A picture is worth 1,000 words.

Pencil protectors and minute calculations aside, the 3/8-1/2 inch of fuel tube wouldn't make any difference here. Air is not a solid, and we are not talking mach speeds.
Thanks for the input, however.
I suppose the lag time or lack thereof is perceptual. In fact, when I read Ed's post, I percieved him to mean length of tube between the NV and the carb = lag time.
If indeed we find any lag time, it is sooooo small, it really doesn't make any difference.
Remote NV = O-Tay.

Well done, Abraxxas!

Jetts

WOW...... massive amounts of posts while i was at work .

ok, that time delay from the NV adjustment to the effect of that adjustment wouldn't really matter would it?.... i mean, you don't adjust the needle valve in mid flight. you're on the ground with an RPM gauge waiting for the RPMs to change ... waiting being the key word.... plus, i can wait a half a second for the flow change if it means making those changes is safer for someone prone to clumsiness, and the looks of the plane of better

ok, about the cowling i was thinking of building onto my trainer (after a while of flying it, just to have a test bed for the act of constructing one before i go ahead and do as i'm planning with my second plane).... air intake will be a 2 inch wooden dowl cut in half longways (to make 2 half circle yet long pieces), then carve out the middle to make something like a pipe. that would be about 1 and 3/4ths inches intake "surface area" (it's really anti-surface area since we're talking about gaps or cutouts ). the outlet would be a 1/2 inch gap between the bottom of the firewall and the bottom lip of the cowling..... with a 4 inch wide firewall that would mean 2" of outlet. not quite 150% (2" to 1 3/4" is about 114%) but def enough of a difference in surface area to cause the suction.

thanks for all of your time guys, and the great info

Rob

Thank you so very much for the pictures. That indead made everything clear!


Thanks again,


Wings

Keep in mind that was measuring "pressure". Pressure does change through out the tube. If the pressure was constant there would be no flow. However flow is uniform throughout the tube unless it is compressible, like air. The amount of flow entering the tubing at the needle must exactly equal the flow coming out of the tubing at the carb. If it doesn't, you either have air in the line or you will explode the tubing.


Wings

Wings,
Thank you very much.
Empirical testing and fact outweigh probablys' and "I'd guess"(s) anytime!


Jetts

I would suggest that the change had something to due with variations in the dynamic response of the fluid (air) travelling through the fluid. The tube will act very much like a filter. This means pressure waves of different frequencies will be attenuated by different amounts, and will experience different phase lags. Changing the tube diameter could affect this. Or it was a red herring. Or I'm all wrong.

As for the remote needle valve, I vote for no delay. The pressure change down stream of the valve happens immediately for all intents and purposes, and that's what matters insofar as flow at the carb is concerned.

edit: added "... pressure waves of ..."

With regard to fuel flows -

I agree with the consensus that there is no macroscopically detectable lag in response in a typical model situation. This was an interesting side issue on the main discussion, and I simply threw in the comment from the book because it was somewhat apropos.

Not intending to confuse things or to challenge empirical observation...

Its all good. Forums are for discussing things.


Wings

Roger that!

Jetts

OK, well I'm not here to argue theory or the why's of it happening. But, my engines with remote needles DO lag in response to needle changes. As I said, it's more than one engine in more than one airplane and they all do it. Point being that nobody is going to convince me that I'm imagining things. But the bottom line is that I'm aware of it, so it doesn't really matter. I just turn the needle slower and give the engine time to catch up.

CM,
Just curious, do all your engines have remote NV's?
All engines of any size/fuel type ect. have some lag time after making setting changes. Remote NV's or not.
Have you tried side by side testing of lag time with the same engine with both types of NV?
Not saying you are imagining things, just asking what you are basing your observations on.
The reason this all started was Ed Moorman implied that with a remote NV the "lag time" was increased, which is simply not true, and so I was just trying to clarify things so people wouldn't think if they placed a NV "upstream" the tuning, or tunability would be affected.
As stated I have had some looong distances between NV and carb, with no adverse affects, including "increased lag time".
Yes- I have done side by side tests, just to make sure my extremely long fuel line between the two would work.

Jetts

I recalled seeing this on Jett Engineering's web site, re remote needle valves:
http://www.jettengineering.com/faq.html#faq7

Case closed.


Jetts

My credentials? Take a look: [link=http://www.airfieldmodels.com]Airfield Models[/link]
30+ years of running probably 100 different engines on 100's of airplanes. Most of the engines I've owned have not had remote needles. If you're wondering whether or not I don't like remote needles, the answer is I don't care either way. Some of my aircraft did have different engines mounted at different times which is one of the things that made me take notice of the phenomenon in the first place.

But, if an article on the internet says that the wall I painted blue is white even though it's never seen my wall, I guess it's right.

ohh.... I put the Jett link there because of the reputation of Mr. Dub Jett. I assumed, incorrectly, that most would recognize the source of the information and judge it in that light.

But, if an article on the internet says that the wall I painted blue is white even though it's never seen my wall, I guess it's right.

CM, ROGER THAT!

Jetts
P.S. your "phenomenon" is in the definite minority.[sm=drowning.gif]

hmmm....

Indeed!

And there's more where that came from. [8D]

CM, O.K. you win, I'm bored, I think the point has been driven into the ground.......

???

Agreed, but that's not what my last comment was about. It was referring to my previous comment.

Decaf?

Jetts

Wow, my RNV question has turned into a pissing contest

Doesn't that make ya feel special?
As I said a few posts ago, case closed.

Jetts
P.S. Did ya get yer' answer?