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Report Cards for Homebuilt Aircraft

(c) Ed Wischmeyer
Originally published in Inflight USA

There is a wide range of accepted handling characteristics among factory built airplanes, and the range is wider still for homebuilts. I continue to marvel at the range of homebuilt handling characteristics, the subtleties, the nuances, the quirks, and the gotchas. The truth of the matter is, homebuilt owner/builder/buyer/pilots are terrible consumers -- we take whatís there, we donít ask the right questions, we adapt where we have to, we make excuses for the manufacturer, and sometimes we die in the effort.

My personal flight records show 120 kinds of aircraft flown, more than two dozen of those being homebuilts. How many of those have, say, been spin tested? Not all of them!

Well, gee, you say, nobody with any skill is going to accidentally spin something like, say, a Whizbang 2000. Thatís a really fast, really high wing loading rocket that only the big buck boys will play with, and they all know how to avoid a spin. Well, maybe they do know how to avoid a spin, but what happens some day in a slightly tight turn to final with a tired pilot in gusty conditions? Is there adequate stall warning and adequate control authority? Is the design so highly tuned that an imprecise customer airplane will not have the safety margin that the factory (hopefully) demonstrated? Is any of this documented somewhere in some standard way so that anybody can find out whatís been tested, what hasnít, and what the results were?

How do you really know what you're getting if you canít get a full envelope checkout, or if youíre a prospect?

Homebuilders have tremendous freedoms in this country, freedoms to allow the individual to experiment, to tinker, to try, to do new things. This is in the best traditions of our country. Itís one thing, however, for an individual to try things (build and fly their own design), then another thing for somebody else to want to repeat the experiment (by buying plans), but quite something else for a manufacturer to offer kits and quickbuilds, do slick advertising, have booths at airshows and all that as a way of pursuing business without bothering with the niceties of acceptable handling characteristics or consumer safety or even full disclosure.

But then, suppose a customer takes a standard design and just has to improve on it a little bit, in that best tradition, and they booger the design and screw the safety margins. Is that caveat emptor or the kit vendorís responsibility? Weíd probably all agree on the former, but the kit builder will still take a publicity hit.

Or suppose the airplane is an entry level plane, not advertised as aerobatic, just a here to there machine. What implicit promise is there, not in a legal sense, but an expectation in the mind of the owner/builder/buyer/pilot, that the airplane will be as safe as a Cherokee or a 172? The mission is the same. The engine is the same. The wife and family are the same. The expectation is the same. The demonstrated safety is not.

Or suppose the airplane is not really aerobatic, and not suited to aerobatics, but, due to marketing pressure, they toss in a video clip of the plane doing a roll. Sure, there may be a disclaimer somewhere, but does that set customer expectations properly?

Or consider, how many of the cross country cruisers are really good for IFR? Then again, how many spam cans are really good for IFR? Fuel imbalance, out of rig airplanes, crappy instruments, bad response to turbulence, lots of spam cans arenít so great, either. Supposedly, a NASA report on general aviation handling qualities some years ago had some uncomplimentary things to say about general aviation handling qualities for single pilot IFR in turbulence.

Maybe we need a report card for homebuilt handling characteristics, to let the prospect know what theyíre getting into. This is not a catalog of aircraft, it is a standardized documentation of how aircraft have been tested. The report card has two parts: to tell how the airplane (at least the test specimen) really handles; and to document and standardize whatever formal testing may have been done.

The gotcha is that the report card has to be repeatable from evaluator to evaluator and from customer to customer and from airplane to airplane, so that anybody can do the tests and everybody will get the same results. Any third party should be able to duplicate factory results. This means quantitative, not qualitative. It also means that the report has to be written in homebuilder-ese, not test pilot-ese.

These tests should be simple enough that they can be completed in a reasonable time, such as three hours. The tests should be done in light chop and a crosswind, not in smooth air, for full disclosure.

What things go into a report card? Some of the simple ones would be:

  • Was the full center of gravity envelope flight tested?
  • The weight and measured performance of the prototype, with speeds done from GPS averages
  • Was spin testing performed? How? At what c.g?
  • What flutter testing, or ground vibration analysis, was performed?
  • What crosswind component has been demonstrated?
  • Static testing, plus and minus, on which components to what limits?
  • Usable and unusable fuel capacity in different configurations.

    There should also be measures of how the plane responds to poor pilot techique. For example, what happens in the flare if a quick tug is put on the elevator? What happens if you stall with the ball one width out of center? What happens if the stall recovery is slow? What happens if you touch down 5 degrees off heading? What happens in various kinds of bounced landings?

    Some of the quirks and gotchas that Iíve observed in flight (most of these can also be found on certificated spam cans) include:

  • Overly sensitive pitch during the landing flare
  • Low pitch forces for wide range of speeds on approach
  • Unusual changes in pitch forces needed during takeoff rotation
  • Poor yaw stability, even in cruise
  • A frisky Dutch roll mode excited by turbulence and very difficult to damp out
  • Inadequate aerodynamic stall warning
  • Significant change in handling characteristics with c.g. change
  • Yaw / pitch control coupling
  • Asymmetric left / right handling
  • High pitch forces on go around
    Iíve also heard about, and avoided flying in, planes which cannot be trimmed to approach speed, or planes which are pitch unstable at landing.

    One (qualitative) way of doing a report card on handling would be to do this on a comparative, not absolute basis. For example, in landing flare, the PieChaser, the Whizbang Y2K, and the Spamcaneroo would all be in one group. The Duck, the Canard, and the PickleFork would all be in another group. This would at least give you a clue as to what you were getting, and this idea, what planes fly similarly, is already well accepted, although not codified.

    Demo flights are not adequate for a prospect to adequately evaluate an airplane. Demo flights are usually too short, too benign, too exhilirating, for a prospect to objectively examine the whole flight envelope. The idea of a demo flight is to sell the customer on the plane, not to inappropriately focus on what may be minor shortcomings. And besides, very few prospects will have the flying skill or experience to evaluate a complete flight envelope.

    There are obstacles to the report card idea, of course. Iíve observed one vendor who was defensive and not objective with regard to his product, and heard him badmouth and discount criticism -- in this case, takeoff figures measured at 1000 feet above sea level and 90 degrees, those being unrealistic conditions for evaluating his pleasure craft. Maybe itís not supposed to be flown in the summer. Several vendors were so accustomed to their product lines that some major handing shortcomings were not considered significant. Yet another design was tweaked by a test pilot who, I suspect, was so skilled that the handling shortcomings werenít noticed. And exaggerating manufacturers are all too common.

    Another obstacle is the quality of the plane tested. A plane with light, low friction, well lubricated and adjusted flight controls will handle differently from one beset with stiction and friction, or one with erroneous angles of incidence. An indication of airframe variation comes from the good folks at Glasair, who some years ago lowered their published performance numbers to be representative of what even their less skilled builders were achieving, not just what the good builders and the factory got.

    There are liability and good will issues, as well. Very few pilot reports are truly candid, because the truth, harshly presented, can hurt the manufacturer, hurt advertising revenues, hurt relationships with organizations, and hurt the sport flying movement. Unfortunately, lack of candor can hurt enthusiasm, can hurt bank accounts, and can hurt occupants. Report cards might help.

     
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