# P51 with Griffon engine?



## Ascent (Jun 3, 2016)

The Mustang with the Allison engine was a decent aircraft hat was made into an excellent aircraft when fitted with the Merlin.

Would it have accepted a Griffon engine and if so would it have been worth the effort to install it?

I ask because obviously the Spitfire was able to step from the Merlin to the Griffon and it made a difference to performance that was worth the effort involved to fit the new engine.

How much engineering effort was required to upgrade the Spitfire and would the Mustang have been harder? easier? the same? and would it have gained the same level of improvement in performance?

Thoughts?

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## drgondog (Jun 3, 2016)

Yes - it 'Could Have' and one of the Reno Unlimited racers has a Griffon with a contra rotating prop.

That said, Schmued wanted to stay on the Merlin track for the Mustang - and already achieved 495mph in the XP-51G with the 14 S.M. engine with combat load of internal fuel

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## pbehn (Jun 3, 2016)

The Spitfire was a short range absolute high performance machine, fitting the Griffon engine kept it at the front in performance. For the P51, it relied on the low fuel consumption of the Merlin while cruising to rendezvous point and on station as an escort plus the trip home coupled with its prodigious performance on max boost in combat. I suspect that the Griffon would have made it slightly faster with a slightly better rate of climb but it would have used much more fuel while cruising due to increased swept volume and increased drag due to weight and frontal area. A Griffon powered P51 would outperform a Merlin engined one in almost every area except the one that made the P51 a game changer and that is its range.

The answer to the question lies in the fuel consumption of the Griffon v the Merlin while in cruise mode.

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## Piper106 (Jun 3, 2016)

As I recall the changes to fit the Griffon engine into a D model Mustang and then repositioning other components to restore center of gravity are fairly significant. Could that change even have been made on a airplane that needed to remain combat capable???


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## FLYBOYJ (Jun 3, 2016)



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## Wildcat (Jun 3, 2016)

Instead of fitting a Griffon to a Mustang, just build the CA-15

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## jimh (Jun 4, 2016)

Jets were on the way! 

Jim

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## nuuumannn (Jun 4, 2016)

Modifying the Spitfire with the Griffon didn't take much change at all; the first aircraft was Mk.IV airframe DP845, which, fitted with the Griffon IIB became the prototype of the Spitfire XII and was test pilot Jeffrey Quill's favourite aircraft. This was the machine Quill provided for the infamous 'fly-off' at Farnborough, in which Arnim Faber's Fw 190, a Hawker Typhoon and a Spitfire were to be put in the air against each other. The Spit was to be just an ordinary production machine to demonstrate the other two aircraft's superiority to it, but Quill took DP845 and caned the pair of them, causing dignitaries present to sit up in alarm; it got the Griffon engine Spit into production. Read Quill's excellent book Spitfire, A Test Pilot's Story for more.

The Spitfire XIV, fitted with a Griffon 65, the two-speed, two-stage Griffon was based on the Spitfire Mk.VIII airframe, so modification of standard production aircraft was initially carried out, as it had been with the Merlin 45 installation in the Spit II to produce the V and the Merlin 61 in the Spit V to produce the IX; the first production Spitfire XIIs were actually Mk.V airframes.

There were proposals to install a Griffon in the Mustang, but it was to be an almost entirely new aircraft; it was a Rolls-Royce proposal named (unimaginatively) the Flying Test Bed and the engine was to be mounted above the wing and aft of the cockpit, which was repositioned forward of the wing. A full scale mock up was constructed using Mustang I AM148's wings and rear fuselage. Info here from the War Thunder gaming site, but it gives images and a line drawing:

FTB Mustang - Suggestions


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## Shortround6 (Jun 4, 2016)

Building a few would be no great trick, building hundreds is a *great* trick. AND the questions include _when_ in addition to how many. 

First production MK XII Spitfires show up in the fall of 1942, but the Griffon II engine they use is a single stage engine and while the power down low is very good power at altitude is not so hot being only a bit better than a Single stage Merlin. 
What is going on at this point in time is that the experiments with the two stage Merlin in the Mustang which offers _about_ the same power thousands of feet higher are starting, orders are being placed before testing is done and Packard is just starting production of two stage Merlins. 
Now as an indication of timing Jeffery Quill flew a Prototype Spitfire with two stage Griffon on 20 January 1943 but it took until October 1943 for the first production machine to fly and until Dec 1943 for it to enter squadron service. 
At this point Packard is building 450-689 two stage Melrins per month (and will build over 1200 in March-44) and North American in building 284-332 Mustangs per month and will build 482 in March-44. 
There is NO Griffon production line in the US (or Canada), it will take around a year or more to set one up and it will take another 6 months to get production up to triple digits. 
Shipping engines from England to the US is pretty much a non-starter. Griffon production is very low and the shipping time is measured in weeks if not months. Best case for Griffon Mustang production is the Dallas Plant (maybe, it only built 3 types of aircraft although in huge numbers) as it is only a few hundred miles from the port of Houston. 
Now are the performance advantages of a Griffon Mustang going to outweigh the production disruption of introducing it and can it be introduced in service _soon enough_ to have any real effect on the progress of the war? 

As an unknown in planning you have the progression in fuel which allowed both the Merlin and Griffon to go from 12lbs boost to 15/16lbs then 18lbs and then to 21 and 25lbs boost which allowed the Merlin to keep increasing in power to "match" the Griffon if allowed to use 3-4lbs more boost. 
In other words if the Fuel had not improved and boost had been limited to say 12-15lbs more effort might have been made to build and introduce the Griffon engine to more types of aircraft. But the increased boost levels allowed increases in performance with little or no disruption in production.

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## tomo pauk (Jun 4, 2016)

Stick the water-injection kit on the 2-stage Packard Merlin already in late 1943/early 1944, and the Mustang goes 470+ mph?


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## Glider (Jun 4, 2016)

Why not just install the Merlin 130 from the Hornet. You get over 2000 hp and installation would be pretty straightforward


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## Shortround6 (Jun 4, 2016)

Timing??
Merlin 130/131s don't show up until some point in 1945.

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## Graeme (Jun 4, 2016)

Stick to the Merlin. Mrs Florence Edgar doesn't wanna be retrained on the Griffon. Just wants the war to end and go home.

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## Glider (Jun 4, 2016)

Shortround6 said:


> Timing??
> Merlin 130/131s don't show up until some point in 1945.


The prototype Hornet was flying from around mid 1944 so its not as silly an idea as it first seems. Of course its behind the Griffon in the development cycle, but not by as much as most people think. The significant changes to the P51 to fit the Griffon would probably take longer to design, test and implement.
The biggest problem would be the change to the production priorities of Rolls Royce at a time when the RAF didn't need better aircraft as the jet was clearly the way ahead.


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## Shortround6 (Jun 4, 2016)

There were quite a few changes to the 100 series engines compared to the under 100 MK numbers. Stronger crankcase, the new end oiling system for the crankshaft, overhung 1st stage in supercharger, stronger valve springs in addition to minor stuff like relocated accessories, the new down draft intake system and SU fuel injection system. 
They might very well have been flying prototype engines in 1944 but production engines had to wait for 1945.


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## Glider (Jun 5, 2016)

No one is trying to pretend that there no or few changes needed to install the Merlin 130 into a P51. All I am saying is that the changes would be a heck of a lot less than trying to fit the much bigger and heavier Griffin.
As for timescales I stand by my view that had there been an urgent need for the Hornet the Merlin 130 would have been available sooner, plus the time needed to alter the P51 to cater for the Griffin would be substantial.


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## Glider (Jun 5, 2016)

Graeme said:


> Stick to the Merlin. Mrs Florence Edgar doesn't wanna be retrained on the Griffon. Just wants the war to end and go home.
> 
> View attachment 345247


I wouldn't bet on that. A lot of women thrived on the money, freedom, friends and independence that war work gave them

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## alejandro_ (Jun 5, 2016)

> Now are the performance advantages of a Griffon Mustang going to outweigh the production disruption of introducing it and can it be introduced in service _soon enough_ to have any real effect on the progress of the war?



I think this is the most important issue. Production of Griffon engines was never that high, and replacing the Merlin would have caused a huge disruption. It took quite a time to supply Spitfire Mk XIV in good numbers to RAF.


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## wuzak (Jun 5, 2016)

Glider said:


> Why not just install the Merlin 130 from the Hornet. You get over 2000 hp and installation would be pretty straightforward





Shortround6 said:


> Timing??
> Merlin 130/131s don't show up until some point in 1945.





Glider said:


> The prototype Hornet was flying from around mid 1944 so its not as silly an idea as it first seems. Of course its behind the Griffon in the development cycle, but not by as much as most people think. The significant changes to the P51 to fit the Griffon would probably take longer to design, test and implement.
> The biggest problem would be the change to the production priorities of Rolls Royce at a time when the RAF didn't need better aircraft as the jet was clearly the way ahead.



I think the V-1650-9 in the P-51H was basically the same as the Merlin 130/131 in the Hornet.

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## wuzak (Jun 5, 2016)

alejandro_ said:


> I think this is the most important issue. Production of Griffon engines was never that high, and replacing the Merlin would have caused a huge disruption. It took quite a time to supply Spitfire Mk XIV in good numbers to RAF.



Indeed, production was king.And Griffon production was barely getting started.

So you have to pick and choose where you use the motors.

As to how the Mustang could have received Griffons, one of the suggestions for the Mustang X program could have been adopted - bring the airframe over to the UK and have Rolls-Royce fit the Griffon at a modification depot.


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## wuzak (Jun 5, 2016)

pbehn said:


> The Spitfire was a short range absolute high performance machine, fitting the Griffon engine kept it at the front in performance. For the P51, it relied on the low fuel consumption of the Merlin while cruising to rendezvous point and on station as an escort plus the trip home coupled with its prodigious performance on max boost in combat. I suspect that the Griffon would have made it slightly faster with a slightly better rate of climb but it would have used much more fuel while cruising due to increased swept volume and increased drag due to weight and frontal area. A Griffon powered P51 would outperform a Merlin engined one in almost every area except the one that made the P51 a game changer and that is its range.
> 
> The answer to the question lies in the fuel consumption of the Griffon v the Merlin while in cruise mode.



The question I have about that is whether the cruise speed using the Griffon would have compensated for the lower endurance and sill have ended up with similar range?

Possibly not the greatest for bomber escort though.


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## pbehn (Jun 5, 2016)

wuzak said:


> The question I have about that is whether the cruise speed using the Griffon would have compensated for the lower endurance and sill have ended up with similar range?
> 
> Possibly not the greatest for bomber escort though.


I was discussing purely from a theoretical point of view. The Griffon dry weight was approx 150Kg more than the Merlin. To get 150Kg to 30,000 ft and keep it there uses power, the Griffon would have to use less fuel per HP than a Merlin just to complete the same mission. I understand what you mean, it is possible that the Griffon could cruise as economically as a Merlin but this only applies to the outward and homeward part of the mission, while escorting bombers it is simply a question of gallons per hour and I am sure the Griffon consumed more fuel, certainly on max boost/power it would. I read a discussion about Reno racers fitted with Griffons and the effects are marginal more power but more weight and frontal area means it is a matter of choice, I suspect the fastest is the one whose owner is prepared to take the biggest risks of a blow up. Also for a time contra prop Griffon engines were available when the Avro Shackleton was retired.

The P51D with max fuel load was at the limits of safety, adding the extra weight of the Merlin may just have been a mod too far and a complete re design required.


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## wuzak (Jun 5, 2016)

pbehn said:


> I was discussing purely from a theoretical point of view. The Griffon dry weight was approx 150Kg more than the Merlin. To get 150Kg to 30,000 ft and keep it there uses power, the Griffon would have to use less fuel per HP than a Merlin just to complete the same mission. I understand what you mean, it is possible that the Griffon could cruise as economically as a Merlin but this only applies to the outward and homeward part of the mission, while escorting bombers it is simply a question of gallons per hour and I am sure the Griffon consumed more fuel, certainly on max boost/power it would. I read a discussion about Reno racers fitted with Griffons and the effects are marginal more power but more weight and frontal area means it is a matter of choice, I suspect the fastest is the one whose owner is prepared to take the biggest risks of a blow up. Also for a time contra prop Griffon engines were available when the Avro Shackleton was retired.
> 
> The P51D with max fuel load was at the limits of safety, adding the extra weight of the Merlin may just have been a mod too far and a complete re design required.



The P-51D with full rear fuel tanks was at the limits of stability, but adding a Griffon up front would move the weight balance forward, so it could be, at least with full tanks, more stable.

(An example of this is the Mosquitoes fitted with the bulged bomb bay for carrying cookies. The MkIV was close to its stability limits, but the MkIX/XVI with the longer and heavier 2 stage Merlins was more stable.)

I also question the increase in frontal area. I think the Griffon would not increase the Mustang's frontal area directly as the fuselage behind the engine would be as large. The area for the radiator duct may need to be increased to cater for increased cooling, but the Mustang's radiator design would have meant that the increase in cooling drag was not as much as the Spitfire's when it went to the Griffon.

As for fuel consumption, the Griffon certainly used more gallons per hour than the Merlin. But in terms of hp/lb/hr they were similar. Simplistically, at cruise rpm and boost the Griffon would be using more gph but also making more power, which should translate into greater forward speed.

I think the reason North American shied away from doing a Griffon Mustang variant was that they felt too much modification was required. From strengthening the airframe to cope with the new engine, to a redesigned cooling system. ANd probably a lot of other small bits and pieces that would have to be considered.

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## Ascent (Jun 6, 2016)

So basically, technically feasible but the gains wouldn't be worth the effort.


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## pbehn (Jun 6, 2016)

Ascent said:


> So basically, technically feasible but the gains wouldn't be worth the effort.


Or the loss of range would make it counter productive. As others have said the whole scene was overtaken by jet engines and increases in power due to improved fuels/supercharging. The Merlin 130 produced over 2000BHP which was the power output required of the Vulture/Sabre intended to replace the Merlin.


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## GrauGeist (Jun 6, 2016)

The F-82 pretty much solved the speed/range need.

Although it arrived in the final days of the war, it was still available much sooner than a Griffon-modified P-51 would have been.


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## Shortround6 (Jun 6, 2016)

The V-1650-9 used in the P-51H was the equivalent of the 100 series Merlin, at least in power rating. Different carb/fuel injection and different cooling (the Hornet used reverse flow cooling like the Mosquito) and perhaps some other details/accessories.

AS an indication of overlap and delivery times June of 1944 sees the P-51D showing up in Quantity in the 8th AF (Production had started in March). The British are still using 5 squadrons of Allison Mustangs in Europe and June 30th sees a contract for 1000 P-51Hs placed.
In Nov of 1944 only 8 (eight) P-51s with Merlins have shown up in the Pacific area (Not China) First P-51H is delivered in Feb 1945 (?) and only 370 are completed by VJ day. Jan 1945 had seen the California NAA plant build 570 Mustangs and Dallas build 728 Mustangs.

It comes down to _when_ the proposal is made, which version of which engine (Merlin or Griffon) is offering or promising what for power at that particular point in time and how soon either engine can be in production in the numbers needed. A few hundred Griffon powered P-51s showing up in July/Aug of 1945 would have made no difference to the war. Even a few hundred showing up in March/April of 1945 would have made no difference in Europe and the project would have had to start in the spring of 1944 if not before.


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## GrauGeist (Jun 6, 2016)

I disagree...there is not much room under the cowl on a P-51D

The Griffon had a 6% larger frontal area, especially the heads due to the 36% larger displacement.

Add to that, the additional weight of the engine, and you'll have some work to be done, in order to get it to fit and perform as well as it does with the Merlin.


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## grampi (Jun 6, 2016)

Shooter8 said:


> The P-51H was certainly the fastest prop plane in service in WW-II and it could run down any other plane with out question, BUT it was far from the best fighter plane of the war. But that is a topic for some other thread.



It probably wasn't the best fighter of the war, but saying it was far from the best is a stretch...with a good pilot it could hold it's own against any prop driven fighter, and better most...


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## Shortround6 (Jun 6, 2016)

Like the bit about synchronized 20mm cannon. I just don't know where they were supposed to come from as the basic mechanism of the Hispano didn't synchronize very well (like not at all) and no, using electric ignition is _not_ going to solve the problem. 
Very low rates of fire and/or blowing your own prop off are not exactly improvements over wing mounted guns.


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## wuzak (Jun 6, 2016)

Shooter8 said:


> Quote "I think the V-1650-9 in the P-51H was basically the same as the Merlin 130/131 in the Hornet."
> Well no it was not the same engine at all. There were huge differences in the American made Merlin and the R-R made Merlin.
> The Hornet's engines made 2050-2080 HP at war emergency power and about 1600 HP at Take Off Power, but well after the war in 1946-7.
> The V-1650-9 in the Mustang made 1595 at Take off Power, but made 2218 HP at WEP. This last is a huge difference and can only be explained by some mechanical difference between the two engines. I have been told by pilots I met at the Oshkosh show that it was better quality pistons and or rods, but I have not been able to find documentation to explain the differences.
> The P-51H was certainly the fastest prop plane in service in WW-II and it could run down any other plane with out question, BUT it was far from the best fighter plane of the war. But that is a topic for some other thread.



The main differences were the supercharger drive system, the carby and the fact that the V-1650-9 used ADI and the Merlin 130/131 did not.

The Merlin 130/131 were being built late in the war. Like other 100-series engines. (of which the V-1650-9 was one). The big change with the 130/131 was the downdraft carburettor.


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## wuzak (Jun 6, 2016)

Shooter8 said:


> The Spitfire XIV was a dog with the griffon engine. Look how long it took them to sort out the numerous problems it had. Over one year between first flight and first kill in semi-operational service. They had to add huge area to the vertical stabilizer to counteract the loss of stability caused by the new prop. All in all, it was a handling nightmare and poor gun platform due to snaking.
> P-51 Conversions with Griffon engines have either fitted entirely new rudders/stabes and or tail planes, or used the P-51H rudder/stabe. Several have also fitted entirely new wings to correct the Center of Balance problems to avoid adding weight to the tail end.
> While there was an on going search for more performance in every nation at war, the practical limits of propulsion had reared it's ugly head and made designer's life very hard. There were no easy solutions to the myriad of problems.



Not you again.

The Spitfire XIV was far from a "dog". In fact, it was considered by many to be the best piston engine fighter of WW2. Including Eric Brown.

The P-51B was also not the most longitudinally stable aircraft, and the P-51D didn't fix that. The P-51H got increased fin/rudder area to cope with increased power and the stability issues caused by the bigger prop.

As for taking a year for first flight to first kill, I would think that to be not unusual. The fact is that the XIV was delayed by a few factors, including the need to continue production of existing marks of Spitfire - the IX and VIII. Then the squadrons have to work up on the aircraft and then they have to actually have the opportunity for a kill - can't get a kill when there is no enemy aircraft in your operational area.

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## Shortround6 (Jun 7, 2016)

wuzak said:


> The main differences were the supercharger drive system, the carby and the fact that the V-1650-9 used ADI and the Merlin 130/131 did not.
> 
> The Merlin 130/131 were being built late in the war. Like other 100-series engines. (of which the V-1650-9 was one). The big change with the 130/131 was the downdraft carburettor.



It seems both had the stronger castings, the end to end oil flow crankshaft and the same valve fittings (springs?). The V-1650-9 used gear ratios for the supercharger that were identical to the Merlin 110-114 in low gear and only slightly off in high gear (same gear ratios as the V-1650-3).

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## wuzak (Jun 7, 2016)

According to Lumsden, the -9 had the same gear ratios as the -3. That is 6.39:1 in Lo and 8.095:1 in high.

It looks like the 130/131 had 5.79:1 MS and 7.06:1 FS.

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## Milosh (Jul 1, 2016)

There wasn't enough Merlins to go around either til Packard began building Merlins.


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## stona (Jul 1, 2016)

Why bother? The Griffon never equaled the Merlin's specific output and other issues, particularly at altitude, have already been mentioned.
The Eagle might have been a better option for development, but then came the end of the war.....and jets.
Cheers
Steve


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## drgondog (Jul 1, 2016)

There was not enough room forward of the P-51B/D/H bulkhead to accommodate the structure, ammo storage and the Hispano II and still manage the plumbing up front. There was no tactical necessity to replace the 50 caliber guns in the wing with 20mm. There were no bombers to shoot down, there were no fighters or bombers 'immune' to 50 caliber API. There would have been a drag penalty and synchronous fire through the prop would have introduced another complexity as well as a dramatically reduced rate of fire.

The P-82 was on the drawing boards beginning January 1944, with the same engine (essentially the 1650-9) but problems with the 1650-9 hindered first flights for both the P-51H and XP-82. The XP-82 ran 465 mph at 67" at 22,000 feet. Projected performance at 90" was approximately 490+mph with full internal combat load - and it had not only all the armament the P-51D/H had, but also a design center pylon to add 8x50 caliber in the pod but would have been easy to put 4x20mm if the need was contemplated.

There was not enough perceived benefit to re-design the Mustang to accommodate the Griffon - which would have taken a P-51H like effort to sort out the firewall/fwd design, change the moment arm in aft fuselage from cg to horizontal stabilizer center of pressure, change the empennage to compensate for the additional Torque, change the structure internally to achieve additional loads - both torsion and tension/compression in the longerons/bulkheads and shear panels.

Simple answer to Griffon - yes it could have been installed but totally impractical given the changes required for such little performance boost over the 1650-9.

Simple answer to 20mm - yes and easy to do but performance penalty due to additional drag argued against it.

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