Aborted takeoff, engine not producing full power

[qbynewbie]

OP: Excellent job on making what was without a doubt a disappointing but also without a doubt the right decision. Taking a suspect plane into the air is never the right decision if you can avoid doing so.

160F before takeoff? What sort of engine would require that? For the Lycoming IO-360 in that 172R, 75F is quite enough.

I like to see at least 130f, that's on just about everything I've flown, also allows the cylinders time to get to 200F or so.

The "in the green" is a crap mindset IMO.

Watch your oil pressure on t/o.

Check your crankcase breather tube for ice on the preflight, and of course you probably should be running multi weight when it's freezing balls outside.

But hey, nothing flys like a rental

When you own, or rely on the plane for a living it's a little different.

It would cook my top end waiting for my oil temp to reach 130* on the ground.

Crankcase breather will almost never be iced on the ground. That happens in flight when it's breathing and the temps are cold. Warm shutdown will clear any ice from the flight.

Just my thoughts.

You'd be waiting a very long time to take off in the winter in most of the USA if you wait for 130F. Where did you come up with that number?

Well, it meets or exceeds every published recommendation from the FAA, every manufacturer of standard aircraft engines (nontraditional engines like a Rotax notwithstanding), and every engine guru with whom I've ever spoken. Do you have some contrary guidance or recommendation from such a source which you can share with the rest of us?

I had an E-I engine analyzer added to my 172G. It's taught me a lot about that O-300 engine. In Fly the Engine (great book, by the way), Kas Thomas recommends waiting until the oil temperature is at least 100 F before applying takeoff power. He also strongly urges against applying takeoff power while the oil is cold, noting that doing so under some conditions may exceed red line oil pressure. Other authors have recommended 120F before applying full power and I have adopted that for myself.

I fly in cold temperatures a lot. In fact, I'm going flying tomorrow at 1:00 pm, when the temp is forecast to be around 10 F and the wind chill around -5 F. I also try to manage my engine in a way that will prolong its life so I want to be aware of things like oil temperature on cold days. When the engine analyzer was installed, I had an oil temperature probe added. That lets me see the oil temperature without even starting the engine. As soon as I turn on the master, the analyzer starts up and I can see the oil temp within five seconds.

I use engine preheat when the OAT will be < 40F and will not attempt a start if the oil temperature < 30F. Plugging it in overnight with a heavy blanket over the cowling will have the oil temperature around 33F on even the coldest nights.

Starting the engine when it's really cold outside is facilitated by letting the priming fuel vaporize. Instead of priming and then immediately cranking the engine, I give it three shots of prime (no more) and then count to 30 before cranking the engine. Waiting that bit of time when it's cold out really makes a difference.

Once taxiing, the oil temperature will rise into the 50s quickly. If I'm taxiing directly to the runway, it's likely close to 80 by the time I get to my run up. On a cold day, the oil temperature will probably still be a bit below 100F when I'm finished with my checks. I could take off, of course, but remember that I want to be kind to my engine so I wait another two or three minutes for the oil temperature to get to 117F. Applying power and taxiing onto the runway will have it at 120F by the time I'm applying full power.

Yes, it's a few minutes of waiting but I like to be conservative about how I manage my engine.

 

[Johann]

Cold air increases drag including the prop.

Good point, but the engine should perform better and even it out

You said you don't usually fly that airplane...maybe it has a cruise prop?

I also agree that if the throttle was stiff, that it is very possible that your muscle memory for your right hand and arm told you subconsciously that it was all-the-way-in when indeed it wasn't. It's hard to believe though that you made the same mistake when you did the run-up after you cleared the runway.

When I fly the 172N models, I don't get much more than 2200 RPM on the take-off roll (sea level airport) and it picks up 100 or so more on the climb out as the airplane gains a little more speed.

You did the right thing by aborting. If you get something you have never seen before...it's time to stay on the ground and get it sorted out.

Gene

I don't think it has a cruise prop. I've flown it before, I think twice (although with an instructor). If the normal takeoff RPM was outside the green arc I'm sure they would have mentioned it. Also I flew not that long ago it's "sister plane", and all was normal.
It's not impossible that they changed the pitch of the prop recently, but I would find it pretty unlikely, specially not mentioning anything, and not saying "oh yeah, we changed the prop, that's why" when I reported the problem.

The throttle was pretty hard honestly, even with the friction lock completely unscrewed. Even though I can't be sure that's not normal, it felt weird. If the plane is around next time I go I'll check the throttle for friction, and I'll ask people that fly it about it too.
This could lead me to believe that I didn't push full in, but then again, I would have had to make the exact same mistake 3 times (every time getting same RPM), and 2 of those times completely stopped and looking down at the panel.

 

[poadeleted20]

I have the POH in front of me now, in the Power Check it says:

You are looking at the power check number for the 180HP 172S or the 172R with the 180HP modification kit. OTOH, if the 172R you were flying is unmodified, its IO-360 is de-rated to 160HP by cutting the RPM redline to 2400 and using a higher drag prop, and the power check RPM range is only 2065-2165 as stated above by Kent. But even in that case, 2000 RPM on the takeoff roll would be too low.

 

[poadeleted20]

You said you don't usually fly that airplane...maybe it has a cruise prop?

There is no climb/cruise prop option on the 172R.

 

[poadeleted20]

I had an E-I engine analyzer added to my 172G. It's taught me a lot about that O-300 engine.

What you see with a Continental O-300 may be very different than what you see with a Lycoming IO-360. Waiting for 130F to take off after a start with a 50F preheated engine on a 20F day is going to take a very long time with that Lycoming.

 

[Johann]

You are looking at the power check number for the 180HP 172S or the 172R with the 180HP modification kit. OTOH, if the 172R you were flying is unmodified, its IO-360 is de-rated to 160HP by cutting the RPM redline to 2400 and using a higher drag prop, and the power check RPM range is only 2065-2165 as stated above by Kent. But even in that case, 2000 RPM on the takeoff roll would be too low.

Unless they gave me the wrong POH, it's a 172R 180HP.
In the 160HP ones, does the takeoff range fall outside of the green arc?. As I was rolling not believing my eyes, seeing that it was outside the green arc was the thing that really convinced me.
Are there airplanes that takeoff with the RPM outside the green?

 

[Henning]

Unless they gave me the wrong POH, it's a 172R 180HP.
In the 160HP ones, does the takeoff range fall outside of the green arc?. As I was rolling not believing my eyes, seeing that it was outside the green arc was the thing that really convinced me.
Are there airplanes that takeoff with the RPM outside the green?

Most all of them will with some extra runway.

 

[qbynewbie]

You may be right, Ron. I wonder if anyone here flies that engine in the winter and has an accurate temp gauge?

 

[poadeleted20]

Unless they gave me the wrong POH, it's a 172R 180HP.

OK, it's been modified and the static RPM range is 2300-2400, as you said. If the RPM was only 2000 on the takeoff roll with a 180HP modified 172R, that was way low, and had you gotten airborne, you would have been "up there wishing you were down here", so you really did the right thing by aborting.

In the 160HP ones, does the takeoff range fall outside of the green arc?.

The green arc is different. With the standard 160HP set-up, it's 1900-2400, so the 2065-2165 range for that installation is in the green. OTOH, with the 180HP modification, the bottom of the green arc is 2100 RPM, and the 2300-2400 static range is within that green arc. And if 2000 RPM was below the green arc, it must have been a modified airplane which matches the POH you were given. And note that along with everything else (prop, tach, etc), the original 172R POH is replaced in toto by a different POH when that modification is done, not just modified by a supplement.

As I was rolling not believing my eyes, seeing that it was outside the green arc was the thing that really convinced me.

Good that you were looking.

Are there airplanes that takeoff with the RPM outside the green?

None of which I am aware.

 

[drgwentzel]

Good point, but the engine should perform better and even it out


The throttle was pretty hard honestly, even with the friction lock completely unscrewed. Even though I can't be sure that's not normal, it felt weird.

It is very common for a throttle, prop or mixture cable to stiffen in the winter or any season for that matter. Usually, the cable has to have some lubrication sprayed in under pressure and worked in and out to loosen it. If that doesn't fix the issue, they usually replace the cable.

Also, I think there is an o-ring in the friction lock that can get hard and make the throttle very stiff in the winter. The throttle shaft can be lubed as well as it passes into the friction lock on the Cessna's 170 and 180 series.

This is off topic now...sorry.

Gene

 

[noobJohn]

This forum is great. I verify "RPM in the green" early in the takeoff roll. From reading this thread, that should be sufficient but I may start pausing my scan long enough to read an actual number.

 

[dell30rb]

You're waiting till your oil gets to temp (160F or so) before take off right???

That's pretty hot. The continental IO360 specs a minimum oil temp of 75F for takeoff. I'd assume lycomings are similar.

I like to see at least 85F.

 

[bflynn]

It is very common for a throttle, prop or mixture cable to stiffen in the winter or any season for that matter. Usually, the cable has to have some lubrication sprayed in under pressure and worked in and out to loosen it. If that doesn't fix the issue, they usually replace the cable.

Also, I think there is an o-ring in the friction lock that can get hard and make the throttle very stiff in the winter. The throttle shaft can be lubed as well as it passes into the friction lock on the Cessna's 170 and 180 series.

This is off topic now...sorry.

Gene

I don't think it's off topic at all. From the symptoms given, I suspect some kind of interference with the throttle. Something in the engine that would cause it to run slow? Maybe something causing a temporary fuel blockage, some ice somewhere? I'm stretching to come up with anything.

But I am well on the side of a problem with fuel getting to the engine, not something with the nut connecting the pilot's seat to the flight controls (because we're all nuts).

 

[poadeleted20]

That's pretty hot. The continental IO360 specs a minimum oil temp of 75F for takeoff. I'd assume lycomings are similar.

If you read what was quoted from the C-172R POH and Lycoming's publications above, you can see the recommendation for Lyc IO-360 in the C-172R isn't even that much (although I personally still wait for "bottom of the green" which is 75F).

 

[Sac Arrow]

Here's one thing you might want to check. The 172R has the Lycoming IO360 right? One thing that is problematic with these engines is that lead deposits can accumulate on the valve stems and cause valves to stick when the engine is cold. The engine may run up normally, but when you apply power and get the RPM's above runup RPM, then the engine will start to bog down and lose power. It generally goes away once the engine is warmed up and is worse in cold weather.

That happened to my Arrow. The solution was to remove the spark plugs, manually fish the valves out using a reach tool, and clean the stems through one of the open spark plug holes.

 

[qbynewbie]

I wondered about sticking valves, too, when I read the OP's account. That would easily account for the loss of RPM he was seeing.

 

[MAKG1]

A couple thoughts:

1) You won't get full RPM on a 172R when at low speeds even when everything is correct, thanks to the fixed-pitch prop. The static RPM range listed on the TCDS for the 172R is from 2065 to 2165.

Not buying that unless you're at high altitude.

~2350 static is normal on every 172 I've flown, including 172R.

 

[poadeleted20]

Not buying that unless you're at high altitude.

~2350 static is normal on every 172 I've flown, including 172R.

Then the 172R you flew was modified from its original 160HP configuration with Cessna Kit MK172-72-01 to a 180HP configuration (as was the OP's 172R). However, Kent was correctly reading the book on the unmodified 172R.

One thing this discussion has pointed out is that you must read the book for the specific plane you're flying, not just apply what you learned about a similar plane. And if you're asking questions about a plane, you have to specify the exact model and any modifications which have been applied or you may get spurious answers.

 

[Johann]

Interesting points on the sticky valves. The plane is going to be flown, I saw it in the schedule. I guess someone will experience this if that's the case.

About the fuel, I thought about two more things that I could have messed up:

1) Mixture: say I didn't push this one all the way in, so the mixture was too lean, could that cause a 300 RPM drop? I would think not without some roughness, which I didn't experience.

2) Fuel selector: The POH calls for both on takeoff. Say I forgot it on the left or right position, could that cause this? Doesn't sound like it, since takeoff is pretty straight and level.

I don't think I did any of these, but if they can cause it then I'm willing to consider that I might have messed it up on one or both. It's been a few days so I can't say I'm 100% sure.

 

[Stewartb]

If you had a sticking valve, aka Lycoming morning sickness, you'd have felt the engine shaking as it was essentially running on three. Very hard to miss.

 

[poadeleted20]

1) Mixture: say I didn't push this one all the way in, so the mixture was too lean, could that cause a 300 RPM drop? I would think not without some roughness, which I didn't experience.

Severe roughness, which you couldn't help but notice.

2) Fuel selector: The POH calls for both on takeoff. Say I forgot it on the left or right position, could that cause this? Doesn't sound like it, since takeoff is pretty straight and level.

No. It could result in the engine stumbling or cutting out, but not just a smooth running 300 RPM low.

 

[MAKG1]

Interesting points on the sticky valves. The plane is going to be flown, I saw it in the schedule. I guess someone will experience this if that's the case.

About the fuel, I thought about two more things that I could have messed up:

1) Mixture: say I didn't push this one all the way in, so the mixture was too lean, could that cause a 300 RPM drop? I would think not without some roughness, which I didn't experience.

2) Fuel selector: The POH calls for both on takeoff. Say I forgot it on the left or right position, could that cause this? Doesn't sound like it, since takeoff is pretty straight and level.

I don't think I did any of these, but if they can cause it then I'm willing to consider that I might have messed it up on one or both. It's been a few days so I can't say I'm 100% sure.

Mixture MIGHT, but only if you had it set exactly right. More likely, it would stumble when you crammed the power, if it was very aggressively leaned (and that's a real good idea to avoid taking off lean).

The reason the fuel selector needs to be on both is for two reasons -- (1) you can fly with one tank empty that way, and (2) crosswind takeoffs and some departures around terrain or way too many obstructions will not be level (so low fuel in the low tank can unport). It will not reduce power at all unless one of these is a factor.

 

[qbynewbie]

If you had a sticking valve, aka Lycoming morning sickness, you'd have felt the engine shaking as it was essentially running on three. Very hard to miss.

Having had a partial engine failure at 450 AGL due to a stuck exhaust valve, I would tend to agree with you. The plane was shaking like mad (my 172, O300, but still...)

However, having had the valve unstuck, a few days and a few states later I heard something that just didn't sound exactly right on run-up. Brent was with me that day. We both heard something but it wasn't anything obvious at all. I decided to do a static runup right then and there. RPM maxed out at about 2000'.

I aborted the takeoff and taxied back. We were at Mount Hawley, Bruce's airport, and had just had dinner with him. Next day, his mechanic -- great guy, by the way -- examines the plane and finds not one but two stuck valves. Had I taken the plane into the air, it would have been a very bad day. With just me aboard and one stuck valve, I was able to get it to a nearby airport flying at best glide. Any other speed initiated a descent. With two of us aboard and two stuck valves, we would have been in the trees. And the only evidence we saw was a slightly different sound that we couldn't identify and a low RPM on the static runup.

 

[poadeleted20]

All things considered, including the successful maintenance run later, I suspect some sort of transient throttle restriction more than anything else, although a transient induction air blockage could also produce similar results (BTDT with a rollback from normal to 350 below normal in my Tiger at about 50 feet after takeoff). In any event, you did the right thing, and that's what counts most.

 

[Tom-D]

Severe roughness, which you couldn't help but notice.
No. It could result in the engine stumbling or cutting out, but not just a smooth running 300 RPM low.

fuel injected engines can run very smooth at lean of peak and be 300 RPM low.

 

[poadeleted20]

fuel injected engines can run very smooth at lean of peak and be 300 RPM low.

Tell you what -- you try that at full throttle on takeoff in a 172R and report back how that works.

 

[Tom-D]

Tell you what -- you try that at full throttle on takeoff in a 172R and report back how that works.

it will work exactly the way it was described in post 1.

172R
The Skyhawk R was introduced in 1996 and is powered by a derated Lycoming IO-360-L2A producing a maximum of 160 horsepower (120 kW) at just 2,400 rpm. This is the first Cessna 172 to have a factory-fitted fuel-injected engine.


If you think not you must not believe GAMI theory either.

 

[Henning]

Also consider how a mechanical tach works and you will find your rpm loss. What you have is a pair of magnets with a calibrated spacing. One is being spun by the engine, and one is connected to a shaft with a needle and has a return spring to '0' wrapped on the shaft.

When the engine is spinning the coupled magnetic fields of the two disks provide a drag that will pull the needle around against the spring to its representative position on the face. One calibrates the unit by adjusting the spacing between the magnets.

When it is cold, that spring will contract and provide greater resistance to the magnetic drag, so you end up with a lower than normal reading.

Here's my questions to you, "How did the engine sound? Strong? Were you accelerating on schedule? Do you keep a count to the 1000' marker to gauge your T/O performance? What was your fuel flow? MP?"

If there was no pressing reason to proceed with the T/O, then I don't fault you for aborting, it should be the default when doubt exists. Thing is for power, tachometers are notoriously crappy instruments, luckily there is a way to check that against a fluorescent light.

The real measure of power though is performance. When I see an off tach indication, first thing I look at is my performance. I got in the habit of gauging my takeoff performance by counting to the 1000' markers from a procedure an old 747 capt gave me. He said they have acceleration landmark times the have to make every 1000' to V1 or they abort. Obviously with a 747 it's a complex procedure calculated for each weight and runway..., but the concept simplified gives a good system of tracking relative performance and detecting a deviation from norms without having to go through all that. If I am not at the mark on time, I need to know why or I shut down.

 

[Johann]

Here's my questions to you, "How did the engine sound? Strong? Were you accelerating on schedule? Do you keep a count to the 1000' marker to gauge your T/O performance? What was your fuel flow? MP?"

It didn't sound weird or rough. But keep in mind that I rent this plane, and haven't flown it in months. I can't judge power by sound within 300 RPM. I understand an owner that flies the same plane regularly might be able to be confident enough to do that, but my case was far from that.

Wasn't keeping track, to be honest, of acceleration with respect to the markers.
It's a good practice for sure, and one that I'll work towards implementing. Of course it will be different for every plane, but it should be close enough.

Didn't check fuel flow, should have when I did the static run-up. Again, regardless of what it showed I would not have taken off since I don't know the plane enough to have that kind of confidence (specially with two passengers), but it would have been interesting to know for troubleshooting.

Fixed pitch prop so no MP indicator.

 

[Henning]

It didn't sound weird or rough. But keep in mind that I rent this plane, and haven't flown it in months. I can't judge power by sound within 300 RPM. I understand an owner that flies the same plane regularly might be able to be confident enough to do that, but my case was far from that.

Wasn't keeping track, to be honest, of acceleration with respect to the markers.
It's a good practice for sure, and one that I'll work towards implementing. Of course it will be different for every plane, but it should be close enough.

Didn't check fuel flow, should have when I did the static run-up. Again, regardless of what it showed I would not have taken off since I don't know the plane enough to have that kind of confidence (specially with two passengers), but it would have been interesting to know for troubleshooting.

Fixed pitch prop so no MP indicator.

As I said, I'm not faulting your decision one bit, if things aren't right and you can't account for them, you abort. There was a 737 that went in the Potomac that would have done well for the crew to remember that.

One thing about developing a count habit is you create a mental database of performance in type that works regardless of which aircraft you are in. It's not exacting as many factors influence performance, however when there is a gross incorrectness in count, you know this plane has a problem.

 

[dell30rb]

fuel injected engines can run very smooth at lean of peak and be 300 RPM low.

In a carb'd 152 I would lean until the RPM's dropped by about 50. You could continue leaning until they dropped by around 100 before the engine started running rough.

 

[flyingcheesehead]

Not being familiar with the engine... static should climb rapidly on take off roll, shouldn't it?

"Static" means that you're stopped. So technically, no.

However, yes, RPM will increase with airspeed with any airplane with a fixed-pitch prop because as the airspeed increases, the angle of attack of the prop will decrease, providing less resistance to the engine.

 

[flyingcheesehead]

No alternate air switch, but:

Ah, yes, the spring-loaded-door. I'm not a big fan of that system where there's no manual switch, because the spring on the door will cause some resistance too, lowering available power. Having not experienced it in that particular airplane, I'd still say it's plausible that you had a frozen-up air filter and the door only got pulled open partway due to the spring having higher resistance in the cold.

Ether way, 2,000 is way low for a 172, even if its the tach it a fix it before flying again.

Not so for the 160hp 172R - See the static thrust limits I posted. Even 2200 RPM is *higher* than the limit for that plane. Remember, there are quite a few different flavors of "172".

Unless they gave me the wrong POH, it's a 172R 180HP.

Aha. Well that would change things.

In the 160HP ones, does the takeoff range fall outside of the green arc?

Nope. Green arc is different. The tach will be changed in the 160-180hp conversion, as both the green arc and the redline (2400 vs 2700) will be different.

Are there airplanes that takeoff with the RPM outside the green?

Yes, but I'm not aware of any that take off with RPM *below* the green. Many planes have a green arc that's for cruise, with a gap between the top of the green arc and the redline.

This is another reason I prefer constant-speed props - You should get redline RPM by the time you get to full throttle on the takeoff roll.

 

[flyingcheesehead]

I thought about two more things that I could have messed up:

1) Mixture: say I didn't push this one all the way in, so the mixture was too lean, could that cause a 300 RPM drop? I would think not without some roughness, which I didn't experience.

2) Fuel selector: The POH calls for both on takeoff. Say I forgot it on the left or right position, could that cause this? Doesn't sound like it, since takeoff is pretty straight and level.

I don't think I did any of these, but if they can cause it then I'm willing to consider that I might have messed it up on one or both. It's been a few days so I can't say I'm 100% sure.

I doubt it was either one of those, but this made me think of another possibility along these lines - Are you sure you were on both mags? Or is it possible that you only moved the key one notch back instead of two after checking the second mag?

 

[flyingcheesehead]

Wasn't keeping track, to be honest, of acceleration with respect to the markers.
It's a good practice for sure, and one that I'll work towards implementing. Of course it will be different for every plane, but it should be close enough.

1000' markers should tell you only one thing in the 172: If you're not off the ground already when you hit them, abort!

OTOH, if you have (for example) a 5800' runway, you should be off the ground well before the 5000' remaining mark.

 

[MAKG1]

1000' markers should tell you only one thing in the 172: If you're not off the ground already when you hit them, abort!

Well, if you're hitting distance remaining markers, you have bigger problems than a weak engine.

 

[flyingcheesehead]

Well, if you're hitting distance remaining markers, you have bigger problems than a weak engine.

You know what I meant - Hitting the distances, not the markers!

 

[Henning]

1000' markers should tell you only one thing in the 172: If you're not off the ground already when you hit them, abort!

OTOH, if you have (for example) a 5800' runway, you should be off the ground well before the 5000' remaining mark.

Exactly! It's a performance gauge. If you aren't off the ground by the 1000' marker in a 172, unless you have major DA issues, you know you have a performance problem akin to an accurate 2000rpm indication. It doesn't really matter to us the detail of scope, it's a rough cross check for early determination of a problem is all, but it's easy and effective as one.

 

[poadeleted20]

Also consider how a mechanical tach works and you will find your rpm loss.

Not a 300 RPM loss.

 

[Johann]

I doubt it was either one of those, but this made me think of another possibility along these lines - Are you sure you were on both mags? Or is it possible that you only moved the key one notch back instead of two after checking the second mag?

Never happened to me before, and I always do two left, two right, one left, one right. But hey, there's a first time for everything, so I guess I can't say 100% no.
Is the performance I was getting consistent with running on one magnet?
Would it hurt if I did a static full power run up on one magnet next time I go just to see the RPMs I get?