1969 Cherokee 140B: Slow to climb

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RonP

Pre-takeoff checklist
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Had an interesting problem I can’t figure out. Barely any wind if any at all, 83 degrees F out and calculated take off weight of 2,000 pounds with a passenger. I have flown with this same person and weather before and could easily achieve a climb rate of 700fpm. With the density altitude according to the performance chart I should be around 600 to 700 fpm. This day I could barely hit 150fpm. Everything looked good from run up to climb RPM (2,400) and Vy of 85 mph. I felt the airplane was not climbing and the rate of climb showed the 150fpm. I thought the ROC was bad and I got a call over the radio from a friend asking if I was having trouble climbing so this was noticeable from the ground. I stayed in sight of the airport and got up to 3,500 feet. I flew an hour away to burn some fuel and landed at another airport. After lunch we took off and the climb was back to 600 fpm an I could feel the difference. I burned about 10 gallons and I can’t imagine 60 pounds lighter making a difference since I was already 150 pounds under max. The weight and balance was done 6 years ago and no changes were made to the airframe that would change the weight. Any idea on what caused this when the numbers all looked where they should be with performance except for rate of climb?
 
@RonP, flaps is a good guess. Try climbing again with the same load and fuel. If you get satisfactory performance with no flaps, descend to 1000 sf, add flaps, and then climb out at WOT.

-Skip
 
He would have noticed the flaps at some point, if not during climb out, then surely during cruise or when he went to extend them for landing and they were already?

How long have you had this plane?
 
The flaps were up so that was not with it. The primer was in a locked but even if it wasn’t RPM was where it should have been on climb out. I would suspect if the primer wasn’t in or leaking I would have had an RPM drop. Have had the airplane for 6 years and never had this happen before.
 
The POH performance chart only shows density altitude and weight to determine climb performance. I got the density altitude from the AWOS. The temperature is what I read on my car and does not factor into the performance charts which was just my observation. The Cherokee may be slow to climb but when the anemic climb rate I am familiar with gets reduced to 1/3 it raises the question what caused it.
 
Bad rpm reading? Was the throttle ALL the way in? Maybe the carb wasn’t partially blocked or not open all the way?

Any engine instruments, fuel flow, egt, cht, etc that you could check for comparison? When I had fuel flow it was nice to see it in the same range every climb out so you knew the fuel was flowing and also no leaks causing excessive fuel flow.
 
ChemGuy said:
Bad rpm reading? Was the throttle ALL the way in? Maybe the carb wasn’t partially blocked or not open all the way?

Any engine instruments, fuel flow, egt, cht, etc that you could check for comparison? When I had fuel flow it was nice to see it in the same range every climb out so you knew the fuel was flowing and also no leaks causing excessive fuel flow.
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I second this, my climb performance was subpar, until I left the throttle in more then I was getting POH numbers. I believe the RPM is off 100-150RPM on my gauge, or might be the angle that I see it, who knows.
 
Were you climbing at WOT or reduced RPM? Asking because in a pa-28-150 with 2 people and full fuel, climbing is slow at WOT. I've flown one older PA-28 model with a specific engine/prop combination that was placarded to avoid continuous operation at some specific RPM range, can't remember the combo, but other than that I've always done climbs at max power in any PA-28 that didn't have a constant speed prop.
 
RonP said:
…I stayed in sight of the airport and got up to 3,500 feet. I flew an hour away to burn some fuel and landed at another airport. After lunch we took off…
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This doesn’t help answer your question, but reading your description of the event left me wondering whether you considered returning to the departure airport to resolve the problem before heading off on a cross-country excursion.
 
I always take off at WOT at full rich mixture. As to the decision to fly an hour away was the cruise climb was where it should be and the cruise RPM and airspeed was where it should be. My home airport has jumpers and I left the area as I was getting in the way circling the airport. I hopscotched over airports that I could land at along the way. The destination airport has an A&P that has worked on my airplane before. Looking back there are tools I could have used that I did not. ForeFlight has a display that gives ground speed, altitude and ROC. I never use it but it would have given me more information during takeoff except for RPM. ForeFlight also has a track log that shows ground speed and altitude I did not have on. This would have shown my performance to review later. The takeoff at the destination airport had no issues. Still baffles me how the RPM and airspeed were where they should be yet a very slow climb.
 
Couple of questions. What engine? What prop pitch? What is your static RPM? Whole bunch of factors that could cause this. Real simple one could be you forgot to switch the mags to "both". On initial climb, I'm at WOT which gives me more like 2500RPM at an 85MPH climb.
 
What was the actual DA? What was static rpm?

Not sure how Foreflight's ground speed would have helped anything.
 
You KNOW you were slow to climb.

You DONT KNOW you were at 2400 rpm or that you were 85 mph, as you only had one source. This is where I’d start looking first.
 
How long did this last, if as you say the cruise climb was normal? Could have been just a wider area downdraft and bad timing?
 
Do you have ADS-B Out? If so, plug your N number into FlightAware and get your time to climb to altitude, then calculate ROC.

At 150 fpm it would take you 20 minutes to climb 3000 feet.
 
Carb heat was not on and mags were both. The tach read 2,400 and airspeed was 85mph (Vy), pretty normal for takeoff. I have a climb prop, don’t know the specifications until I look into the log. That I know for sure. Whether the instruments were lying I have no way to tell. Roll out and rotation were about where it always is distance down the runway. It certainly did not take 20 minutes to get to 3,000 as I went around the airport once and was at altitude. I do have ADS-B out and that’s a great idea to check what those numbers are. There are trees at the end of the runway that have a slot cut thru for landing in that direction. I did hit turbulence as I got above the tree line. Did not expect that on a day the windsock was hanging motionless. The ADS-B data may tell a better story. Good idea.
 
RonP said:
I always take off at WOT at full rich mixture.
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So what does the POH say about leaning for climb in high DA? It says this:

1723742907807.png

Now, students often pick up on the "always rich for takeoff and climb" from instructors who were taught the same thing. And so performance suffers on warm days, especially at higher airports. People have died due to this ignorance.

Lycoming publishes Operator's Manuals for its engines. From the O-320 manual, we get a couple of things:

1723743235178.png
1723743211396.png

That 5000 feet shown there can be interpreted as 5000 feet density altitude. A 3000-foot airport can easily be well above that on warm days.

Those engine operator's manuals should be part of a student's training.
 
I can't think of a way there would be a power loss without an RPM loss in a fixed pitch airplane. Maybe water in the pitot-static system?
 
dmspilot said:
I can't think of a way there would be a power loss without an RPM loss in a fixed pitch airplane. Maybe water in the pitot-static system?
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VSI hanging up mechanically? Sounds like the VSI was the only indication problem.
 
This is going to sound sarcastic but I don't mean it that way. My hope is that it is educational.

Your engine is in an abnormal condition during climb-out and you don't know why. You have an innocent passenger on board yet you decide to risk your passengers life by continuing to fly for another hour?

So far, I have not seen any recognition in this post where you realize your lack of judgement - especially considering you have a passenger on board.

Imo when you have a passenger on board your decision making should be more conservative. If you want to risk your own life, that's one thing, but taking someone with you is unforgivable.

Hopscotching over airports would not help in many scenarios that could have been responsible for the lack of performance.
 
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If everything looked and felt right, plus the fact that everything was as usual on the flight back, I would say it was some atmospheric condition that caused this e.g. DA higher than calculated, downdraft during climb out, etc. I don't think engines fix themselves too often. When I still had my Cherokee, it was eye opening how slow the plane climbs when taking off from high DA with a full load. I bought the plane in the winter, so every takeoff was freezing cold, hence great climb performance. Then I went to Florida for the winter, hence sea level and around standard temp, still great climb. On the way back, I stopped in KRAP and the day we left, it was unusually warm for March. I knew the climb was going to be slow but it's one thing knowing it and a whole other thing experiencing it. And to be fair, the plane initially climbed slower than calculated (still well enough to clear any obstacle) but similar to your situation, nothing indicated there is an issue, rpm, temps, everything was good so I also continued flight. Sure, I was more vigilant and watched my engine instruments much closer and probably would have returned at even the slightest indication of an issue, but there simply was no indication. Once in cruise, I got exactly the numbers I was expecting.
 
How long were you stuck at +150fpm? That might provide a clue. Guessing it wasn't for the full climb. Did you achieve full cruise power/expected KIAS during your flight to the other airport?

Looking at this chart I'm surprised by your expectation to achieve 700fpm in a Cherokee140 with 2 people onboard and fuel on a hot day. You must be in a really low elevation area for 85F to still be a low enough DA to hit those #'s.
You've done it before like you mentioned and you did it in the return trip, but that's pretty strong performance for a loaded 140 on a summer day. That's not to say 150fpm should have been your expectation either, that's extremely low.
1723758590545.png

I think Chris' comment about weather could have merit. Most of my takeoffs where I came in notably/inexplicably below POH #'s on performance were hot, bumpy days where I suffered through downdrafts and other turbulent-y disturbances.
Usually they wouldn't persist throughout an entire climb up to 3500 though... If your poor perf was through the entire climb - that sounds alarming. I would not have flown back (and certainly not with a passenger!).

EDIT: I'd probably have my plane looked at to be safe before embarking on another flight.
 
Spinka said:
How long did this last, if as you say the cruise climb was normal? Could have been just a wider area downdraft and bad timing?
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This was my 1st thought once you said it was normal on the next take off/climb. I have climbed at 2000+ft/min in my glider sustained for 8000 ft. What goes up must come down so somewhere there was an equal mass of air coming down. The secret to soaring is loiter in the up and race through sink. I frequently used this technique to improve the climb and descent when flying Skydivers.

I have also seen Descents of 400ft/min and power and speed settings that should have been giving us a 400+ft/min climb.

Brian
CFIIG/ASEL
 
RonP said:
As to the decision to fly an hour away was the cruise climb was where it should be and the cruise RPM and airspeed was where it should be.
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Your initial post didn’t mention that cruise climb seemed normal. You did mention that a friend contacted you by radio because you appeared to be struggling to gain altitude immediately after takeoff. Those two bits of information suggest that a downdraft or windshear may have been the culprit (as has been stated by others). But while the atmosphere seems to be the most likely suspect, the info you provided does not rule-out other possibilities.

At some airports it’s not uncommon to encounter updrafts, downdrafts, and windshear. Learning to identify such conditions prior to takeoff is well worth the effort, but outside the scope of this thread.
RonP said:
My home airport has jumpers and I left the area as I was getting in the way circling the airport. I hopscotched over airports that I could land at along the way. The destination airport has an A&P that has worked on my airplane before. Looking back there are tools I could have used that I did not.
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And yet, considering the ugly consequences of suddenly finding yourself piloting a (rather poor) glider, no one would fault you for having made a a decision to return to the departure airport. It would be more difficult to explain, after an off-airport landing, why you didn’t. Lndwarrior laid it out in post #26.

Of course, none of us were there, and we can only go by the info that you provided. I’m glad the remainder of the flight went well.
 
Roger Wilco said:
At some airports it’s not uncommon to encounter updrafts, downdrafts, and windshear. Learning to identify such conditions prior to takeoff is well worth the effort, but outside the scope of this thread.
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And/or identifying them when they happen.
 
In 2,000 hours of GA flying I've never experienced such a "downdraft" that inhibited my takeoff and initial climb for a prolonged period of climb. I have been surprised by weight and DA though. I might suggest OP find a long runway, load the airplane to MTOW and test the takeoff performance.
 
dmspilot said:
In 2,000 hours of GA flying I've never experienced such a "downdraft" that inhibited my takeoff and initial climb for a prolonged period of climb. I have been surprised by weight and DA though. I might suggest OP find a long runway, load the airplane to MTOW and test the takeoff performance.
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I suppose it depends on your definition of "prolonged", in my experience 10-15s isn't crazy. Bad perf for an entire climb out would be a little crazy.

In my comparatively smaller 700h there's been a number of times, always on hot days, where I've taken DA into account and there are brief periods where it's not possible to hit the published ROC figures. Then you will hit them 10-20s later, or be much closer.
Similarly there's times, always in colder wx, where accounting for a 0' DA I can blast well past my 900'FPM ROC POH number in a climb for far longer than I'd expect.
 
Clear up a few things. My passenger is a pilot with lots of hours and in type. It was a mutual decision to continue, burn some fuel and go to where an A&P familiar with my airplane is. There was no engine problem, correct RPM for the climb and smooth running. The ADS-B data holds the biggest clue. I was climbing at 85mph indicated. The ADS-B data indicates my ground speed was over 85 KNOTS during the climb. Given no or little wind and assumed to be climbing at 85 MPH my ground speed has to be less than 85mph, not over 85 knots. To me this means the airspeed was not correct and I was flying faster and flatter than I was led to believe. At some point the airspeed error went away or whatever restriction was cleared. No problems for the rest of the day. The ASI will be checked this week.
 
Forgot to mention I am in south jersey and the elevation is 162’ above sea level.
 
RonP said:
Had an interesting problem I can’t figure out. Barely any wind if any at all, 83 degrees F out and calculated take off weight of 2,000 pounds with a passenger. I have flown with this same person and weather before and could easily achieve a climb rate of 700fpm. With the density altitude according to the performance chart I should be around 600 to 700 fpm. This day I could barely hit 150fpm. Everything looked good from run up to climb RPM (2,400) and Vy of 85 mph. I felt the airplane was not climbing and the rate of climb showed the 150fpm. I thought the ROC was bad and I got a call over the radio from a friend asking if I was having trouble climbing so this was noticeable from the ground. I stayed in sight of the airport and got up to 3,500 feet. I flew an hour away to burn some fuel and landed at another airport. After lunch we took off and the climb was back to 600 fpm an I could feel the difference. I burned about 10 gallons and I can’t imagine 60 pounds lighter making a difference since I was already 150 pounds under max. The weight and balance was done 6 years ago and no changes were made to the airframe that would change the weight. Any idea on what caused this when the numbers all looked where they should be with performance except for rate of climb?
Click to expand...
What was the humidity?
 
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