Taming a touchy needle

I have an ST.60 that was built for me by Tom Lay. It is an excellent running engine. The problem is that the needle setting doesn't give me much margin for error. There is a very small amount of movement (1/8th of a turn?) between a really nice 7 minute stunt run & nine or ten minutes of hang-on & hope it quits soon. (Especially since my Shark 45 is rather, uhh, porky.) Obviously this also makes the fuel load critical.
The setup is as follows - .283 T.Lay Delrin venturi with an ST NVA through the middle, 10-29 GMA Powermaster fuel, T-bolt plug, 12-6, 12.5-6, 13-6 repitched & trued wood props, Lay tongue muffler, non-pressure uniflow tank.
Don't get me wrong, this setup works quite well once I get the needle just right, but it would be nice if it was easier to get a needle setting close at a different altitude when I go "down" to where most of the contests are held here in the NW. Would another head gasket help? More nitro? Less nitro didn't seem to help. Any suggestions would be welcome.

TIA,

Hi Nils,
Try this on a spare needle. Use a sharpening stone & slowly grind a more gradual taper in your needle. It will give you more twist movement for finer adjustments. (Super Tigre needles)

>I have an ST.60 that was
>built for me by Tom
>Lay. It is an excellent
>running engine. The problem is
>that the needle setting doesn't
>give me much margin for
>error. There is a very
>small amount of movement (1/8th
>of a turn?) between a
>really nice 7 minute stunt
>run & nine or ten
>minutes of hang-on & hope
>it quits soon. (Especially since
>my Shark 45 is rather,
>uhh, porky.) Obviously this also
>makes the fuel load critical.
>
>The setup is as follows -
>.283 T.Lay Delrin venturi with
>an ST NVA through the
>middle, 10-29 GMA Powermaster fuel,
>T-bolt plug, 12-6, 12.5-6, 13-6
>repitched & trued wood props,
>Lay tongue muffler, non-pressure uniflow
>tank.
>Don't get me wrong, this setup
>works quite well once I
>get the needle just right,
>but it would be nice
>if it was easier to
>get a needle setting close
>at a different altitude when
>I go "down" to where
>most of the contests are
>held here in the NW.
>Would another head gasket help?
>More nitro? Less nitro didn't
>seem to help. Any suggestions
>would be welcome.

I would make sure that the collet is tight, so tight you can barely turn it. ST needles frequently resonate, making tiny RPM changes makes it vibrate, changing the setting a lot. If you think about it, the needle is suspended like a tuning fork by the edge of the threads on the needle. If that doesn't fix it, try a Harry Higley needle. They are a lot stiffer and the threads are slightly larger.

If this doesn't work, (assuming you have a "through-the-middle" venturi), try looseing the spraybar and turning it a little bit. Doesn;t matter which way, just turn it 15 degrees. If still not good, then look around for loose backplate, leaky head, something like that. Or a leaky fuel line or filter.

If it runs OK otherwise, I would be hesitant to change stuff like nitro, venturi, compression, etc. If the above doesn't work, a smaller venturi, less compression, or more nitro will reduce the sensitivity. But that would be the last thing I tried.

OK.....I'll send you an ST-60 sprinkler venturi with a needle behind the venturi.(NC) This will take care of some of your problem..Trust me.

Scott (the checks in the mail)Riese

My thinking is you have a air leak..

OH this plane still have the plastic tank in it?

Can't wait to let you use my ST-60 with the mac's pipe set up

>OK.....I'll send you an ST-60 sprinkler
>venturi with a needle behind
>the venturi.(NC) This will take
>care of some of your
>problem..Trust me.
>

Unfortunately, having a hole drilled in the case for a "through the middle" spraybar makes it pretty tough to go back to stock

The standard east coast fix is to use the needle / spraybar assembly from an OS 40/46 fsr. This setup has a very fine thread, and matches the ST 60. Newer OS needles, while having a corser thread, still work better than the ST. Best guess is that the thin highly tapered ST needle vibrates, while the spring on the OS dampenes the needle, keeping the setting constant.

Guys --- I absolutely dig the Randy Smith Aero needle valve assembly from his PA's on my ST 60's. As far as I'm concerned now, it's the only way to fly! Finer threads, more taper, and the nylon insert on the locking nut holds a smooth adjustment without having to crank it so tight that you finger slips off into the prop! A great buy too, no more expensive than anyone elses. Try it, you'll love it.

I think it will solve the original problem stated also. BUT; the ST needles are normally good enough, but what he describes sounds like the old problem where you've bottomed the needle out too hard and bent the tip, so now it's extra touchy.

If you can't measure the bend or your eyes aren't good enough to see it, take a foot of fuel tubing and attatch it to your fuel inlet on your spray bar, put the other end in your mouth and blow while turning the needle. Do this in a very quite room and listen to the air flow and feel the back pressure. If it has a drastic jump right around the setting where you are flying, or it jumps up and down as you screw the needle in only one direction, then it is most definately a bent needle.

As an aside, this is also how I set my needle when I do a fresh install. Instead of bottoming out the needle and backing it out, I use this method and blow till the needle seals off, and back it out to max volume throughput, and then turn it back in to a middle volume. This is usually pretty close to the ideal running range of the motor, and at the very least, good enough to get the motor started.

EricV

Thanks for the suggestions guys. I'll get back to this thread this evening, right now it's time to head off to Bondoland.....

>>OK.....I'll send you an ST-60 sprinkler
>>venturi with a needle behind
>>the venturi.(NC) This will take
>>care of some of your
>>problem..Trust me.
>>
>
> Unfortunately, having a hole
>drilled in the case for
>a "through the middle" spraybar
>makes it pretty tough to
>go back to stock
>
> Brett

DUAAAAAA

Scott (to much medication) Riese

Nils

Sounds more like a venturi size to me. .285 seems small for a 60 size engine. I found touchy needle settings is usally too small of hole. I would think that a .300 would be a better size. Just my opinion.And there is so many more out there.

Gordie.

Nils,

Did you try replacing the overflow cap-off like we talked about at the Jim Walker Memorial? I've had similar problems trying to use those little vent caps that came with the old Smith's hard tanks. They just didn't seal quite good enough. Also, if you go the NVA swapout route, I've had good luck with the old Enya NVA, like came with the square venturi .35, in my ST 60 as well as the OS.

Good luck sortin' it out.

It seems to me that Paul Walker liked the .285. But you can go to a .312 to .323 to turn the props that the engine is capable of. A lot will depend on prop size, weather, and nitro content.

>>>OK.....I'll send you an ST-60 sprinkler
>>>venturi with a needle behind
>>>the venturi.(NC) This will take
>>>care of some of your
>>>problem..Trust me.
>>>
>>
>> Unfortunately, having a hole
>>drilled in the case for
>>a "through the middle" spraybar
>>makes it pretty tough to
>>go back to stock
>>
>> Brett
>
>
>DUAAAAAA
>
>Scott (to much medication) Riese

If he wanted to go back to a "true" or "Sprinkler" type venturi, a little JB Weld in the holes drilled for the restrictor type venturi will allow you to go back. Some people, however, will fill the back hole when drilling for the restrictor type, so it may still be a bit more of a challenge to convert it back.

All of the previous ideas warrant consideration.

BUT!!!!

Before trying them, I would call Tom Lay. He learned the business from George Aldrich. Also, Tom prepared the engine for you.

Have a nice day>

It's late (1:20 AM) & I've been in the shop for quite a while. Here's what I did tonight- I pulled the engine, tank & all the plumbing out. Removed the needle & it looks just fine. Checked for loose bolts, no problems there. I replaced all the fuel lines. (I checked & none appeared to leak but I replaced 'em anyway, fuel line is cheap.) It's been running a little slow inverted, so I popped the rear off the tank while it was out & moved the uniflow up an 1/8". If it's too high I can move the tank down (but there's no room to move it up, that's why I moved the uniflow tube). I re-checked the tank for leaks & put the whole works back together.
While I was at it I did a little cosmetic work on the wrinkly &%^$#@! black Ultracote & added some trim (I'll never build another black airplane!). It looks considerably better, I hope the sun doesn't come out during the Regionals!
I'll give it a try tomorrow & see what happens. I wanted to try a 12-6 APC just to see what would happen, but the two I have on hand both have huge holes for some unknown reason.
Dave-I tried a different type vent cap yesterday & it didn't make any noticeable difference.

Good night Mrs. Calabash, wherever you are....

Ok.
This morning at the field I put in a fresh T-Bolt plug, in addition to the stuff I did last night.
I'm not sure which of the above did the trick, but everything seems to be Hunky in the (big black) Dory, now. I had to screw the needle in about an additional 1/8th turn from where it used to be to get it running at 8,400-8,600 on the ground (12-6 wood). It was a little rich at the setting where it was running last Wednesday. When I was adjusting it Wednesday I was turning it just enough to feel that I'd moved it. Now it isn't anywhere near as critical.
It runs the same right side up & inverted now too, so I guess the uniflow is in the right place after the midnight adjust job.
I have a feeling there was a piece of ap-cray hiding in the works someplace. Then again, maybe the wrinkly ^%$#@! black Ultracote on the wings was causing a weird harmonic vibration of some sort. Ya' never know....

Scott- Thanks for the offer, but Tom filled the stock spraybar hole with JB Weld. Anyway, I have two more ST.60's with sprinkler venturi's installed & ready to go sitting on the engine shelf. If it hadn't straightened up I had plan "B" & plan "C".

Thanks guys,

It's been running a little slow inverted, so I popped the rear off the tank while it was out & moved the uniflow up an 1/8". If it's too high I can move the tank down (but there's no room to move it up, that's why I moved the uniflow tube). I re-checked the tank for leaks & put the whole works back together.

*is this one of your plastic tanks?
If not your going to have problems. UnIfloe and pick up need to be on the same line. Did I miss something?-

Scott(clueless in Portland)Riese

>If not your going to have
>problems. UnIfloe and pick up
>need to be on the
>same line. Did I miss
>something?-

Maybe. The uniflow and pickup don't necessarily have to be lined up.

Scott- It's a 6 1/2 oz. metal tank, there wasn't room for a plastic one. The pickup & uniflow don't have to line up. my pickup is still in the "bottom" of the "V" & the uniflow is against the tank wall right above it. It works fine now, very close to the same run right side up & inverted. The pickup just has to be where it can reach the fuel, the uniflow height is what matters to the engine. I have twisted the lines on plastic tanks so that the two lines end over/under to adjust *tank height* without moving the whole tank (as suggested by Bob Hunt in his video on the subject). That works too.

>
>>If not your going to have
>>problems. UnIfloe and pick up
>>need to be on the
>>same line. Did I miss
>>something?-
>
> Maybe. The uniflow
>and pickup don't necessarily have
>to be lined up.
>
> Brett

Then why is it when you remove the back of all of the smith and taffs tanks ALL of there's are lined up? Why is it? This is something new to me.

Scott(needs to be educated)Riese

-Then why is it when you remove the back of all of the smith and taffs tanks ALL of there's are lined up? Why is it? This is something new to me.

Scott(needs to be educated)Riese-

I dunno. Maybe the guys at Smith's & Taff's all have more room to adjust their tanks than I do. I DO know it doesn't matter. I'll show you Friday, maybe Thursday if I can get out of the Ol' Body Shop early enough.
There, now you're educated!

Steve, What Nils has done is a common fix for adjusting the height of the tank relative to the spray bar, when the tank cannot be moved. The spray bar "sees" the outlet of the uniflo tube as the center of the tank. By moving this outlet up or down actually changes the "head" to the spray bar.

As to your question, "why do SMP or Taff tanks all have their uniflo outlets mounted on the same centerline as the fuel pickup?", It's because for most people this is where it works best, given that most people don't fly wrinkled garbage sacks and think far enough ahead to build in enough room to adjust their tanks. (Nils)

See you in Portland if all goes well.

>Steve, What Nils has done is
>a common fix for adjusting
>the height of the tank
>relative to the spray bar,
>when the tank cannot be
>moved. The spray bar "sees"
>the outlet of the uniflo
>tube as the center of
>the tank. By moving this
>outlet up or down actually
>changes the "head" to the
>spray bar.
>
>As to your question, "why do SMP or Taff tanks all have their uniflo outlets mounted on the same centerline as the fuel pickup?", It's because for most people this is where it works best, given that most people don't fly wrinkled garbage sacks and think far enough ahead to build in enough room to adjust their tanks. (Nils)
>
>See you in Portland if all
>goes well.
>
>John

I'm going to go out a limb(I'm right handed) and say "If your uniflow is not lined up your asking for built in trouble"
So all of you stunt GODS Please reply.....

Scott(Feel no pain today)Riese

John musta meant Scott. Steve

John -
You won't see ME in Portland, I'm going to the NW Regionals Contest in *Albany*. What are you going to be doing in Portland, pray tell?

G Bag Man

I'll be the guy with the tin cup and an arm full of toy airplanes wandering around looking for the contest.

Out here in the real west, where we have miles and miles of arid land between anyplace you could call a settlement, The distance between Portland, (apparently a moderate sized city located next to a fog bank.) and Albany,(isn't that in Georgia?) is a mild walk in the park. So Nils, will you be leaving a trail of black plastic for me to follow?

-So Nils, will you be leaving a trail of black plastic for me to follow?-

No way. If you can't find the contest I won't have to fly against you.

Nils

Oh ok, I'll give you a hint. Albany Oregon is just NE of Rapid City. Don't leave before Saturday or you'll miss the traffic.

>Nils
>
>Oh ok, I'll give you a
>hint. Albany Oregon is just
>NE of Rapid City. Don't
>leave before Saturday or you'll
>miss the traffic.

Hey Nils, John thinks Albany is in Georgia and I learned it was in New York. Now you are telling me it is in South Dakota. Where, exactly is this place? (It is no wonder you guys don't get a lot of flyers up there. You have to travel all over the country to find it.)

Oops, my mistake. John, head for New York & look for black plastic.
Nils

>Oops, my mistake. John, head for
>New York & look for
>black plastic.
>Nils

BAD NILES...ALBANY is next to Millersburg.

Scott(just like a compass)Riese

Turn left when you get to Alice's stooge and don't forget to duck.