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Slow cruise after annual


marooneypilot

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I just got my 231 back from annual and it isn't cruising as fast as it used to. 

Previously I would cruise at lower altitudes (6kish) at 130 kias, and true out close to 150. Faster as I went higher. This is on 32", 2400rpm and LOP around 9.7 gph. 

Now I'm seeing kias around 115 with the same power settings. 

First flight I noticed that in slow flight the gear safety horn would start beeping around 70 knots (as if I were trying to raise the gear too soon after takeoff). I did a low pass past the tower and they didn't see anything, and the shop swung the gear too and saw nothing out of the ordinary. 

What could be causing this reduction in cruise speed?

 

David

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Two logical causes are either the engine is making less hp or there is increased drag. Some questions that come to mind:

Confirm the flaps are fully retracting?
Was any engine work done other than just checking compression?
Is the engine rough or sound different?



Fly Safe,
Safety Forum Mod

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15 kias slower than expected is worth looking into what is not working as expected....

Review what is really happening from your recent experience... so many things are conflicting... :)

 

wait a minute... the stall horn is sounding?  It won’t be the gear horn sounding... gear horns require two inputs, and none of them are speed related... throttle setting (switch) and gear up (switch)... pull the throttle with the gear up, and the horn sounds intermittently... if the throttle is pushed in, the gear horn is not coming on... (unless the switch is bad)

Slow flight near stall speed the stall horn blares continuously... the switch is based on AOA... it doesn’t know the air speed...

And you are indicating 70kias...  expect something is not working in your ASI... check the pitot and static sources, drains and what ever else can be affecting the ASI...

Use extreme caution in this case... your ASI May be indicating faster than your actual speed.

What got touched during the annual?  Stall switch? P/S system? WnB? Wash water entering the static ports? Did somebody adjust the throttle position switch?

Something is odd... one observation says you are slower than expected, another observation says you are showing faster than expected...

 

then on to other things...

Things to consider for max power...

1) If you can get max power, then the engine is probably working in the rest of the range...

2) T/O distance, did it get longer than expected... use an actual measurement to determine, compare to book value...

3) Climb rate, did it not behave like it did before... compare to book value...

4) Did you include DA in your comparisons? What was the temp out side?

 

Are you experiencing additional drag?

5) gear and doors properly stowed, and fully closed?

6) Flaps fully up?

7) Step put away?

 

Turbo specific things...

8) Max MP, FF and RPM, as expected? Compare to book values...

9) How many hours on the turbo since OH?  What MP controller or intercooler do you have?

10) anything blocking the air intake?

11) Any challenge controlling TIT, is it different than before?

12) Also Consider all the instrumentation used to set Power... if the TIT sensor is used to set power, and it is going away... it may be time for a new sensor...

13) Now would be a great time to post the JPI data to Savvy, and share the link here for all to view...

PP thoughts that come to mind, not a mechanic...

Best regards,

-a-

 

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2 hours ago, marooneypilot said:

First flight I noticed that in slow flight the gear safety horn would start beeping around 70 knots (as if I were trying to raise the gear too soon after takeoff). I did a low pass past the tower and they didn't see anything, and the shop swung the gear too and saw nothing out of the ordinary. 

Usual slow flight is gear down, and flaps deployed, simulating the landing configuration...  lots of drag requiring lots of power...

 

Are you performing slow flight with the gear stored and throttle out?

typically the gear horn won’t sound in level flight...

The power required to maintain level flight will have the throttle pushed in enough to keep the switch open...

Maybe you are descending in slow flight with the throttle pulled back?

Just trying to figure out what is going on first...

PP thoughts only,

best regards,

-a-

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Thanks for the ideas folks!

First off, I should be more specific. I said slow flight but didn't mean "Slow Flight". I noticed at towards the end of a chandelle (so still in high power, no flap, gear-up configuration) as the speed bled off below 70kias the gear safety horn would go off (fast beeping). 

There are two gear horns - one that is linked to airspeed (this ordinarily sounds when attempting to raise the gear too soon after takeoff, and can be overridden with the safety bypass switch next to the gear handle, sounds like a fast beeping), and one that is linked to throttle (this sounds when pulling the throttle to idle or near-idle with the gear still up, different intermittent beeping). These sound different in my aircraft, and it is the former that I am hearing when the airspeed is decreasing. This does not normally sound with the gear up - so something is amiss. It's definitely not the stall horn because the stall horn is a continuous tone, which this is not.

Now, to the thoughts:

Flaps - I can confirm these are fully retracted.

Engine - I believe there was some work done around the turbo. I haven't got the full work log back but understand there were some fittings that were tightened.

Engine sound - Engine sounds the same as normal.

Indicated vs GPS - looking at the track log, and comparing eastbound vs westbound to account for wind, I'm seeing a wind-corrected GS of 139kts. This is barely higher than my regular indicated, so I'm fairly confident the plane is actually going slower. This is a good thought though - next flight I will do more deliberate investigation of this.

Carusoam: I'm confident that the 70kts is _relatively_ accurate, or at least that I'm not flirting with the stall. For two reasons: I did this at altitude near the end of a chandelle, so I am familiar with how the plane starts to feel as it creeps into a stall (it wasn't mushing, wallowing, or buffeting), and the stall horn didn't go off. And I'm confident this isn't the gear-up warning since I was still pushing over 30" at this point.

As far as I know the stall horn wasn't touched during annual, but P/S system was - got IFR cert done.

1) How can I know if I'm generating max power without hooking up a dyno? I can easily red-line (get to 37" and 2700rpm), and it "feels" lively on takeoff, not sluggish.

2) Will measure, but I'm lifting off at the same point on the runway as I always have

3) It's been bumpy here in central Texas, but as far as I can tell it's climbing more or less as usual (I never did get book in my plane)

4) I didn't calculate for DA, but it's hot here, so if anything I'd be expecting my TAS to be higher.

5) I believe so - both tower flyby, and mechanic gear swing confirmed looks good

6) Yes, flaps stowed fully

7) Step is down and welded ;)

8) As expected

9) About 600 hours since overhaul on both the engine and turbo. Has the Merlyn  wastegate, and airflow intercooler.

10) Good question - worth a recheck

11) TIT is in the same range as before

12) I have two TIT gauges, an engine analyzer with CHTs, and fuel flow. Using these in combination to set power as I did before I'm seeing all the same temps and flows. Their consistency makes me think that those readings are as reliable as they were before the annual.

13) Sadly, cannot download from my engine analyzer :( 

Sounds like I have to do a bit more digging around on the ground and in the air. I may also try an in-air mag-check and lean test and make sure that is all the same as before.

Listing out all these answers though makes it sound like it's a drag thing. Could they have messed up the rigging during annual to cause this?

David
(Flying Piper speeds is not why I own a Mooney)

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3 hours ago, marooneypilot said:

Thanks for the ideas folks!

First off, I should be more specific. I said slow flight but didn't mean "Slow Flight". I noticed at towards the end of a chandelle (so still in high power, no flap, gear-up configuration) as the speed bled off below 70kias the gear safety horn would go off (fast beeping). 

There are two gear horns - one that is linked to airspeed (this ordinarily sounds when attempting to raise the gear too soon after takeoff, and can be overridden with the safety bypass switch next to the gear handle, sounds like a fast beeping), and one that is linked to throttle (this sounds when pulling the throttle to idle or near-idle with the gear still up, different intermittent beeping). These sound different in my aircraft, and it is the former that I am hearing when the airspeed is decreasing. This does not normally sound with the gear up - so something is amiss. It's definitely not the stall horn because the stall horn is a continuous tone, which this is not.

Now, to the thoughts:

Flaps - I can confirm these are fully retracted.

Engine - I believe there was some work done around the turbo. I haven't got the full work log back but understand there were some fittings that were tightened.

Engine sound - Engine sounds the same as normal.

Indicated vs GPS - looking at the track log, and comparing eastbound vs westbound to account for wind, I'm seeing a wind-corrected GS of 139kts. This is barely higher than my regular indicated, so I'm fairly confident the plane is actually going slower. This is a good thought though - next flight I will do more deliberate investigation of this.

Carusoam: I'm confident that the 70kts is _relatively_ accurate, or at least that I'm not flirting with the stall. For two reasons: I did this at altitude near the end of a chandelle, so I am familiar with how the plane starts to feel as it creeps into a stall (it wasn't mushing, wallowing, or buffeting), and the stall horn didn't go off. And I'm confident this isn't the gear-up warning since I was still pushing over 30" at this point.

As far as I know the stall horn wasn't touched during annual, but P/S system was - got IFR cert done.

1) How can I know if I'm generating max power without hooking up a dyno? I can easily red-line (get to 37" and 2700rpm), and it "feels" lively on takeoff, not sluggish.

2) Will measure, but I'm lifting off at the same point on the runway as I always have

3) It's been bumpy here in central Texas, but as far as I can tell it's climbing more or less as usual (I never did get book in my plane)

4) I didn't calculate for DA, but it's hot here, so if anything I'd be expecting my TAS to be higher.

5) I believe so - both tower flyby, and mechanic gear swing confirmed looks good

6) Yes, flaps stowed fully

7) Step is down and welded ;)

8) As expected

9) About 600 hours since overhaul on both the engine and turbo. Has the Merlyn  wastegate, and airflow intercooler.

10) Good question - worth a recheck

11) TIT is in the same range as before

12) I have two TIT gauges, an engine analyzer with CHTs, and fuel flow. Using these in combination to set power as I did before I'm seeing all the same temps and flows. Their consistency makes me think that those readings are as reliable as they were before the annual.

13) Sadly, cannot download from my engine analyzer :( 

Sounds like I have to do a bit more digging around on the ground and in the air. I may also try an in-air mag-check and lean test and make sure that is all the same as before.

Listing out all these answers though makes it sound like it's a drag thing. Could they have messed up the rigging during annual to cause this?

David
(Flying Piper speeds is not why I own a Mooney)

Unless your aircraft has a system that is unique, I do not believe the gear horn is anythingn more than a throttle position switch, airspeed is not a factor. The micro switch that activates the gear horn should be adjusted to factory spec. I cannot envision an chandelle scenario that would cause the gear horn to sound.

Edited by Shadrach
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David seems to be describing an add-on announcement...

a gear horn related to speed....

I don’t think Mooney had such a thing...

Got a P2 or some other add-one connected to the audio panel?

 

Review what the annual documented... anything they spent time on Probably was written-up...

If there was no mention of rigging boards, but mentioned rigging... you may have a winner....

PP thoughts only...

Best regards,

-a-

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To clarify, I'm not referring to any add-on, this is a standard safety feature that is in all modern Mooneys. It is in the POH as the gear safety switch and is documented as being airspeed actuated. There is an alarm attached to it, which is annoying when you swing the gear on the ground. I'm not referring to the throttle actuated gear horn, which is a separate system. 

See the attached, this is the red button next to the gear lever

433AD4C3-3EA2-45FA-BB2F-786F0268889C.jpeg

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David,

Speedbrakes will kill 20 KIAS in level flight at cruise, so it's hard to imagine you have an aerodynamic cause.  Speedbrakes are big and situated for maximum damage to airspeed.

Try a 3 way GPS test like this one  and see where you are reference book best economy or best power.  I'd look carefully at pitot static system.

Good luck.

-dan

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1 hour ago, marooneypilot said:

To clarify, I'm not referring to any add-on, this is a standard safety feature that is in all modern Mooneys. It is in the POH as the gear safety switch and is documented as being airspeed actuated. There is an alarm attached to it, which is annoying when you swing the gear on the ground. I'm not referring to the throttle actuated gear horn, which is a separate system. 

See the attached, this is the red button next to the gear lever

433AD4C3-3EA2-45FA-BB2F-786F0268889C.jpeg

Yes, this switch prevents the gear from retracting before flying speed,  as far as I know it does not provide an audible alarm.

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I'm going to put my $0.02 and guess that you have something up (a leak or blockage) in your pitot or static system.

You mentioned you go an IFR cert, so that fits.

I don't know enough about the airspeed switch itself and how it works, but it sounds like it is plumbed directly into the pitot line, but it has a feed line from the static system.  If that line to the static system is partially blocked, one can imagine that the switch will start acting like an ASI with a blocked static line, but your actual ASI will still read normal.  So it might be worth asking them to check the airspeed switch plumbing?

http://knr-inc.com/shoptalk-articles/25-shoptalk/93-201901-electric-gear-safety-system

 

 

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17 minutes ago, Shadrach said:

Yes, this switch prevents the gear from retracting before flying speed,  as far as I know it does not provide an audible alarm.

Oh, holy smokes, yes it does (at least in J models).  When I left my pitot cover on after a plane wash, then took off and tried to raise the gear, I nearly pooped my pants when unfamiliar alarms started going off... :blink:

FWIW, during gear swings at annual, I do recall the same alarm going off

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Just now, jaylw314 said:

Oh, holy smokes, yes it does (at least in J models).  When I left my pitot cover on after a plane wash, then took off and tried to raise the gear, I nearly pooped my pants when unfamiliar alarms started going off... :blink:

I've learned something!  So this would certainly indicate a pitot issue!

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Thanks jaylw314 - glad it's not just mine ;)

Sounds like it's worth confirming the pitot is working by verifying the IAS/TAS readings against GPS - should be easy enough with a methodical flight test. Will do that and report back my results.

Edited by marooneypilot
I'm Pedantic.
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2 hours ago, marooneypilot said:

To clarify, I'm not referring to any add-on, this is a standard safety feature that is in all modern Mooneys. It is in the POH as the gear safety switch and is documented as being airspeed actuated. There is an alarm attached to it, which is annoying when you swing the gear on the ground. I'm not referring to the throttle actuated gear horn, which is a separate system. 

See the attached, this is the red button next to the gear lever

433AD4C3-3EA2-45FA-BB2F-786F0268889C.jpeg

That part we are familiar with...

 

it just doesn’t usually have any sound associated with it... :)

Most Mooneys have two alarms...

  • Gear up... alternating tone.
  • stall... Steady.

 

Some Mooneys get an added system like the P2, that verbalizes all the various tones that could occur...

Seems as if somebody added a sound feature to your ship...

There is a pressure switch attached to the pitot system that allows the gear to operate... the by-pass switch is used when the pressure switch malfunctions...

The pressure switch is a modern version of a squat switch that the older Mooneys use...

Continuing to discuss odd details to help determine how many challenges are being chased.

Why would somebody want the Gear’s air pressure switch to be audible-ized?

PP thoughts only...

Best regards,

-a-

Note: you guys got onto an interesting solution, while I was busy typing.... :)

Still leaves me asking... Why would somebody want the Gear’s air pressure switch to be audible-ized?

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56 minutes ago, carusoam said:

Still leaves me asking... Why would somebody want the Gear’s air pressure switch to be audible-ized?

I think it's supposed to warn you that you've moved the gear to the up position while still on the ground.  Then when you go to take off, the gear could retract before you've lifted off and you'd have a bad day.

Or maybe it's just a way to slap your hand for doing something bad :) 

The caveat to all this is that the alarm should only sound when the gear is still down, once the gear is up and locked this alarm should no longer be in play.

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Yes, this switch prevents the gear from retracting before flying speed,  as far as I know it does not provide an audible alarm.


What he is talking about is this button:

e9fac0c334141b4e98bf19e3bf4f688b.jpg

With either an airspeed or squat switch, if you put the gear in the “up” position (throttle in) and the switch indicates a fault condition (airspeed switch = too low airspeed or squat switch = weight is still on squat), you will get a warning horn.

The red button allows you to override the safety features to retract the gear.

The gear warning switch tied to the throttle activates a horn as well. This would activate if the throttle is out and the gear lever is up.

The switch was not on older Mooneys and many of us with electric gear added it.


Sent from my iPhone using Tapatalk Pro
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On 9/16/2019 at 2:52 PM, steingar said:

If I got  my aircraft back form the mechanic 15 knots slow I'd take it back to said mechanic to fix whatevertheheck it is he bolluxed.

I agree.  @marooneypilot, any chance you can post a bulleted list of what your mechanic did at annual before he/she signed the airplane back into service?  Would likely help identify a culprit.

Steve

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  • 2 weeks later...
On ‎9‎/‎16‎/‎2019 at 3:04 PM, jaylw314 said:

I'm going to put my $0.02 and guess that you have something up (a leak or blockage) in your pitot or static system.

You mentioned you go an IFR cert, so that fits.

I don't know enough about the airspeed switch itself and how it works, but it sounds like it is plumbed directly into the pitot line, but it has a feed line from the static system.  If that line to the static system is partially blocked, one can imagine that the switch will start acting like an ASI with a blocked static line, but your actual ASI will still read normal.  So it might be worth asking them to check the airspeed switch plumbing?

http://knr-inc.com/shoptalk-articles/25-shoptalk/93-201901-electric-gear-safety-system

 

 

Did it sit outside in the wind and rain? Drain your PS system in case you picked up some water. I've heard of this before.

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So after a bunch of trouble with the battery, I finally managed to get back in the air. Here are four photos from that flight, going in four different directions. The short version:

Hdg 140: KIAS 113, GS 135
Hdg 320: KIAS 110, GS 169
Hdg 050: KIAS 115, GS 154
Hdg 230: KIAS 111, GS 147

The average GS is 151, but the TAS is always within a couple of knots of 135 according to the Aspen. This makes me think that the pitot static system is having issues as we suspected. I've asked the mechanic to have another look and see if anything was messed up during the annual.

I have the logs back now, things they did:

  • IFR cert on static system and transponder
  • New air induction filter
  • Cleaned and gapped spark plugs
  • Complied with a fuel injection line AD

Thoughts on how to proceed?

IMG_2716.JPG

IMG_2720.JPG

IMG_2722.JPG

IMG_2729.JPG

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