IAS not correct in DME Mode

[joetemerario]

Hello and thank you for the wonderful products you create.
I don't know if I'm wrong, but in the DME Mode display almost always, after a certain speed the IAS is wrong, for example if you open the link of images i shared, you can see that I'm going at about 130 knots, but the display shows 13.
Thanks

Album:
https://photos.app.goo.gl/E24muLR837VK3nyJ8

or
IMAGE1:
https://photos.google.com/share/AF1QipP ... R4NnlmdWpn

IMAGE2:
https://photos.google.com/share/AF1QipP ... R4NnlmdWpn

[Nick - A2A]

Hello, welcome to the A2A forums and thanks for the clear description and images.

DME works via radio signals between the aircraft and a ground-based navaid. The slant range calculated based on these signals allows the DME set to work out your speed too, but the important thing to remember is that this speed is relative to the navaid.

In other words, DME speed will only match your ground speed if you're flying directly towards, or directly away from the navaid. Even then, the match won't be precise as the speed calculation is based on your slant range from the antenna and not your range along the ground.

At the other extreme, if you're flying perpendicular to the navaid, the DME speed will read close to zero as you're not getting closer to, or further away from it. In your picture, you're pretty close to this situation by the looks of it, with the navaid on your beam.

The other thing to remember is that the indicated airspeed (IAS) shown on the airspeed indicator will also differ from groundspeed depending mainly on windspeed and direction and your altitude. This means that even if the DME was showing the exact groundspeed, there would still be a mismatch between the two instruments.

Thanks,
Nick

[joetemerario]

Hello, welcome to the A2A forums and thanks for the clear description and images.

DME works via radio signals between the aircraft and a ground-based navaid. The slant range calculated based on these signals allows the DME set to work out your speed too, but the important thing to remember is that this speed is relative to the navaid.

In other words, DME speed will only match your ground speed if you're flying directly towards, or directly away from the navaid. Even then, the match won't be precise as the speed calculation is based on your slant range from the antenna and not your range along the ground.

At the other extreme, if you're flying perpendicular to the navaid, the DME speed will read close to zero as you're not getting closer to, or further away from it. In your picture, you're pretty close to this situation by the looks of it, with the navaid on your beam.

The other thing to remember is that the indicated airspeed (IAS) shown on the airspeed indicator will also differ from groundspeed depending mainly on windspeed and direction and your altitude. This means that even if the DME was showing the exact groundspeed, there would still be a mismatch between the two instruments.

Thanks,
Nick

Thank you so much Nick for your explanation.

Sigh, the only solution is to become a real pilot, but it takes 9000 euros here at Rome in Italy for PPL. sigh!

[Nick - A2A]

You're welcome! Yeah, real world flying is expensive which is one of the reasons why simulating it is such a popular approach. We have plenty of real world pilots on the forums here, so hopefully Accu-Sim and the A2A community is the next best thing.

Cheers,
Nick