Are the M20C/D's legal to fly under MOSAIC

[hammdo]

My AI buddy says 

 

“58 KCAS

(67 MPH × 0.868976 = 58.22 knots; IAS ≈ CAS at low speeds, rounded to whole knot per aviation convention”

 

Edited 4 hours ago by Jackk

 

[PT20J]

Interesting. I often find that AI gets things exactly backwards. Recently, it correctly answered a question but then went on and eventually contradicted itself. 

[cliffy]

MAYBE the factory can dig into the certification records and come up with an IAS correction factor at the low airspeeds 

to compute a calibrated airspeed for the stall?   I'm sure its model and airspeed dependent. 

Might be worth a try.

AI ain't as good as many think it is especially in technical matters. 

[ptwffz]

1 hour ago, hammdo said:

 

My AI buddy says 

 

“58 KCAS

(67 MPH × 0.868976 = 58.22 knots; IAS ≈ CAS at low speeds, rounded to whole knot per aviation convention”

 

Edited 4 hours ago by Jackk

 

Makes sense if IAS = CAS at low speeds. 

[PT20J]

1 hour ago, ptwffz said:

Makes sense if IAS = CAS at low speeds. 

The problem, as we may recall from private pilot ground school, is that that the largest airspeed errors (spread between IAS and CAS) usually occur at low airspeeds because the pitot tube is no longer aligned with the relative wind due to the increased angle of attack.

[Hank]

9 minutes ago, PT20J said:

The problem, as we may recall from private pilot ground school, is that that the largest airspeed errors (spread between IAS and CAS) usually occur at low airspeeds because the pitot tube is no longer aligned with the relative wind due to the increased angle of attack.

Then how do you explain THIS: 

Power Off CAS = IAS - 1 at low speeds, climbing ti IAS - 3 at higher speeds.

[ptwffz]

40 minutes ago, Hank said:

Then how do you explain THIS: 

Power Off CAS = IAS - 1 at low speeds, climbing ti IAS - 3 at higher speeds.

All I'm gonna say is I wish that chart was in my Owners Manual.  I'd be golden. 

[PT20J]

18 hours ago, Hank said:

Then how do you explain THIS: 

Power Off CAS = IAS - 1 at low speeds, climbing ti IAS - 3 at higher speeds.

Well, I did sat usually .

And, usually, if there are errors, manufacturers try to get it minimized at cruising speeds because that's rally where we care about absolute speeds. At the low end it doesn't really matter what the calibrated airspeed is since we fly by indicated airspeed.

Mooney evidently did a good job locating the pitot tube. It's not simple because the upwash ahead of the wing changes with angle of attack. That's why test aircraft often have that long probe out ahead of the airplane so as to place it in the free stream relative wind.

[Paul Thomas]

The FAA wrote on the subject; it needs to meet the requirements since certification and it needs CAS from the manufacturer. If the manufacturer had not done CAS testing, the manufacturer can do new testing. IAS is not acceptable as it can be off by more than 5 knots.

[varlajo]

17 hours ago, ptwffz said:

All I'm gonna say is I wish that chart was in my Owners Manual.  I'd be golden. 

My E is 1 - ONE - mph CAS over MOSAIC cutoff 

[ptwffz]

[ptwffz]

The above airspeed indicator was copied from a different post. The owner states it's from his M20 D/C model which is exatly mine. Granted I don't know his year but there's a big difference in his VSo and VS1. Both way lower than mine. What the !!!!!!!!!

[ptwffz]

This is my airspeed indicator. It looks like someone placed black tape over the bottom of the green arc. Like I said, maybe the other airspeed indicator shoud be in my bird. Is my Owners Manual incorrect? I have a 1964 M20D Master and my manual says 1965. I doubt it changed by one year. Nothing is making sence here. Or I'm retarted. 

[ptwffz]

I just noticed the top of my white arc is taped over as well.

[Hank]

For my 1970 C, the Owners Manual says the green stripe is "the normal operating range" and makes no mention of stall.

You really need something like the table I posted before, but for a model year closer to yours, since control throws changed over the years. 

[ptwffz]

Makes sense. I was of the mindset that the bottom of the green arc is the clean stall speed. I guess that's why stall speed clean shows 67 MPH IAS on a different page. I just need to find out what my calibrated VS1 is and convert it to knots. For that I have no chart. Might need the airborn check. 

Any thoughts on that other M20D airspeed indicator with such low green and white arc speeds? I've never seen one so low. 

[Jackk]

On 11/20/2025 at 8:48 PM, PT20J said:

The problem, as we may recall from private pilot ground school, is that that the largest airspeed errors (spread between IAS and CAS) usually occur at low airspeeds because the pitot tube is no longer aligned with the relative wind due to the increased angle of attack.

 I think on the back back side of the power curve, but for this speed, I’d just convert to knots and go with that.

 

 If a ASI is digging this deep to bust you, being administrative “law”, you’re cooked regardless

[Paul Thomas]

The FAA has been pretty clear that it has to be CAS and CAS since original certifications. For aircraft that do not have CAS, manufacturer need to go out and do the testing. During the process, there was push to allow modification to bring under the 59 knots or IAS to be used; the FAA said no to both.

[Paul Thomas]

On 11/21/2025 at 4:40 PM, ptwffz said:

This is my airspeed indicator. It looks like someone placed black tape over the bottom of the green arc. Like I said, maybe the other airspeed indicator shoud be in my bird. Is my Owners Manual incorrect? I have a 1964 M20D Master and my manual says 1965. I doubt it changed by one year. Nothing is making sence here. Or I'm retarted. 

Manufactured dates and model year are not one and the same; my 1984 airplane was manufactured and delivered in 83.

[cliffy]

I would suggest what is on the airspeed indicator is not the "controlling " document. 

It still comes down to what ever the manufacturer published in the Operating Manual. 

If the manufacturer didn't list a CAS speed then one needs to follow what the FAA "suggests" to determine same.

Any other way won't be a problem UNTIL it is a problem. 

Say you have a runway excursion that involves an investigation and you are flying  it as a Sport aircraft-

Do you think that someone MIGHT look to see if it really is a legal Sport airplane during the investigation?

I'm willing to bet someone in the office might look into that. 

Later POHs do list CAS but not our earlier ones. 

Time marched on and left us behind.

In addition- one can't just take the IAS stall speed and do a direct conversion to knots and call it CAS 

It don't work that way   All that does is give the MPH IAS  as KTS INDICATED AIRSPEED  not Calibrated Airspeed

 

[ptwffz]

3 hours ago, cliffy said:

I would suggest what is on the airspeed indicator is not the "controlling " document. 

It still comes down to what ever the manufacturer published in the Operating Manual. 

If the manufacturer didn't list a CAS speed then one needs to follow what the FAA "suggests" to determine same.

Any other way won't be a problem UNTIL it is a problem. 

Say you have a runway excursion that involves an investigation and you are flying  it as a Sport aircraft-

Do you think that someone MIGHT look to see if it really is a legal Sport airplane during the investigation?

I'm willing to bet someone in the office might look into that. 

Later POHs do list CAS but not our earlier ones. 

Time marched on and left us behind.

In addition- one can't just take the IAS stall speed and do a direct conversion to knots and call it CAS 

It don't work that way   All that does is give the MPH IAS  as KTS INDICATED AIRSPEED  not Calibrated Airspeed

 

I guess I'll have to visit FOSDO and see exactly how to document an airborn calibration test and hope for the best. I see it described in the advisory circular but thery're going to believe my test results? Not that I'd lie but I could see a pilot having a very subjective result.

[cliffy]

11 hours ago, ptwffz said:

I guess I'll have to visit FOSDO and see exactly how to document an airborn calibration test and hope for the best. I see it described in the advisory circular but thery're going to believe my test results? Not that I'd lie but I could see a pilot having a very subjective result.

Probably the smartest move  but be aware you may know more about the subject than the one you talk to so  YOU may be doing the educating at first

[Jackk]

15 hours ago, cliffy said:

I would suggest what is on the airspeed indicator is not the "controlling " document. 

It still comes down to what ever the manufacturer published in the Operating Manual. 

If the manufacturer didn't list a CAS speed then one needs to follow what the FAA "suggests" to determine same.

Any other way won't be a problem UNTIL it is a problem. 

Say you have a runway excursion that involves an investigation and you are flying  it as a Sport aircraft-

Do you think that someone MIGHT look to see if it really is a legal Sport airplane during the investigation?

I'm willing to bet someone in the office might look into that. 

Later POHs do list CAS but not our earlier ones. 

Time marched on and left us behind.

In addition- one can't just take the IAS stall speed and do a direct conversion to knots and call it CAS 

It don't work that way   All that does is give the MPH IAS  as KTS INDICATED AIRSPEED  not Calibrated Airspeed

 

 If they dig that deep and go that much on the warpath on a runway incursion, you getting nailed, even if everything was perfect they’d just 91.13 you in that case.

[Paul Thomas]

12 hours ago, ptwffz said:

I guess I'll have to visit FOSDO and see exactly how to document an airborn calibration test and hope for the best. I see it described in the advisory circular but thery're going to believe my test results? Not that I'd lie but I could see a pilot having a very subjective result.

The manufacturer needs to do the testing and I can't see Mooney doing it; maybe they'll be willing to outsource it to you.

[ptwffz]

I wish AI would reveal its source. My Owners manual does list VS1 as 67 MPH IAS. Does anyone on the board have a Master manual that shows CAS conversions at that low of an airspeed?

 

AI Overview

 

The

Mooney M20D Master's calibrated stall speed in a clean configuration  is approximately 58 knots (67 MPH). This figure is derived from the indicated airspeed (IAS) and the airspeed calibration information provided in the aircraft's Pilot's Operating Handbook (POH) and related documentation. 

Details on the Mooney M20D Stall Speed 

• Indicated Airspeed (IAS): The POH for the M20D Master typically lists the clean stall speed as 67 MPH IAS, which converts to approximately 58 KIAS (Knots Indicated Airspeed).