Better To Do Today…
DON’T PUT OFF the maintenance that is needed today before you go flying, or you may not be flying tomorrow.
That’s the moral of this installment. Have you ever had that sinking feeling, knowing that what you are about to do is wrong, but you do it anyway and then you later suffer the consequences?
We can all most likely say, been there, done that!
On a cold fall day, the owner of a Sonerai II LTS wanted to go flying one last time before he pulled his cylinder heads off for a valve job over the winter months.
For the last 20 flying hours, he knew that one of the exhaust valves needed to be serviced, as he stated that he had no valve adjustment left with the rockerarm/valve-adjusting screws. When he pulled the prop through, he could clearly hear the exhaust valve wheezing.
Unfortunately the desire to go flying was a stronger emotion than completing the needed maintenance. So our pilot departed Dupage airport in Illinois and headed to Janesville, Wisconsin, for a late fall breakfast. He arrived there safely, ate breakfast and then headed back to the Dupage airport, when it happened. Bam! All hell broke loose.
In an instant, the aircraft was vibrating so violently that the pilot thought the wings were going to shake off. His forward visibility went to zero as hot oil seeped through the cowling, covering the canopy and jelled, blocking his forward visibility. He could only see through a small area out the side of the canopy. Smoke was also filling the cockpit.
In an instant, he switched the fuel off, turned the engine off and was greeted with the sound of silence, complete with fear and panic. As he searched out the side of his canopy for a place to land, smoke continued to trail from the aircraft.
Losing altitude, he spotted a vacant road for the inevitable emergency landing. Lining up on the road, the wheels touched after what seemed like an eternal flare. Unable to see forward, he did not see the curve in the road that was rapidly approaching.
The aircraft, still traveling at 40 to 50 miles per hour, ran off the road and came to rest in a ditch, crinkled and crunched—a total loss. Thankfully, the pilot escaped with only a few minor scrapes. The engine installed in the aircraft was a 2180cc VW conversion that the pilot had built up with parts from a variety of vendors.
It had a total of 212 hours on it at the time the exhaust valve failed. The compression ratio was 11.5:1, as measured after the accident. 100LL avgas was used exclusively. The high compression ratio was certainly a contributory factor, leading to the valve failing and the subsequent accident.
The high lead content of avgas is what caused the valve to leak in the first place, i.e., lead buildup between the valve face and the valve seat. Photo A shows the line up of valves that were removed from the cylinder head. You may notice that the exhaust valve on the left is missing the valve head. It was never found!
You can clearly see which valves are the exhaust valves in the photo. They suffer a tremendous punishment in any engine. The exhaust valves were a one-piece stainless steel Manley exhaust valve—the best money could buy at the time. Shown in Photo B is a close-up of one of the surviving exhaust valves.
It’s hard to tell in the photo, but the valve had eroded about .040″ in the neck area, just above the area where the white coating ends. Additionally, the sudden engine stoppage caused the valve to bend slightly. This is only a presumption, however, as I have seen valves bend in other engines when they stop suddenly.
The damage done to the cylinder head is shown in Photo C. The spark plug had been sheared off by all the debris flying around in the combustion chamber. Hell has no fury like a broken exhaust valve head on an unscheduled suicide mission.
Photo D shows the external damage done to the engine case and cylinder before the engine was pulled down for examination. If a picture is worth a thousand words, you know the rest. The pilot was very, very lucky that he did not have an engine fire to contend with along with everything else.
Just imagine for a moment, you have a steel connecting rod thrashing around unchecked, beating against the magnesium engine case and cylinder, 3000 times per minute, destroying everything in its path. Magnesium is a very flammable material! The extent of damage done to the connecting rod and engine case is shown in Photo E.
You may make a mental note that the oil cooler location on top of the engine is capped with a block-off plate, meaning there was no oil cooler installed on the engine. Imagine the force it takes to bend a connecting rod like this!
The force was so strong that it even wiped out the top left cylinder head stud. What was left of the pistons is shown in Photo F. The valve head that broke pounded a hole through the #1 piston on the left.
The piston then separated from the connecting rod, welding itself in the cylinder. With all the debris flying around inside the engine, some of it finally found the opposing #3 piston and rod. You can see that the #3 piston had failed also.
Pistons #2 and had to have the wrist pins pushed out, as the lack of oil for just a few seconds seized the wrist pin to the piston. VW’s are supposed to have a floating wrist pin in the piston. Photo G shows some of the damage to the internal engine.
The camshaft gear had teeth broken away. This happened from having metal trapped between the aluminum drive gear on the camshaft and the steel drive gear on the crankshaft. Look at the first two connecting rod journals on the crankshaft.
The rod bearings are welded to it. The #4 main bearing, just behind the prop hub was also seized on the crankshaft. At the bottom of the photo, just below the camshaft, you can see some of the metal debris that was in the engine.
The #1 connecting rod is shown in Photo H. The rod is standing up by itself as if the rod bearing were welded to the crankshaft. The #2 connecting rod is also stationary. You can see the discoloration to the crankshaft, giving a clear indication of how hot the crankshaft got in the few seconds it took the engine to rip itself apart.
The stud side of the engine case is shown in Photo I. This side of the case held cylinders #1 and #2. The #1 connecting rod welded in an instant to the crankshaft and relentlessly pounded the engine case on both the top and bottom of the case, creating additional clearance holes.
The top of the case also had a small hole worn through from the rod as it flailed around freely for a second or two before being welded to the crankshaft. Photo J shows the studless side of the engine case.
Although the damage was not as severe as it was to the stud side of the case, the rod still ripped away the top of the engine case after it was separated from the piston and allowed to rotate unrestricted for a few brief moments in the engine case. Also notice the debris in the oil sump area of the engine case.
Our pilot escaped from this accident with a new respect for not putting off known and needed maintenance that should be done today, and not waiting to do it until tomorrow. Not all deferred maintenance decisions have the dire consequences as depicted here.
VW valves have been described as a weak link in the engine. This is because in the Beetle, the #3 cylinder sits behind the oil cooler in the shroud and runs hotter than the other three cylinders do. VW addressed this by slightly retarding the timing to this cylinder to have it run cooler.
In an aircraft conversion you don’t have this problem, as nothing is obstructing air to the cylinder. The valves used in conversion engines are stainless steel or a standard two-piece welded valve and will give hundreds of hours of service provided the engine is maintained and service is performed when needed.
At a minimum, you should check your valve clearance every time you change your oil. This is recommended at intervals of 25 hours. If you are running 100LL avgas, it has 2 grams of lead per gallon compared to 0 grams per gallon for unleaded premium fuel. The VW engine does not need lead to operate.
Older VW engines had cast iron valve guides that required lead for lubrication. Modern silicon bronze valve guides do not need the lead for lubrication. Avgas has almost four times the lead content of the older, leaded auto fuel we used to purchase.
The main drawback to using 100LL avgas in the VW is lead buildup on the valve face and valve seat. We have seen exhaust valves leak in as little as 10 hours of operation and the cause is almost always lead buildup, caused by the use of 100LL avgas.
If you notice a valve leaking and it’s not out of adjustment, it must be taken care of immediately. One of the best ways to tell if a valve is leaking is to do a differential pressure test, or leak-down check.
When you do a leak-down check, don’t do it with a cold engine. Your engine doesn’t care what it’s doing when it’s not running. It should be close to operational temperature when a leak-down check is performed.
Having an exhaust valve break is not a common occurrence. This is the only example I have seen of a valve breaking in an aircraft application in over 30 years. And, it was 100% preventable!
CARRYING THE LOAD
ONE “MAGNUM PLUS” TO GO
The IS 128 M2 motorglider out of Rumania is a BIG machine, spanning 57 feet! Of all metal construction with fabric covered wings and tail surfaces, the Lark carries pilot and passenger side by side under a spacious sliding bubble canopy and turns in very respectable soaring performance. Don Hall of Borrego Springs, CA has owned his Lark for about a year now. While happy with the airplane, he has been concerned about its sickly rate of climb particularly on a warm day.
I first met Don Hall when I happened to be at Eloy Airport and there sat Don’s big Lark on the ramp in front of the HAPI Engines’ hangar. Don was busily removing, the 1700cc German powerplant.
When I approached Don to inquire about his airplane and what he was doing, he said that he was removing the German and having the HAPI people completely overhaul it and up grade it to their Magnum Plus configuration.
With the Magnum Plus he hoped the rate of climb would go up at least enough to give it a decent rate of climb and get it out of the marginal category at higher field elevations and density altitudes.
Don said that his friend, Tom Stansbury, airport manager over at Borrego Springs had told him to get in touch with HAPI if he needed more horse power in the glider, so he was over here pulling the engine out so that HAPI could do their magic on it.
I shot a few pictures of Don working on his airplane and then went in side to talk to the Taylor family. As usual, HAPI was a beehive of activity with people in the machine shop busily manufacturing parts for the production manager, Patrick Taylor and his ace mechanic, David Roberts, in the engine room to assemble into the various models of HAPI engines.
The last time I was at HAPI the Magnum Plus was not yet in production, though I did have a chance to fly behind one in the Protoype Mark II Dragonfly. HAPI’s Magnum Plus is so far removed from a “Volkswagen conversion” it seems almost unfair to call it a Volkswagen anymore.
The only Volkswagen parts that HAPI is using now is a new Type 3 Volkswagen crankcase that has had a tremendous amount of re-machining done in HAPI’s machine shop and a stock VW Type 4 oil cooler that sits on top of the engine. Other than that, every part in the engine is either manufactured by HAPI or some other non-Volkswagen source.
These new engines that HAPI is producing have several unique and innovative new features on them that are not found in anyone else’s engine. Designer Rex Taylor and his son, Pat seem to really enjoy playing the “what if?” game.
They had found in their experience with Volkswagens in dune buggies and full time occupation of building Volkswagen engines for experimental aircraft over the past ten years that Volkswagen aircraft conversions had four major stumbling blocks.
The first stumbling block was the
Valve adjustment and valve life are always a problem in a Volkswagen air craft conversion due to the configuration of the stock automobile head that was designed to have a blower force feed the air through it.
People flying Volkswagen conversions have just simply learned to live with valves leaking, and constant readjustment of the tap pets as a fact of life. If you want to keep flying them, you have to keep adjusting them.
The Taylors put their heads together and devised a means to install hydraulic valve lifters in their engines and completely eliminated the need for periodic readjustment on the valves. The tappets are set once when the engine is built and the hydraulic lifters are installed then do not require any periodic readjustment at all. As a result, valve life is extended by hundreds of hours and, of course, the engine maintains a consistent high power output because valves stay sealed.
The stock automotive head was still a problem though, because the design was forty years old, the valves were too small for the big displacement engines that the flying public wants and, if made to produce lots of horsepower, they couldn’t dissipate the heat. The engines really didn’t breathe well enough, the combustion chambers weren’t shaped right to produce the kind of horsepower the Taylors were looking for.
About three years ago, a Southern California automotive racing equipment supplier started experimenting with individual cylinder heads for Volkswagen engines and the Taylors were supplied with a set of raw castings to see if there was a possibility of using them on aircraft engines.
They machined up the heads in their shop to the automotive specifications, built up a test engine and were really disappointed to find that the heads didn’t produce the extra horsepower they were looking for in the 3000 to 3500 RPM range.
Flow testing on the cylinder heads revealed the answer very quickly. The heads had been designed to run at from 6000 to 9000 RPM’s and the flow characteristics produced too much volume and not enough velocity at the lower RPM’s the aircraft engines have to work at, so the Taylor’s redesigned the inlet and exhaust ports, resized the valves and, in effect, created a totally different head that the Southern California company now builds to HAPI’s specifications.
It is now designed strictly for aircraft use. This is what HAPI calls their Magnum heads, that now produce a generous amount of bolt-on horsepower, solving the problems that were always inherent with the stock VW automobile heads used in aircraft applications.
But ignition was still a problem. You really can’t get optimum performance with fixed timing as is provided by a magneto. “What if” we had variable timing that gave us optimum timing at any RPM and power setting?
The Taylors designed and built a totally solid state electronic dual ignition that features automatic spark advance, fail safe double redundancy, with the system capable of running on either the battery or the alternator.
The result is super slow idling speeds because the time has slowed down, increased RPM and horsepower output at the top end, because the timing is advancing much farther than is normal with a magneto.
As a welcome side effect of the solid state ignition, which has no points, rotor, distributor or other spark noise generating components for the radio to hear, there’s absolutely no radio noise!
Carburetion is another area that has caused a lot of trouble in VW conversions and the Taylors played their “What if?” game and attacked that one next. An air-cooled engine at 100% horsepower for take-off and climb out gets only about 30% or 35% of the cooling air it will receive at cruise speeds, yet is delivering 100% horsepower and the net result is that they tend to run super hot unless the mixture is enriched considerably.
The simple little carburetors commonly used on VW conversions simply don’t have these capabilities built in. “What if they built their own carburetor and built in an enrichment circuit that automatically richened the mixture at full throttle and then we lean it with the mixture control at altitude just like the $1500 ‘real carburetors’?” Could it be done?
Yes, they decided, it could be done and after three years of development work, the Taylors came up with a carburetor called Ultracarb that does just exactly that. In fact, it goes out of the factory all sealed up ready to automatically keep the cylinder heads cool on climb out or any other time when you apply full throttle and still have the capability of being leaned down to a miserly fuel consumption when you are at altitude cruising at high speed.
Don said that the new features that HAPI had to offer, plus the fact they’ve been in business for a long time and have a good track record for reliability had led him over there. I took a few pictures in the shop and left, promising to get together with Don at his home in Borrego Springs later on be cause I was anxious to see how his big motor glider would perform with the Magnum engine in it.
About three months later in February of this year, I made a special trip to Borrego Springs just to see how the Lark performed. Don keeps the air craft at a little private strip just five miles south of the Borrego Springs air port, where it is tied down outside, no hangar on the airport being big enough to house it.
While we untied the aircraft and got it ready for flight, Don began to tell me about the new performance figures he’d been able to gain with the Magnum. I asked him about rate of climb.
“Well, I used to have a best rate of climb of about 200 feet on a cool day, now with this Magnum engine I’m going up from 450 to 550 feet a minute, so my rate of climb has way more than doubled. My take-off roll is less than it used to be, although I haven’t measured it!”
When I asked about cruise speeds, Don said he used to cruise at 90 knots indicated and now cruises the airplane at about 100 knots indicated. He said the old top speed was about 105 knots and it will now move out at 115 knots indicated.
“How many modifications did you have to make to the airframe and such, Don, to make this change work?” “Well, really not too many. I’m using exactly the same Hoffman three position prop as before. We’ve changed the pitch stops a little bit. Had some very minor alterations to make in the baffling to fit it up over the Magnum heads, but that’s about all.”
“The engine fits right in the same spot that the Limbach took up and actually has a little more room around it. We did have to make a minor change in the control arm that controls the propeller to clear the sensor case on the electronic ignition, but it only took about an hour to do that”
“Have you had any problems with it, Don?”
“No, other than a couple of minor oil leaks that I had. One was out of the fuel pump base where the gasket wasn’t sealing properly and the upper ends of a couple of pushrod tubes leaked a little bit, but those have been remedied now and the engine is running completely dry, doesn’t use any oil, every thing’s just working great!”
Don invited me to pull the prop through the engine before starting just to feel the compression and I was amazed. Four super solid cylinders that don’t feel at all like any Volkswagen. We got the airplane ready to fly and Don invited me to take a ride with him.
The take-off roll was probably 500 or 600 feet and we were airborne climbing out at a good rate although I had problems reading his variometer which is marked in meters per minute rather than feet per second.
We flew around for about twenty minutes and I got a chance to fly the Lark a little bit. The ailerons are very heavy and the elevator is very light. Don plans to install winglets next year and perhaps some servo assist tables on the ailerons to lighten up control pressures there.
All too soon Don lowered the landing gear and we were turning on short final over the long dirt runway. Don, a retired Western Airlines captain, very daintily set the huge Lark in the exact center of the runway. He has to, the wing tips overhang the brush on both sides of the runway so no deviation from the center line is possible without damage.
Don spends his winters in Borrego Springs, CA and spends his summers in Minden, Nevada to avoid the heat plus to take advantage of the tremendous soaring conditions there. He says he is eager to show his revitalized Lark to the soaring community up there. He predicts there will be a lot of motorgliders going to HAPI to get Magnum Plus power put under the cowling.
In doing the write up on this article, I had occasion to call Don and ask him for some of the performance numbers and such that I didn’t have and he just about blew my mind. When I asked him how the Lark was going, he said “Oh, it’s just doing fine. By the way, we just installed a tow hook on it and I’m towing another glider with it, a small single place belonging to a friend of mine!”
I asked how do they go up? Don said, “Well, he gets off first and holds it level and gives me a chance to get off and then we climb out very nicely with plenty of power to get both gliders up there!”
A Volkswagen conversion with enough power to pull a huge motor glider and enough power left over to tow another glider? Well, maybe not a Volkswagen conversion, but HAPI’s Magnum has the power to do the job and in Don Hall’s Lark it is doing it very well.
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