Lancair Legacy BY BRIEN SEELEY, C.J. STEPHENS AND THE CAFE BOARD Sponsored and Funded by the Experimental Aircraft Association AIRCRAFT PERFORMANCE REPORT ere are the keys, please bring it back to us in two weeks”, is what they told CAFE Foundation Chief Test Pilot, C.J. Stephens after his 15 minute checkride in the Lancair Legacy factory prototype, N199L. Such is the confidence inspired by C.J.’s piloting skills as well as Lancair’s faith in their new design. C.J. has flown over 100 different types of aircraft, including many military jets, and is well known as an instructor for race pilots at the Reno Air Races. He is not easily impressed by any aircraft. But the Legacy got his attention right away when he flew it from Lancair’s Redmond, Oregon plant to Santa Rosa along- side the Glasair III that he built with partner Jim Reinemer. The Legacy required only 17 inches of manifold pressure to stay abreast of the Glasair III running at about 22 inches M.P.. Legacy N199Lis one of roughly ten that have been completed out of about 100 kits that Lancair has sold since the kit was introduced in October 2000. It should be emphasized that, though the Legacy’s performance impressed all of us at the CAFE Foundation, even more remarkable was the nifty elegance evident in every feature of its design. No aircraft ever tested by CAFE has scored such high marks in all areas. The name Legacy is appropriate for an aircraft that so clearly incorporates the best in current available technology for light aircraft. From its excellent new Continental engine and new design prop to its highly efficient airfoil and flap system and the structural efficiency of its “H LARRYFORD PRESIDENT Brien Seeley VICE PRESIDENT Larry Ford TREASURER Johanna Dempsey SECRETARY Cris Hawkins CHIEF TEST PILOT C.J. Stephens TEST PILOT Otis Holt DIRECTORS Stephen Williams Ed Vetter Jack Norris Scott Nevin Bill Bourns Darrel Harris The CAFE Foundation, Inc.-- Comparative Aircraft Flight Efficiency, a non-profit, tax-exempt, all-volunteer educational organization:
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Transcript
Lancair LegacyBY BRIEN SEELEY, C.J. STEPHENS AND THE CAFE BOARD
Sponsored and Funded by the Experimental Aircraft Association
AIRCRAFT PERFORMANCE REPORT
ere are the keys, please bring it backto us in two weeks”, is what they toldCAFE Foundation Chief Test Pilot, C.J.
Stephens after his 15 minute checkride in theLancair Legacy factory prototype, N199L. Suchis the confidence inspired by C.J.’s pilotingskills as well as Lancair’s faith in their newdesign. C.J. has flown over 100 different typesof aircraft, including many military jets, and iswell known as an instructor for race pilots at theReno Air Races. He is not easily impressed by
any aircraft. But the Legacy got his attentionright away when he flew it from Lancair’sRedmond, Oregon plant to Santa Rosa along-side the Glasair III that he built with partner JimReinemer. The Legacy required only 17 inchesof manifold pressure to stay abreast of theGlasair III running at about 22 inches M.P..
Legacy N199Lis one of roughly ten that havebeen completed out of about 100 kits thatLancair has sold since the kit was introduced inOctober 2000. It should be emphasized that,
though the Legacy’s performance impressed allof us at the CAFE Foundation, even moreremarkable was the nifty elegance evident inevery feature of its design. No aircraft evertested by CAFE has scored such high marks inall areas. The name Legacy is appropriate foran aircraft that so clearly incorporates the bestin current available technology for light aircraft.From its excellent new Continental engine andnew design prop to its highly efficient airfoil andflap system and the structural efficiency of its
“H
LARRYFORD
PRESIDENTBrien Seeley
VICE PRESIDENTLarry Ford
TREASURERJohanna Dempsey
SECRETARYCris Hawkins
CHIEF TEST PILOTC.J. Stephens
TEST PILOTOtis Holt
DIRECTORSStephen Williams
Ed VetterJack Norris
Scott NevinBill Bourns
Darrel Harris
The CAFE Foundation, Inc.--Comparative Aircraft Flight Efficiency, a non-profit, tax-exempt, all-volunteer educational organization:
graphite skins, the Legacy design team hascreated a new benchmark in kit aircraft sophis-tication.
Lancair, founded in 1984 by Lance Neibauer,has successfully evolved kit production tech-niques through the development of the Lancair235, Lancair 360, Lancair IV and Lancair ES tobe a leader in today’s efforts to help buildersassemble their aircraft in less time with moreconsistent quality. The several fastbuildoptions for the Legacy include the airframe,e n g i n e / a c c e s s o r i e s / b a ffling, and firewall. Vi s i twww.lancair.com for details.
The designer of the Legacy airfoils, flaps andother aerodynamic features is Greg Cole. Themagic in the Legacy’s lift to drag characteris-tics, reflected in this report, affirm that heshould be considered among the best oftoday’s aerowizards.
This is the first CAFE Aircraft PerformanceReport to present the concept of “speed forbest CAFE fuel flow”, or VbC . This new way ofchoosing ideal cruise power is explained in thesidebar that follows and we hope will becomeas familiar a speed concept to pilots as Vne ,Vy , etc. A detailed Legacy report is availableat www.cafefoundation.org.
Legacy N199L
Handling Qualities
By: C.J. Stephens
Introduction
The data reported in this portion of the A P Rwas recorded on a camcorder during flight .Stick force was obtained using a handheld stickforce gauge and temporarily installed 'g' meter.The airplane was loaded with ballast to obtainthe desired center of gravity and takeoff weightbefore each flight.
First Impression
Awesome performance!
The Legacy looks beautiful in every respect sit-ting on the ramp with the bright sun bringing tolife the Flex paint that constantly changes col-ors with each different angle of perspective. Itssleek lines flow into a very graceful, ‘aerody-n a m i c ’ shape. The most noticeable featuresare the larger than standard cowl, whichencloses a 310HP engine, and the largePlexigas canopy that offers the pilot station anunobstructed view.
This aircraft calls to all who pass to take a sec-ond look and at each fuel stop attracts peopleto come closer to admire and comment. T h ewindshield requires regular cleaning beforeflight to remove the nose prints of the manycurious spectators. The Legacy has a beautythat is state of the art in both design and perfor-mance. Not long into my first flight the thought"awesome" was forming in my mind.
External Appearance
The plane sits level on its tricycle landing gear.The double sweep of the leading edge and thecurved wing tips give it a distinctive look of itsown that stands out from other designs.
Cockpit
The wing height is low enough that it is not diffi-cult to step up on the wing non-slip strip whilestill being careful not to step on the flap. Oncestanding on the wing, it is easy to step into thecockpit because the huge bubble of plexiglass
that forms the windshield and canopy swingswell up out of the way on its forward mountedhinges. There is no need for stooping or crawl-ing when entering this cockpit. Once settledinto a sitting position the cockpit is comfortableand gives good freedom of movement withadequate shoulder room. The side-by-sideseating arrangement provides a wide instru-ment panel with enough room to install almostany equipment desired for flight. The Lancair-Legacy prototype had enough instruments tofly light-duty IFR, having no de-icing except forpitot heat.
N199L had three-axis electric trim which oper-ated tabs on the various surfaces. Four buttonson the top of the stick grip operated the ruddertrim and the elevator trim. Since I am moreused to having the roll trim on the stick gripthan the rudder trim this took some gettingused to. The elevator trim worked quite wellbut was very sensitive and called for just a tapof the button in the desired direction to adjustthe pitch trim. I also found that operating ourflight test equipment in the cockpit occasionallycaused things to rest on top of these trim but-tons, which caused sudden and excessiveinputs of unwanted trim. We have been toldthat the final version of the kit will use a differ-ent stick grip configuration for trim control. Theroll trim was operated by a spring-loaded tog-gle switch located on the center console. Bothpitch and yaw trim had indicators to show theirposition but the aileron was easily positionedby simply looking at the left aileron to see trimtab position.
The large baggage compartment is accessiblewhile seated in the cockpit. When fully open,the canopy frame blocks the forward view andmust be lowered most of the way before start-ing the engine. With the canopy in the nearlyclosed position the visibility during taxiing isgood and the ventilation and windshield defog-ging are excellent. Prior to takeoff the canopy issimply lowered the last small amount and alarge lever located between the shoulders ofthe occupants is rotated downward to engagestout hooks that hold the aft canopy framesecurely down and locked. There are no othercockpit indication that the canopy has beenlocked other than observing that the hookshave engaged their receivers. I was told byLancair that if takeoff was performed with thecanopy unlocked, it would not be a major con-cern since the airplane flies just fine in such acase. However, it would be necessary to landin order to re-lock the hooks since the upwardaerodynamic force would makes it impossibleto close during flight.
Once the canopy is fully closed, totally sur-rounding the occupants, the real beauty of thisdesign becomes apparent. There are noobstructions in any direction, giving a field ofview that probably surpasses even that of theF-16.
Ground operations
LARRYFORD
310 BHPC o n t i n e n t a luses tunedintake pipes.
CAFE Chief Test Pilot, C.J. Stephens
Even at maximum allowed gross weight the air -plane starts rolling quickly with minimum powerapplication. The toe brakes work well andsteering, even with cross winds, is very easy tomaster.
The nose gear design is superb. It is an inter-nally damped strut with no external scissors.This small package fits nicely into the smallgear well. It tracks very well using only lightbrake application, and showed no tendency toshimmy.
Takeoff And Climb
The pre-takeoff checks are all of the normalitems for an airplane of this type. The flaps areset to a 15 degree down position visually bylooking at their trailing edge.
As wide open thro t t le is app l ied to theContinental IO-550-N engine, the exhilarationof 310 HP coupled to a lightweight and aerody-namically clean airframe first becomes appar-ent. Takeoff roll is brisk with lift-off occurring at76 KIAS. The electric/hydraulic landing gearsystem raises the landing gear quickly makinga smooth transition to the climb schedule. Fullpower climbs are phenomenal and 25" X 2500RPM climbs are impressive. Climbs routinelyseem to show well over 2,000 fpm. See climbperformance data in other part of this report forgreater detail.
The view over the nose, especially duringclimb, is improved with proper sitting height.This should be checked prior to engine start byclosing the canopy and adding seat cushions toadjust the height. There are literally no visualobstructions in the cockpit and by climbing atan indicated airspeed of 160 KIAS adequateforward visibility is obtained.
Static Longitudinal Stability
With the airplane properly tr immed at itsmaneuvering speed ( Va ) of 150 kts, the stickforce was measured as the airspeed wasincreased or decreased in 10 KIAS intervals
over its useable airspeed range. This wasdone to determine the propensity of the air-plane to return to trimspeed. The push or pullstick force measurements in pounds wererecorded at both forward Cg and, on subse-quent flights, Aft Cg. See graph. for details.
Maneuvering Stability
With the airplane trimmed for Va (150 KIAS) aturn was initiated and stick forces were mea-sured at various 'g' forces as the turn rate wasincreased. (see graph.)
Spiral Stability
With the airplane trimmed for 150 KIAS, a 15degrees bank was established and all controlswere released to observe if the airplane wouldover bank or roll out of the turn. Turns in eachdirection continued at the same bank angle forin excess of 30 seconds. The aircraft thusexhibited neutral spiral stability.
Dynamic Stability
After establishing stable level flight at 190, 150,or 120 KIAS, I introduced a 2g pitch input dou-blet and released the control stick, recordingthe resulting aircraft response. In all cases the
12
10
8
6
4
2
0
-2
-4
-6
Instrument panel IAS, mph
Legacy, fwd c.g., 150 kts.
Legacy, aft c.g., 150 kts.
RV-8A, fwd c.g., 140 mph
Wittman W10 @ 18% MAC
Cessna 152
Trimmed to zero pounds withstick- free and flaps up at Va.
Pull(-)
Push(+)
Static longitudinal stability
Maneuvering stability at Va.
0
5
10
15
20253035
1 1.5 2 2.5 3 3.5
Load in G's
Legacy @12.4% MAC, 150KIAS
RV-8A, fwd c.g., 140 IAS
W10 Tailwind @ 18% MAC
Cessna 152
results were deadbeat and showed no residualpitching. Rapid roll inputs were similarly intro-duced and the airplane stopped instantly whenthe control was released (deadbeat).
Dihedral normally causes an airplane to roll atsome rate with the input of rudder, especiallyas the angle of attack is increased. Wi n gsweep will also cause this dihedral effect.
The Legacy only has 3.7 degrees of dihedralso one would expect it to have a low roll-due-to-yaw response. Before testing this airplane Iexpected it to have a strong tendency to rollwith yaw since it has such an interesting dou-ble leading edge sweepback; however, to mysurprise, it had nearly zero roll-due-to yaw atany of the airspeeds tested.
The aircraft’s nose showed minimal overshootof the zero yaw position upon releasing therudder from a full ball-width displacement yawinput.
Roll Rates
The roll rate was evaluated by timing, with astop watch, the time to change from a 60degree bank in one direction to a 60 degreebank in the other direction while using maxi-mum deflection of the aileron and coordinatingrudder. The resulting time includes the time toaccelerate the roll and therefore reflects a
slightly slower roll rate thanthe steady state rolling ratethat the airplane is capable ofsustaining. The roll rates inboth directions at Va ( 150KIAS ) calculated to 80degrees per second, whichcertainly seemed brisk.
Trim Adequacy
With the airspeed at 150KIAS roll trim had the capaci-ty of producing 2.6 lbs offorce to the left and 0.9 lbs offorce to the right. T h i s
amount of trimming force seemed sufficient fornormal flight.
Stalls
Stalls were explored at 9,000 ft using 8" MP toestablish an approximately a 1 knot per secondrate of deceleration. The clean configurationstalls occurred crisply after mild aft stick forcebuild-up and with little advanced warning. A tthe moment of stall the right wing droppedapproximately 30 degrees but this becamecontrollable using both rudder and aileron asthe angle-of-attach was reduced. The resultingnose drop would cause only about 150 feet ofaltitude loss provided that the stall recoveryinput was commenced immediately.
Stalls with full flaps were explored with resultssimilar to those obtained in the clean configura-tion. The deceleration was quicker due to thedrag of the flaps and the nose attitude waslower prior to the stall. The wings maintained amore level attitude during the stall and recoverythan they had during the clean configurationstalls. The stall was equally crisp and warningwas very brief (less than one knot). A l t i t u d eloss during recovery was 400 feet due to thenose-low attitude obtained during the post-stallphase of controlling angle of attack.
Accelerated stalls and high angle-of-attackmaneuvering were sampled at airspeeds ashigh as 130 KIAS. Mild buffet occurs just priorto accelerated stalls and the stick position iswell aft giving the pilot an excellent cue as tothe wing’s aerodynamic condition.
Stalls in both configurations were comfortableand controllable throughout. Stick force buildup and stick movement were mild but adequateduring stalls.
Field of View
FABULOUS. Steep banked lazy eights wereperformed with several different flight engineerson board. All persons that experienced thehighly banked pivot at the top of this maneuveragreed that the view was just fabulous. T h etotally unobstructed in the upward direction issimilar to the view that a sky diver must experi-ence when first jumping from an airplane, onlyin the Legacy there is no strong wind in yourface.
Descents
The Legacy has a very wide range operatingairspeeds. This helps give it the capability todescend very quickly to any desired altitudeonce the power is reduced and the nose is low-ered. N199L did not have a speed brakeinstalled nor do I feel that one is called for inthis design.
Traffic Patterns
Entering the traffic pattern is very satifying dueto the sense of an excellent view of traffic. The
The double taperedleading edge andsheared wingtip.
Full landing geardoors cover theoleo gear and tires.
#2--2/23/02
#2--2/23/02
#2--2/23/02
clean
full flaps
full flaps
8.5/1821
9.7/2027
10.2/1842
2218
2217
2128
72.4/83.4
59.2/68.2
56.9/65.6 **
fwd c.g. at various
M.P. and RPM's
Wing Baro #3
**panel read 57 kts
Flight/Date Mode MP/RPMWeight,
lbCAS,
kt/mph
Removable glareshield gave goodaccess to instruments.
cockpit workload is minimal and is easilyunderstood with very little training. A d v a n c e dplanning is required so as to be able to reduceairspeed to the landing gear extension air-speed of 122 KIAS. This instrument panel wasarranged so that the landing gear handle andindication were at eye level just below theglareshield, making them easy to operate andm o n i t o r. On downwind at gear speed the for-ward view is adequate and improves as theflaps are extended. The extra drag with gearand flaps down requires only modest additionalpower to maintain level flight. Yet the availablesurplus of drag is sufficient to steepen a theglide slope to well beyond the norm. To me, itfelt like an ideal combination of available dragand power to comfortably manage any traff i cpattern.
Landing
The Legacy has a surprisingly slow landingspeed for its wing loading. It achieves thismainly by virtue of its highly effective and welldesigned displaced-hinge slotted flap.
Several factors go into what makes some air-planes easier to learn to land than otherdesigns. These factors include its approachspeed, rate of deceleration, field of view, sittingheight on the ground (due to gear length), con-trol feel and sensitivity. Because the Legacybalances all of these factors so as to readilyput pilots in the comfort zone, it will undoubted-ly gain a reputation as an airplane with nicelanding characteristics.
Summary
The Legacy is one of the next generation of‘fast glass’ designs that take advantage ofknowledge gained from those that have gonebefore them. It has superior performance andhandling qualities. Although it is not the planefor a beginner, I am confident that pilots withmodest experience and adequate training willbe able to fly it safely. During the 14 hours thatI flew this airplane, I did not find a single thingthat I didn’t like about it. It was with great reluc-tance that I delivered this airplane back to thefactory when our testing was complete.
Vmax, TAS, 8493’dens.alt., 2205 lb, 23.5”, 2550 rpm, 15.7 gphStall speed, 2128 lb, 10.2” M.P., 1842 RPM, dirty, CASMaximum rate of climb, 2158 lb, 2690 RPM, 27” M.P., 28.1 gphT.O. distance., 0 mph wind, 52°F, 125 ft MSL, 2150 lb, 87.1” c.g.Liftoff speed, by Barograph, 2182 lb, CASTouchdown speed, Barograph, 2046 lb, CASMin. sink rate, 2217 lb, 96 mph CAS, 110 mph TAS, flat pitch, 5.9”Glide ratio, idle, 158 CAS, 168 TAS, coarse pitch, 980 RPM, 9.6”, 2127 lbNoise levels, ambient//full power climb/75% cruisePeak oil temp. in climb, 155 mph CAS, full power, 13,000’densityCowl exit air temp, max., 140 mph CAS, 55°F OATCooling system ram recovery, %, climb/cruisePropeller max. static RPMEmpty weight, per CAFE scales
CAFE MEASURED PERFORMANCE, N199L
253.7/292.31 kt/mph56.9 kt/65.6 mph
2632 fpm@ 155 mph CAS1018 ft
73.8/85 kt/mph79/91 kt/mph
1038 fpm13.3 to 1
39/101/100 dBA196° F177° F
117% in climb, 60% in cruise2662 RPM1493.95 lb
The Legacy was lev-eled and weighed onthe CAFE scales beforeeach flight.
Fixed, non-adjustablecowl exits give 38 sqin of total outlet area.
Darrel Harris, left, and C.J.Stephens crewed the flight testing.
FLIGHT TEST DETAILS
11 flights including 4 data collectionflights were made during February2002, all during day VFR conditions.
A Flowscan 201A fuel flow trans-d u c e r was used for the gphdeterminations and was calibrated bymeasuring the weight of fuel burned oneach flight. A PropTach digital tachome-t e r was mounted on the top of theinstrument panel. Performance dataflights were conducted with pilot andflight engineer aboard. Flying qualitiesw e re evaluated using an analog G meterand Brooklyn Tool & Machine Co., Inc.NJ hand-held stick force gauge.
Cruise flight data were obtained withthe wingtip CAFE Barograph (#3)
mounted on a wing cuff with a dummyb a rograph and cuff mounted on the op-posite wing. These were correlated withthe panel airpseed indicator to pro d u c ethe airspeed correction table shownherein.
Cowl exit temp (C.X.T.) is a functionof the OAT & CHT and serves as a keyn u m b e r f o r calculating the cooling sys-tem performance.
Cooling ram re c o v e ry was measure din both climb and cruise.
The Legacy flaps are very eff e c t i v e .They reduce the stall speed from 83.4smph clean at 2218 lb to 65.6 smph withfull flaps and gear up at 2128 lb. Com-putation shows this to re p resent anastounding increase in CLmax due toflap deployment from 1.51 clean to 2.54
Cost of kit, no engine, prop, avionics, paintKits sold to date of 310 BHP version (10/2000)Number completedEstimated hours to build, fastbuild kitsPrototype first flew, dateNormal empty weight, with 310 BHP engineDesign gross weight, with 310 BHP engineRecommended engine(s)
Advice to builders: 3-4 months to kit delivery,multiple fastbuild options, visit website.
Every effort has been made to obtain themost accurate information possible. T h edata are presented as measured and are sub-ject to errors from a variety of sources. Anyreproduction, sale, republication, or other useof the whole or any part of this report with-out the consent of the Experimental AircraftAssociation and the CAFE Foundation isstrictly prohibited. Reprints of this reportmay be obtained by writing to: SportAviation, EAA Aviation Center, 3000Poberezny Road, Oshkosh, WI. 54903-3086.
AC K N OW L E D G E M E N TS
The CAFE Foundation gratefully acknowl-edges the assistance of the several very help-ful people at Lancair, Anne Seeley, EAAChapter 124, and the Sonoma County AirportFAAControl Tower Staff.
SPONSORS
Experimental Aircraft AssociationEngineered Software “PowerCadd” and WildToolsBourns & Son SignsDreeseCode Software at ww.dreesecode.com
WingspanWing chord, root/tip, Wing area, Wing loading Power loadingSpan loadingWetted area fuselage/wing/hor./vert./totalAirfoil, main wing, CLmaxAirfoil, design lift coefficientAirfoil, thickness to chord ratio, max thick @Aspect ratio, span2/ sq ft wing areaWing incidenceThrust line incidence, crankshaftWing dihedralWing taper ratio, root to tipWing twist or washoutWing sweepSteeringLanding gearHorizontal stab: span/area/sectionHorizontal stabilator chord, root/tip/incidencElevator: total span/areaElevator chord: root/tipVertical stabilizer: section/area incl. rudderVertical stabilizer chord: averageRudder: areaRudder chord: bottom/ topAilerons: span/chord at root/tip, eachFlaps: span/chord at root/tip, eachFlaps: max deflection angle, up/downTail incidenceTotal lengthHeight, static with full fuelMinimum turning circleMain gear trackWheelbase, nosewheel to main gearAcceleration Limits
AIRSPEEDS PER OWNER’S P.O.H., IASNever exceed, VneManeuvering, Va , by weightBest rate of climb, VyBest angle of climb, Vx, CAFE est.Stall, clean, 2200 lb GW, VsStall, dirty, 2200 lb, GW, VsoFlap extension speed, VfGear operation/extended, Vge
PROPELLER:MakeMaterialDiameterProp extension, lengthProp ground clearance, empty of fuelSpinner diameter/length
Electrical systemFuel systemFuel typeFuel capacity, by CAFE scalesFuel unusableBraking systemFlight control systemHydraulic systemTire size, main/noseCABIN DIMENSIONS:
SeatsCabin entryWidth at hipsWidth at elbowsWidth at shouldersHeight, seat pan to canopy, torso axisLegroom, rudder pedal to seatback*Baggage dimen. to height of seatbackBaggage weight limitLiftover height to baggage areaStep-up height to wing T.E.
Legacy N199L Specifications: ALWAYS CRUISE AT “VBC”
This report introduces a new termthat the CAFE Foundation believes isvery useful for pilots in selecting theirc ross-country power settings. Theterm “VbC “ can be used much like the
other “V’s” with which pilots arefamiliar, such as Vne and Vy.
What VbC defines is the “velocity for
best CAFE” or best Co m p a r a t i v eAi rcraft Flight Eff i c i e n c y. This is thevelocity that was the quest of all theCAFE 400 air racers in the 1980’s. Itoccurs at the particular mixture settingthat delivers the best CAFE score for agiven RPM, altitude and throttle posi-tion.
Each aircraft has a theoretical singleabsolute best power, mixture, RPM set-ting for achieving VbC at a given alti-
tude. This special power settingdepends on the drag curve of the air-craft, the torque and fuel economycharacteristics of its engine, the pro-peller efficiency, etc. More practical isto find the Vb C that pertains to an
RPM setting and altitude that seemreasonable to the pilot on a given mis-sion. Those are what are depicted inthe several cruise performance graphsthat follow in this report.
Finding VbC is not difficult if a pilotrecords the whole range of level cruiseairspeeds that occur as the mixture isleaned from rich settings to very leansettings. The CAFE score for eachsuch speed is simply determined bycalculating the velocity to the 1.3power and then multiplying it timesthe MPG that occurs at that velocity.
Why the 1.3 power exponent?Consider 3 mathematical expre s s i o n s :V1/gph V2/gph and V3/gphTheir exponents for velocity are either1, 2 or 3 and this determines where onthe speed range of the aircraft thesee x p ressions optimize or reach theirpeak. V1/gph is the same as MPG andthis peaks at around Vy , which is tooslow for cruise. Likewise, V2/gph is Vtimes MPG, which peaks at at Carsonspeed or 32% above Vy, still too slowfor cruise. V3/gph corresponds to theflat plate drag and peaks at maxp o w e r, too fast for cruise. V1 . 3 t i m e sMPG turns out to be just right, peak-ing at cruise power settings of about55-65% power.
Legacy N199L; wide open throttle, CAFE data 2/23/02. CHT for 100 °F day.Cont. IO-550-N engine, 310 HP. VbC = speed at best CAFE fuel flow.
Legacy N199L: EGT and CHT spreads at 12,500', 2550 RPM
= 266.4 smph @ 12.0 gphVbC
12.5K/2550: This graph depicts theimpressive ability of the Legacy to deliverover 270 smph while achieving over 20mpg. Because these values occur at a fuelflow of 13.3 gph and this causes the EGTvalues to be at or near their peak, it is moredesirable to operate at a leaner setting. Ifthe mixture is set for 12.0 gph, the TA Sdrops to 266 smph and the mpg increasesto 22.2. Note also that, at this mixture set-ting, the range increases by 10% over thatobtained at 13.3 gph. Likewise, the CHTvalues are reduced by from 10-30 °F, andthe exhaust gas temperature falls by some-where between 50-70 °F.
The Legacy Cont. IO-550-N engine con-tinued to run smoothly at just 11.1 gph,where a further reduction in temperaturesand increase in range occur.
The spread of these temperature valuesis greater than that for ideal efficiency. Thehottest of the EGTs, likely being the leanestcylinders, also tend to have the highestCHTs. Cylinder #2’s CHT appears to runsignificantly hotter than the rest. This sug-gests that both the cooling airflow to thatarea of the engine should be examined.
Similarly, the CHT/EGT values for cylinder#3 suggest that it is running leaner than theothers, peaking earliest and giving the low-est CHT at every mixture setting. Its lowC H T may reflect locally better cooling air-flow or a relative lack of induction volume.
The fact that the hottest cylinder’s CHT, even for a100 °F day, ran at all times nearly 60 degreesbelow redline suggests a surplus of cooling which,if remedied, would increase airspeed.
The green oval, , points to the speed whose
fuel mixture setting delivers the best CAFE score, ascore computed as the speed to the 1.3 power timesMPG.See VBCIsidebar.
Weight, lb
985.4
508.6
170.0
170.0
366.0
0.0
0.0
2200.0
88.3
6.02
10-25%
74%
2200.0
1900.0
1494.0
706.1
304.8
66.87
81.10
83.86-89.88
Arm*
99.25
45.94
108.61
108.61
99.02
0.00
125.43
Moment
97796
23364
18464
18464
36241
0
0
194329
c.g.
88.33
Legacy N199L center of gravity
Main gear, empty
Nosewheel, empty
Pilot
Passenger
Fuel, 61 gallons
Oil, included 6.5 qt.
Baggage, aft limit
TOTALS
Datum = tip of spinner
c.g. this sample:
c.g. range, inches
c.g. range, % MAC
c.g., % aft of fwd limit
Gross weight, lb
Gross weight, landing, lb
Empty weight, lb
Useful load, lb
Payload, lb, full fuel
Fuel capacity, gallons*
Empty weight c.g., inches
c.g. range
*as determined by CAFE
Legacy N199L, Sample c.g.
The following level flight cruise data graphs show VbCas a green oval. This is the speed for best CAFEscore meaning the speed that gives the highest num-ber when MPG is multiplied times speed to-the-1.3-p o w e r. It will be a regular feature of CAFE perfor-mance reports and should become as familiar to pilotsas are Vx and Vy . The mathematical reasoningbehind this basically comes down to having VbC serveas a succinct way to choosing the bestl economycruise speed. See sidebar.
Darrel Harris, left, and Bill Bourns installedthe test equipment on Legacy N199L.
Legacy N199L; wide open throttle, CAFE data 2/23/02. CHT for 100 °F day.Cont. IO-550-N engine, 310 HP. VbC = speed at best CAFE fuel flow.
Legacy N199L: EGT and CHT spreads at 12,500', 2300 RPM
VbC =262.3 @ 11.6 gph
12.5K/2300: This graph shows severalnoteworthy trends. First is the fact the theCHT and EGT of cylinder #3 are far coolerthan all others tested. This suggests thateither cylinder #3 is not getting as muchinducted charge air as the others or that #3is getting a relative surplus of cooling air-flow, has diminished compression from anynumber of causes or that the #3 tempera-ture probe is in error. This latter is doubtfulbecause the CAFE test probes were care-fully calibrated in a test oven prior to use.
The second noteworthy trend is the other-wise close clustering of the both the CHTand EGT values of cylinders 1, 2 and 5 atthe lean fuel flows (lean of peak EGT).This condition generally favors high fuelefficiency and smooth running of the engineand is a tribute to the Teledyne Continentalengine design team. A particular “sweetspot” is evident at 10.4 gph where theLegacy achieves 248.3 smph at nearly 24mpg. Thus, the Legacy achieves a VFRrange of 1478 statute mi les wi th anendurance of 5.95 hours at this setting!!Here, the EGT spread is only 14° F whilethe CHT spread is just 17 °F for these 3cylinders. It is worth noting that, at this10.4 gph setting, the hottest cylinder’s CHT,corrected for a 100° day, is nevertheless140 °F cooler than the ‘redline’ C H T l i m i t .A closable cowl flap at such settings couldsignificantly increase engine effiiciency andairspeed.
The highest CHTs shown in this graphoccur at 13.2 gph where EGT values areabout 100 °F rich of peak EGT, a settingthat conventional wisdom calls the point of‘best power’. Note that at this setting, theLegacy range is 250 miles less and itsC H Ts are about 70 °F hotter that at the10.4 gph ‘sweet spot’.
Legacy N199L; wide open throttle, CAFE data 2/23/02. CHT for 100 °F day.Cont. IO-550-N engine, 310 HP. VbC = speed at best CAFE fuel flow.
Legacy N199L: EGT and CHT spreads at 8,500', 2300 RPM 8.5K/2300: The striking result evident inthis graph is the very flat curve of TAS (trueairspeed in smph) across a wide range ofmixture settings--with very little speedpenalty in running lean mixtures. Becausethe MPG values steadily increase and boththe CHT and EGT steadily decrease as thefuel flow is reduced, it is sensible to fly theLegacy using just 12 gph with wide openthrottle and 2300 RPM and 8,500 feet.
Cylinder #3 again shows itself to be thecoolest in CHT and EGT. EGT spreads areabout 50 °F at all fuel flows, somewhat bet-ter than is typical of fuel injected horizontal-ly opposed aircraft engines.
All of the CHT values, which as shownare corrected for a 100 °F day, are wellbelow the 460 °F redline for CHT. It isinteresting that the CHTs of cylinders #1and #5 are so very similar at all fuel flows,while their EGT values differ markedly.Cylinder #2 is consistently runs hottest atall the power settings tested.
The Legacy engine continued to runsmoothly at all of the fuel flow settings pre-sented here.
That the Legacy can loaf along at just12.0 gph and still deliver 260 smph is veryimpressive. However, its VbC at this RPM
and altitude is 262 smph and this occurs at12.6 gph, as shown. The V b C s e t t i n g
o ffers the best compromise betweenspeed, fuel economy and engine heatstresses. It is a function of many interact-ing factors including throttle position, RPM,propeller eff i c i e n c y, altitude and the speedversus drag of the aircraft as a whole.
Legacy N199L; wide open throttle, CAFE data 2/23/02. CHT for 100 °F day.Cont. IO-550-N engine, 310 HP. VbC = speed at best CAFE fuel flow.
Legacy N199L: EGT and CHT spreads at 8,500', 2550 RPM
VbC = 282.4 smph @ 14.2 gph
8.5K/2550: This graph depicts the veryhigh cruise speeds that the Legacy canachieve at 8,500’ density altitude. Due toconcerns about leaning the mixture at rela-tively high power settings, the range of fuelf lows examined here is more l imited.Nevertheless, it is evident that the tests didexplore lean of peak mixture settings whichyielded some reduction in CHT in all cylin-ders. The engine ran smoothly at all set-tings presented here.
The CHT values here show that theLegacy cooling system is more than ade-quate at the high cruise speeds at which itnormally operates. The high level of ramair pressure available at such speedsaffords such fast aircraft a substantial cool-ing advantage. However, an ineff i i c i e n tcooling system at such high pressures cancause large speed penalties that go unno-ticed unless the system is critically exam-ined.
The Legacy’s cooling system was testedin both climb and cruise mode to determineits ram recovery. We define ram recoveryas that percentage of freestream total pres-sure that is ‘captured’in the cold air coolingplenum inside the cowling. The measure-ment was made using a pair of probesinside the cold air plenum. One probe wasa piccolo tube that sampled average staticpressure in the plenum. The other probewas a forward facing pitot tube placed justabove cylinder #3’s cooling fins inside thecowl.
The test results showed that the Legacyachieves 60% ram recovery in cruise at240 KCAS but 117% ram recovery in climbat 138 KCAS . The readings of the piccoloand pitot were essentially identical incruise. In climb, the piccolo read 12.4 inch-es of water versus 14.2 on the pitot probe.