How short is too short of a flight?

[DMD3.]

I was listening to a Mike Busch with Savvy Aviation on YT, and in one of his videos he mentions that starting the engine and running it up for a few minutes to prevent underuse is actually bad for the engine, even worse than not having started it at all. He even further states that actually getting airborne on a very short flight doing one quick around the pattern is also bad.

As a renter, I’ve done some fairly short flights. Sometimes after getting off work, I’d buzz around for a bit or do 3 quick t&g’s, logging between .5-.7 hours on the tach (as an owner, I wouldn’t do too many t&g’s, as it’s extra wear & tear). The shortest flight I ever logged was .3 hours. I took off at night and it began to sprinkle (despite the weather forecast). But as a renter, I naturally wasn’t too concerned . But as an owner, I like to think that taking a couple 30-45 minute flights a week would be good for an aircraft, not to mention flying for longer periods on weekends. How short of a flight would be so short that it would do more harm than good? He also mentions not starting the engine just to taxi to/from the fuel pump (I created a thread on that recently).

 

[Salty]

You want to get the oil up to temperature for a few minutes at least. I try to target at least 1/2 hour.

 

[RyanB]

Try to aim for one full hour at operating temps.

 

[Rgbeard]

I guess it's bad to fly from GYR to GEU.

(if y'all aren't familiar, look it up for a laugh)

 

[FPK1]

I would not recommend this flight then...

 

[RyanB]

I guess it's bad to fly from GYR to GEU.

(if y'all aren't familiar, look it up for a laugh)

It is. Your engine will corrode doing that on a regular basis.

 

[Zeldman]

Gallup, NM to Window Rock, AZ.

6 minutes from wheels off to wheels on if the wind is right.

 

[RussR]

A flight I have made several times is HSD to PWA, 4.9 NM, taking planes to or from maintenance. If the Hobbs in the plane is on a squat switch (like many twins), and if the wind is from the south, it's possible to do this flight without even adding 0.1 to the Hobbs.

Lots of close combinations in the Wichita area too.

When I lived in the DC area, it was fun to imagine a flight between VKX and W32 (1 NM away) but being in the FRZ meant you would have to fly 6 NM to the south to exit the FRZ, then come back in again (at least how I remember the rules from about 2005-2006).

 

[Gilbert Buettner]

When I was an owner, I flew regularly and did not worry about very short flights, because the engine was going to get to operating temperature for more than an hour soon enough. But if you are not flying regularly, I would imagine at least 30 minutes at normal operating temperature would be a good idea.

Why not ask Mike Busch to elaborate?

 

[asicer]

I guess it's bad to fly from GYR to GEU.

Yeah, but starting the engine probably cools down the oil in that part of Arizona.

 

[Shepherd]

Try to aim for one full hour at operating temps.

I try to aim for something soft.........
Oh. Engine temperature. Gotcha.
Since it takes a minimum of half an hour to get it out of the hanger, get the radio and other accessories in it, then hand prop it to get it running, flying much less than 2 hours makes no sense at all.

 

[Brad Z]

A flight I have made several times is HSD to PWA, 4.9 NM, taking planes to or from maintenance. If the Hobbs in the plane is on a squat switch (like many twins), and if the wind is from the south, it's possible to do this flight without even adding 0.1 to the Hobbs.

Lots of close combinations in the Wichita area too.

When I lived in the DC area, it was fun to imagine a flight between VKX and W32 (1 NM away) but being in the FRZ meant you would have to fly 6 NM to the south to exit the FRZ, then come back in again (at least how I remember the rules from about 2005-2006).

Before Hyde closed, I’d often fly over from VKX to drop the plane off at the shop. From at least 2010, you didn’t have to leave the FRZ first, and I usually made just a brief check-on with Potomac on comm #2. I’d take off from runway 24 at VKX and turn left base for runway 5 at Hyde. Flight time could not have been more than a minute or two.

 

[Doug Reid]

Usually by the time I get the plane out of the hangar, taxi to runway, fly about 30 minutes, and taxi back to hangar, the engine has been running almost one hour...oil temps in green. Get the oil at least 180-200 degrees to burn off any condensation and you should be ok.

My local sight seeing flights are short when flying 150 knots...when I flew my Stinson at 100 knots it took a bit longer

 

[sourdough44]

Let’s mix in some long then the short is no biggie. A week or so ago I flew to Michigan for an overnight, 2 hours each way. Yesterday I cranked up to go to the fuel pump($4.99), I didn’t even fly. I took my time getting back, included a mild run up of sorts.

Am I worried about this shorter ground run? No!

With so many things people want that sharp line, dark/light. Of course, if a plane spent two years with periodically short ground run ups, that’s not good.

Back to the OP’er. If one rents a plane, does a short flight, chances are the next will do a longer flight. It’s also a rental. For many of us we’ve warmed up 5-8 minutes before that 30 minute flight, plus a little on the back end.

 

[Nathan Hyland]

I'm not a fan of short flights in general. I frequently have to go from KIWA to KCHD for maintenance. I feel like spending such little time in the air, 100% of it on departure and arrival at the same time, is dangerous. I've found myself focused on radios and not looking at the students flying around (both are towered).

Nothing to do with the engine, other than the fact that this means short runs aren't a problem for me since I tend to fly at least 15 minutes out, enjoy the privilege of flying, and head back in.

 

[Pinecone]

If you are getting regular hour plus flights, a short flight is not a big deal. The point is to not ONLY do short engine runs or short flights.

 

[Shepherd]

Nothing against Mike, but.........................
Unless he, or anyone else, can show scientific reproducible evidence, it's all just anecdotal opinion.
His opinion is weighted by years of experience, but it's still opinion.
I'll bet most people on this board have a "there I was at 15,000 ft" story about engine failures or successes.

 

[RudyP]

I let my friend fly my cirrus once from KSEE to KMYF (7nm) to reposition the plane because I was based at MYF but when we got back from our trip, MYF was closed due to an air show at Miramar so we cooled our heels at the FBO at SEE until we could make the short hop back. We took off on on 27R and landed on 28R so it’s a straight shot with essentially no maneuvering. We knew it would be real fast and he’d need to mentally switch quickly from climb to descent without maybe even reaching pattern altitude but he still ended up too high to make the landing and had to go around. Because of that, our 3 or 4 minute flight ended up being closer to 10 minutes.

 

[Skymac]

I may get banned but Mike Busch this, Mike Busch that like he’s some god…

He does have some good points, but just as much good, seems to be an equal amount of B/S. Just fly the planes, be it’s 20 minutes or 5 hours. Just keeping them moving and maintaining common sense goes miles!

 

[Brad Smith]

I may get banned but Mike Busch this, Mike Busch that like he’s some god…

He does have some good points, but just as much good, seems to be an equal amount of B/S. Just fly the planes, be it’s 20 minutes or 5 hours. Just keeping them moving and maintaining common sense goes miles!

Just because they are on YT doesn’t mean they know anything/everything. Most A&P mechanics would agree that bringing the engine up to operating temp and getting the oil circulating is good for the engine. Whatever time that takes is your answer.
Note: To be an expert firearm reviewer on YT only requires that you have a bald head, facial hair a lots of tattoos (preferably sleeves). To be an airplane expert on YT requires even less.

 

[Albany Tom]

In terms of how they work, I don't think the circle of firearms people intersect with the circle of people with YT channels, at all. No sarcasm. I've met a few people that can repair/build/tune handguns well, and none of them were on a computer except to browse. They don't need to. There probably aren't more than 40 of them in the country, taking a wild guess. Maybe less. (Except - extended to the black rifles, I could see an intersection. For a lot of reasons there is a lot of information out there about those, and seem to be quite a few people doing good work in that area.)

Back to the airplane thing, it's an hour drive to where I rent, one way. Even if it weren't, doing a pre-flight for a plane to make a .3 flight seems silly, as others have posted. I like to shoot for about an hour and a half min.

 

[Pinecone]

The point is, just bringing it UP to temp is not enough. It needs be there for long enough for the water to leave the oil. When you run it for a shorter time, you pump moisture into the crankcase, but the water in the oil remains. When the engine cools, the moisture in the crankcase air condenses and adds to the water in the oil, creating more acid to attack the engine. The 1 hour rule of thumb should remove the water from the oil.

 

[texasclouds]

Run it for 4 hours minimum or else it’s your funeral. I like to pull a vacuum and purge with about 2-3psi nitrogen if it’s going to sit more than a week.

 

[Albany Tom]

Run it for 4 hours minimum or else it’s your funeral. I like to pull a vacuum and purge with about 2-3psi nitrogen if it’s going to sit more than a week.

The whole airplane, or just the oil?

 

[mandm]

Short flight compared to?

Why would you only want to fly it 10 minutes or so?

Is it bad? I’m not sure, but I imagine it’s only bad if you do that routine “only”, if you need to do that then you need to do that. I take my time flying because I enjoy it, do the proper run up etc. A 10 minute flight would end up taking me at least half an hour.

I mean you could at least go up, do some turns, some approaches, or full stop taxi backs too.

 

[psween]

I'm based in my back yard and don't have a fuel tank, so I often make a 7 minute flight to the nearest fuel to top up. I can use mogas, so sometimes I'll fill from jugs at home, but still probably do that 7 minute flight regularly. I've never worried about it much. I run cam-guard, and mix in longer flights, so still not going to worry much.

 

[Kenny Phillips]

Nothing against Mike, but.........................
Unless he, or anyone else, can show scientific reproducible evidence, it's all just anecdotal opinion.
His opinion is weighted by years of experience, but it's still opinion.
I'll bet most people on this board have a "there I was at 15,000 ft" story about engine failures or successes.

It's a known fact that corrosion is the enemy, and that engines operating a bunch will reach TBO, whilst those not likely won't.
True for aircraft, true for automobiles.

 

[Sac Arrow]

I would not recommend this flight then...

I've done that flight! As well as SAC to MHR in order to preposition the plane on the ramp for an airshow, so I would have access to cheap beer.

 

[Silvaire]

I think the point is - as a practice - meaning, doing it all the time constantly. It doesn't mean that if you want to move the airplane 300 yards you have to let it idle for an hour.

 

[Pinecone]

I think the point is - as a practice - meaning, doing it all the time constantly. It doesn't mean that if you want to move the airplane 300 yards you have to let it idle for an hour.

Exactly.

The advice came to stop people from going to the airport and firing up the engine for 15 minutes or doing one circuit of the pattern and thinking they were "helping" the engine make TBO.

 

[1RTK1]

I’ve heard the 1 hour time by many mechanic. I would think once your oil hits operating temp for a bit you would be fine.
As long as your engine is running you are pumping more contaminants in. There is a point of demising return If you are out to exercise your plane.

 

[Lindberg]

The point is, just bringing it UP to temp is not enough. It needs be there for long enough for the water to leave the oil. When you run it for a shorter time, you pump moisture into the crankcase, but the water in the oil remains. When the engine cools, the moisture in the crankcase air condenses and adds to the water in the oil, creating more acid to attack the engine. The 1 hour rule of thumb should remove the water from the oil.

What happens to the moisture you pump into the crankcase on longer flights?

 

[Pinecone]

It leaves via the breather.

The idea of a too short flight is one that does not run at proper operating temperature long enough to remove the water from the oil.

When you shut down, there is a certain amount of moisture laden air in the crankcase. As the engine cools, that moisture condenses and enters the oil. If you run for say 15r minutes, you fill the crankcase with more moisture laden air, but you do no drive the water out of the oil, so the new air cools and the moisture condenses. Repeat and more and more water accumlated in the engine.

Fly it for a hour, and the oil get nice and hot the moisture is boiled out of the oil and you end up with just the moisture of one crank case of air.

 

[Lindberg]

It leaves via the breather.

The idea of a too short flight is one that does not run at proper operating temperature long enough to remove the water from the oil.

When you shut down, there is a certain amount of moisture laden air in the crankcase. As the engine cools, that moisture condenses and enters the oil. If you run for say 15r minutes, you fill the crankcase with more moisture laden air, but you do no drive the water out of the oil, so the new air cools and the moisture condenses. Repeat and more and more water accumlated in the engine.

Fly it for a hour, and the oil get nice and hot the moisture is boiled out of the oil and you end up with just the moisture of one crank case of air.

Is there no saturation point?

 

[Pinecone]

If the oil is saturated, the liquid water will collect at the bottom of the sump. So there is no limit to how much water you could collect in the engine with lots of short runs.

 

[Silvaire]

If the oil is saturated, the liquid water will collect at the bottom of the sump. So there is no limit to how much water you could collect in the engine with lots of short runs.

So for long term storage, if you had a quick drain you could just go out there and drain the water out of it every month or so. Seems kinda stupid to churn it all up and try to evaporate it with heat when it just conveniently collects itself at the bottom of the sump anyway.

 

[Dan Thomas]

We've been over this way too many times.

Ram Aviation has a video on engine corrosion, and they will tell you that short engine runs are bad, because some of the water vapor, a byproduct of combustion, gets past the rings in a cold engine and condenses in there until the engine and oil warm up and the clearances close up and pretty much stop it. Once the engine gets hot, the water that got in there will evaporate (heat raising its vapor pressure) and it goes out the breather.

The water than condenses in the case doesn't just sit there. It mixes with the oil; there's a fog of oil flying around in there, flung off the crankshaft, and the water mixes with it and forms a brown milky emulsion. That water will slowly work its way to the bottom of the sump after shutdown. In any case, purging with dry air or nitrogen isn't going to get at that stuff. It's either in the oil or under it. If it was a short run, you might get whatever is still condensed on case surfaces.

One of the Lycoming factory overhauls we put in a 172 showed an oil leak on its first runup. Ten minutes, max. Oil was seeping past some porosity in that brand-new head, so the cylinder had to come off and be replaced. When we removed the rocker cover, we found liquid water in the rocker cover and in the rocker box itself, laying at the bottom, not deep enough to find its way out through the oil drain tube. Suddenly, all those internally-rusted steel rocker covers I'd seen made sense. Water. Lots of it.

An O-235 we had in one of the Citabrias tended to run really cool, so much so that I finally left the winter oil cooler cover plate on year-round. The first time I realized we had a problem was on a scheduled inspection. We always ran the engine up to get it warm so the oil would drain quickly and the compression numbers would be sensible. On this occasion, the screen had aluminum flakes in it that were obviously from the piston pin plugs; they keep the pin centered in the piston and they run lightly against the cylinder wall. I took a cylinder off (water in the rocker box and cover again), and when I pulled the cylinder off the piston I found water droplets on the piston skirt and on the cylinder wall. That water had caused corrosion pitting of the cylinder bore, leading to increased wear of the cylinder wall by the rings, leaving a ridge at the bottom of the oil ring's travel, a ridge that shaved those flakes off the pin plugs. The front two cylinders were the worst, being the coldest, but all four had to be rehoned and new rings and pin plugs installed.

Crankcase condensation is a real thing. Even Lycoming and Continental warn operators against short runs due to it. But too many owners think of that engine as like the one in their cars, but that car does not have an aircooled engine with big cold clearances, and it has a positive crankcase ventilation system, driven by manifold vacuum, something that the aircraft engine does not have because manifold vacuum is tiny most of the time (same as saying high manifold pressure) so it would not pull the air through the case to get that stuff out.

I have seen it too many times. That O-235 would go about 1000 hours between cylinder work due to the corrosion and ridging, an unfortunate interval with its 2400-hour TBO. Lycoming could eliminate some of the problem by using five-ring pistons, with two of the rings below the pin travel, but while solving the pin-chipping problem it wouldn't do much for cold clearances letting blowby gases into the case in the first place.

It's not a car engine. Don't operate it like one. It doesn't work.

 

[1RTK1]

We've been over this way too many times.

Ram Aviation has a video on engine corrosion, and they will tell you that short engine runs are bad, because some of the water vapor, a byproduct of combustion, gets past the rings in a cold engine and condenses in there until the engine and oil warm up and the clearances close up and pretty much stop it. Once the engine gets hot, the water that got in there will evaporate (heat raising its vapor pressure) and it goes out the breather.

The water than condenses in the case doesn't just sit there. It mixes with the oil; there's a fog of oil flying around in there, flung off the crankshaft, and the water mixes with it and forms a brown milky emulsion. That water will slowly work its way to the bottom of the sump after shutdown. In any case, purging with dry air or nitrogen isn't going to get at that stuff. It's either in the oil or under it. If it was a short run, you might get whatever is still condensed on case surfaces.

One of the Lycoming factory overhauls we put in a 172 showed an oil leak on its first runup. Ten minutes, max. Oil was seeping past some porosity in that brand-new head, so the cylinder had to come off and be replaced. When we removed the rocker cover, we found liquid water in the rocker cover and in the rocker box itself, laying at the bottom, not deep enough to find its way out through the oil drain tube. Suddenly, all those internally-rusted steel rocker covers I'd seen made sense. Water. Lots of it.

An O-235 we had in one of the Citabrias tended to run really cool, so much so that I finally left the winter oil cooler cover plate on year-round. The first time I realized we had a problem was on a scheduled inspection. We always ran the engine up to get it warm so the oil would drain quickly and the compression numbers would be sensible. On this occasion, the screen had aluminum flakes in it that were obviously from the piston pin plugs; they keep the pin centered in the piston and they run lightly against the cylinder wall. I took a cylinder off (water in the rocker box and cover again), and when I pulled the cylinder off the piston I found water droplets on the piston skirt and on the cylinder wall. That water had caused corrosion pitting of the cylinder bore, leading to increased wear of the cylinder wall by the rings, leaving a ridge at the bottom of the oil ring's travel, a ridge that shaved those flakes off the pin plugs. The front two cylinders were the worst, being the coldest, but all four had to be rehoned and new rings and pin plugs installed.

Crankcase condensation is a real thing. Even Lycoming and Continental warn operators against short runs due to it. But too many owners think of that engine as like the one in their cars, but that car does not have an aircooled engine with big cold clearances, and it has a positive crankcase ventilation system, driven by manifold vacuum, something that the aircraft engine does not have because manifold vacuum is tiny most of the time (same as saying high manifold pressure) so it would not pull the air through the case to get that stuff out.

I have seen it too many times. That O-235 would go about 1000 hours between cylinder work due to the corrosion and ridging, an unfortunate interval with its 2400-hour TBO. Lycoming could eliminate some of the problem by using five-ring pistons, with two of the rings below the pin travel, but while solving the pin-chipping problem it wouldn't do much for cold clearances letting blowby gases into the case in the first place.

It's not a car engine. Don't operate it like one. It doesn't work.

What was their recommended run time or temperature to reach??

 

[flyingpreacher]

This is too short. Depart RWY 12 at Capitol City, land RWY 13 at Harrisburg International.

 

[Dan Thomas]

What was their recommended run time or temperature to reach??

From https://www.lycoming.com/content/frequency-flight-and-its-affect-engine

We have firm evidence that engines not flown frequently may not achieve the standard expected overhaul life. Engines that are flown occasionally deteriorate much more rapidly than those that fly consistently. Pilots have asked, “What really happens to an engine when it’s flown only one or two times per month?” An aircraft engine flown this infrequently usually accumulates rust and corrosion internally. This rust and corrosion are often found when an engine is torn down.

Some operators are running the engines on the ground in an attempt to prevent rust between infrequent flights. This may harm rather than help the engine if the oil temperature is not brought up to approximately 165˚ F because water and acids from combustion will accumulate in the engine oil. The one best way to get oil temperature to 165˚ F is to fly the aircraft. During the flight, the oil normally gets hot enough to vaporize the water and most acids and eliminate them from the oil. If the engine is merely ground run, the water accumulated in the oil will gradually turn to acid, which is also undesirable. Prolonged ground running in an attempt to bring oil temperature up is not recommended because of inadequate cooling that may result in hot spots in the cylinders, baked and deteriorated ignition harness and brittle oil seals which cause oil leaks.
From https://www.lycoming.com/content/operating-cold-weather

Engine operating temperature is another item that is not usually given enough consideration in cold weather. We usually are very cautious about high oil temperature which we know is detrimental to good engine health, while a low oil temperature is easier to accept. The desired oil temperature range for Lycoming engines is from 165˚ to 220˚ F. If the aircraft has a winterization kit, it should be installed when operating in outside air temperatures (OAT) that are below the 40˚ to 45˚ F range. If no winterization kit is supplied and the engine is not equipped with a thermostatic bypass valve, it may be necessary to improvise a means of blocking off a portion of the airflow to the oil cooler. Keeping the oil temperature above the minimum recommended temperature is a factor in engine longevity. Low operating temperatures do not vaporize the moisture that collects in the oil as the engine breathes damp air for normal combustion.* When minimum recommended oil temperatures are not maintained, oil should be changed more frequently than the normally recommended 50-hour change cycle. This is necessary in order to eliminate the moisture that collects and contaminates the oil.
*This part is misleading. Almost all the water comes from combustion, not "damp air." An airplane on the dry prairies in winter will still get water in the crankcase. Refer back to the first quote where Lycoming says "because water and acids from combustion will accumulate in the engine oil."


From https://www.lycoming.com/content/low-time-engine-may-not-mean-quality-and-value

The point of this discussion is simple. A low-time engine may not add value to an aircraft, and the buyer should be aware of all factors which may affect the condition and value of the engine. An engine which is not flown frequently is subject to deterioration as a result inactivity. When the engine does not achieve flight operating temperatures on a regular basis, the moisture and acids that form as a result of combustion and condensation are not vaporized and eliminated through the exhaust and crankcase breather. As moisture and acids collect in the engine, they contribute to the formation of rust on the cylinder walls, camshaft and tappets.

As the engine is run after rust has formed, the rust becomes a very fine abrasive causing internal engine wear, particularly to the camshaft and tappets. As these components wear, they make more metal which attacks the softer metals in the engine. Piston pin plugs are examples of parts that may wear rapidly when rust becomes an abrasive inside the engine. This wear could eventually lead to failure.

Ram's video:

If you don't want to watch the whole thing, skip to the 3:10 mark.

Note: that picture above is the result of a saltwater corrosion test, not typical internal corrosion.