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Engine basics => Engine set up tips => Topic started by: Jerry Bohn on July 10, 2007, 03:51:46 PM
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I have a older manufactured but new OS.40LA and wish to block the boost port.
How is that done?
I'm sure there are several ways guys do it.
I'm open to methods and suggestions.
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The 40 LA does in fact have a boost port. this was discussed in great length and shown graphically hands on in Puyallup a couple weeks ago. apparantly however the 46 is not so hampered. My understanding from the conversation I overheard was that the boost port on the .40 is a recent development?
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I have an example of the LA 40 with and without boost ports.
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Guys, thanks for the info on how to block boost port.
Turns out my engine has NO boost port.
I raised the exhaust and intake ports 30 thousanths per the artical from Derik Picard in a 2003 issue of Stunt News.
This changing of ports supposedly put the torque and power at a lower RPM, aided 4-2-4 break and made for more user friendly engine.
It was my first time changing port height. The artical described how to do it.
Derik said "if you can use a toothbrush you can do this". I believe it.
Now to take engine out and bench run it.
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I didn't read that article, but in my experience raising the ports, i.e. increasing the port open time, is a speed trick to get more rpm. Unless the engine was very low timed I can't see the benefit in a PA engine.
Also, re: blocking ports. I made a delrin plug (same OD as the sleeve) to replace the sleeve when adding the JB weld. No sanding required after removing the plug when the JB sets.
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In my experience, I was shown how to raise the boost ports on my FP 40s, It does not raise the rpm band, actually it lowwers i, took my motor from 2 stroke break at about 10k to where its running a nice 4stroke break around 9400 makes the FP very managable, that and substantial oil, as in powermaster 10 -22 with an extra 6 oz of castor.
just my experience FWIW
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Mark, Right on.
Tom Dixon did that to my OS.40fp, works great.
Perhaps we need a engine guru (most are at the nats) to confim what is true.
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HI jerry. On the Fp40 I originally found that it wouldn't 4-2-4 or even 4 very well. After playing around with a bunch of port timing mods that didn't do much of anything I decided to try blocking the bost port. I did this not to "de-tune" the engine but to increase the velocity of the airflow in the transfer passages. The engine was designed to run in an RC plane with a 9-6 at 14 to 15 grand. I needed it to four cycle at 8300. Big difference in airflow requirements. My opinion is that the fuel wasn't staying entrained in the airflow with the boost port in use at this lower speed. In the end, closing the boost port caused the engine to trap more charge (due to correcting the velocity problem) at the lower speed. Thus the engine wasn't "de-tuned" it was " re-tuned" to operate more effeciently at the lower speed. Now about raising the liner. Raising the liner is usually something you do to raise the speed (rpm) where the ports are timed appropriately. If you think of the port timing not in degrees of crankshaft rotation timing but in actual time period. As in how long is it open and apply the velocity of the airflow through the engine to this time period. The object of the exercise (from a power perspective) is to trap as much of the charge as you can before the ports close. To do this you need to open and close them to match the flow through the engine. Port timing and flow velocity need to match what you are trying to do with the engine. Does any of this help?? DaveA
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Dave, I understand your thoughts on air vilosity etc. Thank you for sharing them.
I was following the advice of Derek Picard's artical from the Sept/Oct 2003 Engine Tests. This had to due with the OS LA.46.
He mentioned blocking the boost port for sure, then raising the transfer ports and exhaust port by 30 thousanths.
This was to quote:
"The results of this work should be a slightly milder but much sweeter running stunt engine that develops it's useful torque lower in the rev range. It will settle to a 4 stroke setting that bit quicker and retain a stronger 4-2-2 behaviour in the air".
This is what I was looking to get with my OSLA.40.
I don't doubt your credentials, but niether do I Derek's, as he was the Engine Test editor for Stunt News for years.
So I followed his advice with My LA.40. yesterday.
Today I ran it on the bench and to my surprise it ran (first time ever attempting such advanced engine mod). It ran very well.
Put it in a wet 4 cycle at 9,200rpm, tilted the test stand up to about 2 o'clock, it broke into a 2 cycle and tached at 10,200. Put it down and it immediatly went back to same 4 cycle rpm run.
Now if it performs like that in the air I will be a happy camper.
Power/Torque I don't no, that will be found in the air after getting the right prop and fuel massage.
Derek did not explaine why it does that.
Your explanation was a bit more thorugh and helpful as far as why what causes what.
This whole thing was an experiment to see if I could change the port heignt and not ruin the engine as well as getting a sweeter running engine, we shall see when it is in the air next time out on my old Oriental profile which has a Tom Dixon modified OS.40fp in it. That ran fine so I will have a good comparison as to how things truly worked out.
I may post the results after flight.
Thanks, Jerry
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Congrats on your engine work. Welcome to the fraternity! Engine work isn't hard if you remember that the round things like to remain round, the smooth things smooth, etc. I'm not familiar with the mod technique. Did you cut the liner or put in a shim? I'd be interested in how the mod affects fuel economy. Raising the exhaust port reduces the expansion work you get from the boom. This could also be why the engine seems milder. It is...
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Thanks Dave. I do feel kind of proud that I didn't ruin the engine.
I would be glad to fax you the artical, Derek explains more of what the mod is all about.
I'll e-mail you and if you would give me a fax number, It would be the best thing to do. Windows Vista made my scanner obsolete and can't afford a new one rigth now.
It's a 3 page articale.
In worst case I could make a copy and snail mail it to you.
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Jerry; No where in Derek's rework does he mention raising the exhaust port. It would be better if you could lower the exhaust, but that is not so easy to do. The reason for raising the transfer ports is to lower the blow down between intake and exhaust. Helps the engine to run steadier with not so hard of a break when going to 2 stroke, and also keeps it from running away.
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Jim, You are correct. I did it because I had heard about the blow down thing and stopping runaways. As long as I had the engine apart doing the Picard mods, I threw that in. Hopfully it will be a more user friendly engine as far as what fuel, prop and weather conditions are presented to the engine. Also I fly at 5000' altitude. That sometimes makes getting a good engine run hard to achive.
Thanks for correcting me and informing others about what was actually in the artical.
The engine broke very nice in and out of 2 cycle on the bench. Hope it performes as well in the air.
Wish I could post the artical on this forum so all may see exactly what it's all about.
Hopefully those that have been in PAMPA for the last 5 years and saved their Stunt News can referance the artical and figure out how to post it.
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Raising just the transfer ports does make a lot of sense.
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Reading through this thread I see what might be a "terminology" problem. I feel pretty sure (since I remember Derek's article) what Jerry is talking about is simply cutting the top of the ports and not raising or lowering the sleeve. 20-30 thousandths is the typically quoted measurement to remove from the top of the ports. Of course, doing it by hand means we are lucky to get "close", but the blowdown is reduced and the engine will give a better "4-2 run" 99.9999% of the time. And due to the less than CNC specs of hand work, each one might be a touch different. H^^ D>K
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Hi Gents, I performed Derek Pickard's mods on a converted r/c LA .46 a while ago.
The final result was transfer ports raised 0.030", factory OS venturi (unsure of size), ST nva and some home made head shims (roughly 0.010").
Running 10/22 home brew fuel (50/50 castor/synthetic).
Initially it was very thirsty, guzzling about an oz per minute! but settled down fairly quickly.
I found myself releasing the plane @ a 9400 rpm four stroke with an 11x6 apc. It cackles a bit like a B 40 in level flight.
Lower pitched props didn't seem to give enough airspeed at these rpms as it didn't speed up a whole heap in the switch to 2 stroke.
Model used for the testbed was an o/d with about 570 sq" area and heavy (50oz).
I'm thinking about building something LIGHTER in about the 650 sq" range using a box stock LA 46 running in a wet 2 stroke to compare the power delivery difference.
The modified example seems to be happy in the typical 550- 600 sq" classic sized ship if the weight is kept decent.
Cheers, Rob.
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Rob, I'm curious to know what the engine did when you used a higher pitched prop.
My test with the LA.40 will be a 555 sq.in. Oriental profile (presently being powered by a OS.40fp Dixon mod.), weight-.48 oz full load. Fuel 15%N -22oil-50/50, 10x5 APC prop. Flying at 5000' high. I plan to fly it tomorrow, Wind Gods permitting.
The ultamite goal is to put it in a full body Oriental which I believe I can hold the weight down to a max. of 48oz.
I do have a box stock LA.46 (except it has a ST needle valve and metal backplate), in reserve in case of power shortage. It flew a Mike Pratt Profile Force originally, plans are from Stunt News, it had flaps, at a chubby 52oz. Don't remember the sq.in. OOps too low of an outside loop, minus 6"altitude. Re-kit.
In your poinion was the modification to your LA.46 worth it so far ?
Bill, correct, cutting the top of the ports.
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Hi Gents, I performed Derek Pickard's mods on a converted r/c LA .46 a while ago.
The final result was transfer ports raised 0.030", factory OS venturi (unsure of size), ST nva and some home made head shims (roughly 0.010").
Running 10/22 home brew fuel (50/50 castor/synthetic).
Initially it was very thirsty, guzzling about an oz per minute! but settled down fairly quickly.
I found myself releasing the plane @ a 9400 rpm four stroke with an 11x6 apc. It cackles a bit like a B 40 in level flight.
Lower pitched props didn't seem to give enough airspeed at these rpms as it didn't speed up a whole heap in the switch to 2 stroke.
Model used for the testbed was an o/d with about 570 sq" area and heavy (50oz).
I'm thinking about building something LIGHTER in about the 650 sq" range using a box stock LA 46 running in a wet 2 stroke to compare the power delivery difference.
The modified example seems to be happy in the typical 550- 600 sq" classic sized ship if the weight is kept decent.
Cheers, Rob.
Hi Rob,
That concerns me that a 46 "seems to be happy in the typical 550- 600 sq" classic sized ship if the weight is kept decent." I would expect the 40 to be plenty in that size ship.
To me a 46 should pull a plane that size "while idleing"! (??)
Bill <><
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Guys, thanks for the info on how to block boost port.
Turns out my engine has NO boost port.
I raised the exhaust and intake ports 30 thousanths per the artical from Derik Picard in a 2003 issue of Stunt News.
This changing of ports supposedly put the torque and power at a lower RPM, aided 4-2-4 break and made for more user friendly engine.
It was my first time changing port height. The artical described how to do it.
Derik said "if you can use a toothbrush you can do this". I believe it.
Now to take engine out and bench run it.
Jerry;
Did you perhaps use a timing wheel and get the blowdown timing that you finally ended up with?
V/r
Bob
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I have my LA46 in a 60 oz. full bodied stunt ship. I too modified the sleeve by raising the transfer ports .035 thousands. I was shooting for .030 but I over did it by .005. It runs in a solid 4 stroke in level flight and breaks into 2 stroke when the nose is lifted. Prop is an APC 11 x 4 pitch. Fuel is the standard Power Master 10% nitro, 18% oil and I added 6 oz. of sig castor. It really runs sweet, I love it. This is the third one I've done. The other 2 were for friends and run the same sweet 2/4 break.
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Hi Bill,
What I was getting at was that I think the typical 550-600 sq" classic size model is a total no brainer with this set up.
I'm sure that in this instance the modified engine can certainly handle a bigger model. My 46 just "loafs" along in a model this size without any hint of trying to run away.
For an advanced beginner stepping up to models in this size range I think it would be an easy transition using this powertrain and many of the arf's and arc's available. Certainly allows more time at the handle.
Cheers, Rob.
P.s Jerry, I found that the engine behaved exactly the same going from an 11x5 to an 11x6, the model just sped up a bit giving me more tension in the overheads. In any case I really think that my engine could handle a bit more prop. Also at your altitude a higher pitch 5-6" may be beneficial in giving you a bit more "bite" and subsequent line tension.
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Thanks, Rob, that makes sense. ;D
I have seen a few Classic ships of the size you refer to with the LA 46 in them, stock I would guess. Very easy for a relative newbie to get in a bunch of flights! I guess the power is such that the needle is just not as critical. It's nice when you can miss the needle a *little* and still get a "decent" run.
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FWIW. I have a LA .46 on a 570 inch profile, I use a 12x5 wood prop cut from a zinger 13x5. my engine just loves this prop, my other ship, and ARC P-40 is abotu the same weight that is to say 48 oz, I use an APC 11.5 x 4 on it, again the engine just loves it. different set off speed with the apc, but I fly this one over the grass and dont want to spend 3 hours doing a prop for it only to loose it in the grass. The comments about missing the needle are very relivant to me, I am still learing about these littel marvels we call engines so sometimes I miss it rich or lean a bit, that motor just pulls away happy as a clam.
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I am flying a LA 40 in a ARF Oriental, turning an 11-6 PwerPoint on 10% Omega fuel. The engine is box stock with a .265 venturi & OS needle. In a word the engine runs PERFECT and loafs around with the 550 sq-in bird - no doubt it could fly more.
If I was to power-up this bird with a LA46 I would expect it to be more powerful, probably use a bigger prop, and probably a little more fuel. However I would also have to go from .015 lines to .018, then add a little tip weight, and probably increase the (inefficient) line rake. In sum the "power-up" would cost me additional weight and flying performance, in order to deliver the higher power.
Now the clincher: if I take that LA46 and "detune" it by revising the timing, then I would be consciously giving up power (possibly to lower power than the 40?) but I am still stuck with the big lines tip weight line rake and extra fuel!
This does not sound like the trade I want to make... No free rides!
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Jerry:
Oriental is trimmied out at 48.5 oz. I have flown it with both a tounge and pipe muffler, stuck with the pipe because I needed the noseweight. However, no real difference in mufflers (I like the sound of the tube bettter tho)
In retrospect, I built in about 3 oz of tailweight, then added noseweight with the heavier muffler. Obviously I could switch back to the toungue muffler, and remove some tailweight to net out a 1.5-2 oz. total weight save, then again it is working pretty well as it is...
Flying on .015x63' lines at a 4-cycle lap times in the 5.3-5.6 range - does not really break 4-2-4, but you can here it "digging in" during manuvers.
In the "what have I done" catagory, you have modified an engine, got the change you were seeking and didn't break anything Is it "detuned"? I suggest the more pertainent question is does it WORK for you?
May I instead suggest that you have consciously made a modeification to an engine and got the result you were aiming for.
In short you have achieved the lofty position of ENGINEMAN!!! :)
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Hi Dennis,
You make a very valid point, sharing the view of many others from what I have seen on the various forums.
My employment for the last few years has stopped me being able to commit to regular club comps though a recent job change has seen my weekends free up of late.
For the last few years I have only been fun flying socially, mostly on private property and haven't had to meet any regulations. We pull test to minimise any chance of an ugly incident though.
From what I can gather most of the guys out here run LA.46's on .015" lines, they only have to meet the pull test requirement. The only real concession is the extra fuel consumption.
I guess if I was in the position of most of you guys (under AMA rules) I would certainly be leaning towards using a .40 sized engine.
If cost wasn't a factor I guess the ultimate would be to run something like a PA .40, VF .40 on pipe or a saito .40 and reap the benefits of .49- .60 size performance on the end of .015's.
Cheers, Rob.
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blocking one right now on a Tiger (new onemade in China) 51...........
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If cost wasn't a factor I guess the ultimate would be to run something like a PA .40, VF .40 on pipe or a saito .40 and reap the benefits of .49- .60 size performance on the end of .015's.
Cheers, Rob.
Hi Rob,
Way back when..... when 40s with pipes first made the scene, I was talking with Bob Hunt about that. He was a little nervous of running the set up with .015 lines, but as he said, that is all the AMA required! But he also said he would NOT fly it on .012 solids, which the AMA also allowed.........
With the .40 VFs we ran, you could feel a *little* stretch in the lines sometimes. I felt the optimum was actually .014 solids. Strong enough to fly a hot ST .60 on, yet smaller than the .018 strandeds.