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Fuselage Design and Crosswind Component?

Farmboy

Farmboy

MEMBER
Middlebury, VT
As I was chasing airplanes and flying barn doors this morning, it struck me that some NASA guy or other Aerodynamic Engineer from any number of startup aircraft companies must have examined the effects of fuselage design on an aircraft's crosswind component. A quick google on the subject did not net me much results, so in geek like fashion I'll throw this out to all of you to discuss.

- Do you feel that fuselage design has a great impact on crosswind?
Shorts 330 vs an oval shaped Beech 1900? (unknown vs 25 knots)
Flat sided Beaver vs a round sided 206? (Apples and Oranges here, but POH shows 10 kt max vs 20 kt max respectively, whereas the 185 seems to call out 12 kt max demonstrated.... so darn close to the Beaver)
- The mighty AN-2 has a "tolerable" crosswind component of 8 kts.

- What have you flown that was noticeably better or worse than others?
- What did you attribute it to? Rudder? Fuselage side profile? Fuselage length? Roll control/authority? Gear width?

Throw it out here and bash it around.

pb
 
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A bit of the Xwind component has to do with the landing gear layout. As you state the Beaver and 185 are close where the 206 is considerably more generous.
On a tricycle with the main gear further aft there are many aspects that naturally stabilize the plane.

The fuselage itself could well have some effect on the factor but I expect the stability or lack of once on the ground has a far greater effect on the rating.
 
According to AOPA, Some of the numbers for trikes are impressive -

Cessna Skylane RG, 18 knots;
Beech Sierra, 17 knots;
Bonanza V35, 17 knots;
Cessna 172, 15 knots.
 
“Demonstrated crosswind Component” is simply the greatest crosswind component that test pilots experienced during flight test. It is not considered a “limit”, and is often well below that which the airplane can actually handle.

That said, there are clearly Aircraft that are more tolerant of crosswinds than others, probably for a variety of attributes.

MTV
 
CharlieN said:
A bit of the Xwind component has to do with the landing gear layout. As you state the Beaver and 185 are close where the 206 is considerably more generous.
On a tricycle with the main gear further aft there are many aspects that naturally stabilize the plane.

The fuselage itself could well have some effect on the factor but I expect the stability or lack of once on the ground has a far greater effect on the rating.
Click to expand...

This would suggest that the C/W numbers are a result of the roll-out phase or post-touch down phase of the landing over the actual touchdown. Is this the case, or would one believe that prior to getting all wheels on the ground that the gear layout should affect crosswind handling?
 
mvivion said:
....there are clearly Aircraft that are more tolerant of crosswinds than others, probably for a variety of attributes.

MTV
Click to expand...

This is what sparked my early morning interest... just what do we believe those attributes to be, and what compromises are made when one does not have those. Seating/Cargo/Speed/etc...
 
Wing loading. Airspeed. Tail authority. Just to name a few. A high lift wing and a go fast wing are very different with respect to the question. I don't think the fuse is very important. To explore that maybe discuss a ski plane versus the same plane on floats. The side area is very different yet the plane is equally capable.

If the wind's blowing 25 straight across the runway? Give me my Skywagon, because I know that plane in those conditions. My Cub will fly slower than that so I hope to never try 25 across in that plane.
 
So a skywagon runs a wing loading in the 18-19 lbs/sqft as compared to cubs in the 8-10 lbs/sqft. Huge loading difference, bigger tail, higher speeds proportionally... Beaver seems to have about the same wing loading at gross, say 20 lbs/sqft. (Does the Beaver provide a much smoother ride than a cub?)

A Beaver's crosswind component isn't showing it will help over a Cub although a much higher wing loading.
 
stewartb said:
You need to revisit MTV's post #4. Demonstrated crosswind component isn't an important number.
Click to expand...

Lol, well Stewart, unless we can get some folks to chime in on what numbers they will regularly fly, it's the only numbers we have to work with. Until then its an important number as that is what some test pilot at the mfg flew it at, and decided to stop at that point. Perhaps conservative, but so be it.

This was to be a largely theoretical discussion on what design attributes affect crosswinds components, and to what degree.
 
Farmboy said:
Until then its an important number as that is what some test pilot at the mfg flew it at, and decided to stop at that point.
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No, that is not the case. As I noted earlier, demonstrated crosswind is simply the highest crosswind that a test pilot happened to encounter during regular scheduled flight test operations. Indeed a test pilot may have chosen not to fly on a particularly windy day, but it likely had more to do with the effects of the wind and turbulence on proving test data points.

And demonstrated crosswind is not is not an important flight test parameter.

Compare this number for airplanes which are built in windy (Kansas) with those built in not so windy places (Downsview, Ont., Afton, WY). You may find location of flight test to be more a function than airplane design.

MTV
 
Farmboy said:
This would suggest that the C/W numbers are a result of the roll-out phase or post-touch down phase of the landing over the actual touchdown. Is this the case, or would one believe that prior to getting all wheels on the ground that the gear layout should affect crosswind handling?
Click to expand...

Consider it this way, you are on approach, just what is a crosswind when you are flying? It does not really exist since you adjust your heading to achieve a certain coarse. So a crab a slip or whatever is needed to get to a desired point but you essentially are flying a heading into the air.

Once touching down though your tires dominate over the aerodynamic loads as such you now have a "crosswind". You do not need all tires down, just enough grip to dominate over the aerodynamic loads.

A pilot with great experience landing in tricky conditions has a considerably greater crosswind componant than a timid, slow reacting pilot without placing consideration as to what the plane is.
 
Had a Bushmaster years ago. Could get it on the ground rolling in a strong,crosswind but knew if I slowed it was the brush or roll into a ball. If a wider runway, land crossways. Was at Dillingham, big sign 'No take offs from the ramp'. Dang near crashed trying to use the Runway.
 
Okay, I retract my statement that crosswind numbers have any validity. That wasn’t the point I was making, but it also doesn’t matter.

So it seems the above feel the amount of fuselage sidewall is of little matter in regards to crosswind effects. Obviously rudder size/authority/effectiveness matters.

What else and why?


Sent from my iPhone using SuperCub.Org
 
Tire contact patch in relationship to center of gravity and center of pressure.
Consider a Luscombe to a Cessna 402
The Luscombe CG and CP is high above and aft the narrow gear.
The Cessna is low slung with a wide stance with CG and CP forward of the contact patch.

The high aerodynamic and weight loadings will pose allot of destabilizing forces that one must stay ahead of compared to the docile nature of the low slung twin.
 
The #1 factor is pilot competence in the airplane. I used to ask friends this hypothetical question. I'm stuck on a sandbar. The weather is low, the sandbar is 500-600' long, and the wind is blowing 20g30. What airplane do you choose to come get me? The answers (Cub or Cessna) reflected what that guy was most comfortable/competent in.
 
always thought it was the crosswind speed where you run out of rudder keeping the nose straight
 
For the anally retentive here's some fodder based upon which certification regulation was in effect at the time. They evolved apparently. Vso * 0.2 is a minimum standard that's to be demonstrated I believe for two of the three below. Fuselage design - not addressed but should influence performance.

CAR 4a 1938 focus is on flight and landing loads and other structural items. I didn't find any reference to crosswinds except inferred side load limits during landing.

From CAR 3a 1949:

§ 3.145 Directional stability and control.
(a) There shall be no uncontrollable looping
tendency in 90-degree cross winds up to a
velocity equal to 0.2 Vso at any speed at which
the aircraft may be expected to be operated upon
the ground or water.
(b) All landplanes shall be demonstrated to
be satisfactorily controllable with no exceptional
degree of skill or alternates on the part of the
pilot in power-off landings at normal landing
speed and during which brakes or engine power
are not to maintain a straight path.
(c) Means shall be provided for adequate
directional control during taxiing.

And a similar requirement from FAR Part 23 2011:

§ 23.233 Directional stability and control.
(a) A 90 degree cross-component of wind velocity, demonstrated to be safe for taxiing, takeoff, and landing must be established and must be not less than 0.2 VSO.
(b) The airplane must be satisfactorily controllable in power-off landings at normal landing speed, without using brakes or engine power to maintain a straight path until the speed has decreased to at least 50 percent of the speed at touchdown.
(c) The airplane must have adequate directional control during taxiing.
(d) Seaplanes must demonstrate satisfactory directional stability and control for water operations up to the maximum wind velocity specified in paragraph (a) of this section.
[Doc. No. 4080, 29 FR 17955, Dec. 18, 1964, as amended by Amdt. 23-45, 58 FR 42159, Aug. 6, 1993; Amdt. 23-50, 61 FR 5192, Feb. 9, 1996]

Add: The CAR or later FAR under which the plane was originally certified is typically shown a ways down on the Type Certificate Data Sheet (TCDS; http://www.univair.com/type-certificate-data-sheets/) under "Specifications Pertinent To All Models; Certification Basis". For the J-3 it's CAR 4a and the PA-18 it's CAR 3a, and so on. That set the original testing requirements.

Gary
 
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The "official" demonstrated crosswind component for my 180J is 12 kts. My personal max demonstrated was 23 kts at 90* off runway heading. I remember. On that day I was complacent on approach. It took a second pass to get it down, and that landing was uneventful. At my cabin strip it isn't unusual to have winds as high as 30g40 at 45* off runway heading. That's a 16 kt component and a guaranteed white knuckle ride down. Numbers mean different things in different locations.
 
S2D said:
always thought it was the crosswind speed where you run out of rudder keeping the nose straight
Click to expand...

That was always my feeble understanding / concept of it.
Not saying right or wrong, but that was my perception.
 
Weight is also a factor. The lighter the aircraft the more effect the crosswind will have on the aircraft. The forward inertia energy of heavy aircraftall overcomes the crosswinds for a bit allowing them to get the mains down (crab and kick). So If Crosswind pilot skill, wind, and runway never changed. Then fuselage shape and aircraft weight formula could be developed. But then we have to consider crosswind gear and previous night whine/beer formula to add the the final outcome. I have had to use brakes just to taxi and take off in a straight line due to crosswinds. I am glad I was going somewhere else to land.
DENNY
 
To add to Denny's Post #23 I suggest using momentum (speed x weight) to help overcome light weight when landing. It's nothing novel or new just add some speed to maintain control. But yes once we slow on the ground then we're back to just weight as a factor. Brakes can help but on skis it gets interesting.

Gary
 
I watched a guy with lots of time in ultralight type planes just about lose one the other day. It had no fuselage covering and the rudder looked just as big if not bigger than a Cub’s on a long arm, seemed way too big for the plane. I’ve watched this guy land RV’s in pretty nasty crosswinds, and he almost bought the farm with a crosswind less than 5 mph.

It seems to me rudder size size and the arm length are a bigger factor than fuselage shape.
 
I would wonder if anyone tried a small tail and oversized rudder, based on your thoughts above. Less tail to be affected by the wind, more rudder to counteract it.


Sent from my iPhone using SuperCub.Org
 
Farmboy said:
I would wonder if anyone tried a small tail and oversized rudder, based on your thoughts above. Less tail to be affected by the wind, more rudder to counteract it.
Sent from my iPhone using SuperCub.Org
Click to expand...
Common design going back to the teens and twenties.
 
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