Utilizing the P-51D's instability

[Krusty]

Originally posted by BaldEagl
Bad analogy Krusty.  I think that NASA engineers have a lot more training, experience and comprehension than any 3 year-old.

By his logic, apparently they don't.

I, personally, think they're pretty smart.

[SlapShot]

EDIT: Let me try and put it in a way so simplistic even you could get my point:

There ya go again getting all high and mighty and full of yourself and finally resort to a condescending attitude to really bring it home ... par for the course when someone takes you to task.

LOL ... I accomplished what I set out to do ... that a self-proclaimed know-it-all really doesn't know it all. Your very good at painting with a broad brush and your expertise at using smoke and mirrors is superb.

Want an example of a "broad brush" ...

You notice wind tunnel mockups don't actually fly?

Want an example of "smoke and mirrors" ...

Your RC plane weighs a few pounds, max. Wingspan (let's say) 2.5 feet. P-51 average wingspan, 50 feet. That's 20x the scale. Now weight... P-51 let's say 12,000lbs. Divide by 20 (the scale of the RC plane) and the little tiny 2.5-foot RC plane has to weigh 600lbs to even come close to approximating the P-51.

The scaling ratio is in size ... not weight ... too funny smarty-pants.

Take the exact same engine and machine every component down to it's 20x scale and assemble it and you would now have the correct "scaled" engine and mathematically ... it should fit inside the 20x airframe of the P-51.

I'll stop here as to not cause you any more embarrassment.

[Bronk]

1 word for this thread.
Hyperbole
I'll let you figure out where it belongs.

[Bosco123]

Originally posted by mtnman
That looks a lot like a maneuver I do with my radio controlled planes.  To do it, I throw both control gimbals into the top inside corners, or both into the top outside corners.

That would be full throttle, full down elevator, full left aileron, and full right rudder.  Or full throttle, full down elevator, full right aileron, and full left rudder.

I generally prefer to do it while nose up at least a bit, sometimes even vertical.  Letting my controls go neutral stops the maneuver, at least with my RC planes.

I've done it with RC Corsairs, Ponies, Cherokees (Piper), Ultimate biplanes, and Pitts biplanes.  The aerobatic planes do it best, followed by the war birds.  The Cherokee will do it, but it's not as quick and impressive.  

I don't know how close those planes are to AH's flight model though.  For one, the power/weight ratio is probably quite different.  The wing loading and airfoils are different too...

I've done that manuever in the TA, DA, and offline, and it does work, but I've never tried it in the MA.  I know there were complaints for a while way back when of people doing snap rolls, and (lag?) made them look awful to the guy following.  Those complaints seem to have died down, maybe the smoothing effect HTC added helped?  Use to be called stick-stirring, even though it wasn't...

MtnMan

This in modeling is what we call a snap, most of you know that already and myself knows how to do it. you can probably do it in the mossies and the 110's very well, but you have to know how to get it out of this manuver, down and opposite rudder the plane is doing.
Thats a neat trick right there.

[Bosco123]

Originally posted by Krusty
Er.... RC planes can also hover on their props.


Don't think a real life war plane can do that.


Just because a 2-lb. plane with enough thrust to break orbit can do it doesn't mean a 12,000lb plane with a single engine and slow acceleration can do it.

You get my point?

Warplanes, or warbirds, will never hang on their prop because they just cannot have the power to pull the airplane strightup like that. Unless you put somthing that is way too overpowering for the plane, you will snap the wing in half just as a result as speed. Now some airplanes maybe able to "hang on the prop" but those airplanes are designed for that specifically. They are the exact same thing just smaller.

[dtango]

Originally posted by Krusty
dtango, they cannot tell you the intertia, torque, or some other aspects of the real deal, because it is a model. Even if it has the scale WEIGHT, it does not have the same weight-to-surface area ratio....

....You can't just make something bigger and have it act the same way. The density increases while the ratio of mass to surface area decreases. There's a lot more at work than I think you give credit for.

I'm sorry Krusty.  That is absolutely incorrect.  Wind tunnel tests on models can give you all that.  In aerodynamics it's called applying the right scale and similarity parameters.  If we have the same similarity parameters (reynolds and mach number, mass distriubtion, control surfaces, etc.) between a scale wind tunnel model vs. real life then the ratio of forces experienced in the wind tunnel scale model are the same ones that you experience in full-scale.  This is what makes wind tunnel testing even of value.

My little X-29 chart gives you hints at that, and that's only the tip of the iceberg.  It tells you what they estimate the REAL X-29 is going to be like in terms of how it responds in the roll and yaw axis at different angles of attack.  It's a direct result of analyzing the forces on the model like the following:



These are the sideforce, yawing, and rolling moment derivatives from the model for different at a given aileron deflection across a range of flight angles of attack.  They expect that full-scale X-29 to demonstrate the same values.  This means that the ratio of forces acting on the model in the wind-tunnel replicates what the full-scale aircraft will experience at that same flight regime.  This concept is paramount when it comes to the validity of tests on scale models in the wind tunnel.

Just for grins here is a picture I really like of the X-29 flying at 80 degrees aoa in free flight wind tunnel testing .



We haven't even touched on things like vertical wind tunnels and rotary balance tests which test a whole host of other characteristics like predicting the aircraft's stall and spin departure and departure recovery etc.

==============

Originally posted by Krusty
P.S. The whole wind-tunnel side-track was Slapshot trying to divert the issue.

I understand where the conversation has been going.  I've purposely have stayed out of the whole discussion about RC craft etc.  I don't know that anyone is showing that an RC P-51 will do the maneuver.  The generalization from Kweassa and others are that real life acrobatic and RC planes can do some pretty amazing tricks, therefore since the physics are similar it's reasonable to assume that it's not impossible for a Mustang to do the same.  From an aerodynamics standpoint, this is a much more compelling argument then saying it's not even possible because an RC model isn't a life-size aircraft.  You chose to go down the line of reasoning which lead to the wind tunnel discussion about the value of scale models to defend the RC vs. life-size aircraft physics position.

==============
Slapshot: nice find on the X-48 .  I'm still amazed they put working "jet" engines in those free flight models.

Tango, XO
412th FS Braunco Mustangs

[Ack-Ack]

Originally posted by Widewing
Push your stick all the way forward and all the way to the left while applying full right rudder.

Mtnman described it exactly.

While Murdr was flying behind me in the TA running film, I was actually able to flip the Mustang backwards and see his pursuing 109K in my windscreen as he blew past. He said there was no chance to get guns on the P-51 as it literally dropped straight down as it rotated.

Murdr, if you're reading this, maybe you could post a portion of the film...

My regards,

Widewing

Also sounds like the maneuver Erich Hartmann describes doing a number of times on the Eastern Front to evade an attacker on his six position and to force the attacker to overshoot.  

ack-ack

[moot]

Why do you have so much trouble admitting you're wrong Krusty?  This time, there was evidence in advance of the full refutal that you could have reassessed the basis of your arguments with, and recognized why dtango and others argued against you.. and seen what you argued was just plain wrong.

[mars01]

OMG Krusty you are clueless, a snap roll is an accelerated stall and spin along  its longitudinal axis while maintaining its general horizontal direction.  It has everything to do with the angle of attack and the angle the wing stalls at.  Every airplane is capable of spinning as well as snap rolling.

Pulling back abruptly on the stick increases the wings angle of attack to the point where the wing stalls.

Kicking the rudder induces yaw which sends the plane spinning on the horizontal, torque and gyroscopic precession also contribute or negate the affect depending on which way your propeller is turning and what rudder you hit.

Pushing the stick forward unloads the airplane and reduces the drag from the elevator essentially accelerating the aircraft spin.

A snap roll is one of the basic Aerobatic maneuvers.  If you watch any Aerobatic videos you will see many snap rolls.  I am amazed at how few know this maneuver on here.

When a snap roll is judged in Aerobatic competition the judges look for the nose being displaced up or down ( up = positive snap, down = negative snap) before the roll is initiated.  IF they don't see the nose displacement then they will zero the snap roll figure and claim all the pilot did was an aileron roll.

I have to admit the depiction of the snap roll in dogfights was just plain bad.  What they portrayed graphically was nothing short of garbage and looked nothing like a snap roll.

[MajIssue]

Isn't that a slip? Turing rudder in the opposite direction as ailerons... If done while chopping throttle and deploying flaps in rapid succession you are GOING to decellerate and drop like a brick, works in the real world and AH.  The trick is to reverse the manuver as soon a your opponant starts to pull in front as you. My PFI taught us about slips as a solution to being high and/or hot on approach, but the manuver has it's roots in ACM.

[RoGenT]

I'm definetly going to try that move (and pratice it alot as well) once I get playing back in the game

[mtnman]

Hoffman-"Krusty, if an RC aircraft can do the maneuver, and the only difference between a P-51 and an RC aircraft are size and engine power."

Krusty-"Your RC plane weighs a few pounds, max. Wingspan (let's say) 2.5 feet. P-51 average wingspan, 50 feet. That's 20x the scale. Now weight... P-51 let's say 12,000lbs. Divide by 20 (the scale of the RC plane) and the little tiny 2.5-foot RC plane has to weigh 600lbs to even come close to approximating the P-51."


There are some other differences that do play a role, other than size and engine power.  Almost always, the airfoils are quite different.  RC planes generally have thicker-than-scale airfoils, and often, if not normally, different airfoils entirely than actual warbirds used.  These different airfoils affect stalls, etc.  An RC plane probably won't stall identically to its full-size counterpart.  Wing loading varies as well.  My RC F4U has a wing loading of around 34oz/sq ft, while it appears that the actual F4U-1A has a wing loading of around 36lb/sq ft.  Those numbers look much more different than they really are.  

There are lots of other differences.  The end result still has the RC plane behaving very similarly to the full-size plane, and being influenced by the same forces.  NASA thought RC planes flew similarly enough to full-size planes to make extensive use of RC space shuttles in design testing.

Krusty- Your knowledge of RC planes appears limited, and if you're trying to compare the itty-bitty department store RC planes with the ones referred to in this thread your confusion is easily explained.  A 2.5 ft wingspan styrofoam RC corsair or pony look-alike is nothing like what we're talking about.  That little thing DOESN'T fly like a full size warplane, any more than it flies like the "real" RC planes we're referring to.  Sure the aerodynamic forces in play are the same, but it won't "look" the same in flight, or be capable of the same maneuvers the full size plane or the "normal" RC planes are capable of.  Those little things are for little kids.  Generally only have rudder, and MAYBE elevator control.

The RC planes I'm familiar with seldom have wingspans that small.  They're larger, faster, heavier, and very true-to-life.  My RC corsair has a wingspan of over 5ft, and weighs between 8 and 10lb.  It's 1/7 scale.  My largest RC plane had a wingspan of almost 12ft.  The full size F4U has roughly a 41ft span.

You're weight scale conversion theory doesn't work the way you describe.  As you double size, you don't double weight.  Weight builds much faster, but not necessarily at a predictable rate.  I have three firearms that shoot round lead balls (spheres).  One is .50 cal, one is .75 cal, and one is 1 inch (1.00 cal.)  The .50 cal ball weighs 175gr, the .75 weighs 565gr, and the 1 inch weighs around 1500gr.  So as size doubled, mass increased much more rapidly (roughly 8x, in this case...)(in Avoirdupois weight 1lb = 7000gr).  My 1/7 F4U does not, and SHOULD NOT weigh 1/7 the weight of the full size aircraft.  Nor should the engine produce 1/7 the thrust, etc...  Think of a 1 inch cube (1 sq inch).  Now double the dimensions, to a 2 inch cube.  The two inch x two inch cube is actually 8 sq inches.  A 7"x7" cube would be 343 cubic inches.  Assuming identical materials for the model F4U vs the full-size F4U we'd assume the full size plane would weigh not 7 times what the model weighs, but 343 times what the model weighs (2744-3430lb in this case).  Identical building materials are obviously not used.

The redtail hawk and the golden eagle are VERY similar (but not identical) in shape and flight.  The redtail has a 4ft wingspan, and is 21 inches long.  The golden eagle has an 8ft span, and is 42 inches long (roughly).  It would appear that the redtail is 1/2 the size (and it is, more or less).  The redtail weighs 3-4lb.  The golden eagle weighs 12-16lb.  So size doubled, but mass quadrupled in this case.

Your arguments based on size/weight lead me to believe a P51 and a Boeing 747 don't operate on the same principals and respond to the same aerodynamic forces.  Is the weight ratio between the P51 and the 747 correct?  

Interesting discussion, but we're not comparing apples to apples...

MtnMan

[mtnman]

Originally posted by dtango

  I don't know that anyone is showing that an RC P-51 will do the maneuver.  
[

I've done it with RC P51's, F4U's, Piper Cherokee's, Ultimate Biplane's, and Pitt's Biplanes.  All did the maneuver, but with varying "crispness".  The Biplanes being aerobatic planes did it "best"(by far).  The Cherokee does it the "worst".

For what it's worth, the RC P51 and F4U do it "much better" than the AH model does, at least in my eyes.  The AH model seems to do it in slow motion compared to what I see from the RC planes.  It's really not a "P51 thing", lots of planes would do it I expect.

I would expect this maneuver to be possible in the full size plane, but I sure wouldn't want to be involved, hehe.  I wouldn't argue that the full size plane should be able to do it exactly like the RC versions...

MtnMan

[Wolfala]

Originally posted by Kweassa
On the contrary, I find it an amusing testament to the accuracy of AH FM.

 With the same sequence of stick inputs, the AH P-51 entered a state of accelerated stall that is virtually identical to those of the real-life P-51s piloted by Cpt. Bryan and Lt. Candelaria.

 In other words, under similar conditions, the AH P-51 reacted almost exactly as the real life P-51 did.

 Now if that's not a testament to how accurate and reliable AH FM is to the real thing, what is?

 Anyone seen a P-51 in other sims ever do that? I sure haven't.

So basically, you are saying the Cobra wasn't a Russian invention, but North American?

[Charge]

Well, I tend to be with Krusty on this one.


a) possible -Maybe, with luck you might even survive it, As far as I remember anykind of spinning was not recommended in Mustang. Do I remember wrong?

b) did happen -Really? We only have one person's somewhat inaccurate interpretation of what happened.

c) was documented -Errr, so?

d) is repeatable -In a real Mustang?

e) can be observed in airshows with real planes -Yeah, different "acrobatic" planes, very much different from Mustang.

f) already well known amongst real pilots -Maybe, although it may well be that you are not even talking about the same phenomenon.

g) simulated by a FM claiming to be close to that of real life physics -Sure, to me it looks like an anomaly in FM. In WW2OL flight model there does not seem to be anykind of damping for yawing momentum causing the 109 and P39 to be very unstable in yawing maneuvers. Is this hard to model in FM maths?

h) simulated by scaled-down RC planes -By scale Mustangs? Any vid? Any data of COG and weight vs scale? Depending of the speed in real plane the G stress might tear the plane apart.

From Homeboy's post:

"Never attempt to slow the aircraft by yawing the rudder."

http://forums.hitechcreations.com/forums/showthread.php?s=&threadid=223808

Skip Holm said that while 109s can be yawed significantly in flight to take a shot but Mustang cannot. Why do you think that is? The answer might be the huge side surface of the Mustang. I don't know really, but i suspect that to  be the reason. Any ideas?

Besides what the hell does a modern wind tunnel have to do with this topic?
Was Mustang model tested in a modern wind tunnel and data gathered? Wind tunnel testing does not replace the need for real flight testing where the aircraft is spun and twisted and according that recommendations are made of permitted maneuvers. In wind tunnel you get the initial idea of what happens in different states of flight in  u n i f o r m  air flow. That means that spin tests need to be done with a real plane.

***

Like so many times this thread too seems to be heading to personal mockery devoid of objective reasoning.

-C+