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  #1  
Old 11-05-2013, 08:28 AM
agirard7a's Avatar
agirard7a agirard7a is offline
 
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Default Bank angle wing loading data??

Does anyone know where to find data for the 9a
Or any model for that matter of bank angle load factor?

For example, Vans Data 9a: at Gross weight 1750 lbs (160 hp)
Stall speed is 50 mph. What would the stall speed be with
a 45 deg bank? 60 deg?

Does this data need to be computed by each individual
POH?

The bottom line: when I am at a base to final turn, or any turn, I don't want to
guess at my airspeeds weight dependant to keep from stalling.
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  #2  
Old 11-05-2013, 09:01 AM
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rmartingt rmartingt is offline
 
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Location: Savannah, GA
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Quote:
Originally Posted by agirard7a View Post
Does anyone know where to find data for the 9a
Or any model for that matter of bank angle load factor?

For example, Vans Data 9a: at Gross weight 1750 lbs (160 hp)
Stall speed is 50 mph. What would the stall speed be with
a 45 deg bank? 60 deg?

Does this data need to be computed by each individual
POH?

The bottom line: when I am at a base to final turn, or any turn, I don't want to
guess at my airspeeds weight dependant to keep from stalling.
The traditional bank angle vs. load factor graphs/calculations will only be valid for a level turn at that bank angle.

For example, I can go out and pull 6g with wings level (at least until I run out of airspeed) and I can do 1g with 80 degrees of bank (though I will run up to redline very, very quickly). If I'm trying to bring the nose up while banked, that implies a higher g load than a level turn.

That said:

For level turns, load factor = 1 / cos (bank angle)



15deg bank = 1.04g
30deg bank = 1.15g
45deg bank = 1.41g
60deg bank = 2g
75deg bank = 3.87g

or restated:
1.5g = 48deg
2g = 60deg
3g = 70.5deg
4g = 75.5deg
5g = 78.5deg
6g = 80.4deg



Now, we have to relate that to stall speed.

Lift = 1/2 * (density) * (velocity^2) *(wing area) * (Cl)

Since we're concerned about relative stall speeds only, we can ignore the density, and wing area and CL are constant.

Now, if we pull 2g's, that means the airplane needs to generate twice as much lift; since all the other factors are assumed constant, (velocity^2) needs to double, too. So, stall speed at load factor X = square root (x) * 1g stall speed.

Stall speed factors:
2g = 1.41 * original stall
3g = 1.73
4g = 2
5g = 2.24
6g = 2.45

If your airspeed indication is truly calibrated and accurate for all AOA ranges, you could compute it from this formula. But it's possible that airspeeds can indicate lower due to installation differences, and relying on these calculations could give erroneously low airspeeds for stalls at high load factors.



In my humble opinion, worrying about trying to compute a constantly-varying stall speed for a given bank angle and G load while you're trying to fly the airplane is an attention hog. It would be far better to fit an AOA indicator (and even better, one with an audible tone) that shows how close you are to stall regardless of airspeed or load factor.

Last edited by rmartingt : 11-05-2013 at 09:03 AM. Reason: Clarifying
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  #3  
Old 11-05-2013, 09:04 AM
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agirard7a agirard7a is offline
 
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Default Solution

Ok. I called Vans about this. This data does
not exist from their knowledge. Maybe someone
has done it with extensive flight testing.

Solution: install an AOA! Computed for
5 mph above stall speed.

Sounds like a plan and a life saver.
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  #4  
Old 11-05-2013, 09:40 AM
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agirard7a agirard7a is offline
 
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Default Computation

Bob. Thanks! That was the info I was looking for to at
least try to quantify rather than guess or assume.

With your formula: ( if i am correct) with a 48 deg bank, stall
Speed is increased 1.5 x 50mph ( stall for 9a
At gross 1750) = 75 mph stall speed.

Interesting! Being that most people seem to
Recommend pattern speed in the 9 at 70 mph,
That better not be at or near gross weight or near
48 deg of bank! Obviously 80 mph at gross is a safer bet
And a go around if you overshoot the base to final!

I wonder how many people have died making this mistake?
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  #5  
Old 11-05-2013, 09:47 AM
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Neal@F14 Neal@F14 is offline
 
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When you're descending in a turn with the wing "unloaded" the stall speed is going to remain pretty low even with a steep bank angle.
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  #6  
Old 11-05-2013, 10:19 AM
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Eddie P Eddie P is offline
 
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How over the top "numbers slave" you want to go? That will dictate the answer, but at the end of the day approximations are close enough for human based flight ops Engineering data will vary depending on the aircraft specific configuration and particulars - airframe flex, planform particulars, aerodynamic twist under load, etc. But for general rules of thumb, Post 2 spells it out. Wing loading affects stall speed - you can determine *approximate* stall speed delta per unit bank angle quite easily.

The reason Van's Does not have the data for the 9A is because it is a generic question and the base line equation remains the same for the 9A or the B-747-8I when you are talking about rules of thumb and figures decent enough to give accurate situation awareness.

For example, a 30 degree bank angle, typical pattern maneuvering, your G loading is 1.15 and stall speed is 1.07*Vso. So you have an adequate maneuvering margin with pedestrian bank angles to be at final approach speed though it is obviously reduced somewhat while maneuvering compared to wings level. That's why it is common practice to delay reducing that final 5-10 kts (to final approach speed) only once aligned with the runway, wings level.

For a stall speed of 50KTS in smooth air and in coordinated flight:

30 Deg Bank ~ Vso*1.07 = Stall appx 54kts
45 Deg Bank ~ Vso*1.19 = Stall appx 60kts
60 Deg Bank ~ Vso*1.41 = Stall appx 71kts
75 Deg Bank ~ Vso*2.00 = Stall appx 100kts

PS a wing won't stall at 0 G. But you will be arcing to tierra firma pretty quickly none the less.

Landing configurations are going to be limited in G capability in many designs and also there may not be a stall speed below limiting flap speed in some bank angles nor would anyone want to be normally maneuvering in some configurations at 75 degrees bank for example. Therefore it's a good idea to also do some figuring with clean wing stall speed and add a margin for "turbulence", "uncoordinated flight", "pilot control technique" and other complications that may also increase stall speed if you want to get a good feel of what to expect. Then experience in the airframe will give you a seat of the pants feel and some level of innate situation awareness.

Simply saying "who cares, install an AOA indicator" is not good enough, it's too reactive. To be proactive and occupy the seat with enough SA to fly safely, we all still need a good handle on what to expect with various bank angles. An AOA gauge is a great tool as long as it's not a crutch. (Edit - Paul is right a few posts from here, my original statement on a "crutch" applies only if we use a tool without the knowledge of how a tool works and don't know how to anticipate it's best use)

Expanded article that covers some of this:
http://www.experimentalaircraft.info...ll-speed-1.php

Last edited by Eddie P : 11-05-2013 at 10:57 AM.
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  #7  
Old 11-05-2013, 10:26 AM
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The same data as above for a constant altitude banked turn stall speed.

It may be easier to see in graphical form in the right hand chart -

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  #8  
Old 11-05-2013, 10:28 AM
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Eddie P Eddie P is offline
 
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Quote:
Originally Posted by agirard7a View Post
Interesting! Being that most people seem to
Recommend pattern speed in the 9 at 70 mph,
That better not be at or near gross weight or near
48 deg of bank! Obviously 80 mph at gross is a safer bet
And a go around if you overshoot the base to final!

I wonder how many people have died making this mistake?
Lots of people have died making this mistake, normally they know much better in a 1G day on the ground, but it's during the "impossible turn" after an engine failure where many factors may contribute to stalling and spinning.

Also, you numbers are a bit off. The way I see it (see the link I posted for an expanded mathematical breakdown) you will stall about close to the figures listed in my post. (we are all posting at about the same time, sorry for the redundancy). Keep in mind your clean wing stall speed will be higher, and any uncoordinated flight or turbulence will also factor in to a higher stall speed. This is not to scare you into flying too fast, there are hazards with that too. Just good situation awareness is all that is required and then plenty of stick time feeling the envelope of the aircraft in real life at a safe altitude and with a good aerobatic/spin CFI if possible.
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  #9  
Old 11-05-2013, 10:29 AM
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agirard7a agirard7a is offline
 
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Location: Newport, RI
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Default Airspeed

Neal. Assuming in the decent you are gaining
Airspeed. However, in landing configuration, approach
Speeds are wanting to be constant so although descending,
Airspeed remains the same so the stall factor would remain
a constant. I would agree with you with a banked turn in the open sky where speed would naturally increase in decent. Greater airspeed
reduces stall.

Please corrected if I am wrong but decent angle
Should be irrelevant if you are maintaining constant
Speed.
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  #10  
Old 11-05-2013, 10:34 AM
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Ironflight Ironflight is offline
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Sorry Eddie, but the AoA is no more a crutch than the Airspeed indicator and a bunch of mental gymnastics to recalculate the current stall speed given the flight path, bank angle, gusts, etc, etc. The AoA does all of that compensation for you.

Ideally, we'd all be superior pilots who simply feel the airplane in the seat of our pants and never accidentally stall becasue we are one with the machine. That hasn't worked too well for a lot of dead folks over the last century.

If you want a reliable indicator of where the airplane is relative to the stall under all flight conditions, and you want that to be somethign other than your hind-quarters, AoA is the far superior instrument.
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