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Frequently Ask Questions about LS2/LS7 Engine Conversion for Aircraft. |
Jason Day / Vesta Inc.
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Have auto engines been used in aircraft before? The use of auto engines in aircraft is not a new idea. Aviators have been installing auto engines into aircraft for a 100 years, starting with the engines from the model T to the present Chevy LS2/LS7 engine. During World War II the best of the high altitude fighter aircraft were liquid cooled and supercharged approaching 2000HP. Other similar characteristic now found on the LS2/LS7 were "V" type configuration with sodium filled valves. These high performance WWII liquid cooled engines passed on many new advancements to the then evolving liquid cooled auto industry. After WWII the commercial aviation industry embraced the concept of air cooled engines and has maintained the same designs with dual magnetos to the present date. In parallel one can observe the auto industry over 50 years evolving and advancing the liquid cooled engine both in performance and high volume production. Today one will find auto engines available, like the 366-427 Cu. In. LS2/LS7 from Chevrolet, to be in high production (millions) and utilizing modern features such as a computerized distributorless ignition as a standard feature. The end result is that one can observe the aviation industry producing thousands of 300-350 HP air cooled engines designed in the 1940’s costing $50,000-$70,000. In comparison a person will find the auto industry producing millions of a modern 350-450HP auto engine in the price range. of $5000-$6000. In conclusion, the idea of installing an auto engine in an experimental aircraft has been a popular notion, and for the past 30 years these aircraft have been growing in numbers. There are too many experimental builders converting auto engines to mention, both on the professional and amateur level. The best resources to read about these flying auto engine conversions are in the Contact Magazine books or the EAA and Kitplane magazine archives. What are the advantages of using an auto engine in an aircraft over a traditional FAA certified air-cooled engine? 1. LIQUID COOLING: The advantage of liquid cooling provides even engine temperatures and eliminates the rapid cooling changes causing thermal shock which is so detrimental to air cooled aviation engines. The elimination of the “thermal shock” is one of the main reasons auto engines are a rugged and reliable solution. Problems associated with the fracturing of the cylinder heads on an air cooled aviation engine are eliminated. Another advantage of the liquid cooling is that unlike air-cooled aviation engines, the modern automotive V8 does not need excessive gasoline to cool the cylinder heads like the air cooled aviation engine. Therefore a typical liquid cooled auto engine will burn about 3-4 GPH less than the air-cooled aviation engine for the same horsepower. That is about $15-20,000 in fuel savings over 2000 hrs. 2. V8 SMOOTHNESS: The modern Chevy LS2 V8 engines have a significantly smother operation compared to the 6 cylinder aviation engine. The 90 degree power pulse and harmonics of a V8 Engine are very reduced compared to a 120 degree 6 cylinder engine. The results are a tremendous improvement in airframe vibration and stress on the crank. Also, on the Chevy LS2/LS7 V8, the main crankshaft journals are much heavier than the ones found on typical aviation engines like the IO550 and IO540. Continental and Lycoming engines are notorious for their cracking crank shafts. 3. COST: Price or dollars per horsepower is another big reason for using an auto engine conversion. The FAA certified engines in the range of 300-350HP approach $50,000-$70,000. and cost $25,000-$30,000 to rebuild. One can buy an “over the counter" all aluminum V8 auto engine with 350-400HP for $5000-$6000. The cost to rebuild is under $2000. Note on cost: Including the upfront cost, fuel savings, and rebuild cost, at a TBO of 2000hrs., a builder can save $50,000-$70,000. 4. RELIABILITY AND DEPENDABILITY: A V8 automotive engine is every bit as safe as an FAA Certified Aviation engine. The qualities of liquid cooling and the smoothness of the V8 crankshaft actually provide an advantage. The quality assurance of General Motors is the most advanced in the world and service and parts will always be available. Modification techniques, like the HyVo chain reduction have been in use for 30 years and are mature and well established. I have heard of agricultural aircraft that have as many as 4000 hrs. on a HyVo chain. Will the LS2 endure 75% continuous HP? The most common question asked is whether the Chevy LS2 V8 engine can handle 70-75% continuous HP. My answer is yes. GM designed the LS2 V8 engine to be rugged and versatile. Just because the auto industry only uses the engine at 45-50% continuous HP, does not mean the LS2 engine wasn’t design to take 75% continuous HP. GM engineers knew that other industries such as the racing industry and marine industry would want to use the LS2 engine and therefore the design reflects this. The LS2 was designed to take higher RPM for long periods of time. For example the ASA racing network uses the LS2/LS7 engine up to 6000-8000 RPM(110%HP). The marine industry uses the V8 engine the same way aviators fly. Boats cruise 3000-3800RPM, and use 4500RPM for short sprints like water skiing. I have heard from GM engineers of a life test performed on the LS2 by GM of up to 1000hrs. at 50%-100%HP without failure, ending with the engine still running. FAA certified engine testing is quite tame comparatively and only requires 150hrs of engine life testing, of which only 20 hrs of the testing is at 50-75% HP, and only 30 hrs. is at 50%-100% HP. Also note that aviators are trained to operate air cooled aviation engines with extreme care and monitoring. This is because air cooled engines are extremely vulnerable to thermal shock and have tremendous torsional vibration problems. In the end, the most important factor in the safety of either the air cooled aviation engine or liquid cooled auto engine is the installation and the maintenance. Some general rules to use during an auto engine conversion is to use redundancy, do not over modify, use as many factory parts as possible, and test all systems thoroughly. What kind of HP does the LS2 produce? Estimated performance Engine RPM
(See LS1 spec sheet) www.GMpowertrain.com Note: GM spec sheet is “rear wheel” HP. Add 30 hp for aircraft. Note: LS2 spec are 15HP higher, and LS7 specs and 45hp higher
How do I get 400 HP ? For those applications like seaplanes where max HP is of prime importance, I recommend using a LS2 + supercharger or the LS7. Because the LS2 is a high compression engine already (10.5:1) we want to be careful not to use excess boost that may cause detonation. Therefore I recommend only 2psi boost at takeoff for 120 seconds only. This will produce about 40-50 additional HP (400HP) until the aircraft is airborne. Then the operator can reduce the manifold pressure to a climb mode (350HP). In addition to additional HP, you get 18k ft normalization as a bonus. The LS7 is GM's new 427 cu. in., 7 liter engine with stroker crank can produce 405 HP normally aspirated or 450Hp with 2 psi. What does the LS2/LS7 engine installation weigh? The weight of the LS2 engine out of the crate with the heavy GM exhaust headers removed is 348 lbs. By the time you add the PSRU, radiators, and flywheel,…ETC, the installation will be in the same weight an space envelope as a continental 550 or Lycoming 540 installation. (550-600lbs). I use the battery as a tool to fine tune the weight and balance by either moving it to the tail or putting two batteries in the tail.
Why use a LS2 from Chevrolet instead of Ford or Chrysler? My preference in auto engines is the GM Chevy LS2 engine that is used in the Corvette. My reasons for preferring GM over such companies as Ford and Chrysler is that GM builds significantly more engines than any other company and their LS1 engine is high performance, low cost, and readily available. There is also a much larger selection of “aftermarket” performance parts available for the GM engines. Chevrolet has produced tens of millions of V8 engines since the 1950s and is approaching 8,000,000 LS1/LS6/LS2/LS7/LQ9 type engines since 1997. A GM factory engineer told me that the GM factories typically build about 120,000 LS1 type engines a month. GM has made the LS2 series V8 engine the core engine for their entire line of SUVs, Pickup trucks, high performance cars. A person can have confidence in the quality control in a GM factory that produces tens of millions of engines. Their quality assurance department is the finest in the world because it has to be. Note: GM Chevrolet is the only auto company that offers a 350-400HP all aluminum, high performance V8 production engine that weighs 348 lbs and cost apx $5500 including the entire fuel injection system. You can’t beat that value anywhere!!! (See LS1 spec sheet) www.GMpowertrain.com What kind of redundancy is provided in the ignition and injection system? Computer description..... The computer is adapted for the LS2 by Vesta Inc. The pickups, and wire harness are integral to the Vesta PSRU. The need arrived for this computer when research using the standard LS1 GM computer failed to provide a fully redundant operation. There were also problems with the O2 sensors being coated with 100LL, and difficulty building a reliable dual wire harness for the 12 sensors of the complex GM computer. The new computer is very simple (only three sensors MAP, IAT, CKS) and it is fully redundant, with dual circuits, dual sensors, and dual pickups. Because O2 sensors are not used, 100LL is very usable as well as auto gas. In the cockpit there is a Computer A and Computer B switch (like Magnetos switching) which gives the operator instantaneous switching capability (no restart). The fuel and timing curve are adjusted in an open loop configuration and the operator has manual override over the mixture control (using and EGT gauge). The operator also has control of the programming. The operator can create what ever timing or fuel curve they want. An emergency mode can be created that will go to high rich and retard in the event of coolant loss. There are over 300 of these computers flying in aircraft today. What type of PSRU does Vesta Inc. make? The PSRU (Prop speed reduction unit) or “chain drive” is manufactured by Vesta Inc. The PSRU “chain drive” is an adaptation of the Morse HyVo chain and sprocket design pioneered by Fred Geschwender. The chain, bearings and seals are lubricated on the inside by a pressure oil flood. The PSRU housing is machined out of billet aluminum. “off the shelf” tapered roller bearings are used to provide either a “Tractor or Pusher” style of thrust. The Rockwell hardened shafts are capable of providing oil pressure to drive a constant speed propeller. I recommend a 2000 hr. TBO, at which time the chain, bearing, and seals are replaced (apx. $350 “off the shelf” parts). Unlike gears, the HyVo chain runs 80% cooler and does not produce the same kind fictional heat, nor does it have the same kind of torsional vibration problems. How does the PSRU manage torsional vibration? Concerning torsional vibration: The object is to prevent an unstable or severe resonance from happening which may cause damage to the propeller or crank shaft. What I mean by unstable resonance is an oscillation where the magnitude of the swing is increased on every oscillation cycle until infinity. This happens where the natural resonance of the elements of the PSRU and propeller are at the same frequency as the engine power pulse and it’s harmonics. The solution is to first provide a heavy flywheel that uses momentum to dampen and reduce the power pulse. This is a greatly reduced power pulse because it comes from a smooth 90 degree V8 instead of a 120 degree 6 cylinder. Then the natural dampening characteristics from the centrifugal force on the floating HyVo chain prevents the fundamental of the power pulse from creating an unstable resonance. This is unlike a "gear box" or a direct shaft connection on an aviation engine where the torsional vibration is pasted directly through to the propeller and all of the harmonics are reflected back. At what ratio does the Vesta PSRU operate? The first issue, of course is to reduce the engine RPM from a 4500 RPM down to 2300-2700 RPM at take-off where the propeller wants to see it. Vesta uses 2700-3800 engine RPM as a cruise setting depending on how much gas you want to burn and your propeller selection. Vesta can adjust the ratio from 1.52:1 – 1.96:1 in the HyVo PSRU by adding or removing sprocket teeth and chain links. What is the TBO of the PSRU? Concerning the TBO of the PSRU: Note about chain slack: The chain is initially installed very tight. After about 20 minutes of running it will debur and have a slight amount of slack. As the chain wears the slack will increase, which can be measured by the movment in the propeller. At RPM the chain will ride up on the teeth of the sprocket and provide a natural dampening effect because of the centrifugal forces. The slack is taken up and the chain rides very smoothly and quietly. It is not necessary to provide a mechanism to tighten the chain because you want to let the chain ride up on the sprocket to allow it to adjust it’s own pitch diameter. If a mechanism (like shaft adjustments or spring loaded dampers) prevents the chain from riding up on the teeth. The pitch diameter will not match and the chain will start cutting into the sprockets. New sprockets cost about $1000.00 apx.
What other failure modes are there? Concerning a self centering spline: Beside the vibration problems caused by "gear boxes" one of the the most common reason that I found for PSRU failure in aircraft is from the lack of providing angular and parallel misalignment tolerance between the crank and the lower drive shaft. Because of the difficulty of measurement accuracy, it is unlikely that a perfect center matching of the PSRU shaft and the crank shaft can be achieved. GM engineers have told me that they cannot guarantee +/_ .005 tolerance on the center of the bolt hole circle of the LS2. Therefore it is necessary to provide a self centering spline in order to prevent the possibility of an uneven bearing load on either the bearings of the crankshaft journals or the PSRU. Have there been any accidents involving a V8 engine in an aircraft? Concerning NTSB reports: So far I have only been able to find 8 NTSB reports that involve a V8 auto engine. ( This is out of 2466 total accidents of experimental aircraft since 1990). So far, the main observation is that none of these accident had anything to do with the V8 engine itself, but were the cause of mainly pilot error, maintenance error, or the PSRU. All of which can be prevented in the future. We thank the following builders for the valuable and expensive lessons they pass on to us. Using a V8 in an aircraft is too good an idea too give up on. REF: NTSB (National Transportation Safety Board) www.ntsb.gov
Why did I choose a supercharger instead of a turbo charger for altitude? I use a supercharger to compensate for altitude for several reasons. The supercharger is a simple rugged and reliable mechanism that is cost efficient and easy to rebuild. With a supercharger system an operator is no longer dealing with TIT temperature of 1600 degrees and does not have to worry about the thermal shock on the impeller like a turbocharger. Unlike a turbocharger, the operator does not need a complicated wastegate controller because the throttle body/pinch off /butterfly valve can be move to the front of the impeller input and operates very much like the “black knob” on the normally aspirated engine. A single supercharger will maintain 75% power at 18k ft., and two superchargers will maintain 75% power to 26k ft. The supercharger draws about 5 HP of drag in a vacuum, and as the operator climbs the throttle (black knob) is opened to maintain the desired manifold pressure. At 18k ft. the supercharger intake will be 100% open and a “critical altitude” will be established. The engine will begin to lose power after climbing above 18k ft. To descend the operator will close the throttle and adjust the desired manifold pressure on the way down (about every 1,000-2,000ft.). An intercooler will be used to reduce the intake air temperature (IAT) to below 90 degrees and prevent any possibility of detonation. The manufacturer of the supercharger estimates TBO to be apx 3000 hrs and will rebuild the blower for apx. $600. How do I build a radiator system? I use an all welded radiator, which is visually inspected before the tanks are welded and pressure tested. Using rubber vibration dampers the radiator is mounted in a position where there is not a direct path of impact for any particle that may fly off the propeller. The main problem with cooling aircraft is getting enough airflow on the ground. There is plenty of airflow once airborne. There are two electric fans mounted with the radiators that act like electric cowl flaps. On the ground and during taxi, the fans can be switched on by the operator or by an automatic 170 degree thermostat switch in the engine compartment. The fans help the propeller create differential pressure. There is an expansion tank mounted at the highest part of the cooling system which also acts as an air accumulator and steam collector. Can I get insurance? Concerning Insurance: Yes, insurance is available for auto engine conversions. Insurance companies typically will want the engine to be in the same HP, weight, and space envelope as the airplane was designed for. They will require 40hrs for the initial test period. They will want to see all the documentation such as operation manual, service/maintenance manual, engine log, and engine manual. So far I have seen price quotation about the same as with a FAA aviation engine. The insurance companies may prefer some kind of builder assist or training from the manufacturer. What is the future of auto conversions? Observing the interest and excitement of using the LS1/LS6/LS2/LS7 V8: I expect the LS2 V8 conversion will become a very popular alternative engine installation and there will be a large network of builders and many vendors. There are hundreds of pilots installing auto engines and more and more are airborne every year. Like the Subaru revolution the Chevy V8 will prove to be very safe, very powerful, and very affordable. Maybe 5 years from now, as the perception of auto conversions evolves, and as the EAA industry becomes more educated, the notion of using a LS2 V8 engine to replace the IO500/540 may become the preference. After all isn't that what the EAA is all about……making safe flying affordable. Where can I find more information about LS1 and auto conversions? Some good reading material…..
Can a builder put a LS2 engine in a FAA certified aircraft? I have heard that it is possible to get a FAA field STC certification for your Bonanza or Cessna with a LS1 engine (depending on which DER you talk to). Basically you would have to perform the FAA requirements with a FAA witness or DER for validation. The LS2 would easily pass the fuel, induction, ignition, lubrication, and vibration requirements. Then you would be require to perform a 150 hr life test of which some of the test are as follows
You would have to produce documentation such as operation manual, service/maintenance manual, engine log, and engine manual. The Part-91 STC field approval would be for your and only your aircraft and would not be a type certification for manufacturing. Other Notes: Fuel system: Dual electric fuel pumps with filters are installed for redundancy. Two switches are installed in the cockpit for the pilot to control. Exhaust system: The heavy double walled factory exhaust headers are replaced by lighter ceramic coated exhaust header in order to insulate and remove as much heat as possible out of the cowling. If weight allows, bullet mufflers can be installed for noise reduction. Mounting System: The engine is mounted on a 4130 steel welded tube frame. Aluminum brackets are bolted to the engine and vibration dampers are installed between the brackets and the mount.
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