Test Flights — Sonerai With Jabiru Engine Upgrade to 3300

November 2018

You may remember Bill Evans’ series of articles about fitting Hoerner wingtips to his Sonerai. The purpose of installing the wingtips included using them as auxiliary tanks since the 3300 uses fuel faster than the 2200 it replaced. Here is an account of his flight testing. Be sure to check out the video link below. — Ed.

Test Flight No. 2 September 12, 2018

During this test flight, which is largely a repeat of the first test flight, I recorded as much flight and engine data as possible.

The first takeoff was at 1300 Eastern. It was measured at 1,100 feet for both takeoffs on this flight. As soon as I was airborne, I started a climb test at 85 mph. It took 100 seconds to climb 1,000 feet. The ceiling prevented continuing climb tests higher, so I reduced altitude and started a second climb test at 75 mph. It took 60 seconds to climb 1,000 feet at 75 mph. Thus, best rate of climb is 1,000 fpm at 75 mph with 125 hp. I’ve got to say, the Jabiru 3300 engine pulls really hard at 75 mph. I found the nose to be quite high.

At the top of the 75 mph climb, the rpm was 2800, cylinder head temperature (CHT) was 275 degrees F, oil pressure was 40 psi, and oil temperature was 195 degrees F.

I set the cruise at 100 mph and redid the maneuvering tests described in the first test flight. I did a rate one turn at 100 mph and noticed it lost some altitude so I adjusted the power until it would hold altitude in that turn. The rpm to hold altitude is 2400. The Jabiru engine won’t stand being run between 2000-2400 rpm due to vibration. It was very easy to coordinate the rudder to keep the ball centered in this turn. I reversed the turn, and the power needed was the same. As it turns out, there is no actual need to run the engine between 2000-2400 rpm. All the controls are very light, needing just two fingers and two toes.

CHT at 2400 rpm was 225 degrees F.

The max speed test was duplicated at cloud base, and once again it reached 3300 rpm and 150 mph. I leveled the nose and reduced power to 2900 rpm, which is about 75 percent for this engine. Airspeed showed about 140 mph — I would like more. I started this test adjacent to Lancaster Airpark Airport (CLA6) flying east. Two or three minutes later I looked down, and I was over Valleyfield more than 30 kilometers away. It’s hard to believe it covers ground that quickly, but it does.

I had been asked to record the engine temperatures after descent to circuit height, and I did. I descended 1,000 feet at 120 mph and 1200 rpm. CHT showed 200 degrees F, oil temperature showed 180 degrees F. Oil pressure showed 30 psi. Good enough. Below 1200 rpm, oil pressure will drop to 20 psi. At 400 rpm, oil pressure is 11 psi. The low-pressure light stays off unless one mag is switched off at 400 rpm.

The propeller does not develop any significant thrust at 1000 rpm so one can land with that. I set minimum idle at 400 rpm because I thought I’d need it to land, but I didn’t.

I entered the airport area at 2400 rpm and stayed with that until I was established on final. Once I was on final, I had to reduce to 2000 rpm to get down to 80 mph. Descent rate was perhaps 300 fpm. Over the fence, I eased the throttle back more (maybe 1800 rpm) and got it to hold at 75 mph.

My first landing was not corrected enough for a light crosswind and it was a bit squirrely on roll out but held the runway. I touched down maybe 1,000 feet down the runway and had to brake.

The second landing was within an inch of the centerline at 75 mph and rolled out very nicely. On the second landing, once I crossed the numbers I pulled the throttle to idle, and the aircraft settled in quickly. It was a three-point landing, very smooth. The point of touchdown was staked and measured at 500 feet. I hasten to add that I always try for a Navy/tailhook-type landing. This landing was the exception. I did not need brakes and was at taxi speed at 1,200 feet — the threshold on a 2,400-foot runway.

Since I was getting airborne halfway down the runway on takeoff, I tried to level off after liftoff and build up speed in ground effect, then pulled up before the tall trees at the end.

The photos I’ve shared alongside a previous article (“Sonerai Cowl Flap,” June 2017) show a really big cowl flap — 12 inches by 12 inches or larger. Since the engine temperatures are so mild, I am considering cutting off around half the length of that cowl flap. Thank you to all who helped.

Most of this flight was captured on video by a camera in the chase plane, and an interview on the ground.

Test Flight No. 3

The purpose of the third test flight was to establish and record engine reliability data. In flight, things were better than they were on flights one and two. I was up for an hour and recorded engine data at every throttle setting from 50 percent to 100 percent. The cloud base was broken at 3,500 feet.

In flight, if I chop the throttle to idle, the engine does not quit, so that is better news. But it does want the pump off at idle.

I redid all the engine data with the aft tank selected. With the pump off, I lose between 25 rpm at 70 percent power and 100 rpm at full throttle. Thus, I know where (rpm) the engine wants the pump on.

The throttle tends to close if left unhanded so I’ve tightened the pivot again and will work at a spring to move it toward takeoff as it moves toward idle now.

I had to memorize the engine data as there was no chance of taking notes in flight. No chance of map reading either.

I did manage to get over Valleyfield and, as no one was flying there, did two low-and-overs at speed. Even with the throttle setting low, the Sonerai built up speed quickly in descent. I got it down to around 25 feet over the runway at 140 mph and then opened the throttle and accelerated to 155 or 160 mph. When I pulled up, it climbed to 1,000 feet before the speed was converted to altitude. Great fun, that.

I was on the main (rear) tank for that, and during one beat-up the rpm fell to 2400. Thus I think that gravity is able to overcome the facet pump to some extent. The lesson is don’t pull up so high that the rpm falls off. I might have been at 60 degrees nose-up. I was not pulling much g as the blood did not drain from my head.

I’m guessing that I burned between 5 and 6 gallons. Hopefully it’s closer to 5. The main tank is 10 gallons, and it was down to reserve (45 minutes) when I got home. Thus, I’m not sure how much fuel was in it at takeoff. I might need the tail raised to level to refuel.

I tried to get my speed back to 75 for landing, but felt I was fast. It did a wheel landing, which made me nervous. Once I had the tail down I needed to get on the brakes hard the rest of the runway.

For that matter, I found the takeoff run long. But I find all my Sonerai takeoffs long.