Zodiac CH601 XL
A Plans Built Experimental Airplane
Daniel Dempsey
Updated: June 13, 2015
Flight Testing

On this page I'll record the flight testing results.

Flight Test Plan

Flight Test 1 (First Flight!) Notes:
June 6, 2014
Hobbs at start 7.5 hours.
The plan was to fly above the airport for about a half hour while investigating flight characteristics necessary to land the plane safely.
That plan was quickly abandoned soon after take off.
About 4 minutes into the flight as I was climbing out the engine started loosing power and got very hot.
I saw 450 degrees on the CHT guage and 280 oil temperature. The EGT gauge was not working.
Smoke started entering the cockpit, leaking from around the cabin heat box.
The oil pressure dropped to around 15 to 20 psi. I made a quick return to the runway.
Total duration of the flight was 6 minutes.
Luckily the airplane was very controlable, and I made a smooth landing.
The engine ran smoothly on my taxi back to the hanger.
Hobbs at the end of the test 7.9 hours.

Diagnosing the Problem.
What had gone wrong? I had taken panes in the Wide open throttle test to be sure the engine would function during a climb.
However the WOT test had only been about 2 minutes in duration, and my problem during flight developed after almost 4 minutes of climb.
I immediately started second guessing my plenum design, and my use of the stock Corvair oil pump.
I went ahead and ordered a high volumn oil pump that night from Clarke's Corvair.
A week later I was pulling the engine to install the oil pump.
The rear accessory housing had to be removed from the engine.
I also found that the new alternator had a twisted belt, such that it was going around the engine pulley side ways.
I think this was because the 2 pulleys were not well aligned.
Another thing I found was that dead stink bugs were clogging the cooling fins.

While the engine was accessible I did a compressiong check.
On the right side of the engine (cylinders 1, 3, and 5 all had 130 psi compression. That's good exactly what the Corvair maintenance manual calls for.
The other side was a different matter. Cylinder 2 had 90 psi, cylinder 4 had 130, cylinder 6 had 110.
The manual said there should not be more than 20 psi difference between cylinders.
I decided to pull the head on the side with low compression.
When I removed the intake manifold I figured out what had happened!
The gasket between the intake manifold and head had failed, probably during my climb out.
I had made this gasket out of rubberized cork. I wanted something that would be resilient enough to seal the imperfections in my intake manifold.
This had caused that bank of cylinders to run much too lean and possibly cause detonation.
Pulling the head confirmed my fear. When I started to untorque the heads I found there was very little torque on cylinder 2.
Once I got the head off I found the head gasket area at cylinder #2 had been sunken down.
The depth of the surface was 0.595, where on the other 2 cylinder gasket areas it was 0.575.
The copper head gasket had been driven into the aluminum head by 20 thousandths.

June 20, 2014
I made a hand tool today to fix my damaged head.
June 28, 2014
I added a quart an half to the oil capacity.
June 29, 2014
I resurfaced the damaged head.

July 3, 2014
I found that cylinder #2 was scored, so I've ordered a replacement from Clarkes Corvair Parts.
I decided to revisit my engine cooling set up.
I found this artical by John Thorp that was very informative.
Based on his artical I'm going to try to increase the amount of cooling air.
July 4th, 2014
Here are before and after photos.

July 20, 2014
The deeper oil pan required lowering the carburetor by about an inch, which necessitated remaking the brakets and intake manifold.
I elected to remake the manifold with aluminum tubing to save a little weight over the stainless steel being replaced.
I've purchased aluminum brazing materials from McMaster Carr to join the manifold pieces with.
One thing I realized when trying to align my alternator was that the belt I had been using was too wide.
It didn't rest far enough down in the harmonic balancer pulley groove, so I think that's why it got twisted.
I'm replacing the belt I had with a narrower and shorter belt.
This will help keep it a little further away from the motor mount.

August 29, 2014
The aluminum intake fabrication went badly so I went back to stainless.
Remade the intakes in stainless using materials from bathroom safety hand holds.
The engine is back in the plane, alternator has plenty of space around motor mount.
The intake pipe fits well.
I'm remaking the cooling air baffles to provide more cooling air.
I've found that the airfilter housing doesn't fit now that I've move the carburetor down an inche.
I'll have to modify it.
This is all taking a LOT of time, given that I can only get to the airport on weekends.

Here's a list of all the modifications I'm making before flying again,for complete, O for not complete:

Fix damaged heads
Openned up air inlets on nosebowl.
Openned up air exit.
Installed High Volumn Oil Pump.
Increased oil capacity with oil pan modification and deep oil pan pickup.
Larger oil pan also requires moving carburetor down 1", remake intake manifold and brackets.
Replaced air plenums with more conventional baffles.
Extend oily air vent tube into slip stream.
Move oil temperature pickup to better measure oil temperature.
Modify exhaust to aim it away from gascolator.
Seal the heat muffsthat I have around exhaust manifolds so that air doesn't blow upward and disturb airflow through the engine.
Add small NACA vents to allow air to cool fuel pumps and lines as well as coils, alternator, battery.
Adjust air filter housing to fit with space to move.
Use some exhaust insulation wrap to prevent heat from pipes overheating fuel lines.
Add some insulation to cowling blister to prevent it overheating, perhaps a small vent hole as well.
Fix the EGT gauge. This was working at one time, fixed broken wire.
Install the fuel/air intake manifold pipe with the proper high temperature gasket.
Install SCAT tubing between carb air intake and airfilter box to prevent air disturbing cooling airflow.
Lastly, I need to modify the left wheel pant to not rub the break caliper.
And after all the changes I'm going to have to do some ground testing, including a WOT test.

Sept 22, 2014
Today I made a temporary cover for my air baffles so that I can run the engine with the cowling off and not over heat it.
The cover fits much like the top cowling.
The engine was hard to start because the timing hadn't been set yet. Once I got it started and set the timing it ran strong.
I recorded the following temperatures after running the engine WOT for 2 minutes using IR hand held thermometer.
Engine ran 2600 RPM.
All temperatures are in farenheit.
Ambient temperature was 87 degrees.
CHTs: 1 322, 2 340, 3 326, 4 342, 5 306, 6 312
EGTs maxed out at 1400.
Oil pan registered 165. Oil Plug 185, Block 239. Oil temp reached 290 according to the oil temperature gage.

I have few minor adjustments I want to make.
First I need to shorten some of the spark plug wires now that they have a new route.
The engine ran on the lean side according to the fuel air mixture gage.
It ran between 13.8:1 and 14.4:1.
I've change the geometry of the mixture linkage in order to try to limit how lean it can go.
I may have over done it.
I am having trouble trusting the fuel air mixture gage.
I found after purchasing it that it's not meant to be used with leaded fuel and that leaded fuel will fowl it.
I just don't know how long it's good for before it gets fowled.
I had it out during the engine tear down and it looked clean.

Flight Test 2
November 08, 2014
Wind was South directly across the runway at about 10 MPH.
Outside air temperature was 65. Sky was clear.
Flew a short flight around the pattern.
The engine ran more and more lean as I climbed.
Climbed out at 80 MPH with RPM around 2500 RPM>
EGT was near top of the gauge 1550 degrees.
Oil temps were high.. 350 or so.
CHT was 350 or so.
Fuel Air Mixture showed 13.7.
Other issues include AOA or LRI not really working.. Shows very low reading even while in level flight.
Used full flaps on landing.
It got too slow and landed hard. Post flight review I found that the airspeed was at about 40 mph when I touched down.
I was also struggling with the cross wind.
One of the wheel pants was cracked.
Adjust linkages to get more travel. Make sure mixture travels all the way in.

Flight Test 3
November 11, 2014
Took a short flight around the pattern.
The engine continued to lean out as I climbed.
EGT reached 1500
Mixture was more than 14:1
I'm pretty sure that what is happening is that ram air is causing the engine to lean out, because this is not happening on the ground.
Try blocking off ram air.

Flight Test 4
November 23, 2014
Wind was calm and south, at about 5 mph.
Outside air temperature was 50 degrees.
Sky was overcast. Visibility was excellent.
I took a short flight around the pattern.
This time ram air was blocked off. While taxiing the engine was running very rich.
EGT remained at 900 and Mixture showed around 10:5 with mixture set all the way lean.
THis time as I climbed out the engine did not overlean. The engine ran well.
I climbed out at 80 MPH with 2500 RPM. EGT was 1200 and CHT was 260.
I don't think it was making full power. Maximum RPM on climb out was about 2600 RPM.
Achieved 120 MPH briefly just as I leveled off, but pulled back power as I was in the pattern. I think this is the final test for the SU carburetor.
It's taking too much fiddling with, and doesn't have the control I want.
Also found that the pilot side strobe was not working.

I've bought a new Marvel Schebler MA-3SPA carb from aircraft spruce... price $1500.00!
Back to fabricating manifolds, brackets and linkages.. not to mention heatbox and airfilter housing..
Here's a picture of the new carb with the old SU behind it.
It's going to be tight squeeze!
Dec 20, 2014
Here's a picture of the carburetor manifold flange.
Febuary 24, 2015
Here's a picture of the new Filter housing.
March 10, 2015
Fixed the strobe, it need a new strobe sender unit. Pain in the neck to access.
April 3, 2015
Tried to start the engine. It wouldn't start! Burned the battery down 3 times.
April 10, 2015
I asked the local A&P what I should do since my engine won't start with the new carb.
His advice, send it back!
I'm glad I decided to ignore his advice. I gave the idle mixture control 3 turns out (more rich) and it started right up!
Now to figure out how to tune it.
Now I'll need to do some ground testing before it's ready for the air again.

April 11, 2015
Got advice on how to tune the carb.
Engine should idle around 750 RPM. For now I'm adjusted mine to 800 RPM to be on the safe side.
I can back off on it later when I'm comfortable that the engine won't shut off on final approach.
With the engine warmed up and idling there should be a slight RMP rise of about 50 when you pull the mixture all the way lean.
That's what mine is doing now.
Did a full power test for 2 minutes at full rich. Nothing got too hot.

Flight Test 5
April 12, 2015
Finally back to the air after the new carburetor installation! Wind was calm and south, at 5 mph.
Outside air temperature was 64 degrees.
Sky was clear. A beautiful day!
I kept close to the airport.
Ascended to about 4000 feet above the field and circled the airport several times.
Engine ran at 14:1 mixture ratio on the ground and in the air. EGT got to 1350 and stayed there.
CHTs rose to a maximum of about 320 degrees F.
Engine remained at 14:1 for the duration of the flight with the mixture set at full rich.
The engine ran well and was very smooth. Climb was at 2500 RPM and 500 FPM.
Upon leveling out the engine speed increased to 2700 RPM and the airspeed climbed to 120 MPH.
I throttled back to about 2200 RPM and maintained a cruise speed around 100 MPH.
The performance was much like the last flight with the SU.
I was carrying more fuel this time with about 3/4 full left and right main tanks, and aux tanks empty.
I made a better landing this time. I think the fact that I didn't have to concentrate so much on mixture control was a help.
Total duration of the flight was 40 minutes.
I forgot to turn the camera on. I'm adding "camera on" to my preflight check list.
Post flight inspection found no issues, but is it running to lean?

April 14, 2015
Got some advice from Ron Lendon and Bob Martin on how to test if the engine is running too lean.
With the plane tied down, and engine warmed up, run the engine at full power at full rich.
Pull the mixture toward lean and there should be a slight RPM rise.
Hold it there for a few seconds and record the EGT. Don't keep the engine lean like that for more than a few seconds.
If the RPM rise occured it isn't too lean.
In my case I'll probably do it more than once so that I can also record what the fuel air mixture says at peak.
Theoretically, it should be 14.8:1.
Next time I'm at the airport this will be the first thing I try.

April 17, 2015
I ran the full power test. The results are, it's too lean!
But I think I knew that. The big question I have now is, have I damaged my engine AGAIN, by operating it in this condition.
When I ran the test at first it was making 2500 RPM. The EGT reached 1300 degrees. The Fuel Air ratio was 14.0:1.
When I leaned it to find peak, it immediatly started sputtering, and I quickly returned it to full rich.
There was no slight rise in RPM before it sputtered.
It must have been operating at or lean of peak.
What I noticed, and is really bothering me is that when the test ended I was no longer making 2500 RPM.
It was slightly less, around 2450. The fuel ratio had risen to 13.8:1, not sure how to explain that.
So now I wonder if the test caused it to detonate enough to blow a head gasket, again!

April 18, 2015
I've got the carb out and appart, and have ordered new gaskets from aircraft spruce.

April 19, 2015
I did a compression check and all 6 cylinders are between 145 and 150 psi.. This is good!
I drilled the carburetor nozzle from 0.092 to 0.095 inches.
If we do the math PIxRxR we have 0.00665 sq inches before and 0.00709 sq inches after.
Which gives it 1.066 of the original area, or an extra 7%.
I've ordered gaskets from ACS.

April 25, 2015
I got the gaskets I needed and put the carburetor back together and reinstalled it.
Took all day. The weather was too poor for testing.

Flight Test #6
May 2, 2015
Ambient 75, baro 30.03 calm, duration 1 hour Engine Power was good. WHen I leveled out at about 4000 feet above field elevation the RPM went to 2700 and speed increased to 120 MPH.
CHT was 300, EGT reached 1400.
Mixture was showing around 14.0:1.0, but I'm not sure I trust it now. The EGTs and CHTs are good. However it does seam like there is no room for making it leaner.
Oil pressure was good, maintained 50 PSI
Climb performance was good, about 500 to 600 FPM.
AIS reached 140 when I was accidently in a slight descent while trying to get it trim level.
Radio is working well.
Aileron rigging is good
Flaps are good.
Things that aren't working right.
1. My landings aren't pretty (saying it mildly).
2. Altimeter is way off. Can't even make it read field elevation of 480. At the correct baro, it reads 200 feet too high.
3. Oil temp is a concern. It reached about 280 to 290, then cooled during a long descent.
4. Elevator rigging is a concern. Hard to trim for level flight. I think I had most of the trim in and still was nose heavy.
5. GPS never acquired satellites so I went without it.
6. LRI is not working at all.
7. There is now a small nick in the propeller near the tip. Must have picked up piece of gravel.
8. It was clear I need a check list. I left the transponder and video camera off.

Flight Test #7
May 3, 2015
It was a beautiful evening and even though I haven't fixed all the issues found on the last flight I took a short flight.
Ambient temperature was 75, and winds were calm. This time oil never got above 240 but the flight was shorter and I didn't climb as high.
CHT and EGT were good.
I confirmed that I do have a nose heavy condition. I'm able to trim it out with most of the trim.
The GPS was working but I gave it a long time to acquire satellites. I just replaced that expensive garmin battery 8 months ago!
It was the most uneventful flight to date, but landing was still a stinker.
LRI problem, I took a closer look at the drawing and it appears I've got it plumbed backward, with high pressure going to the bottom hole.
THat's what my intuition thought was right, but evidently is wrong!
Having an LRI might help my landings, since I don't have a stall horn.
I'm thinking more about my oil temp issue too. I'm not even sure I have an issue. The gauge has these tick marks: 140, 190, 210, 230, 320. With only a little space between 230 and 320.
I might try a different gauge, with a better spread.
Repeating my list of problems, here's my plan.
1. Landings. Fixing the LRI might help.
2. Altimeter. I found info on how to adjust it.
3. Oil. I'm going to get a new gauge and also use my IR thermometer to see if I can verify it.
4. Elevator Rigging. I may live with this for now. Solution may be to give elevator some negative angle of attack but that's a substantial mod.
5. GPS, I saw a page in the menus that let you select what happens when power is turned on. One of the selections was "charge battery". I need the read the manual about this, maybe I've got it set so that it doesn't charge.
6. LRI, swap the 2 lines, maybe it will fix it.
7. Propeller Nick. Live with it for now.
8. Check List. I made one and will take it to the plane next time I go.

May 7, 2015
I found information on the altimeter HERE.
Applied the fix tonight. Looks like it's good to go.
Swapped the AOA lines. I'll have to fly it to know if it fixed it.
I've read up about the issue I have with my Garmin 296 GPS taking a long time to acquire satelites.. Evidently it's common.
The issue is that there's a little internal watch battery that goes dead over time.
If you're using the GPS everyday it tends to stay good.
If the internal battery has to be replaced you can read about replacing it HERE.
I've also read about fixing the main battery pack when they nolonger charge.
I probably could have fixed the one I replaced.
May 8, 2015
My 8 month old Garmin GPS 296 battery is NOT taking a charge, but it is remembering the time and date now.
I'm trying a force charge as described HERE.
Nothing to loose!
I'm also considering opening up the carb main jet a few more thousandths. It is still running on the lean side (I think).
The Fuel Air Ratio gauge is saying about 14.0:1.0 on climb out, and EGTs are hovering around 1400, with the carb full rich.
I'm going to try 0.0975, originally 0.092, which is 12% larger in area than the original orafice.
May 10, 2015
I wasn't able to restore the Garmin Battery, so I've purchased another one. Cost: $43.00!

Flight Test #8
I replaced the Oil Temperature gauge with a nice Stewart Warner gauge from Summit Racing with a much better spread.
I've opened the carb orafice up to 0.0975.
I've swapped the lines on LRI
I've made myself a pre-flight checklist.
The weather was hot and hummid. Ambient temperature around 90.
I was sweating profusely until I started rolling down the runway.
The ventelation works great to cool the cockpit.
The plane flew well although as I've mentioned earlier most of my elevator trim is used up.
I flew for about a half an hour at 3500 feet above and near the airport.
Oil temperature was still pegged, even though after the last flight I didn't really believe it.
All other temperatures where looking great. CHT was around 320.
EGT was 1200.
The carb mixture problem looks like it's finally solved!
I was making around 2600 RPM in the climb at close to 700 FPM.
The RPM would come up to about 2700 once levelled out.
In level flight I pulled the throttle back to about 2400 RPM and was making 100 MPH IAS.
I returned to the airport with oil temperatures remaining much to high (at least on the gauge.
My landing was OK, but not great.
My manual flap actuator is working very good.
Despite swapping the lines to the LRI it still wasn't working.
I noticed when taxiing that there was a slight skertch, skertch, skertch noice that I could hear only if I took the headset off.

When I purshased the new Oil temperature gauge I also got a new sensor made for the guage.
I decided to replace the sensor and try again.
The new gage sensor was longer than the old one, so I had to turn the angle slightly to make it fit in the space I had.
In order to make that adjustment I had to loosen an an fitting for the oil line that goes to the 5th bearing.
After making the adjustment I found that one of the wheel pants had been rubbing, so I removed it opened it up a little more
I also adjusted the LRI probe to have a steaper angle to the wing.

Flight Test #9
I hate reporting this because it was an almost catastrophe :(
I took off with the intention of repeating the last test, to check the oil temperature gauge. I was keeping a close eye on the oil temperature as I climbed.
Once I got to pattern altitude I noticed the oil pressure warning light come on.
The oil pressure was at ZERO psi!
I did a very tight pattern back to the field.
I completely missed my turn to final (overshot it) and would have normally done a go round.
I knew I probably had only one shot at a landing so made the correction and got lined up in time.
The engine ran normally (with zero oil presssure) as I taxiied back to the hanger.
I didn't even hear any valve rattling like you might if the lifters weren't pumping up.
When I got to the hanger I saw a big oil puddle where I had done my run up!
I knew immediately what had happened.
I had forgotten to retighten the fitting to the oil line when I had adjusted the angle of the oil temp sender.
Here is the lesson:
The entire bottom of the plane was covered in oil.
Of course the question was, had I ruined the engine?
The entire flight it ran completely normally eventhough no oil pressure was showing.
After cleaning up the oil mess from the taxiway and the plane, I put oil back in the engine and did a full power run up for 2 minutes.
The engine ran the same as it has been. I could detect no change in performance.
It took 4 quarts to fill the oil resevoir, which indicated I had a quart and half left.
I drained the oil again and removed the filter.
I cut the filter open and found NO metal shavings using a strong magnet.
After replacing the oil I wiped all the remaining oil off of EVERYTHING as best I could.
With the cowl off and plane tied down, I did a run up to check for leaks.
Finding none I reinstalled the cowl.
Oil continued to drip from various places for days.
Before the plane was completely back together the weekend was over.
Flight Test #10
I have a deal worked out with my wife that I spend every other weekend working on the house trying to get it ready to sell.
The first chance I had to fly was on June 5, but I wasn't comfortable with the weather ( a bit gusty ).
Flight test #10 comes exactly one year to the day since N978ER's first flight!
The weather was excellent. Ambient temperature was 78 degrees. Winds where calm with about 5 knot crosswind.
I put 5 more gallons of fuel in each of the main tanks, so that they are both about 3/4 full.
After doing a thorough preflight, I took off and climbed to 3500 feet.
All the temperatures were in the green!
CHT was 310, EGT 1200, Oil Temp 230.
Oil pressure was good. Starts around 50 psi when it's still cold, then drops a little as it gets hot.
The engine was making about 2500 on climb out at around 600 to 700 fpm.
The main goal was to test that the engine was not going to quit after the stunt I had pulled.
Other than that I'd try to verify my instruments and finally get around to doing some stall tests.
I flew back and forth for one hour an easy glide back to the airport.
My AOA or LRI (if you prefer) was finally working good!
I tried a stall clean by powering all the way back and pulling the noseup.
It was loosing altitude fast but there was never really any buffeting until I got down under 40 MPH.
It recovered easily with a little nose down and throttle.
The LRI showed it just falling out of the yellow band during the stall.
The landing was my best yet.
I came in a little faster, keeping my speed about 80 MPH on final.
I used 2 notches of flap, then pulled the power all the out about a 500 feet from the numbers.
I flared just above the runway and let it settle down on it's own.
It touched down around 55 MPH. I managed to keep the nose wheel up for another hundred feet or so.
Flight Test #11
I went flying after work, getting the airport at about 7:00 PM. Conditions were perfect. Very little wind. 75 degree temperature and no other traffic!
This time I zoomed my video camera in on the flight instruments to try to get a set of data to compare between GPS and other instruments.
The flight was uneventful! You don't know how good is to say that!
I flew for a half an hour just long enough to collect some data and returned to the strip.
I made another OK landing.

I reviewed the flight video, but couldn't read the EFI or the GPS very well and the Altimeter was making no sense to me. Here's some somewhat incomplete data.
0 200 200 205 0 0 0 490 480 ? run up
500 260 260 245 70 68 66 1650 2200 ? climb
0 85 90 102 85 100 75 1750 3000 3200
0 90 100 115 80 95 76 ? 3012 3200
0 55 55 50 80 95 72 ? 3006 3200
-300 265 250 248 50 50 43 ? 2950 3100 stall
-300 280 270 255 80 75 74 ? 2680 2800 stall recovery
-100 125 130 155 85 95 79 ? 2100 2300
-800 325 315 285 105 100 90 ? 1500 ? entering pattern
-300 270 270 255 95 80 76 ? 1250 1500 in pattern
0 90 92 102 60 65 60 490 490 720 touch down

I could make no sense out of what I was seeing on my altimeter.
I went back and reviewed again how to read it, and found I had it set very wrong!
Instead of being set to 490 feet (field elevation) I had it set at 34,900 feet!
I also noticed in the data the EFI speed was low.. Came to find out I have it set to knots, not MPH.
Correcting for the units problem makes it agree perfectly with ASI.
The differences in ASI and GPS are mostly due to wind speed and direction.
The big surprise was that the EFI_C (electric compass) is apparently way off in some headings.
The GPS coarse was agreeing pretty well with vertical card compass (VCC). After relearning how to read an altimeter I went back to the airport and set it correctly.
I also found it was easy to change the units in the EFI to knots and also to set the Barometer in the EFI so that the field elevation is correct.
I'm not going to worry about the EFI compass for now.
I was able to use the timer on the video and increase in altitude to verify that the Vertical Speed indicator is correct.
I noticed while doing an inspection that there seems to be oil dripping still (possibly from the oil pan gasket), but it could be residue left over from the near catastophe.
I was using a flash light and looking from the air outlet at the bottom of the cowling and could see oil drops at the end of a motor mount bolt.
It looked as though the motor mount had compressed enough that the oil pan may be touching or nearly touching the motor mount metal.
I'll try to space that up, and perhaps replace the mount rubber, before the next flight.

June 12, 2015
I went to the airport to uncowl the engine to look for the source of the oil drip.
I found nothing obvious, but was concerned that there was very little space between the oil pan lip and the engine mount at the bolts.
I could also see where my new heat box is rubbing the bottom of the cowl.
I made (4) 1/4" aluminum spacers to raise the engine up and installed them.