Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: bustr on April 18, 2012, 11:51:59 PM
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Recently I read a conversation on a warbirds forum where it was pointed out the owner of a P51 wanted to remove the guns. So he had a mechanic take them out and he went up for a ride. Seems the mechanic did not add weight to the tail and the owner of the P51 had a very scary ride and landing along with a visit from the local FAA rep.
Is this real in terms of P51's and removing the guns in the first place? Secondly, how was this handled with all the external ordinance many aircraft carried for specific roles? 109's and their gondola. 47's/51's and drop tanks, bombs, rockets. 190's and removing the outboard cannon. Tiffy firing rockets and so on.
What happened to the CG balance when the weight of ordinance suddely was gone and the pilot had to dogfight?
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Recently I read a conversation on a warbirds forum where it was pointed out the owner of a P51 wanted to remove the guns. So he had a mechanic take them out and he went up for a ride. Seems the mechanic did not add weight to the tail and the owner of the P51 had a very scary ride and landing along with a visit from the local FAA rep.
Is this real in terms of P51's and removing the guns in the first place? Secondly, how was this handled with all the external ordinance many aircraft carried for specific roles? 109's and their gondola. 47's/51's and drop tanks, bombs, rockets. 190's and removing the outboard cannon. Tiffy firing rockets and so on.
What happened to the CG balance when the weight of ordinance suddely was gone and the pilot had to dogfight?
Why would adding weight to the tail help; after you have already removed weight from the front/center of the aircraft?
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Seems like you would just want to add some weights in the gun bays - dont see why you would add it in the tail.
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They added ballast to the tail if the nose was too heavy. If the tail was too heavy, well I don't know.... Maybe all planes had a ballasted tail were it could be easily reduced if needed?
Ballast weights were used at least in 109s and Spits.
http://www.spitfireperformance.com/ab197.html
Considering ordnance the placement of ordnance should have been near CoL or forward of CoL if possible (eg. ME410 bomb bay). Having tail weight was considered very dangerous and more so in aircraft which already had a tendency to be tail heavy. E.g Yak was known to be a tail heavy aircraft making it somewhat unbalanced in maneuvers as it tended to tighten the turn by itself and had to be "pushed out" of turn. Having a heavy nosed a/c would make it sluggish in maneuvers but sometimes when loaded with ordnance that would also be desirable. Weight distribution was one of the defining qualities of a good combat aircraft and also one of the limitations where the ordnance could be carried and also in which order it had to be dropped if the weight was distributed length wise, which it usually wasn't but all stacked near CoL.
In some aircraft all the new additions posed new problems, as in P-51 when additional internal fuel was required the tank was added behind the pilot and it moved CoG aft and the aircraft would become dangerous in maneuvers when the tank was full. Same with FW190 with additional fuel tank.
Maybe they should have removed ballast from tail in P-51 gun case?
-C+
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http://www.engbrasil.eng.br/index_arquivos/rs/rs4.pdf
Great link to remind me of why ditching math class was a bad idea.....
Anyway, what was the MAC of the 51D? How much weight did the removal of the guns contribute to one side or the other of the CG range? I did about 5 minutes on line and did not find anything free or unsubscribed that may have talked CG range on a real mustang.
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There was probably more going on than just the weight.
Did they do more than just remove the guns? ......or did they just take them out.
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I always wondered how a liquid moving around (fuel) affected the COG or stability in an aircraft, especially the camel in WW1 at slow speeds and in stalls.
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The short answer is that every aircraft has a Weight & Balance chart, and so long as things are loaded properly (and not overloaded), the aircraft will be within CG design limits. There will of course be performance differences for a heavier aircraft than a lighter one, but presumably WWII pilots (like modern day pilots) were trained on both "clean" and "heavy" aircraft.
As to fuel, I've never felt or perceived any effects on stability from it moving around in the wing tanks of a Cessna, whether fast, slow, stalls, spins, etc. So long as it stays within the CG limits (which it will, regardless of how much sloshing is going on, because it's confined to the fuel tanks), I don't see how it would make much difference.
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The short answer is that every aircraft has a Weight & Balance chart, and so long as things are loaded properly (and not overloaded), the aircraft will be within CG design limits. There will of course be performance differences for a heavier aircraft than a lighter one, but presumably WWII pilots (like modern day pilots) were trained on both "clean" and "heavy" aircraft.
As to fuel, I've never felt or perceived any effects on stability from it moving around in the wing tanks of a Cessna, whether fast, slow, stalls, spins, etc. So long as it stays within the CG limits (which it will, regardless of how much sloshing is going on, because it's confined to the fuel tanks), I don't see how it would make much difference.
The difference is I have read modern aircraft have baffles in the tanks to restrict fuel moving around as one mass, in a WW1 fighter as far as I know it literally was just a steel box. This a model but show were the 2 tanks are positioned.
(http://www.ipmsgreatplains.org/Camelimages/IMG_0528.JPG)
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The difference is I have read modern aircraft have baffles in the tanks to restrict fuel moving around as one mass, in a WW1 fighter as far as I know it literally was just a steel box.
True, but the tanks in modern aircraft are a lot larger than a WW1 era aircraft, both in terms of size and capacity. And if baffles are part of the design to meet acceptable CG parameters, then it is what it is, and that was a design choice/compromise made by the designer.
Still, any aircraft design will take into account changes in CG throughout flight and what the limitations are before flight becomes unstable. I fly Cessnas (and not Camels or P51s or F15s) so I certainly can't speak about all aircraft, but I do know that I do one Weight & Balance check as part of a pre-flight, and then don't worry about CG since any changes within flight are necessarily within the flight envelope.
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I'll need to look it up, but if I am recalling correctly they had to put an additional heavy counterweight in the tail of some P-51s to offset very heavy ordnance options (150gal DTs, 1000lb bombs, rockets + 500/250lb bomb combos, etc.). Mostly to prevent ground looping/nose planting I think.
As it sounds like this particular mustang was purchased from the military by the owner with the guns, it's more likely it saw actualy use by the military, and more likely it had this modification already made and possibley even the mechanic had no knowledge of it's existence or installation on the aircraft.
But even then, so much more doesn't make sence about this and more information is truely needed if we're to understand and make some of it... If it had the 50-cals, it probabley also had the auxiliary fuel tank in the aft fuselage as was GI.... a relatively small tank, but it amongst many other things that were removed by private aviators do add up... it's anyone's guess if the heavy/clunky original GI radio set was or wasn't still crammed behind the pilot/cockpit or if it had been converted to a spare seat and he had a passenger, etc., etc., etc..
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How was CG balancing handled in WW2 aircraft?
Trim :aok
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I did about 5 minutes on line and did not find anything free or unsubscribed that may have talked CG range on a real mustang.
try http://www.wwiiaircraftperformance.org/ (http://www.wwiiaircraftperformance.org/). if the document exists, its probably on there somewhere :aok
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Trim :aok
Trim is to make the control forces manageable. Aircraft design and load management keeps the CoG in check.
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Trim :aok
The only thing trim does it takes the extra force off the controls, it has nothing to do with CG. If your aircraft is unable due to CG the only thing you can do the help it is remove/add some weight or move some of the weight to a different part of the aircraft.
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Recently I read a conversation on a warbirds forum where it was pointed out the owner of a P51 wanted to remove the guns. So he had a mechanic take them out and he went up for a ride. Seems the mechanic did not add weight to the tail and the owner of the P51 had a very scary ride and landing along with a visit from the local FAA rep.
Is this real in terms of P51's and removing the guns in the first place? Secondly, how was this handled with all the external ordinance many aircraft carried for specific roles? 109's and their gondola. 47's/51's and drop tanks, bombs, rockets. 190's and removing the outboard cannon. Tiffy firing rockets and so on.
What happened to the CG balance when the weight of ordinance suddely was gone and the pilot had to dogfight?
When you drop bombs (or make any change to the weight of the aircraft) your CG changes. Normally aircraft are designed to with a large envelope so when you drop a bomb the aircraft will continue being flyable. Looks like this P-51 (or all) was not designed to be flown without guns so it's CG was in the tail which made it less stable.
Here is the difference in forward and aft CG:
Forward:
Longer T/O roll
Longer Landing distance
Harder to rotate
Slower cruise TAS
Higher fuel burn rate
More stable
Less maneuverable
Easier to stall
Easier to recover (from a stall)
Aft:
Shorter T/O roll
Shorter Landing distance
Easier to rotate & flare
Higher cruise TAS
Lower fuel burn rate
Less stable
More maneuverable
Harder to stall
Harder to recover (from a stall)
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What is the source of this information please?
Perv is that your model Sopworth?
Concorde could pump its fuel fore and aft to maintain CofG, I think you can do the same with your Camel and your enamel tea mug :banana:
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What is the source of this information please?
Are you referring to my post?
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Were the guns de-milled? Did the P-51 owner have a class 3 license and a half dozen M2 machine guns? I'm confused.
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Are you referring to my post?
Yes.
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Yes.
Oh that's just something I wrote out based on physics and aerodynamics. If you have any questions I'll be glad to explain it.
If your really interested in it here is an FAA book that describes effects of CG: http://www.faa.gov/library/manuals/aircraft/media/FAA-H-8083-1A.pdf (http://www.faa.gov/library/manuals/aircraft/media/FAA-H-8083-1A.pdf)
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Thanks, I'll read that.
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unless anyone can show that WWII fighters were ballasted for different loadouts I'll stick with my answer. elevator trim was used to compensate for changes in CG, because they were designed to operate within a range of CG and normal loadouts would keep the aircraft within this range. bombers and transports, another matter.
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unless anyone can show that WWII fighters were ballasted for different loadouts I'll stick with my answer. elevator trim was used to compensate for changes in CG, because they were designed to operate within a range of CG and normal loadouts would keep the aircraft within this range. bombers and transports, another matter.
But the question was "how was CG balancing handled," which (to me at least) means "how do you keep the plane's center of gravity within its limits, given different loads?" That requires the crew to figure out where on the plane to put different weights - if you can put them on/in the plane at all. This is important for any flight in a plane loaded to or near its max weight (and sometimes even if you're not near the max). Otherwise you'll be out of your CG limits and no amount of trim will save you.
- oldman
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unless anyone can show that WWII fighters were ballasted for different loadouts I'll stick with my answer. elevator trim was used to compensate for changes in CG, because they were designed to operate within a range of CG and normal loadouts would keep the aircraft within this range. bombers and transports, another matter.
Trim only effects control forces felt by the pilot. It only compensates for changes in CG in the sense that a pilot can use trim to make his life easier.
In other words, any aircraft can fly within its CG limits regardless of whether it has elevator trim.
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Thanks, I'll read that.
You'll probably find it somewhere in that link, but the way to think of "why" is to think of the tailplane as an upside down wing, meaning that the lift vector generated by the tailplane is down. So if an aircraft is tail heavy, the tailplane is generating less "down lift" , so performance characteristics which benefit from increased "up" lift will improve.
That said, never, ever, ever exceed the aft CG limit (or the fore one, for that matter) in a real world aircraft. Never.
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But the question was "how was CG balancing handled," which (to me at least) means "how do you keep the plane's center of gravity within its limits, given different loads?" That requires the crew to figure out where on the plane to put different weights - if you can put them on/in the plane at all. This is important for any flight in a plane loaded to or near its max weight (and sometimes even if you're not near the max). Otherwise you'll be out of your CG limits and no amount of trim will save you.
- oldman
Again, the flight manuals for all aircraft have Weight & Balance charts. They tell you exactly how much weight you can put where. So balancing is handled by knowing the weight of various things, and then knowing where you are going to put them, and then looking to the charts to see if you're still within the permitted CG envelope.
And, again, trim has nothing to do with balancing CG or staying within CG limits.
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ok so thats Wmaker, MachFly and BravoT who think that WWII fighter pilots DIDNT use the elevator trim to trim the aircraft for level flight to compensate for changes in CG due to fuel use and ords release. anyone else?
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ok so thats Wmaker, MachFly and BravoT who think that WWII fighter pilots DIDNT use the elevator trim to trim the aircraft for level flight to compensate for changes in CG due to fuel use and ords release. anyone else?
Pilots use trim so that their arms don't get tired. The same way they use trim when dropping flaps on final approach. The same way they use trim if they make a change in power. Pilots also use trim in all phases of flight, and not just level flight. That's why every real world pilot knows what PAT (or APT) means.
I didn't say that they didn't use trim to compensate for a change in CG. I said that pilots use trim to compensate for forces on the controls, and that elevator trim isn't used to "manage" CG.
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because they were designed to operate within a range of CG and normal loadouts would keep the aircraft within this range.
Heh. I think this is the statement we have problems with. It may be possible that you can hang 2x500 pound bombs and full MG ammo on a P-51 with only 50 gallons fuel in the main tanks and still be within CG limits, but I'd want to work through those calculations before I believed it.
- oldman
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... elevator trim isn't used to "manage" CG.
indeed, its used to "manage" the effects of changes to CG, as I said.
a subtle distinction, but enough to argue over apparently.
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Now when a pilot does weight and balance calculations, we use arms and weights to determine the moment, (Weight x Arm = Moment) which we then verify is (the moment) within CG limits. I have always been curious if arms, and the whole idea of the moment of the aircraft was used in WWII times.
Does anyone know?
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ok so thats Wmaker, MachFly and BravoT who think that WWII fighter pilots DIDNT use the elevator trim to trim the aircraft for level flight to compensate for changes in CG due to fuel use and ords release. anyone else?
I don't think you disagree, you're just talking about 2 different things.
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certainly RAF aircraft had tables with all the weights and moments for removable loads:
http://www.spitfireperformance.com/rb141weights.html (http://www.spitfireperformance.com/rb141weights.html) has a transcript of the XIV's weight/moment chart.
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certainly RAF aircraft had tables with all the weights and moments for removable loads:
http://www.spitfireperformance.com/rb141weights.html (http://www.spitfireperformance.com/rb141weights.html) has a transcript of the XIV's weight/moment chart.
Awesome! Thanks for that. I figured that it was used then, but never bothered to research.
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Did anyone notice this from the weights paper for the XIV?
2.2. In addition to the above load the following alternative items may be carried:-
...........(a) 30 gallon tinned steel drop tank.
...........(b) 30 gallon vulcanized fibre drop tank.
...........(c) 30 gallon wood drop tank.
...........(d) 90 gallon tinned steel drop tank.
...........(e) 250 lb. G.P. or S.A.P. bomb.
...........(f) 500 lb. G.P., M.C. or S.A.P. bomb.
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That's why every real world pilot knows what PAT (or APT) means.
This one doesn't know. So what does it stand for?
Btw does anyone else use CIGAR and FTP?
HiTech
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Gurgelsnort!!!!!!!!......... :huh :headscratch: :bhead :bolt:
You saying your comic book airplanes are grown in a test tube? Who are the gene donors?..... :)
"Cigar" (Compact Idiosyncratic Gapped Alignment Report) format is a compressed (run-length encoded) pairwise alignment format. It is useful for representing long (e.g. genomic) pairwise alignments. It is used in SAM format to represent alignments of reads to a reference genome sequence.
An 'extended' CIGAR string must be following motif: ([0-9]+[MIDNSHP])+|\*. Each character is preceded by a number, giving the base counts of the event, MIDNSH or P.
standard cigar:
M match
I insertion
D deletion
extended cigar
N gap
S substitution
H hard clipping
P padding
= sequence match
X sequence mismatch
Complete genomics data specific
B= move back (1 complete genomics read consist of several contiguous stretches, separated by gaps, in which first two stretches may overlap)
REF: AGCTAGCATCGTGTCGCCCGTCTAGCATA CGCATGATCGACTGTCAGCTAGTCAGACT AGTCGATCGATGTG
READ: gggGTGTAACC-GACTAGgggg
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ok so thats Wmaker, MachFly and BravoT who think that WWII fighter pilots DIDNT use the elevator trim to trim the aircraft for level flight to compensate for changes in CG due to fuel use and ords release. anyone else?
Trim has nothing to do CG. As some people explained trim is just to relive pressure from the stick, CG changes the performance of the aircraft.
For example as you accelerate you start producing more lift and the aircraft wants to pitch up, so instead of keeping constant pressure on the stick you trim the nose down. When your cruising (even without autopilot) you want to trim the airplane for straight and level flight at that airspeed so you can let go of the stick and relax, the plane will fly on it's own.
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That's why every real world pilot knows what PAT (or APT) means.
This one doesn't know. So what does it stand for?
I think it stands for Power Attitude Trim and the other one is Attitude Power Trim. But I had to google for it and had no idea what it meant before, and I'm still not sure what your supposed to do with that acronym. Also the only place where I could find the definition was a forum of some other flying game...
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Now when a pilot does weight and balance calculations, we use arms and weights to determine the moment, (Weight x Arm = Moment) which we then verify is (the moment) within CG limits. I have always been curious if arms, and the whole idea of the moment of the aircraft was used in WWII times.
Does anyone know?
Most modern aircraft have that so you could simply calculate it. But on the Decathlon that I fly (70s design) the POH gives you a chart with Weight on the Y axis and Moment on the X axis so you can do the whole W&B without worrying about the arm. However I think this more depends on the manufacturer than the time when the aircraft was designed.
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This one doesn't know. So what does it stand for?
Btw does anyone else use CIGAR and FTP?
HiTech
Power Attitude Trim and Attitude Power Trim
Really? I thought it was one of the basics taught to all pilots. Then again, I'm a Canadian so maybe we do things differently, eh? :)
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Obviously, WW hasn't seen this yet...THEN, we will know!
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ok so thats Wmaker, MachFly and BravoT who think that WWII fighter pilots DIDNT use the elevator trim to trim the aircraft for level flight to compensate for changes in CG due to fuel use and ords release. anyone else?
Of course trim can be used in these kind of situations. I've read that a single adult person moving through the passenger compartment of DC-3 can be felt in the controls.
indeed, its used to "manage" the effects of changes to CG, as I said.
a subtle distinction, but enough to argue over apparently.
*shrug*
I think it is a pretty clear distinction. When the only word to a question how aircraft CoG is managed is "Trim". Aircraft are designed so that consumables are usually located near the CoG or consumed in an order which keeps the CoG in check even though a fuel tank for example has a long moment arm.
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Trim has nothing to do CG.
Incorrect. If there is a change in the C of G there will be need for a trim change.
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Now when a pilot does weight and balance calculations, we use arms and weights to determine the moment, (Weight x Arm = Moment) which we then verify is (the moment) within CG limits. I have always been curious if arms, and the whole idea of the moment of the aircraft was used in WWII times.
Does anyone know?
Of course it was, how else would you figure W&B?
For the B-24, and probably many other aircraft of that era, they used a slide rule to do the W&B calculations.
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Of course trim can be used in these kind of situations. I've read that a single adult person moving through the passenger compartment of DC-3 can be felt in the controls.
On my 182 I could trim for level flight and simply leaning forward in the seat would start the nose down. Old skydiver trick is to let the pilot get trimmed in the climb then gently move slightly forward or aft requiring him to retrim. Once the pilot has retrimmed trimmed you move opposite the first move, repeat until he yells at you to hold the frack still.
[/quote]
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Incorrect. If there is a change in the C of G there will be need for a trim change.
Yes in order to relive stick pressure, the way the aircraft performs however will not change. For example if the airplane is unstable due to CG trim will not help.
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CIGAR and FTP are 2 mnemonics I was taught for pre takeoff check list on small aircraft that you have flow a lot.
CIGAR is before taking runway.
Controls
Instruments
Gas
Avionics
Runnup.
FTP After or During taking runway.
Flaps
Transponder
Pump
HiTech
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CIGAR and FTP are 2 mnemonics I was taught for pre takeoff check list on small aircraft that you have flow a lot.
CIGAR is before taking runway.
Controls
Instruments
Gas
Avionics
Runnup.
FTP After or During taking runway.
Flaps
Transponder
Pump
HiTech
I'm jealous, my emergency checklist alone is 38 pages long, and that's for a GA aircraft!
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Of course trim can be used in these kind of situations. I've read that a single adult person moving through the passenger compartment of DC-3 can be felt in the controls.
In 1948 my father had just graduated from Lackland AFB, San Antoino TX as an Airman basic. He was the single passenger on an empty C47 that happened to be going to his first duty station. Having spent all of his 16 years of life on a farm in the backwoods of Alabama before signing up at 17, he was extatic about being in an airplane. So much so he went rushing up and down the isle in the aft area to look out all of the windows. The co-pilot had to come back and make him strap in one place because he was causing the C47 to go through a minor roller coaster ride. Back then it was a common occurence for C47 pilots leaving Lackland.
Even though he was not an Airforce pilot. In 1965 when he was stationed at Kelly AFB in San Antoinio as a Tech Sargent with the USAFSS, my father earned his civilian ticket at the Kelly AFB flying club. Subsiquently he flew with the Texas Civil Air Patrol before moving to his next duty station. In 1969 when he retired as a Master Sargent with a multi engine civilian ticket, the Army tried to commission him as a Captain to continue flying for them in South East Asia.