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PostPosted: Thu Nov 10, 2016 11:43 pm 
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I gave this exercise a bash the other night, in both the Mk1a with VP prop and the Mk2a with CS prop. Took off from Biggin Hill (where else?? :D ) in cold, cloudy but dry weather using ASN for the weather. The Mk2a did it in 6 min 20 seconds with power set at +8 boost for as long as possible and 2850rpm. The Mk1a did it in more or less the same time, but I left the pitch at full fine. I have no idea what my air speed was because when I came out of cloud, my ASI had iced up so I had no speed indication for most of the climb. My poor Spitfire got a pounding too, as the revs rose to 3,100rpm at some stages, though I believe the Merlin was safe to 3,600rpm. In both attempts, I arrived at top of climb with the engine at about 115 degrees, but I opened up the radiator vent at 110 degrees.

I must try it again in warmer weather and see what the results are. I'd also like to compare it to the P-40, as this is more in period to the early Spitfires. The Mustang is a later beast with the benefit of development, and should be compared to a Mk9. A Griffon Mk14 would eat the Mustang to 20,000, as tests at that time showed. Pity we don't have a later A2A Spitfire to play with here.


Cheers,
Mike

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PostPosted: Fri Nov 11, 2016 1:48 pm 
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So I gave it a shot with the MkI with the DeHavilland two speed prop keeping the rpm at 2600 and following Darryls speeds.

Killratio wrote:
Climbing speeds for the Spitfire I:

0-12,000 - 185mph
To 15,000 - 179mph
to 20,000-169mph

With a prewarmed engine including engine start I did it in 8min 51s.
i also took the time starting with the takeoff and I managed to do it in 8 minutes dead.

I did not use 12psi for takeoff only full throttle with the throttle gate on.

The two speed prop increases the work load quite a bit compared to the constant speed one in my opinion. One always seems to have to fiddle with it :wink:

Happy flying

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PostPosted: Sat Nov 12, 2016 2:07 am 
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More great tries guys. Keep them coming.

Quick answers.

1. 3600rpm yes, but in a dive and with throttle at least 1/3 open (vis, unloaded prop).

2. Yep, eliminating workload and variable performance were the reasons that the Rotol was favoured.

3. Piper..good stuff. Now try at 140mph all the way up. Full throttle, 2600rpm. You will see how much more demanding it is BUT quicker if flown accurately.

Back in the A2A Spitfire's early days (before the automatic mixture was slightly adapted to work more closely to the real aircraft) you used to have to ALSO keep adjusting the throttle to maintain climbing boost until you got to full throttle height. It made all the performance testing hard but fun. Many hours spent with a kneeboard marking off times, heights, temps and other performance figures. Of course I "cheat" using Moody Blue...which means that I can just fly exactly the same as flying a real aircraft...not looking for this or that button, having real travel on the controls and being able to physically glance at individual gauges whilst continuing to monitor attitude etc with peripheral vision! The A2A Beta testing is, he said modestly, superb. There is always someone with time on type, always someone testing the real aircraft or detailed performance figures with a real pilot's eyes, always someone to test all of the damage modelling deliberately and always Cody and Lewis to test the damage modelling accidentally :P :P :P


regards

Darryl

Must dash off now and test fly the Connie for a while... (Oohh..sorry, did I say that aloud? :) )

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PostPosted: Sat Nov 12, 2016 9:50 am 
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Killratio wrote:
3. Piper..good stuff. Now try at 140mph all the way up. Full throttle, 2600rpm. You will see how much more demanding it is BUT quicker if flown accurately.

Thanks you Darryl. This challenge is so much fun.

I did give it a try with 140mph and the time was 7:40. So not really that much faster than the 8minutes I did with the higher speeds. Is that time to be expected or is it incompentece on my end that made it slower?

Happy flying

PS: how dare you teasing us with the Connie! :wink:

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PostPosted: Sun Nov 13, 2016 6:07 am 
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Not incompetence at all...the difficulty in fine control at 140 and the lack of significant difference is exactly why the recommended speeds were increased and nose angle lowered....and stated to be for those reasons.

We are now getting better times than the test aircraft but that is because we are fiddling with the Variable Pitch. All the tests I have seen data on were done at a climb speed with the DeH Airscrew moved to full coarse at 2000ft and take what rpm you get. 11.4 for a slightly tired Merlin II (K9793) , 10.7 minutes for a Merlin III (L1007).

For reference, Merlin XII / Rotol combination should do it in 7 minutes flat.

If you are getting 8 minutes or thereabouts then you are doing almost as good a job of being the CSU as ROTOL did...albeit a heavier airscrew again compared to the DeH.

Merlin III / ROTOL aircraft made the climb in 7.7 minutes.

The one thing that REALLY makes me happy about all this is that it bears out the modelling on the Merlin, the DeH and the airframe!!


P.S. Sorry for the delay in reply, I've been flying the....oh...never mind :) :) :)

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PostPosted: Sun Nov 13, 2016 8:14 am 
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Piper_EEWL wrote:
So I gave it a shot with the MkI with the DeHavilland two speed prop keeping the rpm at 2600 and following Darryls speeds.

Killratio wrote:
Climbing speeds for the Spitfire I:

0-12,000 - 185mph
To 15,000 - 179mph
to 20,000-169mph

With a prewarmed engine including engine start I did it in 8min 51s.
i also took the time starting with the takeoff and I managed to do it in 8 minutes dead.

I did not use 12psi for takeoff only full throttle with the throttle gate on.

The two speed prop increases the work load quite a bit compared to the constant speed one in my opinion. One always seems to have to fiddle with it :wink:

Happy flying


I followed this, prewarmed engine, scramble position near the active runway.
No boost cutout override. Was a bit too fast at the beginning and came out in 9 min 3 sec from engine startup to 20k ft.
Really challenging to fiddle with the prop, adjusting pitch to hold the recommended speed and keeping the course.

Will try with the boost cutout override next time.

Regards
Jens

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PostPosted: Sun Nov 13, 2016 8:35 am 
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Nice stuff Jens,

This is turning into a lot of fun. I never dreamed that an off the cuff challenge would drum up such interest!

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PostPosted: Sun Nov 13, 2016 11:12 am 
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Killratio wrote:
Not incompetence at all...the difficulty in fine control at 140 and the lack of significant difference is exactly why the recommended speeds were increased and nose angle lowered....and stated to be for those reasons.

Well thank you. I was expecting a much faster time after you recommended to me to try at 140mph. But I'm relieved that it wasn't me screwing up :wink: It makes a lot of sense that they increased the speeds if the times aren't better and it decreases the workload on the pilot and the stress on the engine (due to easier temperature management I imagine?).

gulredrel wrote:
I followed this, prewarmed engine, scramble position near the active runway.
No boost cutout override. Was a bit too fast at the beginning and came out in 9 min 3 sec from engine startup to 20k ft.
Really challenging to fiddle with the prop, adjusting pitch to hold the recommended speed and keeping the course.

Very nice time Jens. With starting the engine it took me about 8min 20sec. I haven't tried with the MkI with the boost cutout override yet. Will be looking forward to your time on that.

Killratio wrote:
P.S. Sorry for the delay in reply, I've been flying the....oh...never mind :) :) :)
:twisted: :twisted: :mrgreen:

Happy flying everyone

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PostPosted: Sun Nov 13, 2016 2:59 pm 
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pre-warmed engine, but dark cockpit. From engine start to 20.000 ft in MkIa DeH Prop with boost cutout override in 8 m 31 s. So I as half a minute faster as with cutout boost.

Next time, MkIIa Rotol prop (don't know when, cause new week starts).

Quote:
P.S. Sorry for the delay in reply, I've been flying the....oh...never mind

:evil: :evil:

Image

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PostPosted: Sun Nov 13, 2016 4:12 pm 
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gulredrel wrote:
pre-warmed engine, but dark cockpit. From engine start to 20.000 ft in MkIa DeH Prop with boost cutout override in 8 m 31 s. So I as half a minute faster as with cutout boost.

Next time, MkIIa Rotol prop (don't know when, cause new week starts).

Good time Jens. Just tried the same. Full throttle including boost cutout override to about 2000ft AGL then on with "normal" full throttle to 20kft took me about 8m 40sec. So about 10seconds faster then my time without boost cutout override.

The question is how long can you leave the engine at 12psi?

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PostPosted: Sun Nov 13, 2016 8:51 pm 
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Piper_EEWL wrote:
The question is how long can you leave the engine at 12psi?


What I do is keep a close watch on the engine cowling. If you start to see dents appear in the top, throttle back :) :) :).

12 lbs/sq in is allowable at takeoff until 1000ft. This, to me, indicates that using it in the climb is an extreme load on the engine.
That makes sense. I have read many mémoires that talk about "pulling the tit" and climbing to meet bandits when they are sighted.
What I don't recall ever reading is leaving it on contrary to the 1000ft takeoff restriction. Having said that, leaving it on would shortly
send temps off the charts at a low forward airspeed.

ALWAYS keep in mind that the 12 Combat Concession IS subject to Oil 95C (the "emergency" not "Climbing" maximum) and
Radiator 120C (later relaxed in light of experience to Rad 135C but NOT at BoB, although I am sure they did it!

My method is to use it until 1000ft, then off, then again from 5000ft to 10,000ft after which the extra boost is sapped by altitude.
This is different to FTH (11,400ft) which is the point above which the boost will fall below 6 1/4.

That is why I really only expect to get an extra 5-10 seconds knocked off the time. Not a great amount in a climb test but then put that
extra climb in the context of a 30 or 40 second time to contact and it becomes a handy edge.

regards

Darryl

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Last edited by Killratio on Sun Nov 13, 2016 9:08 pm, edited 1 time in total.

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PostPosted: Sun Nov 13, 2016 8:57 pm 
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gulredrel wrote:
Image


Oh, OK. The A2A Simulations Connie will have 4 engines.... but PLEASE, keep that quiet or you'll get me thrown off Beta!!

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PostPosted: Sun Nov 13, 2016 11:42 pm 
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Killratio wrote:
gulredrel wrote:
Image


Oh, OK. The A2A Simulations Connie will have 4 engines.... but PLEASE, keep that quiet or you'll get me thrown off Beta!!



Oh, that's interesting. Not all of them did, so I'm told, for parts of the flight. :lol:

Cheers,
Mike

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PostPosted: Mon Nov 14, 2016 1:26 am 
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Killratio wrote:
What I do is keep a close watch on the engine cowling. If you start to see dents appear in the top, throttle back :) :) :).

:lol: :lol: :lol:

1000ft? :shock: That's basically after raising the gear! Which btw increases the workload immensely in the MkI with the manual pump!

Killratio wrote:
ALWAYS keep in mind that the 12 Combat Concession IS subject to Oil 95C (the "emergency" not "Climbing" maximum) and
Radiator 120C (later relaxed in light of experience to Rad 135C but NOT at BoB, although I am sure they did it!

Is it really "only" temperature limitations? The additional boost surely puts more mechanical stress on the engine too. And my guess would be that the extensive heat development points to very high combustion temperatures too.

Very interesting subject!

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PostPosted: Mon Nov 14, 2016 2:19 am 
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G'day Mate,

Yes, exactly. The problems caused by high boosts are numerous. However, as with most mechanical problems, the damage is done before the symptoms become apparent.
The Merlin was strengthened and changed to eliminate many of the problems. 100 Octane helped eliminate "knocking". But the structure would only take so much.

If you put yourself in the place of the pilot, at the time, "on the scene', as it were, your first indication of damage might be fire, smoke, shocking vibration, bits flying
off or all combined. What you need is some way of operating that allows you to head off these problems. And that is where the "limitations" come in. I honestly can't tell you what normal operating temperature of oil is in a C172. Not a clue...
I just know Yellow = not ready, Green = OK, red = very, very bad. The temperature gauges exist ONLY to show problems that might be developing. I doubt any pilot is too interested in the number itself...just what it means.

So no, it is not "only" temperature limitations. In fact radiator temperature in particular is a very flexible limit even though the engine placards are, allegedly, "absolute" limits.
Largely it is all "11th Commandment" stuff. (Thou shalt not get caught....). Essentially the limitations are indicia of settings that will prevent engine failure and extend engine life under most circumstances.

In the early Spitfire I Pilot's notes it actually says something like "Warm up and taxi should not be unduly prolonged. If Radiator Temperature is 130C before taxiing they will become excessive
if there is any distance to taxi". Seriously!!??? And this with an absolute limit 120C ?? But of course, those early notes show a limit of 120C operating temp in flight .
Implied in this, is that the thing is a beast on the ground and we'll turn a blind eye if we see you taking off trailing steam.
In fact if you start at even 120C before going to takeoff power, you'll crack 140C by the time you are airbourne...and that IS too high in anybody's language.

Messrs Rolls Royce, of course, set an absolute 120C but, you are talking about a supplier who doesn't want "warranty" problems. Even during wartime, business is business.
You pitch where you are least likely to encounter problems.

Now, I really must get some work done for this Monday!


Darryl

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