Text Box: WARBIRD NOTES # 25    5 Apr 99   (29)         ENGINE RUN-UP BEFORE TAKEOFFI’ve lost track of how many times I’ve heard, “Now – what do we need to do on this engine run-up?”  Or, “This checklist is incomplete, it doesn’t have a section telling me how to do the run-up!”  I agree that checklists are important and necessary in our flying lives – but I also utterly refuse to let them dictate my life or thought processes! 


Many checklists include two sections that’re almost guaran-dang-teed to drive me bonkers, “starting” and “run-up”.  If a pilot is absolutely dependent upon reading a checklist in order to start a machine or to accomplish the run-up, then I guess I’d also have to seriously question his ability to fly it!  Think about it, do you believe that one needs to (or does) carefully look at each checklist item - in sequence - while he’s engaged in starting a B-17?  As “proof-of-the-pudding”, consider a deliberate omission on the B-17 checklist several years ago.  The first year out on tour, a majority of the pilot group felt that the B-17 absolutely needed an “engine starting checklist”, how in the world else would we ever start it!  So, we included it – but then noticed that no one referred to it in anyway during the starting, it just sort of provided a source of comfort and satisfaction to know that all was right with the world because it was – there! 


So the second year - operating with the same pilot group - that section was quietly removed when the checklist was revised.  More than halfway through that flying year, someone finally noticed that it wasn’t there and – in high dudgeon – wanted to know why not?  Of course, the obvious answer was that it had been gone for nigh onto a year by that time and no one had ever missed it or looked for it or needed it.  The “gouge”/”cheat sheet”/”procedures” for the airplane is in the B-17 pilot’s manual, if one needs to research the starting procedure at the beginning of the year, he only needs to open his manual to that section and it’s right there – written in exhaustive detail!  But it only takes up valuable space on the cockpit checklist, one that could better be devoted to a larger type or on some subject that we don’t do every day.  So, this is also a thought on the “run-up” section, why would anyone need a checklist telling him/her what to do on a preflight check of the engines and such?


With this proviso in mind then, let’s just describe a generic run-up, an all-purpose one that will serve the purposes of the vintage reciprocating engined fleet that we’re trying to write about in the these Warbird Notes.  And, before we get started, if you haven’t read Warbird Notes #14 (Magneto Check) and Warbird Notes #8 (Field Barometric Power Check) lately, you’ll need to read them first – or again – before reading this one.


First of all, a brief commercial here – if you’ll permit me!  Years ago this wouldn’t have even needed to be said, but almost none of the present day air carrier fleet needs to do a run-up!  Many’s the time I’ve come clattering merrily along a taxiway in a two or three or four engined jet – and all of a sudden found my way blocked by a <gasp> relic, a piston engine airplane doing a run-up!  Now it used to be so that the airport authorities knew that all, repeat all, airplanes required a run-up and testing of their engines before takeoff – so they provided large concrete run-up pads at the ends of runways.  No more!  Now the world had passed us by and if you really want to be looked at with disfavor and re-ignite a discussion of removing these old artifacts from polite society, just block a jet’s access to the runway.  It’s a source of continual amazement to me that no one seems to consider the other guy, we really are not all alone.  Seriously, take a quick look behind you and remember that they are probably going to be ready to go when they get there.  So, in addition to making sure that our prop blast is not going to blow someone over, we also need to not block the taxiway.  More things we need to think about before setting the brakes for our run-up.  OK?


OK, airplane straightened out and either the tail wheel locked or the nosewheel not cramped?  Area behind’s clear of objects?  Another thing to think about here is any limit on propeller crosswinds during run-up, sometimes mentioned in the limitations section of the flight manual.  Something to consider, just in case you weren’t in the habit.  Engine temperatures all warm enough to permit the run-up RPM’s?


1st, the RPM on all engines can be advanced to whatever’s prescribed by the pilot’s manual.  In general, I’ve found that 1500 RPM works fine for the B-17’s and Wright DC-3’s.  The Pratt DC-3’s and B-25’s, etc. seem to work better at 1700 RPM.  You do need enough that the generators “cut in” and operate because they'll be checked during this procedure.  Just be aware that you probably shouldn’t use any more RPM than necessary since the excess just heats the engine(s) up faster, a situation to be avoided if at all possible.  And while we’re on the subject, don’t “dawdle” setting a precise and exact RPM, close enough for government work will be just fine!


2nd, pull the prop controls full back to decrease and let the RPM’s decrease a few hundred as engine oil is forced into the dome, moving the blades towards a higher pitch.  You don't have to wait to reach the absolute lowest possible RPM this time, just make sure the prop functions correctly as the oil is forced into the dome.  Return the prop controls to full increase and let the RPM recover as the blades again move towards low pitch. 


3rd, this is a good time to check the carburetor heat.  When you pull the prop levers back the first time, pull the carburetor heat levers to full hot on both engines.  As soon as the CAT gauge indicates an adequate rise, return the carburetor heat lever to the cold position and check for an associated CAT drop.  This is an important step, otherwise the carburetor heat may remain stuck on.


4th, repeat the propeller cycling as necessary to get a good prop response as progressively warmer oil from the engine is introduced into the prop dome.  During the last cycle you're going to perform (after you're satisfied with the response), let the prop controls remain in the full decrease RPM position long enough that the prop governors reach their full minimum governing (high pitch) position of approximately 1100 – 1200 RPM.  Note this RPM to ascertain that the propeller governors are performing their job and to determine the minimum governing RPM.  (This is the same RPM you would expect to see later in flight after unfeathering a propeller.)  Following this check return the prop controls to full increase and note that the RPM re-achieves the value you first set.           


5th, check the feathering circuits.  Twist the red feather button a few turns clockwise to assure it's screwed on securely, lest it later come off in your hand when you attempt to pull it out.  Next, press the button down and check that it is magnetically held in by the electrical “holding coil”.  Check that an appropriate load from the electrical feathering pump shows on the generator electrical meters and that the RPM decreases.  As soon as a decrease of a couple of hundred RPM is seen, pull the button out to interrupt the feathering cycle.  As you pull the feathering button out again, note a corresponding decrease in the electrical load as the feather motor ceases to operate.  If the feather button should stick in the FEATHER position or the button comes off in your fingers the electrical holding solenoid can be released by immediately turning all batteries and generators off.  Repeat the check on the other engine(s).  As soon as that check is complete pull the propeller levers back and note an associated decrease in RPM, then return the props to full increase to assure that the propeller governor has resumed control of the RPM.  You don't need to wait for the propeller to recover from the feathering check before you do this, all that is necessary is to see a slight RPM drop to indicate that the propeller controls are functioning.


6th, accomplish the power check (Warbird Notes #8) by advancing the throttle to the MP (field barometric pressure) you noted before start. By the way, a part of this portion of the run-up is to set the throttle friction for the ensuing takeoff.  The desired friction setting is that which allows throttle movement as desired without changing the friction lock but also tight enough to prevent "creep" if left unguarded.  After you set “field barometric pressure” the RPM should be that given in the appropriate airplane manual.  If your manual is an early one and does not provide this figure , then you’ll have to use one derived from past experience, day-to-day operation, discussions with past owners, etc.  In addition to rereading the referenced Warbird Notes #8 I’d also suggest to be suspicious of prop settings from shops that may have improperly indexed the low pitch stops for whatever reasons, even good ones!  Now then, back to the run-up.  While doing this, note the engine temperatures and pressures for correct indications.  You can check two engines at a time if ambient and cylinder head temperatures permit.  If desirous of the least possible increase in CHT this check may be accomplished on each engine, one at time, if the nosewheel and the pilot’s manual permit it.  


7th, check each engine's magnetos (Warbird Notes #14), looking at both the tach and the engine cowling for excessive drop/roughness.  Max allowable is as described in the appropriate airplane manual.  For trouble shooting purposes, a fast drop is indicative of a fouled plug(s), a slow drop is indicative of retarded timing (fast-fouled, slow-timing), and a zero drop indicates that either the mag switch or "P" lead probably is bad with no grounding taking place.   Retard the throttles after the mag check is completed.  The engine instruments are an integral and continuous part of the above checks.


There now, you’ve completed a workmanlike run-up of a garden variety vintage airplane with normal 23E50 (or equal) propellers without reference to a checklist or any stumbling around or inordinate delay – all the while with the engines heating up.  I can’t imagine making it any shorter and still getting everything checked.  If there is, then I’m sure that we’d like to hear about it to include it in this procedure.                                                             


R. Sohn © 1999

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