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.

TOGA Button… Work in Progress

I thought I’d share this idea to see if I can get some feedback from other builders. I found a  DPDT (couldn’t find a DPST) switch small enough to fit nicely in the end of the throttle handle. I just had to remove some of the threads on the switch and will probably use some RTV to hold it in place. I think this would be a very convenient place for the Go Around button so I’m hoping to get this to work. The other idea was to use a button on the control stick, but since a DPST switch is needed (As stated by Garmin) and all the switches in the stick grip are SPST, then I’d have to use a relay and I’d like to avoid that if possible. So with the switch able to fit in the throttle handle I just need to figure out a nice way to route the wiring. I need to run 3 #22 wires so it’s not too large of a bundle. I know I can drill out the center of the throttle handle a bit and get the wire to the throttle arm pretty easy. The hard part is running the wiring down the throttle arm and into the center console. I’m thinking maybe down the back of the arm using a snap on plastic U shaped cover or maybe through a small aluminum tube that’s epoxied onto the arm. Anyways if anyone has any ideas I’d be glad to hear.

The switch fits nice into the bolt hole in the throttle handle and is short enough to allow for the wires to get soldered as well. I purchased the switch from DigiKey, it’s an NKK LP0125CCKW01F (Digikey #360-2524-ND). I believe there’s also red and grey. Now I just need to figure out how to run the 3 #22 wires to it. Fortunately I have an extra throttle handle and arm for hacking…. I mean testing.

Horizontal Stabilizer Finalized

Time: 1.5 hrs

Today I checked to make sure the HS was completely straight. I was wondering how I was going to check this. Thinking maybe of using a laser level or make some kind of apparatus like a water level of something, but then there is was on Peter V’s site. Just hang it by the hinges and the use plumb lines down each of the ends… so easy. Anyways the HS checked out to be straight with no visible twists so now when I get the elevator skin I can clamp it to the HS and rivet the skin on and hopefully all will line up nice.

After checking for straightness I just sanded the rivets and pinned the short wire from the tail cone area through the HS to connect to the elevator of the pitch trim servo. The receptacles of the CFC connectors are back ordered so I’ll just have to install that when they come in, but besides that I think the HS is good now.

Rivets all filled and pins on the receptacle side of the wire.

The other rend of the wire with the connector on… might need to add a lightening wire bracket here, but I’ll see when I have the elevator on.

Strobe Light Rewire

Time: 0.5hrs

Yesterday I finished up the rudder and VS, but the way the wire runs out of the VS and up into the top of the rudder top has bugged me for a while. I saw on Peter V’s site that he reran it inside the rudder and out through a grommet in the hinge area of the rudder. Unfortunately I can’t do that without drilling out rivets and pulling some of the rudder skin off. After a bit of thinking I came up with a compromise. The wire still runs outside past the hinge and into the top of the rudder, but it now runs through a grommet in the hinge area so that it’s a more direct connection into the VS and makes for a more secure run for the cable. The cable no longer has to flex back and forth around the hinge when the rudder turns and now works more like the elevator to HS connection. 

Drilled a 3/8″ hole below the last rivet in the hinge area of the rudder. I also added some sheathing to the wire just in case there is any rubbing against the metal. 

Cable has been rerouted through the grommet. 

The cable joins up in the same place in the VS. I’m still thinking  maybe I need to add one of the lightening hole mounts to be able to tie wrap the wire to it after the rudder is connected. I’ll have to see if you can even get in there with the rudder attached…. I don’t think so though. 

Vertical Stabilizer and Rudder Finalized

Time: 3.5 hrs

Today I finished sanding the rivets on the rudder and VS. I also finished up the Wiring for the connectors that attach the strobe/nav light through to the tail cone. The VS and rudder are now done. I also took a look into the poor alignment of the elevator and HS. I was pretty careful when I built the HS to make sure the ends  were level, but I guess I wasn’t careful enough. From the look of it one end it about 0.7 degrees off from level. That may be why the elevator was off. After a bit of deriveting and reriveting I managed to get it to 0.2 degrees.


Right side level

While left side is off a bit. 

Got it to 0.2

Strobe connector wired up. 

Strobe connected to the rest of the wiring. 

Strobe mounted and all wiring/connectors fit fine inside. 

Rudder with rivets filled, sanded and connectors done. 

Elevator Issues

Time 2.5 hrs

Today I wanted to just check that the empennage fit the fuselage correctly and all components lined up. The idea was to check them, fill and sand the rivets and finish up the wiring so I can call it done (well minus the pitch trim in the HS for now). Well I mounted the HS on the fuselage which went fine. I then attached the elevator to the HS… ah that didn’t go so well. The ends of the elevator were a little off from the HS. I was hoping I could fix it by removing a few rivets then clamp it and rerivet. No such luck. I worked for a while and was able to get it so it was not about 1/8″ off which I was almost was going to say was good enough, but I really wanted to get it perfect. I twisted it a little more to see if I could get the frame to move a bit more under the skin and I guess I pulled a little too hard. The skin bent at the trailing edge (will have to get a photo). Well I think TAF has a skin in Torrance so hopefully it’s only a week or so set back, I’ve got plenty more to do so I’ll just move onto another project while waiting for that part. 

Sling out getting some sun. The garage ceiling isn’t high enough to put the rudder on so I have to fit everything outside. 

When the left side is like this

The right side is like this 😦

Clamped the left side with some wood and a bolt, then pulled most of the rivets from the right side. I was able to get it pretty close to lined up, but then I over did it. 

Well now I need to wait to see if they have a skin at Torrance. I’ll try to remember to get a photo of the skin to detail my handy work :-), such a dumb mistake. 

More Connector Wiring

Time 2.5 hrs

Well the heat shrink labels came today so I was able to finish the connectors that I had stated to wire up the day before. 

Control stick wires labeled and pinned. 

Control stick pins in the connector. 

And finally the TE mini CPC connector mounted under the control stick. The gribs will have the female side of the connector on the pigtail. If I ever have to remove a control stick then I just de-pin the connector and pull the pigtail wires back through the control stick. 

I also wired up the connectors and VOR coax on the tail cone.