No engine run ups and magneto failure while hot

[nig71]

Chatting to a professional pilot the other day and he says the task of the pilot is to get the aircraft to the keys as quick as possible and the engine is cooking if you do a runup on the pad.  He also said magnetos fail when hot not when cold so do a mag drop after landing in preparation for the next flight. 

 

He claims he's never runup his Lycoming (in a cessna 206) and it's a 100 hours from overhaul and doesn't use a drop of oil. 

 

Also chatting to the new owner of vixxen and he says he has to wait a long time to get oil temp to 50C for takeoff. He's busy masking off the oil cooler to decrease time required. 

 

Is this all necessary? Is it required for the engine life? I imagine in the first 3 minutes that most of metal expansion has occurred in the engine easily accomplished by taxiing straight for takeoff. 

 

Major drawback I can see is a fuel issue may not have time to surface until you are at a critical phase of the flight. 

 

Ps just got my license a week ago. I see a lot of pilots do shortcuts or change procedures (seemingly vast majority) and I figure as an impressionable inexperienced pilot I should be asking a few questions. Regards Michael. 

 

 

[cscotthendry]

WRT the oil temp for takeoff

 

1) Rotax specify that as a minimum

 

2) I have heard that this is because there is a bypass valve in the oil filter that remains open until the oil is at 50 degrees

 

3) I masked off a third of my oil cooler because my oil temps were too low during flight, but especially on descent. Now, my oil temps run in the middle of the green arc during flight, climb to the top of the green/bottom of the yellow on a sustained climb and sit at the bottom of the green on descent. Clearly, the Rotax supplied oil cooler on my airplane is providing more cooling than my engine needs. I have a simple normally aspirated 100HP 912ULS.

 

As for not doing runups before takeoff? Not this little black duck. I do them every time. I want to know that both mags are sparking before I go hurtling down the runway with a fence at the end of it.

 

WRT to cooking the engine? IMO, if you're keeping an eye on the temp gauges, you shouldn't be cooking the engine. I couldn't vouch for air cooled engines, but the Rotax doesn't cook like that. I have had an occasion with a warm start on a very hot day when my coolant temp rose above normal, but as soon as I started my takeoff roll, the temp came down about halfway down the runway.

 

So, how a pilot treats his own aircraft with Lycomings is his business. That it "doesn't use a drop of oil" says only that his engine is still in reasonably good condition, but it doesn't logically follow that his lack of runups is the reason. That's a bit like saying that because rain comes from clouds, if there are clouds in the sky it must be raining.

 

Finally, WRT to the long warmup time for the Vixen, yes, he probably had a similar setup as most Rotax engines. I think the standard oil cooler has been designed to cope with the higher power and turbo charged engines. With the standard oil cooler on a normally aspirated 80 or 100HP engine it can take a while to get the oil temp up, especially in the winter, but it's still required by Rotax.

 

 

[facthunter]

 A magneto that fails when hot is the most common failure type but I've never had that type of failure in an aircraft magneto. it's also in high hours  (or shelf  time ) windings and condensers.. Condensation forming in tropical places overnight has been my most common fault. Also internal gears can strip and may fail ONE of the magneto's distributor drive. The other one stays serviceable  and you can keep the engine running if you isolate the  affected part (To complete the flight or get to  a suitable aerodrome. Don't initiate a flight with the magneto in that condition. You should know YOUR engine and what type of magneto's are used on it..

 

  In cold areas, (Frosty night) especially if the engine is not using a multi grade, stick to the minimum temps allowed as per the POH. Making your engine deliver full Power with thick oil is asking for trouble. It takes  about 30 minutes  in flight for an engine to achieve stable warmed up fully status (or even longer). Having hydraulic lifters makes warming up more necessary. I spent over 15 minutes at Corryong last time I was there to get the temp to the required figure.. When you are taxiing you are only at Idle power and that doesn't make it warm up much at all if it's a cold ambient.. 50 degrees C is not that hot, either. Some engine installations don't get the oil temps in the right range, ever. IF the running temps are too cool the oil will go milky and holds water . You need to see 85 degrees oil temp or a bit more to avoid this, and don't do short flight or engine runs if you can avoid it.

 

   ALL engines use SOME oil. The oil level can rise if there's dilution of it by water or fuel, or it can mask the oil usage. 

 

  Checking the mags after a flight is a good idea.  Just check for a complete cut and don't do the run up. necessarily. unless you want to trouble shoot some fault . You should select both OFF  at low rpm, briefly to confirm the switches do actually work.. The magneto is alive till you short it out, unlike a "normal" ignition system where you energise it by supplying current from an external source. Nev

 

 

[Jaba-who]

I do a mag ( ignition coil on the jab) check on both start up and shut down. 

 

The rationale also being that if I do a check at the end then I’ve got no pressure and heaps of time to sort out the problem. 

 

If you find it when you are running up you often have time pressure and pressure to convince yourself it’s not as bad as it seems. 

 

Also things do go wrong while it’s on the ground. had a distributor fill up with water when I washed the aircraft )(after a successful shutdown check). Don’t know for sure how it got there but it did. But point being it ran “fine” on one distributor on tacking to run up bay,  till I checked it at the pre take off check. 

 

So I wouldn’t be following your mates “completely at odds with the rest of the world” advice. 

 

 

[derekliston]

I always pull the propeller through 8 compressions and always do a mag drop check and a full power run up. I’d always prefer to find problems on the ground rather than half way through my climb out!

 

 

[fallowdeer]

I have a 912ULS with an air box temperature gauge.  My SOP on shutdown is to park into wind if practical and open the oil filler/check  flap to on top of the cowl to let as much hot air escape as possible.

 

Heat is the enemy of electronics and those very expensive CDI boxes are sitting right on top of the engine and they're likely to get a whole lot hotter after shutdown.  It's quite interesting seeing the air box temperature on a hot day after shutdown, it can go past 50 degrees C.

 

My second consideration given this situation is if I start up again and the engine has "hot soaked" so I'm seeing temperatures in that range is to not take off till I see a drop in air box temperature below 40 degrees. Even though my installation has a fuel return I figure I'll be less likely to get a vapour lock if that temperature has fallen and I've definitely used up the fuel in the carb bowls and have started running on fresh slightly colder fuel.

 

I might be over cautious here but there's not much penalty to wait a few minutes.

 

Peter

 

 

[kgwilson]

The Lycoming driver can do what he likes. I wouldn't fly with him though. I do 3 mag checks per flight and was taught this when I trained many moons ago. I also always pull the engine through 12 compressions (6 cyl Jab) before a cold start. After start & setting rpm at around 1200 I do a mag check. Once the CHT is up in the green & oil at 50 deg minimum I'll do the runup with Mag check at 2000 rpm, usually at the taxiway holding point. In cold weather most of the warm up is done before I move at all. After the flight & returning to the hangar I do a Mag check at idle before shutting down. An engine that doesn't use a drop of oil will seize. I change the oil & filter every 25 hours without topping up during that time. A filter at $10.00 & oil at $30.00 is very cheap. The only problem is actually seeing the oil on the dipstick as it stays quite clean throughout the 25 hours so I just lay the dipstick on a paper towel to find the level.