Elevator Redux

Time: 1.5 hrs

I went down to Torrance TAF yesterday and got my new right elevator skin. So today I de-burred and primed the skin. I used the old epoxy primer so I need to let it dry for a few days. I’ll probably try to put the skin on this weekend since it should be dry by then.

In other news I talked to Jean about the 915. Let me just say there are a quite a few changes that are going to be made to the airframe in order to be able to fly at full power. I guess I shouldn’t really disclose all the changes since they are still preliminary and should wait for an official announcement from TAF. One that I should report one though is that it seems like they are going to move the parachute box back to aft of the bulkhead. TAF had moved it forward into the luggage area for better CG with the 914. However the 915 is around 40lbs heavier then the 914 so that will move the CG a bit more forward. I mention this because having the correct CG for the 915 is the one necessary item from the list of changes. The other items are really only if you want to take advantage of the higher cruise speed that the 915 will give you. For me the problem is that I already put on the top rear fuselage skins so if want to be able to use the 915 I have 4 a few choices:

  1. Remove the top rear fuselage skins and install the new parachute box aft of the bulk head. I have all (or at least) most of the parts so that should be an issue. But it means removing hundreds of rivets and prepping all the alternate parts. The plus side is that I’d be able to install the new magnetometer bracket much more easily and I’ll have all the luggage are space back. However then I’m absolutely committed to using the 915.
  2. Don’t install a parachute. The more I think about it the more of a pain the parachute will be. It needs to be repacked every 6 years or so and that means drilling out rivets to remove the skin that covers the parachute opening and sending the parachute in to be repacked… not sure if the rocket needs to be replaced as well. I guess it’s still easier then the older Cirrus models, but still an added cost and hassle. But I suppose it could be worth it if you find yourself in the position were you have to use it. If I don’t install a parachute I believe I can remove the box as well and gain the luggage space back, but I’m not exactly sure what happens with the “big ass” cables that tie into the fuselage.
  3. Don’t use the 915 and just stick with the 914. There’s nothing wrong with the 914. When I flew the Sling for the first time I was amazed at how it climbed out and performance seemed very good. So it’s easy to lose that and get caught up in the “latest and greatest” syndrome. The 915 is quite a bit more expensive, heavier, and the performance gains are pretty minimal (once again I saw the preliminary numbers so I don’t want to say anything). The 914 is fairly rock solid, unlike the 912is which has been plagued with problems (and if the 915 is based on the 912is then well…). I think with some time TAF will have a great Sling 4 using the 915, but I think it will take a while to work out the issues. Also while I think Rotax did their work in testing the 915 you never really know until you get a few out in the field to see what the problems will be.

So well there it is, my conundrum. Do I build the plane with all these uncertainties just to use the newest engine and hope that it’s really all Rotax is saying it is or do I stick to what works? It would be nice to get a little better climb out performance, lower fuel consumption, and easier integration (the 915 uses Can Bus for most of the sensors). On the other hand I’d like to fly and enjoy my airplane when it’s done. I don’t want to be dealing with ADs and making costly repairs both to the engine and airframe. I guess I’m leaning towards playing it a bit safe and just build the plane for the 914 (also my wife said she won’t fly in it if I use the 915 because she’s worked there will be problems, but that’s why there;’s a parachute 🙂 ). If the 915 does work out well then I suppose I could always build another Sling using the 915. By that time it would probably be a few years down the road and the engine and airframe will have all the bugs worked out. I also need to consider that the parachute location is just one of a multitude of other changes needed to take advantage of the higher cruise speed. I can’t really justify spending quite a bit more money just for a little better climb and slightly better fuel consumption. So if I use the 915 then I want to do it right and make all the necessary changes to take full advantage of the 915.

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