Norman E. Howell
Originally published November 1993
This is not going to be your normal EAA Chapter newsletter article.
Recent events in Chapter 49 and 1000 have prompted me to write this paper on the handling qualities of the Lancair 360. As many of you know, EAA Chapter 49 member Bob St. Clair of Palmdale damaged his Lancair 360 (N123ST) in a landing accident on September 29th. Previously, Bob had only flown the aircraft for about 14 hours of the 18 on the airframe. The accident scenario proceeded as follows: Bob landed on runway 07 at Mojave after flying a 1.9 hour mission and reported that it was the smoothest landing he had ever made in the aircraft. The configuration was 10/D (flaps 10°, gear down), and the CG at the time was at FS 25.7 (inches) which was in the forward range of the CG's he had flown, but not the extreme. He had previously flown at CG's ranging from FS 25.19 to FS 29.1 during the flight test program...the published CG limits from Neico being FS 24.5 to FS 30.3. After touchdown, the nose of the Lancair began to rise, and Bob corrected with a small amount of forward stick pressure. The nose continued to rise and Bob added more forward stick pressure and actually moved the stick a bit to get the nose down. He was cognizant of the need for measured small responses in pitch in the flare from previous flight tests and the reports of others in the Lancair newsletter. However, he could not arrest the nose rate fast enough or precisely enough, and his plane (which was now airborne) stalled and fell in from about 4 feet, failing all three landing gear.
Why did this accident happen? Many people would be quick to blame the man, since placing the fault on the pilot would be a natural reaction to this type of accident. However, in weighing all the data collected by Chapter 1000 members on Bob St. Clair's airplane prior to the mishap and my own experiences in Larry Wright's Lancair 360, I reach the following conclusions:
The mission of the Lancair design, as stated in Neico's information package, is high speed. One would expect to use that high speed to fly cross country. To have any utility in cross country, the aircraft must be fully capable of IFR day/night operation. Many Lancair builders have outfitted their aircraft with this capability. Therefore, from conclusions 2, 3 and 4:
Now I realize these are some pretty strong statements. And I should probably disclaimer them as applying only to a stock Lancair 320/360 airframe with the Lycoming parallel-valve 180hp engine and constant-speed prop. However, my observations and the observations of two other test pilots (Doug Shane, also of EAA Chapter 1000, and Chuck Berthe of CALSPAN Corp) are nearly identical, and those observations were drawn from three completely separate examples of this airframe/engine configuration. These observations and recommendations do not apply to any other configuration of the Lancair 320/360, nor do they apply to any permutation of the Lancair 235 airframe. Those combinations have not been tested so no observations may be drawn.
What's Wrong With This Picture?
Well, to answer that, and most importantly, to come up with some possible solutions, we need to take a look at the data. The first sub-question is, why is this airplane so hard to land? For good landing characteristics, FAR Part 23.175 (Demonstration Of Static Longitudinal Stability), paragraph (d) (Approach and Landing) states the following:
"The stick force curve must have a stable slope at speeds between 1.1 VS1 and 1.8 VS1, with-
(1) Wing flaps in the landing position:
(2) Landing gear extended:
(3) The airplane trimmed at a speed in compliance with §23.161(c)(2)(ii):
(4) Both power off and enough power to maintain a 3 degree angle of descent.
For the Lancair 360, VS1 is 62 mph. Therefore, the stable trim slope should be evident from 68 to 113 mph. Also, the trim speed should be at 1.3 VS1 (81 mph). We have the following data:
These data are preliminary and are not quite in line with FAR 23 in that the trim speed is higher than 81 mph and the gear is up. However, notice that the elevator position does not change at all for the curve 10/U-100 CG 27.92 (10° Flap, Gear up, trim speed 100 mph, CG at FS 27.92) from 110 to 73 mph, then the elevator position decreases slightly slowing to 69 mph! The 30/U-90 curve for this CG is a dead straight line. The other two curves are only slightly better. What one would want to see is a steadily increasing elevator deflection as the aircraft slows down. The stick forces associated with the above conditions should also have a nice negative slope. It's easy to get confused here, but for a stable slope in long stat as described in the FAR's you want to see the graph of stick force and stick (elevator) deflection versus airspeed run downhill from left to right. This assumes one calls a pull stick force positive. The CAFE report in the recent Sport Aviation on the RV-6 used push forces as positive (non standard) and further confused the issue.
Let's relate this to what you feel in the cockpit. You are on final approach with your airplane trimmed at 1.3 VS1. Then you allow the airspeed to slow down 10 mph. You should expect to be pulling slightly aft with a slightly greater aft stick (yoke) position (slightly greater elevator deflection) and if you let go of the stick, the airplane would want to go back to its trimmed airspeed. It does not have to want to go back very badly but it should not want to stay at 1.3 VS1 -10 either. Now let's look at the Lancair 360 stick force data with the mental picture you now have in mind of the forces resulting from an off-trim condition on landing approach:
Notice the lack of stick force cues in the 30° flap configuration. Also, in the 10° flap configuration there is a slightly stable slope right up to the point at which you flare, then the force curve reverses. Also note these data are for a forward CG condition! This poor speed stability in the approach configuration and the very low stick forces associated with it is what makes the Lancair 360 so susceptible to pilot induced pitch oscillations on approach and landing.
So how do you fix this problem? Many folks would say to solve this through good pilot training. Neico Aviation, in their letter to Lancair builders on the tail issue (dated 31 March 93) said the following:
"...the existing tail configuration offers documented, good stability in all cruise ranges. In the slow speed, aft CG segment of the envelope, the stability is neutral. This essentially means the stick (and aircraft) will stay where you put it, not returning to the previously trimmed attitude. In the real world, this means you should not fly hands off during short final approaches! We think that's excellent advice for any aircraft.
Are we unique? No. It's interesting to note that a great many aircraft (many military planes) are neutrally stable throughout a large portion of the flight envelope, sailplane pilots typically ballast their gliders with water to achieve overall neutral stability which increases performance through the reduction of trim drag." [emphasis in the original].
I am being generous and polite by stating these explanations are vacuous. The example of the military airplanes is not pertinent since these airplanes are designed to be flown be highly trained, carefully selected aircrews. Even then, I would question the contention of neutral long stat throughout the majority of the flight envelope for military airplanes. The sailplane example is interesting, but the primary reason sailplanes are water ballasted is to shift the entire drag polar allowing higher speeds in racing. Reduction of trim drag is a side effect, and this is offset by the induced drag increase caused by the higher gross weight. And, oh by the way, the sailplane drivers all dump their water prior to landing!!
To fix this problem you must fix the machine, not the man. Neico offers a larger tail for the Lancair 320/360 that complies with the Australian CAA requirements for long stat. Peter Denholm, an Australian Lancair builder, reports "excellent results to FAR 23 standard with the carbon fiber 360 horizontal stabilizer". I would consider the larger tail a mandatory revision to all future Lancair 320/360 airframes. Those still building, and those flying but unhappy with the landing characteristics, should retrofit the larger tail. In addition, any friction in the pitch control system would tend to greatly degrade the handling qualities. The maximum acceptable friction in the Lancair pitch axis should be 0.0000 pounds. Got it?
The larger tail should take care of the first three major deficiencies I stated at the beginning of this article. The fourth, poor lateral stability, is not so easy to fix. Mr. Denholm fitted outward canted winglets to his Lancair to increase the effective dihedral. That may not be the solution for everyone. I think a good wing-leveler or autopilot would be sufficient to handle the lateral stability problem and make the aircraft suitable for IFR flight.
This article will no doubt cause a reaction from many in our hobby. I would hope that Neico would take a similar stance as the people from Stoddard-Hamilton did with their problems and solutions to the Glasair II-S and 1) Admit there are major handling qualities problems with the Lancair 320/360 design. 2) Offer the tail kit at reduced cost to all who desire it, and 3) Make the commitment to fully refine (through substantial and documented flight test) any new Neico/Lancair aircraft to recognized standards prior to releasing kits to the public for construction.
I look forward to flight testing the improved tail Lancair when the opportunity arises and hope to report the same observations as Chuck Berthe did on the Glasair Super II-S in the October issue of Kitplanes:
"The Glasair Super II-S is an excellent example of a case where a designer recognized a problem, fixed it thoroughly, with the result being an airplane with excellent flying qualities. This is an indication to me that our homebuilt industry is truly maturing. Stoddard-Hamilton people should be proud of their performance on this one."
...Norm Howell is a USAF Test Pilot currently assigned to the F-16 CTF. He is a graduate to the USAF Test Pilot School, and a member of the Society of Experimental Test Pilots. His flight experience includes an enviable number of different types of aircraft from his record setting Quickie, the Mighty Sherpa (C-23), the latest F-16s, and many aircraft in between including a number of sailplanes, spam cans, and lots of homebuilts. In addition to his tour as a military instructor pilot, he has logged numerous sorties in the F-4G Wild Weasel during Desert Storm!...[--contributing editor]
Lancair 360 First Flight - June 1993
Test Pilot Report - Lancair 360 First Flight - June 1993
President's Column - December 1993 - Neico's semi-official non-response to the handling qualities issue
Big-Tail Lancair 360 Update - September 1995
Contents of The Leading Edge and these web pages are the viewpoints of the authors. No claim is made and no liability is assumed, expressed or implied as to the technical accuracy or safety of the material presented. The viewpoints expressed are not necessarily those of Chapter 1000 or the Experimental Aircraft Association.
Revised -- 2 March 1997