Thrust testing 85 and 100 hp engines

Builders,

Here is another set of testing from the days at our Edgewater hangar.  Thrust testing is a very common number to quote, but it is also the most commonly faked or deceptive piece of data people quote.  It is very easy to set a ground adjustable prop so low on pitch that it produces fantastically high thrust numbers, but the plane would be required to have a 40mph cruise speed to use them. (airboats operate in this range)

For data to be useful for more than inpressive sounding number in a brochure or website, it must have two elements. First, the prop pitch must be realistic to the type of flying you will be doing. Second, you have to use the same equipment on the same day to test known engine prop combinations like the O-200 C-150 for comparison.

All of this can take time and be a real bother comparied to just making up a number that sounds good.  After years of this type of testing, a am going to guess that 75% of the numbers people quote on this topic are simply made up. Just stop and think about how many times the numbers you have seen came without any kind of photo of the test being conducted. I have found that people wo like to talk about planes they will build one day most often cite numbers known to be fake. On the other hand, buiolders who are working on the plane they will finish and fly  follow data like this story.

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Thrust Testing;

Zenair 601, Cessna 120, Cessna 150, Hudson Corvair, Shop Corvair, Corvair Turbo

Friends,

Over the years we’ve done a lot of thrust testing in order to compare the output of engines, the thrust of different propellers, and the effects of systems installations. The method used to measure thrust is a hydraulic cylinder attached to a remote gauge. It is easy to calibrate because you can hang a known weight from it. In our case, the thrust is 1.54 x the number shown on the gauge. This is because the piston in the hydraulic cylinder has more than 1 square inch of area.

A few days ago, we tested a lot of different combinations at the hangar for comparative purposes. All tests that we’ve done recently are conducted on 100ll fuel. All of the Corvairs were tested with 32 degrees total ignition advance. The only exception to the ignition was the turbo engine, which was set at 22 degrees total. A $300 digital, optical tachometer was used to measure rpm. Weather conditions are measured on the spot with digital instruments. Here you’ll see tests of certified engine and propeller combinations also. Over the years I’ve been working with alternative engines, I’ve noted that many people who are fans of alternative engines know very little about certified engines. Being an A&P mechanic, I have the greatest respect for certified powerplants. I like everything about them except for the expense of obtaining and operating them. All my work with the Corvair motor is patterned after the success of certified engines. I use their performance as a baseline, and their level of reliability as a goal. Anyone who tells you that alternative engines have superior reliability, or fantastically better performance than certified powerplants is either not telling the truth or has no practical experience with them. In our case, we own, maintain and fly certified powerplants in addition to our work with Corvairs. This gives me a greater range of experience and a more balanced view of the capabilities of alternative powerplants, specifically the Corvair. The next time you hear somebody comparing alternative to certified powerplants, either pro or con, ask them if they’ve owned and operated both and you’ll find that very, very few people have personal experience in both fields.

The Zenvair 601

Above is our 601’s engine measured as installed in the aircraft. The only thing different about this engine is that it has roller rockers and our modified cylinder head intake pipes. I doubt either one of these mods would have a substantial effect on the output of the engine. The prop pitch setting of 11.5 degrees at the tips would be an appropriate setting for a direct drive Corvair motor to move the 601 at 140-150mph. If the prop was set flatter for a slower speed airplane, or used a slightly larger diameter prop, the thrust numbers would be even higher.

Engine: Corvair

Displacement: 164cid, .060 over

Carburetion: MA3-SPA

Exhaust: Collected, open

Cowling: WW 601 Corvair Cowling, 13″ spinner

Propeller: Warp Drive 2-blade HP hub and blades, stock tips, 66″ diameter, 11.5 degrees pitch measured at tips

Temperature: 85F

Humidity: 35%

Pressure: 30.11

Density Altitude: -174

Wind: 4-9mph headwind

Performance

Thrust: 347 pounds static

RPM: 2550

MAP: 29″

1946 Cessna 120

In the photo above is Gus Warren’s 120 that he rebuilt from a basket case to 1998 Oshkosh Champion. It lives in our hangar. The engine has about 100 hours on a first class overhaul. It has flow matched Superior cylinders.

Engine: C-85-12 Continental (85hp, redline 2575rpm)

Displacement: 188cid

Carburetion: Stromberg NAS-3, 1 3/8″ Venturi

Exhaust: Stock 120

Cowling: Stock 120

Propeller: McCauley 71×46 Met-L, aluminum (This is a climb prop for a 120)

Temperature: 85F

Humidity: 35%

Pressure: 30.11

Density Altitude: -174

Wind: 4-9mph headwind

Performance

Thrust: 340 pounds

RPM: 2350

MAP: 29″

Larry and Cody Hudson’s Corvair Engine

This father/son team from Indiana built their own engine, in the photo above, from our Conversion Manual and components last year. They dropped it off at our shop before Sun ‘N Fun for a break in on our test stand. The prop installed is appropriate for a 180mph airframe. This is why it has low static thrust numbers. It is good for comparative purposes, and is the same prop used on some of the 2002 tests. This engine is not fully broken in, as it has less than two hours of test stand time on it.

Engine: Corvair

Displacement: 164cid, .030 over

Carburetion: MA3-SPA

Exhaust: Cast iron manifolds, automotive muffler

Cowling: None, cooling baffle only

Propeller: Sterba 62×58

Temperature: 82F

Humidity: 51%

Pressure: 30.05

Density Altitude: -122

Wind: 5-7mph headwind

Performance

Thrust: 225 pounds

RPM: 2445

MAP: 29″

Cessna 150

Pictured above is our neighbor Arnold’s 1959 Cessna 150. The engine in this aircraft is one that is the subject of the AD that requires the timing to be reduced to 24 degrees. The engine is a mid-time engine that just came out of a 100-hour inspection. It can be considered to be in good working order. Contrary to what most people think, O-200s in 150s are only certified to use propellers up to 69″ diameter. No 150 left the factory with a propeller diameter of 72″.

Engine: Continental O-200, 100hp, 2750rpm redline

Displacement: 200cid

Carburetion: MA3-SPA

Exhaust: Stock 150

Cowling: Stock 150

Propeller: McCauley Clip Tip 68″ diameter, aluminum, standard pitch

Temperature: 82F

Humidity: 51%

Pressure: 30.05

Density Altitude: -122

Wind: 5-7mph headwind

Performance

Thrust: 335 pounds

RPM: 2332

MAP: 29″

Shop Test Engine

We built up a test engine, below, from parts in our shop. We built it up to use in potentially destructive ground testing. Since it’s made of used parts, it is not only dirty, but also fully broken in and has very low internal drag. I believe this is why it will turn slightly higher numbers than the Hudson engine. We utilized the same distributor, intake, carb and exhaust on this engine and the Hudson engine. The only difference would be the status of the internal assemblies.

Engine: Corvair

Displacement: 164cid, standard bore

Carburetion: MA3-SPA

Exhaust: Cast iron manifolds, automotive muffler

Cowling: None, cooling baffle only

Propeller: Sterba 62×58

Temperature: 75F

Humidity: 71%

Pressure: 30.06

Density Altitude: -133

Wind: 2-3mph headwind

Performance

Thrust: 231

RPM: 2520

MAP: 29″

Turbo Test Engine

The engine above is the same as the test engine, with the addition of a new Garrett turbocharger, which we had specifically sized and set up for a drawthrough condition. I wanted to test this on a junk motor with a mild steel exhaust to evaluate the sizing of the turbo, and to ensure that it produced boost in the rpm range we wanted. Turns out that the sizing and the trim of the turbo are nearly dead on. We’re going to run a lot more ground tests, and then develop our flight installation package. Based on early tests, we should have absolutely no problem getting 100hp at 10,000 feet on a 164cid engine. While the installation looks very Mad Max, it gave us the data we needed. Keep in mind that everything on this installation was less than optimal, and it has already met my expectations. Despite being told by armchair experts of the antiquated nature of drawthrough installations, and the requirement for an intercooler, this simple installation of a modern, efficient turbocharger worked exceptionally well. At full output, you could reach up and put your hand on the steel intake manifold, and it was not too hot to touch. While it would be hotter at altitude, I think the installation’s off to a great running start. A little practical testing has once again shown that you can learn a lot more by testing rather than talking.

Engine: Corvair

Displacement: 164cid, standard bore

Carburetion: MA3-SPA

Exhaust: Cast iron manifolds to Garrett T04B turbo, 2.5″ outlet pipe 18″ long

Cowling: None, cooling baffle only

Propeller: Sterba 62×58

Temperature: 74F

Humidity: 62%

Pressure: 29.92

Density Altitude: -1

Wind: 3-4mph tailwind

Performance

Thrust: 331 pounds

RPM: 2950 (there was more power available, but I did not want to boost the motor past 45″ without working EGT in place)

MAP: 45″

Conclusions

We have more testing lined up on the turbo engine, and we’re going to maintain a separate Turbo Testing Page on http://www.FlyCorvair.com for it. We have a 72″ Warp Drive propeller we’ll be installing for a maximum thrust test, which will give fans of 80-120mph aircraft a better idea of the potential of the powerplant in their speed range. Please keep in mind when you read these statistics and look at the pictures that all the data is factual. I frequently read stories where people claim to have VWs which produce 500 pounds of thrust and Subarus which produce even more. We professionals in experimental aviation get a good chuckle out of inflated numbers from advertising brochures and press releases. But, people new to sport aviation should know that you can come down to my hangar any time and I’ll gladly duplicate these tests.

Thank you.

William Wynne