Stall speeds and ASI arcs

[Bob_Belville]

...things I should already know department...

 

The original generic "Owner's Manual" for my '66E indicates stall speed is 67 mph clean and 57 mph w full flaps. Vso and Vs.

 

But the 9/3/1965 FAA signed AFM specific to my tail #, serial number does not list stall speeds per se but does dictate the ASI markings. The white arc is defined as 63 to mph 100 and the green arc as 70 to 150 mph.

 

I interpret that to mean that    Vs = 70 and Vso is 63. (Instead of 67 and 57)

 

I can imagine that individual airplanes of the same make and model might vary a few mph in actual stall speed but I don't think that is what is going on here.

 

Someone know what I should consider stall speed for 943RW?

[BigTex]

Take the plane up and stall it in both configurations and use those speeds.

[Bob_Belville]

Big Tex, I knew that was coming. That might help me fly the plane. Then should I repaint the ASI and reprogram the Aspen? What will my friends at the FAA think about that?

[Bob_Belville]

BTW, how is your ASI marked? '65C?

[BigTex]

White arc: 63 - 100 MPH

Green arc: 70 - 150 MPH

Yellow arc: 150 - 189 MPH

Red line: 189 MPH

[Marauder]

Bob -- something is strange about your ASI... I thought all of the pre-J models had MPH on the outer scale Knots on the inner scale. I had mine converted from MPH on the outer scale to Knots.

 

[BigTex]

Here's a picture of my ASI:

 

 

[Bob_Belville]

White arc: 63 - 100 MPH

Green arc: 70 - 150 MPH

Yellow arc: 150 - 189 MPH

Red line: 189 MPH

Thanks. We're the same.

[Bob_Belville]

Bob -- something is strange about your ASI... I thought all of the pre-J models had MPH on the outer scale Knots on the inner scale. I had mine converted from MPH on the outer scale to Knots.

 

Mooney ASI.jpg

Chris, I just put my camera phone up behind the panel and voila, my ASI is a United Instruments part no. 8125. It was built or overhauled, in '76 so it was not original. But the install was not logged. (I walked by my friend's 67F - it has a Mooney logo in the center of the ASI and MPH on the outer scale.)

 

What paperwork did you do to change yours?

[Marauder]

Bob -- something is strange about your ASI... I thought all of the pre-J models had MPH on the outer scale Knots on the inner scale. I had mine converted from MPH on the outer scale to Knots. Mooney ASI.jpg Chris, I just put my camera phone up behind the panel and voila, my ASI is a United Instruments part no. 8125. It was built or overhauled, in '76 so it was not original. But the install was not logged. (I walked by my friend's 67F - it has a Mooney logo in the center of the ASI and MPH on the outer scale.) What paperwork did you do to change yours?

I just had the ASI overhauled and tagged. Since my POH is in both units, it was interchangeable according to the avionics shop. And BTW, mine is the same unit, just relabeled.

[Hank]

Bob,

The Book is written in True Airspeed; the gauge is, of course, marked in Indicated Airspeed. Check your Book for corrections at 57 and 67, see what the Indicated Airspeeds are.

My 70 model has MPH on the outside and Knots on the inside.

[Bob_Belville]

Bob,

The Book is written in True Airspeed; the gauge is, of course, marked in Indicated Airspeed. Check your Book for corrections at 57 and 67, see what the Indicated Airspeeds are.

My 70 model has MPH on the outside and Knots on the inside.

Hank, not sure what you are saying. All speeds like Vne, Vso are based on IAS aren't they? When you push the nose over and do a high speed descent you watch the IAS to keep it below the red line. You don't calculate TAS which will exceed Vne.

[Hank]

They are generally pretty close, 2-3 mph different. At high speed, that's ~1%; at stall, 3 mph is 5% of 60.

You're going to make me get out my spare Book and see exactly what it says. Tomorrow. But I think it is written either in True or Corrected airspeed, while the AI is striped in matching Indicated speeds. But my Primary Instruction was a while back, and I try to not fly in that speed range except briefly passing through on Takeoff and Landing.

[jetdriven]

Bob,

The Book is written in True Airspeed; the gauge is, of course, marked in Indicated Airspeed. Check your Book for corrections at 57 and 67, see what the Indicated Airspeeds are.

My 70 model has MPH on the outside and Knots on the inside.

It is that way at least until 1977 or 1978.

[Bob_Belville]

The '66 "Owner's Manual" page 

 

They are generally pretty close, 2-3 mph different. At high speed, that's ~1%; at stall, 3 mph is 5% of 60.

You're going to make me get out my spare Book and see exactly what it says. Tomorrow. But I think it is written either in True or Corrected airspeed, while the AI is striped in matching Indicated speeds. But my Primary Instruction was a while back, and I try to not fly in that speed range except briefly passing through on Takeoff and Landing.

The '66 E Owners Manual, page 39, has a chart of stall speed vs. bank angle. The chart is labeled IAS, power off. The zero bank, full flaps stall speed is 57 mph. 

The AFM for N943RW dated 1965 shows the bottom of the white arc at 63 mph.

That's 10% difference. Both should be IAS.

 

From Wikipedia: "A redline mark indicates V_NE, or velocity (never exceed). This is the maximum demonstrated safe airspeed that the aircraft must not exceed under any circumstances. The red line is preceded by a yellow band which is the caution area, which runs from V_NO (maximum structural cruise speed) to V_NE. A green band runs from V_S1 to V_NO. V_S1 is the stall speed with flaps and landing gear retracted. A white band runs from V_SO to V_FE. V_SO is the stall speed with flaps extended, and V_FE is the highest speed at which flaps can be extended."

[Bob_Belville]

Hum, is it possible that the bottom of the white arc is with gear retracted? How much does the gear position change stall speed in a Mooney?

 

No. The bottom of the white arc is Vs0, 

 

Vs0
The beginning of the White Arc is the power off Stalling Speed with gear and full flaps extended, also known as Vs0. The Vs0 (Velocity Stall 0) represents the Stalling Speed of the aircraft configured for landing. (i.e. Gear Down and Flaps Down) An easy way to remember this is to think of the Velocity (V) of Stall (s) with everything hanging Out (0) or Vs0.

 

 

So... I still have a conflict - is Vs0 for my 66E 63 or 57 mph?

[Marauder]

Bob -- I would see if anyone has an E near your serial number. I know that my POH lists applicability for the POH for planes within in a certain serial number range. If your manual doesn't list this range, if you found a couple of people with serial numbers on either side but close to yours, you could verify what it should be. I suspect when your ASI was changed out, some hanky panky may have gone on and the wrong ranged ASI was installed. Etther that or you have a unique bird.

[Bob_Belville]

Chris, my ASI white arc 63-100 mph matches the AFM that was specific to my ser. # 929 and signed by the FAA 9/65 (929 is a 66 model built in late '65).

 

Can't see where the ASI is a problem (except that the Knots scale is primary if that is an issue) 

 

Mostly just interesting but I might go up high enough and do a couple of stalls @ landing config and see if the plane is still flying below the white arc.

[Marauder]

Chris, my ASI white arc 63-100 mph matches the AFM that was specific to my ser. # 929 and signed by the FAA 9/65 (929 is a 66 model built in late '65). Can't see where the ASI is a problem (except that the Knots scale is primary if that is an issue) Mostly just interesting but I might go up high enough and do a couple of stalls @ landing config and see if the plane is still flying below the white arc.

Bob -- as far as the markings go (knots versus mph on outer scale) you would need to go back to the certification of CAR 3 for our generation of plane. CAR 3 may or may not have addressed it (the same for Part 23 certified planes). If I get some time, I will see if I can find a copy of the reg and see if it talks about it.

[MB65E]

Hi Bob, our original white arc ASI from pictures was marked 63-100 MPH. 65E s/n 551. We replaced the gauge with a one with a TAS calculator in it and had it re-faced to knots. This brought the white arc down to 55kts or so. I could not find in our AFM a published stall speed. I would think it would be around the 57mph as you mentioned. I believe there is some certification basis to stall at 61kts or slower. In several aircraft that 61 kts seems to be the Magic number. Lancair tries to stick to that. Flew a super hot legacy for a while that would actually finally quit flying at that 61kts. More to read it looks like.

[Awful_Charlie]

Not sure if it affected the 66 E's, but have you had a gross weight increase at some point?  Increasing the gross weight increases the stall, and getting one normally includes new AFM pages and a new ASI

[Bob_Belville]

Hi Bob, our original white arc ASI from pictures was marked 63-100 MPH. 65E s/n 551. We replaced the gauge with a one with a TAS calculator in it and had it re-faced to knots. This brought the white arc down to 55kts or so. I could not find in our AFM a published stall speed. I would think it would be around the 57mph as you mentioned. I believe there is some certification basis to stall at 61kts or slower. In several aircraft that 61 kts seems to be the Magic number. Lancair tries to stick to that. Flew a super hot legacy for a while that would actually finally quit flying at that 61kts. More to read it looks like.

55 K is the same as 63 MPH so that's not a change. My AFM does not list Vs0 but it does define the bottom of the white arc, which by definition is Vs0,as 63 Mph (55K). 

[Bob_Belville]

Not sure if it affected the 66 E's, but have you had a gross weight increase at some point?  Increasing the gross weight increases the stall, and getting one normally includes new AFM pages and a new ASI

No. 

[Bob_Belville]

Guys, I appreciate all the feedback. I guess I have not defined the basic question I am asking. Let me try again.

 

What is Vs0 for a '66E? (Or a C which should be the same.) I don't care whether you tell me in Knots or MPH, I majored in math at a decent engineering school, I can convert.

 

I have 2 documents that were printed at the time the plane was built. Neither lists a speed for Vs0 

• My AFM says 63 MPH (actually it defines the bottom of the white arc on the ASI, same thing)
• My Owner's Manual agrees with the bottom of the white arc @ 63 MPH but also includes a chart of stall speed vs. bank angle. The zero bank, full flaps, @ gross weight, power off  is 57 IAS MPH. (The manual for a '66C has the same chart.)

The bottom of the white arc is suppose to be Vs0. I have not figured out where the lower stall speed comes in to play. 

[Hank]

Bob,

The Owners Manual for my C says this under Operating Limitations:

White Arc--63 to 125 MPH CAS. (Denotes speed range in which flaps may be safely lowered)

In Section VI. Performance, there's a page titled Stall Speeds, two pages before Cruise & Range. I took a picture, let's see if I can attach it on the phone.