Citabria What drives the 162mph Vne limitation?

[kubark42]

I read an interesting article about Vne, which explains that Vne can be due to flutter, or other structural limitations: https://www.australianflying.com.au/news/vne-and-flutter-explained

It got me wondering about the 7ECA, which has a 162mph Vne. Is it flutter or is it something structural? If it's flutter, then I have to rethink doing aerobatics at 5,000', and that means that a 140mph dive for a loop is actually closer to 155mph TAS-- just 7mph short of the 162mph limit.

However, @BB57 once said that Vne was the speed where the Citabria's windshield collapsed. That's a pretty cool way to know that no one has ever oversped the airframe, no matter what errors might have accumulated in the pitot-static system. If @BB57 is right, then the Vne limitation is 162mph CAS, as the pressure on the windscreen is a function of CAS, not TAS.

 

[Big Ed]

Discussion: https://www.pilotsofamerica.com/community/threads/how-does-vne-vary-with-altitude.63133/

People have been flying acro in Citabrias for 7 decades now. If acro at 5K were an issue, someone would have identified it by now.

 

[Bob Turner]

Probably the windshield. The Decathlon has an extra brace in the center of the windshield.

 

[Ron86654]

CAS and IAS are the same at 100 mph on my 7ECA according to the manual. When the aircraft is at published stall speed of 51 MPH CAS there is an 8-9 MPH error in the guage making the IAS Vs around 43-44 MPH. I don't know what the guage error is above 100 MPH, never looked at it.

 

[Hiperbiper]

Marion Cole always called the windshield brace on the Decathlon the VNE bar. A good enough explanation for me...

Chris

 

[kubark42]

I don't know what the guage error is above 100 MPH, never looked at it.

11mph error when going close to Vne:

 

[Big Ed]

11mph error when going close to Vne:

But in the direction opposite of which would cause a safety issue. Eg speedo says you are at Vne, but you are actually slower.

The AFM for my Super D says IAS and CAS are identical to 140mph, then increases as follows:

IAS - CAS
140 139
150 148
160 158
170 167
180 176
190 185
200 194