Why do a run-up?

[N941WR]

This is not intended to be an ad but is a serious question I?ve been struggling with.

With the EICommander installed in my plane, I can look over and see exactly what the condition of the ignition is.

The unit?s TDA screen shows me that the ignitions are firing at the correct time, the current advance of each unit, and that my plugs are firing correctly (Not fouled and there is no broken leads).


TDA Screen (Typically the ignition harness graphs are all the same height, this is just a mockup.)

Since I have a fixed pitch prop, is there any legitimate reason to perform a run-up?

[Geico266]

To see if the engine will make power before you pull on the runway?

[L.Adamson]

Originally Posted by Geico266

To see if the engine will make power before you pull on the runway?

The instrument would probably tell him that, before hand.........I assume.
I suppose you'd know from experience of using it for awhile.

L.Adamson

[RV10inOz]

To see if the engine will make power before you pull on the runway?

NO!!! That is what you do on the first part of the takeoff roll. Sitting stationary with the brakes on against full power, not a good idea. Stone damage being the first thing, and jamming more heat under the cowl for no good reason.


The only thing a run up is good for is to verify that you have not had a magneto stolen

In this guys case maybe there is none at all.

Set around 16-1700 RPM, leaned to peak or just a bit more, and do a check looking to see all egt's rise consistently on each mag.

Best time to do a mag check is by running LOP and at altitude.

[hydroguy2]

more stuff to check than just mag drop.

oil pressure
smooth and proper linkage operation
sound/vibrations
EGT
proper Fuel flow

[L.Adamson]

Originally Posted by hydroguy2

more stuff to check than just mag drop.

oil pressure
smooth and proper linkage operation
sound/vibrations
EGT
proper Fuel flow

I consider the rest.........a before takeoff check, and on the roll check.

Just no runup for mags, etc.

[aerhed]

Prop operation and carb heat also. Vacuum (for jurassic panels). Maybe ammeter check too.

[Sig600]

Takeoff is the most critical phase of flight. The airplane must prove it's ability to get airborn, and stay there. Where as landing, if the engine quits the runway is already in front of you.

Your instrumentation tells you all kids of great things about the health of your engine, right now. Doing a run up gives it one last chance to tell you what may happen. Never mind all traditional reasons, but cycling the prop, pulling more fuel through the lines (maybe there is water coming), moving fluid around at normal pressures, all those things idle taxi won't expose.

Is the 45 seconds you save really worth your last chance opportunity to identify a potential failure? With one engine and runway behind you, better be **** sure.

[N941WR]

This is good input and food for thought.

Originally Posted by aerhed

Prop operation and carb heat also. Vacuum (for jurassic panels). Maybe ammeter check too.

No vacuum system and I don't use carb heat. (I've found the carb temp goes up just by slowing down.)
I check the ammeter when I flip on the landing and taxi lights.

Originally Posted by Sig600

... cycling the prop, pulling more fuel through the lines (maybe there is water coming), moving fluid around at normal pressures, all those things idle taxi won't expose...

No prop to cycle in my installation and water in the line is a good thought.

Originally Posted by hydroguy2

more stuff to check than just mag drop.
oil pressure
smooth and proper linkage operation
sound/vibrations
EGT
proper Fuel flow

At the start of my takeoff roll, I always verify oil and fuel pressure and I do watch it rise on startup. The linkage operation I get during warm up, even if I only bring the engine up to 1000 RPM. Sound & vibrations are valid comments. Fuel flow I see when I turn on the boost pump. CHT's and EGT's are watched as the engine warms up, so I know they are working properly.

I still perform a run up, only I do it at 1400 RPM. One of my main reasons for thinking of dropping the run up is to save the prop and reduce heat under the cowl on hot days.

Thanks for the input!

[pierre smith]

Originally Posted by Sig600

..... The airplane must prove it's ability to get airborn, and stay there. .

Very good reason!

About a month ago, I was taking off in the Air Tractor with 400 gallons of defoliant aboard and during the takeoff run, I lost power...some power, not all of it. I was comitted because the end of the runway was getting close, so we staggered into the air and finished the job. Turns out that my bleed air valve had shucked the diaphragm and I lost 400 ft lbs of torque...it normally pulls 1630 lbs but I was down to 1200 or so.

Best,