Your Flying Sonex - How many years old, Hours, & Repairs

General
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To Sonex Owners And Pilots (SOAPs lol),

Just curious as to how these aircraft are holding up over time. This month will be 28 years since the big event noted on the Sonex site:

On February 28, 1998 John Monnett lifted-off from Wittman Regional Airport in Oshkosh, WI in a completely new aircraft: Sonex serial number 1, or “SX1.

Myunn will be 14 years old this year with ~400 hours in service. I’ve been very pleased to have had no major airframe or engine issues. Maintenance has been quite routine with tires, brake pads (once with TOB), and oil & filter changes as needed. I did pull a head on the Corvair early on when carbon was preventing a valve from closing but since I’ve learned how to lean it properly and the use of Decalin that concern has vanished. I also replaced the distributor cap and rotor. Oil feed line to the fifth bearing was replaced but again that’s a maintenance issue.

I have the original canopy that last year showed a small crack in the pilots side that was stopped using the hot needle method. I also had to chase an intermittent strobe issue that turned out to be a poor crimp connection that I made.

But all of this is small stuff in all the years she’s been flying both from pavement & grass.

I was reading today about a pilot looking for a spinner for his 55 year old certified airplane and was stunned (seriously stunned) that a replacement spinner was over $7,800.00 (yes that’s correct)!

Somedays I don’t believe we really understand just how blessed we are!

So what’s your journey after the build been like? How long do you think a Sonex airframe will last?

Curious,

Dale
3.0 Corvair/Taildragger

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I’m at 3.5 years and 420 hours. Most of my downtime has been AeroVee related, especially cylinder heads. The original tailwheel bracket has failed me twice. I needed to add structure under the seat sling. Original canopy and windscreen, doused in 100LL once. Lots of tires, one flat. Had to replace the mini rudder hinge, but my fault as I accidentally used the rolled hinge instead of the extruded ones specified. I have a hard time keeping the lower motor mount to firewall flush screws tight. Looking forward to earning the 1000 hour prop tag at Oshkosh.

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78,000 or 7,800?

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11 years young :wink: First flight January 2015.

380+ hours TT Aerovee 2.0 and airframe.

Not much down time; rebuilt the cylinder heads 3X, replaced the electronic ignition coils due to one failed at 350 hours, 2X new tires, all system batteries replaced at 10 yrs, small canopy crack 1” developed on the rear passenger side at 300 hours emanating from frame mounting screw - stop drilled.

All in all has been very reliable and looking forward to hearing from high time Sonex Aerovee fliers to see what we can expect getting to 1000+ hours.

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Oh yeah same here. I’m on my third set of magnetrons too.

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My bad .. real bad. You are correct 7800 is what I meant … :confounded_face:

Edited original post …

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Just sold my Sonex in Nov. of last year. First flight July 2012, about 588 total hours, Jabiru 3300 replaced by CAMit 3300 hours at about 150 hour mark. Original canopy cracked one day after installation, Todd’s canopy has been in use since first flight, no cracks.

David A.

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Legacy/Rotax 912ULS - currently doing 200 hr service. Canopy cracked within 200 hrs. Attempt at repair, caused more cracking (my fault). Exploring Australian made preshaped/oven replasement. :smiling_face_with_horns:

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Just crossed 500 hours after a little over 10 years. Had an AeroVee turbo originally. That was a disappointment. Replaced it with a Jabiru 3300 Gen 4 and love it. The engine also had some early pains but Jabiru took care of me.

on my second canopy and this one also now has small cracks that I stop drilled.

overall this is exactly what I expected. And it leaves me with a smile every single flight.

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Dale,

Sonex A SG DS serial #0525 kit here, purchased end 2002. Construction begun march 2003. First flight was may 5, 2005. Hobbs presently shows apprx 650 hrs.

Presently it is on its third engine- the first was a new gen 2 Jab 80 HP with which the plane was underpowered, especially on grass fields, the second was a pre owned gen 2 Jab 120 HP, which after a while started consuming oil to an alarming degree. Had it been possible to source critical components such as new cylinders and pistons, I would have kept it- however Jab ceased production of these critical items because they tooled up for the gen 4 series (I was told). Present engine is a 123 HP EP915ECI, which has been sitting in the airframe for 5 seasons and 150 hrs; so far absolutely no issues.

All these years (20!) the airframe has been essentially trouble free: only issues that required immediate attention were fractured gear leg retaining bolts (se the Sonex SB), a cracked engine attachment stud in the 120 HP mount (see another Sonex SB), and a cracked weld in the tailwheel spring attachment bracket.

The plane is presently sitting in the hangar waiting for the subzero temps and the snow to go away- I am too old to freeze up there!

Kai

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I’m guessing that thing is a hoot to fly! :wink:

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Dale,

I am running a fp Sensenich two-blade up front (it looks scary!). Home field elevation is 38 feet amsl.

On a standard day atmospheric conditions, with this prop I get wot static 5050 rpm and 29.5 in Hg mp. During the t/o run, it torques to the left like there is no tomorrow: full right rudder and aileron! If I flog it a little, there is no problem to get 1500 ft/min on the vsi. I cruise the thing att 4800 rpm and 22-23 in Hg mp. At 3000 ft the asi will then show 125-130 kts. Flat out same altitude the engine gradually increases to 5800 rpm (I then always forget to check the mp gauge…..), with the asi showing 156 kts.

At that airspeed the plane is rock hard in the air :scream: But I am still running the original canopy, albeit with a few minor cracks down at the corners.

And-pray tell: what is the hot needle method for canopy repair?

Kai

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Kai,

I used the stop drill method with good success on my first Sonex.

On this plane I decided to try something different. I read of using a hot needle to make a small hole at the end of the crack to stop the crack from spreading. It was actually very simple but I had a helper. I took a small needle (it was a tiny nail) and held it with vise grips. My helper had a propane torch and we heated the nail and then I pushed it through making a tiny hole at the end of the crack.

It is said that this is better as is melts the Plexiglas and that prevents the crack from starting again. It is quite important to be certain that you are at the very end of the crack. Sometimes the end can be difficult to see. After doing this mine has been good even after flying off of some rough and bumpy grass fields.

Perhaps I should make a video about this as I didn’t find one on the tube …

Dale
3.0 Corvair/Taildragger

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I was loosing canopy screws on mine. After 4 had fallen out I replaced them. I wondered why I hadn’t used locktite to hold them in when I built the canopy. So I put a dab on each new screw. The next day I realized and remembered why I hadn’t used locktite. Locktite and plexiglass do not get along. I now had four cracks abput 2 inches long in the canopy, extending out from each new screw. I stopped drilled them and then applied some crazy glue to the Crack. I put some masking tape up very close to each side of the Crack as crazy glue is pretty runny. From experience I knew that this glue works well with plexiglass. The cracks are still there a year later but have not worsened.

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I’ll leave the engine part for another post but using the first flight as a birthday, Waiex 0082 will be 16 years old in May 2026. Total “engine running” time is 1257 hours and my Garmin GPS odometer reads 140992 statute miles with 1670 landings.
As far as the airframe goes, the only thing not original, excluding basic wear items, is the windshield! It became too crazed after 13 years (as did my Gen 1 AveoFlash light lenses). A canopy replacement was my fault and of course I’ve gone through tires, brakes, and the general wear stuff. My original tailwheel bracket is still in use. Failures seem common in this area over many iterations and the factory version’s side plates are to be watched especially if used on a lot of grass operations. The forces transmitted from the surface to our springless tailwheel design must be enormous.
Regarding canopy screws, from day one I drilled all the way through the bow and used nuts versus internal Loctite. It might not look as good, but I’ve never had a problem there.
Fortunately, I have not needed to go to the “Sonex Store” for years and that says a lot.
I’ll add that I have the cable brakes, manual flaps, and generally no frills so there’s less to go wrong.
One day, my Dynon D-180 screen won’t initialize and then I’ll be looking at a panel upgrade.
Thank you Becker avionics for a transponder and comm radio that still work like new.
In the near future, I am considering the placing all of the landing gear bolts based on some recent incidents. That’s pretty cheap insurance.
I just flew the airplane 1600 miles in 3 days last week and I don’t have a concern about the airframe integrity at all.

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Waiex 121YX is 14-1/2 years old and I’m at 1258 hours. I did 454 hours behind a thick finned Gen2 before installing my Camit in 2016. Airframe holding up very well. Things that will need attention before too long is tailwheel fixture getting loose on titanium rod. Maybe find a way to use shim stock? Other area is the vertical split cowling. I did flush rivets and now paying the price. Fiberglass too thin for long term. I’ve gone back and used the conventional head rivets in certain areas to reinforce the hinges line on the bottom. Next big thing will be top overhaul. I made contact with Kevin in UK one time and he said he would get back. Never did. Hard to get inspiration to send parts to UK for overhaul when the seemingly “only person” with the parts won’t engage with the customer. I visited Casey Cooper while RVing in AZ last month. Looked hard at the Rotax conversion but now even that option is thrown into doubt with the factory collapse. I could go on but I’ve felt for a very long time that what’s held Sonex back and resale price low is a failure to embrace a viable engine line. The AeroVee is barely adequate in the East and a no go out here in the West. Jabiru could run a clinic on how to destroy customer satisfaction. UL seems to be on the edge of space and almost irrelevant. Rotax has been the logical solution for at least 10 years and in my opinion, the factory waited too long to engage. Just my opinion and update after almost 15 years with this airframe.

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I bonded mine on. It was loose from the start. That’s awesome to be at 1258 hours!

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My comments about Jabiru, I’m referring to AU and not the U.S. service. The U.S. service has always been great in getting me whatever they could supply. Before buying the Camit I lived through all the service bulletins of the Jabiru. Most times the user community were the ones responsible for the actual product upgrades. As mentioned in other posts on various forums, had Jabiru embraced the Camit engine that Ian Bent developed they would be light years better off. This engine I’ve had for 10 years is superior in virtually every aspect you could dream up compared to my original Gen 2. Neither has failed me but inspections over time have consistently proven to me the benefits of Ian’s design experience applied to the basic engine design. Of course Jabiru gave the middle finger, the split ensued and Camit collapsed when orders were withdrawn. We the users always inherit the damage. Keeping small planes like Sonex viable has and will always be a challenge.

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Just curious as to how these aircraft are holding up over time.

Here are the stats & info on my bird:

  • Model: Sonex (“Legacy” design, taildragger, center-stick)
  • S/N: 1339
  • TTAF: ~150
  • Engine: AeroVee 2.1 Turbo
    [Purchased before supplemental cooling system was deemed necessary; had to retrofit the system prior to first flight]
  • Propeller: Prince P-Tip [54/50PK]
  • Vy climb rate: 1100-1200 fpm
  • High cruise (33” - 35” MAP, 8.5 GPH): ~128-130 KIAS [TAS: 148kts / 170mph @ 8500’]
  • Normal cruise (28” - 29” MAP, 7 GPH): ~118-120 KIAS [TAS: 135kts / 155mph @ 8500’]
  • Began: 11/2009 w/plans construction, switched to kit 09/2010
  • Distracted: 2009 - Present (sailplane racing, record-setting, and mentorship)
  • First Engine Start: 01/2018
  • Wastegate/MAP troubleshooting: 2018-2019
  • AWC Issued: 09/2022
  • First flight: 05/2023
    [FAA med-branch screwup grounded me for 6+ months the day after my AWC was issued. While many parts of the FAA are admirable, my experience validated every boogeyman story you’ve heard about that branch]
  • Phase 1 Testing Completed: 07/18/2023 [Numerous cooling problems slowed testing]
  • Flight to OSH began: 07/20/2023
  • Engine failure: 07/30/2023
    Head stud ripped out of engine block on way home from OSH. Aircraft disassembled & trucked home; damage sustained to H-stab in transit, requiring reskinning of stab.
  • Rebuilt Engine First Start: 08/01/2025
    Slow rebuild due to custom machining of non-standard engine heads and other minor mods to improve cooling and engine robustness.
  • Second “First Flight”: 08/20/2025
  • Hrs since “second first flight”: 60

While the Turbo engine has been finicky, the airframe has held up very well. Notable squawks:

  • 2020: Excessive radio noise due to MGL EFIS screen blasting EMI at the turtledeck-mounted radio antenna
  • 2021: Stuck oil-pressure plunger caused excessive pressure, oil cooler ruptured during early engine test-run, sending oil everywhere.
  • 2022: Canopy bonded with Sikaflex, then lightly screwed to skirts & bows. Very small canopy cracks at aft pax-side corner a couple of days after mounting. Stop-drilled with plexiglass drill bit, no change since.
  • 2023: Engine cooling problems. Numerous cowling & baffle changes attempted to improve the situation.
  • 2023 - 2025: Odd periods of electrical “noise” in engine sensors. Traced to B&C voltage regulator - unit was not intended for use with AeroVee-style stator alternators. B&C replaced with proper unit at their expense.
  • 2025: Inconsistent throttle response due to slop in AeroInjector & throttle cable. Re-routed cable and replaced AeroInjector needle-carrier.
  • 2025: 1 flat tailwheel (early model Anson pneumatic; replaced with newer, wider unit)
  • Current Squawks:
    • Minor/surface cracks in gelcoat around wheel-pant attach screws at axle (i.e. outboard side of pants)
    • MGL current sensor (hall-effect type) very finicky, giving inconsistent alternator output readings. Unclear if original B&C voltage regulator damaged stator or if MGL sensor just poor quality.
    • Weak engine starts at times. Can occur even when battery has just been plugged into charger. Excessive voltage drop is occurring on weak starts. Have tried 2 different EarthX batteries, but issue remains; considering replacement of starter.
    • Small oil leak from rear of engine (location obscured by accessory plate and flywheel) - just enough to make a mess in the lower cowling and belly.
    • Engine is sagging on mounts even with Urethane bushings - need to dismount engine and add shims to the engine mount pins (but turbo system & exhaust makes this a PITA).
    • #2 CHT is ~50+ degrees cooler than other cylinders. #2 EGT is ~100 degrees cooler than other cylinders. No intake leak found (so far), but leaning tests indicate a mixture imbalance and not just a difference in cooling airflow.

…As the list above shows, the Airframe has been solid and trouble-free. Besides the flat tailwheel, the only airframe maintenance has been bleeding the brakes and dealing with the Lexan windscreen being very prone to scratches (choose your cleaning cloth very carefully, don’t let anyone else touch the windscreen).

NOTE - my airframe has a few mods that may help with robustness/wear (YMMV):

  • Anson steering rod
  • Anson tailwheel pivot & pneumatic tailwheel (the new wider “scooter” type)
  • Additional steel tab welded onto each mainwheel axle mount, providing a second attach point for the hydraulic brakes (to spread load and prevent holes from wallowing out over time)
  • Gear-leg fairings do not attach through the floor (again, avoiding a hole that can wallow out). Fairings are closed with split hinge pins and held in place with industrial velcro/dual-lock on gear legs.
  • Canopy has no slot cut for external latch/handle (fewer corners for the canopy to crack). I made a small access hatch in cockpit sidewall instead, so you can reach in and manipulate the canopy handle from outside the airplane.
  • Hinge material attached to cowlings with soft aluminum solid rivets (using hand-squeezer), to avoid cracking.
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G’day Noel,

My Legacy /912ULS /Airmaster CS / with wing tanks, 2 x 30L & fuselage 40L header (no external fill point) tank has almost exactly the flight performance of yours.

I flight plan at 5000 rpm, 130 knots True @ /15L/hr (actual 14.25L /hr)

I have only just completed the 200 hr service (bit over 2 years since hatched).

Initial problems with engine oil cooling in the air and radiator on the ground , solved by a complete rethink/design.

Irritating issues with the main gear leg fairings (have the ever-growing hole in the floor design) may have been fixed during the 200 hr service (live in hope).

The plain - white paint job was applied by professional - not happy! Flaking along seams and solid rivet heads.

Operating of a grass field, the 4" tail wheel is marginal. Will be swapping it out for a 6" when the Au$ looks a bit heathier.

Tinted windscreen had nasty dark blemishes in the polycarbonate - no refund from US supplier. Replaced it with a locally sourced clear one - all good so far.

Canopy had no cracks, until about 4 months ago. Suddenly developed a 50 mm (2") vertical crack up from the left/opening side. In my efforts to “fix” made matters worse, ended up with a collection of cracks. Made a good temporary fix (curtesy of Ian Link sailplanecanopies@gmail.com) using copious quantities of cheap superglue and some left over wing fabric. Will purchase a new canopy from Ian when funds permit.

Storage room being in short supply, I have created an extra space, for always carried stuff, behind the seat pan - access through two small hinged panels. The main baggage area reserved for going away trips. I am contemplating doing the same again for the space below the seat pan - more complicated .

I am trying to figure out how to install a simple right wing up / left rudder trim for when I have an adult passenger - Last aircraft used “shock cord”, pullies and a ratchet cleat to achieve this very effectively.

If I was to do this project again I would :

  • Opt for a centre stick - better access & leg room.
  • Have a larger (60L) fuselage tank giving 120L usable.
  • Use the (at the time unavailable) Rotax compatible engine Ring Mount

Shes a wonderful little aircraft but would like to have 600kg Max TO weight.
:smiling_face_with_horns: