Aero-Engines vs. Auto-Engines for Use in Aircraft

Dave Gevers - EAA Chapter 256 – 03/15/2014

What this discussion is Not: • Just one answer (yes or no) • My expert opinion (I am not an expert. I am a

sceptic. I have learned that much of what I was taught is incorrect.)

What this discussion includes: • Data/info/background for your personal decisions • Examples of what can work (and not work) • Discussion of reliability of information & topics for

further discussion

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Common Opposing Opinions • Importance of Torque (Aero) vs. Horsepower (Auto) • Reasons for Redundant Ignition (controversial?)

• Most Updated Technology (Aero vs. Auto) • PSRU (Prop Speed Reduction Unit) Type and Reliability • Efficiency of Air Cooled vs. Water Cooled (Cooling drag vs thrust) • Position of Radiator (Mosquito, P-40, Me/Bf 109, P-51) • Overall Engine System Weight (including PSRU/Redrive) • Forces on Crankshaft Bearings • Why Aircraft Engines Cost More • “Auto engines not designed for continuous high rpm” • “Aircraft Engines are more rigorously tested” • Clearances – Oil Consumption (controversial?)

• Temperature, Piston Speed, MEP, Design Details

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Types of Information/Data

Aircraft Engines Are Better

Auto Engines Are Better

“Amateur” Data

“Engineering” Data

Expert Opinions

Expert Opinions

NASA PAVE (Personal Air Vehicle Exploration) project

“Existing” Data

Dual Ignition per FAR Oil consumption & formula per TSDS Crankcase flow vs. Pressure Partial fill recommended

Focus Points

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“A/C maint.” Data

Risk Progression

Fly not Drive

Drive not Fly

Fly Retractable not Fixed

Gear

Fly IFR not VFR

Auto Engine not Aircraft

Engine

Build Kit not Buy Certified

Plans-Built not Kit-Built

Complex, High

Performance not Simple

Higher Risk, Insurance Cost, Effort, Time,

Satisfaction, Skill Level, Accomplishment, Chance of doing it wrong

Lower

Aerobatic not

Standard

Tail wheel not Nose

wheel

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Risk vs. Reward

Experimental Airframe: • Detailed Instructions available • Few major decisions • Many good examples • Likely to succeed.

Auto Engine: • No detailed Instructions • Many major decisions • Few good examples • Risky.

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Existing Examples of Certified Auto-Engines in Aircraft

ORENDA – Canada’s primary jet engine supplier from

1950s through 1970s

ORENDA V-8 Displacement: 495 cubic inches (8.1 liters) Bore: 4.433” Stroke: 4.000” Dimensions: 59.5”(l) x 32” (w) x 32.5 “ (h) Compression ratio: 8.1:1 Weight: 740 pounds dry (335.6 kg) Performance: 600 hp @ 4,400 rpm takeoff (447 kW), 500 hp continuous (373 kW) Fuel Consumption: 0.44 lbs./hp/hr (100LL) TBO was established at 1800. Power-to-weight ratio: 0.81 hp/lb (1.33 kW/kg) 6

Existing Examples of FAA Certified Auto-Engines in Aircraft

ORENDA (continued) Orenda and a number of third parties also started the process of developing modification certifications for various popular aircraft. It was tested as a potential replacement engine on a number of aircraft, including the Air Tractor 300 and 400 Series, de Havilland Canada DHC-2 Beaver and DHC-3 Otter, the Beechcraft C90 King Air, Aero Commander 500 series, and AEA Explorer 500R. Basically any widely used aircraft with an engine around 600 hp was considered as a potential target, which Orenda calculated at about 30,000 flying examples with the PT6, Pratt & Whitney R-1340, Wright R-1820, and various Eastern Bloc engines of similar power. Several new aircraft were designed around the engine as well, including the TAI ZIU, Hongdu N-5, LZ-400 Rhino and the Lancair Tigress. Orenda opened a new service depot known as Orenda Recip at the former CFS Debert in Debert, Nova Scotia. Here they intended to install and service the OE600. At the time they offered a supplemental type certificate conversion for the Otter, planning to follow this with the King Air. They were also interested in smaller and larger versions of the engine, floating a trial balloon at a 750 hp size (the OE750) before deciding on a naturally aspirated 500 hp version instead.

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Unfortunately, the events of 9/11 required Orenda to re-focus entirely on their military projects, and the OE600 project was canceled. The design was later purchased by a group of investors who intend to sell the engine under the Texas Recip brand, but it is unclear if this project is continuing. On August 29, 2006 the president of Texas Recip, Paul Thorpe was sentenced to 3 years and five months for defrauding investors, telling them the money was being invested in the engine project, or other investments, when it was actually being used to pay off investors in a previous scheme. TRACE Engines More recently the project has been picked up by TRACE Engines of Midland, Texas and is certified by the FAA. Yorkton Aircraft is handling Canadian installations in agricultural aircraft. A Canadian DHC-2 has received a temporary certificate with the engine in 2012 during a complicated registration process.

Existing Examples of FAA Certified Auto-Engines in Aircraft

ORENDA (continued)

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Existing Examples of Certified Auto-Engines in Aircraft

TRACE – Purchased rights from ORENDA in 2006

Today, TRACE offers six models of production engines built and ready for sale, as well as a fully FAA Certified production and testing facility. The TRACE water-cooled V-8 engine is the only FAA certified piston engine capable of producing 600 horsepower at takeoff and 500 horsepower continuously, making it the most powerful reciprocating aviation engine in production. TRACE currently powers aircraft from Cessna Caravan, Air Tractor 301, 302, 401, 402, and De Havilland DHC-2 Beaver , DHC-3 Otter, King Air-90, Grumman Ag Cat rated in the 450 to 750 horsepower range.

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Robinson Seabee LS1 Corvette engine – STC

Certified

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Early Examples of Certified Auto-Engines in Aircraft

TOYOTA-Lexus V-8, PORSCHE-911 Aircooled 6 CORVETTE-LS1 in Seabee

Ford, Crosley, Hudson, Terraplane, Plymouth, Studebaker, Packard,

Packard-Merlin, etc. “These Auto manufacturers have produced more aircraft piston engines than Lycoming, Continental, and Franklin” ?-don’t have the data.

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Quotes from NASA PAVE Project (Personal Air Vehicle Exploration)

• “It is our belief that an airframe, designed from the outset for an automotive engine, can yield a well performing aircraft at a very reasonable cost.”

• “Auto engines are liquid cooled, making them less susceptible to detonation than aircraft engines.”

• “Auto engines have cooling flexibility. Cooling drag may be reduced with liquid cooled engines… Considering that cooling drag can make up to 20% of the cruise drag, this is a significant aerodynamic issue.”

• “Auto engines are quieter. Automakers have really focused on this area while aircraft manufacturers and completely ignored it.”

• “Auto engines are generally more compact, due mostly to liquid cooling, and utilize 60 to 70% of the volume of air cooled, permitting easier packaging.” 12

Quotes from NASA PAVE Project (Personal Air Vehicle Exploration)

• “Aircraft engines are very good at what they do and are the way they are for some very good reasons. However, if the price is right, the automotive engine doesn’t need to be ‘the best’. It just has to be good enough.”

• “While current certified reciprocating aircraft engines work very well, their cost is high. This is almost entirely due to the low rate of production that they enjoy and the recurring costs of certification…”

• “The heart of the change in the automotive industry is that quality is built in and not inspected in. A similar approach by the FAA could yield similar benefits.”

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𝑃𝑜𝑤𝑒𝑟 ℎ𝑝 = 𝑇𝑜𝑟𝑞𝑢𝑒 (𝑓𝑡 − 𝑙𝑏𝑓) ∙ 𝑆𝑝𝑒𝑒𝑑 (𝑟𝑝𝑚)

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Engine-Allison V-1710: 2,000hp, 3,500ft-lb, 3,000rpm

Drive Shaft: 2,000hp, 2,626ft-lb, 4,000rpm

Intermediate Gear: 2,000hp, 1,750ft-lb, 6,000rpm

Prop Shaft: 2,000hp, 4,200ft-lb,

2,500rpm

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Ignition System: • “FAR 33.37 Ignition system. Each spark ignition engine must have

a dual ignition system with at least two spark plugs for each cylinder and two separate electric circuits with separate sources of electrical energy, or have an ignition system of equivalent in-flight reliability.”

• Design Rule “Reliable or Redundant (parallel not series & without single source of failure)”

• Continental advises to disassemble, inspect, (overhaul if necessary) magnetos every 500 hrs.

• Magneto installations are not necessarily redundant, only in case of complete open circuit failure, not in case of plastic distributor gear failure. Also consider D2000/D3000 dual mags have only one drive, pressurized mags have only one air source and filter.

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Other Redundant Systems: • Series or parallel? Dual is not necessarily redundant. • “If you can’t make it reliable, then make it redundant” • Is the backup system (vacuum pump, alternator) ever tested? • Very low percent of the engine is redundant? Mechanical, fuel

two pumps but only one carburetor and set of fuel lines, oil, Ignition, one regulator, battery, and alternator (rarely two), one air source and filter on two pressure mags.

Dual in Parallel Redundant

Dual in Series NOT Redundant

Oil consumption – different standards for Auto and Aero:

Lycoming Operator’s Manual for IO-540 AE1A5 allows .78 qt/hr at rated power = 1gal per 5.1hrs. Lycoming general recommendation is up to .5 qt/hr is OK. In a car, I qt. per fuel tank is about 1 qt. per 5-10 hr.

For a 12 qt. sump, it can have 6 qt. unusable. For an 8 qt. sump, it can have 4 qt. unusable. But for a 4 qt. sump, it has to work at 2 qt. “2/3” * 8 qt = 5-1/3 qt. 5-1/3 – 4 = 1-1/3 qt. usable 17

=4 unusable =6 unusable

=4 unusable 18

Typical Wet-Sump Oil System

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8

7

6

5

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First “Quart”

Second Quart

Third Quart

Automotive testing is WOT (wide open throttle) for 600-1,000 hrs FAA requires only 150 hours.

A 30-hr run @ 5 minutes of TO power and 5 minutes @ 55% A 20-hr run @ 1-1/2 hrs @ 90% alternated with 1-1/2 @ 55% 20 hrs at max cruise (75%) alternating with 1-1/2 hr of 55%

• Assumption is “Automotive engines are not designed for continuous running at high power”.

• Comes from observation that automotive engines are not normally used at high continuous power.

• Automotive engines are designed for long life with minimum maintenance and maximum abuse.

• Aircraft engines are designed to be closely maintained.

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Cooling drag Comparison of converted WWII fighters without change to external shape. Liquid Cooled vs. Air Cooled Bristol Beaufighter. 1280hp Merlin 330 mph, 1590 hp Bristol Hercules 323 mph. Hawker Tempest I. 2240hp Napier Sabre 466 mph. Tempest II 2520hp Bristol Centaurus 440 mph. Reggiane RE 2001. 1175hp Alfa Romeo 337 mph. RE 2002. 1175hp Piaggio 329 mph. DC-4/ Northstar. 353mph with 1760hp Merlins, 280 mph with 1450hp Pratt R2000s.

Cooling thrust can be realized by proper design of inlet and outlet.

The radiator is much more efficient for heat transfer than the cylinder cooling fins – consider the total exposed area and smoothness of pressure cowl design

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Cruise

Climb

As angle of Attack increases, Lift (on top) increases forward. Pressure (on bottom) spreads out toward the rear.

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Similar to Jet engine: Intake, increase pressure, add energy, expand through nozzle

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Carefully consider where to position crankcase vent. Cuin divided by 5 = mph

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Crankshaft Forces

• Inertia forces are mostly balanced by counter weights – Power forces are not.

• Power stroke forces are downward on the main bearing caps and bolts. • Gearbox gears add to down force – belt drive and chain drive lifts up,

relieving cap and bolt forces.

Assumption: “Automotive main bearings are not designed for side forces”

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Rear Main Bearing Forces

Power Stroke

6,000 lbf

Power Stroke

Power Stroke

Belt, Chain Tension 335 ft-lb / (1/3 ft) = 1,000 lbf

Gear Separation

Gear Separation Crankshaft

Propshaft

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PSRU (Redrive)

Cog Belt Gear Box

Hyvo Chain

External Gears: Force added to cap bearing, needs oil supply (closed case with seals), not inspectable

Chain: Force helps cap bearing, needs oil supply (closed case with seals), not inspectable

Timing Belt: Force helps cap bearing, oil not needed (open case), inspectable, provides damping

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In 1978 Lycoming ad says that it built 230,000 engines in its history AIRCRAFT AUTOMITIVE

Chevy built that many in one month Production Original Cost Production Original Cost

4600 $60,000 2,760,000 $6,000 Cost of new GM 350

Remove 20% for Certification and Liability Insurance x80% $48,000 $3,200 Cost of PSRU

If production is doubled x80% 9,200 $38,400

If production is doubled x80% 18,400 $30,720

If production is doubled x80% 36,800 $24,576

If production is doubled x80% 73,600 $19,661

If production is doubled x80% 147,200 $15,729

If production is doubled x80% 294,400 $12,583

If production is doubled x80% 588,800 $10,066

If production is doubled x80% 1,177,600 $8,053

If production is doubled x80% 2,355,200 $6,442

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Aircraft Engine

Automotive Engine in Airplane

Automotive Engine in Car

POWER Lyc-IO-720 GM LS1 GM LS1

Max Advertised HP hp 400 370 370

Max Practical HP hp 400 340 300

Cruise HP hp 300 250 40

Bore in 5.125 3.898 3.898

Stroke in 4.375 3.62 3.62

Cubic Inches in^3 722 346 346

RPM at Max advertised rpm 2,650 5,800 5,800

RPM at Max Practical 2,650 4,500 4,000

RPM at Cruise rpm 2,300 4,000 2,000

Max Piston Speed ft/sec 88 126 63

Max Piston Acceleration ft/sec^2 702 1,011 505

Relative Piston Mass 1 0.65 0.65

Piston Force from Accelaration 702 657 329

No. of Cylinders # 8 8 8

Max Practical Brake Mean Effective Pressure psi 166 173 172

Cruise Brake Mean Effective Pressure psi 143 143 46

Max Crankshaft Torque ft-lbf 793 335 335 31

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Summary (from one point of view)

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• The auto engine, installed in the car is more robust and maintenance free than the aero engine installed in the airplane.

• To install the auto engine in an airplane keeps some of the robustness and provides opportunity for some improvement, but introduces possibilities for many serious mistakes.

• The greatest chance for improper installation is in the cooling system and the prop mounting and drive system.

• Much less help is available for engine installations than for airframe construction.

Review EAA webinars and videos, especially Bob Kohler’s Websites: http://www.epi-eng.com http://www.homebuiltairplanes.com http://www.v8seabee.com/ http://www.pra.org/publicdl/Diagrams%20Plans/crossflow%20aero%20psru.pdf http://www.beltedair.com/BAFAQ.htm

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