Originally Posted by AlanTN
Scott, I do not mean any disrespect to you or to Van's. I am a Mechanical Engineer with some training in aircraft design and experience running a high speed wind test facility. I like Van's. I have been to this forum and Van's website hundreds of times over the last several years. I think the RV-12iS is a brilliant design.
As a prospective builder of this aircraft I just would like to know how the original data was derived and what has changed. The reason I used the quote is that it suggests to me that I can count on the numbers, and now they are not the same. Can you help me through this?
My (limited, I admit) understanding of the written English language is that when quotation marks are used it implies that that exact phrase has been heard used.
Yes, Van's does say that all published data is valid to the highest accuracy possible with no embellishment. and backed up with test results (and to the best we can it is), but I don't think it has every been said the way you quoted it (I bit snarky but I may have read something into it that wasn't intended).
Anyway, to answer your questions....
A lot of flight testing was recently done. Some with the ULS and iS prototypes flying side by side (climb tests while ballasted to same weights, cross country, etc).
The performance values currently on the web site and in the brochures are based on that testing.
The reason for differences when comparing to the previously publish data for the ULS airplane can not be established. The person who developed that data no longer woks at Van's and the used are inconclusive to determine where the error was induced. I am certain it was not intentional.
The reported reduced range at a slower engine speed is based on the test data available at this time (proof it is not being manipulated, since it doesn't totally make sense).
The iS airplane is still rather new. As more experience is gained perhaps an understanding will develop that will explain it, but it is likely related to the control software mapping for the engine.
As has already been published, the iS airplane, with the propeller pitch setting currently being used (which is .4 degrees courser that the setting on the ULS) climbs 100 FPM faster at Vy compared to the ULS (and at a higher RPM), when at the same weight.
The two airplanes flew together for the entire trip to OSH and back. With the iS airplane at the max. eco mode throttle setting and the ULS throttled to right at 5480-5500 RPM, the TAS is matched at 120 Kts but at the final fuel stop headed to OSH, the ULS airplane had used 60 Gal for the trip and the iS airplane had used 45 Gal.
Side note - All of the published range figures on the web site are absolute range (the point that you would run out of fuel).
It is taken for granted that pilots are (should be) capable of planning their own reserves with the FAA requirements.