Assessing necessity – wind tunnels at Cessna

Our Vice President of Engineering (hereafter called just the VP) at Cessna during my time there in the Golden 1950s was sort of a contrary guy. For instance, he didn’t like attending meetings with the FAA, which he rarely did, I guess because he thought the Feds were so bureaucratic to deal with.

And he tenaciously stuck by certain requirements he put forth, like having all the fuel on the twin engine Model 310 in tip tanks, to get that hazard away from the passengers in case of an accident, even though we proved by flight test that having tip tanks on the airplane compromised some of its otherwise better flying characteristics. (OK, its characteristics with the tip tanks on were still pretty fine.)

Wind tunnel test
We don’t need no stinkin wind tunnels…

And he was absolutely sure that wind tunnel tests were a waste of time. Up to the time of the four engine Model 620 the only one of the current Cessna airplanes that had been tunnel tested was that M310 (which testing was conducted before my time and I don’t know how that was allowed – I did come on board in time to do the analysis of its test), though I thought I saw a model of the also “before my time” M190-195, but it might have just been for display.

But I had gotten in on the beginning of the 620, when it was only a “What if” exercise answering what would an airplane that met a recent business aircraft association survey of desired qualities look like, and could it be a Cessna product?

A board designer laid out the fuselage according to the stated preferences of the potential customers, and I got to select such aerodynamic things about the configuration as wing and tail areas, airfoil sections, and trailing edge device size and deflections.

The resulting design looked pretty good, met the survey specification, and had promise as a Cessna offering, so management authorized proceeding, incrementally, with the project. But the proposed configuration had four engines – engines of the type we were certainly used to dealing with, but not in such quantity.

So I petitioned for a wind tunnel test of “my” design, arguing that it was necessary because of the overall importance of this financially challenging undertaking and because estimating power effects on such a configuration was difficult, and I believed needed to be confirmed by test. After heartfelt discussion, our VP reluctantly agreed to let us do it.

We conducted the comprehensive powered model tunnel tests as I proposed, and I oversaw the analysis of the data. Things had worked out great and we were sure we had a design that met the business airplane sector’s recently stated desires and FAA requirements too, even though we would probably certificate the airplane under the airline category because it was big and we had distant ambitions for it as a commuter airliner as well.

And not a thing was altered due to the wind tunnel tests, except from them I selected one of four wing-fuselage fairings we had configured that were evaluated in the tunnel routine. So I proudly circulated the overall results of the tunnel testing to the proper company officials, with the implied recommendation that the company proceed with the Model 620 business aircraft program.

Soon after I saw the VP enter our infrequently visited area at the back of the Experimental hangar, and he seemed to be headed for my desk. I thought, he’s going to compliment me on the great job I did selecting a configuration for the 620 that met all requirements and, unprecedented, without one change due to the model testing.

He stopped at my desk, said “See, I told you we didn’t need a wind tunnel test” and walked on.

P.S. That precocious 620 wind tunnel model is now on display in the Cessna exhibit at the Kansas Aviation Museum in Wichita.

4 Comments

  • My first endeavor was to launch a perfectly build glider, wingspan 32 inch, me aged 9-10, unfaithfully she couldn’t lift the weight required for to compansate the useal heavy empanage, many years later I extended her bow by 10 inching by stolen knittin’pin, poor mom, but ýellow flew the way she was suposed to do, as A queeny. ciao, joja.

  • I really enjoy these stories of engineering that you share from time to time. An engineer myself I can appreciate this one especially!

  • Great article by harry clements. He is correct in describing father as contrary, which may require some clarification. I too did design work for him after his retirement. He had set requirements in mind at the beginning of most efforts and stuck with them. One of my coworkers at Beech had an on board review by father and Jerry Gertise one day and father was critical of his design to the point he felt he would be starting over. Jerry came by later and said father liked his work. Father wanted to be sure you believed in your design, which required critique. He was very commited to safety and felt very strongly about the fuel issues. He was very affected by accident situations he witnessed and reviewed. He was also flustrated by the advances in engine technology in automobiles and the lack of advances in aircraft. He would have liked the diesel era that is coming.

  • I attribute the VP’s reluctance to meet with the FAA to not wanting to deal with their bureaucratic ways, because I never heard him actually say so. But they sometimes wasted the company’s time and money by requiring a test on a change that couldn’t possibly have affected the characteristic they insisted on re-testing. Some of them were more realistic and would just waive that test.
    What I liked about the VP was him saying he disagreed with what you wanted to do, but go ahead and do it anyway. I don’t even remember who was right more of the time, because – as in the article – we were just trying to get it right and there were no repercussions.

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