IowaRV9Dreamer
Well Known Member
In this month's Flying, Peter Garrisons article describes how Vne is determined for certified aircraft. Using his method and plugging in number for an RV, I can't get it to align to Vans numbers.
Peter states the following
My confusion is that if I plug in an RV wing loading (say 12.9 lb / sq ft for an RV-9A from Vans website), I get the following:
Vc = 118 kts
Vd=166 kts
Vne=149 kts or 171 mph
That Vne is too low - it comes out 33 kts or 38 mph below Vans published Vne. In fact it is below the listed cruise speed (189 mph) for a 160HP RV-9A.
For comparison I plugged in the numbers for a Cessna 172R (wing loading 14.1). The computed Vne is much closer, only off 6.9 kts from the published value.
Am I doing something wrong here, or is there more to the story?
I wonder if this is just a result of the fact that certified aircraft manufacturers are required to use more conservative calcuations than the experimental kit manufacturers choose to?
Peter states the following
- Design Cruising Speed (Vc) = 33 * Sqrt (wing loading)
- Design Dive Speed (Vd) = 1.4 * Vc
- Never Exceed Speed (Vne) = 0.9 * Vd
My confusion is that if I plug in an RV wing loading (say 12.9 lb / sq ft for an RV-9A from Vans website), I get the following:
Vc = 118 kts
Vd=166 kts
Vne=149 kts or 171 mph
That Vne is too low - it comes out 33 kts or 38 mph below Vans published Vne. In fact it is below the listed cruise speed (189 mph) for a 160HP RV-9A.
For comparison I plugged in the numbers for a Cessna 172R (wing loading 14.1). The computed Vne is much closer, only off 6.9 kts from the published value.
Am I doing something wrong here, or is there more to the story?
I wonder if this is just a result of the fact that certified aircraft manufacturers are required to use more conservative calcuations than the experimental kit manufacturers choose to?