Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: nrshida on May 10, 2016, 02:09:10 AM
-
Have a little experience of turbochargers but ones that (mostly) stay on the ground. I understand the principals of supercharging but one thing confuses me. As I climb in my Ki-84 the power drops off, especially above 7k. As I hit something like 10,400 feet I get a sudden burst of climb rate which I'm infering matchies a bulge of power again. Since the atmosphere presumably thins at a constant rate, how come there's a bulge of power there, is it to do with coincidental gearing in the supercharger? Also WEP makes no difference at certain alts but this also appears to not be linear. What's going on? :old:
-
Is your ki84 restored to original specs or modified?
-
Is your ki84 restored to original specs or modified?
Hush Floob, you'll invalidate my warranty :eek:
-
The Ki-84 had a two speed supercharger. At around 14,000 feet (or 12K on WEP) the second gear kicks in and spins the supercharger up to a higher RPM increasing the boost available to the engine. Below this alt the slower gear stops the engine over-boosting and blowing its gaskets.
(http://www.hitechcreations.com/wiki/images/thumb/b/b6/Ki84clmb.jpg/300px-Ki84clmb.jpg)
-
Oooooh, all this time I thought it was single speed. Thanks.
-
LOL.. what timing.. just last night I was flying the Ki-84 and noticed the power fluctuations at around that altitude and was thinking.. WTF?
Thanks for the post!
-
So it tricks the engine in to thinking its at a lower altitude?
Japanese planes were poo because they lost the war
-
Many other planes in-game do the same thing, I always figured it was due to the two-speed superchargers that were widely used.
-
So it tricks the engine in to thinking its at a lower altitude?
Japanese planes were poo because they lost the war
The NIKI owns the F4U ! :old:
:uhoh
Ok, every one of you to the DA! :old:
-
(High blower engages!)
Let's see how many of community understand that reference. :devil
-
(High blower engages!)
Let's see how many of community understand that reference. :devil
<raises hand>
Sent from my XT1585 using Tapatalk
-
(High blower engages!)
Let's see how many of community understand that reference. :devil
Star trek? :)
HiTech
-
(High blower engages!)
Let's see how many of community understand that reference. :devil
AW. Go BZ! :joystick:
-
So it tricks the engine in to thinking its at a lower altitude?
Yes it has the same air density at say 10k as it would at sea level because of the supercharger.
-
(High blower engages!)
Aw
Semp
Let's see how many of community understand that reference. :devil
-
OK, so what is the difference between the supercharger on the Ki-84, and the supercharger on the P-38? One of the things I like about the Lightning is the fact that the power curve is stable. It stays pretty much the same all the way up, there aren't any gaps like you mentioned. What makes the difference?
-
OK, so what is the difference between the supercharger on the Ki-84, and the supercharger on the P-38? One of the things I like about the Lightning is the fact that the power curve is stable. It stays pretty much the same all the way up, there aren't any gaps like you mentioned. What makes the difference?
because there is a turbocharger. The turbo would maintain boost due to the maintained load and exhaust on the engine.
-
(High blower engages!)
Let's see how many of community understand that reference. :devil
:aok
-
OK, so what is the difference between the supercharger on the Ki-84, and the supercharger on the P-38? One of the things I like about the Lightning is the fact that the power curve is stable. It stays pretty much the same all the way up, there aren't any gaps like you mentioned. What makes the difference?
Most WW2 aircraft had one or two superchargers driven through gears off the engine's crankshaft. If a two speed gearbox was fitted it allows the supercharger to cope better with differing air pressure, but in steps. The P-38's engines had both a single speed crankshaft-driven supercharger and an exhaust-driven turbocharger. The turbo's RPM was controlled by dumping excess exhaust gas using a waste gate. This allowed it to maintain a constant air pressure to the engine up to its critical height, above this altitude the turbo was working flat out and the engine progressively lost power.
This sort of two-stage supercharging had some advantages to the two-stage crank driven set-up used in the later Merlins. Apart from the lack of altitude pressure steps the turbochargers were powered by waste exhaust energy rather than the engine itself. OTOH the turbo-charging set-up used in planes like the P-38 was both bulky and heavy, needed more pilot attention and groundcrew maintenance, was more vulnerable to battle damage and lost the jet effect the Merlin got from its exhaust.
-
(High blower engages!)
Let's see how many of community understand that reference. :devil
Hmmmm.....something to do with drugs and oral sex? :D
-
The 109's engine had a barometrically controlled fluid coupling which automatically compensated for altitude. Pretty cool feature.
Was the gear selection in two speed superchargers manually controlled then?
-
It was automatic control on the 109 :old:
It used a slide and pressure system which extended the slide on a internal worm gear :old:
-
Was the gear selection in two speed superchargers manually controlled then?
On the two stage Merlin the gear change was automatic.
-
That's a throwback Del. :salute all. Still in the middle east. Might be back on this summer.
Fear the Ki 43!
-
Most WW2 aircraft had one or two superchargers driven through gears off the engine's crankshaft. If a two speed gearbox was fitted it allows the supercharger to cope better with differing air pressure, but in steps. The P-38's engines had both a single speed crankshaft-driven supercharger and an exhaust-driven turbocharger. The turbo's RPM was controlled by dumping excess exhaust gas using a waste gate. This allowed it to maintain a constant air pressure to the engine up to its critical height, above this altitude the turbo was working flat out and the engine progressively lost power.
This sort of two-stage supercharging had some advantages to the two-stage crank driven set-up used in the later Merlins. Apart from the lack of altitude pressure steps the turbochargers were powered by waste exhaust energy rather than the engine itself. OTOH the turbo-charging set-up used in planes like the P-38 was both bulky and heavy, needed more pilot attention and groundcrew maintenance, was more vulnerable to battle damage and lost the jet effect the Merlin got from its exhaust.
To add to this, super charged engines can also have a waist gate. But a supercharger is geared to the engine so its speed is a function of engine speed. If you size the supercharger to diliver a certain volume of air at 3000rpm at sea level, then as you you went up in altitude and the air got thinner the supercharger can't speed up to compensate unless it has multiple speed gearing. A turbocharger is a two sided air driven bump. One side is a turbine driven by exhaust gas. The turbine rotates a comon shaft which turns a centifugal compressor. the speed of the compressor/turbine is limited by the pressure balance across both wheels. So as atmospheric pressure drops so does boost and resistance on the compressor side. This lack of resistance creates a pressure unbalance across the turbine/compressor with the tubrine being higher, so the turbocharger accelerates until balance is re-achieved. Hence the turbo is a variable speed constant boost device.
Hope that helps. :salute
-
(High blower engages!)
Let's see how many of community understand that reference. :devil
about 19k in a p51 8)