Tech Talk - Crosswind Landings
by Huff Enpuff, for Macon Aero Modelers
"Most anyone can land an RC airplane in ideal conditions, calm winds or winds that are on your nose. Unfortunately, OTX usually has a continual crosswind and given the fact that we have trees and other obstructions on the southside of the airport, winds from the south seem to provoke a lot of turbulence which can make a good landing difficult to achieve. Coming in from the normal western end of the airport and about 200 feet out, we pick up a good bit of turbulence but once across the threshold things seem to even out quite a bit. Perhaps that plastic fence or a combination of the fence and the shed, the air calms down.
Winds from the north seem to have less turbulence and probably because there are no obstructions for the wind to bounce up, over and around from that direction. The air flow is smoother.
There are two basic ways to make a crosswind approach and landing in full scale aircraft and which one you use depends on the type of aircraft. Assuming a 90 degree crosswind, and assuming the wind is constant, or close to it, one usually simply drops one wing into the wind which allows the aircraft to slide into the wind and you drop the wing just enough to offset the wind. All the while, you are holding the nose straight down the runway. When you flare for a landing, your nose is pointed straight down the runway.
This is sometimes a little difficult to perform in a low wing aircraft like the Mooney because the landing gear is fairly short and you could end up dragging a wing tip on the runway if the crosswind was fairly strong.
The other method is to simply crab the aircraft slightly into the wind. Again, how much crab you use depends on the wind strength. Pilots are not thinking in terms of headings but simply keeping the aircraft headed down the runway centerline. Crabs are established with the combination of ailerons and rudder. However, the rudder is held just for a second or two to establish the crab and then eased off. If the wind is gusty the pilot may add or lessen the degree of angle into the wind. One never holds the rudder in place because the aircraft would end up going in a circle. In some aircraft, holding the rudder over could result in a snap and buying the farm. The wind force usually dies within a few feet, not always, but usually, and if you hold the crab angle too long you may drift off the windward side of the runway. But, in a full scale aircraft, when just about to touch down at flare, you must straighten the aircraft out or you may end up wiping out the landing gear or even ground looping. The old Aircoupe was famous for a landing gear that would caster which was necessary because it, in the older models, didn't have a rudder pedal but steered with the control column.
Some are under the impression that slipping is used to offset a crosswind and to some degree this may be true, but again, this depends on the type of aircraft. Slips, as used on a J-3, are used only to lose altitude in the event of a too high approach and serves as a substitute for flaps. One simply applies rudder and opposite aileron which causes the aircraft to fly sideways and increases drag and thus loss of alititude. Although I've heard it can be done, one would not want to do this with a 747, however.
Well, what can we learn from all this stuff about flying a full scale aircraft? For the most part, the same principles apply to our RC models. Given the fact that things happen in landing a model much quicker than they do in a full scale aircraft the RC pilot must be prepared to make instantaneous corrections. We all know that in gusty turbulent condtions it would be all but impossible to establish a final approach glide that we could stick to. The turbulence won't let us settle into a solid railroad track approach. The minute we get the glide set up we get a blast of turbulence that gets us off course.
Probably the best course of action is to crab into the wind. The problem here is that as we near touchdown the wind usually eases off and we end up too close to the fence. We can't really drop a wing into the wind as the full scale aircraft do because turbulence is rocking the wings too much so I would have to rule this type of approach out.
Besides, our model landing gears are not as sensitive as full scale aircraft and we can touch down even in a crab angle with no damage to the landing gear. The winner here then, is the crabbed approach.
I've seen pilots, really, really good RC pilots, establish a crab angle way out and make beautiful landings with minor corrections. I've never been able to make them that pretty and end up either off to one side of the runway or the other. Personally, in gusty conditions, I like the carrier approach close in to the end of the runway because it keeps me clear of the turbulence developed over the trees and obstructions at the far end of the runway. It has the further advantage in that it gives me a better view of the aircraft as opposed to being difficult to see when you have nothing but a backdrop of trees which tend to hide the aircraft. Additionally, you can judge the airspeed better and avoid a stall near the end of the runway.
As we all know, there is no substitute for practice. Lots of RC'ers will avoid flying in any kind of wind but this is probably the worst thing they can do. Crosswind landings, in gusty conditions, are very difficult to do and this is all the more reason for doing them. The more difficult the maneuver, the more you need to practice doing them.
Situational awareness is a strong factor in crosswind landings since one must be aware of changing wind patterns, turbulence and gusts that carry you to one side of the runway or the other and then near the ground, a calm condtion which screws up your entire approach.
If there is anything to be learned here, it is the need to practice and practice in windy, gusty conditions.
We know that the crab method of offsetting a crosswind is really the best way we can land our models in a crosswind so now it just becomes a question of practicing what we know. Winter is almost here and we will be getting our usual north winds and unless you want to wait for a month or more between flights, get out there and fly in the wind. And don't forget that old golden rule of just going around again if you screw up your approach and try again."
Macon Aero Modelers, Inc.
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