Relation of cruise Cl and wing loading

It is interesting to look the parameters of different airfoils. One notable thing is that the glide ratio of the given airfoil is in relation to the Cl at cruise condition, and the wing loading has a direct effect to the cruise Cl of the airfoil, the higher the wing loading (the smaller the wing area in relation to weight), the higher is the cruise Cl. With some aifoils, this relation is stronger than with others, since the low drag laminar bucket is at some specific Cl, and it is not always in a favorable position for use in a light aircraft, it may be quite often designed for airliners which have very high wing loadings (and very high stall speed as a result as well, unreasonably high for a personal aircraft, which makes surviving a crash unlikely (which would be unacceptable for a personal single engine aircraft)).

I calculated some rounds of weights, wing areas, wing loadings (I have been calculating with wing loadings between 18 lbs/sqft to 25 lbs/sqft (e.g. Lancair Legacy has 23 lbs/sqft)) and subsequently the Cl-cruise and the L/D at the given Cl. Some airfoils are particularly poor at low Cl whereas at least, if Javafoil is at all to be trusted (the methods it uses aren't very accurate), the already mentioned NLF414F is a rare exception. It has excellent lift/drag relation exactly where it should be in a light aircraft with low wing loading. It would be easier to say for sure, if I could see some wind tunnel data for the NLF414F but so far I haven't found enough information. Also it would be interesting to compare to the Wortmann FX63-137. According to Carmichael [1] it does have good L/D charasteristics, but would be great to be able to determine, how good exactly at Cl 0.1, 0.15 and 0.2 (as this is the usual range in light aircraft). The low drag potential is wasted if it can be only utilized at Cl higher than e.g. 0.4, which is not practical or even quite possible in a lightweight personal high performance aircraft and it is also interesting, that many aircraft that are using airfoils which have very low drag potential, may be operating the airfoil outside the best cruise Cl area, and the result is not that good, not that different, or in many cases worse, than if the airfoil was a low drag traditional one, like NACA 66-212. I haven't found so far the wind tunnel data for the Wortmann either, seems like it is not at least available in the Internet, at least not for free.

Found latest LH-10 flight video from Youtube

Here is the latest test flight video of LH-10 prototype (see earlier article where I blogged about the French new plane with low drag body, tandem seating and high aspect ratio wings, LH-10):

http://fr.youtube.com/watch?v=IJjEoPiv66U

Pilot Performed Preventative Maintenance in FAA system

FAA system allows pilot maintenance more than EASA/JAA-system.

Here is a list the pilot can do a type certificated aircraft:
- Remove, install and repair tires
- Clean, grease or replace wheel bearings
- Replace defective safety wire or cotter pins
- Lubrication not requiring disassembly other than removal of non-structural items such as access covers, cowlings or fairings
- Replenish hydraulic fluid in the hydraulic and brake reservoirs
- Refinish the airplane interior or exterior (excluding balanced control surfaces) with protective coatings
- Repair interior upholstery and furnishing
- Replace side windows
- Replace bulbs, reflectors and lenses of position and landing lights
- Replace cowling not requiring removal of the propeller
- Replace, clean or set spark plug gap clearance
- Replace any hose connection, except hydraulic connections, with replacement hoses
- Clean or replace fuel and oil strainers, as well as replace or clean filter elements
- Replace prefabricated fuel lines
- Replace the battery and check fluid level and specific gravity

After any of the above work is accomplished, appropriate logbook entries must be made.

Means that pretty much 50 hours maintenance can be made by the pilot, using a mechanic is not necessary. Mechanic is needed for annual.

Airfoil documents

There is an interesting document on Selig's page:
http://www.ae.uiuc.edu/m-selig/uiuc_lsat/vol4/NREL-SR-500-34515.pdf.

It covers for example wind tunnel results for Wortmann FX63-137 at low Reynolds numbers.

Links to NASA tech papers about airfoils
Covers NLF 215F

Airfoils in dwg format

Airfoils in dwg format

Low cost UAV design

LINK: Low-cost Expendable UAV Final Report

Reynold's number calculator

http://aero.stanford.edu/StdAtm.html

Aircraft calculator web page

I found this:

http://anton.panchishin.com/docs/aircraftcalc.html

I am not sure how useful it is, but just for fun, enjoy.

Airspeed at sea level

I got interesting airspeed calculator Excel-sheet from Petri Flander. I have been calculating those things with my aircraft design program and by hand before, but it is surprisingly handy to see the effect of various flat plate drag areas and their effect to the airspeed. Great input for my program which I am writing the UI for with Qt right now, I may do also graphical output for these parameters, would be fun to have. This was actually also useful to reverse-engineer the flat plate drag areas of various aircrafts. For example I came up with 4,7 ft2 for Cirrus SR20 where Lancair ES (=same as Columbia 400) is 4,0, so Cirrus is a slightly less efficient than the Columbia (which is evident also from the performance numbers comparing SR22 and Columbia 400). Interesting is that I came up with 9 for C152, which is a terribly bad figure. And Zenair CH701 produced a number around 18 which was reverse-engineered from real performance numbers I have heard from a Zenair pilot. Couldn't get much worse than that. BD-5 has very low figure of 0,9 and Vmax probe is at 0,3 (these were obtained from elsewhere). A composite BD-5 with rear body laminar flow suction (with more laminar body shape as well) and some high tech airfoil like the NLF414F could be super-efficient. However, the issues with low Reynolds number from Vmax probe apply, it will have seriously dangerous stall charasteristics without modifications to the airfoil or wing.

Here is a copy paste from the sheet with flat plate drag areas from 0.3 (Vmax probe) to 4 (Lancair ES):

        Aircraft speed, km/h                    Prop eff        0,85    Dens.ratio      1,000       $

Drag area            
ft2     25      40      60      80      85      90      100    <- Total hp  (Rotax 914)
4       148     173     198     218     223     227     235     127,053 kts
3,00    163     191     218     240     245     250     259     139,840 kts
2,40    176     205     235     259     264     269     279     150,639037908943        kts
2,30    178     208     238     262     268     273     283     152,791314948939        kts
2,20    181     211     242     266     272     277     287     155,07211859505 kts
2,12    183     214     245     270     275     280     290     156,998677308782        kts
2,10    184     215     246     270     276     281     291     157,495511877874        kts
2,00    187     218     250     275     281     286     296     160,077864487362        kts
1,90    190     222     254     280     285     291     301     162,838370152973        kts
1,80    193     226     259     285     291     296     307     165,799714672936        kts
1,70    197     230     264     290     296     302     313     168,988949701208        kts
1,60    201     235     269     296     302     308     319     172,438652178898        kts
1,50    205     240     275     303     309     315     326     176,188487565227        kts
1,40    210     246     281     310     316     322     334     180,28735558483 kts
1,30    215     252     288     317     324     330     342     184,796395706893        kts
1,20    221     259     296     326     333     339     351     189,793294797389        kts
1,10    228     266     305     336     342     349     361     195,378626469698        kts
1,00    235     275     315     346     353     360     373     201,685471089846        kts
0,90    243     285     326     359     366     373     386     208,894550582996        kts
0,88    245     287     328     361     369     376     389     210,46524527855 kts
0,50    296     346     396     436     445     454     470     254,107770484061        kts
0,31    347     406     465     512     522     532     551     298,003054739616        kts

Reference library

Here is list of some of the books I have:
Aerodynamics for Engineers
Fundamentals of Aerodynamics, by John Anderson
MODERN AIRCRAFT DESIGN, Volume 1 5th Edition, by Martin Hollmann.
MODERN AIRCRAFT DESIGN, Volume 2 4th Edition, by Martin Hollmann.
COMPOSITE AIRCRAFT DESIGN. REVISED 2003. By Dr. Hal Loken and Martin Hollmann.
MODERN AIRCRAFT DRAFTING by Eric and Martin Hollmann.
ADVANCED AIRCRAFT DESIGN by Martin Hollmann.
BRUCE CARMICHAEL'S PERSONAL AIRCRAFT DRAG REDUCTION

Aircraft Design : A Conceptual Approach

Daniel P. Raymer / Hardcover / 4th Ed. Published 2006

Theory of Flight

Richard Von Mises, Richard Von Mises

Aircraft Performance and Design

John D. Anderson / Hardcover / Published 1998

Sportplane Construction Techniques : A Builder's Handbook (Tony Bingelis Ser.))

Tony Bingelis; Paperback

Interesting aircraft design - LH10

This plane has some of the elements I have been thinking of an efficient aircraft to have:

http://www.lhaviation.com/site_frame/bases_marges/index.htm

Specs promise 200 kts with 100 hp. Lets see. The plane has already flown, but not yet tests that determine top speed.

According to my calculations, providing they are right, this is not that much out of place. This plane in fact, is pretty much like a two place Vmax Probe. If the airflow stays laminar in the fuselage and wings, the 200 kts might be doable. The relation of stall speed and top speed of the 3.77 projected for this plane is a reachable value. Very interesting to see how it performs and if it does not go 200 kts, why. According to what I have read and would estimate, the drag coefficient of the LH10 should be very small unless there is something wrong that causes the airflow to separate.

The view from the LH10 seems to be as spectacular than from a glider. Would be excellent aircraft for flying for fun.

The airfoil used on this aircraft is particularly interesting. Reasons:
- E.g. NLF414F produces very low drag and very high glide ratio, but not without restrictions - the area of usable Reynold's number is limited which limits the chord of the wing to a rather long one, and the wings of the LH10 would already be below that limit. They say that it is a wind turbine airfoil. I haven't tried simulating the wind turbine airfoils yet, it has not occurred to me that they could be actually be useful on aircraft. However, this seems to prove that this was wrong assumption, and they are in the UIUC database for a reason. Lots of airfoils to investigate...

Full span flaps effect on NASA LS417-karoliinamod

I changed the LS(1)-417 so that the trailing edge gap is zero (=sharpest achievable) instead of the large gap present in that airfoil (Janne's Mini-Sytky does not have this gap while Panu's Mini-Sytky has). According to simulation with Javafoil, this decreases the drag quite significantly. The airfoil has good Clmax at the same time with the low drag (approaches almost NLF414F).

I calculated that Clmax of 2.88 is possible with this profile with full span flaps with fowler inboard section. 

Quick calculation with aerocalc shows that the following might be theoretically achievable:

AR 9

Clmax 2.88

Wing area 4.6 m2

span 6.4 m

Wing loading 144 kg/m2 29 lbs/sqft

L/D max 22

Stall speed 55 kts

Max level speed 260 kts 480 km/h with Rotax 914 (90 hp required out of 115, max continuous 100 hp->ok)

best glide speed 150 kts

empty weight 366 kg

mtow 666 kg

Idea: Full span flaps

Full span flaps with flapped ailerons:

In board wing has 60% span fowler flaps. Outboard wing, the remaining 40% consists plain flap type flaperons with similar mechanism than used in Mini-Sytky.

deltaClmax_fowler = 0.6 * 1.67 + 0.4 * 0.9 = 1.362

For airfoil with Clmax 1.2 the maximum Clmax on landing configuration is thus 1.32 + 1.362 = 2.68

This allows smaller wing area and higher wing loading to be used without sacrificing takeoff and landing performance too much.

Another variation with single slotted flaps:

deltaClmax_singleslotted = 0.6*1.18 + 0.4*0.9 = 1.06

+1.06 in Clmax still is a very good value and better that would be obtained with full span flaperon (+0.9). For airfoil with Clmax of 1.32 this yields Clmax of 2.37.

This idea has not been tested in practice and is not guaranteed to work.

Effects on aircraft:

Aircraft with 60% span plain flap and Wortman FX 38-153 (no full span high lift device):

Clmax = 1.3 + 0.9*0.6 

deltaClmax = 0.54

Clmax => 1.84

86 hp required for 200 kts cruise

wing loading: 92 kg / m2

wing area: 7.2 m2

stall speed: 55 kts

design cruise: 200 kts

Cdtot = 0.011 (with boundary layer suction)

Same aircraft with full span flaperon and Wortman FX 38-153:

Clmax = 1.3+0.9 =  2.20

Same aircraft parameters:

76 hp required for 200 kts cruise

wing loading: 110 kg / m2

wing area: 6 m2 

Aircraft with full span flaps with slotted inboard section:

Clmax = 1.3 + 1.06 = 2.36 

Same aircraft parameters:

74 hp required for 200 kts cruise

wing loading: 118 kg / m2

wing area: 5.6 m2

Aircraft with full span flaps with fowler inboard section:

Clmax = 1.3 + 1.362 = 2.66

70 hp required for 200 kts cruise

wing area: 5 m2

wing loading: 134 kg / m2

For the most extreme case theoretical savings over usual configuration:

Power = 86-70 = 16 hp (18%)

wing loading: 134-92 = 42 kg/m2 (31%)

wing area: 7.2 m2 - 5 m2 = 2.2 m2 (30%)

Karoliina model 1 iteration 1

Karoliina model 1 concept iteration 1

200 kts with Rotax 914

Specs:
2 places: side by by side staggered seating (co-pilot a bit behind pilot)
Configuration: Pusher with Y-tail.
Engine: Rotax 914 115 hp (100 hp continuous), Propeller: Woodcomp SR3000
Body: 60% laminar flow body.
Body laminarity target: 100% laminar flow with suction.
Landing gear: Trigear, retractable nosegear, Steve Wright noselift. Main gear connected to wing spars at 90 degrees angle.
Wing configuration: Conventional, midwing position
Wing loading: 82 kg/m^2 (16.8 lbs/sqft)
Airfoil: NASA NLF(1)414F.
Flap config: Single slotted flaps with external hinges
AR = 10
L/Dmax = 19.8 at 115 kts
L (wing chord) = 0.8 m
wing area = 8 m^2
wing span = 8 m
Re min (stall) = 1829224
Re cruise = 4217074
Re max cruise = 5586254
empty weight = 366 kg
gross weight = 666 kg
fuel capacity = 140 liters
max cruise speed = 200 kts 370 km/h at 7000 feet
stall speed = 50 kts 92 km/h
approach speed = ~70 kts 130 km/h
drag coefficient target = < 0.016 (total drag). Lower is better. With 100% laminar flow body, a much lower drag coefficient might be possible, this figure is conservative.

Hello

Hello, my name is Karoliina Salminen and the intention of this blog is to follow topics related to light aircraft design. I do have a dream and want to share it with you.