The Re.2005 VDM situation is crazy

[FeetPics]

It seems you are just applying a rule of thumb to make a gross calculation that does not line up with real world observations.

Here is a real tested example. Let’s use your math to see how it stacks up.

By your estimation,

@Coffee Fanatic

v2^2/v1^2 = (720 km/h)^2/(650 km/h)^2

(380 mph)^2 / (364 mph) ^2 = 1.089

That means that by your estimation, the P-51 should only take 1.089 times it’s normal engine power to increase its top speed from 364mph at sea level to 380mph at sea level. This means we would arrive to the correct engine power for 75 inches of manifold pressure by multiplying the 67 inches manifold pressure number by 1.089.

V-1650-7 67" Manifold Pressure = 1500hp
V-1650-7 75" Manifold Pressure Theoretical = 1500 x 1.089 = 1633.5hp
V-1650-7 75" Manifold Pressure Actual = 1800hp

The difference between the power required in your calculation and the actual power required is 167 horsepower. It significantly underestimates the power required to increase the top speed of the airplane.

Your estimate is that the Re.2005 would experience around an 11 percent increase in top speed from a 24% increase in power. The P-51B in real life only achieved a 4.3 percent increase in top speed from a similar increase in power. This is in spite of being an exceptionally low drag airframe with it’s laminar flow wing.

[Coffee_Fanatic]

Issue is not in the math, but the fact I made quite an embarsssing calculations error:

As velosity is precent both in equation of drag and equation of thrust, the power required is relative to cubes of velocities, ie.

P2/P1 = (v2 x D2)/(v1 x D1)
= v2^3/v1^3
P2 = v2^3/v1^3 x P1

For P-51 this would be (taking 1630 hp with 67" msnifold pressure as per this document

P2 = (384 mph)^3/(366)^3 x 1630 hp
P2 = 1854

For Re.2005 this would be:

P2 = (720 kmh)^3/(650 kmh)^3 x 1450 hp
P2 = 1970 hp

Which overshoots power available quite a lot. Now there are a lot of factors that might explane this, most likely beign the new engine having considerably better high altitude performance.

Hope you guys in Rome find some raw data.

[D0N_SALVAT0RE]

hoping that the usual diligence of cultural heritage and the rest of every other national institution does not get in the way
what a beautiful country.

[FeetPics]

I will have to compare the power figures of the Series 0 engine vs DB 605 ASM engine when I get home.

However I think that no matter what way you end up looking at it, the likelihood of Re.2005 making 730kph off of only a 300hp power increase is slim to none.

The high altitude capable DB.605 did not go into service until 1944…and from the looks of things it is not until the middle of 1944 if the date on this document is correct.

[FeetPics]

Yeah it is basically impossible that the Re.2005 VDM was able to make 730kph top speed at 7300m.

These are the power curves for different variations of the DB.605 and various supercharger setups in-game. At 7300m, the DB.605 in the Series 0 develops 1475hp. This skews the power required function a little bit higher than your initial estimate. In order to make 720kph at 7300m, the DB.605 would have to be developing 2005 horsepower.

No DB.605 variant, including the 1.98 ATA power setting on the Bf.109 K-4, is capable of producing 2000 horsepower at 7300m. The most optimistic scenario in regards to top speed is that the VDM was equipped with the DB.605 ASM; however this would still place it 326 horsepower required in order to reach 720kph.

Due to the fact that we know the relative power ratios between the engines, we can actually plug the values in which will generate a reasonable estimate for what the top speed should be.

DB.605 ASM Calc. (x = new top speed)
1675/1475 = 1.13 <— This will be the ratio of P2/P1
x^3 / 650^3 = 1.13
x^3 = 1.13 x 650^3
x^3 = 310,326,250 <----- Cube Root for X
x = 677 kph

If the plane did not use the DB 605 ASM and only used to engine/supercharger arrangement that was found in the Bf.109 G-6, then the top speed would work out to 667 kph. This supercharger arrangement in-game would probably be preferable to the high altitude supercharger as it produces more power at all altitudes below 6,700m. The greatest spot of disparity is an 18% power difference at 5,900m.

Using the same set of mathematics but substituting 650kph for 630kph (my tested top speed with 0% radiator and WEP on the in-game Re.2005 Series 0, one would expect at new top speed of 665kph at 5,900m.

[The_diddler2]

i did my test with improvement the 495 give to the re2005 and the top speed at 7056m was amazing

[LafayеtteGPool]

Spoiler

Use IAS? Need true air speed TAS.

Then.
7km height and 650kmh TAS calculation.

Re.2005-0 - 1245hp at 2600rpm(historical limitation)
DB605AM(powerplant from Bf.109G-6) - 1462hp(WEP)
1462/1245=1.17
x^3 = 321 311 250
x = 684.9 kmh

At the same time, it should be taken into account that in War Thunder’s flight model the maximum speed is often limited by the increase in the glider’s drag. The Re.2005 reaches 650 km/h not at 100% throttle, but at WEP. Therefore, the glider has more drag than it should.

Spoiler

In conclusion 720 km/h at an altitude of 7300 m using WEP seems quite realistic to me.

[D0N_SALVAT0RE]

the only time you might have the chance to climb to that altitude is in simulator, and it’s not even a given that you need it, in rb it’s extremely rare to shoot down a bomber that usually operates at that altitude, since I’ve been playing and I’ve played a lot I’ve shot down only two bombers with the normal reggiane, one of which in simulation

[FeetPics]

I have already considered this ahead of time when I was doing the math last night. This makes the assumption that the drag model in-game performs on WEP to match the 2600rpm limited numbers of the first prototype. There is some truth to this but it is not entirely correct.

If this was the case, then we would expect the Re.2005 to only be able to make 613km/h true airspeed at 5,900m on WEP. In-game it makes 630 km/h on WEP which indicates that the in-game flight model is not as hampered by drag as your assumption. However on 2600 rpm limitation it will only make 592 km/h which does indicate that the in-game drag value is too high; it is just not as high as people here assume.

720 km/h is the most optimistic prediction. It would only be feasible if the Italians were ahead of the Germans in terms of supercharger development, or if they were fitting the larger DB603 supercharger to the DB605. As far as I know this is a development that would post date the prototype. And even then we are also assuming that the Re.2005 was much more aerodynamically efficient than the Bf.109G series…so much so that it would have a noticeable top speed advantage over it while also having a significantly larger wing area.

[The_diddler2]

" the 2005 Series 0 achieved a maximum speed of 630 km/h at an altitude of 5,550 meters with its 1470hp engine Considering this performance a 300hp increase might result in a speed gain of roughly 50 km/h or potentially more or less These estimates remain speculative at this stage and serve only as preliminary hypotheses rather than confirmed results for now at least"

let’s take p51h as an example for now it has 1560hp at 100% and 2239hp at low altitude but 1810hp at 4km and upwards so at 5550m with 100% can do 711km in straight line

but p51h with wep 1810hp around 300hp gain from pervious only 100% throttle of 1560hp at same altitude did 753km/h an 42km improvement in same airframe just more power so if we take this example in game and translate it to re2005 we should have somewhat of close gain in speed in exchange of gain power at 5550m so the new fixed re2005 with 300+hp gain from upgraded engine and to make final conclusion we should expect similar gain in speed exchange in power

[Nufeneguediz]

Remember that the pic you used is using data feom early MM494 which had an engine in bad shape and couldn’t use WEP. Probably even when at 100% it wouldn’t develop all the hp it should have so the serie 0 should definitely perform better than this.

[Nufeneguediz]

It depends if they give VDM the same efficiency as the Piaggio propeller. In theory the VDM should be more efficient so we’re not just talking about a raw 300hp, even though that should be the bare minimum.

[FeetPics]

I tested the plane with and without WEP and at the 2600rpm limitation. In WEP, it is faster than what the document claims by 11 kph and without WEP it is slower by 20 kph.

Historically speaking, the DB 605 was a fairly problematic engine that had a whole lot of teething issues that were not just limited to the Italian version. It appears that the Bf.109G with the DB 605 w/ larger DB603 supercharger was not even test flown until late summer of 1943.

The only way to make the 720kph number even plausible is if you assume that the Germans prioritized development of the Italian airframes, provided them with an engine that their own domestic aircraft manufactures would not have access to until a good bit later, and that the Italians had also developed an airframe with extremely low drag ratios relative to it’s size; i.e the Re.2005 has a wing with laminar flow design and the production capability and design considerations to have the same return of investment as the P-51. And that they were capable of equaling late model P-51 Mustangs around a year before it went into service…all the while utilizing inferior fuels.

And it is important to keep in mind that the only thing that supports this claim is that a test pilot allegedly said that the plane reached 720km indicated airspeed at 7300m. The indicated airspeed is an important note because 720km at 7300m is going to be equal to over 1000km of true airspeed; which would make the Re.2005 the fastest propeller driven airplane in the world by an extremely wide margin.

So what is more likely? Italy developed the worlds fastest propeller driven fighter in 1943 and Germany decided to never to produce it. Or that something was lost in translation somewhere along the lines and secondary source authors never bothered to evaluate the 720 km/h claim?

[D0N_SALVAT0RE]

As others have already pointed out in the past few days, this topic was not created to have a discussion on feasibility and go offtopic, but to collect the various data of the aircraft in question so that the developers can make a correction. It would be more correct to move the discussion on who is right and who is not to another topic, so as not to clog up this one and risk ending up in offtopic.

[D0N_SALVAT0RE]

the challenge of who has the longest in historical matters, although interesting at least in my humble opinion, is not part of the current discussion

[Nufeneguediz]

The MM.495 just got a DB605AM, not the one with the bigger compressor. We are quite sure about it.

I wrote the 720km/h performance as that’s the only number we have rn. I don’t want the plane to go that fast if it couldn’t irl and I’m not gonna die on this hill.
My comment was purely on the Re2005 serie 0 performance vs that of MM494: I don’t want to increase confusion on the various prototypes performance. The last thing we need is to give gaijin excuses to nerf even the serie 0 to MM494 levels.

As I think I stated in some comments and in the post, rn the priority is to give the plane the DB605AM and its extra 300hp. After that I’d like to see it get better prop efficiency. For top speed and climb rate idk if we’ll ever get any data so any calculation is welcome.

[paolgand1975-psn]

Really interesting work on the numbers and test results so far — nice job! Just one small note though: I’m not sure if you guys ran the tests the same way they were actually done back in the day. The method used at the time was pretty specific, and all the major air forces followed roughly the same procedure — Luftwaffe, Regia Aeronautica, RAF, USAAF, you name it.

They didn’t just climb up to 7 or 8 km and see what speed they got in level flight. The usual process was to climb above the target altitude, usually by about 500 to 1000 meters, then make a shallow dive down to the exact test height — say around 7,000 meters — and let the plane build up to top speed naturally. Trying to accelerate to max speed in level flight at those altitudes was almost impossible, so the dive was standard practice.

Once they hit the test altitude, the pilot had to hold the plane steady and fly straight and level at full power. Then came the actual measurements: several passes along a fixed course, always in both directions to cancel out wind effects. People on the ground — using theodolites, cameras, or timing gear — would measure the time between markers, and from that they’d calculate the average true airspeed. The final speed figure wasn’t just what the cockpit gauge said — it was corrected for air density, temperature, and pressure.

So if you want to do it properly in the sim, try to follow the same steps. Don’t just climb and read the speed indicator. Go a bit higher, dive gently to your test altitude, stabilize, and make a few straight passes in both directions over the same line. Average the results, and you’ll get something much closer to how the real tests were done back in the day.

I know it’s not exactly the same thing, but I actually used the same way years ago trying to hit the mythical Mach 2.2 in the F-104S in level flight — and it worked!

[The_diddler2]

“for now let’s focus on finding and making bug report on db605am because this is more than enough to make great change in flight performance extra 300hp + are big upgrade” and then we can do the vdm with better prop efficiency and so on"

[The_diddler2]

lets take at what smin1080p said

The Re.2005 VDM situation is crazy

Hey The report combined multiple aspects, which is something we always advise against doing for this very reason. Each issue should focus on one individual matter at a time, not combine multiple. The sources included were insufficient to provide any changes in performance. If the engine is incorrect, then a report can be made solely focusing on that aspect and with as many sources as possible (not using just these same ones) to show this. It will need to include some sources relevant to the …

[LanceLynxx]

I think there’s not much use speculating anything without having the proper sources. And from what I’ve read, Regianne’s archives are closed for the time being.

I did find a very in-depth book on it, interesting things to note

m.494 was cursed with several issues causing it to crash several times.

It also had a faulty engine, and according to test pilot De Prato, rumor was that FIAT sabotaged the DB 605 engines meant for Macchi and Reggiane by delaying deliveries (possibly also sabotaging the engines themselves)

First crash was in 10 May '42, on the first flight, due to a landing gear leg not deploying properly requiring a belly land which consequently a prop strike, and possibly damaged the engine further.

It also didn’t help that m.494 Piaggio propellers were also faulty and didn’t maintain constant RPM, causing instability and possibly engine damage.

July 18 '42, De Prato (test pilot) tries to ferry m.494 to Guidonia but has to abort due to engine malfunction.
July 20 '42, they ferry m.494 to Guidonia, without completing landing gear tests to avoid missing the trials, and without a seal around the engine firewall, which caused exhaust to leak into the cockpit.

On the first take-off at Guidonia, before even clearing the airfield, the engine vibration caused the DB 605 water coolant loop tubing to crack and leak boiling water on De Prato’s leg, and overheating the engine, the only one they had, causing him to crash land m.494 yet again

July 20, during dive tests, the landing gear fairings detached when approaching 900 kph, damaging the aircraft, resulting in m.494 being sent back to Reggiane for repair and reinforcement

Semptember 23, there was yet another crash caused by engine ceasing to function during landing approach, resulting in yet another crash landing and prop strike, during the Guidonia trials, piloted by colonel Angelo Tondi

from October onwards, m.495 is sent to Guidonia and partakes in tests with the old prop, the VDM prop, and a new engine, requested to be tested by Germany. Sadly, no performance data is included.

It does specify:

1. The engine is a DB 605-A1 with MW-50 water-methanol injection
2. Different compression ratio
3. German VDM prop
   
   

Important to note that the exact sentence regarding the 720 kph claim in level flight is “a German pilot assured that the anemometer’s needle touched, in horizontal flight, the 720 km/h mark”

Anemometer is the airspeed indicator. It does not say if it is indicated or true. It also doesn’t state the altitude. But the common sense here is that it is TAS. But alas, it’s not performance data.

m.495 also swapped the 12.7mm wing-mounted machine guns got swapped for MG151 20mm cannons

m.495 was later taken by Germany to Reichlin Experimental Center.

in Guidonia Experimental Center, in the serie-5 trials, (does not specify if it’s m.494, 945, or any mods of both) from the evaluation commission:

Serie 0 in game features a DB 605 A with 1310 HP at max power, and 1477 HP WEP/Takeoff, so using the Serie 0 to compare m.494 (mod 1. and mod.2) and m.495 is pointless, because Serie 0’s engine is nowhere as anemic as m.494 or 495 regardless of the VDM or not.