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 Post subject: Cheetah Miscellanea
PostPosted: 16 Jun 2020, 16:23 
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The following snippets and quotes are copied from the Air Force Talk Whatsapp group and placed here for ease of reference.

Kev
Quote:
Fuel tanks and transfer levels differed between the D, D2 and B. Used a french Christmas tree fuel indication system with lights that illuminated when a tank was empty - the only way the pilot could tell he had not suffered a fuel transfer failure was to continuously monitor the fuel DEBI (fuel used gauge) to check the tanks emptied at the correct fuel total. Fuel was only accurately indicated for the fuselage tanks. B transfer lights came on really late so the pilot only knew he had used the fuel when it was almost too late to do anything about it. Otherwise we all referred to them collectively as a “Cheetah D” but intimately as a B,D or D2. D was certainly supersonic although she suffered from drag issues relative to the C. C I’ve taken to M1.77 but in SA getting Mach 2 was a challenge due to the climate conditions. Chileans got their Panteras Mach 2 down on the southern tip of South America. I have no doubt the C would have achieved Mach 2 in those conditions too. There was a Mach 2 run with the A-A probe off but that was not an approved config.


"Casper"
Quote:
The B and D had the same transfer levels and the D2 was a bit differrent due toe the fixed rearbay tank of the D2.

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 Post subject: Re: Cheetah Miscellanea
PostPosted: 16 Jun 2020, 16:51 
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Cheetah Avionics - Cooling:
Kobus explains:

"The Mirage III has two air-conditioning systems. Look on the spine of the fuselage behind the cockpit, there are two scoops.

Image
The two scoops mentioned. The larger one is post Cheetah upgrade.

These push air through heat exchangers to cool high pressure air bled from the engine compressor. One system provides cooling to the avionics in the bay behind the cockpit for the Mirage III C and E. and the second system provides cooling air and cabin pressurisation for the pilot and cockpit electronics. The Mirage III B and D had less avionics than the single seaters so the second system helped with the cooling of the second pilot.(Who was occupying the avionics bay space).

The Cheetah mod specifications wanted the same avionics in both versions, so we had to develop the bigger nose for the single seater and even bigger nose for the dual seater to accommodate the avioinics since the avionics bay behind the pilot in the single seater was not there in the dual. Also there were way more black boxes in the Cheetah vs the Mirage and they needed more cooling than the old boxes. So the heat exchangers in the spine were made much bigger (which caused lots of headaches in the engine tunnel). In the single seater we cooled the avionics in the avionics bay with the new bigger supply from system one. System two cooled the pilot and the cockpit and we dumped the used air into the nose to cool the extra avionics there in the bigger nose. The outlet you see on the Cheetah E and R2 is where we dump the used cockpit/nose avionics air.

Image
The vent where used cooling air is dumped on a Cheetah E. All Cheetah variants had a air dump in this area.

On the daul seater it was more complex. System one cooled the two pilots and cockpit avionics. Then we dumped that into the first part on the nose and out under. System 2 was piped under the fuselage (you can see 2 pipes running along under the cockpit) and that air was used to cool the rest of the avionics. However it heated up and lost pressure due to the piping route, so a small additional heat exchanger was fitted to the dual seater nose. that is the inlet/outlet you see on the nose of the 2 seaters."

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Heat exchanger intakes on the D.

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Cooling air pipes from the heat exchangers to the nose. Note the fairings covering the pipes are not present.

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System one vent.

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Air intake for the nose tip heat exchanger.

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System two & nose tip heat exchanger vent.

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Last edited by mamba on 16 Jun 2020, 17:07, edited 1 time in total.

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 Post subject: Re: Cheetah Miscellanea
PostPosted: 16 Jun 2020, 17:06 
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Cheetah R
Q&A as posted to Kobus:

Q: What role was the Cheetah R supposed to play in the era of external camera pods? Did it make sense for the SAAF to have a dedicated Recce aircraft?

A: Recce is a dark & very secret world. If you have high resolution satellites, you can fly 'lower quality' optic and most probably no IR/Radar & EW recce equipment in a pod as supplementary recce info. Pods are draggy and weigh a ton, need external electricity and take space on a pylon where you could have carried fuel.

The Cheetah R was designed around some very sophisticated cameras that could photograph a car's licence plate from a very high altitude and side distance at Mach 2. There were also other sensors in the suite. You could do complex tactical recce that could be fed straight into the mission software of the fighters (in this case the D & E).

The high speed recce aircraft carried no weapons, we even removed the cannons/ammo & built a special fuel tank to fit in its place (The cannons were fared over too). The aircraft had to be the fastest and therefore sleekest of the Cheetahs and of course had the Atar 09K50. We also re-engined a Mirage III RZ (836) with a F1 engine to see if we could make the RZ's into the same high speed recce aircraft.

The nose was entirely designed around the very heavy & complicated cameras. Temperature in the camera bay had to be +- 2 deg C throughout the whole flight even at sustained high Mach no's! That was a nightmare to solve. I had to find a balance between the aerodynamic needed for the high speed cruise and the space for the cameras! The windows in the nose was a masterpiece and had to be polished like camera lenses & we had to make sure we did not get aero distortion due to shock waves from the nose. You would take off with covers over the windows to avoid sandblast or dust on the windows & then when you are ready the covers could be blown away by compressed air. The nose was bigger & heavier that that of the Cheetah D but in my opinion better aerodynamically designed.

Q: How was the temperature in the nose controlled to +- 2 deg C?

A: The actual temperature was not the problem, it had to be stable within +- 2 deg C. We never had a way to cool it and keep it at +- 2 deg C so we heated the whole nose with friction heat (from air friction on the nose) and an electrical heater to 40 deg C and we could keep it within +- 2 deg C with the heater!

Q: If speed was so important to the Cheetah R, did the canards have a big drag impact?

A: The canards provide extra lift, so you can move the Center of Gravity (CoG) forward a bit. This allowed a CoG range that would give the Cheetah E the capability to carry bombs on the two new pylons under the canards. It also carried two 30mm Defa cannons and ammo in that area. The Cheetah R2 did not have the new pylons and no cannons and ammo. The fuel we carried in the gun bay was much lighter that then cannons and ammo. We kept the controllable CoG range the same as the other Cheetahs, so that we did not have to develop new flight control software and also so that the pilots would not feel the difference between the different models.
The canards' main role is to energize the wing airflow and to help with sustained turn rate in Air Combat. Their drag is relatively low and is actually less than the inlet of the D nose heat exchanger or the radar warning antennae.

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 Post subject: Re: Cheetah Miscellanea
PostPosted: 16 Jun 2020, 22:08 
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Referring to the antennae in front of the under nose vent of the Cheetah E.

Image

Image

Kobus
Quote:
These antennae were 'passive' EW system sensors. They only see radar and radar guided missiles illuminating you. The other antennae you guys are posting were part of ' active' EW that could see incoming IR missiles.

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 Post subject: Re: Cheetah Miscellanea
PostPosted: 17 Jun 2020, 07:21 
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More on cooling system on Cheetah C & D:

"Casper"
Quote:
Both the Ds and Cs has got the precooler inlets on the spine area that is tapped from the engine. On the Ds (under) the nose (tip) is all the avionics and heat exchangers, a water evaporator and 2 turbos. On the Cs the avionics is in the avionic bay behind the cockpit and active radar in the nose that needs cooling from 2 excangers that is in the nose wheel bay port and stbd. No water evaporator on the Cs. The intakes for the Cs is on the boundary layer intakes in the centre between the 2 tunnel cooling intakes


Image

Image

Image

Quote:
This is the intake of a C. The top and bottom arrows is the tunnel cooling intakes into the engine bay. Top goes over the top of the engine and bottom under the engine. Centre intake is for the cooling for the heat exchangers in the nose wheel bay PORT and STBD sidea.

Image

Forward HPA cooling on the Cheetah C (High Power Amplifier, part of the EW system)
Image

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 Post subject: Re: Cheetah Miscellanea
PostPosted: 17 Jun 2020, 07:32 
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Casper
Quote:
The avionics cooling is a system on its own and cockpit cooling/persurisation is the other.


Kobus
Quote:
Yes and the heat exchangers for those are on the spine, left and right. This was for all Cheetah E/D/D2/ R2


Quote:
There is no engine cooling, just engine tunnel cooling.


Casper
Quote:
Precoolers where in the spine/engine bay area


Q: So a tunnel per say around the engine where heat get's radiated to and then cooled by the air taken in at the boundary intakes?
Kobus
Quote:
Yes, it has layers of shielding and the engine nozzle at the back createsbla low pressure so sir from the


Casper
Quote:
At Denel we got a separate cooling unit and on the disply the temp is around 0°c. With the Cs the cooling is the same supply externally but can do alignment with no cooling. It had its own cooling fan that is good enough for system alignment.


Kobus
Quote:
Low pressure so air is sucked in from the boundary layer splitter & cools the tunnel. Keeps engine heat(especially with afterburner use) away from the structure.

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 Post subject: Re: Cheetah Miscellanea
PostPosted: 17 Jun 2020, 18:46 
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Excellent info :smt023 . I always thought the ducting on the forward lower fuselages of two seater Mirages and Cheetahs was for electrical cables.


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 Post subject: Re: Cheetah Miscellanea
PostPosted: 17 Jun 2020, 19:23 
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On cannons:

David
Quote:
Cheetah E 842 had a gunpack that consisted of the ammobox and the two Defa cannons. The ammobox is the big square box and the two side panels are the gundoors. They were used for access to the cannons. If that is what you talk about.


Quote:
The original fwd facing scoop was a single half round unit. It was modified to dual square intakes to accommodate the 412 pylon if my memory is still intact.

On the D an E the cannons were fixed onto the gunpack itself. On the C the cannons were fixed to the airframe with the ammobox as an independent unit.


Quote:
The Cheetah were never too good with guns. The F1 was far more superior with that. But don't let them know I admitted it. Calibration was done by shims on the cannon itself. There was a sight fitted into the barrel and aligned to a board in front. The avionics boffins were aligning the systems with that and we the cannons to that. So in the end the cannons and the avion systems were aligned. But the Cheetah cannons were firing in a flat "infinity" sign shape so the accuracy was not the very best.


Quote:
Once me and a very good friend reloaded Cheetah E cannons at LBWG in under 10min. When the pilot got out of the cockpit to inspect the aircraft the gunpack was on it's way back


Quote:
The Cheetah 30mm (round) was local and available in HE, HEI, SAPHEI and of course the practice round.


Kobus
Quote:
Cheetah D & E had the same gunpack as in the Mirage III. I have photos. The whole pack dropped out, barrels stayed behind. You could also swap the gun/ammo pack for a fueltank.


David
Quote:
Never seen it done though, but we did remove a lot of gunpacks for access to a fuel panel inside the gunbay that sprung a leak. Always thought why that freaken panel was built at that location.
Quote:


David
Quote:
When removing the gunpack, one first had to unlock and pull the barrels forward to remove them from the cannons. Then 4 bolts were loosened and the gunpack was lowered with a cable pulley system and placed on the red gunpack stand, the yellow Steinbuck 2as used to raise and lower equipment and bombs. The barrels were then pulled backwards out of the aircraft and replaced in the cannons for the loading. The ammunition was stored inside the centre between the two cannons. The cannons were hand cocked and took some practice to master a smooth cocking action. Many old armourers today complain of tennis elbows today (me being one) :lol: . Here on the picture we have on the left Piet du Toit (RIP) and on the right Blakie Swart (RIP). The guy in centre I cant remember.


Image

Quote:
Yes the reverse to install. If the cannons were cycled with loading, there was a chance that the pressure ring on the drum can be dislodged

That is now without the barrels. If that happens the pressure is escaping at the barrel contact point and the gundoor is lost in flight. The cannon will not cycle and the recoxking cartridge will fire. But as soon as the next one fires in that location, the cannon will not cycle again and because there is no more re-arm cartridge the cannon will jam.

That is why the SAAF looked into modifying the Defa to take more re-arm carts. It was done but never used in Cheetah.


de Beer
Quote:
The barrel need to be fitted to prevent the sealing rings to dislodge from the front of the drum in the canon. When the round is fired the ring move slightly forward and push against the face of the barrel to form the seal and prevent pressure lost


Q: Looks like blue training rounds

David
Quote:
That is correct and it looks like the tips were dipped in yellow which means it is at Lbwg for AA firing on the flag. Red, yellow, blue and green were the colours for flag firing.

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 Post subject: Re: Cheetah Miscellanea
PostPosted: 19 Jun 2020, 05:30 
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 Post subject: Re: Cheetah Miscellanea
PostPosted: 21 Jun 2020, 15:50 
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Hi there, just a small thing, were there not problems with the c of g on the cheetah with the new engine, remember reading it somewhere but can`t remember!


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 Post subject: Re: Cheetah Miscellanea
PostPosted: 21 Jun 2020, 21:09 
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Red Baron wrote:
Hi there, just a small thing, were there not problems with the c of g on the cheetah with the new engine, remember reading it somewhere but can`t remember!


Kobus explained that that was a myth. They had a shorter and lighter engine so they could place it where they wanted. The engine face was about 600mm further back than on the Atar while they used the same fuel system to keep the CoG range the same.

I think this rumour arouse because the Cheetah had a much less public career than the F1 which flew at SAAF 75 and plenty AAD after that. The Cheetah only flew in '95 and the project was axed only a short while later. Paramount took over the F1 so she flew for quite a few more years.

There is a forum thread on the Cheetah/F1 with the SMR engines. :smt023

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 Post subject: Re: Cheetah Miscellanea
PostPosted: 25 Jun 2020, 01:44 
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Red Baron wrote:
Hi there, just a small thing, were there not problems with the c of g on the cheetah with the new engine, remember reading it somewhere but can`t remember!

No that is not true. I have seen this nonsense often being mentioned. Why I do not know! The engine was lighter and shorter, so we could place it where we wanted. We did not want to change the handling, or the CAS and SAS boxes, so we placed it that the handling was exactly the same, the only thing was that the A/C was lighter. That was a bonus.


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