Aces High Bulletin Board

General Forums => Aircraft and Vehicles => Topic started by: Stoney on April 12, 2010, 08:49:37 PM

Title: Selected Stall Speeds
Post by: Stoney on April 12, 2010, 08:49:37 PM
Ok Gents,

Ran some tests to get some stall speeds in-game.  I'm posting these so folks can give me a comparison to what they have from both in-game tests and out-of-game source material.

These speeds are for the aircraft, at the weight listed, in the clean, power-off condition.  Speeds were recorded using the auto-pilot auto level function.  Throttle was retarded slowly to give about a 1 mph IAS deceleration per second, so it was a more precise reading.  As soon as a visible burble or wing-dip was identified, the speed was recorded.  Fuel burn set to zero.

FW-190A5 2XMG151
Fuel State25%50%75%100%
Weight7962816783758584
Vs IAS100101 102 102

FW-190A8 2XMG151
Fuel State 25%50% 75% 100%
Weight 86008854 9108 9360
Vs IAS 104 105106107

FW-190D9
Fuel State25%50%75%100%
Weight8793899892069415
Vs IAS105106107108

Ta-152H1
Fuel State25% 50%75%100%
Weight10318107111110511499
Vs IAS 106107110111

If you see any errors outside of a +/- 2% margin of error, let me know.
Title: Re: Selected Stall Speeds
Post by: thorsim on April 13, 2010, 08:46:50 AM
can i ask why you are testing the light loads on the As ?

a8 in game does not give a specific variant so that one will be tough to confirm ...

and as data varies what is the source or sources you wish us to use to validate the numbers?
Title: Re: Selected Stall Speeds
Post by: Stoney on April 13, 2010, 09:36:04 AM
can i ask why you are testing the light loads on the As ?

a8 in game does not give a specific variant so that one will be tough to confirm ...

and as data varies what is the source or sources you wish us to use to validate the numbers?

I figured if we tested the light armament configurations, we'd have the lightest weight/lowest stall numbers.  As an approximation, the stall speeds for the various weights among all the A models and the D model will be very similar, given the wing area, airfoil, and planform are identical.  So, for example, an A5 at 9100 lbs (if they can get that heavy) should stall at the same speed as the A8 at 9100 lbs.  However, I can set those various configurations up to be thorough, if desired.

If it looks like a legitimate source, its good enough for consideration.  Right now I'm merely looking to see if my numbers are consistent with real world numbers at the same weights, +/- a small margin of error.  This will validate the technique I used to determine the stall speeds.
Title: Re: Selected Stall Speeds
Post by: thorsim on April 13, 2010, 10:27:18 AM
i'm not so sure as i am pretty sure both the wing and the fuselage changed in TRW between the types ...

i know the wing was redesigned how much the shape of the airfoil changed i am not positive but somehow they managed according to my source to strengthen and lighten the wing between the a-6 and a-7 and when the heavier engine was added i am pretty sure the rear fuselage was lengthened to re-establish the COG ...

so depending on the detail of the FM the results may not be the same because the actual airframes were to the best of my knowlege different between the A-5 and the A-8

if someone strongly disagrees i will look into my sources and understanding of them but on memory i am pretty sure of what i posted above.

BTW is there a "HUDRECORD" command or some kind of flight data recording command available in the game?  that would make all this testing and graphing much easier. 

+S+

t
Title: Re: Selected Stall Speeds
Post by: Kweassa on April 13, 2010, 11:03:25 AM

How did you define "stall" when you tested it out?

IIRC a stall is defined as the point where a plane cannot stay level and maintain altitude at the given speed.

Title: Re: Selected Stall Speeds
Post by: Stoney on April 13, 2010, 11:16:58 AM
How did you define "stall" when you tested it out?

IIRC a stall is defined as the point where a plane cannot stay level and maintain altitude at the given speed.



As soon as a visible burble or wing-dip was identified, the speed was recorded.

And, just to expound a bit.  Flying into the stall with the aircraft properly trimmed is difficult.  So, using the auto-level feature keeps the plane perfectly trimmed for the stall.  Luckily, the aircraft tested still had a conspicuous (or what I thought was conspicuous) "burble" or wing dip at the speed I listed.  I went back and hand flew a few to see if it was consistent, and it appeared to be.  While the entire wing may not be "stalled", IMO, tip stall that interferes with maneuvering the aircraft is a "stall".
Title: Re: Selected Stall Speeds
Post by: FLS on April 13, 2010, 12:19:07 PM
Minor point. The wingtip should stall later than the root due to washout. You'll see the movement at the tip but the stall is probably occurring at the inner part of the wings.
Title: Re: Selected Stall Speeds
Post by: Stoney on April 13, 2010, 01:00:34 PM
Minor point. The wingtip should stall later than the root due to washout. You'll see the movement at the tip but the stall is probably occurring at the inner part of the wings.

Well, maybe if they hadn't designed so much airfoil thickness taper into the wing design.  Almost all of the planes in-game suffer from tip stall before root stall.  That's why they want to roll over on their backs when they stall.  Washout, IMO, is overrated, and in the case of most WWII aircraft that had it, useless.

(http://i125.photobucket.com/albums/p61/stonewall74/ClComparison.jpg)

Title: Re: Selected Stall Speeds
Post by: thorsim on April 13, 2010, 01:45:42 PM
And, just to expound a bit.  Flying into the stall with the aircraft properly trimmed is difficult.  So, using the auto-level feature keeps the plane perfectly trimmed for the stall.  Luckily, the aircraft tested still had a conspicuous (or what I thought was conspicuous) "burble" or wing dip at the speed I listed.  I went back and hand flew a few to see if it was consistent, and it appeared to be.  While the entire wing may not be "stalled", IMO, tip stall that interferes with maneuvering the aircraft is a "stall".

FYI i believe that game stall behavior is directly contradicted in the flight tests, which was my original point in another thread.  i.e. why does the 190 behave that way in the game, and how does that effect comparative playability.   
Title: Re: Selected Stall Speeds
Post by: Stoney on April 13, 2010, 02:55:35 PM
FYI i believe that game stall behavior is directly contradicted in the flight tests, which was my original point in another thread.  i.e. why does the 190 behave that way in the game, and how does that effect comparative playability.   

How so?  Basically what I'm describing is the wing tip stalling before the root.  This makes the aircraft extremely unstable around the roll axis and usually leads to the plane wanting to flip over on its back.  Are you saying that the actual flight test data states it has benign stall behavior?  Again, we have to discuss exactly what "benign" meant.  How far into the stall did they fly it? 

My flight instructor and I never performed a fully developed power-on stall in my AA-1B because those planes have some very nasty spin habits.  I've never experienced a really bad, poorly coordinated stall in that aircraft because I don't want to.  Most of the stalls I performed were very gentle, right on the edge of the buffet-type stalls.  Given some of the caution expressed in those reports about not pranging the captured aircraft, in order to preserve it for training, I doubt they got as aggressive with it as I did in-game.
Title: Re: Selected Stall Speeds
Post by: thorsim on April 13, 2010, 03:04:59 PM
How so?  Basically what I'm describing is the wing tip stalling before the root.  This makes the aircraft extremely unstable around the roll axis and usually leads to the plane wanting to flip over on its back.  Are you saying that the actual flight test data states it has benign stall behavior?  Again, we have to discuss exactly what "benign" meant.  How far into the stall did they fly it?  

My flight instructor and I never performed a fully developed power-on stall in my AA-1B because those planes have some very nasty spin habits.  I've never experienced a really bad, poorly coordinated stall in that aircraft because I don't want to.  Most of the stalls I performed were very gentle, right on the edge of the buffet-type stalls.  Given some of the caution expressed in those reports about not pranging the captured aircraft, in order to preserve it for training, I doubt they got as aggressive with it as I did in-game.

yes if you go through the tests you can find online the power on stall is described as drama free with no tendency to roll off one way or another and a simple recovery ...

for example here is a USAAF d9 flight test posted on these boards recently, see part g ...

http://www.wwiiaircraftperformance.org/fw190/wright-field-fw190d-9.pdf

they all (that i remember) are worded a bit different but they all concur pretty much across the types
(not positive about the 152) with the possible exception of that USN test i took issue with elsewhere.

+S+

t
Title: Re: Selected Stall Speeds
Post by: Charge on April 13, 2010, 03:52:20 PM
"i know the wing was redesigned how much the shape of the airfoil changed i am not positive but somehow they managed according to my source to strengthen and lighten the wing between the a-6 and a-7 and when the heavier engine was added i am pretty sure the rear fuselage was lengthened to re-establish the COG ..."

The airfoil did not change. The structure was lightened but I have no information that it would have got stronger, only lighter -maybe it was just a bit overdone in earlier variants? The rear fuselage length was not changed. It was lightly modified structurally e.g. the aux tank access hatch was put in and side access hatch was larger in A8.

When considering the wash-out keep in mind that while the inboard thickness was 15% of the chord the tip thickness was only 9% of the tip chord affecting the maximum allowable AoA quite much. While wash-out of 2 deg brings the AoA tolerance of the tip closer to that of the root they are not the same unless the closeness of fuselage and the greater dynamic pressure of the wing tip even things up.

"As an approximation, the stall speeds for the various weights among all the A models and the D model will be very similar, given the wing area, airfoil, and planform are identical."

I though that for basic lift equation you do not need to know airfoil properties or planform aspect ratios, just wing area, especially if you already have an approximation of the CL of the wing?

-C+

Title: Re: Selected Stall Speeds
Post by: jdbecks on April 13, 2010, 04:17:49 PM
How so?  Basically what I'm describing is the wing tip stalling before the root.  This makes the aircraft extremely unstable around the roll axis and usually leads to the plane wanting to flip over on its back.  Are you saying that the actual flight test data states it has benign stall behavior?  Again, we have to discuss exactly what "benign" meant.  How far into the stall did they fly it? 

My flight instructor and I never performed a fully developed power-on stall in my AA-1B because those planes have some very nasty spin habits.  I've never experienced a really bad, poorly coordinated stall in that aircraft because I don't want to.  Most of the stalls I performed were very gentle, right on the edge of the buffet-type stalls.  Given some of the caution expressed in those reports about not pranging the captured aircraft, in order to preserve it for training, I doubt they got as aggressive with it as I did in-game.

Might sound like a silly question, when you fly a real plane, does the plane buffet on the edge of the stall? or is that a visual aid for a simulator?
Title: Re: Selected Stall Speeds
Post by: hitech on April 13, 2010, 04:40:54 PM
Might sound like a silly question, when you fly a real plane, does the plane buffet on the edge of the stall? or is that a visual aid for a simulator?

Some do some don't.

Accelerated stalls in P51's gave me no warning what so ever.

Cessna's give a nice little buffet.

Marcheties (spelling) sound like elephants stomping on the wings.

RV gives a nice little tickle. Inverted stalls are very nasty and produce nice 270 degree snaps with out trying. (first inverted push at top of loop, nice way of finding out inverted stall speed very high:) )

HiTech



Title: Re: Selected Stall Speeds
Post by: Charge on April 13, 2010, 04:45:32 PM
If the stall is uneven you will feel buffeting as one part of the wing has lost lift and the flow becomes heavily turbulent. A wing that stalls evenly may not warn you at all in higher speeds but it stalls right away, where as in slower speed there is time to notice the slight buffeting when the flow above the wing starts to become turbulent as the airflow replaces the small local lower pressure areas above the wing, also causing rumbling noise and bumpy feel of motion. How radical the stall is depends on the wing thickness and profile. Thicker profiles tolerate more AoA and stall quite slowly above max AoA where as thinner profiles stall at low AoAs and very quickly once max AoA is exceeded, and at what speed that happens depends on profile properties e.g. where the maximum chord thickness is located.

-C+
Title: Re: Selected Stall Speeds
Post by: hitech on April 13, 2010, 04:55:09 PM
Stoney: Your numbers are in the ball park. But if you wish to use them for CL calculations you will also have to take into account Horizontal stab forces do to CG's.

HiTech
Title: Re: Selected Stall Speeds
Post by: thorsim on April 13, 2010, 05:43:01 PM
The airfoil did not change. The structure was lightened but I have no information that it would have got stronger, only lighter -maybe it was just a bit overdone in earlier variants? The rear fuselage length was not changed. It was lightly modified structurally e.g. the aux tank access hatch was put in and side access hatch was larger in A8.

ok i will re check my sources, question if not fuselage length then what do you suggest was done to offset the COG rearward again after they added the weight upfront ?

EDIT: NM found it, they fuel in an aft tank, sorry for the confusion.
Title: Re: Selected Stall Speeds
Post by: FLS on April 13, 2010, 06:13:19 PM
Well, maybe if they hadn't designed so much airfoil thickness taper into the wing design.  Almost all of the planes in-game suffer from tip stall before root stall.  That's why they want to roll over on their backs when they stall.  Washout, IMO, is overrated, and in the case of most WWII aircraft that had it, useless.

Edit: Mixed up and down.  :headscratch:
Wouldn't the wingtip with the trimmed down elevator have a slighter higher AOA than the trimmed up elevator and stall first? Even though the difference is small the loss of roll damping at the stall combined with a slightly higher AOA seems like it would be enough to initiate a roll.
Title: Re: Selected Stall Speeds
Post by: hitech on April 13, 2010, 08:19:31 PM
Quote
Wouldn't the wingtip with the trimmed down elevator have a slighter higher AOA than the trimmed up elevator and stall first?

I assume you are meaning Aileron not Elevator. If this is case the answer is no, but your thinking is correct. Since the Aileron is creating more camber in the wing, its Max AOA is going down, and hence it will stall sooner just as if it had a greater AOA.

HiTech
Title: Re: Selected Stall Speeds
Post by: Krusty on April 13, 2010, 08:50:42 PM
The only changes in the A6 wing was to allow better incorporation for the internal weapons trays and the larger weapons setups that the A-5 could not handle. Maybe it was "lighter" by removing the ribs directly inside the ammo compartement, but overall that's negligible. You'll find wild claims all over the Internet that the wing was greatly enhanced in either weight savings, strength, span, or any number of other claims but the real answer was: It's the same wing. It just just holds different guns.

The overall airframe dimensions between our A8 and A5 are identical with the exception of the bulged cowling to cover the larger guns.

The idea here is interesting, but I don't think it will be very useful.

You might weight a A5 down to the same level as an A-8, but that won't necessarily mean much. Even if the level stall speeds are the same, the turning ability will be greatly affected by the CoG shift of all this added or removed weight ballast.

So while scientifically interesting, it won't mean much in comparing actualy combat performance IMO.
Title: Re: Selected Stall Speeds
Post by: Stoney on April 13, 2010, 09:10:26 PM
Stoney: Your numbers are in the ball park. But if you wish to use them for CL calculations you will also have to take into account Horizontal stab forces do to CG's.

HiTech

i.e. trim analysis?
Title: Re: Selected Stall Speeds
Post by: Stoney on April 13, 2010, 09:14:46 PM
You might weight a A5 down to the same level as an A-8, but that won't necessarily mean much. Even if the level stall speeds are the same, the turning ability will be greatly affected by the CoG shift of all this added or removed weight ballast.

So while scientifically interesting, it won't mean much in comparing actually combat performance IMO.

Assuming all the weight is being added in the wing, which would probably be close to the CG anyway, I believe the weight increase would have very little impact on turn performance, with respect to CG.  My point is/was that the same wing planform, with the same airfoil, and same wing area, stall speed will be the same, at the same wing-loading.  I guess I should test to see.
Title: Re: Selected Stall Speeds
Post by: FLS on April 13, 2010, 09:43:40 PM
I assume you are meaning Aileron not Elevator. If this is case the answer is no, but your thinking is correct. Since the Aileron is creating more camber in the wing, its Max AOA is going down, and hence it will stall sooner just as if it had a greater AOA.

HiTech

Yes I meant Aileron. Brain shut down earlier than usual today. So the down Aileron would also effectively change the incidence and washout for the side that the aircraft wants to roll towards from the spiral slipstream.
Title: Re: Selected Stall Speeds
Post by: Krusty on April 14, 2010, 02:00:15 AM
Assuming all the weight is being added in the wing, which would probably be close to the CG anyway, I believe the weight increase would have very little impact on turn performance, with respect to CG.  My point is/was that the same wing planform, with the same airfoil, and same wing area, stall speed will be the same, at the same wing-loading.  I guess I should test to see.

But it won't be... Lightening the A8 will remove weight from the fuel tanks, making the tail lighter. Weighing down the A5 will add gas to the tanks, making the tail heavier. Just sayin'  ;)
Title: Re: Selected Stall Speeds
Post by: hitech on April 14, 2010, 09:54:24 AM
i.e. trim analysis?

I.E. if wing cl is 6" behind cg with a 15 ft tail.

A 10000 lb plane would require about 10333 lb lift for level flight. (10000 * .5 / 15) + 10000

HiTech
Title: Re: Selected Stall Speeds
Post by: Ardy123 on April 15, 2010, 04:53:31 AM
I.E. if wing cl is 6" behind cg with a 15 ft tail.

A 10000 lb plane would require about 10333 lb lift for level flight. (10000 * .5 / 15) + 10000

HiTech

This is probably a dumb question but isn't the h-stab of most planes have symmetrical camber, thus creating equal lift on both directions of the y-axis? ie, if the plane is horizontal, the lift force up is the same as the lift force down? I don't profess to be an aeronautics engineer so I may be way off with this.

Title: Re: Selected Stall Speeds
Post by: FLS on April 15, 2010, 07:39:19 AM
Lift is created by angle of attack. I believe camber is more about efficiency than usable lift.
Title: Re: Selected Stall Speeds
Post by: hitech on April 15, 2010, 09:05:19 AM
Ardy, if the Cl of the wing is behind the cg, the plane is trying to always pitch down. This must be compensated by a down force from the Horizontal stab/elevator to keep the plane from pitching. That down force then must be compensated by more lift from the wing, or the plane would be sinking but not pitching. Hence nose heavy planes require more lift to fly.

HiTech
Title: Re: Selected Stall Speeds
Post by: Stoney on April 15, 2010, 10:37:00 AM
I.E. if wing cl is 6" behind cg with a 15 ft tail.

A 10000 lb plane would require about 10333 lb lift for level flight. (10000 * .5 / 15) + 10000

HiTech

What happens with increased load factors?
Title: Re: Selected Stall Speeds
Post by: FLS on April 15, 2010, 10:53:04 AM
Stoney wouldn't it be proportional? A 2G load would require 20666 lbs of lift if 1G requires 10333? I'm guessing that there's something I'm missing or you wouldn't have asked.
Title: Re: Selected Stall Speeds
Post by: Stoney on April 15, 2010, 12:07:01 PM
Just wanted to make sure load factor didn't impact the formula differently.
Title: Re: Selected Stall Speeds
Post by: hitech on April 15, 2010, 01:14:39 PM
Stoney, Load factor, or more accurately AOA would effect the numbers slightly do to the definitions of lift being perpendicular to Vel vector. And as you rotate the plane, the moment arms of tail and wing change in respect to the CG. I.E. (extreme example) when you are straight up, and your vel vector is parallel to the ground. You CL is now below the CG. Now drag is creating the torques and lift is not creating any. The same effects are happing at any AOA. But this is a very small effect and can be estimated by simply multiplying the additional lift with the cosine of the AOA.

HiTech
Title: Re: Selected Stall Speeds
Post by: Soulyss on April 15, 2010, 01:44:42 PM
I do enjoy these threads even if I can only wrap my head around about half of it and even that small portion gives me a headache.

:)
Title: Re: Selected Stall Speeds
Post by: Stoney on April 15, 2010, 02:35:12 PM
Stoney, Load factor, or more accurately AOA would effect the numbers slightly do to the definitions of lift being perpendicular to Vel vector. And as you rotate the plane, the moment arms of tail and wing change in respect to the CG. I.E. (extreme example) when you are straight up, and your vel vector is parallel to the ground. You CL is now below the CG. Now drag is creating the torques and lift is not creating any. The same effects are happing at any AOA. But this is a very small effect and can be estimated by simply multiplying the additional lift with the cosine of the AOA.

HiTech

So, using your example earlier:  A 10,000lb plane in unaccelerated flight with the CL 6 inches behind the CG and tail at 15 feet would have lift = to 10,000*1.0333.  Assuming the plane stalled at 15 degree AoA, lift would equal 10,333*cos(15) = 9980?  If that same aircraft stalled during a 3g sustained turn, lift at the stall would be = to 9980*3?  Or, would it simply be better to assume the 1g lift number to determine Clmax and then use that to plug into the Clmax during the 3g turn?  I'm assuming the latter.

Ultimately, I don't have any weight and balance data for these aircraft, so I assume I'll just have to add a disclaimer.
Title: Re: Selected Stall Speeds
Post by: hitech on April 15, 2010, 03:39:10 PM
Stoney


((CG - CL) / TailLengthFromCG * Cos(AOA)  + 1) * Weight;


HiTech
Title: Re: Selected Stall Speeds
Post by: hitech on April 15, 2010, 03:40:10 PM
Or in your example

10000 + (333 * cos(16)) - (Thrust * sin(AOA - IncidenceFromThurstLine)) is Required lift;

HiTech
Title: Re: Selected Stall Speeds
Post by: Ardy123 on April 15, 2010, 05:10:35 PM
The spinning of the prop creates a spiraling/corkscrew airflow behind the prop correct? wouldn't this affect the AoA on the wing roots where the prop-wash would hit the wing? Is this impact negligible?
Title: Re: Selected Stall Speeds
Post by: Krusty on April 15, 2010, 05:18:34 PM
It's not negligable. You notice it in left/right turns.

EDIT: I mean right turns as compared to left turns, and vice versa.
Title: Re: Selected Stall Speeds
Post by: Ardy123 on April 15, 2010, 05:29:13 PM
Oh I thought the pull to the left or right was the engine torque? or is the thing I mentioned above not modeled.
Title: Re: Selected Stall Speeds
Post by: Krusty on April 15, 2010, 05:36:40 PM
Well, there's the torque, but I thought it also had to do with which wing had more airflow over it because of the prop direction..

Now that you mention it, I could be totally wrong.

Title: Re: Selected Stall Speeds
Post by: FLS on April 15, 2010, 06:25:21 PM
Oh I thought the pull to the left or right was the engine torque? or is the thing I mentioned above not modeled.

The engine torque is negligible compared to the spiral slipstream. IIRC both are modeled.
Title: Re: Selected Stall Speeds
Post by: Charge on April 16, 2010, 04:16:28 AM
"10000 + (333 * cos(16)) - (Thrust * sin(AOA - IncidenceFromThurstLine)) is Required lift;"

Errr, so even with a trim change the total weight of the aircraft does not "increase" because it is absolute. Dynamically it "increases" if you use it as a function to e.g. available thrust but I'm not sure if I understand it that way.

The FWD heavy trim difference would cause a need for a change in elevator trim that would turn into drag and into a need for more thrust if the same speed is to be maintained. With this logic you could extend the CoG a certain distance ahead from CoL until the tail would run out of either aerodynamic elevator authority, or leverage, or the a/c would run out of thrust to maintain level flight. Well, dynamically it resembles the situation where the plane suddenly got "heavier" but only as a function to control authority and that way to drag and again that way to available thrust?

But if the CoG is aft of the CoL the aircraft is not "lighter" but the elevator drag increase for correction is almost the same as is the need for additional thrust to make up for the difference or the speed will again decrease.

Am I even close?

-C+
Title: Re: Selected Stall Speeds
Post by: FLS on April 16, 2010, 07:06:36 AM
No one said the weight increases. The weight is a load on the wing and the load on the wing increases because you're adding the downforce on the tailplane needed for level flight.
Title: Re: Selected Stall Speeds
Post by: hitech on April 16, 2010, 07:54:25 AM
Charge to think about it, take a stick and hold it up with a finger under each end. as long as each hand does not cross center , the sum of the weight on each hand is = to the weight of the stick. This is the case where both tail and wing are lifting.

Now take the stick and move your left hand underneath the stick 1/4 of way from the right and your right hand on top of the stick on the right end.


Your left hand is now holding the weight of the stick, plus how much your right hand is pushing down on the stick to keep it level. This is force we are speaking of.

HiTech
Title: Re: Selected Stall Speeds
Post by: OOZ662 on April 16, 2010, 08:25:56 AM
Not sure if this would help in this discussion, but NASA has a few Java applets that demonstrate airfoil effects, such as this one (http://www.grc.nasa.gov/WWW/K-12/airplane/foilsimu.html).