Author Topic: Vortex Generators Retro Permission  (Read 1049 times)

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Offline murray44

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Vortex Generators Retro Permission
« on: March 30, 2018, 06:57:01 AM »
I need help. I have a Long Ez in the UK and have completed the airtest to increase the MAUW to 1600 lbs. The aircraft is fitted with VGs on the canard and wing (I bought it like this). However, a local difficulty with the authorities means I have to submit paperwork to regularise the VG set-up. I also have to come up with specific CG calculations with min front seat weight. Despite the aircraft having done three test pilot flights, I have to prove the safety aspects of the installation and the effects on 'stalling' speed - it nods at 50 kts. I found that Micro Aerodynamics declare, and issue a placard, of airworthiness provided no more than 5 VGs are missing. I can supply photos of the installation but am short of a suitable/professional diagram of placement and chord etc detail that would satisfy the scrutineers  Can anyone point me in the right direction?

Offline Marc Zeitlin

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Re: Vortex Generators Retro Permission
« Reply #1 on: March 30, 2018, 04:37:23 PM »
First, let me suggest that you post safety related questions of this (or any other) related nature on a forum that has more members, viewers and activity - you'll get far more response and from far more people.

Despite the aircraft having done three test pilot flights, I have to prove the safety aspects of the installation and the effects on 'stalling' speed - it nods at 50 kts.
At what CG does the nose bob at 50 KT (I assume KIAS - you don't state whether KIAS, KTAS or Kt GS). At what Gross Weight does it bob at 50 Kts (I'll assume IAS for expediency)? Have you tested the stall speeds at forward most CG (97") all the way back to aftmost CG (103"), and with weights from minimum achievable up to your proposed 1600 lb. MGW? At all intermediate combinations as well? And accelerated stalls, from 0 to 60 degrees of bank? Once you've done all that, you'll actually know the characteristics of your plane - until then, you don't.

I found that Micro Aerodynamics declare, and issue a placard, of airworthiness provided no more than 5 VGs are missing.
At least in the USA, there is no such thing as "airworthiness" for experimental aircraft - only type certificated aircraft can be "airworthy". Don't know if it's the same in the UK. In any case, Micro Aerodynamics can have no knowledge of and can make no categorical statements regarding the safety of a plans built, one off experimental amateur built aircraft - them saying "up to five missing VG's" is a good start at understanding the possibilities for your plane, but not particularly meaningful.


I can supply photos of the installation but am short of a suitable/professional diagram of placement and chord etc detail that would satisfy the scrutineers  Can anyone point me in the right direction?
So here:

http://cozybuilders.org/cad_files/

down near the bottom under "Miscellaneous" are some PDF's of VG size and placement used for COZY MKIV's. The Long-EZ would be essentially identical, measuring from the strake/wing intersection for the wing placement and from the fuselage side for the canard placement.

But whatever documents you provide, only a full test program and results presentation will show that the plane is, in fact, safe within the approved operating envelope under all circumstances.

Offline murray44

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Re: Vortex Generators Retro Permission
« Reply #2 on: March 31, 2018, 06:56:03 AM »
Hi Marc, I really appreciate your helpful response. We don't have the Experimental category; ours is a Permit to Fly issued by the UK Light Aircraft Association delegated to it by the CAA. Three test flights were completed, one at 102.7 and two at 101.7. Yes, we need to cover 97 to 103. Our 'stall' speeds, 50  at 1466 lbs and 61  at 1600 lbs were all KIAS. I read an article that illustrates the difference between certified and non-certified aircraft as regards VGs, the former being massively more expensive to take account of all their testing. Seems we shall be doing much the same testing.

Offline dorr

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Re: Vortex Generators Retro Permission
« Reply #3 on: April 14, 2018, 03:09:16 PM »
While those who like the vortex generators are OK with small reduced top speed and a much harder to clean surface, it would seem the easier route would be to remove the vortex generators - the CAA has approved the Long EZ without them, right?

Yes we are luckier in the US to be able to experiment by simply flying off major modifications and trying anything less. 

David Orr
David A.C.Orr
"Beagle"
www.canardfinder.com

Offline murray44

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Re: Vortex Generators Retro Permission
« Reply #4 on: October 15, 2018, 10:45:54 AM »
An update. The UK LAA has approved VGs for G-RAEM and the increase of MTOW to 1600lbs - it took a while and a lot of paperwork. Thanks to all who helped.