HUD Altitude and actual altitude

[cptmrcalm]

Hi all. 

I saw a video of someone trying to get the maximum altitude in an F16. I heard him say "88,000". I turned to look at the video and saw the HUD showing 70,000 ft.

 

He was using a digital readout at the bottom of the screen from the external view.

I had another go and trying to beat my own record. I didn't have external views allowed at the time and didn't have a digital readout at the bottom of the screen either.

 

My HUD showed 78,000 ft. I understand the HUD wont show altitude exactly - But based on the other video, is there a conversion formula I could use? ie. if HUD shows X altitude, then actual altitude will be Y?

 

Just curious. If not, I will do it again and this time use a digital readout too.

 

 

[Furiz]

1 hour ago, cptmrcalm said:

My HUD showed 78,000 ft. I understand the HUD wont show altitude exactly - But based on the other video, is there a conversion formula I could use? ie. if HUD shows X altitude, then actual altitude will be Y?

HUD will show barometric altitude based on the air pressure, the higher you go the lower the pressure, it also depends on time of the year and temperature, so in summer the pressure is lower while winter has higher pressure. That's why HUD may be wrong, also why you should set your altimeter to 0 while on ground lvl.

[cptmrcalm]

Yes I know. I just wondered if there was a conversion formula I could use?

Interesting that he showed 70000ft and registered 88000ft. I wondered what 78000ft on the HUD would register at.

[cptmrcalm]

Ok. Had another go. 

 

94576ft. HUD maxed out at 80000ft and wouldnt go past that. 

 

I will upload the video asap.

 

[razo+r]

53 minutes ago, cptmrcalm said:

Yes I know. I just wondered if there was a conversion formula I could use?

Interesting that he showed 70000ft and registered 88000ft. I wondered what 78000ft on the HUD would register at.

First, make sure you set the altimeter to the correct QNH. 

Then, to correct for temperature, subtract 4% of the indicated altitude per 10 degrees C below ISA, or add if the temperature is above ISA. 

18 minutes ago, cptmrcalm said:

Ok. Had another go. 

 

94576ft. HUD maxed out at 80000ft and wouldnt go past that. 

 

I will upload the video asap.

 

There is a max altitude that the altimeter and HUD will show. Above it and it will just read the max number and stay there, so above a certain altitude you MUST use the external info bar if you want to know your altitude. 

Edited April 7, 2024 by razo+r

[cptmrcalm]

Thanks a lot for the replies. The jet was started in the air so I assumed all of the settings would be set correctly? 

 

But fantastic response. Appreciate it. Looks like that digital info bar is the one to definitely use. Quite pleased with my result. Thanks again. 

 

[cptmrcalm]

Here you go. As promised. 

 

 

[modsat]

Moonlighting as an astronaut I see . Nice one mate