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View Full Version : C310 Airspeed Guage Lies?



someone
01-31-2005, 05:24 PM
To be honest, I haven't loged much time in the C310 since I bought it the day it was released. I just got a CH Throttle Quadrant, so I dicided to take the C310 up for a flight today and test out the TQ. I noticed some wirdness with airspeed gauge.

This first shot is while cruising at 10,500ft.
http://img65.exs.cx/img65/8135/c310cruise3fu.jpg

Notice the text is showing IAS=175 TAS=203, and the needle on the gauge agrees with the TAS. I checked my settings, and it is set to display IAS:
http://img26.exs.cx/img26/8209/fssettings1ao.jpg

I pulled out my E6B to calculate my true TAS. I was using the standard weather (15°C, 29.92, no wind), so calculating TAS was easy. The OAT gauge was showing -6°C, since sea level pressure is 29.92, my pressure alt. is 10,500. If my IAS was really 203kts, then my TAS would be 234kts. If my real IAS was 175kts, then my TAS would be 203kts, so that lead me to believe the text overlay is correct and the gauge is displaying TAS. Then I rememberd that I was flying with no wind, so ground speed equals TAS. The GPS was showing 203kts GS, so that proved the gauge was showing TAS and not IAS.

Then it got weirder as I descended:
http://img65.exs.cx/img65/2407/c310descend15ow.jpg

The GPS is covering the altemeter, but I have descended to 7,500ft. Now the gauge needle is showing 175kts, but the text overlay is showing IAS=151 and TAS=168. The GPS is showing a GS of 169, so I know my TAS is 169kts. Again, this seems to show that the text overlay is correct, but now the gauge is showing something totally different.

It got worse the farther I descended:
http://img65.exs.cx/img65/1082/c310descend32vw.jpg

Now I'm at 2,500ft. The AS gauge needle is now pointing to 190kts, but the text overlay is showing IAS=164 and TAS=169. The GPS again agrees with the text overlay. I'm convinced the overlay is telling the truth, but what is going on with the airspeed gauge?

I have installed the recently released upgrade, but like I said I haven't flown it much so I don't know if it has been like this before the upgrade. BTW, I uninstalled the C310 and did a complete re-install of the C310 from the wrapper before applying the new patch.

89kraus
02-01-2005, 12:09 AM
Look closely at the ASI of the 310. It has two rings. The outer ring displays the IAS in Miles Per Hour (MPH). The inner ring shows the IAS in Knots. This is also noted in the 310 Orientation Manaual.

If you look at your screen shots, the outer needle is showing a little over 200 MPH, and the inner needle is correct at 175 kts, which matches the digital readout of 175. So the digital readout is in knots, not miles per hour, hense the difference.

So it looks like your 310 is working correctly. :-)

someone
02-01-2005, 06:22 AM
DOH! http://www.pbase.com/jchaney/image/31506658.jpg I knew that. I do recall converting the kts to mph on the E6B, guess I looked at the wrong ring. Why doesn't the overlay display MPH since the gauge is in MPH?

How odd is that that I would be cruising at the right altitude and conditions so my TAS in KTS equals my IAS in MPH?