Low-level speed of Cold War aircraft

[Doc72]

Hi everyone,

 

just out of curiosity (and to discuss nerdy aircraft stuff) I wondered how fast Cold War aircraft actually flew at low-level or would have flown in an actual mission. Handbooks often give top speeds close to 1.000 km/h at sea level for many jet types, but these are highly theoretical figures. Of course, it would  depend to a great deal on payload, fuel, the specific mission profile, exact altitude and other factors. Furthermore, there is a different between the possible and the bearable speed (the speed the pilot and the airframe can endure over a certain period). Nevertheless, I think, we can talk about a range of typical speeds.

It would be interesting to know how much faster were aircraft designed for the low-level role (e.g. Buccaneer, Tornado, B-1) compared to others that were just adapted for this role. And how slow was the A-10 really compared to types in its natural habitat?

 

By just looking through my bookshelf I found the following figures quoted in the literature. Sometimes it seems to refer to the attack speed and some time to the max cruising speed:

 

Avro Vulcan: 375 kts (695 km/) with an one-time acceleration to 415 kts (769km/h). Interestingly, the limiting factor seems to have been the structural integrity of the airframe. (McLelland, Avro Vulcan (2019))

 

EE Canberra: 300-420 kts ?? (556-778 km/h) (Brookes, Canberra Boys (2017)

 

Lockheed F-104G: “speed at low level” between 778 – 889 km/h (F-104 G Jabo Tiel 1, F-40, No. 27)

 

Fiat G.91: “penetration speed” 666 km/h (recce), 555 km/h (fighter bomber), “combat speed” 740 km/h (Fiat G.91, F-40, No. 29)

 

Do you have additional data for more types (Tornado, Buccaneer, Phantom, B-52 ...)? Any comments?

[bentwaters81tfw]

F-111F would come tops, followed by MiG -23.

[Graham Boak]

I recall that only the F-105 and Tornado were cleared to 800 kts.  The majority of the faster jets of the period were restricted to 700 or 750 Kts.  I don't recall what the F-15/F-18 were cleared to.

[Murph]

If you're talking actual speed flown versus maximum, it was typically a multiple of 6 for planning purposes in the western air forces.  That allowed the pilot to break the route down into miles per minute for timing and pounds per minute for fuel usage.  That meant most strike aircraft were typically flying in the 480, 540, or 600 knot range.

 

Regards,

Murph

[Herb]

Concur with Murph, multiples of 6 for strike planning and execution. Virtually all external payloads keep attack aircraft firmly subsonic due to drag. On egress, fuel consumption and threat is more likely to determine your speed. 

 

A-10 guys are different. Like to hear from one, but think they stay in the realm of 250-300 knots most of the time.

[TheyJammedKenny!]

I was NOT an A-10 guy, but I worked with them during my brief career.  The A-10 is/was notoriously slow, but it probably didn't matter, because in a land war in Europe, they would have flown round-robin push CAS missions, meaning that they would be sent to a "contact point" to work with a particular FAC or FACs.  This would greatly shorten their response time during an end-of-world scenario.  I think 250 knots for an OA-10 / A-10 at low level (below 10K feet) is actually a bit fast, depending on temperature and humidity.  I spent part of one summer as a cadet with the 314th TAW in the 80s.  During exercises A-10s flew threat suppression for the Hercs at low level, but if they dog-legged to handle a threat, they had difficulty catching up to the low/slow C-130Es, operating at about 250 AGL and 180 kts in the heat and humidity of southern Arkansas in the summer.  You can just imagine.  The higher the humidity, the less dense the air, the lower the performance of the engines.

[bentwaters81tfw]

Groundcrews checked for birdstrikes on the trailing edges of the A-10.

[Antti_K]

Hello all,

 

It seems that all important factors are already listed: you want to use a speed that is a multiple of 6, you want to keep a close eye on your fuel burn, your payload dictates the maximum speed allowed and finally you don’t want to give your location away by loud roar or by a sonic boom.

 

Your Ground Speed (GS) has to be a multiple of six because this gives you an easy way to manage your mission timing. Let’s say that you are flying at an Indicated Air Speed (IAS) of 480 kt. at 200 feet. Your True Air Speed (TAS) increases roughly by 2% for every 1000 ft of altitude. So your TAS will be ca 482 kt. In zero-wind conditions it means that you have to throttle back to maintain an IAS of 478 kt. to maintain a GS of 480 kt. And now the tricky part: Your Time Over Target is set in your orders. Today RAF allows something like +/- 3 seconds deviation in Hawk operations. If you are late (for example) for six seconds, you have to increase your GS by 6 kt. and maintain that for roughly eight minutes to reach correct TOT. All this means that faster you fly the smaller the margin for navigational errors will be. If you are ahead of the planned timing, you have to waste time. One very good way to do this is to throttle back and use the air brake.

 

Path Finder Force (more accurately the Squadron Navigation Officer of No 35 Squadron) devised a method of time wasting. Whenever the navigator realized that the flight was ahead of its time table the pilot turned the aircraft directly into wind. The navigator then calculated the exact time to fly into wind before turning 180 degrees back toward the original track. This may sound complicated but it is actually pretty simple using a “modified” Point of No-Return formula.

The maximum speed is another interesting factor. I can’t recall the exact figure for a MiG-21BIS but it was around 2400 km/h. The aircraft could accelerate easily beyond that speed but flying at air speeds beyond the “Red Line” started to tear parts away from the aircraft. They actually tried that in the Soviet Union… MiG-23 was easy to mess with if you could drop down your own air speed. For example Soviet MiG-23s tried to intercept our Learjet 35 on a maritime patrol mission over the Baltic Sea. Whenever the MiG was spotted the first thing was to decelerate down to 115 kt, open the flaps and enter a turn with a bank angle of 25 degrees. The wings of the MiG were rocking from side to side as the pilot tried to follow us. The Soviet pilot had to calculate his flight path, air speed and G -load very quickly and accurately, otherwise he would have been hit the water. MiGs were built for speed.

 

Finally: the noise. Close to sea level the speed of sound is 667 kt. There are very few aircraft that can reach that speed at low level, in level flight and without the use of re-heat. The noise will be very loud giving the position away. Because of the compressibility the aircraft’s surface temperature will be very high causing possibly problems with guns, missile heads and stuff like that.

So here we are. I would say that a speed range from 350 kt. to maybe 600 kt. sounds good for low level missions.

 

Cheers,

Antti

[Lord Riot]

I'm sure I read that the maximum for the Buccaneer was 646mph. No idea what that is in 'knots', or if they actually ever did that over the north sea or wilds of Scotland, but I bet it would have been an amazing sight. 

 

Did Lightnings ever get down in the weeds when playing with mud movers? Probably not many bomber types that could outrun them. Until the Lightning had to knock it off to refuel!

 

 

[alt-92]

25 minutes ago, Lord Riot said:

I'm sure I read that the maximum for the Buccaneer was 646mph. No idea what that is in 'knots'

for an approximate result, divide the speed value in (land)miles by 1,15. So about 560 kn.

[bentwaters81tfw]

Lightnings were supersonic in the weeds, but I don't know by how much. Then again, there was TSR2.......

[Blimpyboy]

 

You could bend the throttles as much as you liked, but it still felt like you could get out and run faster.

 

 

Edited August 17, 2020 by Blimpyboy

[Blimpyboy]

 

And (if it were needed) proof that your ground speed can actually get into negative figures...

 

 

[Murph]

5 hours ago, Lord Riot said:

I'm sure I read that the maximum for the Buccaneer was 646mph. No idea what that is in 'knots', or if they actually ever did that over the north sea or wilds of Scotland, but I bet it would have been an amazing sight. 

 

Did Lightnings ever get down in the weeds when playing with mud movers? Probably not many bomber types that could outrun them. Until the Lightning had to knock it off to refuel!

 

 

One of my RTU instructors flew the Lightning on an exchange tour.  He talked about one airfield defense mission where he took off, fought directly over the base, and landed running "on fumes".  Total flight time was 18 minutes.

 

Regards,

Murph

[bentwaters81tfw]

You could empty an early Lightning in 15 minutes in full Burner. You could also exceed it's fatigue index in one flight. Such was it's power and manoeuvreability.

[stever219]

A turning fight at low level in the Lightning using full reheat would cover a lot of ground.  Roland Beamont recounted his experience of testing an early Lightning at supersonic speed up the Irish Sea in one of his books; on closing the throttles he entered a decelerating descending turn at around 2g and described the turn as encompassing most of the Lake District.

[John B (Sc)]

Interesting discussion. The snag with many of the 'book' speeds is that they are not achievable in practice with real loads. The Tornado is a case in point; excellent performance, if not great acceleration when clean, but much slower when the drag of tanks and weapons was added.  Good range at lower speeds, as you'd hope for from a turbofan. It was said that when transiting to Cyprus and such like, when being escorted by VC-10 tankers, the Tornadoes had to ask the VC-10 to reduce speed to their range optimum.

 

As for the Buccaneer, since it stored the weapons internally and had low drag slipper tanks, it could in that fit achieve fairly close to its max allowed , which I believe was ~640 knots low level, not mph. 

A Phantom air defence pilot I knew recalled that if they encountered a Bucc, at low level, at max chat,they would ignore it unless they were in ahead on approach.  His view was that the only way to catch He reckoned the only way  the Phantom  could catch a fully wound up low level Bucc was to bang off the tanks, hit full burners, and call fro a tanker ASAP because you will need one very soon...   Not many machines could stay as close to the deck as the Bucc and stay so fast.

'Bananas, bananas'. 

 

A much missed machine.

[72modeler]

50 minutes ago, bentwaters81tfw said:

You could empty an early Lightning in 15 minutes in full Burner.

Pilot's notes for F6 takeoff:

Release brakes

Engage reheat

Retract undercart

Disengage reheat

Start looking for tanker

Mike

[JosephLalor]

41 minutes ago, stever219 said:

A turning fight at low level in the Lightning using full reheat would cover a lot of ground.  Roland Beamont recounted his experience of testing an early Lightning at supersonic speed up the Irish Sea in one of his books; on closing the throttles he entered a decelerating descending turn at around 2g and described the turn as encompassing most of the Lake District.

It seems to me then that the Lightning had low endurance but could achieve reasonable range by dint of sheer speed.

Edited August 17, 2020 by JosephLalor

[Giorgio N]

The actual speed of the AMI F-104S during low level strike missions was 420 Kts increasing to M 0.9 (around 600 kts) when approaching the target. Such missions saw a bomb (replaced by a pod in peacetime) on the centreline and 4 tanks, two on the tips and one under each wing (but by the time the aircraft reached the target the underwing tanks may have been jettisoned, I have to check this).

Maximum speed at low level was M 1.2. IIRC the 104 could reach such speed with wingtip tanks in place.

Edited August 17, 2020 by Giorgio N

[Graham Boak]

34 minutes ago, John B (Sc) said:

 It was said that when transiting to Cyprus and such like, when being escorted by VC-10 tankers, the Tornadoes had to ask the VC-10 to reduce speed to their range optimum.

Similarly during the Transatlantic Air Race the Victors had to  restrict their speeds to match the Harriers.  But the VC-10 wouldn't have done much at 50ft.  Horses for courses.

 

I rather suspect that it would have been more fuel efficient to go on ahead and then orbit until the fast jets caught up.  However, rendezvousing in those days would perhaps have been rather morr marginal than nowadays.

[DrumBum]

The F-105 was pretty quick down in the weeds, about 830 knots indicated. Vic Vizcarra in an interview states that any faster than about 830 and the canopy would start to become opaque from the heat. 

But yes the F-111 was probably the lowest and fastest. Grab a coffee and tune into Aircrew Interviews on Youtube interview with Jeff Guinn, awesome stuff. 

[bentwaters81tfw]

As was said about the Bucc, there were other airframes that could carry more, go faster, go further than a Bucc low down, but not all at once.

A Lightning from brakes off to empty tanks flat out took 15 mins - and halfway to Norway!

[72modeler]

13 minutes ago, DrumBum said:

any faster than about 830 and the canopy would start to become opaque from the heat. 

I seem to recall reading that another blindingly fast jet, the XF8U-3 Super Crusader's top speed was limited only by the heat limit of its windscreen. The F-105's engine and planform were perfect for going really fast down in the weeds- very stable at full speed; couldn't turn worth a darn, but once the burner was lit, it was hang on for a wild ride!

Mike

Edited August 17, 2020 by 72modeler
corrected spelling

[Lord Riot]

Actually I remember many years ago at Finningley airshow asking an American F-4 crew (can't remember if it was an RF-4C or F-4E) how fast it would go, and being slightly disappointed when they said 800mph. I was expecting 1,500 like in all the books! 😂

 

Similarly a Tornado crew told me "about 600mph", when I said I thought it was over 800 at low level they said "maybe a brand new one, with no underwing stores". So they lose engine power, like old cars?