Bob_Belville

Basic, basic question. What's the correct stall speed?

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I may have posted this before, it's been nagging at me for a very long time.

For my 1966 M20E: the bottom of the white arc on the ASI is 55 knots (63 mph). This agrees with the "FAA Approved Airplane Flight Manual" Issued Dec. 3, 1965.

But there's a chart in the "Owners Manual" that is labeled "stall speed vs. bank angle" (gross weight, IAS, power off).

That chart shows stall speed with zero bank and full flaps as 57 mph = 50 knots. 

What's the difference?

IMG_20171110_141410929[1].jpg

IMG_20171110_141524362[1].jpg

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26 minutes ago, N201MKTurbo said:

Go out and stall it and see who's right!

 

25 minutes ago, Mooney1 said:

Load factor 

Rich, we all know that actual stall speed varies with CG, weight, etc.

Mooney1, what are you telling me with the cryptic "load factor"?

What I'm asking is FAA paperwork stuff, not stick and rudder stuff. 

Thanks!

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See who re-screened the ASI...

With KIAS on the outer ring, it may not be original...?

Some ASIs have steps in the thickness of the white arc, for the different grades of flap... T/O or landing...

From old fuzzy memories, that could be terribly inaccurate... not a CFI...

Hoping this is helpful,

-a-

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2 minutes ago, carusoam said:

See who re-screened the ASI...

With KIAS on the outer ring, it may not be original...?

Some ASIs have steps in the thickness of the white arc, for the different grades of flap... T/O or landing...

From old fuzzy memories, that could be terribly inaccurate... not a CFI...

Hoping this is helpful,

-a-

Anthony, the ASI is not original but the marking agree with the AFM dated 1965.

Again, my question is what determines the "official" Vso? I assume that is 55 knots. But that leads to a second question, why does that chart I posted a pic of, which was in your C's Owner Manual I'm sure, show 50 knots (57 mph) for gross weight, power at idle, full flaps stall speed?

This is not entirely academic. I have a new AOA in my Aspen that needs to be calibrated. Prior to the calibrating flight I need to program in several weights and speeds... including Vso.

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15 minutes ago, Bob_Belville said:

 

Rich, we all know that actual stall speed varies with CG, weight, etc.

Mooney1, what are you telling me with the cryptic "load factor"?

What I'm asking is FAA paperwork stuff, not stick and rudder stuff. 

Thanks!

Ok, fair enough.

but you are worrying about half a needle's width.

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9 minutes ago, N201MKTurbo said:

Rich, did you find a Vso there? I have that doc pinned on the bulletin board in the hangar. Vso is not listed for M20Es. or Fs, Gs, Js, Ks, Ls...

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Bob,

I think I may have found it...

1) Reviewing My C's POH...

2) From The limitations section...

The white arc 63 to 125 CAS calibrated air speed in mph.  55 to 109 kts CAS.

 

3) From the performance section...

Stall speed chart...

  • Gross weight
  • Power Off
  • IAS In MPH 
  • Forward CG
  • Gear down (accept for 0° flap)
  • Power off

Does this cover the difference you are seeing?

Let me know if you need a copy of the Airspeed correction chart that is in the performance section.

Best regards,

-a-

 

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8 minutes ago, carusoam said:

Bob,

I think I may have found it...

1) Reviewing My C's POH...

2) From The limitations section...

The white arc 63 to 125 CAS calibrated air speed in mph.  55 to 109 kts CAS.

 

3) From the performance section...

Stall speed chart...

  • Gross weight
  • Power Off
  • IAS In MPH 
  • Forward CG

Does this cover the difference you are seeing?

Let me know if you need a copy of the Airspeed correction chart that is in the performance section.

Best regards,

-a-

where 

Anthony, you're saying that the difference is CAS vs IAS? I have a C manual with the performance section. (The Stall Speed vs Bank angle is chart 4 on page 36.)  

I don't see where the adjustment from IAS to CAS is shown. I know the definition but I don't ever remember seeing any specifics. 

If I go up and carefully stall the plane while watching the ASI how would I calculate a CAS from what I read on the ASI? 

 

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2 hours ago, N201MKTurbo said:

Go out and stall it and see who's right!

I just go with the stall horn--it's never wrong since it's right there, just before the stall :P

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Reviewing again....

Airspeed limitation markings, Page 4-3, CAS.

 

Performance Stall speed chart, Page 6-6, IAS.

Unfortunately, My pages and charts are not individually numbered...

But the SECTIONS are named...

 

Section 4: AIRSPEED INSTRUMENT MARKINGS

Section 6: STALL SPEEDS (POWEROFF)

 

Best regards,

-a-

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Just now, Shadrach said:

57 is Power Off. What's power on stall?

I think Vso is defined as "landing configuration" which I would take to mean throttle at idle. I noted the power off but I didn't take that literally as that would not be all that useful, and it might not be different from idle.

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Since we are picking nits down to the 1 mph. It will probably vary with each airframe.  Each airframe is hand built and the stall strips are custom to that airframe.  Applied after test flights.

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Just now, carusoam said:

Reviewing again....

Airspeed limitation markings, Page 4-3, CAS.

 

Performance Stall speed chart, Page 6-6, IAS.

 

Best regards,

-a-

Anthony, you must have a later model C manual. My several manuals from 65-67 do not have chapter coded page numbers. Does your chart match the one I pictured in OP?

 

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Bob...I agree, this is odd.  What I notice is that in the limitations section for airspeed markings, they mention the “significance” of the color and number.  Oddly, they say that the significance of the white arc “Denotes speed range in which flaps may be safely lowered”.  Really odd wording, implying that you could not lower the flaps below 63mph and saying nothing about stall speed.  I suspect that the white arc really extends to indicate stall speed at less than gross weight as well.  I think the proper way to mark your Aspen would be to these markings, which are from the CAA approved manual.  I don’t think the chart in figure 4 falls in the same category, as it comes from the owners manual, which is a Mooney manual, but not CAA approved.  Even in new aircraft, part 2 is not FAA approved, but Part 1 is.  I suspect that as we dig in, we will find the difference is between gross and some below gross number.

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Just now, Bob_Belville said:

Anthony, you must have a later model C manual. My several manuals from 65-67 do not have chapter coded page numbers. Does your chart match the one I pictured in OP?

 

Bob--

My 1970 Owners Manual is also not paginated that way. But the Downloads section here has a modern version, 1976? 1977?

Either way, imwould expect your E to stall at a different speed from my C.

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Just now, Yetti said:

Since we are picking nits down to the 1 mph. It will probably vary with each airframe.  Each airframe is hand built and the stall strips are custom to that airframe.  Applied after test flights.

The difference is 5 knots, 10%! 50 kts vs. 55. 

We're not talking about a specific plane, just the paperwork. 

If Anthony (and Hank) or on the right track then the CAS at low speed is 5 knots higher than the IAS. 

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2 minutes ago, takair said:

Bob...I agree, this is odd.  What I notice is that in the limitations section for airspeed markings, they mention the “significance” of the color and number.  Oddly, they say that the significance of the white arc “Denotes speed range in which flaps may be safely lowered”.  Really odd wording, implying that you could not lower the flaps below 63mph and saying nothing about stall speed.  I suspect that the white arc really extends to indicate stall speed at less than gross weight as well.  I think the proper way to mark your Aspen would be to these markings, which are from the CAA approved manual.  I don’t think the chart in figure 4 falls in the same category, as it comes from the owners manual, which is a Mooney manual, but not CAA approved.  Even in new aircraft, part 2 is not FAA approved, but Part 1 is.  I suspect that as we dig in, we will find the difference is between gross and some below gross number.

Rob, that all makes sense. Except for your last point about less than gross weight as being helpful to explain the difference since the performance chart specifically references gross weight and it is where the lower (50 kts) Vso is. That would imply that at 2400 pounds that Vso would be lower than 50 kts IAS.

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My C POH, was printed Oct 1977 Issue.

I bought it as recommended by some guy at the factory I spoke with on the phone.  I also bought the 65C owners manual to match the airframe...

It took me a while to figure out that the same Bill Wheat had signed off the AW in my airframe logbook in 1965....

Best regards,

-a-

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8 minutes ago, Bob_Belville said:

Rob, that all makes sense. Except for your last point about less than gross weight as being helpful to explain the difference since the performance chart specifically references gross weight and it is where the lower (50 kts) Vso is. That would imply that at 2400 pounds that Vso would be lower than 50 kts IAS.

Yup, getting tired and didn’t think it through....but now I see your dilemma. Leaning toward what Anthony and Hank posted, but it is certainly not clear.  I started looking at the old CAA regs and they start off simple enough, but then throw in some variables.

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It may take a CFI or instrument guy that really knows the details...

0° 67/58

15° 64/56

33° 57/49

Flap angle mias/kias

I believe all the markings are in CAS, accept Vne... which is IAS...?

The latest POH has both the knots and the mph in it.

Best regards,

-a-

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