why does 109G10 climb so bad??

[Nashwan]

I modified those charts to demonstrate you the effect of the supercharger design. The blue line connects both critical altitudes. Now i draw a horizontal line from the AH critical altitudes, this gives me now the power with the new critical altitude. In case of the climbrate i can go down vertically (green line) or in case of the speed i draw a parallel line to the given curve.

That's the part I don't understand.

How does connecting the MS critical alt and the FS critical alt give you the power available to a differently geared MS at a different alt?

Regardless, you can look at the power charts yourself

Griffon 61 (with modified MS, by the look of it)
http://pub47.ezboard.com/fallboutwarfarefrm1.showMessage?topicID=754.topic

Lots of Russian figures, including a Spit XIV and what looks like an un-rammed Griffon
http://pub47.ezboard.com/fallboutwarfarefrm27.showMessage?topicID=282.topic

Any further details avaiable for the charts of butch2kīs page? Aircraft description, weapon load, surface condition, speedcorrection and so on?

If you compare the chart for the modified MS gear Spit XIV on Butch's page with the A&AEE figures, you will see they are almost exactly the same for FS gear.

That suggests the plane condition, ammo load etc are as set out in the A&AEE report.

[Wmaker]

Viper that 109 HO pic looks very cool! Where did you get it?

[niklas]

Nashwan, MS gear and  FS gear are two independent choosen gear ratios.
In the FS gear (high altitude) the engine power output, though using same MAP and RPM, is lower than for the MS gear.

Letīs take an example, a fighter that should have the critical altitudes of the charger at 5000ft and 20000ft, for both 2.0 ata / +18lb. In 5000ft atmosphere pressure has dropped to 0.84kg/m^3, so you need a compression ratio of 2,38:1 to reach 2.0 ata. in 20000ft atmosphere pressure has dropped to 0.47, so you need a compression ratio of 4.25:1 to reach 2.0ata.

Logically you need more power in the FS gear due to your higher compression ratio. This is the main reason why your engine has less power avaiable to drive the propeller in the FS gear. The problem is that for charger with fixed gear ratios, you have only 1 altitude where your charger runs optimal. The speed of the charger is constant also in other altitudes as long as your engine rpm is constant, this means you compress in my example near ground the air with a ratio of 2,38 to 2,38ata, or in 10000ft you compress the air with a at.p. of 0.70 and 4.25:1 to ~3ata. Way too much.

Letīs assume the engine produces 2000hp in the MS gear at 5000ft, and 1500hp in the FS gear at 20000ft. Now you want to change the first gear in a way that you reach 2.0ata in 10000ft with it. How much power will you have in 10000ft then? Logically it will be somewhere between 2000hp and 1500hp. Now what i did was a simple linear interpolation between those 2 points.

Check this picture. I modified now the engine chart that was made for speed (it includes ram-effect). Here i went the opposite way from a real griffon to the AFDU griffon. Check first the bottom green line. It gives you the bhp near ground when you would use the FS gear at sealevel. Connecting the critical altitudes gives me again the maximum bhp avaiable for any cricitcal altitude. So when i choose only 5k, my bhp goes up to way over 2000hp.



now it shcould be clear.

about the other docs. They basically say that the spit14 could reach 4800-5000ft/min with only 1850hp near ground. This improves the power to weight ratio advanatage of the G10 even more. And the question becomes even more valid why the G10 climbs poorer.

niklas

[HoHun]

Hi Niklas,

I think you have a point with regard to the Me 109G-10's climb rate. Here's an extrapolation of the initial climb rate for the Me 109 types I did a while ago:

Basis:

Me 109F-1: 2728 kg, 1175 HP, climb rate 18.5 m/s

Extrapolation:

Me 109F-4: 2890 kg, 1350 HP, climb rate 20.9 m/s

Extrapolation, 10% drag added over Me 109F-1

Me 109G-2: 3100 kg, 1475 HP, climb rate 21.2 m/s

Extrapolation, 10% drag added over Me 109G-2:

Me 109G-6 (MW50): 3320 kg, 1800 HP, climb rate 24.8 m/s

Me 109K-4: 3362 kg, 2000 HP, climb rate 27.8 m/s

Drag is not a major factor in the climb due to the low speed, it requires about 280 HP for the Me 109F-1 and about 340 HP for the Me 109K-4 to overcome.

If for example I'd add another 10% of drag to the K-4 numbers to account for the G-10's poorer aerodynamics, that would still leave it with an initial climb rate of 27.3 m/s (compared to 27.8 m/s).

The calculated value of 27.8 m/s equals about 5500 fpm, which matches the published figures for the Me 109K-4 quite well, so I'm confident my calculations are good enough to give a coarse impression of the Me 109 variants' climb rates.

A climb rate of just 4600 fpm (23.4 m/s) seems a bit low for a 2000 HP Messerschmitt. That's even below my calculation for the 1800 HP Me 109G-6 with MW50 (24.8 m/s).

Regards,

Henning (HoHun)

[Fishu]

Originally posted by funkedup
Fishu is WW2Mod for GR ready yet?  

at this rate.. never :I



Karnak,

well, at least they got their worst spit IX manufactured by highest bidder
thats the whole issue here, not who gets the best model, but whos models are best manufactured.

Ps. happen to remember the time when Spit IX was nearly a spacecraft?

[Wmaker]

Originally posted by funkedup
You are considering only power and weight.  Thrust and drag are important too.  Have you ever seen a G-10 up close?  It's skin is covered with bumps and protuberances and many unstreamlined features, which must cause a lot of drag compared to the quite smooth features of the Spitfire.

I agree that Spitfire is easily more drag-free design. I also agree with Ho Hun that at speeds between 300-200km/h drag is nearly a non-issue...we are VERY far from top speeds of these planes here.



According to my sourches (Daimler-Benz performance sheet) DB-605D with MW-50 could put out 2200hp at sea level.

[Pongo]

Originally posted by Daff
"then the stupid twits wrecked it...."

Yeah and that stupid twit was Mark Hannah, who died in hospital later and him and his father has been one of the best promoters and restorers of WW2 aircraft...what a bunch of twits.

Daff

Doenst matter who it was. It is stupid to fly a one of a kind historical treasure.

[Nashwan]

Okay, wrote a long reply and the board lost it

Niklas, your method doesn't take eficiency into account.

FS gear on a Griffon turned the impeller with tip speeds faster than mach 1. Got to be less efficient.

According to your method, the Spit XIV with 1850hp at sea level is only 8 mph faster than the Spit LF IX, with 1500 hp at sea level.

23% power increase, 2.5% speed increase.

According to the tests you don't believe, that 23% power increase gives 8% speed increase, which seems closer to the mark.

Your method should also be applicable to the Spit LF and HF IX, as iirc the Merlin 66 and 70 differed only in supercharger gear ratio.

If you apply your method to the LF and HF, it doesn't work. Climb is out, and speed is wrong as well.

In fact, speed is quite close at medium altitudes, but gets increasingly worse the higher or lower you go, suggesting efficiency at the extremes is the problem.

Your method would also give the Spit XIV lower climb rates at low level than the Spit IX, only 4500 ft/min (the critical altitude in climb was just over 9,000ft, not the 8000ft you used.)

In fact, there is a difference between the Spit prototype tests and the later ones, the raising of critical alt has made a difference, just nowhere near as large as you are suggesting.

[Nashwan]

Sorry, just had a look at the speed approximation again.


You hve used the wrong critical alt for the Spit, the later chrts show just over 12,000ft. I know you are calculating for AH, but just for a minute apply it to real life.

Your figures suggest that if critical alt is raised to 12,000ft, speed at sea level will be down to around 335mph. Is that correct?

If so, it implies raising critical alt by 7000ft decreases speed at sea level by nearly 30mph.

The Spit LF IX had a critical alt of 10,800, the HF of 15,400, a difference of 4,600. That decreased speed by about 5 mph.

[wells]

Going by the manifold pressure gauge, it looks like WEP is giving you only 1.8 atm which implies the 605DB engine (1800 hp) for the 109G10.

[niklas]

Do you mean with impeller the supercharger? Why should it be less efficient?  What are the gear ratios? I assume 1:10 and 1:15 or so. I bet even for the MS gear the tips run with more than Mach1. But this is not a propeller, the airflow is from the inside to the outside and not vertical like for a propeller, so it isnīt so critical. In opposite, for a compression this is maybe an advantage. Even the LF test mentions : "These modifications had the effect of raising the supercharger top speed, thus improving the efficiency".

The LF version had a Merlin66 engine that produced with +18ata 1700hp. The report mentions some improvments, so maybe power output was even higher. Gun ports were sealed. Maybe the cooler were also smaller than for the spit14? Maybe the lighter and more compact Merlin didnīt need as much balance from the elevator (less deflection), resulting in a bit less drag? And more than 1300lb less weight (~7100lb, from the graph image) has generally also a minor influence. Anyway, let it be 350mph for the spit14 - no problem here from my side.
Climbrate: The spit14 has at low altitudes roughly 200hp more power. Actually a bit less.  This is 12% more power (actually only 11.7) compared to 1700hp, but it has 13% more weight. So power to weight ratio got worse. No contradiction to my theory, in opposite, climbrates up to 5000ft/min of the spit14 becomes more and more questionable for a "normal" spit14 and favour my theorie that those tests were done with griffons doing 2200hp or even more.

That the spit LF equipped with a lower MF gear ratio (spit 354) was SLOWER  than the Merlin66 equipped spit surprised even the engineers obviously:
".It is a matter of interest that at sea level, Spitfire BS.354 with the RM-9SM engine, although nominally develping 50 B.H.P. more power than the Merlin 66 engines BS.543, is 7 m.p.h. slower, indicating either that the nominal powers were not realized and/or that there was a considerable difference between the drags of the two aircraft."
BUT this DOES confirm my theory. Why does the RM-9SM produce 50hp more power ehh? lower critical altiutde my friend This does exactly confirm my theory!


niklas

[Wmaker]

Originally posted by wells
Going by the manifold pressure gauge, it looks like WEP is giving you only 1.8 atm which implies the 605DB engine (1800 hp) for the 109G10.

According to this profile drawing AH's G-10 has (or should have) DB-605DCM engine.

[Wotan]

By Doc 109, May 2001

The DB605AS was born around the concept that it could be possible to recycle the existing DB605A into a high altitude engine, comparable to the new DB605D. The DB605D needed 2 bulges on the forward edge of the underside cowl due to the slightly different profile of the valve covers.  Otherwise, the engine had similar dimensions to the A version.  The AS and D versions had virtually identical performance ratings as well. This may look weird from our point of view, but there is a rational explanation.

The DB605D was intended to be the sole high altitude version of the DB605 but the program encountered huge delays.  The situation deteriorated to the point that in the spring of 1943, the increasingly desperate Luftwaffe ordered an interim solution to be found. That solution was to install the DB603 supercharger on the DB605A. Performances were almost identical to the coming DB605D. In fact, when the DB605D entered production, the DB605AS continued to be produced as well since it allowed for the recycling of existing engines.

After autumn 1944, DB605D engines were only delivered to factories producing new 109G-10s and K-4s, while the DB605AS engines were delivered exclusively to the workshop and repair centers, which explains why it’s possible to see a G-10 with a DB605AS- it would have been installed during a repair. The DB605AS was not suitable for the K-4, however, since this aircraft relying upon the engine compressor to supply pneumatic pressure for the centerline MK108 cannon (The G-10 still used bottles).

So, from a visual perspective, the general rule is no DB605D= no bulges= no enlarged oil cooler.

However:  A few of the last DB605AS produced (installed on G-14/AS) got the new valve covers from the D version therefore needing the bulges.

To add even more confusion, some G-14/AS got the lower cowl with bulges in order to use the enlarged oil cooler from the K-4/G-10 versions.

Thus, to reiterate:  GENERALLY, there were no bulges on the AS version, but as we've seen, there are exceptions.

Finally, let's not forget the Erla produced G-10 which had a totally new enlarged underside cowl which makes the plane look like a G-14/AS...

Maybe read this too

The 109g10 we have is said to be have a DB605D engine. It shouldn't have the bulges or oversized oil cooler if so drag would ne less then a g14 or g6/as.

[gripen]

Niklas,
The speed of the supercharger in the DB 605 series was variable just in the gven range (typically between about 7-10:1) . For example at 1,42ata  the DB 605 utilized variable speed between 2-5,7km, outside these altitudes it was a fixed speed system. It should be also noted that hydraulic coupling allways wastes some energy (2-3%).

gripen

[Nashwan]

What are the gear ratios? I assume 1:10 and 1:15 or so.

I remeber seeing 5.5 and 8, but I can't remeber where.

The LF version had a Merlin66 engine that produced with +18ata 1700hp. The report mentions some improvments, so maybe power output was even higher.

I have seen peak output quoted for the Merlin 66 as 1670hp or 1760hp. That looks like a misunderstanding to me, but could be a genuine power difference.

Anyway, let it be 350mph for the spit14 - no problem here from my side.

It's not a question of let it be. You can't come up with a way of working out performance, and when the result is too low say ok I'll agree it's more, and expect your model to be accurate. If your model shows 335, and you don't want to accept that, your model doesn't work properly.

Your calculations show 335mph at sea level for a Spit XIV with FTH of 12,200ft in MS gear. That is the same speed as a Spit LF IX. That suggests to me an error in your method.

Again, a change of 4,600ft in FTH in the Merlin produced a speed difference of 5 - 7mph.

Your figures show a difference in FTH of 7000ft in the Griffon producing a speed difference of 28 mph. I find that impossible to believe.

Climbrate: The spit14 has at low altitudes roughly 200hp more power. Actually a bit less. This is 12% more power (actually only 11.7) compared to 1700hp, but it has 13% more weight. So power to weight ratio got worse. No contradiction to my theory, in opposite, climbrates up to 5000ft/min of the spit14 becomes more and more questionable for a "normal" spit14 and favour my theorie that those tests were done with griffons doing 2200hp or even more.

The LF IX had around 1700hp at 7,000ft (FTH). ROC was 4700ft/min. Weight 7485lbs.

The XIV had 2000hp at 9000ft. ROC was nearly the same. Weight was 8400lbs.

That gives the Spit XIV 4.2lbs/hp, and the LF IX 4.25lbs/hp if you assume 1760, 4.48lbs/hp if you assume 1670hp.
Those figures seem in line to me.

That the spit LF equipped with a lower MF gear ratio (spit 354) was SLOWER than the Merlin66 equipped spit surprised even the engineers obviously:
".It is a matter of interest that at sea level, Spitfire BS.354 with the RM-9SM engine, although nominally develping 50 B.H.P. more power than the Merlin 66 engines BS.543, is 7 m.p.h. slower, indicating either that the nominal powers were not realized and/or that there was a considerable difference between the drags of the two aircraft."
BUT this DOES confirm my theory. Why does the RM-9SM produce 50hp more power ehh? lower critical altiutde my friend  This does exactly confirm my theory!

This is getting bizarre.

A plane that is supposed to have more power, but doesn't seem to have more power, confirms your theory?

If BS 354's odd performance was down to drag, presumably climb would not be so affected. However, it was badly affected with BS354 trailing well behind in climb rates as well.

In fact, BS354 seemed to have similar climb performance in FS gear, indicating it had less power in MS gear, not more.

In other words, their theory being wrong confirms your wrong theory as well?

, climbrates up to 5000ft/min of the spit14 becomes more and more questionable for a "normal" spit14 and favour my theorie that those tests were done with griffons doing 2200hp or even more.

Okay, now I have real problems.

Why would they try to hide the fact if the Griffon was producing 2200hp or more?

If a Griffon could be run at 2200hp at 18lbs boost, I would think they would acknowledge that fact, and make them all that way.

Secondly, a Spit LF IX doing 4700ft/min has a lbs/hp ratio of 4.48 to 1.

A Spit XIV with 2200hp would have a lbs/hp ratio of 3.81 to 1.

A Spit XIV with 2050hp (usuall quoted figure) would have a ratio of 4.09.

In other words, assuming it wasn't all some giant conspiracy, and using the figures published, the Spit XIV should be much better than the IX anyway.

The other point is that a 2200hp Spit should go faster than 363 at sea level.

If a 1500hp Spit IX can do 335, you think that 46% more power would only get you 8.4% more speed?

Which Spit figures do you disbelieve, and which do you believe?