visitors to this page.
High Wing / Low Wing
First published: 20 February, 2002
Minor revisions and additions: 22 February, 2002 & 23 April, 2002
Minor spelling revision, 23 February, 2008
Accident picture added, 5/19/2008
Purpose of this tutorial
Airplanes. They're everywhere. Big ones, small ones, civilian, military. And, they share one singular defining form difference; some are high-wing, and some are low-wing. Why is that so? Isn't one format better than another? In this tutorial we'll discuss some of the differences in the two concepts, why one style is more prevalent than the other, and lastly, try to address a major safety issue of the two designs: their propensity to collide with one another in the air.
The historical aspect
The first successful powered airplane, the Wright Flyer, didn't venture into the future discussion- it was a biplane, with one wing high, and one wing low. After the amazing feat of the Wright brothers, airplane design concepts exploded, and wouldn't you know it, some of them were high-wing, and some were-low wing.
So, which is best. Well, let's take a look at Mother Nature. Ever see any low-wing birds out there? So, here we have one major clue into "design concept": a winged object is inherently more stable with the weight suspended below the wing. And, when you think about it, that just makes sense.
So, if that's the case, why do we continue to have the two formats?
The practical aspect of design
Landing gear. Just where are you going to put it? On a high-wing airplane there isn't much choice, it's got to go into the fuselage. There are some exceptions to this, one of which was the Fairchild F-27, a popular plane used by the old Ozark Airlines, among others.
Note how the turboprop engines allow the gear to be retracted into the engine nacelles. The small physical size of the engines made this possible. If you were to remove the engines, their fire walls would be about two feet in front of the wing's leading edge. Now, if this was a pure turbine aircraft, it would not be possible to attach the gear this way as the engines need the space all of the way back to the trailing edge of the nacelle.
Also, consider the length of the gear. The longer it is, the stronger has to be. This equates to weight. Weight reduction is everything in an aircraft design. Larger landing gear becomes an engineering problem when it comes to storage space. Just where are you going to retract the gear? Most transports today use the fuselage for gear storage. If the aircraft is lighter, and therefore the mechanism smaller, the gear can be retracted into the wings, as it is in most General Aviation twin-engine aircraft.
Military fighters that roam around at high speed use thin airfoils that don't have enough thickness in the wing for gear stowage.
Another consideration is crosswind landings. Generally speaking, the farther the main landing gear is spaced, the higher the demonstrated crosswind landing component is.
Given this train of "logic", why are there any high-wing aircraft at all? Well, there are always the exceptions that prove the rule, and engineers have the lateral to design as they wish, but the number of high-wing aircraft with retractable landing gear designs that are out there are indeed few and far between.
An outstanding exception is the world's largest airplane- the Antonov 225.
Cessna vs. Piper
Back in the early 60's and 70's Cessna and Piper were duking it out for General Aviation supremacy in the air just like Ford and Chevy were on the highways. Cessna's fleet was high-wing, Piper's was low-wing. Although Cessna did use the low-wing concept for its twins, the exception being the Skymaster, model 337. Flight schools tied their allegiance to one manufacturer or the other. Student pilots would get into heated debates over which was the best trainer, the Cessna 150, or the Piper 140.
In a bit of aviation humor, the airplanes had the ability to extract their own "revenge" on the student pilots that abused them so harshly during their training. The Pipers did this by way of the height of the wing's trailing edge in relationship to the pilot's groin area. The Cessnas got their pound of flesh with the wing's trailing edge placing a diamond shaped scar on the pilot's forehead. Mine healed up quite nicely.
These events usually occurred only once per student.
So, which was best? The Cessna, or the Piper?
Each had its strengths and weaknesses. It was generally accepted that the Piper was easier to fly, and easier to land. Surprise! It had a wider gear stance because it was a low-wing airplane. The Cessna required more attention to rudder control in turns, the Piper had a rudder/aileron interconnect system that allowed turns to be made almost with your feet on the floor. Because the gear struts on the Piper were vertical, oleos (the aviation version of the automotive shock absorber) could be used for a more comfortable ride on the ground, and improved cushioning on the landing touch-down. The Cessna gear had to be angled out from the fuselage, and therefore could not use oleos. Cessna had to use a spring steel landing gear that, while beautiful in simplicity, could make for some exciting landings.
Creative landing gear design
As mentioned earlier, Cessna used the high-wing concept for all of its aircraft except for the twin-engine models. The exception to this was the model 336/337, the Cessna Skymaster. The 337 was an "in-line thrust" twin-engine aircraft, with a tractor engine in the front, and a pusher engine in the back.
Personally, I always liked this airplane, but because of its perceived "non-machoness" it was heavily derided by "real pilots". "Mixmaster", "Push me, pull you", it attracted its share of euphanisms. For the first couple of years the gear was "welded in place", but the creative fellows at Cessna actually came up with a way to retract the gear into the fuselage. The gear would drop down to a vertical "trailing" position, then retract rearward into the fuselage.
From the ground, watching this dance of gear doors and pivot points after a Skymaster departed was a thing of beauty.
Things that go bump in the air
This is where the two designs come into their ultimate conflict. It's a sad fact of aviation that high-wing airplanes and low-wing airplanes tend to collide with one another. In fact, there is an established scenario.
- They collide in the airport traffic pattern.
- To be more specific, they collide on the final approach segment of the airport traffic pattern.
- The low-wing aircraft collides with the high-wing aircraft from above.
- One of the airplanes usually has made a straight-in approach, by not flying a traffic pattern.
- Usually, the high-wing aircraft comes out the worse for wear because the cabin, the propeller, or the control surfaces are struck. The low-wing aircraft sustains damage to less critical areas, usually the landing gear. In most cases the two damaged aircraft make it to the surface safely, in some cases the high-wing aircraft sustains the worst damage and does not make it to the airport at all.
Why does this happen? In a word: visibility.
Picture yourself sitting in a single-engine airplane without wings. The view in front is obstructed only by the engine cowling. How about up? Same thing, what with the view being limited only by how far up the windshield curves. And to the rear? Not a great view, but available. Now, let's put some wings on this imaginary bird of ours.
Let's put them on the top first. Hmmm, no changes so far, except to the side. Oh, that's a big except. When you look to the left or right and up, you can't see anything but aluminum. The view down is great though. OK, let's put those wings on the bottom of the airplane. Now we have just the opposite situation. You can see the sky just great, but looking down is another matter. Well, this is all pretty straight forward so far, but how does it relate to the two design styles propensity to run into one another when landing?
Let's take our wing-less aircraft and place it on the downwind leg of an airport traffic pattern. Any airplanes out there? If there are, in our wingless bird you'll most likely see them. Now, let's put the wings on the top. If there is conflicting traffic above you, most likely it will be obstructed by those big wings. Down below you any traffic is easy to pick out. Swap the wings to the bottom, and you have the opposite situation.
Now we get into the tricky and dangerous part. Make the turn from the downwind leg to the base leg. In your low-wing bird the entire area to your right that is the final approach course is obstructed by the wing.
And that is where the airplane that you are going to collide with is located.
Put the wing on top and make the same turn, downwind to base. Oh, what a view. You can see the sky to your right, but you can't see inside the turn because the wing is down and obstructing your view.
That's where your date with destiny is flying.
Let's make the turn from base to final. Our high-wing airplane has a great clearing view of the sky above and to your right (we're flying a standard left-hand pattern). But down and to the left? You don't have a chance. With the low-wing as you turn base to final, you can see just the opposite- down and to the left is good, up and to the right is just aluminum. Aluminum that is blocking your view of the intruder that awaits you. Now we're on final. The high-wing airplane is below, and can't see any conflicting traffic. The low-wing airplane is above, happy as a clam thinking that the area is clear of any landing aircraft.
The sickening crunch, and its aftermath are a foregone conclusion.
05/15/08 - Roanoke, Texas
What can you do as a pilot to prevent this from happening?
First and foremost, understand that it
can and does happen. That's number one. Realize that if two airplanes
are going to meet in the sky, that they are going to do it where
airplanes are the most concentrated- near the airport. Also, realize
that this is a time when you can be distracted inside the cabin.
Try to complete your landing checklist as much as possible before
you enter the traffic pattern. Try to leave just the flaps and
gear as your remaining check list items. This will leave you with
minimum inside duties, and allow you to be looking for conflicting
aircraft in the pattern.
Never, never make a straight-in approach to landing. If you approach your destination airport more or less in line with the landing runway, enter the pattern on the upwind leg. Sure, it will add a few minutes to your trip, but it will certainly increase your odds of not having a bad day.
Use your radio. Use the appropriate frequency and make pattern calls. Be a pain in the butt, clog the airwaves. Well, do it in a professional manner. "Oxford traffic, Cessna five seven golf is five miles south, landing Oxford." "Oxford traffic, five seven golf is entering the downwind leg, runway one eight, Oxford." Oxford traffic, Cessna five seven golf is turning left base, runway one eight, Oxford". "Oxford traffic, Cessna five seven golf is on a two mile final, runway one eight, Oxford". "Oxford traffic, Cessna five seven golf is on the ground and clear of all runways, Oxford."
Well, that's great, but what if you are on a straight-in instrument approach? You're on an IFR flight plan, you have been authorized by Air Traffic Control to be there, and you have been issued a clearance for a straight-in approach. Surely, you have the right-of-way. Don't you?
No Grasshopper, not always. If the field that you are landing at is a controlled airport, then the tower will coordinate any traffic in the pattern and clear you for a straight-in landing. But, if the tower is closed, or if the field is non-controlled, and if the weather meets the VFR minimums, some fellow could be out there grinding around making touch and gos. Not smart on his part perhaps, but legal nonetheless. And, when it comes to landing rights he has every bit of right of way as you do. In fact, inasmuch as he is flying a pattern, he out-trumps your straight in approach.
No matter if you fly a low-winger, or a high-winger, be aware of the visual limitations of the design that you are in. Don't just "look". "See"! Do everything in your power to look for conflicting airplanes.
Things that the pilot should consider when transistioning from one format to another
- You are used to the visual limitations of "the other type", remember that now everything is reversed.
- You will find that your landings will "change". Most pilots look down the runway while landing the aircraft, but pick up their visual cues to landing height above the runway by way of peripheral vision. (See the tutorial Landings and Peripheral Vision). In a high-wing airplane this information is readily available because there is no obstruction to your vision. The opposite is true in a low-wing. High-wing pilots transitioning to low-wing airplanes will find that the visual cues that they are used to are no longer available, and may have a tendency to drive the airplane into the runway. Conversely, low-wing pilots transitioning to high-wing airplanes may be startled by the new visual cue "rushing up at them", and flare high above the runway, making an "air landing". The situation will vary from model to model, just be aware that it will most likely happen. After awhile, your mind will establish a new reference point, just give it some time.
- Low-wing airplanes get more "float" during landings due to "ground effect"- the cushion of air that as a general rule extends a wingspan underneath your airplane. While still there, this phenomena is less apparent in a high-wing airplane. Many a pilot transistioning from a high-wing airplane to a low-wing have found themselves blissfully floating along waiting for the gear to make contact while the opposite end of the runway was rapidly approaching.
- In addition, crosswind landings change from type to type. Generally speaking, low-wing airplanes are easier to land in crosswinds than their high-wing brethren. The high-wing offers more area for that crosswind component to "get under" while in the wing low attitude for landing.
- Taxing with the control surfaces in the proper position is much more critical in a high-wing airplane than one with the wing on the bottom. The same gust of wind that makes the low-wing shudder a bit can flip a high-wing airplane on it's back. Pay particular attention to quartering winds when on the ground in a high-wing aircraft. See the diagram for control surface positions in the tutorial Crosswind Landings.
- Remember that there will be new area of aluminum obstructing your sight lines- and the airplanes that hide behind them. When practicing air maneuvers, you are trained to make clearing turns prior to your practice. A low-wing pilot turns left, and "clears" the area to his left because the wing has dropped down making that area of the sky available for viewing. The opposite is true for the high-wing driver. To clear the area to his left he must make a gentle turn to the right, raising the left wing for better visibility in that area. Don't do these turns just out of habit. Look. See. And if you're new to the high or low-wing type, be especially vigilant in your clearing turns.
- Preflight inspections change, some parts are easier, some are more difficult. Inspecting tire condition is easier on the high-wing (assuming that there are no wheel pants installed), checking fuel levels is easier on the low-wing. Draining fuel sumps is easier on the high-wing, checking fuel levels is easier on the low-wing. Just use your common sense, after all it's your life that will be climbing inside of the aircraft.
Oh, and lastly don't forget about those low-wing groin shots and the high-wing forehead "tattoos".
© 9 February, 2002
This tutorial was written after a suggestion by David W. Hutcheson. Thank you David.
4/23/02: A correction was made in the description of the two aircraft positions on final after an error was pointed out by Ellen Geertsema. Thank you Ellen.
2/23/08: Corrected the word "flair" to "flare." Thanks to Alan Larson for pointing this out.
Additions? Corrections? Please contact me.
This narrative, along with aditional content, is available as a CD or an eBook.
For CD information click here. For eBook information click here.
Click here to return to the Aviation Tutorials index.
Click here to return to the Stoenworks home page.