The SAAF Forum

Discussion on the SAAF and other southern African air forces.
It is currently 14 Jul 2020, 22:45

All times are UTC + 2 hours




Post new topic Reply to topic  [ 11 posts ] 
Author Message
PostPosted: 15 Jun 2020, 12:39 
Offline
Site Admin
User avatar

Joined: 29 Jun 2004, 17:19
Posts: 7891
In the mid-1990s South Africa re-engined Mirage F1AZ '216' (which then became known as 'Super Mirage F1') and Cheetah D 847 with modified RD33 engines, the SMR95A and SMR95B respectively, in place of the Snecma Atar 09.

South Africa also integrated the Russian Vympel R-73 (AA-11) infrared guided short range air-to-air missile with the Mirage F1CZ. The Mirage F1 flew 70 times during trials with the SMR95 engine, while the Cheetah flew 10 missions to "prove the concept".

The following is from a Whatsapp group whereby Kobus (member CheetahR2) shared the following regarding the installation of the SMR-95 engine into the Mirage and Cheetah.

1) Modified intakes and the modified "Mice" with associated modifications.

The SMR 95 (Midified Mig 29m engine) needed a lot more air! It also responded to throttle inputs very quickly, which makes it good in A/A combat. We redesigned the inlet lip, cut it back and changed the shape og the D-shaped 'mouse' that runs up and down the intake to control the airflow and shockwave. On the Mirage, the old 'mice'; were pushed back and forth by a screwjack, but that was hopelessly too slow! We used high speed hydraulic rams driven by a small computer linked to the fuel control & air data system. The engine is also much cooler that the Atar, so we could reduce the boundary layer bleed that is sucked off at the intake and pushed through the tunnel gap between the engine engine and airframe tunnel.

Photo 1 to 3 & 5 of mouse mod. Photo 4 is boundary bleed mod.
Image

Image

Image

Image

Image

_________________
How come every time my ship comes in, I'm at the airport?


Top
 Profile  
Reply with quote  
PostPosted: 15 Jun 2020, 12:42 
Offline
Site Admin
User avatar

Joined: 29 Jun 2004, 17:19
Posts: 7891
2) Movement of the SMR aft with the new heat sink.

The engine was lighter and shorter. We extended and straightened the afterburner. We did not want to change any of the fuel system (CG movement during flight as fuel is burned and during in-flight refueling). We alsom did not want to change the handling or control sensitivity, so we opted to place the new, lighter engine and new gearbox with new starter,/generator, fuel and oil pumps & alternators in such a way that both the modified a/c will be lighter but same cg range as before.
This meant we had to make an extension of the intake inside the fuselage. Since modern a/c can never have enough cooling and electricity for the modern avionics, the team came up with the idea to make this extension into a heat exchanger where we get a lot of additional cooling air for avionics without any drag caused by radiator type exchangers and inlet scoops etc.
photo 1 to 3 shows position of engine & the length of space which we could turn into an exchanger and the actual exchanger.

Photo 4 shows the CG plot, a/c is lighter but cg shift is similar to the original a/c.
Image

Image

Image

Image

_________________
How come every time my ship comes in, I'm at the airport?


Top
 Profile  
Reply with quote  
PostPosted: 15 Jun 2020, 12:44 
Offline
Site Admin
User avatar

Joined: 29 Jun 2004, 17:19
Posts: 7891
3) The new tailcone.

The new engine had a much more effective converging/diverging nozzle, driven by hot fuel as hydraulic fluid vs the Atar which used engine oil for the actuators. If the a/c is hit by a heat seeking missile, the tail area is normally damaged and if the engine oil leaks out, the engine seizes. If you use fuel for the actuators, you have a chance to get home or safe territory because you have much more fuel on board that any other liquid. Also, the 09K50 had better engine nozzle flaps, so we could improve the Cheetah base drag more that the F1. The structure at the back of the Cheetah was also more easily modifiable, the F1 has has frames in that area that carries the elevator loads.

photo 1 & 2is F1 tailcome for SMR
photo 3 showing Cheetah tail being modified.
photo 4 new Cheetah tailcone.
Image

Image

Image

Image

_________________
How come every time my ship comes in, I'm at the airport?


Top
 Profile  
Reply with quote  
PostPosted: 15 Jun 2020, 13:48 
Offline

Joined: 20 Aug 2010, 14:40
Posts: 2523
Thank you Kobus and Dean =D>

_________________
https://www.flickr.com/photos/141742650@N08/albums


Top
 Profile  
Reply with quote  
PostPosted: 15 Jun 2020, 21:36 
Offline
User avatar

Joined: 08 Apr 2013, 19:28
Posts: 396
The difference in airflow and engine air requirements vs throttle settings between the Cheetah with 09K50 and the Mirage III with 09C was not that big, so we could just adjust the mouse position further back (to allow more air in the throat) and cut the outer lip back a bit( so that the shockwave still attaches on the outer lip even though the mouse is further back). See photo.
Once you have done this , you have a problem with the mouse being too far back and the splitter plate does not allow the excess air and boundary layer to bleed away, so we had to cut the splitter plate back a bit at the top & bottom.

With the SMR, it needed way more air and the shock cone laws and speed of reaction to throttle input was also very different, so we had to change the shape of the mouse itself and the way it travels up and down the throat of the intake, so the outer lip was cut back less. Added to that the SMR needed less cooling in the engine tunnel so we had to dump more excess air at the splitter plate, hence the strange splitter plate shape

Image
Sketch to show differences.

Image
The SMR intake lip.

Image
09K50 upgraded Cheetah D

Image
Schlieren imaging of shockwaves at intake.

_________________
MAMBA

Keep your feet on the ground, and reach for the skies!


Top
 Profile  
Reply with quote  
PostPosted: 16 Jun 2020, 09:12 
Offline
Site Admin
User avatar

Joined: 29 Jun 2004, 17:19
Posts: 7891
Thanks Mamba! Those sketches help a lot. :smt023

_________________
How come every time my ship comes in, I'm at the airport?


Top
 Profile  
Reply with quote  
PostPosted: 16 Jun 2020, 11:33 
Offline
User avatar

Joined: 08 Apr 2013, 19:28
Posts: 396
The topic of a short engine service life for the Russian engine is commonly brought up when the SMR upgrade is discussed. While the SMR did indeed not have the service life of the Atar's the SAAF had, this was due to a difference in philosophy between Eastern & Western operating ideologies.

Kobus explains:

"The story about the SMR-95 short life is a rumour that (I think) that was started when the politicians and some SAAF guys got excited about buying new a/c rather than supporting SA technology. The Russian way of doing maintenance is very different from the West. They pull and engine quickly on the frontline, change a whole module (since the engine is designed to be assembled in modules) and push it back into the a/c. The old module is sent back to the factory, opened, inspected and overhauled as required. They do not see that as an engine change or life expectancy. It is a quick preemptive maintenance procedure.

The SAAF would fly an engine for the prescribed 'life' and then take it apart completely. You cannot compare 'life' between the engines based on that. The Russians also have certain modes you can select for operating the engine. Most of their training & regular flying is done in a mode that reduce performance marginally but extends time between turbine module exchanges by quite a margin. If you need to fight, you select 'combat mode' & you have shorter time between module swaps, but huge performance gains. The engine was also less that 50% of the cost of other engines."

The common understanding is that the Soviet methodology was to prepare for war. Thus loads of aircraft are produced at cheaper prices and less complexity than their Western counterparts as you expect to lose a few when a large engagement takes place. Being numerically superior was seen as an advantage. They have a saying 'quantity is a quality on its own'. The SMR as a derivative of the RD-33 is thus developed along the same lines. You want as much combat aircraft serviceable as possible at any given time. It is thus easier to simply change a module on the engine and send the faulty one away. The aircraft is thus serviceable again in only a few hours instead of days. Cheaper engines also mean you could have a much larger spare inventory aiding in this quick change philosophy.

The more expensive Western engines have longer service 'lives' but fewer spares can be kept ready because of the costs likely meaning the Squadron looses an aircraft for a certain period of time if deep engine maintenance is required.

_________________
MAMBA

Keep your feet on the ground, and reach for the skies!


Top
 Profile  
Reply with quote  
PostPosted: 16 Jun 2020, 17:52 
Offline

Joined: 14 Jun 2020, 09:05
Posts: 6
Mars wrote:
Thank you Kobus and Dean =D>


Thanks, it is nice to share some of the history!


Top
 Profile  
Reply with quote  
PostPosted: 17 Jun 2020, 07:40 
Offline
Site Admin
User avatar

Joined: 29 Jun 2004, 17:19
Posts: 7891
Kobus
Quote:
a high bypass ratio engine needs less tunnel cooling. since the engine was much shorter, we had to make an extension from the intakes to the engine face. We designed this extension as a heat exchanger using the 'spare' air and added about 39;% avionics cooling capacity!

_________________
How come every time my ship comes in, I'm at the airport?


Top
 Profile  
Reply with quote  
PostPosted: 18 Jun 2020, 17:02 
Offline

Joined: 03 Jun 2012, 09:08
Posts: 79
Location: Brooklyn
Super interesting stuff, thank you for all the contributions :smt023

Fun to stroll down the lane of what-ifs.


Top
 Profile  
Reply with quote  
PostPosted: 19 Jun 2020, 05:18 
Offline

Joined: 14 Jun 2020, 09:05
Posts: 6
Some comments.

The SMR-95 was a modified RD-33 that we worked on with the Russian team. It was the same engine for both the Mirage F1 and CheetahD. I do not recall a SMR-96 A and B?

The Vympel missile was integrated and tested on Mirage F1 216, which was a AZ.

The CheetahD , 847, flew more than 10 sorties, it flew the complete flight test plan and comprehensive comparative performance data was created for the SAAF to use.
Image

Image

Image
Image


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 11 posts ] 

All times are UTC + 2 hours


Who is online

Users browsing this forum: No registered users and 19 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
cron
Powered by phpBB® Forum Software © phpBB Group