why does 109G10 climb so bad??

[Zigrat]

thrust decreases linearly with airspeed. drag increases quadratically (zero lift drag) and it dominates at near vmax speeds so as a very rough approximation you can say that a x increase in power should give a x^.3333 increase in speed  (as i said very rough because ignores prop eff. but if you resign the prop you shoudl be able to achieve comparable efficiecies). It also ignores the larger induced drag present even at high speeds due to the greater weight.

hence a 46% increase in power should yield about a 13.4% increase in speed ie i would expect a 2200 hp spit to be able to optimistically reach nearly 380 on the deck.

if the griff could truly produce 2050 on the deck you would expect around the ballpark of 366. but like I said thhis cube root rule is very optimistic.

[funkedup]

at speeds between 300-200km/h drag is nearly a non-issue.

Induced drag is quite significant in that speed range.

Only about 60% of the engine's power goes towards increasing energy (climbing) at best climb speed.  Where is the other 40% of the power going?  Prop inefficiency and drag.  You can't just ignore 40% of the power requirement and expect to answer why one plane outperforms the other.  At least not if you are actually interested in answering the question objectively...

[Nashwan]

Sorry all, but I'm still trying to understand this.


I've looked at this again, and I can see I was wrong in thinking you meant 2200 hp at sea level. Looks like you are suggesting 2130 at sea level.

Apart from the performance differences you'd expect, this chart seems wrong to me.

You have taken the power beyond what a Griffon could do at 21lbs boost. My understanding of what you are saying is that gearing the supercharger to produce the same boost at a higher altitude means more power is used for the supercharger at all altitudes, because it has to spin faster. (not sure about above rated alt, but we are talking below anyway)

I accept that, I just don't think it's as large a power loss as you think.

This chart is instructive, because it shows you think raising the FTH meant the supercharger consumed an EXTRA 300 hp, over and above what the supercharger was consuming in the Griffon rated for the lower altitude.

Taking your chart to extremes, and calculating a supercharger rated for 0 ft, we see that the Griffon rated for 12,000ft is using 500hp more to drive the supercharger than one rated for 0 feet.

The zero feet rated supercharger would have to add 18lbs per square inch pressure, the 12,000ft superchrager would have to add 22lbs pressure. The one rated at 0ft would have to compress at approx 1.8 to 1, the one rated at 12,000ft at 3.2 to 1.

I'm getting confused here, but if you assume double the power to raise boost to 18lbs at 12,000ft that it would take at 0 ft , and it takes 500 hp MORE for the 12,000 ft rated engine, that implies the 12,000ft rated engine is using 1000hp for it's supercharger, in MS gear.

Your chart also implies the prototype with the lower FTH would be faster all the way up to 7000ft than a Spitfire XIV running 21lbs boost with 150 octane fuel.

Considering 150 octane was first authorised for V-1 chasing, which took place below these altitudes, and that great effort as put into making high octane fuels, experiments with NO2 etc, it seems a waste when all they would need to do is change the gear ratio in the supercharger.

Changing a gear ratio doesn't sound like a huge amount of effort to me, not when compared with the efforts actually used to fight the V-1s.

A chart showing speed increase that could be obtained by using high octane fuel at 3000ft shows the Spit XIV at 372 mph at 3K at 18lb boost, which is the same as the revised production figures, slower than the prototype figures (about 380 at 3K)

With 21lbs boost, it shows speed increasing to 393, with 25lbs boost 410mph.

Your horsepower extrapolations show lowering the gear ratio would mean horsepower mid way between the 21lb and 25lb figures, for a speed of around 400 mph.

As it was, early Spit XIVs were limited to 21lbs because of bearing weaknesses, so just by changing gear ratios the Spit XIV could have been faster chasing V-1s than it as running on 150 octane fuel.

Sounds wrong to me.

When there was an effort to make a Spit V faster at sea level, they cropped the supercharger impeller to reduce the ammount of power used by the supercharger. Why bother if changing the gear ratio would do the same?

[wells]

Originally posted by Wmaker


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

It might be, but the manifold pressure is still only 1.8 atm for 1800 hp.  If it were 2000 hp, you should be seeing 1.98 atm (59" Hg) on the gauge and the climb rate would be better.  

[gripen]

Nashwan,
Some supercharger gear ratios of the RR  engines:

Merlin 61: 6,39 and 8,03
Merlin 66:  5,79 and 7,06
V-1650-3: 6,39 and 8,095
V-1650-7: 5,80 and 7,35
Griffon VI: 9,0 and 11,07
Griffon 65: 5,84 and 7,58

gripen

[HoHun]

Hi Funked,

>Only about 60% of the engine's power goes towards increasing energy (climbing) at best climb speed.  

Could you elaborate on how you arrived at that number? By my own calculations, the Me 109K-4 expends about 83.5% of its engine power for climbing.

Regards,

Henning (HoHun)

[SUP0NGO]

Spanish

Pido perdon por esta mala traduccion al ingles, pero uso "altavista translator" y posiblemente no esten mis palabras lo suficientemente claras para los angloparlantes, Si alguien puede hacer una mejor traduccion, por favor, haganlo. Gracias.

Todos Los datos que se escriben en estos post son datos procedentes de pruebas de la RAF o USAF, y como muy bien dice Niklas en ellos se omiten muchas cosas, estoy seguro que intencionadamente por motivos propagandisticos. Mi pregunta es:
No hay esas mismas pruebas comparativas entre Spitfire, P51 versus 109 o 190 en los archivos capturados de la LW?
Si existiesen, podrian ustedes hacerlas publicas?



English

I request pardon by this bad translation to ingles, but translator "altavista" use and the sufficiently clear thing for the English-speakers possibly do not esten my words, If somebody can make one better translation, please.  Thanks.  

All the data that are written in these post are data coming from tests of RAF or USAF, and as Niklas in them says very well omit many things, I am sure that deliberately by propagand reasons.  My question is:  There is those same comparative tests between Spitfire, no P51 versus 109 or 190 in the captured archives of the LW




Supongo

[Angus]

Woo-hoo, what a lot of data. Thanks everybody, I collect that kind of stuff

It seems that the best way to get the world's best data is to let out a thesis if this kind in the AH forum.
Now we have a lot of numbers here, I do not want to add a lot more. I'll keep to what real ww2 Pilots said.
Firstly, The Spitfire and the 109 were practically on par in climb rate pr. Hp, the Spitfire winning by a slight margin if anything.
Example: Spitfire I would be able to hang on a 109E's tail, except for the Steep angle of the 109E. I guess that would mean the 109 generally climbs steeper at a slower speed.
(various sources)
Spitfire Vb would catch a 109F in a prolonged climbing race.
(T.E.Jonsson)
Spitfire XIV would not need to worry against anything. In Spitfire XIV pilots would even allow themselves to be bounced, just to get the german plane to the fight, once they were at the same altitude, the german had no chance of escape
(J.Johnsson, R.H.Harries)
Looking at the aircraft this looks logical. The Spitfire simply had a more efficient wing, and most often a lower wing loading too. Increased Hp would just exaggerate the difference between these two aircraft.

Now there was quite some data about manifold pressure, WEP, constant speed props etc etc.
There was a reason why the spit XIV had more propeller blades than earlier versions. With more power, you need some way of turning it into torque, and lengthening the prop was out of the question because of the bladetips breaking the sound barrier. Thus more blades.
Looking at the 109 prop I am a wee bit confused, - how did they turn 2000 Hp properly into torque through THAT?
WEP is another abstract  factor. With only 5 minutes of WEP recommended, the RR engines were known to be able to take up to 30 minutes without damage. I do not know about the DB, but I do know that for some reason it would wear much quicker than the RR, losing power earlier in its lifetime than the RR. That however applies to real life and not our sim.
And finally, when it comes to variable pitch/constant speed, I think I am right in saying that at the time, the Germans were not ahead (any more? of the Allies.
Well, enough now, keep on flaming

[niklas]

Originally posted by Nashwan

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?

No. First i used indeed AH altituted. Furhtermore you can see that the gradient down from the 2nd gear is steeper. If i use a mean gradient speed wonīt become so bad.
You donīt want to understand obviously. Those lines drawn in 20seconds are not 100% correct and i donīt want to say the spit performed exactly this way. I just want to give you an imagination about the effect. You better look at the climbrates, which depend much more directly on power instead of speed.

Those other docs with 12k alt are nice, but it is noteworth that
A) no further detail are available compared to the data from mwīs pages. Just lines that could be also calculations, and which can be drawn by every child in 20seconds.
B) the date in the bottom right corner says July 46. Those charts were made over 1 year later then the end of the war, or 2 years later then the introduction of the Spit14 in the RAF. You have to decide yourself whether you consider those charts, maybe from spits produced under civil circumstances instead of wartime (what also could mean not in armed mode), are representative for a ī44 spit14.

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.

I assume that one power output is for sealevel, the other for the critical altitude of the 1st gear. The power outputs for the RR engines are very often given for the critical altitude of the 1st gear, what is usually higher than sealevel output. The griffon is given with 2050hp, but at sealevel the output was only 1850hp-1900hp. This way the power output looks better, german engines are usually given with sealevl output AND sometimes, especially in case of the 801 with the reduced poweroutput due to rameffects. (static thrust 1800PS, dynamic 1730PS or 1700hp).

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

The first time i donīt understand. The spit is supposed to have more power, but look what the engineers said, they assumed drag problems or unknown loss factors. So practical results vary from theoretical predictions, like so often, but the important fact is that the R4.. engine is supposed to have 50hp more with a reduced critical altitude of the 1st. gear.

Your doubts about the influence of the gear ratio on power are valid. The differences look also very large for me. But i only can repeat those charts from me were basically made to demonstrate you the effect, and not to make an exact calculation.

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.

Yes, but i donīt believe those gauges. The tempest gauge goes up to only +9lb, does this mean it climbs 4600ft/min with only 2100hp? Well, even when it should be +11lb and 2300hp, when 4600ft/min are modelled for such an average powerloading, then iīm not surprised why the Tempest flies like it does fly. Even 2600hp canīt explain imo the climbrate.

But even with 1800hp near ground, the G10 has a powerloading of 0.243hp/lb, the spit14 with 1850hp near ground 0.219hp/lb. This means the powerloading of the G10 is still 11% (!!!) better. And it climbs 300ft/min worse???

Originally posted by Funked
Induced drag is quite significant in that speed range.

The steeper you climb the less is the influence of induced drag, because your wing must produce less lift. The aircraft with the higher wingloading becomes superior, less wingarea, less drag. This changes in high altitudes, where usually low wingloadings can keep the advantage.

Originally posted by Agnus
The Spitfire simply had a more efficient wing

I really wondered myself when someone brings up the unique "the elliptical wing explains everything" argument. Actually the wing of the 109 was much superior. The wing of the spit can described by only 2 words: wing area. Lot of wing area, thatīs all. No slats, cannons and guns in the wing, only one setting for flaps.. actually a very primitive wing. Nevertheless it can achieve with a very gentle slow speed handling the lift coefficients of a 109 that uses slats and has no disturbing weapons in the wing(same for Tempest, Typhoon), but i already said that i consider RAF planes the most overmodelled ones in the set. The naca test says the spit had a surpisingly low CL btw, and this was a wing with 8*30. Installing the large cannons booms reduced cl by another 2-5% for sure!
What remains for the 109 is the poorer arment of only one central mounted cannon....and even dispersion is very close to that of a spit where the cannons are mounted far outside in a rather "soft" environment (wing)... ahh i better stop...

nik

[214thCavalier]

OK just one observation to make regarding lift and drag, the higher loaded and smaller surface area wing on the 109, to produce an equal amount of lift to the spits would have to be at a greater  AoA and would generate higher drag.
Your argument that drag is really small at slow speeds does not appear to consider the higher drag caused by the wing flying at a greater AoA.
Now i have nothing like the aeronautical knowledge of some of the guys who could answer this, but it seems logical to assume  at slower speeds the drag caused by the larger surface area of a wing would have less of an impact than the drag caused by a wing having to fly at a higher AoA.
Anyway flame away if you wish or correct me but saying "i  dont believe it" aint good enough.
And you cannot put me into either camp as i rarely fly both there just  too hard for me

[HoHun]

Hi Cavalier,

>Your argument that drag is really small at slow speeds does not appear to consider the higher drag caused by the wing flying at a greater AoA.

The point is not how the drag between two aircraft compares, but that it is very small compared to the power available for lifting the aircraft. Drag differences can't explain large climb rate differences.

Let's have a look at the Me 109K-4. It climbs at about 5500 fpm - as you can tell from climb rate and aircraft weight, this is equivalent to 1250 HP just lifting the aircraft. Assuming a propeller efficiency of 75%, the Me 109K-4 has only 1500 HP available. Accordingly, only 250 HP are left for overcoming the drag.

If you now add a ridiculous amount of extra drag, like +50%, you'd have 375 HP lost to drag, and 1175 HP left for climbing. This would still leave the Me 109K-4 with a climb rate of 4900 fpm.

This is still more than the 4600 fpm that Naudet quoted.

Wells' observation that the Me 109G-10 according to its instruments runs only at 1.8 ata, which would suggest just 1800 HP power, leaves us with similar numbers:

1800 HP total, 1350 HP available, 250 HP spent on drag, 1100 HP left for a climb of 4800 fpm.

The conclusion: There's reason to speculate that the Me 109G-10 in Aces High is equipped with an engine of 1800 HP (or less).

Regards,

Henning (HoHun)

[hitech]

Prop designs for climb or speed, the never ending problem gets much worse with more HP.

Just curious anyone every think what happens to thrust when the prop airfoil stalls? And hence why the padle blade was devloped?

Or about such simple things as the effect of the prop to eng gear ratio?

[funkedup]

Hohun here's an example, Fw 190A-5.

h_dot (rate of climb) = 3900 ft/min = 65 ft/s
W (weight) = 8600 lb

Rate of energy change (assuming constant TAS climb) = W * h_dot = 8600 * 65 = 559000 lb-ft/s = 1016 hp.

(conversion factor is 550 lb-ft/s per hp)

P (engine shaft power) = 1700 hp

W * h_dot / P = 1016 / 1700 = 0.598 = 60%

This is the fraction of engine shaft power which is used to increase the energy of the airplane at best climb speed.

WWII fighters tend to fall between 55% and 65% in my experience.

[GRUNHERZ]

Has anyone actually seen a G10 prop? It only has three blades but they are very very wide. Much wider than the 5 blades on the Spitfire XIV.  Every succesive 109 model introduced wider blades to harness increasing power with the G10 and K4 having
enourmous paddle blades.  

Look this certainly wouldnt be the first time AH had a FM performance error, maybe we just found a new one. Certainly this is a reasonable discussion using facts.

[funkedup]

Ho-Hun - I just read through the rest of your posts.  The difference between your result and my result was the power figure.  I'm using shaft power and you were using power available (shaft power times prop efficiency).  Both of our results are valid, they are just answering different questions.

My point:
Niklas' rudimentary power/weight analysis did not include drag or prop efficiency as a possible reason for the performance variations between aircraft.  

But it's clear that about 40% of the engine's power is wasted by the prop and drag.  Obviously a variation in prop efficiency or drag could explain the performance variation.

But Niklas didn't seem to want to acknowledge this fact.  Probably because it doesn't agree with his theory about incompetence and dishonesty by HTC and various Allied aeronautical agencies.