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2 to 3 months... HA! As if this teaches you jack crap on manufacturing realities or maintenance realities.
Worth a reply. True regarding not enough time to graduate to Manufacturing/Process Engineer, not enough time to scratch a surface regarding tooling, machine tool set up or plant layout. Having said that, working with the manufacturing engineers reviewing Change Orders that slipped past Design review and caused issues with practical incorporation or best practices forces an airframe design engineer to re-think how his brilliant concepts cause issues on the shop floor. Maintenance has become a real discipline as post production labor costs and 'up time' for complex systems is a real problem - and the reason the F-14 was retired (among many other 60-s-70's designs. IMO you learn nothing (about Maintenance or Field Service or Spares Planning) on the shop floor except for better understanding of access to critical components when installed 'As designed"
I can tell from your reply that you were one of those sit your behind in the chair guys behind the computer screen. You think that by being able to shave an 100g off an existing structure, using FEA, makes you a good engineer. No. It makes you a good analyst. Not a good engineer.
If you can tell that from your viewpoint, you may not a.) be an engineer, and b.) maybe not be an acceptable analyst
An engineer views the ENTIRE project as a whole. He is not narrowly focused in structures. Structures is the minor field in engineering.
I believe I mentioned that in my post #70 above. The paragraph may have been a little too complex in citing attributes that I consider important to airframe engineering for you to grasp holistically - you failed to note that 'structures' is but a step in the process I outlined for you regarding my definition? IMO, based on your rants, you have toiled away in whatever career you have mostly irritated by folks that don't agree with you - and further, based on that observation, You STAY in a constant state of 'Irritation'?
I can tell you 100% have no clue what I am talking about and never will as you do not have the framework built in your mind to visualize what I am saying as you are tied up in your own structures FEA world. GregP has a much better grasp at what I am talking about than you do in this case. Same goes for most of those production engineers on the manufacturing floor that you were deriding in your post.
You have a severe reading comprehension problem - I never 'derided' production engineers, quite the contrary. I learned more from the Production Engineers and Shop floor supervisors as Program Manager for GE's AFCAM participation in the mid 70's by 'walking around and talking shop at Boeing, Lockheed, GD, MACDAC, GE Aircraft Engine Group and LTV than I ever learned as a design engineer - as USAF tried to get control of costs via synthesizing concepts from CAD/CAM and Drawing Classification systems.
Anyone can do FEA. Dime a dozen.
Ah, anybody with a sound background and experience can be trained to perform Finite Element Modeling tasks which are a.) reliable in concept, and b.) lead to sound detail design, but - hardly a dime a dozen.
Lets just end it there.
16K memory in the 60's? Lord have mercy, that must have cost a fortune!!...IBM 600 series with (IIRC) 16K of memory.
Greg - you have zero to apologize for, now and in the past.
This doesn't look right, I know a Spitfire VIII was tested up to Mach 0.891, though that was pushing the airplane into a territory that was beyond the placard limit (0.85)after a look-araouns I found some additional critical Mach-speed figures:
From Lunatic (compare P-47 vs. F4U):
Spitfir MK IVX: 0.89*
I assume that's the MMO, right?P-47N: 0.83*
Actually, from what I remember there was a narrow set of conditions where the Me-262 could actually exceed Mach 1, and some recent tests corroborated it. It might very well put the plane very close to structural damage or worse (it'd likely require both stab-trim and elevator application which can sometimes overstress the aircraft): I can't say whether Mutke managed to do it.Recovering alone doesn´t proove that it was no terminal dive Mutke´s claim to break Mach 1 in a Me-262 dive (which I don´t believe) underlines that. He was able to recover from his terminal dive at very high subsonic speed (but not Mach 1, the airframe of the Me-262 couldn´t sustain the stress).
From what I remember the placard limit of the P-51D was 0.75, and was dove once to Mach 0.84 or 0.85 with skin buckling occurring. I'm not sure how much different the dive speeds were with the P-51B and D, though the -D might have had more drag due to it's canopy.Figures I have are 0.84 for for the P-51B, 0.82 for the P-51D because of the slightly thicker wing and the bubble canopy.
Was this the MMO or placard limit? I'm actually quite fascinated about the placard speeds for the Bf-109/Me-109 and Fw-190 variants: I do remember something to the effect that either the stabilizer or the rudder balance imposed some kind of flutter restriction that was eventually fixed and allowed dive speeds faster than the P-51.I also recently found the mach number of the Bf-109G was about 0.78, the 109F was about 0.80.
To some degree the thickness was made necessary because of the high aspect ratio: High aspect ratios produce more flexing of the wing, which require more thickness or more internal support members.The P-38 mach number is so low because it has a very thick (by proportions) conventional wing with the maximum chord well toward the front.
I think you might be mixing up several different scenarios.going off memory
The piston engined aircraft with the highest Mach speed is a late model Spitfire, which in the hands of a test pilot reached Mach 0.98 in a dive, though the aircraft almost fell apart, and its propellor fell offFortunately the pilot managed to land OK
The kink didn't affect the dive speed?The P-51 wing was the same until the P-51H. The only difference was the inboard leading edge angle depending on the wheel/gear uplock design changes made on the D/K.
I thought loss of control was predominantly related to the shockwave strength, turbulent flow, and loss of the downwash until you were nearly sonic, when the loss of the upwash shifted the C/L to 0.50% MACBoth the P-47 and P-38 had increased longitudinal stability induced by the transonic separation - both by the reduced downwash on the horizontal stabilizer but also due to the change in wing moment coefficient as the shock wave moved aft past the 1/4 chord point of approximate maximum chord thickness.
I didn't know spanwise flow would occur under these conditions. In fact I thought it was mostly an issue related to stalls.As the swept wing goes through the transonic region it will start to lose lift in the outer wing panels due to the spanwise flow contribution.
I didn't think the tail produced positive lift, merely it stopped producing most of it's negative load.When that happens, the wing/body lose lift and will pitch up causing the downwash over the low tail to Reduce- causing the tail to have positive lift - counterbalancing the wing-body pitch up.
This doesn't look right, I know a Spitfire VIII was tested up to Mach 0.891, though that was pushing the airplane into a territory that was beyond the placard limit (0.85)
Was that the MMO or placard limit? Neither, that velocity was well past design limits, Placard speeds and Mcr.
Was this when supersonic flow appeared on the wing, when mach effects started to take hold (heaviness on the control column), or the maximum operating mach number?
Mcr is that freestream velocity at which the velocity over the surface (i.e wing, windscreen, etc) reaches M=1.
I wouldn't be surprised if that's the speed supersonic airflow started to form over the wing, but from what I was told around 0.68 was when control-problems began, with a total loss of control at Mach 0.74.
There is no constant Mcr for any airplane class or type, although aircraft with exactly the same wing (airfoil and T/C ratio) will be very close.
From what I remember the placard limit of the P-51D was 0.75, and was dove once to Mach 0.84 or 0.85 with skin buckling occurring. I'm not sure how much different the dive speeds were with the P-51B and D, though the -D might have had more drag due to it's canopy.
No difference in Placard velocity - basically wing related and the B had same airfoil as D. The drag on the D canopy was slightly less than the B. That said, the ammo cover doors were beefed up on the D due to visible 'balloon' effect during full blown shock wave formation as the airframe (wing) entered Drag Divergence regime. Drag Divergence is defined as the Velocity envelope at which a full separation and shock waves (indicating chaos in flow in which local shock waves are created) appear. In this velocity envelope the adverse pressure gradient exists in the region of shock wave formation - resulting in complete separation. This is the Transonic region and responsible for great turbulence downstream of the separation region. Selecting a 'Point' for Divergence was traditionally that 'point' at which the Total Parasite Drag increased 10%. Drag increased exponentially in this region.
In your example above - the .82-.84M velocity is Vne. whereas the .75M is the Placard velocity for the P-51. Different airframe manufacturers established the Placard velocity via test dives pushing the envelope then applied a safety factor for the Placard Speed. It (Placard) was the manufacturer's (and AAF/USN) way of saying " you should not go past this speed, but if you do you might survive it - proceed at your peril".
Placard velocity was near or slightly > Mcr, depending on the fighter, but less than Vne. Vne was determined by limit loads due to Dynamic pressure, whereas the Placard Velocity was lower than Vne with a margin of safety
Wait, if the plane couldn't even do Mach 0.83, why was that speed listed?Neither, that velocity was well past design limits, Placard speeds and Mcr.
Just to be clear, do you know what mach number the plane would either suffer control heaviness of a degree that recovery would be impractical/impossible, or that the tail would get blanked and tuck-under would occur?Mcr is that freestream velocity at which the velocity over the surface (i.e wing, windscreen, etc) reaches M=1.
That makes sense because I was responding to several peopleToo many questions and repetitive assumptions to comment on past this point.
Recommended reading:drgondog
Wait, if the plane couldn't even do Mach 0.83, why was that speed listed?
Just to be clear, do you know what mach number the plane would either suffer control heaviness of a degree that recovery would be impractical/impossible, or that the tail would get blanked and tuck-under would occur?
That makes sense because I was responding to several people
Firstly, if you were able to identify which book would be the most valuable, what would you recommend?Recommended reading:
1. Aerodynamics for Engineeers - Bertin and Smith
2. Introduction to Flight - Anderson
3. Fluid Dynamic Drag - Hoerner
4. Aircraft Design - A conceptual Approach - Daniel P. Raymer
Secondly, I'm not sure I'd be able to provide an answer if I read those books as math was never my strong suit (B/C average)
I'm not sure that's entirely accurateWhy ask a question if you cannot understand the answer?
Yet some of what he's saying I can actually follow to some extent: There was an earlier thread I posted, then momentarily lost track of, and now I found againOn most aviation subjects drgondog can lose 90% of this forum, on his real specialities he (and some others) can lose 99% of the forum.
i suppose it would be more accurate to say that if given the mathematics equation I'd probably require guidance on the more complicated stuff as mathematics has never been my strong-suit.You are asking for answers to very involved questions about aerodynamics which you admit you dont have the math to follow
Please dont suggest that some people here cannot explain what you are asking, the problem is you cannot follow the explanations without knowing all the theory behind it and so just ask more questions.As I see it, this number is completely meaningless unless it was based on the shape without factoring in things like structural strength, which is purely theoretical and not data that reflects the facts.
Structural strength is a fact based on the measured strength of the material under discussion and the use to which it is put.
Yet some of what he's saying I can actually follow to some extent: There was an earlier thread I posted, then momentarily lost track of, and now I found again
That is because you are being given a simple explanation boiled down so that a layman can understand
Some of what he was saying got me lost a little, but the basics of it I could actually follow on some level: A thinner wing tends to do better at a higher mach number, a lower camber wing tends to do better at a higher mach number, a wing with the crest further back tends to yield a higher mach number for the same t/c ratio.
i suppose it would be more accurate to say that if given the mathematics equation I'd probably require guidance on the more complicated stuff as mathematics has never been my strong-suit.
As for the textbooks: I usually would not refer a person to a textbook if I was capable of answering the question; if I could not answer it any other way,.
I didn't say they couldn'tPlease dont suggest that some people here cannot explain what you are asking
That would have never occurred to me...the limits are for the whole aircraft and while the wings are important there are other factors, a poster here did the calculations on a spitfire and it is the windscreen that is its worst feature.
ThanksAnderson's Introduction to Flight