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Miscellaneous Thoughts DATE:
January 2005
Some idle newbie thoughts that have been floating
through my mind; resolved thoughts are in
green italics.
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.
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.
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.
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.
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.
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....
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.
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.
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...
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.
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-008 MISCELLANEOUS - PIANO HINGE
75
SONEX-010 DUAL STICK HARDWARE 6
DATE: March 2005
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
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.
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