Red markings on D9 speedometer

[Customizer171]

As the title say, what is these markings (2k,3k,5k,7k and 9k) in the Fw 190 D9?

 

[LukeFF]

Max indicated airspeed at the noted altitude. 

[Customizer171]

19 minutes ago, LukeFF said:

Max indicated airspeed at the noted altitude. 

 

I always thought that higher speed was reached at higher altitudes??

Or did I misunderstand your answer?

[MattS]

20 minutes ago, Customizer171 said:

 

I always thought that higher speed was reached at higher altitudes??

Or did I misunderstand your answer?

This is TRUE airspeed that increases, not INDICATED airspeed. 
 

As the air gets thinner at higher altitudes, the airspeed indicator (Indicated Airspeed) will show a lower number than how fast the plane is moving through the air (True Airspeed) because there are fewer air molecules ramming into the pitot tube.

 

So while there is less of a concern about the plane going faster than it can structurally handle from the air physically hitting it, at high TRUE airspeeds at altitude where the speed of sound is lower, a fast airplane has to be careful of MACH problems (shock waves forming on the airfoils).

 

For airplanes like a Cessna 172 trainer, there is only 1 “red line” (Vne) because it does not fly fast enough or high enough to worry about MACH. 
 

Jetliners have a dynamic redline (barber pole) that changes with altitude.

Edited June 17, 2023 by MattS

[Customizer171]

23 hours ago, MattS said:

This is TRUE airspeed that increases, not INDICATED airspeed. 
 

As the air gets thinner at higher altitudes, the airspeed indicator (Indicated Airspeed) will show a lower number than how fast the plane is moving through the air (True Airspeed) because there are fewer air molecules ramming into the pitot tube.

 

So while there is less of a concern about the plane going faster than it can structurally handle from the air physically hitting it, at high TRUE airspeeds at altitude where the speed of sound is lower, a fast airplane has to be careful of MACH problems (shock waves forming on the airfoils).

 

For airplanes like a Cessna 172 trainer, there is only 1 “red line” (Vne) because it does not fly fast enough or high enough to worry about MACH. 
 

Jetliners have a dynamic redline (barber pole) that changes with altitude.

 

Are the red marks the fastest allowed speed (IAS) at the corresponding altitudes?

 

I understand that the thinner air makes less pressure on the pitot tube and because of that show a lower speed at high altitude.

 

If the red marks are the safe limit I get a bit confused. Would not 920 km/h IAS at 2000m stress the aircraft more than 485 km/h IAS at 9000 m??

 

[MattS]

4 hours ago, Customizer171 said:

 

Are the red marks the fastest allowed speed (IAS) at the corresponding altitudes?

 

I understand that the thinner air makes less pressure on the pitot tube and because of that show a lower speed at high altitude.

 

If the red marks are the safe limit I get a bit confused. Would not 920 km/h IAS at 2000m stress the aircraft more than 485 km/h IAS at 9000 m??

 

At lower altitudes, it is a matter of the force of the air against the aircraft’s structure…920 km/h IAS down at 2,000m is apparently the maximum that it can take (of course there must be some small safety margin above that).

 

At higher altitudes, the force of the air hitting the airframe is not the problem at all. 485km/h IAS is easily borne by the airplane’s structure. But at 9,000m, that represents a true airspeed of 755 km/h or Mach 0.69 in a standard atmosphere, if the calculator that I used is to be believed.

I don’t know what the limiting Mach number is for this particular airframe, but in general MACH becomes the limiting factor due to shock wave formation that can damage the airplane outright or render the control surfaces useless, with deadly results.

 

Edit: I should also say that the speed of sound decreases at higher altitudes, so down low the structural impact of high speed (IAS or TAS, they are pretty close to each other down low) is the limit, while up high MACH is the limit.

 

 

 

Edited June 18, 2023 by MattS
Added info

[Customizer171]

10 hours ago, MattS said:

At lower altitudes, it is a matter of the force of the air against the aircraft’s structure…920 km/h IAS down at 2,000m is apparently the maximum that it can take (of course there must be some small safety margin above that).

 

At higher altitudes, the force of the air hitting the airframe is not the problem at all. 485km/h IAS is easily borne by the airplane’s structure. But at 9,000m, that represents a true airspeed of 755 km/h or Mach 0.69 in a standard atmosphere, if the calculator that I used is to be believed.

I don’t know what the limiting Mach number is for this particular airframe, but in general MACH becomes the limiting factor due to shock wave formation that can damage the airplane outright or render the control surfaces useless, with deadly results.

 

Edit: I should also say that the speed of sound decreases at higher altitudes, so down low the structural impact of high speed (IAS or TAS, they are pretty close to each other down low) is the limit, while up high MACH is the limit.

 

 

 

 

Thanks a lot for taking the time to explain.

I appreciate it. 

[1Sascha]

Pretty good online IAS/TAS converter/calculator here:

 

Click!

 

 

Not to derail the thread, but I always wondered about that warning label on top of the speedo... particularly about the gear entry:

 

"Fahrwerk aus - über 200 km/h" translates to "undercarriage out (down) - above 200 kph". Which doesn't seem to make sense to me.

Unless it would've been possible to lower the gear at *any* speed (like 500 kph IAS) without risking damage to it - and the only worry would've been lowering it at too low an airspeed making the plane unstable. The former of which doesn't seem realistic, but what do I know?

 

Doesn't seem to be an error on the game's part, since it says exactly that on this authentic D-9 instrument-panel I found on the web:

 

Also note that these scribbled on altitude labels indeed seem to have been common-place - both on the speedo and on the rev-counter. I'm guessing these were already applied at the factory. Given the less-than-ideal situation of German industry in late 44/early 45, it's not surprising that they'd resort to such a rather crude method instead of producing updated dials (with "integrated" markings) for the instruments themselves.

 

S.

Edited July 18, 2023 by 1Sascha

[Customizer171]

On 7/17/2023 at 9:57 AM, 1Sascha said:

 

"Fahrwerk aus - über 200 km/h" translates to "undercarriage out (down) - above 200 kph". Which doesn't seem to make sense to me.

Unless it would've been possible to lower the gear at *any* speed (like 500 kph IAS) without risking damage to it - and the only worry would've been lowering it at too low an airspeed making the plane unstable. The former of which doesn't seem realistic, but what do I know?

 

Doesn't seem to be an error on the game's part, since it says exactly that on this authentic D-9 instrument-panel I found on the web:

 

 

 

I have been thinking about this as well, because I never understood what it meant.

Similar information in other aircrafts talk of the MAXIMUM speed at which the gear can be lowered , I never seen minimum speed before.

Can anyone explain this?

[czech693]

I would think that means don't lower the gear below 200 kph as the sudden onset of drag could cause a stall at that speed.  But, there should be a maximum gear speed also.

[Customizer171]

14 hours ago, czech693 said:

I would think that means don't lower the gear below 200 kph as the sudden onset of drag could cause a stall at that speed.  But, there should be a maximum gear speed also.

 

That could be the correct answer.

I agree that a maximum gear speed would be great to have.

[Yogiflight]

On 8/16/2023 at 4:01 AM, czech693 said:

I would think that means don't lower the gear below 200 kph as the sudden onset of drag could cause a stall at that speed. 

I don't know about that particular aircraft, but the main landing gears of German aircrafts often didn't get lowered at the same time. So one gear being already halfway down, while the other one still up, would cause more additional drag at one side of the aircraft, which, at very low speed, certainly would cause some stability issues.

 

On 8/16/2023 at 4:01 AM, czech693 said:

But, there should be a maximum gear speed also.

My guess is, it was no issue, because the landing pattern routine gave a maximum speed to fly at the airfield for safety issues (other flights being around). If so, the allowed speed was lower than the maximum speed for lowering the gear, but higher than the maximum speed for lowering the flaps, as you have the warning to lower the flaps under 295km/h (Landeklapp. aus unter 295km/h)