There has been some discussion about the effectiveness of the ventral strakes sold by Advanced Aviation, Inc.  Here are the results of some testing I performed on my ES:

Density altitude 8400, 2090 rpm, 18" MAP.

Without - 134to 136kts, with 132/133 kts.  The air temp and pressure altitude were slightly different so the speed might have been closer than that.  There are two numbers given for IAS - the first is that displayed by the Chelton/pinpoint and the second is that indicated by the mechanical ASI.  Note:  All the tests below are with feet on the floor - the rudder was allowed to "weathervane."

First test - rudder depression and release
without - 3 oscillations to damp, period - 2.8 seconds;  with - 3 oscillations to damp, period - 2.0 seconds period, although there might have been a timing error that made it a little more than 2 seconds.  It was noticeable that the second oscillation without the fin was a higher amplitude than with.  With the strake the plane seemed to be more aggressive in returning and the second oscillation was noticeably less even though the total number of cycles to steady state was the same.

Second test - 5 deg. bank using aileron only - time to achieve a 30-degree heading change.  The idea was to put the plane into a slip and see how long it would take to start turning.
Without - 25 seconds required.  With - 15 seconds required.  Noticeably less time required to achieve a steady-state turn rate.

Third test - effect on trim speed.  With full flaps and no power, trim full nose up and allow it to reach trim speed.  Idea is to see if there is an effect on elevator effectiveness.
With and without stabilized at 102 kts.  So at least at full nose-up trim it appeared as though the strakes generated no vertical lift.  At full forward CG there was no perceived difference during the flare for landing.

It may have been just my imagination, but without the strake it was difficult to get the plane to stabilize its heading within 1 degree as there was an easily-excited 1-degree oscillation in yaw.  It seemed to not have that tendency with the strake.

There was either a 2-knot loss in speed or none - the conditions slightly favored the "without" test, so the 1.5 percent observed speed loss might have been less than that ( I have had others report that the 2-knot reduction is real).

I debated on whether to keep it, but finally we decided to glue it on.  Not a really big difference but I felt it was just enough to justify it.  And the 3 pounds added to the tail can't hurt.

If I were building one I would put it on - it would be much easier to fit with the fuselage upside down, although it wasn't a big job with the plane upright.  It fit very well, but does take a little effort to get it to be perfectly aligned and level.  I found it easiest to clamp it in place and then put in a couple of screws to hold it while the Hysol cured.

If I had an ES the plane were painted I don't think I would go to the trouble to add the strake.  I have heard some comments that go something like this:  "it is necessary for the IVPT, very desirable for the IV and helpful for the ES."  I'm not an expert, but since the fuselage and tail are the same for all of these planes I expect that the relative improvement would be the same.  If one is concerned with spin recovery wouldn't the ES, with its longer wingspan be more likely to respond than a IV?  The converse is that the higher power of the others is destabilizing and therefore puts the plane closer to the edge for power on/off stability, especially in the case of the IVPT.  Why does the strake improve the stability by as much as 30% when it is nowhere near that percentage of the total fin area?  I'm guessing it is because the strakes are thin and sharp-edged, so the lift vs angle of attack curve is very steep.

Gary Casey
ES 157, N224SG, slower now, but more stable