Author Topic: Needle valve inverted on profile (Read 3706 times)

DanielGelinas · « **on:** March 02, 2012, 07:08:07 AM »

Hi Guys,

Is there any problems in inverting the needle valve on a profile stunter? Other than the obvious fact that it will be tedious to use, I'm thinking I might save a few broken needle valves while learning the pattern.

Will the stunt run be affected?

Thanks,

-Dan

Bill Little · « **Reply #1 on:** March 02, 2012, 07:24:33 AM »

Hi Daniel,

I have never experienced a difference except you burn your fingers a lot!

BIG Bear
RNMM/AMM

Paul Taylor · « **Reply #2 on:** March 02, 2012, 07:34:54 AM »

Dan,
I know it is not the best NVA but if you use the remote NVA from a OS you can mount it on the back plate so that you can turn it sideways. It is not bullet proof but that is what I did while I was still learning.

Also you can bend a U shape music wire and glue it into the top of the fuse. Not real nice looking but may save the needle on a inverted landing. Stole that idea from Ty.

Rafael Gonzalez · « **Reply #3 on:** March 02, 2012, 10:46:08 AM »

Quote from: Bill Little on March 02, 2012, 07:24:33 AM

Hi Daniel,

I have never experienced a difference except you burn your fingers a lot!

BIG Bear
RNMM/AMM

FLOYD CARTER · « **Reply #4 on:** March 02, 2012, 11:41:33 AM »

I built a profile club trainer. The needle sticks up such that an inverted landing will wipe it out. So I epoxied a half-loop of 1/16" piano wire to the profile fuselage enclosing the needle. Now, an inverted landing will not hurt the engine.

Floyd

Grady Widener · « **Reply #5 on:** March 02, 2012, 01:55:21 PM »

Conventional outboard setup requires tank above engine centerline for even insides and out.
Hot finger needle will require tank below engine center for same.
Best,
Grady

Tim Wescott · « **Reply #6 on:** March 02, 2012, 01:59:07 PM »

And you've backed this theory up with experimentation?

Where the knob is has no bearing on things.

The total head drop is from the tank to the needle valve orifice, whose position does not change when you swap it around.

Mark Scarborough · « **Reply #7 on:** March 02, 2012, 02:19:56 PM »

Tim, what you say is correct mostly,, there has actually been some investigation,, it appears ( If I recall correctly ) that the needle orofice is not the deciding factor, its something about the pumping volume center? or something,, determined by crankcase size and shape.. but ultimatly, as you state. given the same engine, same tank, rotating the needle handle will not require moving the tank

Tim Wescott · « **Reply #8 on:** March 02, 2012, 02:30:14 PM »

Well, if you made some mutant venturi/needle valve combination that put the spraybar hole at a markedly different elevation, then I would expect that you'd need to move the tank to match. But there aren't many engines (other than four strokes) that don't have the center of the venturi on the centerline of the engine.

Bill Little · « **Reply #9 on:** March 02, 2012, 02:46:32 PM »

Quote from: Tim Wescott on March 02, 2012, 02:30:14 PM

Well, if you made some mutant venturi/needle valve combination that put the spraybar hole at a markedly different elevation, then I would expect that you'd need to move the tank to match. But there aren't many engines (other than four strokes) that don't have the center of the venturi on the centerline of the engine.

The much beloved ST G.21 series (in the past) had the venturi off set and the NVA much higher than others.

NVA placement is not the real factor in how much a tank has to be shimmed. I do not remember the explanation (I do remember a pumping center of the crankcase that Mark mentions). Tank shimming is an individual model thing. Identical models with the same engine/tank set up might actually need a different tank shim from one model to the next.

BIG Bear
RNMM/AMM

Steven Kientz · « **Reply #10 on:** March 02, 2012, 02:51:08 PM »

You can make your own Rnva holder like the combat guys do.Spend a little time at your favorite hardware store, you're bound to find exactly what you need. I modified some small plastic curtain hooks to hold the nva and use the Os spraybar. Mount the Rnva on the side of the fuse where you can get to it SAFELY.

Steve

Don Hutchinson AMA5402 · « **Reply #11 on:** March 02, 2012, 03:39:10 PM »

Would someone with a real understanding of physics and fluid mechanics please explain the mysterious "center of pumping pressure" to us and how it relates to tank position?
Don

Mark Scarborough · « **Reply #12 on:** March 02, 2012, 04:06:54 PM »

Don, I recall reading about it on SSW I think probably like 3 or 4 years ago. someone had conducted extensive experiments as I recall with varying the placement of the needle,, with respect to the tank, and concluded that there was some other relationship at work,, but I have no specific recollection of the actual dynamics, in fact I am pretty sure that the end result of the research was to the effect that, well they didnt really KNOW either, so basically, shim the tank until it works right,, LOL,,

@ Tim,, I was agreeing in principle with you,the location of the handle on the needle has no bearing on tank setup, but trying to make the point that the needle orifice is not the defining location relative to the tank,,

Jim Thomerson · « **Reply #13 on:** March 02, 2012, 06:02:40 PM »

I think the experiments were done by Ted Fancher and Al Rabe. However, my experience leads me to put the end of the uniflow on the same horizontal level as the hole in the spraybar. Sometimes I have to make a small correction, which I blame on my poor soldering ability not having put the uniflow exactly where I think it is in the tank. I have never had to move a tank more than maybe 1/16 inch. Fact of the matter is start out where you think it will work, and then move the tank if needs be to make it work to suit you, regardless of what I or any one else tells you.

jim ivey · « **Reply #14 on:** March 02, 2012, 08:58:39 PM »

brush-guard in front of nv

pick up point in tank must be on engine C/L on profiles and c/l of spraybar for upright or inverted mount.

Sean McEntee · « **Reply #15 on:** March 03, 2012, 02:10:39 PM »

Get the Harry Higley's Super Tiger-like NVA, and just cut down the Needle valve, and make the 90 degree bend so you can turn it just shy of clearing the fuselage. Another way to do it is build a guard on the nose out of ply that keeps the NV above the ground. Ive waxed off several needle valves in my day.....huh, dad??

Bill Little · « **Reply #16 on:** March 04, 2012, 07:20:54 PM »

Quote from: jim ivey on March 02, 2012, 08:58:39 PM

brush-guard in front of nv pick up point in tank must be on engine C/L on profiles and c/l of spraybar for upright or inverted mount.

Hi Jim,

Years ago I did exactly what you say about tank mounting. When I got back into going to meets and competing I found that I would, more often than not, have to move the tank above the C/L on profiles. As much as 3/16th" for Fox .35 to get upright and inverted times the same.

Same deal with upright/inverted mounted engines, but not as much. Usually 1/8th" or less. I have never had to lower the tank, only raise it.

BIG Bear
RNMM/AMM

Wynn Robins · « **Reply #17 on:** March 04, 2012, 08:24:27 PM »

if you want a crash proof needle valve - cut a rear NVA off of an LA motor and just connect it using two lengths of fuel tube. it you hit the deck - the tube pops off but the NVA is fine

Joseph Patterson · « **Reply #18 on:** March 04, 2012, 08:43:19 PM »

Near as I can recall (my recalling mechanism may be defective at this stage in my life) Frank Williams did an article or two in "Stunt News" years ago on tank head pressures, TK heights, suction head relating to venturi size, and a few other things relating to this subject. He conducted a pretty in depth set of tests and calculations, none of which I can recall the results and conclusions- sorry I warned yawl about my recall thingy. Yea, I need some enlightenment on this center of pumping pressure too!!??
Doug

jim ivey · « **Reply #19 on:** March 05, 2012, 03:06:07 AM »

I picked up a vintage fox in a yard sle 50 cents . it had a top-flite white nylon prop, brittle as hell, right? my room mate picked up and tried to flip it. The prop cut his finger so he dropped it and broke the 50 year old prop and the needle valve. I wanted to kill him

jim

Lauri Malila · « **Reply #20 on:** March 05, 2012, 04:33:32 AM »

Hi.

From my experience, the point to look at is the very point inside the needle valve where the regulation happens. Usually it´s very close to the outlet hole in spraybar so it's difficult to tell the truth.
But I may be wrong with this, after experimenting with a remote needle I noticed that it's not that straightforward in reality.
I have modified Randy´s needle valves by drilling the needle cavity deeper, so that the point of regulation is as close to outlet as possible. At least I noticed a difference in tank position after moving the point of reg. 7mm down (horizontal cylinder).
As I see it, after the point of regulation, (and before spraybar outlet) the fuel flow is affected more by G forces.
I would also like to have rome reliable information about this issue, not just guesses

But to the original question, with normal valves (ST, PA etc.), the engine will most propably work just the same. Be prepared to move the tank down a few millimeters anyway.

Lauri

EddyR · « **Reply #21 on:** March 05, 2012, 11:22:26 AM »

Quote from: Jim Thomerson on March 02, 2012, 06:02:40 PM

I think the experiments were done by Ted Fancher and Al Rabe. However, my experience leads me to put the end of the uniflow on the same horizontal level as the hole in the spraybar. Sometimes I have to make a small correction, which I blame on my poor soldering ability not having put the uniflow exactly where I think it is in the tank. I have never had to move a tank more than maybe 1/16 inch. Fact of the matter is start out where you think it will work, and then move the tank if needs be to make it work to suit you, regardless of what I or any one else tells you.

I agree with Jim. I guess I have built as many profiles as most guys who started flying them in the early 50's and I never had to move the tank up untill my first uniflow tank and the uniflow was below the fuel pickup and all I was doing was getting the uniflow pickup in line with the needle valve. Also tanks with standard venting did not have the Fox burp.

Ed

Eric Viglione · « **Reply #22 on:** March 05, 2012, 11:40:59 AM »

Hey BIG, not if you use a K&B Green head!

Funny, when I came back to flying, to get my bearings back I used an old Banshee I still had, with you guessed it, a Greenhead .35 running Sig full castor fuel.
Poor Paul Sequira & Ed Ruane, They patiently launched me with a smile, never complained, even though my unmuffled, upward facing exhaust, used to blast his ears, gas him and coat his glasses in castor fumes every time.

Many years gone by, Paul & I still laugh about that one. He likes launching my piped PA's much better now too!

EricV

Quote from: Bill Little on March 02, 2012, 07:24:33 AM

Hi Daniel,

I have never experienced a difference except you burn your fingers a lot!

BIG Bear
RNMM/AMM

Bill Little · « **Reply #23 on:** March 05, 2012, 01:49:59 PM »

Quote from: Eric Viglione on March 05, 2012, 11:40:59 AM

Hey BIG, not if you use a K&B Green head!

Funny, when I came back to flying, to get my bearings back I used an old Banshee I still had, with you guessed it, a Greenhead .35 running Sig full castor fuel.
Poor Paul Sequira & Ed Ruane, They patiently launched me with a smile, never complained, even though my unmuffled, upward facing exhaust, used to blast his ears, gas him and coat his glasses in castor fumes every time.

Many years gone by, Paul & I still laugh about that one. He likes launching my piped PA's much better now too!

EricV

Hi Eric,

Back in my childhood, my flying buddy put a K&B GH .35 in a Midwest Cougar, upright mounting. He actually used the first "Chicken Stick" I ever saw. A tobacco stick which he used to wallop that K&B. It was truly a Knuckle Buster!

BIG Bear
RNMM/AMM

Chris Wilson · « **Reply #24 on:** March 05, 2012, 07:04:45 PM »

Quote from: Lauri Malila on March 05, 2012, 04:33:32 AM

Hi.

From my experience, the point to look at is the very point inside the needle valve where the regulation happens. Usually it´s very close to the outlet hole in spraybar so it's difficult to tell the truth.
But I may be wrong with this, after experimenting with a remote needle I noticed that it's not that straightforward in reality.
I have modified Randy´s needle valves by drilling the needle cavity deeper, so that the point of regulation is as close to outlet as possible. At least I noticed a difference in tank position after moving the point of reg. 7mm down (horizontal cylinder).
As I see it, after the point of regulation, (and before spraybar outlet) the fuel flow is affected more by G forces.
I would also like to have rome reliable information about this issue, not just guesses
But to the original question, with normal valves (ST, PA etc.), the engine will most propably work just the same. Be prepared to move the tank down a few millimeters anyway.

Lauri

Interesting points Laurie.

I have a friend who flies using a MVVS 51 rear intake rear exhaust engine in an inverted position (spigot type spray bar) and he had to raise the tank considerably to get even runs both upright and inverted.

The major difference with this engine as compared to the front intake MVVS's is the height of the spray bar.
So I see it as some engines consider the spray bars position more than others, go figure!

I remember tests done here in Australia with an inverted Super Tigre 46, it had a telescopic venturi with the spray bar attached to it and the range of varied heights made no difference to it .

Good luck with finding some reliable information on this subject!

Bill Little · « **Reply #25 on:** March 05, 2012, 07:44:34 PM »

Over the years I have seen several studies which pointed out that the actual dimension related to the NVA was not important on uniflow systems and tank shimming. Another case in point is the ST G.51 in stock mode. The NVA is set WAY off the mounts, but that doesn't matter much.

I dont know what actually matters I just shim the tank to get it equal. Not interested in the "whys", just interested in the final job.

BIG Bear
RNMM/AMM

Author Topic: Needle valve inverted on profile (Read 3706 times)

Grady Widener

Eric Viglione