Discussion
Ginetta G15 Girl said:
Nobody has mentioned B/A ratios yet and how they affect a/c handling at high alpha.
You're right. Could have quite an effect on handling.http://www.urbandictionary.com/define.php?term=B%2...
eharding said:
I have spent my fair share of time handling aircraft at high alpha, but I'm yet to see what my Boob-to-Arm ratio has to do with it.
I suspect I'm missing something though....
B/A ratio in a/c is the ratio of inertial moments between the wings and the fuselage - imagine if you will that the a/c is effectively 2 dumbells, one being the wings (A), the other the fuselage (B).I suspect I'm missing something though....
Generally straight winged a/c have a low B/A ratio meaning that the aerodynamic forces outweigh the inertial forces at high alpha. This means that high alpha handling is good (with progressive buffet), the stall is relatively benign and the a/c will exhibit stable (although possibly oscillatory) spin characteristics. A Tucano or Jet Provost would be a good example.
Swept wing FJ a/c generally have higher B/A ratios (especially as the ZFW rises) because they require a small wing (for high speed and low transonic drag/Mach drag) but are required to carry a large amount of mission equipment/weapons, etc. As the B/A ratio increases then the a/c becomes tricky to handle at high alpha because the inertial forces will rapidly overcome the aerodynamic forces with things like Yaw/Roll cross-coupling occurring. In extremis the a/c will 'Depart' extremely violently with a totally unstable spin and/or inertially coupled auto-rotation (dependent upon IAS).
One example would be the F4 Phantom - at high alpha, roll inputs could cause a Departure so rudder had to be used for manoeuvre.
A worse example would be the Jaguar (especially with centre-line stores), overcome the alpha limits and the a/c would go into 'Wing-Rock' (an undemanded roll oscillation), keep pulling (eg mishandle a rolling 'Pull-out' or 'On track attack' manouevre) and the a/c would depart viciously with virtually no hope of recovery. In cases of inertially coupled auto-rotation below 5000ft the advice was to eject. In cases of a spin occurring (IAS below 170kt), upto 15000+ft would be required for recovery. The 2-sticker would not recover.
If you ever get a chance to see the film of the Jaguar spinning trial it's quite sobering - at one stage the a/c is descending tail first with the jet exhaust flowing out of the intakes.
Ginetta G15 Girl said:
If you ever get a chance to see the film of the Jaguar spinning trial it's quite sobering - at one stage the a/c is descending tail first with the jet exhaust flowing out of the intakes.
I think I saw that somewhere years ago, a flat spin down and down? Closest I can find (but different) is www.youtube.com/watch?v=NpGwst3VQiM&playnext=1...Simpo Two said:
Closest I can find (but different) is www.youtube.com/watch?v=NpGwst3VQiM&playnext=1...
T45 Goshawk. Quite amazing how oscillatory that spin was compared to the Hawk T1, although it looks like he was assessing a mishandled spin by using out-spin and in-spin aileron inputs.I'm guessing the T45 has a higher B/A than the T1 (owing to the navalisation) which exacerbates things. Certainly the T1 had an oscillatory spin, but would recover quickly if you just let go of the controls - in fact you had hold pro-spin rudder to get it to spin at all, otherwise you just got autorotation.
CelicaGT said:
Simpo Two said:
I do wonder how much faster these jets would go if they were a bit bigger and carried the ordnance inside instead of hanging over all the place like washing. The drag must be significant. Missiles could be on a rotatey-door thing.
I'm sure all the ordinance reduces the maximum speed but they probably wouldn't be using the max speed anyways. I don't know the Tornado's attack profiles but I'm guessing going supersonic during a low/medium level bomb run isn't part of it, so the bombs, etc. probably have little effect on the speed they plan to fly. However it certainly affects fuel consumption and maneuverability. I remember reading that on an F/A-18 having a full load of bombs and drop tanks increases fuel consumption by something like 30-40%! We did a air-air photographic shoot with 2 GR4s carrying a full load of Brimstones and ALARMS, all done at relatively low level - the whole sortie was only about about 45mins due to fuel use
Delta Hotel, a firm fave of mine. Good question! I think it was about 4 years ago but all a little blurry now, I can check when I get back in the office on Thursday. There was video at the same time, all shot by Geoff Lee of www.planefocus.com
Ginetta G15 Girl said:
B/A ratio in a/c is the ratio of inertial moments between the wings and the fuselage - imagine if you will that the a/c is effectively 2 dumbells, one being the wings (A), the other the fuselage (B).
Generally straight winged a/c have a low B/A ratio meaning that the aerodynamic forces outweigh the inertial forces at high alpha. This means that high alpha handling is good (with progressive buffet), the stall is relatively benign and the a/c will exhibit stable (although possibly oscillatory) spin characteristics. A Tucano or Jet Provost would be a good example.
Swept wing FJ a/c generally have higher B/A ratios (especially as the ZFW rises) because they require a small wing (for high speed and low transonic drag/Mach drag) but are required to carry a large amount of mission equipment/weapons, etc. As the B/A ratio increases then the a/c becomes tricky to handle at high alpha because the inertial forces will rapidly overcome the aerodynamic forces with things like Yaw/Roll cross-coupling occurring. In extremis the a/c will 'Depart' extremely violently with a totally unstable spin and/or inertially coupled auto-rotation (dependent upon IAS).
One example would be the F4 Phantom - at high alpha, roll inputs could cause a Departure so rudder had to be used for manoeuvre.
A worse example would be the Jaguar (especially with centre-line stores), overcome the alpha limits and the a/c would go into 'Wing-Rock' (an undemanded roll oscillation), keep pulling (eg mishandle a rolling 'Pull-out' or 'On track attack' manouevre) and the a/c would depart viciously with virtually no hope of recovery. In cases of inertially coupled auto-rotation below 5000ft the advice was to eject. In cases of a spin occurring (IAS below 170kt), upto 15000+ft would be required for recovery. The 2-sticker would not recover.
If you ever get a chance to see the film of the Jaguar spinning trial it's quite sobering - at one stage the a/c is descending tail first with the jet exhaust flowing out of the intakes.
Interesting - thankyou. My experience has (obviously) only been with straight-wing (supposedly, but that's another story) aerobatic types. Spinning stubby swept-wing things, where invariably you lack the option of applying power to re-energise pitch and roll authority if required, has always looked like a particularly dangerous form of voodoo. I do recall seeing that Jaguar spinning video - although in retrospect it looked like thing thing just ended up tumbling rather than any classical form of autorotation, but then I suppose that is the net effect of a fully developed spin in that general type of airframe.Generally straight winged a/c have a low B/A ratio meaning that the aerodynamic forces outweigh the inertial forces at high alpha. This means that high alpha handling is good (with progressive buffet), the stall is relatively benign and the a/c will exhibit stable (although possibly oscillatory) spin characteristics. A Tucano or Jet Provost would be a good example.
Swept wing FJ a/c generally have higher B/A ratios (especially as the ZFW rises) because they require a small wing (for high speed and low transonic drag/Mach drag) but are required to carry a large amount of mission equipment/weapons, etc. As the B/A ratio increases then the a/c becomes tricky to handle at high alpha because the inertial forces will rapidly overcome the aerodynamic forces with things like Yaw/Roll cross-coupling occurring. In extremis the a/c will 'Depart' extremely violently with a totally unstable spin and/or inertially coupled auto-rotation (dependent upon IAS).
One example would be the F4 Phantom - at high alpha, roll inputs could cause a Departure so rudder had to be used for manoeuvre.
A worse example would be the Jaguar (especially with centre-line stores), overcome the alpha limits and the a/c would go into 'Wing-Rock' (an undemanded roll oscillation), keep pulling (eg mishandle a rolling 'Pull-out' or 'On track attack' manouevre) and the a/c would depart viciously with virtually no hope of recovery. In cases of inertially coupled auto-rotation below 5000ft the advice was to eject. In cases of a spin occurring (IAS below 170kt), upto 15000+ft would be required for recovery. The 2-sticker would not recover.
If you ever get a chance to see the film of the Jaguar spinning trial it's quite sobering - at one stage the a/c is descending tail first with the jet exhaust flowing out of the intakes.
eharding said:
Interesting - thankyou. My experience has (obviously) only been with straight-wing (supposedly, but that's another story) aerobatic types.
YMW.Obviously in your Pitts when you carry out 'flick' manoeuvres such as a Porteus Loop or a Lanjevak then you are using inertial forces to 'tumble' the a/c. However owing to the lower B/A these inertial forces don't build up too quickly and can be rapidly overcome by the aerodynamics when you centralise (or in the worst case you use propwash to give back aerodynamic control).
In a fast jet the inertial forces build so quickly that (almost) if you don't recognise it before it's happened you are along for a very uncomfortable ride followed by a Martin Baker let down. That is why very strict alpha limits are employed for various stores fits and why the alpha read-out is so prominent in the HUD.
eharding said:
Spinning stubby swept-wing things, where invariably you lack the option of applying power to re-energise pitch and roll authority if required, has always looked like a particularly dangerous form of voodoo.
I couldn't agree more!AFAIAA, aside from Test Flying, the only FJ where intentional spinning is permitted is the Hawk. As I said earlier it doesn't really spin as such, more violently auto-rotates. Certainly it surprises students the first time they see it.
My understanding is that for some of the swept-wing jets (I'm thinking of the Hunter) spin recovery requires the use of aileron rather rudder. Apparently the Hunter's rudder wasn't very effective in a spin. That said the Hunter was one of the few front line swept-wing jets approved for spinning. It is indeed another kettle of fish compared to spinning straight-wing light aircraft. There's a video of spin testing a Tornado prototype & the result was similar to the Jaguar spin mentioned above. Irrecoverable flat spins seems to have been a issue for a number of fast jets.
Penguinracer said:
Irrecoverable flat spins seems to have been a issue for a number of fast jets.
There's one airplane where you can recover by lowering the U/C. Except it doesn't really exist. Guess what it was!Is this inability to recover a spin in a fast jet not hazardous in dogfighting, where the pilot might enter a spin unintentionally? Or do you just eject and become POW?
The test-pilot in the Youtube clip seemed to have a small chute to help but I guess operationally that's not an option.
KieronGSi said:
You have a favourite tornado? Geek! (My favourite Harrier is ZD322 but don't tell anyone). 
How do I find out about my favourite airframes? I am a civvy who used to work very closesly with the armed forces, especially the RN.Lynx 345 - Wildcat 45 is my Log On in tribute to her. She used to be an HAS3 and ran off the back of HMS NEWCASTLE.
Lynx 306 - Ex HMS ARROW.
SEA KING ?82 ASAc 7.
I know the frame numbers are different to the side numbers.
Ginetta G15 Girl said:
If we ever go up against an enemy with decent Air Defence assets and an integrated Radar and Sam system then medium level operations in an attack aircraft would be suicide. I would warrant that were that to be the case a/c would rapidly be repainted for low level operations.
The Americans rarely seem to fly that low, do they expect to be able to wipe out the enemy air defence then go in at medium level? 
wildcat45 said:
How do I find out about my favourite airframes? I am a civvy who used to work very closesly with the armed forces, especially the RN.
Lynx 345 - Wildcat 45 is my Log On in tribute to her. She used to be an HAS3 and ran off the back of HMS NEWCASTLE.
Lynx 306 - Ex HMS ARROW.
SEA KING ?82 ASAc 7.
I know the frame numbers are different to the side numbers.
By extensive googling, i know the harriers because i was working with them .Lynx 345 - Wildcat 45 is my Log On in tribute to her. She used to be an HAS3 and ran off the back of HMS NEWCASTLE.
Lynx 306 - Ex HMS ARROW.
SEA KING ?82 ASAc 7.
I know the frame numbers are different to the side numbers.
http://www.google.co.uk/imgres?imgurl=http://www.a...
Simpo Two said:
Is this inability to recover a spin in a fast jet not hazardous in dogfighting, where the pilot might enter a spin unintentionally? Or do you just eject and become POW?
During the Korean war the F-86 pilots would try to provoke the Mig-15 pilots into a spin for this exact reason. The USN F-4 Phantom pilots would try to lure the Mig-19s into a situation where the Phantoms shorter stiffer wing enabled them to roll their aircraft at high speed but the chasing Migs would suffer aileron reversal, hopefully into the ground.
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