sobek

I've tried my hand at this, the repercussions were ... considerable.

Sigs are clearly separate from the message body. Also (at least hypothetically) there's rules for sigs keeping their size and form at bay. As is 99% of what goes on on this forum ;) The reason they are "old" now is that people favor fancy colors and html smiley BS over readability. Yeah, how on earth did humanity come so far without heated bum cussions? Nevermind that cars today could easily operate at 60mpg if we hadn't turned them into SUVs (or how i call them, armored personell carriers). ;)

How many people (including Yo-Yo btw.) does it take to tell you that you're on the wrong track?

Except that you chose to read this thread. You have no choice whether you want to read those sigs or not... In the old Usenet days, you would have been skinned alive for stuff like this. :) Netiquette and so on...

Yes, really. I have a degree in audio engineering and i do know a thing about resonance in open, half open and closed pipes. I can tell you with full certainty that the sound we are talking about is not principally caused by any form of resonance, period, even more so in the Merlin stack, because of its extremely short length. That doesn't mean resonance doesn't occur or is not used to optimally scavenge the burned charge at certain RPMs in some engines, it just means that this sound is not caused by resonance. The article you quote clearly lists faults that would lead to afterfire occurring during powered flight. Nobody contested that that would lead to damage. Yes i am familiar with harmonics. Just a few questions for you before you blindly quote some textbook that doesn't apply: Do these incidents occur at a fixed RPM and multiples of that RPM number? No they don't. Do these incidents occur when revving up as well as when decreasing RPM? No they don't. Please Crumpp, just this once consider that you are off base. This theory is cyclotron grade baloneyum.

I'd say having it detonate in the exhaust is impossible under the conditions prevalent there. The harmful effects you describe would only manifest themselves if afterfire were present while the engine is running at power. When throttling down, it's normal for such an old engine.

And why does that happen only so sporadically and not at every exhaust stroke? I'm getting the popcorn, this theory of yours keeps getting better and better.

24"? That must suck for a "mobile" device. :P;)

How does that work, such an impulse collapse? You must have a basic understanding of the mechanism if you can say with such certainty that this is what's responsible and not afterfire.

It's a waste of space on everybodies monitor, that should be a consideration for mobile devices. Also it's a waste of everybodies time.

Please Crumpp, are you going to tell us that you will have the same peak pressure inside an exhaust that is only a few cm long and has a very low flow restriction compared to inside the cylinder where the charge is precompressed and can not expand? Who talked about detonation? You are aware that you need considerable pressure and temperature for the charge to detonate, yes? Both those conditions are surely not present in the exhaust. We are talking about deflagration here. How is that even possible in such a short exhaust system? I bet that the shockwave and even it's reflection are long gone out the pipe before a new exhaust cycle starts, especially at low RPM where this phenomenon occurs. Besides if it's just caused by the pressure gradient between subsequent exhaust cycles, why don't we see it at all RPM ranges? I'm perfectly aware that it should under no circumstances happen in a modern engine where the injection is metered by an electronic ECU, however, you can't hold these old engines to those standards and i'd be seriously surprised if it causes them any harm.

There is one distinct difference that you overlooked. Tapatalk posts its sig inside the message body. Forum signatures are clearly not part of the message body.

I am well aware, please follow the thread. ;)

Yes, it doesn't have the impulse qualities one would expect, it also seems that the audio is abruptly cut out or in without regard to where playback of the audio sample is at, resulting in some very unnatural onsets and cutting out of the samples. WIP i guess.

How do you explain that the condition sometimes persists until well after the throttle was closed? Observe the following video: [ame] [/ame] He starts closing the throttle at 8:02, the throttle is fully closed at 8:05, yet the poping noises continue until 8:10. Either this shockwave theory is hokum or Kermit Weeks keeps his P-51 in awful shape. Edit: Here's another video of a different P-51D afterfiring distinctly upon closing the throttle on landing (around the 1:50 mark). [ame] [/ame] I'm sorry but i'm just not buying it.

I strongly contest that theory as i doubt that any sane pilot would close the throttle fast enough to create a shockwave, yet the noise occurs quite frequently on some engines, e.g. at landing. Given that the fuel regulator on the merlin is of a relatively simply pneumato-mechanic type, i find it much more plausible that the engine would remain running rich for the fraction of a second compared to that shockwave hypothesis of yours. Besides the exhaust of the Merlin is very short and rather sturdy, i doubt that the pressure gradient from a small yet rapid deflagration would cause any harm to the engine. Edit: [ame] [/ame] If this is indeed what we are talking about, you can clearly make out the flames coinciding with the bangs from afterfire when he revs the engine up and down at the end of the vid before shutting it down.

If it's after-fire (no pun intended) that you are referring to, that is caused by the engine running very rich when you throttle back, resulting in combustible fuel being left after combustion in the cylinder finishes, which then mixes with oxygen inside the exhaust, causing violent audible bangs (and sometimes visible flames) from the exhaust. If it's modelled, it's quite possible that there is a physical model underneath it.

3D Model detail has no bearing on anything. They continuously update old models to or beyond the standard established with BS, regardless of the unit being player-controllable or not.

Do you perhaps mean backfiring? Detonation would never be caused by lowering the manifold pressure.

The necroing is strong in you.

They usually use relatively small and nimble types for mountain rescue (at least here in Austria (EC 135) and Switzerland (AS 350/Alouette II)). I suspect that purchasing/operating cost is the driving force there.

There's a documentary floating around on youtube following around a few pilots in the Himalaya. It might provide you with some insight why sane pilots usually don't fly at these heights and why the machine is only rated for a much lower ceiling. Edit: I just remembered it's about a Swiss medevac team operating in Nepal and training local pilots and it's in German, so that's probably not of much use to you. :noexpression:

There's very few companies that need to operate their helicopters at such heights, therefore it's commercially rather unattractive to design a helicopter solely for extremely high altitude operation. You're going to have a hard time finding a machine beating the AS350 B2/B3.

IMHO there've always been these increments with major releases.

Das würde ich am ehesten in der Rubrik Wunschdenken einordnen. ;)