cylinder damage. Finally not many CPL students seem to be aware that no mag drop is a no go item as it indicates that some part of the mag control circuit (switch, switch wiring or P lead) is a faulty.
4) The Carb heat check is two checks, first that the crab heat is actually working with an immediate and significant (at least 200 RPM) drop) and that the engine has no carb ice. The second requires you to wait at least 15 seconds to give the chance for the heat to work. Pulling out the knob and then immediately pushing it back, which I often see with CPL students, won't check for carb ice.
5) The mixture check is IMO the most egregiously mismanaged check in the runup. The most common procedure is to yank the mixture knob out until the engine dies and then smash it back in. All this proves is that the mixture functions as an engine on/off switch. A far more useful check IMO, is to leave the carb heat on and then slowly lean the mixture. The RPM should rise as the overly rich mixture created by the less dense heated air is compensated for by the reduction in fuel returning the mixture ratio to best power (ie highest RPM). Continued leaning should cause the RPM to fall as the mixture becomes too lean and power (ie RPM) drops. A 100 RPM drop will prove the carb is working properly. In any case under No circumstances should the mixture be pulled so far back that the engine dies.
5) The runup should be done as part of a flow check and not by reading a checklist as a cue for each action and should not take more than about a minute.
Well that ought to get the electrons humming........
My first (of many) votes
Teaching the RUNUP:
I think the flight training industry in general does a very poor job of teaching how to do a proper runup. It seems to be often mindlessly performed by rote with little or no understanding of what the engine/systems are actually telling you. Things that I think should be included, but hardly ever are:
1) Pick a runup spot that doesn't have the prop over loose gravel with the airplane not unnecessarily blocking other traffic and with the prop wash not going to blast somebody/something, even if this means the aircraft will not be exactly into the wind
2) Start by setting the POH recommended RPM. I have seen several instances where some other RPM setting is used because somebody thought their number was "better". After the engine is stabilized at the runup RPM setting ask yourself do the gauge indications make sense. By that I mean is the oil temp and pressure correlating with the conditions. If it is a cool day and the first flight I would expect to see low oil temp and high oil pressure and conversely on a hot day with an airplane that has just flown higher oil temp and lower oil pressure would be expected. If I saw for example a cold engine that had bottom of the green oil pressure the flight would be over right there. I also want to see some correlation between battery condition and charge rate. If the engine was a bit slower slower turning over at start than normal then I would expect to see a fairly high rate of charge on ammeter. No charge with a weak battery or a high rate of charge with a strong battery are red flags.
3) The characteristics of the RPM drop when the mags are cycled tells you a lot about the health of the engine ignition system. A properly set up engine should have both mags show a 75 to 100 RPM drop. A larger drop indicates that side is not delivering the power it should be (usually as a result of worn spark plug(s) ). If the drop is within limits this is not a show stopper but it should be mentioned to maintainance. A big difference in drops or a mag with a very low drop is indicative of poor mag timing and again should be discussed with maintainance as if left this condition could result in cylinder damage. Finally not many CPL students seem to be aware that no mag drop is a no go item as it indicates that some part of the mag control circuit (switch, switch wiring or P lead) is a faulty.
4) The Carb heat check is two checks, first that the crab heat is actually working with an immediate and significant (at least 200 RPM) drop) and that the engine has no carb ice. The second requires you to wait at least 15 seconds to give the chance for the heat to work. Pulling out the knob and then immediately pushing it back, which I often see with CPL students, won't check for carb ice.
5) The mixture check is IMO the most egregiously mismanaged check in the runup. The most common procedure is to yank the mixture knob out until the engine dies and then smash it back in. All this proves is that the mixture functions as an engine on/off switch. A far more useful check IMO, is to leave the carb heat on and then slowly lean the mixture. The RPM should rise as the overly rich mixture created by the less dense heated air is compensated for by the reduction in fuel returning the mixture ratio to best power (ie highest RPM). Continued leaning should cause the RPM to fall as the mixture becomes too lean and power (ie RPM) drops. A 100 RPM drop will prove the carb is working properly. In any case under No circumstances should the mixture be pulled so far back that the engine dies.
5) The runup should be done as part of a flow check and not by reading a checklist as a cue for each action and should not take more than about a minute.
Well that ought to get the electrons humming........