Are VGs a "major change?"

[sprucemoose]

More than a few RVers have experimented with adding VGs to their aircraft, with varying degrees of success. I don't want to open another debate on the topic, but I have a question for those who have gone down that route (or for DARs or other knowledgeable folks)- Was the addition of the VGs considered a "major change" as defined by FAR 21.93 and covered in our operating limitations?

I'll be asking my FSDO about this in the morning but since it is Sunday night I though it worth asking about here.

No it's not going to be for my RV.

 

[Ironflight]

It’s probably debatable, but if a change affects the controllability of the airplane, it probably needs to be put back into Phase 1. We added VG’s to our Tundra when it was still in the original Phase 1 because we were tinkering with pitch trim ability, and it significantly changed the landing feel, so I would call that a major change. If you’re just lowering stall speed with wing VG’s….hmmm, I could see both sides of that argument.

 

[rv6n6r]

I went through a similar exercise regarding a different change a while back and since it seemed ambiguous, I just went ahead and did it. Per my OpLims, it was just 5 hours back in Phase 1 and a logbook entry, no need to involve the FSDO. That said, your situation (and OpLims) may be different.

 

[plehrke]

Depends on what the intended purpose of the vg’s is.

My opinion is until you fly you don’t know the effect. If you don’t know the effect before you fly, you should be doing some sort of flight test program to determine the effect. That sounds like phase 1 to me.

 

[WillyEyeBall]

VGs

I added VGs in front of my ailerons and rudder to attempt to increase effectiveness, not to reduce the stall speed. However, could not perceive any improvements in roll rate using video camera, and didn't see any difference with spin entrances either upright or inverted. No entries in the logbook and VGs are still mounted.
Bill McLean
RV-4 slider
lower AL

 

[rongawer]

It will change your stall speed (hopefully lowering it a few knots) that you should have previously documented in your logbook per your Operating Limitations as per 91.319(b). Vso is a flight characteristic of the aircraft identified in what is generally paragraph 14 of Op Lims...so I would say yes, a major change.

I'm interested to hear what your FSDO says.

 

[RV8JD]

It will change your stall speed (hopefully lowering it a few knots) ...

Not necessarily, and not on the RV-8 apparently (as an example):

Nigel Speedy did some extensive flight testing on his RV-8 to identify the effect of VG's on several different performance parameters. One thing he did not test was the chordwise location of the VG's.

On his RV-8 with VG's the the stall speeds were unchanged (but note the 'Easier Landing' comment in the table below).

The wing VG's reduced the cruise speed by approximately 4 KTAS (The table below shows 5 KTAS, but 1 KTAS was due to the VG's installed on the underside of the horizontal stab).


KitPlanes article--> https://www.kitplanes.com/vortex-generators-on-an-rv-8/

 

[moespeeds]

I asked about VGs on a popular RV8 Youtuber's channel, and this was his answer:


@ArlingtonRV
Thanks. No, the VGs don't really do anything beneficial. They don't really affect low speed flight / stalls at all, but they do cost me 4-5 MPH in cruise.

This guy has a great channel: https://www.youtube.com/@ArlingtonRV

 

[ArlingtonRV]

Just to clarify, the comment I made was in regard to my specific RV-8 configuration, it was not meant to cover all applications in all RVs.

Thanks

I asked about VGs on a popular RV8 Youtuber's channel, and this was his answer:


@ArlingtonRV
Thanks. No, the VGs don't really do anything beneficial. They don't really affect low speed flight / stalls at all, but they do cost me 4-5 MPH in cruise.

This guy has a great channel: https://www.youtube.com/@ArlingtonRV

 

[vic syracuse]

Properly designed and installed VG's on certified aircraft come with an STC. Sounds like a modification to me.

If they are properly designed and installed they should affect the flight characteristics, which is a sanity test for a major mod.

There's no harm in placing it in Phase I and performing some tests.

Vic

 

[2theskyy]

I’ll put it on the same stc as for lcp cracked holes.
But seriously.
Experimental or certified mods are always good to test flight. Paperwork first then “phase 1” to run it through the ringer in flight tests. You always want to know the envelope you are wanting to stay within.

 

[sprucemoose]

To be clear about this, my intent is to place it back into phase 1 and do extensive testing. My question about the major change is more of a legality question, the answer to which drives how much I need to get the FSDO involved. Obviously I’d like to keep that to a minimum but if only I’m on solid legal ground to do so.

More specifically my ops lims require me to notify the FSDO of my plans and get their concurrence on the new phase 1 area- if it is a “major change.” I had a busy and delay-filled day at work so I was not able to reach out to the FSDO. I’ll try again tomorrow.

 

[Mel]

To be clear about this, my intent is to place it back into phase 1 and do extensive testing. My question about the major change is more of a legality question, the answer to which drives how much I need to get the FSDO involved. Obviously I’d like to keep that to a minimum but if only I’m on solid legal ground to do so.
More specifically my ops lims require me to notify the FSDO of my plans and get their concurrence on the new phase 1 area- if it is a “major change.” I had a busy and delay-filled day at work so I was not able to reach out to the FSDO. I’ll try again tomorrow.

If your op lims require FSDO notification, then that's what you do.

Operating Limitations rule!

 

[sprucemoose]

If your op lims require FSDO notification, then that's what you do.

Operating Limitations rule!

Fully understood on that point. I’m just trying to tease out whether or not this particular modification qualifies. I have a call into the Milwaukee FSDO and I’ll report back here on their answer.

In the mean time, what say you, Mel? Are VGs a “major change?

 

[Mel]

Fully understood on that point. I’m just trying to tease out whether or not this particular modification qualifies. I have a call into the Milwaukee FSDO and I’ll report back here on their answer.

In the mean time, what say you, Mel? Are VGs a “major change?

Yes, as said before, VGs may (Probably) change the flight characteristics of your aircraft, so they would qualify as a "Major Change".