Crumpp Posted October 27, 2015 Author Posted October 27, 2015 Yeah the math, a reduction of 5.2" from 12.6" is 7.4" aft of CG according to you own submitted Spitfire stability report on the MkIX, this ties in very nicely with the modern day MkIX's having the aft limit set to around 7.2" and the ones with rear tanks having a higher limit. My math had nothing to do with that footnote and does not solve for EWCG. You are turning in circles chasing your tail. Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
bongodriver Posted October 27, 2015 Posted October 27, 2015 Run the math....Run the math... You are lost in the sauce, bongo. I solved for the LEMAC the NACA was using and compared their datum point to the RAE/Supermarine datum point so I could correct evaluate the CG locations. Yeah the math, a reduction of 5.2" from 12.6" is 7.4" aft of CG according to you own submitted Spitfire stability report on the MkIX, this ties in very nicely with the modern day MkIX's having the aft limit set to around 7.2" and the ones with rear tanks having a higher limit, I don't care what method you have used to complicate it, the real sauce is right there staring at us in the face.
Crumpp Posted October 27, 2015 Author Posted October 27, 2015 5.2" from 12.6" is 7.4" aft of CG Is not the Aft CG limit for the Mk IX. It is just telling you where it will be with the rear fuselage tanks empty of fuel. (-7.4-21.89)/85 = 34.45% MAC 31.4%MAC - 34.45%MAC = 3.05% AFT of the NACA tested CoG location. Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
bongodriver Posted October 27, 2015 Posted October 27, 2015 My math had nothing to do with that footnote and does not solve for EWCG. You are turning in circles chasing your tail. I am not chasing my own tail, I am successfully putting counter evidence to every single claim you make, it's easy really, I just don't cherry pick.
bongodriver Posted October 27, 2015 Posted October 27, 2015 Is not the Aft CG limit for the Mk IX. It is just telling you where it will be with the rear fuselage tanks empty of fuel. (-7.4-21.89)/85 = 34.45% MAC 31.4%MAC - 34.45%MAC = 3.05% AFT of the NACA tested CoG location. No, it's the aft CG when all rear fuel is burned but still has a pilot, ammo and full forward tanks, which is well inside the CG range. I already said your maths is irrelevant here, we already have all the data we need.
ED Team NineLine Posted October 27, 2015 ED Team Posted October 27, 2015 You guys almost done? Dunno about the Spitfire, but this thread is getting more and more unstable... Forum Rules • My YouTube • My Discord - NineLine#0440• **How to Report a Bug**
Crumpp Posted October 27, 2015 Author Posted October 27, 2015 No, it's the aft CG when all rear fuel is burned but still has a pilot, ammo and full forward tanks, which is well inside the CG range. I already said your maths is irrelevant here, we already have all the data we need. Yes it is well within the CG range. But it is NOT the wartime AFT CG limit is it? The wartime AFT CG limit for a NORMAL Spitfire Mk IX without tanks is 9in aft of datum!! But as you nicely point out proving my point, we can see why most modern Spitfire Mk IX aft CG limit is even more restricted can't we? Bongodriver says: this ties in very nicely with the modern day MkIX's having the aft limit set to around 7.2" You so nicely proved to yourself exactly what I was trying to show you pages back when I posted so many Spitfire Mk IX Type Certificates! If you had just taken the few minutes to read the details like I asked we could have ended this then. :thumbup: Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
JtD Posted October 27, 2015 Posted October 27, 2015 Here:Thanks a lot. So, with a fuel tank in the rear that's empty you'll have a CoG of about 6.8" (31.2% MAC) back and without the empty fuel tank it's somewhere around 6" (30.2% MAC) . That makes sense, given that the a near identical VIII is at 5.8". NACA btw. still tested at ~7"(31.4% MAC).
bongodriver Posted October 27, 2015 Posted October 27, 2015 (edited) Yes it is well within the CG range. But it is NOT the wartime AFT CG limit is it? The wartime AFT CG limit for a NORMAL Spitfire Mk IX without tanks is 9in aft of datum!! But as you nicely point out proving my point, we can see why most modern Spitfire Mk IX aft CG limit is even more restricted can't we? You so nicely proved to yourself exactly what I was trying to show you pages back when I posted so many Spitfire Mk IX Type Certificates! If you had just taken the few minutes to read the details like I asked we could have ended this then. :thumbup: A CG limit that a MkIX with full war load (no rear tanks) and including tail ballast would not even reach....yeah they really limited the hell out of that. Funny how modern MkIX's with rear tanks have higher aft limits just like the wartime ones and shown in the many type certificates I didn't cherry pick. Edited October 27, 2015 by bongodriver
Crumpp Posted October 27, 2015 Author Posted October 27, 2015 (edited) Thanks a lot. So, with a fuel tank in the rear that's empty you'll have a CoG of about 6.8" (31.2% MAC) back With an empty rear tank you will have a rear CG of ~7.4in just like the RAE says. You can run the math on the weight and balance sheet I posted to confirm it. Do you know how to do it? Your figures above are wrong so I am thinking you might be doing something wrong. Once I determined the LEMAC the NACA was using, I was able to crosscheck that LEMAC with the RAE MAC computations to confirm the accuracy. NACA btw. still tested at ~7"(31.4% MAC). Yes, there is less than an inch difference between the NACA datum and RAE. The NACA tested the Spitfire at a normal CG location. It was not some wildly aft location, just what you could see flying it. Edited October 27, 2015 by Crumpp Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
Crumpp Posted October 27, 2015 Author Posted October 27, 2015 A CG limit that a MkIX with full war load (no rear tanks) would not even reach....yeah they really limited the hell out of that. Umm, the NACA actually tested at a normal CG location. It is not very far back and certainly is a location that a operational Spitfire would use.... Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
bongodriver Posted October 27, 2015 Posted October 27, 2015 Umm, the NACA actually tested at a normal CG location. It is not very far back and certainly is a location that a operational Spitfire would use.... NACA did not test a MkIX in your report and 7" is nearly as far back as you can load a MkIX without rear tanks, how did they get a MkV to 7"? without loading it tail heavy?
Crumpp Posted October 27, 2015 Author Posted October 27, 2015 It was not at 7"...it was at 31.4%MAC. That is about ~5.5 inches aft of datum on the RAE scale. I did not convert the NACA location to RAE datum arm... I converted the RAE MAC to RAE datum arm once I calculated the NACA LEMAC and confirmed that LEMAC agreed with the RAE CG calculations. 31.4% RAE MAC = ~4.8 inches aft of their datum point. Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
bongodriver Posted October 27, 2015 Posted October 27, 2015 here's another video that sort of demonstrates stability, let's see how long it takes for the penny to drop.
JtD Posted October 27, 2015 Posted October 27, 2015 With an empty rear tank you will have a rear CG of ~7.4in just like the RAE says.Actually they say 7 for that particular plane, and their fuel isn't even at 6lb/gallon.
Crumpp Posted October 27, 2015 Author Posted October 27, 2015 It was not at 7"...it was at 31.4%MAC. That is about ~5 inches aft of datum on the RAE scale. I did not convert the NACA location to RAE datum arm... I converted the RAE MAC to RAE datum arm once I calculated the NACA LEMAC and confirmed that LEMAC agreed with the RAE CG calculations. 31.4% RAE MAC = ~4.8 inches aft of their datum point. Corrected. There is about a 3% error in the conversion. Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
Crumpp Posted October 27, 2015 Author Posted October 27, 2015 Actually they say 7 for that particular plane, and their fuel isn't even at 6lb/gallon. 7.2lbs per gallon by the weight and balance sheet. That is probably your error. Your fuel is too light. Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
bongodriver Posted October 27, 2015 Posted October 27, 2015 7.2lbs per gallon by the weight and balance sheet. That is probably your error. Your fuel is too light. He has mixed up between US and imperial gallons, it is 7.2lbs for imperial and 6lbs per US gallon.
Crumpp Posted October 27, 2015 Author Posted October 27, 2015 Yep Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
Friedrich-4B Posted October 28, 2015 Posted October 28, 2015 (edited) NACA did not test a MkIX in your report and 7" is nearly as far back as you can load a MkIX without rear tanks, how did they get a MkV to 7"? without loading it tail heavy? Actuallly, NACA calculated the MAC at 85"; see sentence stating MAC may be in error: while the A&AEE drawing shows the MAC was 84" This is the drawing referred to by Crumpp as "RAE (sic! should be A&AEE) aerodynamic data"; it has been adapted for a flight sim (among other things, the data is for the Mk. VB Trop while the title says Spitfire Ia & Ib); nor does it show a MAC of 85". Edited October 28, 2015 by Friedrich-4/B [sIGPIC][/sIGPIC]************************************* Fortunately, Mk IX is slightly stable, anyway, the required stick travel is not high... but nothing extraordinary. Very pleasant to fly, very controllable, predictable and steady. We never refuse to correct something that was found outside ED if it is really proven...But we never will follow some "experts" who think that only they are the greatest aerodynamic guru with a secret knowledge. :smartass: WWII AIRCRAFT PERFORMANCE
Crumpp Posted October 28, 2015 Author Posted October 28, 2015 Actuallly, NACA calculated the MAC at 85"; note note stating MAC may be in error: No, the RAE set their MAC at 84" based the RAE LEMAC. I did not solve for the RAE LEMAC...I solved for the NACA LEMAC. You could do the RAE one with that data easily. It won't change anything. The NACA LEMAC works with the NACA MAC and converts well...just don't use the NACA LEMAC with the RAE MAC. It is accounted for.... Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
Friedrich-4B Posted October 28, 2015 Posted October 28, 2015 (edited) No, the RAE set their MAC at 84" based the RAE LEMAC. I did not solve for the RAE LEMAC...I solved for the NACA LEMAC. You could do the RAE one with that data easily. It won't change anything. The NACA LEMAC works with the NACA MAC and converts well...just don't use the NACA LEMAC with the RAE MAC. It is accounted for.... Not quite; Crumpp's calculation doesn't show that the A&AEE's (NOT the RAE as stated by Crumpp) MAC was 84"... RAE aerodynamic data on the Spitfire says the aft CG limit is 2.638 feet from the LE of the wing root. 2.638ft *12in = 31.656in - 9in = 22.656 difference in the Leading edge distance to Aft limit in the NACA and RAE 22.65in - 21.89in = .766in -.766 = 8.2 (-8.2-21.89)/85 = .354 x 100 = 35.4% MAC is the rearward limit of the Spitfire at 9 inches aft of the datum. Let's check it against the RAE MAC... -9.9-.766 = 9.1 (-9.1-21.89)/85 = .364 * 100 = 36.4% Hopefully this will reduce the questions as to where the .766in correction comes from... That is what is needed to align the RAE moment/arm datum point with the NACA LEMAC. (-8.2-21.89)/84 = .3582 * 100 = 35.82% rounded down = 35.8% MAC @ 9" aft of datum (-9.1-21.89)/84 = .3689 * 100 = 36.89% rounded up = 36.9% Edited October 28, 2015 by Friedrich-4/B add revised data for 84" MAC [sIGPIC][/sIGPIC]************************************* Fortunately, Mk IX is slightly stable, anyway, the required stick travel is not high... but nothing extraordinary. Very pleasant to fly, very controllable, predictable and steady. We never refuse to correct something that was found outside ED if it is really proven...But we never will follow some "experts" who think that only they are the greatest aerodynamic guru with a secret knowledge. :smartass: WWII AIRCRAFT PERFORMANCE
Crumpp Posted October 28, 2015 Author Posted October 28, 2015 (edited) Actuallly, NACA calculated the MAC at 85"; note note stating MAC may be in error: while Supermarine's own CoG drawing shows the MAC was 84" This is the drawing referred to by Crumpp as "RAE aerodynamic data" - actually adapted for a flight sim (among other things, the Spitfire VB didn't use 87 octane fuel at 7.2 lbs/imp gal); nor does it show a MAC of 85" No issues... The NACA MAC is not in error, they just did not have the RAE numbers. They did it the conventional way by jacking the tail up and taking out a tape measure. First let's prove the LEMAC on the document you posted. It is listed at 19.5in. .317 * 84 = 26.6in 26.6in-19.5in = 7.128in That is a 1% error. We can say the RAE LEMAC Gear Down is 19.5in. 31.4% MAC = 6.87in aft of datum. A normal CG for the Spitfire series undercarriage DOWN. But, that is not the case for Spitfire Mk IX data, it is found undercarriage up just as the NACA MAC is located. But let's look if we use RAE Gear Down LEMAC for our 9.5: [(9.5+19.5)/84] * 100 =34.5% MAC .012/.357 = 3.4% error That does not give very good agreement with the RAE Spitfire Mk IX MAC of 35.7%. Why? Length was added to the engine compartment changing our LEMAC. Simply solving for the NACA MAC gives good agreement with the Spitfire Mk IX data. Using the RAE 84”MAC; the LEMAC is 20.7in vs 21.8in for the NACA LEMAC at 85%. It just does not matter that much and does not change the stability picture of the design at normal to aft CG. 20.7/84 = .257*100 = 25.7% 21.8/85 = .256*100 = 25.6% So no conspiracy theory required. Edited October 28, 2015 by Crumpp did the math for the LEMAC percentage between RAE and NACA Answers to most important questions ATC can ask that every pilot should memorize: 1. No, I do not have a pen. 2. Indicating 250
JtD Posted October 28, 2015 Posted October 28, 2015 (edited) He has mixed up between US and imperial gallons, it is 7.2lbs for imperial and 6lbs per US gallon.No, the weight and balance table gives 74 gallons rear tank capacity with 7.2lb/gallon and corresponding CoG movement of 5.5". The snippet from the test report has 74 gallons rear tank capacity with 6.8lb/gal and corresponding CoG movement of 5.2". No mix up, just reading. Edited October 28, 2015 by JtD
JtD Posted October 28, 2015 Posted October 28, 2015 Also to do a proper short conversation between the rather insignificant differences between 85" and 84" MAC: The 85" MAC is naturally situated a little bit more inward, and if you look at the Spitfire wing, you'll see that the wing edges in that area are swept at a ratio of about 1:2 (conservatively), so that the 84" chords starts about 0.3" behind the 85" chord and ends 0.7" before it does. So NACAMAC%*85 - 0.3 = RAFMAC% * 84 So where the Spitfire V was tested at NACA at 31.4% MAC, this translates to 26.7" behind the trailing edge at 85" which is 26.4" behind the trailing edge of the 84" RAF MAC and corresponds to 31.4% RAF MAC. With datum point 19.5" behind the LE of the 84" chord, we're at a CoG of 6.9" aft the datum. Pretty much the same as we have for a fully loaded IX with an empty rear tank and about 1" behind a fully loaded VIII or IX without a rear tank.
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