Sonex High Wing!

[Scott Todd]

You make it sound like this is a design flaw or shortcoming of a Sonex. Clearly you built a single place airplane. John Monnett would cringe looking at that list. He probably would have recommended a different airplane had you told them you wanted all that stuff up front. I've owned two and flown 4 different Sonex's. I've helped broker a few more sales. They were all around the 650 mark and nicely equipped. They all flew as advertised.

[Skippydiesel]

Scott -
I am the finisher/completer - I purchased an almost finished Sonex, that came with all that I listed. Some was already installed, some I installed.
Many of the additions, to basic/standard Sonex, are to make the aircraft more suited to Australian flying conditions.
As I understand it (?) , the US (home of the Sonex) is blessed with a fairly comprehensive airfield coverage, most of which are paved. The result is an aircraft with fairly limited range, small wheels and a reduced concern over internal noise (oilcaning/engine).
Australian airfields tend to be very far apart (except on the coast, where they are concentrated around major population centers), grass/dirt and have poor fuel availability
The first builder, of my aircraft, sought to address these shortcomings by having larger diameter wheels, greater fuel capacity and reduce the internal noise generated by unpaved strips.
Even the choice of the Rotax engine (reputation for reliability & fuel econamy) goes some way to Australianising the Sonex.
I agree that the CS prop is an overreach but boy does it help in achieving great all round performance. This combined with the Rotax frugal thirst, helps to acheive great duration /range.
The beauty of the home built is that it can be customised - why stick religiously to the plans?
I am disappointed at the empty weight of my aircraft. I had hoped that the wing tanks may allow for a higher MTOW but Sonex seem particularly resistant to any change in the basic design (look how long it has taken for Rotax to be, sort of,recognised).
Check out the RV12 (a competitor) Empty Weight 366 kg (740 LB) MTOW 599 kg (1320 LB)

Oh! and one other innovation - My Sonex is solid riveted throughout. I don't know if this is weight neutral/light/or heavy but would hope adds to the structural integrity and the argument for a MTOW weight increase.

I also forgot the cowling - My Son designed & built it from scratch. It's his first composite build, so is a tad heavy. We went for the scratch built to accommodate the Rotax & its cooling requirements, which includes a pilot activated (electric) cowl flap. I have a Sonex vertical split cowling (considerably lighter) which may, someday, be modified to replace the home built - we will see.

[Scott Todd]

Well that was a really good post :) It explains a lot. I see it all the time where people 'mod' homebuilts to make them 'better'. Of course its all relative. 'Better' is not always 'better. As a Mechanical/Aerospace Engineer, I've helped homebuilders modify their Gross weights to accommodate situations like yours. However, in this case, I tend to agree with Sonex. It only has 98 Sq feet of wing. I've test flown them on hot days at gross and it can be marginal. The RV-12 has 127 sq ft of wing with loading around 10% less than a Sonex. It really shows in its performance.

The Sonex was meant to be a simple, easily built, minimal airplane. Yours has obviously diverged from this original intent. Good luck in your endeavours. Maybe a new build is in your future. There are lots to choose from. Maybe that Sonex HW will fit the bill :)

[Skippydiesel]

Hi Scott,

"I've test flown them on hot days at gross and it can be marginal."

Ah yes! but did the aircraft have a Rotax 912ULS, powering a CS prop? AND might this have changed the[ i] "marginal"[/i] observation ??

[Bryan Cotton]

Oh! and one other innovation - My Sonex is solid riveted throughout. I don't know if this is weight neutral/light/or heavy but would hope adds to the structural integrity and the argument for a MTOW weight increase.

I used to work at Sikorsky and Schweizer as a helicopter engineer. I believe the aluminum rivets will be slightly lighter, and better in fatigue. They have a lower shear strength than our pops though. The key parts for structural considerations are the spars (already solid riveted), their attachment to the fuselage, and the tail.

I am sure the airplane is strong enough to go over weight. Maybe you don't get the full 4.4G utility load factor. But you also get higher stall speed, etc.

Weight is the enemy.

[Skippydiesel]

Bryan/Scott

In Australia, the builder can nominate the MTOW, however I am not an engineer (farmer) so am reluctant to move above the Sonex nominated 522 KG MTOW.

FYI -In Australia, Sonex can be registered GA or RAA.
From my perspective, the main operational difference are;
GA allows easier access to CTA and the aircraft can be used for aerobatics. Annual airworthiness inspections are more expensive than RAA.
Having no interest in aerobatics and little need to enter CTA, I have gone with RAA, which forbids aerobatics. RAA is arguable cheaper all round, as the owner/builder is allowed to do all maintenance/inspections & membership includes third party insurance.

I mention the registration/aerobatic prohibition, as I would have expected that an aircraft stressed for aerobatics, would have the structural integrity (along with wing tanks/solid rivet construction) to allow for a higher MTOW.

Either of you guys wish to comment?

[Bryan Cotton]

I personally would not fly a Sonex that heavy. Though I don't think the wings or tail would fall off, what about the stall, climb, and approach speed? Those are going up. What about the landing gear? Will it be sufficient for that extra weight? I know a few people have bent their mains, and if you are flying out of rough fields or just do a particularly bad landing you are at risk there.

On a long x-c my son and I can take 14 gallons of fuel, or 3.5 hours worth. We tend to land with an hour's fuel but that is still 250nm worth of range. That's not enough?

[builderflyer]

Bryan/Scott

In Australia, the builder can nominate the MTOW, however I am not an engineer (farmer)

Either of you guys wish to comment?

Not either of the guys.............but isn't this the same airplane that the original builder thought, amongst many other things, that he knew better than the designer and that he needed to and, in fact, did change the angle of incidence of the wing? This is one of those airplanes that John Monnett would say "please don't call it a Sonex". Not meaning to offend you, but personally I would have passed on this purchase. Depending on what was or what is the actual desired mission of the original builder or yourself, there must have been a better alternative out there. Just my opinion.

Art,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[Kai]

My own polished Sonex Legacy dual stick tailwheel has fairly frugal instrumentation including a 40 l seat back auxiliary fuel tank, 5.00 tyres, an Icom 200 and a mode C transponder. With the Edge 915 ECI including oil and coolant, it puts 680 lbs on the scales. It was not always like that: it started out very basic with the small Shinn tyres and a Jab 22A, but no auxiliary tank. The result was 618 lbs. This only shows that you need to be extremely careful when you start loading on the goodies. The sword above your head are always those 1150 punds.

[Skippydiesel]

I personally would not fly a Sonex that heavy. Though I don't think the wings or tail would fall off, what about the stall, climb, and approach speed? Those are going up. What about the landing gear? Will it be sufficient for that extra weight? I know a few people have bent their mains, and if you are flying out of rough fields or just do a particularly bad landing you are at risk there.

On a long x-c my son and I can take 14 gallons of fuel, or 3.5 hours worth. We tend to land with an hour's fuel but that is still 250nm worth of range. That's not enough?

All very good points -

Naturally I would expect higher stall & approach speeds , reduced climb & probably cruise (for a given power setting).
As a for undercarriage - bad landing are always a risk no matter the MTOW and although I am likely to be using dirt (grass/gravel) strips I would not expect them to present much more of a challenge than a paved strip - the bigger issue is the impact of rapid gear oscillation on the fiberglass wheel pants.

Very roughly, outer Sydney to outer Melbourne (I would not be using the international airports) is about 360 Nm. I burn ULP, not carried by most airfields. When on a long trip, it behoves me to carry as much fuel as I can. The alternative is to find a lift/hire a taxi, into the nearest town/petrol station, with two 20L collapsible fuel bladders - something I have done many times but can eat into the available flying hours.