Rotax Vs Jabiru 3300 (straight from Van's)

I have inquired about Van's interpretation of the LSA cruise speed regulation. I have received a response from a Van's tech person that helps clarify the difference between a Rotax 912S equipped aircraft and one with a Jabiru 3300 (or other similar engines). The following is excerpts from that response.

My question:

> Please clarify Van's interpretation of the LSA speed of 138 mph at
> max
> continuous, at sea level. Would this not provide a cruise of about
> 150 mph
> at 7500 ft? Maybe I need a bit of an education on the matter.

The answer:

> There's no "interpretation" to be made. These are the LSA rules:


> Maximum speed in level flight with maximum continuous power of 120k CAS.


> Calibrated Air Speed (CAS) - The indicated air speed of an aircraft, corrected for position and instrument error. CAS is equal to true air speed in standard atmosphere at sea level.


> Because the Rotax is rated for 90% power as max continuous, the highest CAS will be low down, not at 7500. It can be run continuously at full throttle/5500rpm at sea level, so %power decreases as you climb, (no more throttle to add), so TAS does not increase with altitude, at least for Rotax 912ULS powered LSAs, unless the prop is pitched so you cannot use full throttle low down.


> With other engines that have a lower max continuous power eg 75%, TAS may be higher than CAS at altitude, because the engine is more restricted low down (throttled back), so you can maintain the 75% as you climb by adding MP. So power stays the same but drag decreases.

I also asked about the wheel pants option and got the following response:

>We intend to offer wheelpants, but there is no projected date or guarantee that they will be available.

Given this clarification, a Rotax powered aircraft is not in my future. The reason I have been involved in the previous threads on this forum was for research purposes, in order to make a decision on which aircraft is best for my wife and I. Not to "stir the pot" or find out how to break LSA rules, as implied in the new lycoming 10-233 thread.

The 12 is a great design (except for the engine choice, in my opinion ). It has a number of great features. It is just not for me. If I can develop the necessary funds, I will not hesitate to build a 9. Now there is a great aircraft. I was lucky enough to take a ride in one and fly it for a short time. The most balanced controls that I have ever felt.

I have learned a lot during this process. I am sorry my intension's were mis-interpreted.

12 vs 9

On the plus side for the 12, it is probably easier/faster to build, you can keep it in your garage and save on operating costs. The 9 out performs the 12, at both the slow end and the fast end. It takes time and persistence, but it is not difficult to build for the average skilled builder. I had no skills and completed mine and I have a fun, slow, fast airplane. And I can't imagine how the 12 could handle any better or easier. Go for the 9(A).

Yup, you can keep the 12 in your garage and save money on a hanger. Yup, I can do that with my kitfox, do I do it, no way. When I do something, I like convenience. I have the hanger, I open the doors, pull out the fox and taxi to the runway, hit the power and I'm off flying in minutes. I know a guy that has his kitfox on a trailer, takes him 30minutes to put it together, fuel it, check things over(that part scares me, what if you miss something). Then finally gets to go flying. I like the convenience factor, I've gotten sour twards things in the past because it's just too much trouble, snowmobiling, boating. But to just open the hanger(doors need to be easy also) and pull out the plane and go fly, priceless.