Miscellaneous Thoughts

DATE: January 2005

Some idle newbie thoughts that have been floating through my mind; resolved thoughts are in green italics.

  1. How much faster would it fly if flush rivets were used on the wings/fuse/tail?
    Resolution: Not enough to make it worth it; the Sonex is already fast for the type of aircraft it is, but it is not an all-out speed machine and is never going to compete in top end speed with an RV7 etc.

  2. How would flush rivets on the wing affect the stall speed? Perhaps the protruding blind rivets may actually induce turbulence which helps adhere the boundary layer airflow to the wing?
    Resolution: Unsure, don't care. See Q1.

  3. How hard would it be to modify the brakes/rudder-pedals to get mechanical (or hydraulic) differential braking?
    Resolution: Probably not too hard, but also probably not worth it. Sonex suggest it is a very bad idea. I'll build the standard brakes and then decide if I want something better after flying it. That said, some people are using TracyOBrien hydraulic brakes on their Sonex's.

    Update 2009-02-11: I'm not keen on the quality of the standard Azuza cable brakes, so am thinking about using (non-differential) hydraulic brakes, such as made by TracyOBrien. But I have heard reports that the TB brakes sometimes overheat and fade. Other people have also used Hegar and Great Plains brakes.

  4. How corrosion resistant is 6061 aluminium, really? I will be regularly flying near and over the ocean.
    Resolution: Not sure, but I don't want to complicate things. This is a simple aircraft. I may alodine some parts and dip the rivets in something before installing them, but that's all. I want to keep the weight as low as possible, so won't be using any chromate, primer, paint etc. If it corrodes away on me I'll build another one, hey? ;-) I haven't heard of any Sonex with a corrosion problem... yet.

    Update November 2005: I've changed my mind slightly on this. I'm planning to alodine as many parts as possible, and also lightly dust joining surfaces and the inside of all the skins with Zinc Chromate. This adds negligible weight, and increases corrosion resistance enormously.

  5. In Tony Spicer's video, he does a 2-turn spin with an easy recovery. What happens if you let the spin develop beyond 2-turns?
    Resolution: Marty Smiltneek has spun the Sonex for 10 turns without any reported drama apart from nearly being sick! Apparently the rotation is quite fast and by turn 5 the decent rate stabilizes at around 600ft per turn. I now feel confident about the Sonex's spin recovery characteristics. See Sonextalk message #13723.

  6. What size are the wheels? How rough an off-field landing can be handled without concern for a flip-over?
    Resolution: I am told the plans have a larger wheel option for really rough fields. I'll see what I think when I get my own copy. Update: Now that I've got the kit, these wheels look small! They're smaller than the one on my garden wheelbarrow! Hmm....

  7. What size is the baggage compartment?
    Resolution: I am told there isn't one!! But you can fit stuff in behind the seats, in a plastic box or whatever. I'm wondering about the feasibility of wing lockers. It seems to me that I'll run into aft-cg problems before reaching MTOW. I don't like aft-cg luggage!
    Update: Forget the wing lockers. I don't think aft-CG is an issue with the Jabiru 3300 engine.

  8. How comfortable is the "sling" seat arrangement?
    Resolution: Apparently it's pretty comfy. I understand there are some approved modifications you can do for improved head clearance etc. I'm only 5'10" though, so doubt I'll have any problems. I may do the 'dropped-seat' mod anyway, and use a thicker seat cushion. I believe the 'dropped-seat' mod is now standard on the Waiex and Xenos designs.

    Update 2009-02-11: It also now seems common to raise the windshield bow an inch or so which improves windshield-canopy line as well as providing a small increase in headroom.

  9. With the Sonex's 4:1 speed range, what sort of props are people using? Does anyone use an in-flight adjustable prop for improved climb/cruise performance?
    Resolution: Again, it's a simple airplane. Fixed pitch is simple, and works plenty well enough. Sonex have done an awful lot of prop testing to arrive at the best solutions. I'm not going to argue with them! That said, the Airmaster AP332 3-blade carbon-fibre constant speed prop is relatively light, and works with the Jabiru 2200 & 3300 engines. I suspect there may be engine cooling issues however, as the Sonex - and most other Jabiru installations - require a high blade pitch near the hub to push air into the cooling ducts.

    Update 2009-02-11: I'm currently leaning towards a Prince P-tip prop. I have heard they have a very high pitch near the hub which helps with engine cooling...

  10. How feasible would it be to make an aluminium cowling instead of the standard fiberglass one? Rick Henry made a metal cowl for his Mustang-II with a small fiberglass nose bowl. It looks and works great, with easy hinging access to the engine, and also has the benefit of being much lighter.
    Resolution: I'm buying the full kit, which includes a glass cowling. So that's what I'll be using! I plan to build the airplane stock-standard. I want to get it completed as soon as possible. If I umm and ahh about all these things I'll never get it built! When it's built and flying I'll have a much better idea of any changes (if any) I'd like to make.

  11. I was a bit confused about which Wicks/ACS hardware kits are needed in addition to the Sonex full easy-build kit. I asked Jeremy @ Sonex and he recommended the following Wicks Sonex Kits, for a standard gear dual stick aircraft:
    SONEX-001 WING HARDWARE                  US$130
    SONEX-002 TAIL HARDWARE                      13
    SONEX-003 FUSELAGE HARDWARE                 250
    SONEX-004 TAIL DRAGGER HARDWARE              44
    SONEX-007 SQUARE TUBING                      59
    SONEX-010 DUAL STICK HARDWARE                 6

DATE: March 2005

  1. What about a ram-air intake? Sonex's generally all seem to use a simple air-filter sucking (what temperature?) air from inside the engine cowling. Kent Paser had some amazing results on a Mustang-II, from a ram air inlet which protruded forward so that it almost touched the propeller. He then 'timed the prop' so a blade would pass in front of the air-intake at the same time that an engine inlet valve was open. This experiment (and much more) is detailed in his book 'Speed with Economy'.
    Resolution: After posing the question on the Sonex list, it turns out that a) there may be issues using the aerocarb TBI with a ram-air intake, and b) someone has already tried it and noticed no change in performance. So, I think I'll forget about it for now. Perhaps I'll look into it again if I ever decide to make an Aluminium cowl.

DATE: December 2005

  1. Extra Fuel. The one aspect of the Sonex design that I think I would really like to augment is the range. And thus fuel capacity. I know it conflicts slightly with the Sonex's original mission profile, but I really do want more range. And yes, my bladder is good enough to allow it... :-) I like the existing main tank, but am thinking about adding some extra fuel capacity by way of leading-edge wing tanks. This is the standard arrangement in the Mustang-II, and there are some pictures of such a tank/wing being built on John Peacock's site, here: http://pages.cfu.net/~peacock/wetwing.htm

    Resolution: I'm going with the standard fuel tank per the plans, for now. Although it looks quite possible to add integral wing tanks to the Sonex, working out the details was bogging me down too much. I just want to get these wings finished! I think an easier, retrofittable (and also easily removable) option is to mount a marine type fuel tank behind the seats with a transfer pump to top-up the main tank. Moeller Marine make a huge range of these types of tanks.