NV position

[Gary Dowler]

If your fuel pickup line exits your uniflow tank pointing down, and your NV is mounted above it, assuming proper tank position will it make any difference if you invert the NV?  This will better protect the NV and greatly simplify the file tubing.  If it won't matter that the NV is above or below the tank. 

Gary

[Tim Wescott]

If it's a conventional needle valve, keep in mind that you want to avoid fondling your muffler if the engine is running.

[Gary Dowler]

If it's a conventional needle valve, keep in mind that you want to avoid fondling your muffler if the engine is running.

Good point. I'll have to check that. This remote needle on this OS is proving to be a bit of a pain. I might end up having to make a new mounting bracket for it, or replacing it with a standard NV assembly at the Venturi.


Gary

[john e. holliday]

If your remote needle is similar to the OS, it will take flying and adjusting to get it to work to your satisfaction.   I know on one of my OS's I have to run muffler pressure and adjust the needle accordingly.

[Tim Wescott]

Good point. I'll have to check that. This remote needle on this OS is proving to be a bit of a pain. I might end up having to make a new mounting bracket for it, or replacing it with a standard NV assembly at the Venturi.

I can't remember where you are in your journey to Stunt Excellence.  If you're still at the "Sir Crashalot" phase, then you want the needle situated where it's easy to get at and won't touch the ground in a crash.  On a profile, that works out to parallel with the cylinder and behind it (you can do this with any of the OS remote needles that aren't molded in to the backplate, possibly at the cost of having to take some sheet metal and bending your own mount).

[Tim Wescott]

I forgot to mention: in theory, if you have no fuel leaks and the tubing is full, what matters to fuel draw is the position of the spraybar hole with respect to the tank's vent (if it's submerged) or the top of the fuel (if the vent is uncovered).  I'm not sure if every plane I've flown has actually sat down and read that theory book, but they seem to be pretty close.

The biggest drawbacks to a remote needle are that bubbles go through the needle at a different time than fuel comes out the spraybar, so Bubbles are Bad, before the engine is running it's easy to break the siphon at the spraybar and have air draw back to the needle, making starting a pain, and finally, when you run out of fuel the engine will go rich when the fuel in the tube up to the needle changes to air, and then the engine will give a really brief lean burst at the very end.  That last one isn't bad unless you like the burst of speed, but it takes some getting used to.

I wouldn't recommend flying with a remote needle once you're past crashing all the time unless you're knowingly doing something screwy, for your own reasons, you know why it's screwy, and you're accepting of the downsides (which pretty much describes my needle valve situation on my competition plane).

[Gary Dowler]

Tim, you nailed every problem I'm having.  I've had issues with bubbles, it has a noticeable delayed effect between adjustments and results, etc.   I am flying ok, my only issues have been with outside manuevers. I've made 3 unintentional horizontal landings with this bird. But I've learned that a significant part of this was due to lack of understanding of trim.  Much of this problem in now addressed.  Just awaiting finishing the paint touch up to get back in the air.

Gary.

[Tim Wescott]

Bubbles will still screw you up, and the remote valve adds no delay. If it takes time to respond to the needle it's either clearing fuel out of the case our it's thermal

[Gary Dowler]

Bubbles will still screw you up, and the remote valve adds no delay. If it takes time to respond to the needle it's either clearing fuel out of the case our it's thermal

Interesting, because regardless of being on the plane or the stand there is always a noticeable delay between adjustments and results. Sometimes 5-10 seconds. This is my first remote NV engine so I have no experience to compare this to.  I was inclined to think this delay was the result of the inch and a half or so of fuel tubing between the NV and the spray bar.

Gary

[Tim Wescott]

Interesting, because regardless of being on the plane or the stand there is always a noticeable delay between adjustments and results. Sometimes 5-10 seconds. This is my first remote NV engine so I have no experience to compare this to.  I was inclined to think this delay was the result of the inch and a half or so of fuel tubing between the NV and the spray bar.

Gary

You know how, when your wife is in the shower and you flush the toilet, she starts yelling immediately?  It's the same thing with that tubing twixt needle and spraybar: the message about the drop in pressure travels at the speed of sound in the tube, not at the speed of the fluid.

All of my OS FP and LA engines tend to be slow in responding to needle changes.  I'm in the habit of pinching off the muffler pressure or putting my finger over the vent & letting the engine speed up a bit, then listening or taching the thing as it comes back down.

[Sean McEntee]

Dad and I had a conversation about this very thing a couple months ago.  When running an inverted motor, he prefers the NV on the inboard side.  This puts the spray bar inlet inline with the pickup tube of the tank, making for the shortest distance between the two possible.  I, on the other hand, prefer the NV on the outboard side.  This puts the NV on the opposite side of the muffler so the muffler isn’t in the way.  Also it makes adjusting the NV with the right hand a bit easier (my left hand is almost useless)

Different approaches but they both work.  As for a side-mounted engine, however, getting under the muffler and the engine, combined with poor visibility of the NV makes it seem a bit unsafe imo.  If you’re trying to protect the needle valve from sheering off during inverted landings, a “skid” made of plywood or sheet metal that is a bit higher than the NV and placed on the fuselage near the NV will help.

[Dan McEntee]

     When Sean was younger, and still shy about putting his hand near the prop to adjust the needle, I used the rear needle set up that OS started putting on their FPs at that time, including the .20. It's the best needle valve set up as far as I'm concerned for a rear needle. No "O" ring to wear out and leak. I don't recall any delay in adjusting the needle. And I use that very same NVA on my Fox .35 speed model in a rear needle set up and there is no delay. I think you may be having an issue elsewhere. If it is the rear needle like what is used on the LA series of engines, that one uses an "O" ring and I don't know why OS went back to that.  I had no problems using that set up in Sean's younger days, because combat guys used it with good results, and so did speed and racing guys. You just have to have the venturi the correct size for the spray bar. It is smaller in diameter that a standard NVA. You have to choke it more on a cold start as there is less fuel dumping into the venturi, and when the tank runs out, if you don't have the tank kicked out at the rear a little bit, you get about 10 laps of false quitting while it decides that it is really out of gas. If you are experiencing this delay, check your venturi for a good, solid, tight fit as well as the spray bar.
  Type at you later,
  Dan McEntee

[Steve Helmick]

Having only used two remote NV's in over 60 years of modeling, I must say that both showed a delay in mixture response and quickly fell out of favor for that reason. The engines were (most recently) an OS .25LA-S, and (long ago) a ST G.21 .29 fitted out with a remote NV Assy. that OS made for the OS Max III .29X....pretty sure it was called a .29X, but maybe S or R or whatever. The .25LA was not easy to hand start, because of the bubbles. I would choke it good, but the fuel would run back out of the line between venturi an NV. Using a digital starter, it would fire off but die before fuel got back to the venturi. With the electric finger commonly used by the R/C bods, I'm sure it would have been just fine. If you're using a high pressure fuel system like a combat bladder, the remote NV delay is completely eliminated. Muffler pressure does not help.

Regarding NV Assy. position, other than bubbles not helping with starting and that delay thing, I don't think it will matter. Ted Fancher and Al Rabe both experimented with moving conventional spraybars up and down in the air intake. Both used different methods of doing that, but both reported the same results, which was that the spraybar height did not (NOT!) affect tank height adjustments. Ted's conclusion was that the only factor that mattered was the engine's internal layout, and coined the term "Pumping Center". I don't know if Al had any explanation for his results.

Knowing this, when I needed to add fuel capacity to the 6 oz tin tank in my SV-11, I fabricated a sump to fit, sawed (Danger Disc) a large rectangle out of the bottom of the tank, and soldered on the sump. I did not expect to have to adjust tank height. I added over 1 oz capacity, and it worked perfectly fine. With a Uniflow, the engine only "sees" the end of the Uniflow tube inside the tank. Without Uniflow, you're on your own. I have not seen any reason not to use Uniflow, except 4-strokes and weak 4-2-4 engines like the Faux .35.

Have you noticed that sometimes, stuff doesn't work exactly like the engineers expect? My brother, a life-long bachelor, was shocked to find out that when the toilet flushes, the shower goes hot. He is a retired "Rockit Scientist", lead engineer on the Sidewinder development at China Lake Naval Weapons Test Center. His simple minded machinist brother, wife and kids knew all about the shower/toilet flush effect, but not he!  Steve

 

[Tim Wescott]

Have you noticed that sometimes, stuff doesn't work exactly like the engineers expect?

That's because management consistently underfunds our research budgets.

[Steve Helmick]

"That's because management consistently underfunds our research budgets."


  Steve

[Randy Cuberly]

"That's because management consistently underfunds our research budgets."


  Steve

Actually that is very true and it always proves the axiom that there's never enough money to do it right but always enough to do it over!!

Randy Cuberly

[Mike Haverly]

Actually that is very true and it always proves the axiom that there's never enough money to do it right but always enough to do it over!!
and make it more complicated.  Another simple-minded machinist point of view

[Tim Wescott]

Actually that is very true and it always proves the axiom that there's never enough money to do it right but always enough to do it over!!
and make it more complicated.  Another simple-minded machinist point of view

Mike, I really don't know what you mean about engineer's making machinists' lives more complicated.

[Steve Helmick]

My view has always been that since there are no new elements (speaking in terms of chemistry), if engineers were really as good as they think, they'd have designed all the amazing current and future stuff hundreds or thousands of years ago. Steve     

[Tim Wescott]

My view has always been that since there are no new elements (speaking in terms of chemistry), if engineers were really as good as they think, they'd have designed all the amazing current and future stuff hundreds or thousands of years ago. Steve   

Then why didn't machinists get to it before the engineering eggheads got a chance?

[Steve Helmick]

We'uns jus' sit in the lunchroom waiting for engineers to send down bad CAD drawings with ridiculously close tolerance requirements. I've gotten blocks of 1018 for parts that said "any aluminum" on the PL, either ordered by, or sawed up by an engineer. Steve

[Lauri Malila]

Regarding NV Assy. position, other than bubbles not helping with starting and that delay thing, I don't think it will matter. Ted Fancher and Al Rabe both experimented with moving conventional spraybars up and down in the air intake. Both used different methods of doing that, but both reported the same results, which was that the spraybar height did not (NOT!) affect tank height adjustments. Ted's conclusion was that the only factor that mattered was the engine's internal layout, and coined the term "Pumping Center".

Hi Steve,

I guess you are talking about height of conventional spraybar that goes through venturi tube? (Because height position of remote valve between spraybar and venturi does not matter.)
From a very basic physics point of view, there is no such thing as "Pumping center". Only thing that matters if you want a constant fuel head pressure in static situation (level/inverted flight) is spraybar at same level with uniflow & pickup tubes.
What Ted actually figured out is some sort of a pseudo value (of tank height versus nv) where 2 faults compensate each other in best possible way. So you create a fault (tank height) in attempt to compensate asymmetric behaviour caused by the internal flow dynamics & oil accumulation inside crankcase.
Sometimes it's possible to find an acceptable compromise but a better way is to find an engine position where running is symmetrical when nv hole and pickup & uniflow tubes are at same height.

L

[RandySmith]

 " Regarding NV Assy. position, other than bubbles not helping with starting and that delay thing, I don't think it will matter. Ted Fancher and Al Rabe both experimented with moving conventional spraybars up and down in the air intake. Both used different methods of doing that, but both reported the same results, which was that the spraybar height did not (NOT!) affect tank height adjustments. Ted's conclusion was that the only factor that mattered was the engine's internal layout, and coined the term "Pumping Center". I don't know if Al had any explanation for his results.  "

That is  actually not  correct, when you move the venturi up and down, it does the same thing as moving the tank, NOTE...  you are not doing anything to the pumping action of the engine, but it does indeed change the  run.
I have made many adjustable venturi setups for people, Kaz Minato is one that can tell you it does work. The way it works is a center venturi is slipped into an outer venturi body, the center has the feed holes, and can be  moved up and down in the outer venturi body.
The NVA  position makes little difference, what does make a difference is the point where the flow exits the venturi and enters the airstream, moving this   will   change the run, and  is  dead reliable in making  tank adjustments, without having to  touch the  tank

Regards
Randy