Green Arc

[TimHicks]

Does anyone know where the bottom the Green Arc (in mph) on an airspeed indicator is supposed to be for a 1946 BC-12D?

I'm sending my instruments to be overhauled. They'll paint arcs/marks on the dials.
I think that the top of the Green Arc is at 95 mph.

The yellow arc, I believe, goes from 95 to 140mph.

A red line goes at 140mph, right?

On the tachometer, I'll have a redline at 2300 rpm (I have an A-65).

Oil pressure gauge gets red lines at 10 psi and 35 psi, right?

And Oil Temp get a red line at 220°F.

[3Dreaming]

Re: Green Arc

from the TCDS Level flight or climb 105 m.p.h. Glide or dive 140 m.p.h.

[Robert Lees]

Re: Green Arc

Tim,

Don't be fooled by modern requirements for instrument markings.

The only required ASI marking under 1946 CAR (CAA) rules is the VNE (140mph in the case of your BC12D). And you are right with the other instrument markings. Also, you do not need to make a separate placard that shows those limits if they are marked on the instruments themselves.

Only markings mandated under those CAR rules or specified by the manufacturer back then are required for your aircraft.

As a matter of personal safety, I treat the manouevering speed (or to use modern terminology, "yellow arc") as 85mph, but since there is no legal or engineering or design specification that agrees with that, your mileage may vary and you will get differing opinions on that speed from others here.

Don't let your IA bully you into marking things that are not required and are not specified.

Rob

{edit: As Tom says; the markings are on the TCDS}

[Guest]

Re: Green Arc

from the TCDS Level flight or climb 105 m.p.h. Glide or dive 140 m.p.h.

I recall that the 105 mentioned is manuevering speed but I can't recall where or how I saw or knew that.

Maybe an old airworthiness certificate had it printed on it.

Dave

[TimHicks]

Re: Green Arc

OK, I think that I've got it.
So the top of my green arc is 105 mph. The bottom of my yellow arc is also going to be 105mph.

Robert makes a good point. And he's largely right (about my IA). Notice the stick-on arcs on my airspeed indicator above. My IA insisted I put those on during an annual years ago.
And frankly, I don't really want to confront him on this issue.
It's relatively easy to have the dials painted professionally during the course of the re-cover project.

Tim

[TimHicks]

Re: Green Arc

I guess that if nobody has an opinion about the bottom of the green arc, I'll put it at 40 mph.

[Hank Jarrett]

Re: Green Arc

If you are using Keystone for your instruments I seem to remember they had the correct numbers for a LOT of planes. I had sent in what I wanted on mine and they confirmed them. Wish I remembered what numbers they said but it was a little different depending on the year and model.
Hank

My instructor asked me one time what airspeed I came over the fence at and I answered I had no idea. I had never looked at the ASI on short final, I was always looking outside. As I remember, that was the right answer since I think he saw I was always approaching at the same speed. When I was fling with any regularity I seem to remember I never looked at the Tach either.

[TimHicks]

Re: Green Arc

I called Keystone. But they didn't give my much confidence over the phone.
Just to capture some of the facts of the conversation:
$225 to test tachometer
$189 overhaul ASI without new dial
$189 - $200 overhaul 0-2000' R.o.C. indicator
$235 altimeter
$225 Turn n Bank
$150 compass diaphram overhaul
$35 for new dial
$5 for new glass
$5 for new rubber gaskets that some instruments may need
I won't get into the details of the rest of the conversation. But I decided to keep looking.

I had called Airparts, also in Lock Haven PA, more than a week ago. But they didn't answer the phone and they never returned my call.

Yesterday, I called Rudy and talked to Meredith. She answered all of my questions patiently and clearly.
Some more facts:
$ 65 dial refinish, 1 week leadtime
$ 125 ASI overhaul
$125 Tach overhaul
$15 just to paint red marks on the oil pressure dial
About 2 weeks leadtime for these 3 instruments.

I sent the 3 instruments (ASI, tach, oil pressure)to Rudy Instruments yesterday.
I'll report back to y'all on the cost, how they look, any problems etc.
Depending on how I perceive the bang-for-the-buck, I may send my other intruments to them.

[otrcman]

Re: Green Arc

I'd like to make just one clarification in the interest of safety. The top of the airspeed green arc is NOT the maneuvering speed.

The top of the green arc (or the beginning of the yellow arc) defines the the maximum speed at which the airplane should be flown in rough air. The certification standards specify a "maximum sharp edge gust" for which an airplane must be designed. Above some speed the airplane could suffer structural failure if it encountered such a gust.

Va, or maneuvering speed, is the maximum speed at which full control deflections can be made without causing structural damage. Typically, Va is much lower than the top of the green arc. And typically Va is not specified for older airplanes. There are often weasel words in the older manuals, such as for the L-2 in which pilots are advised to maintain speeds lower than 70 MPH for sharp maneuvers. But the manufacturers usually didn't call it maneuvering speed.

For an airplane with a limit load factor around 4 G's positive, you can approximate maneuvering speed by doubling the indicated stall speed. That's really rough, so don't bet your life on it. But maneuvering speed will definitely not be much more than that. So if your indicated speed at stall is 35, then your Va might be around 70. If your "maximum speed in level flight or climb" per the TCDS is 105, then that's the beginning of the yellow arc. And of course the "maximum speed in glide or dive" will be the redline.

I'm not aware of any U.S. certification standard which required the maneuvering speed to be placarded on the airspeed indicator. One of the reasons is that Va varies with the weight of the airplane. Lighter weights correspond to lower stall speeds, and in fact maneuvering speed is also lower at lighter weights.

Dick

[Robert Lees]

Re: Green Arc

Just to add to Dick's post above; I believe Va is the maximum speed at which full control deflection ON ONE CONTROL AT A TIME can be made without causing structural damage.

Unless I am mistaken; please corrrect me if wrong.

Rob

[Guest]

Re: Green Arc

Here are some CAR 4 "snippits" relative to this subject.

I have a better .pdf file but it is too big to upload

[Guest]

Re: Green Arc

If you are interested in the link to CAR 4 here it is:

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgccab.nsf/Frameset?OpenPage

Dave

[barnstmr]

Re: Green Arc

Here's my airspeed indicator. Stock BC12D with A65

[TimHicks]

Re: Green Arc

Thank you, Terry.
That's what I was looking for. It appears that the bottom of the Green Arc should be 35 mph, not 40.

[barnstmr]

Re: Green Arc

Tim,
I have no verification that mine is either correct or incorrect. I am just showing you how it is currently marked.

Maybe this has already been stated... If so I apologize for repeating it.... After researching CAR 4 and CAR 3, I found that there are no specific airspeed indicator marking requirements under CAR 4. It appears to me that the DO NOT EXCEED 140 MPH placard was the only requirement related to airspeed limits under CAR 4. CAR 3 airplanes (including the later model 19 and F19 Taylorcrafts are required to have the color markings.) So it seems someone has attempted to update my airplane to the later CAR 3 rules. This is legal if the numbers are correct. But unnecessary.