bad engine performance today

BDS wrote:

Maybe someone forgot to untie the tail and you were dragging a large
piece of the airport along with you :)


Now that makes perfect sense. Couldn't be seen from the cockpit, and it
probably bounced off on landing so nobody noticed what the actual problem
was..

And the error is
always on the low side: the tach will under-read because the magnets
in it weaken with age.

How does a tach work? Were I to design one, I'd count the revs
individually and do the math.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

Jose wrote:
And the error is
always on the low side: the tach will under-read because the magnets
in it weaken with age.

How does a tach work? Were I to design one, I'd count the revs
individually and do the math.

Jose

There are several ways they can work and most of them do in fact do the math
in one way or another. But something has to sense the revs.

There are several ways they can work and most of them do in fact do the math
in one way or another. But something has to sense the revs.

How would weakening magnets affect a tach? If they get so weak they
start missing revs (that are counted individually), I would expect the
tach to be very erratic at that point.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

In article ,
"BDS" wrote:

Anything that would cause a decrease in
power should also cause a decrease in rpm with a fixed-pitch prop.

Are you certain they are the same pitch?
Just because it is fixed pitch does not mean they are the same pitch.
There are "cruise" props, there are "climb" props and there are props
with their pitch somewhere inbetween.

The club I am in has to C172N's.
One has an intermediate pitched prop, the other has a cruise prop.
Both read the same RPM, but the cruise prop equipped aircraft does not
climb as well as the intermediated pitch equipped aircraft.
In level flight cruise, it is 10 kts faster, however, at 2300 RPM.

On Apr 30, 9:55 am, Brian wrote:
Were you leaning the engines before take-off. As it gets hotter this
can be more critical for best power. I haven't done the math but I
suspect that warm you are getting close to a 5000 ft density
alititude.

As noted in the post it doesnt take much of an RPM change to affect
performance so you might not notice on the tach. Also even small
differences in the propeller can affect performance greatly

Brian

I pulled the mixture back a little bit on the second circuit on
upwind, but it didn't help performance one bit.

Jose wrote:
There are several ways they can work and most of them do in fact do
the math in one way or another. But something has to sense the revs.

How would weakening magnets affect a tach? If they get so weak they
start missing revs (that are counted individually), I would expect the
tach to be very erratic at that point.

Jose

Remember I'm not saying that that is the problem the OP was having but if
you are counting something that happens 2800 every minute (46/sec) and you
start missing say 10% you'd see a 280 RPM drop. Even with that 10%
randomized somewhat the tach could keep up with the change enough for it to
show up as wild swings and would probably not be any worse than that caused
by vibration.

The magnet causes eddy currents in a bit of aluminum which
causes the aluminum to have a magnetic field...

Thanks.

Jose
--
Get high on gasoline: fly an airplane.
for Email, make the obvious change in the address.

------snipped for brevity-------

Maybe someone forgot to untie the tail and you were dragging a large piece
of the airport along with you :)

BDS


I've heard of that being done, although not in a C152, and really wish I
could have been a "mouse in the woodwork" :-)

OTOH, presuming that the OP does routinely use both of the aircraft in
question, and that the weight was normal, the only thing that occurs to me
is a notch of flaps. They seem easy to see, and difficult to miss; but I
have seen it done with a C172--and I have done it myself in a PA38, which is
a mildly amusing story: I had forgotten to retract the flaps following the
preflight, for a dual flight, and then taxied out and completed the run up;
and was still blissfully unaware. This was c1980, before headsets were in
common use; and just as we took the runway, I noticed my instructor
confiding something into the microphone--so I presumed that we were about to
have some sort or "emergency." I later learned that he was sure that the
Tomahawk would not take off with full flaps on an 85 degree day, and had
told the tower to expect an aborted take off. Actually, it would and did,
and quickly climbed to the top of ground effect (at an abnormally low
airspeed) and then I discovered that it is possible to press the release
button in a little too far (and get it stuck inside the flap handle... But
I promised to be brief; so I will only add that we did safely resume the
climb, I learned to be more thorough, and I also learned not to get the
button stuck inside that damned handle!

Peter

"buttman" wrote in message oups.com...
Today I was doing some touch and go's in a C152 with one of my
students to prepare for his first solo. It was a very hot day (35C),
but density altitude was only 2500 or so.



I'm surprised no one mentioned gross weight...