CHT info taken from test flight of 601XL

Builders,

Note: The columns in the chart are shifted over one heading, it is a discrepancy between how excel and the wordpress format here presents printed data, wordpress automatically tries to center it, look past this and understand the story, I will try to reformat this and get a link to the full sheet later today-ww

Below is a chart of CHT data taken from Ken Pavlou’s 2,700 cc 601XL, which now has about 20 flight hours on it. The layout of the data Ken gathered is particularly interesting. Ken’s engine and installation is nearly 100% done according to our manual. His data collection is fed through his Dynon panel. His data is a very good representation of what any builder can expect if he is willing to follow our recommendations.

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First let me say that Ken is a very experienced pilot and astoundingly talented electrical engineer who really understands computers and instrumentation, so that eliminates a lot of variables right there.  But keep in mind that Ken was no ‘motor head’ before building his Corvair. I am pretty sure it is the first engine he ever built, thus it also represents what anyone willing to follow the proven path can expect.

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I have long told builders that 1) CHT temps measured under the plugs read far higher than if they are measured in the stock GM location on the Bottom of the heads. That is counterintuitive because the cool air enters on the plug side, but it is reality because CHT measurement under plugs tends to measure the plug temp, not the head temp. (this is not just a Corvair thing all Lycomings have the CHT port on the bottom of the head also, they are not correctly measured under the plugs either) I have long pointed out also that 2) the baffling style that we recommend for Corvair planes, with aluminum baffles with a rubber strip sealing it to the cowl, just like 95% of certified planes use, works period.

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I can not spend a single day at an airshow with out having at least one person tell me that I am not right about both 1) and 2), and they are sure of this because they read it on a website somewhere. At least once a day a guy will tell me that he is going to build Jabaru 3300 style fiberglass ducts because “they will work better and cool evenly.” Below is data that refutes such internet lore. I am not sure why anyone would be tempted to copy a cooling design from an engine known for running hot, but my field of expertise is engines not psychology.

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Ken is not the first guy to perform this test. 601HDS-TD builder Rich Whittington was one of the first. Rich’s plane is a 3,000 cc Corvair fed by a Stromberg, a good but slightly off the mainstream combination. Ken’s 2,700 cc MA3-SPA tri-gear plane is more typical. Get a good look at the data and see that the CHT in the GM location is running 80 to 100 F cooler than the plug reading; Also note that the L-R cooling spread on the engine is about 5 degrees. Does that sound like a problem? I doubt that there is a single certified plane that can beat that, yet I have had an army of people eyeball the baffling we use and proclaim it a defective design.

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The data is taken from a large sample of a whole flight with a climb to 6500′ and a decent and landing. The sample here is typical of the climb data. In the decent phase the L-R temp difference went down to one degree F.

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Below, a revised chart I am having a hard time making bigger:

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Original chart with shifted column headings:

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Left Bank Stock CHT Location

Average Left Bank (2,4,6) Plug Temp

Average Right Bank (1,3,5) Plug Temp

Difference L vs R Bank Plug Temps

L Stock Location vs L Plug Temp

Average

277

365

369

-4

Min

241

272

270

-9

Max

302

406

405

7

288

376

372

4

-88

288

379

375

4

-91

288

383

379

4

-95

288

387

383

4

-99

290

391

385

5

-101

292

393

388

5

-101

293

395

390

5

-102

294

396

391

5

-102

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Great internet answers: I was looking for the make and  model of a specific truck that appeared in a movie from the 1980s. I Google searched the question, suspecting the truck to have been a 1960s Kenworth. There were about 6 answers, all of which I knew to be wrong, all posed by people who claimed they were experts, including one guy who said he worked on the assembly line. At the bottom, one guy who writes in saying it was an Autocar A64, like the one pictured below. The 5 experts jump on him and call him a fool, several people chime in to confirm this, one even questioning if there was such a thing as an “Autocar,” The guy writes back with pictures of the actual truck that was in the movie, it’s current location, the name of the owner, and a link to it being for sale on Ebay. Doesn’t matter, they still think he is wrong. The internet, an endless chance to wonder about the sanity of mankind.

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More stories on CHT

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Corvair CHT, letters and notes.

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CHT part #3, Letters, notes, sources and inlets.

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CHT Part #4 more notes

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CHT part #5, flight data from Zenith 750

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Measuring Cylinder Head Temps on Corvairs.

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Cowling Inlet Area, marketing, accident stats, Darwin where are you?

About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at www.FlyCorvair.com and in more than 50 magazine articles.

One Response to CHT info taken from test flight of 601XL

  1. Harold Bickford says:

    Good information. Ken observed, measured and recorded the data and here it is presented for the benefit of all. The Corvair does not run “hot” as some have tried to tell me. The key is in paying attention to what works from those who have done the work.

    Harold

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