1969 Cherokee 140B: Slow to climb

OP giving us too little to go on. Details are vague. We are literally guessing. Maybe try the magic 8 ball?
 
You cannot reliably infer airspeed from ground speed. Too many variables. Wind is not constant, it changes direction and magnitude.

What did ADS-B tell you about time to climb?

I sometimes travel with a few Cherokees. TBH it freaks me out watching them clear the trees by 50 feet on takeoff. My aircraft has a much higher climb rate, so I'm usually at 500 AGL by the end of the runway. But then we level out and I can't keep up!
 
How did the yoke feel? Heavy? Light? Normal?
Where was stabilizer trim set?

The one time I experienced an inexplicably low climb rate the trim was way forward and the yoke was way heavy. Learned a lesson there.

The most serious explicable climb rate I've experienced was leaving Douglas, WY (DGW), midday, 90+F, full tanks, at gross. Learned a couple lessons there.
 
Thanks to those that had great answers. There was little to no wind. Everything felt normal on the controls and even roll out and rotation. Unless the tach was lying RPM was where it should be and engine running smooth. The ADS-B data was quite telling. Initial climb out was around 150fpm but ground speed was greater than 85 mph. This differs from IAS of 85mph. Given no headwind the ground speed should not be greater than IAS (think of a triangle with the hypotenuse the climb, each side of the triangle has to be less than the hypotenuse). At around 1,000 feet I leveled off and airspeed jumped to 100mph and kept increasing. I then initiated a climb at 100mph (WOT) and ADS-B data showed a climb around 300fpm which was close to the ROC I was seeing. Per the ADS-B data the airspeed was off during the initial climb out. We did have lots of rain the 2 days prior to the flight. Living near the coast it rained hard enough to evacuate some areas due to flooding, that’s a lot of rain. I keep the pitot covered when tied down but that does not mean something, even water droplets, could get in during taxi or run up. That’s all the info I have. If it happens again I will have more info using other tools I did not use with ForeFlight. Thanks for all the constructive and cautionary information.
 
Remember that indicated airspeed is lower with a higher DA.
 
RonP said:
...the ground speed should not be greater than IAS (think of a triangle with the hypotenuse the climb, each side of the triangle has to be less than the hypotenuse).
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If you do the math, you will find that this hypothesis could not explain the situation you described. An IAS of 85mph and a VS of 150fpm would result in a climb gradient of about 2% (still air) and a climb angle of about 1.15°. I'll leave the rest to you.

Reviewing the info that you have provided, a few facts stand out:

1. You were flying a familiar airplane, at a typical weight, in unremarkable weather.
2. RPM and acceleration were normal during the takeoff roll.
3. The takeoff roll was not abnormally long.
4. Initial climb was only 150fpm, vis-a-vis the 700fpm that you have come to expect under similar conditions.
5. Another pilot observing from the ground noted your shallow climb angle and was alarmed enough to make a radio call to check on you.
6. At 1000' you initiated a level-off and the airspeed "jumped to 100mph...".
7. After the airspeed jumped and you resumed climb, you found cruise climb to be normal and performance seemed normal for the remainder of the flight.
8. On a subsequent flight, performance was normal.

One important piece of information, conspicuous in its absence, is pitch attitude. Was your initial pitch attitude consistent with what you typically use for climb?

Taken together, nos. 1-8 do not add-up in a way that suggests a malfunction of the engine or instruments. You stated that the flaps were retracted, and of course the gear is fixed.

Given the above, the only reasonable hypothesis that seems to fit all of the facts is a windshear or downdraft encounter. Oh, there is one other possibility: your pilot buddy was %^#@ing with you when you weren't looking.
 
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RonP said:
Given no headwind the ground speed should not be greater than IAS
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If your DA is high, TAS will be higher than your IAS and therefore your GS will be higher than your IAS. Your IAS measures how much air molecules go through your pitot tube. If the air is hot, it's less dense, hence you need to go faster to get the same amount of air molecules through your pitot tube. TAS adjusts for that difference. GS is TAS adjusted for wind. If there was 0 wind, your GS would be equal your TAS and your TAS would be higher than your IAS.
 
Chrisgoesflying said:
Your IAS measures how much air molecules go through your pitot tube. If the air is hot, it's less dense, hence you need to go faster to get the same amount of air molecules through your pitot tube.
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The air doesn't really go very far in that tube. The pitot opening is the only opening in the pitot system. Pressure is created when air rams against that hole, and warm air is less dense just like air at altitude, so it has less impact force and the pressure generated in the system is less. K=½MV². When Mass is lower, K is less. the V² is velocity squared, and is the reason there is such a taper on the airspeed dial even when there are mechanisms in the ASI to reduce that taper.

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Compare the distance between 40 and 60 to the distance between 180 and 200. See the taper in the scale. That's V² at work.
 
Dan Thomas said:
The air doesn't really go very far in that tube. The pitot opening is the only opening in the pitot system. Pressure is created when air rams against that hole, and warm air is less dense just like air at altitude, so it has less impact force and the pressure generated in the system is less. K=½MV². When Mass is lower, K is less. the V² is velocity squared, and is the reason there is such a taper on the airspeed dial even when there are mechanisms in the ASI to reduce that taper.

View attachment 132529

Compare the distance between 40 and 60 to the distance between 180 and 200. See the taper in the scale. That's V² at work.
Click to expand...

Makes sense. Never been good at physics and certainly not good at explaining it lol. End result is the same though, if DA is high, IAS is lower than TAS and therefore GS is higher than IAS if there is 0 wind.
 
Ice? I know Lycomings aren't supposed to ice at those temps according to popular wisdom, but our 172M would routinely generate limited carb ice at any temperature. Or is there a baffle/seal problem in the carb heat box/air select? Does the throttle shaft go all the way to the wide open stop on the carb? or might the throttle cable housing be slipping in it's retention system?
 
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