Strakes

[tonyjohnson]

I found this strake on the website of RV8 builder Mike Robbins http://www.romeolima.com/RV8//MikeRobbins.htm





Mike says that he gets a 4 kt stall speed reduction with no reduction on the top end. Does anyone else use this strake or know anything about it?

[Andy Hill]

I would doubt these have a genuine effect on a (full) wing stall. What they may well do is keep the boundary layer attached for longer at the root (only). Effect of this?
1. Delay root breakaway and hence natural stall warning (buffet onto the tailplane). NB in the UK the RV-8 does not require a stall warner due to the good natural warning - the SBSs RVs do require one. This may well remove this advantage.
2. When you get a stall, it will not be at the root, but the tip. Great idea - a nice docile stall becomes a wing drop This will come down to individual wing characteristics and 2 perfectly constructed / matched wings may not exhibit this dangerous characteristic until you enter the stall with any aileron / roll rate applied when you will get the full wing drop (opposite to aileron applied)

I would be very careful making any aerodynamic modifcations unles you know exactly what you are doing... and would refer these back to the designer.

[rv8ch]

Originally Posted by tonyjohnson

...Mike says that he gets a 4 kt stall speed reduction with no reduction on the top end. Does anyone else use this strake or know anything about it?

I've spoken to a lot of guys that have strakes, and without exception, they were very happy with them. As Andy mentioned, it would be a good idea to make sure you do a lot of stall testing at altitude to make sure you are comfortable with any changes in behavior that these might induce.

[tonyjohnson]

Andy,

I understand what you mean about the stall being moved outboard toward the wing tips and the consequences of that. I appreciate your thoughts. Perhaps some of the guys that Mickey has talked to who are using the strakes will chime in. My first thought is that if the strakes provided a 4 kt stall reduction without a downside, every RV would have them.

Mike Robbins indicated on his wesite that the strakes actually improved the full stall, however he did not speak to stalls in various attitudes.



Tony

[Kahuna]

I would check the RV-List. THis has been discussed for years.

Best,

[tonyjohnson]

Larry Bown posted this on the list some time ago:

For what it is worth, after we added the strakes, I did a whole stall
series. This included all kinds of power on accelerated stalls. What was really amazing was that ,in a banked stall, the aircrft righted it
self to wings level flight. We did spins up to 3 turns. Recovery from
the spin was near instant. The stall itself was much milder than any RV
I have flown.(I competed in IAC Sportsman competition with my 6).The
wing dropped appeared to be less and the plane was flying sooner. The
indicated stall was a couple of knots slower. Terry B.

The good news is that Larry had no trouble with stalls, the strakes actually seemed to help, no mention of buffet removal (some buffet is desirable of course) the bad news is that his stall speed reduction was only "a couple of knots"

[osxuser]

I didn't look too far at his website, but those look like they're off of a twin cessna? I know that those are part of the VG kit for Cessna 340's and 414's.