My New Project … The Onex from Sonex

Onex Build Site

Carburetor

I had rebuilt a used carb and it has been running mostly OK but had a few problems.  It has always run a bit rich and with the thinner hot summer air it was getting really rich.  It didn’t idle smoothly and would always stumble on acceleration.   I came to the conclusion that there were at least two problems and with some help found which parts would need to be replaced. Looks like there was excessive play around the mixture shaft, and likely a leaking accelerator pump outlet check valve.  Pricing the parts got me to half the price of a factory re-manufactured one so I bit the bullet and paid the money.  Spruce got it to me in 2 days and I had it on the next.  It made a big difference.  Idle is smooth, no hesitation on takeoff, runs smoother throughout the rpm range too.  Unexpectedly it also solved an annoying “automatically” advancing throttle too.  I kept having to use the throttle lock to keep it from slowly advancing to full.  a worn butterfly and shaft were the problem there.   I expect to see a little better fuel economy but I can’t prove that yet. Best part is that i won’t be worry about it while I am flying now.

HT Tail Fairing

Sorry, a little out of sequence here.  I made these just before starting on the vinyl wrap.   The open area in front and under the HT tail bothered me.  It just didn’t look finished.   some builders have claimed better elevator control at low speeds but I really can’t say that it made a difference. That wasn’t my motivation for covering up the space anyway.    Made some templates with construction paper that fit the way i wanted.  They are removable so i can inspect the important stuff under there still. Door edge protector made a nice edge up against the tail.

Vinyl Wrap

I didn’t really want to go through the hassle of painting and wanted to keep much of the metal showing so vinyl seemed like the way to go.  Watched several YouTube videos and then just bought some vinyl and started messing with it.  It has been a learning experience but I am happy with how it came out. I may go back and re-do the cowl top at some point as it was my first attempt.  I always found painting stressfull as you can screw it all up in an instant.   With vinyl you don’t need a sterile environment and you don’t have to do it all in one shot.   I found a store online that i am very happy with.  MetroRestyling in Michigan.   I have ordered several times and had no problems there.  This took me a long time to apply but unlike paint, I could stop at almost any point and come back to it when I wanted.  Its not hard to put on but it does take some getting used to.  Good thing is you just peel it off if you aren’t satisfied. I have some polishing left to do and need to do something for color on the wing tips still but its looking like a ‘Real’ airplane now.

Here are the things I wish i knew before I started:

• Colors are very different in the sun.  Buy small samples of every color you plan to use.
• Don’t cover parts that aren’t attached to something bigger.  You need to be able to pull and stretch the vinyl and a flimsy fiberglass cowl on a table doesn’t work.
• Use Knifless tape to cut lines.  You will never get things lined up so put it on larger than you need and cut to size using this tape.  I didn’t believe a thread would cut a smooth line but it works better than a knife or scissors.  Lines, curves, panel lines all work with this stuff.
• Buy some vinyl primer and use it near edges or areas you know are going to pull away over time. This stuff is easy to put on from the 3 oz applicator bottle and it makes the vinyl stick when it didn’t want to.
• Yes, it goes over rivets just fine but you have to work it up to each one, squeeze out the air bubbles and then continue on the other side.  Not hard, but it is tedious.
• Overlapping pieces do show. you can see exactly where you overlap so both cut lines need to be neat and straight.  I suggest no more than 1/4 inch and use the knifeless tape to get it right.

Oil Cooler

Well after the outside temps were getting up there, the Oil was again getting hot even with all the different ventilation I had done.   Looking around at other o-200 powered 750s most had an oil cooler.  The hardest part was finding an appropriate adapter to go under the Oil Filter.  I am on my second one since the first one was a leaky piece of junk.  Seems these are often called an ‘Oil cooler sandwich’ by the car people.  After i learned that name I was able to find several sources and got a good one now.  I think i got a 9 row cooler and some good sized oil lines.  Oil stays cool now even when air temps are in the 90s.  I even had to close off some of the airflow from the baffles keep the Oil temp up and the CHT down.  No leaks and plenty of flying now.  Up to 35 hours now so getting close to done.

High Oil Temps

The oil temps have been creeping up the longer the flight.  Since it was rising slowly it seemed like it must be inadequate flow though the cowl.   I cut a hole just under the spinner and made a small deflector in from of the exit on the bottom.  This helped but it was still getting up to 190 after about 30 minutes.  This isn’t a problem except that it was 40 degrees out and its going to be too hot when the summer comes.  CHT are looking good about 350 and don’t get worse.  I am resisting installing an oil cooler as many similar aircraft don’t need one and it adds another point of failure with flexible oil lines etc.  I ended up making a bigger front intake and used the baffles from an ercoupe to make a good sized channel back to the oil tank.  Its still showing hotter than I would like in this weather but it stabilized at 175 on a 36 degree day.  I may open up the bottom of the cowl some more but I think I should wait to see how it does when the outside temperature comes up some.  Until this last change, the oil temp never stabilized it just kept rising the longer it flew.  Now it stops and only goes up or down a little depending on the throttle setting.

More fixes and Tweaks

More flights and more things to fix.   Started getting a pretty big drop on one mag.  I decided to send it off for a 500 hour inspect and refurbish. The other mag was an older Eiseman and it would start missing when it was hot.  Decicide to just bite the Bullet and buy a brand new Slick.  Mag drop is low now and both are the same.    In all the messing around with the mags, I got a backfire that jammed the starter clutch.  The darn clutch cost as much as a new lightwieght Air-tek  so guess whats on there now ?  Guess I should have just spent the money on new accessories (mags and starter) from the start instead of trying to get the old ones to work.

The heavy wing is finally fixed.  Ended up just bending the trailing edge of the flaperaon a little using a 3 foot 2×4 with a groove in it.  Worked great and she now flies hands off.

2nd flight

Well she flew again, so it wasn’t a fluke. The 2nd flight was quite a bit longer, over a half hour. The engine still ran well but Dave reported that it was pretty rough at low throttle with carb heat. The “heavy” left wing was very much improved but still present. The AS was now reading correctly and agreed with the 100mph wot. Part way into the flight the battery voltage started dropping a bit, so that is a new issue.

Inspection after the 2nd flight revealed a leaking voltage regulator. What looked like tar was leaking out the side and it stunk. I replaced it with a new unit and the alternator then showed a steady 14.1 charge. The previous one would vary from 12-13.5 so I think it was defective from the start. I adjusted the idle stop and mixture some which improved the idle behavior. We will need to recheck the carb heat in flight again but on the ground it acts as it should. I talked to several people about further measures to correct the heavy wing. As you might expect I got several different answers. At this point I am going stay away from adding a trim tab. This may become necessary but the suggestion was to try other methods first. The most prominent suggestion was to squeeze the trailing edge of the light wings flaperon. This is to narrow the airfoil and provide less lift by the control surface. I also decided to add a couple more mm of washout on the left by filing the bolt hole a little. Both of these changes were made easily. So we need to check: heavy wing, alternator voltage, idle and carb heat on the next flight.

FIRST FLIGHT !

First flight November 2nd.

My friend Dave was the test pilot. It went pretty well but the need for some adjustments were obvious. There was a strong roll “left wing heavy” and the airspeed stopped reading at 50 mph. The engine ran well and he was seeing gps speeds 115 and 95 (downwind/upwind) so it looks like the prop pitch is right on. RPM was 2650 wot.

I re-checked everything with a digital level and was happy to find all was in alignment. I did find that with my stick centered that I had 2 degrees more down on the right flaperon. A few turns on the rod end brought this back into place. Doing some research on the builders site it became obvious that a “heavy” left wing is common and that it is often corrected by reducing the cable tensions on the elevator. The asymmetry in the control design will increase stick pressures when rolling right and slacken some to the left. Reducing the tension just enough can minimize this effect. After experimenting with tensions I found that I needed a little more cable length to give a good number of threads in turnbuckle barrel so I made up a new cable assembly that was a half inch longer. I just replace the shorter end by the bell crank so it was no big deal. Much happier with the adjustment range now and the stick move right with almost no tension increase. While thrashing around trying to sleep, I figured out that the AS indicator must be leaking on the pitot side. If it were plugged it would have been insensitive at low speeds but it wasn’t. Pulled the gauge and took it for a test drive in my car. It read fine so it had to be the pitot line. The next trip out to the airport, I started tracing the line an sure enough, it was not full engaged in the quick connect at the wing root.

 

Flyin Papers!

Here is Frank(DAR)handing over N750XZ ‘s special air worthiness certificate. Now it IS an airplane and not just a bunch of parts. Should be some air under those tires soon!