PPRuNe Forums - VG's on light twins

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Brian Abraham

15th Oct 2007 01:15

VG's on light twins

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

15th Oct 2007 03:47

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

15th Oct 2007 04:32

Quote:

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That requirement is outdated, from CAR 3.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

15th Oct 2007 05:36

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

15th Oct 2007 06:42

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

15th Oct 2007 14:14

Quote:

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

15th Oct 2007 14:18

Quote:

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

15th Oct 2007 20:36

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

16th Oct 2007 10:21

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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