VG's on light twins

[Brian Abraham]

Some light twins, Piper Chieftain for example, have a gross weight increase when fitted with these after market STC items. I know what VG's do in terms of energising the boundary layer but not sure how it enables a weight increase. What otherwise limiting factor is being enhanced? Many Thanks.

[212man]

I had assumed it was a Stall Speed function, and some research seems to bear this out. I found this article which seems to cover the issues (around page 6/7 I think)

http://cobweb.ecn.purdue.edu/~andris...001/twnvgs.pdf

[Nathan Parker]

The gross weight increase offered by the VG STC is a direct
result of the reduction in stall speed. Under the FARs, light twins are required to have an engine-out rate-of-climb (in feet/minute) equal to .027 times the square of Vso (in knots). If you lower Vso by a few knots, the required single-engine ROC goes down. At the same time,

That requirement is outdated, from CAR 3. The current Part 23 climb requirement is not related to the stall speed.

[Brian Abraham]

212man - thanks, its marvellous how you can't see the woods for the trees at times. So obvious. Will have to improve internet skill apparently. Trawled net for info but all I found dealt with resolving aero issues on heavies. But still don't see how it can increase the ZFW.

Nathan - FAR 23.67 details the climb requirements and are based on Vso.

[212man]

Nathan, I assume you mean the RoC climb requirement has changed and is now a climb gradient requirement?:

http://rgl.faa.gov/REGULATORY_AND_GU...8?OpenDocument

[Nathan Parker]

Nathan, I assume you mean the RoC climb requirement has changed and is now a climb gradient requirement?:

Yes.

(Now gotta make the message longer.)

[Nathan Parker]

Originally Posted by Brian Abraham

Nathan - FAR 23.67 details the climb requirements and are based on Vso.[

Yes, the existence of a climb requirement depends on Vs0, but the actual rate of climb does not.

[No_7DAD]

Rate-of-climb

Just an ahah - the requrement for some aircraft (<6000 lbs, reciprocating engines) IAW FAR 23.67(a)(2) is to determine a ROC at 5000 ft., it does not mean the aircraft can climb, this could and sometimes is a minus (decent) number.

[FlyingForFun]

I was about start a new thread, linking to a question I've asked in Private Flying. Then I saw this thread, and realised it's very closely connected to my question.

I wonder if I could trouble you to click on this link and add any comments?

Thanks!

FFF
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