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bobbysocks
Chief Master Sergeant
i saw a formula for calculating the surface area of each on a homebuilt aircraft forum once...not sure how close that related to these ac but it had to be factored in somehow. i am sure drgondog could shed a lot of light regarding this...
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I think a look at some kit models is enough.
GregP
Major
I've seen some analyses of US types that included the wing area, flap area, aileron area, vertical tail area, rudder area, horizontal tail area, and elevator area, but have not seen a specific analysis of the Bf 109, not have I looked for one.
Usually there are some rather standard aerodynamic formulas for calculating the tail area required and the area of the surfaces and I never really analyzed the Bf 109 because, although I used to think the tail areas might be small, I also never heard any pilot complaints about controlability except for lack of trim tabs on rudder and aileron and the stiffening up of the control surfaces at speed. I never saw anything in a combat or flight report that made me think it might be anywhere close to the edge of what might be required.
In fact, if the flight reports are to be believed, the Bf 109 has probably the most benign stall characteristics of all the WWII fighters, making me feel that an analysis of this would be a waste of my time ... the areas are sufficient or there would be complaints about the stability or controlability. Since there are none to speak of, I never thought about it.
The first requirement would be to dig up specification that show the areas of the flying surfaces and control surfaces. We already know the power installed but, again, I've never seen the areas broken out before for the Bf 109... though since I wasn't looking for it, I may have come across it and just never considered it as something to save.
If I were a betting guy, I'd bet Bill has these areas. I also bet he won't find the Bf 109 areas too small relative to standard area percentages for a WWII fighter since the Bf 109 was an EXCELLENT fighter design and probably ranks at the top all-time for effectiveness. The Bf 109 was used to shoot down a LOT of enemy airplanes, so it isn't exactly a flying mistake.
In the design of RC models, it is pretty standard to have the area of the horizontal surface come out to 0.7 ~1 = (Sw/St)* (L/MAC) where Sw is wing area, St is tail area, L is the distance between the center of pressure of the wing and tail, and MAC is mean aerodynamic chord. You choose about 0.7 for more maneuverability and about 1 for more stability.
For the vertical stab area, you choose in the neighborhood of .05 = (Sw/St) * (L/b) where b is span.
The function of the aircraft must be taken into account. A fighter is NOT an aerobatic plane nor is it an airliner, so the designer starts with some designs and refines his numbers as he goes on ... depending on how the real aircraft designs fly with regard to intended purpose. If he designs a fighter that flies more like an airline, then he'll change the size of the surfaces to compensate.
It's a bit more involved with full scale aircraft but, with RC's ... the numbers fall into a small group depending on the desired function of the plane.
I have Hoerner's lift book in pdf format, but it's 65Mb in size and not practical to reproduce in here. I also haven't read it much for a couple of decades or longer. If I were to go back into aerodynamics again, it would be for a good reason ... that is, a project.
Usually there are some rather standard aerodynamic formulas for calculating the tail area required and the area of the surfaces and I never really analyzed the Bf 109 because, although I used to think the tail areas might be small, I also never heard any pilot complaints about controlability except for lack of trim tabs on rudder and aileron and the stiffening up of the control surfaces at speed. I never saw anything in a combat or flight report that made me think it might be anywhere close to the edge of what might be required.
In fact, if the flight reports are to be believed, the Bf 109 has probably the most benign stall characteristics of all the WWII fighters, making me feel that an analysis of this would be a waste of my time ... the areas are sufficient or there would be complaints about the stability or controlability. Since there are none to speak of, I never thought about it.
The first requirement would be to dig up specification that show the areas of the flying surfaces and control surfaces. We already know the power installed but, again, I've never seen the areas broken out before for the Bf 109... though since I wasn't looking for it, I may have come across it and just never considered it as something to save.
If I were a betting guy, I'd bet Bill has these areas. I also bet he won't find the Bf 109 areas too small relative to standard area percentages for a WWII fighter since the Bf 109 was an EXCELLENT fighter design and probably ranks at the top all-time for effectiveness. The Bf 109 was used to shoot down a LOT of enemy airplanes, so it isn't exactly a flying mistake.
In the design of RC models, it is pretty standard to have the area of the horizontal surface come out to 0.7 ~1 = (Sw/St)* (L/MAC) where Sw is wing area, St is tail area, L is the distance between the center of pressure of the wing and tail, and MAC is mean aerodynamic chord. You choose about 0.7 for more maneuverability and about 1 for more stability.
For the vertical stab area, you choose in the neighborhood of .05 = (Sw/St) * (L/b) where b is span.
The function of the aircraft must be taken into account. A fighter is NOT an aerobatic plane nor is it an airliner, so the designer starts with some designs and refines his numbers as he goes on ... depending on how the real aircraft designs fly with regard to intended purpose. If he designs a fighter that flies more like an airline, then he'll change the size of the surfaces to compensate.
It's a bit more involved with full scale aircraft but, with RC's ... the numbers fall into a small group depending on the desired function of the plane.
I have Hoerner's lift book in pdf format, but it's 65Mb in size and not practical to reproduce in here. I also haven't read it much for a couple of decades or longer. If I were to go back into aerodynamics again, it would be for a good reason ... that is, a project.
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bobbysocks
Chief Master Sergeant
those are probably the same formulas i saw....but since that stuff is all greek to me....and anything i build is going to be in kit form where someone else already has it worked out ( and the plane has a decent flight record to prove the design )...i didnt make a note of them. principals of ac surface area of RC vs ac surface area of real ac "should" be the same...or relative. weight and proposed cruise speed of the ac may also a factor in...idk
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I think with the Bf 109 it comes down to Willi's design ethos. The wing was quite small in area by comparison with similar fighters of the era because he wanted the most powerful engine in the smallest possible airframe. Drag reduction was very important to him. I have to agree with Greg in that the size of the Bf 109's ailerons didn't have much impact on its ability to do its job, as on the Friedrich they were actually reduced in span (as were the slats) over the Emil when the wing was redesigned, despite having a greater overall span, mind you, the Friedrich's wing was more lightly loaded than the Emil's since it had no wing guns. At high speed, the ailerons on all Bf 109s became quite heavy and at speeds between 380 to 400 mph they felt like they had seized.
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The spitfire carried all its armament in the wings, a large weight to "roll". The larger wing is detrimental to roll rate, some models were "clipped winged" to increase roll rate at lower altitudes. I believe the spitfire wing in earlier models was not as rigid as other AC. Those who know about aileron reversal and such things will be able to advise better than I.
The heavy ailerons on the 109 at high speed were probably intended so no pilot would overstress the rear fuselage with hard maneuvers. A modification to the ailerons would probably require strengthening the rear fuselage to counter this.
In general the ailerons sizes/shapes have always to be adapted to the aircraft-specific aerodynamic profile. Weight or engine power increases sometimes require a size incrrease of the ailerons to restore balance/guarantee optimum effect in the desired mission profile.
In general the ailerons sizes/shapes have always to be adapted to the aircraft-specific aerodynamic profile. Weight or engine power increases sometimes require a size incrrease of the ailerons to restore balance/guarantee optimum effect in the desired mission profile.
You'd have to also look at control travel with size. A smaller aileron, for instance could travel further (up to a point) and provide the same force as a larger aileron with less travel. It would also account for why the 109's ailerons were heavier. Has anyone got any info on this?
GregP
Major
Actually I can GET the data becasue we are restoring a Hispano Ha.1112 at this time and HAVE been.
Let me se what I can come up tomorrow.
Let me se what I can come up tomorrow.
drgondog
Major
Short answer - there are sizing equations used in preliminary design, primarily to estimate drag and stability and control relationships. Even today, the actual designs are fine tuned in wind tunnel.
The empennage design will initially focus on the requirements for low speed Vert Stab/rudder authority and yaw moments required for stability and control, while the Horiz stab/elevator sizing include the sizing and moment arm from the center of gravity to compensate for the pitching moments estimated for the wing and wing/flap.
While the first estimate Horizontal (Sht)and Vertical Tail (vt) Volume coefficients (Cht and Cvt) are proportional to their respective horizontal tail (Svt) and vertical tail (Svt) areas.
Additionally the Sht are proportional to the Wing Area and the Mean Aerodynamic Chord of the wing, but inversely proportional to the Distance from the 1/4 M.A.C of the wing to the 1/4 M.A.C. of the horizontal tail.
The Svt are also proportional to the Wing Area, the Wing Span but also inversely proportional to the distance from 1/4 MAC of Wing to 1/4 MAC of vertical tail.
The big recip transports like the Constellation and DC-6 had Cht of 1.115 to .972, and Cvt of .089 and .056 respectively.
The Cht for the F-4E and Mig 21 were .277 and .214, the Cvt were .065 and .08 respectively.
The point is that it would have been luck to get both the sizing of the wing and tail and moment arms right from these calcs - but as designers gained more knowledge over time and more data, there were better refinements of the preliminary tail Coefficients to start the process with.
The aileron design ranges are usually bounded by low speed/high AOA for one envelope and roll rates desired for maneuverability. For the latter, you dive into the structural requirements for the tail to remain a part of the airframe in high G/high Q maneuvers.
One of the iterations for the horizontal tail is to keep the associated trim drag at cruise below 10% of the Total aircraft drag
The empennage design will initially focus on the requirements for low speed Vert Stab/rudder authority and yaw moments required for stability and control, while the Horiz stab/elevator sizing include the sizing and moment arm from the center of gravity to compensate for the pitching moments estimated for the wing and wing/flap.
While the first estimate Horizontal (Sht)and Vertical Tail (vt) Volume coefficients (Cht and Cvt) are proportional to their respective horizontal tail (Svt) and vertical tail (Svt) areas.
Additionally the Sht are proportional to the Wing Area and the Mean Aerodynamic Chord of the wing, but inversely proportional to the Distance from the 1/4 M.A.C of the wing to the 1/4 M.A.C. of the horizontal tail.
The Svt are also proportional to the Wing Area, the Wing Span but also inversely proportional to the distance from 1/4 MAC of Wing to 1/4 MAC of vertical tail.
The big recip transports like the Constellation and DC-6 had Cht of 1.115 to .972, and Cvt of .089 and .056 respectively.
The Cht for the F-4E and Mig 21 were .277 and .214, the Cvt were .065 and .08 respectively.
The point is that it would have been luck to get both the sizing of the wing and tail and moment arms right from these calcs - but as designers gained more knowledge over time and more data, there were better refinements of the preliminary tail Coefficients to start the process with.
The aileron design ranges are usually bounded by low speed/high AOA for one envelope and roll rates desired for maneuverability. For the latter, you dive into the structural requirements for the tail to remain a part of the airframe in high G/high Q maneuvers.
One of the iterations for the horizontal tail is to keep the associated trim drag at cruise below 10% of the Total aircraft drag
Spit aileron reverse speed according to April 1941 test report was 477mph IAS that means 477mph TAS at SL, 555mph at 10000ft TAS and 654mph TAS at 20000ft. That was calculated from test data, earlier based on conventional theory was appr. 550mph IAS
The RAE 1231 (DSIR 23/12865) gives reversal speed 580 mph EAS for the Spitfire V with standard wings and that value is calculated from flight test results.
The RAE 1231 (DSIR 23/12865) gives reversal speed 580 mph EAS for the Spitfire V with standard wings and that value is calculated from flight test results.
GregP
Major
I measured the Hispano Ha.1112 we are restoring. It corresponds to a Bf 109G-2.
Each Elevator: 686 sq in; 4.764 sq ft; 0.443 sq m
Each stabilator: 1028.668 sq in; 7.144 sq ft; 0.664 sq m
Rudder: 887.833 sq in; 6.166 sq ft; 0.573 sq m
Each Aileron: 660 sq in; 4.583 sq ft; 0.426 sq m
I HAVE the flap area but they are not important to combat maneuverability in the Bf 109. The slats cover from the outer edge of the aileron inward for 70.75 inches, putting them slightly longer than the ailerons, as expected. Can post if anyone is interested.
Unfortunately I got interrupted doing this and completely forgot to measure the vertical fin … next time.
These areas are my own estimates based on measurements. They probably aren't exact, but are damned close.
Each Elevator: 686 sq in; 4.764 sq ft; 0.443 sq m
Each stabilator: 1028.668 sq in; 7.144 sq ft; 0.664 sq m
Rudder: 887.833 sq in; 6.166 sq ft; 0.573 sq m
Each Aileron: 660 sq in; 4.583 sq ft; 0.426 sq m
I HAVE the flap area but they are not important to combat maneuverability in the Bf 109. The slats cover from the outer edge of the aileron inward for 70.75 inches, putting them slightly longer than the ailerons, as expected. Can post if anyone is interested.
Unfortunately I got interrupted doing this and completely forgot to measure the vertical fin … next time.
These areas are my own estimates based on measurements. They probably aren't exact, but are damned close.
Hi Greg,
It has been a long time since you posted. Since the Hispano is basically the same thing as the BF109, I've wondered too what the horizontal tail coefficient is.
In order to calculate the horizontal tail volume coefficient, we need the control arm. Can you measure from the CG of the airplane to 1/4 span of the horizontal tail? If you can do that, we can calculate the hor. tail vol. coefficient.
With that information and what you have already supplied, I can tell everyone exactly what it is by punching the numbers in my Preliminary Design Spreadsheet available on my website www.JayMc.com/McAir
As you can see, horizontal tail volume coefficients in most light general aviation aircraft range from .3 to .7. I'm sure the BF109 and the Hispano are at the bottom of that range. A longer moment arm and the speed of the aircraft would probably be why the designers made it that way.
The Commemorative Air Force in Midland, Texas had a BF109 when I was there a few years ago. I could always get hold of them to find out what the moment arm is.
Jay McMullan
Orlando
A comment on maneuverability, there is no advantage on restricting aileron effectiveness at speed. This was a big fault of the "Zero". Rolling as such does not apply much stress on the airframe, it's loading by use of the elevators which will cause this. The F4U was famous for having very effective ailerons and instantaneous maneuverability can be an important asset. Considerable research effort including test flying was expended in getting the servo tabs just right.
Cheers: T
Cheers: T
GregP
Major
Hi Jaymc, I didn't read this one for a long time.
I don't know the CG. The airframe is EXACTLY the same as for a Bf 109 G-2. The only change is from the firewall forward, wing modification for two 20 mm cannons (hole in the spar), outboard wing tanks (we removed them and patched the spar), and gun mounts. Everything else is identical to the Bf 109 G-2. I have a pdf of the German manual for the Bf 1409 G-3, but it is in German.
I don't know the CG. The airframe is EXACTLY the same as for a Bf 109 G-2. The only change is from the firewall forward, wing modification for two 20 mm cannons (hole in the spar), outboard wing tanks (we removed them and patched the spar), and gun mounts. Everything else is identical to the Bf 109 G-2. I have a pdf of the German manual for the Bf 1409 G-3, but it is in German.
