stunthanger.com
Engine basics => Engine set up tips => Topic started by: cory colquhoun on October 08, 2017, 06:13:43 PM
-
Would appreciate some advice,have la 46 nib with Rc carb and rear assembly, what's the best Venturi set up for sport stunt flying ,I don't mind the ra or would it run better with standard Nva ,also best place to get parts
Cory
-
Few guys here sells parts such as Venturis. Tower Hobbies has venturis and spring needles and NVA's as well.
Sent from my SAMSUNG-SM-G891A using Tapatalk
-
Read this thread (https://stunthanger.com/smf/engine-set-up-tips/list-'your'-set-up-for-the-os-46la/) before you go any further.
I'd only recommend the remote needle if you're still crashing all the time (because on a profile, you can relocate it out of the way of a crash). Otherwise, go with a normal needle setup.
The most common setup uses an ST needle valve from Randy Smith, and a right-sized venturi to go with it. I can't remember the correct size, but it'll be here. Note that the area of the venturi matters, so the right diameter hole if you're using the stock 3.5mm spray bar is different from the right diameter hole if you're using the 4mm ST needle.
No matter what, I recommend getting a slightly oversized venturi, and putting layers of nylon mesh over it -- more layers means (effectively) less venturi size, and you can tune it to match your plane.
-
Personally I think that starting with an oversized venturi is a bad idea; a smaller one has better fuel draw than a larger one, and you could always machine it out on a lathe if needed. Overly large venturi's make engines run poorly, from what I have seen. I know that when Tim says to start big, he means "ever so slightly too big", but a too small venturi will be more usable than a too large one.
To me, the panty hose means that you missed on the right size, although it is a good fall back plan if you should go too large.
And, it should keep dirt out of the engine, so not all bad...
-
Yes, start with the small venture. Then if you want to experiment on sizes, Lees Machine Shop has quite a variety.
-
Tim is a very smart and in-the-know gentleman, and I don't mean to be a contrarian, but it just seems like lots of people have more trouble from overly large venturi diameter than too small a diameter. And, the latter seems much more flyable than the former (from my limited observation here).
Easier to make the hole bigger than smaller later, as well, even if it isn't THAT easy, it's doable generally.
The panty hose tip is a great one if you are very close, and it also confirms which way to go for the ideal size.
R,
Target
-
I think there is a day's worth of reading pinned to the top of the engine section of this forum titled "LA.46 Set-Ups. If the information ain'tthere you probably don't need to know it.
Type at you later,
Dan McEntee
-
Would appreciate some advice,have la 46 nib with Rc carb and rear assembly, what's the best Venturi set up for sport stunt flying ,I don't mind the ra or would it run better with standard Nva ,also best place to get parts
Certainly there are many very good cottage industry suppliers. But you can also do the most obvious thing:
https://www.towerhobbies.com/cgi-bin/wti0010p?&I=OSMG9340
and
https://www.towerhobbies.com/cgi-bin/wti0005p?&I=OSMG1447&P=X
The correct size is 7.0mm (~0.276") if you use the stock OS needle (recommended). DO NOT start with a larger venturi and work it smaller with filters unless you have some expert assistance available, because you might not be able to recognize the symptoms, particularly if you are going to put it on a smallish airplane (35-sized or so). Many people get in trouble with too large venturis to "Get More Power" and then go off on a tangent with other changes (usually stacking in large numbers of extraneous head gaskets) and never actually try to get the venturi the right size. The stock venturi is about as large as you could conceivably use.
If you have venturi(s) made by aftermarket suppliers, it makes sense to get a range of venturis from about .260 to 275. Then use the general approach in this thread:
https://stunthanger.com/smf/engine-set-up-tips/fuel-consumption-48110/msg499234/#msg499234
Every place you see "close the throttle a tiny bit", substitute "change to a venturi .005 smaller" and every place you see "open the throttle" substitute "use a venturi .005 larger". Once you get close, then you can make small adjustments with little 1.5x1.5" squares of panty hose material held on with an o-ring to fine-tune it.
You can use alternate spraybars like the PA or RO-Jett, but that will require you to drill out the hole it goes through and doesn't provide much advantage. Teh fact that they are "continuous" instead of discrete clicks can be taken advantage of for extremely fine adjustments but it can make the unwary too prone to making tiny, irrelevant changes. Clicks are good and it's not too coarse that you will not be able to dial in the right setting - and if it is, you have an excessively large venturi.
The venturi sizes would also have to be generally larger because the alternate spraybars are much larger than the stock item, and its very difficult to put it back to stock once you have done it. Note that replacement crankcases ARE NOT currently available, nor are they likely to be in the future.
I haven't run the 46LA in any of my airplanes (it's too big for my usual test goat) but I have certainly helped with many of them, as recently as this morning. Stock, straight out of the box, it's a very good stunt engine and we could have only dreamed of the sort of reliability/repeatability/power like this back in the supposed "Good Old Days". It doesn't need much of anything done to it to get it to work very well, use ~4" pitch props, get it flying at a decent speed, adjust the performance in the maneuvers with the venturi size, and for the most part, leave it alone.
Brett
-
Tim is a very smart and in-the-know gentleman, and I don't mean to be a contrarian, but it just seems like lots of people have more trouble from overly large venturi diameter than too small a diameter. And, the latter seems much more flyable than the former (from my limited observation here).
Easier to make the hole bigger than smaller later, as well, even if it isn't THAT easy, it's doable generally.
The panty hose tip is a great one if you are very close, and it also confirms which way to go for the ideal size.
I suppose that you could go overboard with anything -- but I like being able to dial in a plane by stacking filters. Just one isn't going to have much effect at all on the engine performance, but it WILL keep the air coming in a bit cleaner, and it'll catch the droplets of fuel that a stock 46LA will spit out that do nothing but mess up your finish.
And yes, I meant that you should start with a venturi that's just a bit big and dial it down, not that you should start with some humongous thing recommended by your local speed pilot for getting the ultimate in horsepower out of the engine.
It's really pretty easy to dial in. I do just what Brett just said, instead of where he says to close the throttle or narrow the venturi, I put on another layer of mesh. I've never gotten above four with the mesh that I use. If you can figure it out doing what he says with the size of the opening, you can do it with layers of mesh.
If you want to go the venturi-only route, then do make sure you have a variety of sizes, as Brett recommends. The difference between really good and too big or too small is not a large one.
-
From Brett's post above, I got the link for the venturi, but the other link didn't take me to the needle assembly. Here is the stock O.S. needle assembly:
https://www.towerhobbies.com/cgi-bin/wti0001p?&I=LXCR49&P=M#technotes (https://www.towerhobbies.com/cgi-bin/wti0001p?&I=LXCR49&P=M#technotes)
I'm still a crasher, so when they got back in stock last month I got the three needle value pack. I know a lot of guys have put a lot of time into variations on venturis and needle assemblies, but I'm just a plain sport flyer so I just stick with stock.
Mark
-
Would appreciate some advice,have la 46 nib with Rc carb and rear assembly, what's the best Venturi set up for sport stunt flying ,I don't mind the ra or would it run better with standard Nva ,also best place to get parts
Cory
Hi Cory
If you setup the 46 LA with stock parts its better to use the smaller 25 LA venturi (252) with the OS NVA, if your going to use the larger diameter spray bar such as the ST or PA or ENYA then use the larger one .281. I have setup 100s of these for stunt flyers and this works the best, using the stock LA 46 venturi with the stock 20 Needle assembly makes the ventuir effectively around a 310 size the way we normally measure, because the tiny OS 20 needle is much thinner diameter
I have all parts in stock for the OS LA 46
Randy
-
At the end of the day I'm still learning, getting through beginner pattern now without crashes , been flying a .15 size spitfire on 52 ft lines ,I find for me this has been the best to learn on,it's quite touchy I figure if i can master this I can move on ,my son flys our larger ships as he is more advanced, but getting back to the 46 la just want a good easy reliable set up, so standard Nva sounds like it would be fine , thankyou gents for all help and advice
Cory
-
using the stock LA 46 venturi with the stock 20 Needle assembly makes the ventuir effectively around a 310 size the way we normally measure, because the tiny OS 20 needle is much thinner diameter
About .295 or 0.0233 square inches, which is right at the edge of the usable limits, as big as you could ever imagine using. That's why I am nervous about "starting too large" because it will work only when you permit the engine to rev up. The stock setup does work with sufficiently low-pitch and low-efficiency/small diameter props, but it is very marginal if you treat it like an ugly-looking ST46, or a really heavy Fox. Unfortunately that's what a lot of people try to do. Which strangely leads them to stacks and stacks of head gaskets, instead of venturi diameter which is the root cause.
I agree that a much smaller venturi would be just fine, and depending on the airplane, I would much rather see someone work their way up rather than down. Panty-hose filters are swell (and I probably was the first person to make extensive mention of them, after having been suggested to me by Richard Oliver) but I still think you should get the venturi about right and then use extra layers for fine adjustment, not trying to take a .275 down to .260.
I fought the same issue with the 20FP and 25LA, getting endlessly ragged on about the venturi being too large, and then find people trying to use 10-6s at 7800 rpm. The solution was to bolt on a 9-4 and rev it up to 12000 with the assembled experts all predicting it was going to seize because it was running in a 2-stroke. The pilot generally liked it, since it flew like gravity had been cancelled for the day.
Brett
-
" About .295 or 0.0233 square inches, which is right at the edge of the usable limits, as big as you could ever imagine using. That's why I am nervous about "starting too large" because it will work only when you permit the engine to rev up. The stock setup does work with sufficiently low-pitch and low-efficiency/small diameter props, but it is very marginal if you treat it like an ugly-looking ST46, or a really heavy Fox. Unfortunately that's what a lot of people try to do. Which strangely leads them to stacks and stacks of head gaskets, instead of venturi diameter which is the root cause. "
Brett you maybe right ?? However It was 301 not 310, that is what my program showed, and using it, it seems to "act " larger than that, at any rate the Os 20 bar is .134, the PA is .157 , that is .023 thou smaller across the largest point of the diameter of the venturi, So 23 thou across the largest part only make a .281 a .295?? that is only 14 thou difference, at any rate doesn;t matter because either your or my measure is TOO large, and the .281 work almost perfect with a PA ST or ENYA, or the OLD OS 40 size NVA which is .155, and it is not on the small size, its about right, because a .275 works very well too. The size range on the 46 with a .157 bar ( ST PA size ) is from .265 to .285
I have 100s of the LAs out there and people rave about how they run, and they are all over the country, and many other places in the world, so even ones I have in Georgia, and California, run very much the same
While I am at it this setup will run well with a 3.75 to 5 pitch prop
And the Merlin Hot Big Bore 2004 runs very well on these.
Regards
Randy
-
" About .295 or 0.0233 square inches, which is right at the edge of the usable limits, as big as you could ever imagine using. That's why I am nervous about "starting too large" because it will work only when you permit the engine to rev up. The stock setup does work with sufficiently low-pitch and low-efficiency/small diameter props, but it is very marginal if you treat it like an ugly-looking ST46, or a really heavy Fox. Unfortunately that's what a lot of people try to do. Which strangely leads them to stacks and stacks of head gaskets, instead of venturi diameter which is the root cause. "
Brett you maybe right ?? However It was 301 not 310, that is what my program showed, and using it, it seems to "act " larger than that, at any rate the Os 20 bar is .134, the PA is .157 , that is .023 thou smaller across the largest point of the diameter of the venturi, So 23 thou across the largest part only make a .281 a .295?? that is only 14 thou difference, at any rate doesn;t matter because either your or my measure is TOO large, and the .281 work almost perfect with a PA ST or ENYA, or the OLD OS 40 size NVA which is .155, and it is not on the small size, its about right, because a .275 works very well too. The size range on the 46 with a .157 bar ( ST PA size ) is from .265 to .285
I mentioned it only because I was very uncomfortable with the "start too big and work down" plan. What that seems to lead to is people concluding the engine "runs away" and then they go grab a handful of head gaskets and a Dremel tool. I know the stock venturi will work at sea level with a low pitch prop, but anything else and it's really iffy, based on what I have seen. Profile at the Northwest Regionals made me want to cry, one screeching , sagging run after another, from a combination of "too large venturi" and "stunt props" (i.e. too much pitch). Some Brodak 40s apparently come with a .308 venturi and people were running them at 8500 rpm - or at least that's where they started.
One thing people seem to very consistently miss is the relationship between rpm/HP and venturi size. There's another thread here where someone is trying the 20FP wth a 9-6 instead of a 9-4, and it won't draw fuel - probably because the flow rate difference is ~33 lower.
Brett
-
I mentioned it only because I was very uncomfortable with the "start too big and work down" plan. What that seems to lead to is people concluding the engine "runs away" and then they go grab a handful of head gaskets and a Dremel tool. I know the stock venturi will work at sea level with a low pitch prop, but anything else and it's really iffy, based on what I have seen. Profile at the Northwest Regionals made me want to cry, one screeching , sagging run after another, from a combination of "too large venturi" and "stunt props" (i.e. too much pitch). Some Brodak 40s apparently come with a .308 venturi and people were running them at 8500 rpm - or at least that's where they started.
One thing people seem to very consistently miss is the relationship between rpm/HP and venturi size. There's another thread here where someone is trying the 20FP wth a 9-6 instead of a 9-4, and it won't draw fuel - probably because the flow rate difference is ~33 lower.
Brett
Yep I have seen what your saying for decades, That is why I like to get the venturi size as close to right as possible, I know from experience the .281 works pretty well with the PA bar diameter, and the .253 works with the OS 20 bar diameter. And as I stated these setups will work great with 3.8 to 5.0 pitch props. I think the best Prop I have ever seen run on a OS LA 46 was the Old Bolly 11 3/4 x 4.25 and the 12.2 x 4.2 , I am making moulds on these, and these also work extremely well on the OS VF 40 - 46 PA 40-51 , Many other engines . Its a shame the 46 LA has been discontinued, I have about 12 left here but I think OS Should have kept this one. However I am working with the 35 ball bearing AX and it is looking good
Randy
-
However I am working with the 35 ball bearing AX and it is looking good
I would expect that to be a very strong engine as well. The only reason I don't have one right now is that it's clearly WAY too much power for the Skyray and I am not inclined to build a larger airplane just to test engines. Although the Imitation is legal for both Super 70's and NOS30...
Brett
-
I would expect that to be a very strong engine as well. The only reason I don't have one right now is that it's clearly WAY too much power for the Skyray and I am not inclined to build a larger airplane just to test engines. Although the Imitation is legal for both Super 70's and NOS30...
Brett
I am looking for something to be in the same power range as the TT 36 or Aero Tiger, and still be LIGHT, This engine is very light, and would be good in a Vector 40 SV40 Dreadnought 40, Stiletto , Chipmonk, Nobler Ares type airplanes, It would also be good in twister and larger Profiles, This one seem to be a good candidate
Randy