Prop choices LA46

I have had my Vector40 back in the air for 6 weeks or so after the pushrod failure/lawn dart incident.
Some specifics :LA46 w/ tube muffler, Zinger 11x5, launch at 9600 rpm, 5% fuel, line length is 63' eye to eye, 5.2sec laps. Engine is in a 4 stoke most of the time except for consecutive loops and overhead eights. I like this setup but have to admit that windup in the wind is a problem. I have noticed that many people are recomending flatter pitched props and I am trying them but feel that I don't get enough speed out of them.There is also a noticeable loss of turn whenever I bolt one of the APC's on (althought I haven't tried to adjust CG to try to get some of the turn back) I have seen that those who use the 12.25x 3.75 and 11.5x4 are launching at 10,300 or so. Is this full 2-stroke mode or is there still some break?

Regards,
Monty

I've seen the 12.25x3.75 APC work extreemly well on the LA46 in the wind, but yes the corner did suffer and the model trimmed to suit. It was really the only time an LA46 has impressed me.

I might want to suggest that since these engines have been supplied from the factory with all sorts of venturis (the venturi of the week is...) that you might want to check the size of your venturi before moving off to what someone else has tried. And deck heights are going to vary. Your engine may not be the same as his. Trial (and error) is called for to see what works best for you.

But, yes, when running the low pitch props, the engine will be screaming on the ground. You never want to set it full lean and it should riched a bit in the air if the prop is right for the engine and venturi (and head shims and muffler and nitro content and...)

Sometimes trimming an engine is like trimming an airplane. You keep trying new things until you get it (close to) right.

Oh, and for that engine, I don't think a 5 or 5.5 inch pitch is all that bad if you get it set up right. And if diameter is hurting your turn, then you probably have the CG set too far forward.

I am running an LA-46 in a 47 ounce Buccaneer on a 12.25 x 3.75 APC cut down to 12 inches. The engine is box stock except for the venturi and needle. I run it on 5-22 powermaster and the only screws that have ever been touched were the two that held the rear needle bracket to the back plate.

Except for maybe fuel, this is the exact airplane and set-up that Doug Moon won Expert with in Dallas a couple of years ago. It is also the only airplane I have ever had that could fly the pattern doing 6 second laps in 10-12 MPH wind.

That prop works, I wouldn't even bother to try anything else...

LAST EDITED ON Jun-25-03 AT 03:03 PM (CDT)
 
>I am running an LA-46 in a 47 ounce Buccaneer on a 12.25 x
>3.75 APC cut down to 12 inches. The engine is box stock
>except for the venturi and needle. I run it on 5-22
>powermaster and the only screws that have ever been touched
>were the two that held the rear needle bracket to the back
>plate.

Bob;

I take it that you are using the 46LA in the Buc 740, not 746. Am I correct?

Sorry, yes it is the 740. Also forgot to mention running a FP-40 tongue muffler from RSM that I opened up by enlarging 10 of the 14 exit holes to .096

>Sorry, yes it is the 740. Also forgot to mention running a
>FP-40 tongue muffler from RSM that I opened up by enlarging
>10 of the 14 exit holes to .096

Why thank you, sir, for the info.

Tight lines.

I
>have seen that those who use the 12.25x 3.75 and 11.5x4 are
>launching at 10,300 or so. Is this full 2-stroke mode or is
>there still some break?
>
No. Actually, the engine purrs along in pretty much a solid 4 cycle if the diameter is trimmed to 12".

>I
>>have seen that those who use the 12.25x 3.75 and 11.5x4 are
>>launching at 10,300 or so. Is this full 2-stroke mode or is
>>there still some break?
>>
>No. Actually, the engine purrs along in pretty much a solid
>4 cycle if the diameter is trimmed to 12".

Brad;

Is that with the stock muffler, custom tongue, or ... ?

In as much as I pioneered the use of this engine in Stunt 4+ years ago I have stayed with the same set up for the most part ever since! I run fuel consisting of 6 or 7% nitro, 22% castor oil and 3% synthetic (Klotz). The best prop for me and my engine has been the 11 X 6 Top Flite wide blade which has become increasingly hard to find. Depending on the time of year and humidity I rarely launch at above 8900 rpm. This engine just purs and purs along! The one on my Model Air Profile , a kinda Gieseke Nobler, has way over 300 patterns on it and keeps on trucking! My venturi started out at .266 and maybe a tad larger now but not too much. As Leonard has sad it's try and fit deal for you to discover all by your self! The deck height on mine is at .043. Phil Spillman

LAST EDITED ON Jun-25-03 AT 10:44 PM (CDT)
 
Just got back from Riverwalk Park. Mike Haverly had his Buccaneer 740 out again, trying to trim it out. It has an OS .46 LA and Big Art tube muffler. He started out today with the 12.25 x 3.75 cut down to 11.5", launched at 9.3k and it turned 5.47 sec laps on 62' lines, 10 x 22 GMA Powermaster. The venturi would be .281", with a .156" spraybar. The airplane is heavy, tho I don't have numbers, and it was too slow. Next Mike tried a 12-4 cut down from a 13-4 APC. Seemed like it would be too much, too thick, etc, but worked pretty well. The one time I flew a similar engine and muffler on a Humongus, I liked a 12-5 APC or 11-6EW RevUp, tho I think the 12-5 might be better trimmed toward 11.5". I contend that if you can't replace it with an online purchase (delivered in time for next weekend), it isn't worth knowing how wonderfully it works, and I don't need it. JMHO.

Phil, am I right in thinking that the .043" is head clearance, not "deck height"? Deck height would be from the top of the liner to the top of the piston at TDC. Steve

Hi Steve, As I measure it the deck height is the space between the head's bottom edge and the piston's top at TDC. This is the dimension changed by adding shims. The ideal measure may change over the course of a year but my particular favorite engine has retained the same set up since established in late 1998/ early '99.

I've been running a LA46 on a Brodak Cardinal for three years now, the last two with a Top Flight Power Prop 12x6, cut down to 11x6, launching at 8000-8500 rpm, depending on temp, etc.
Lines:.018x67'lines, I plan to try shorter lines but tension is ok, so I'm slow to change, 5.3-5.35 lap times.
Engine: 2 head gaskets, .285 venturi, S.T. needle
Fuel: 22% oil, 5% nitro
Had been using a Thunder Bolt and a Merlin plug, about the same RPM for same needle, ran mostly in a four cycle mode, breaking late or not at all, gobs of power.
This year tried a (colder) Swanson Fire Ball Hot, now it breaks earlier and power(line tension) is still great! 2-4-2-4-2-4-2-4! I've tried low pitch props, and they might be quicker to dial in, but I take the sound of a 2-4-2 anyday.

LAST EDITED ON Jun-25-03 AT 11:42 PM (CDT)
 
I'm running a 46LA with a .272 venturi, .135 spraybar, Thunderbolt R/C long idle bar glow plug, stock head shims, Powermaster 10% 22% 50/50 oil, APC 11.5 x 4 prop, launch at 10,200, .018 x 62 foot eye to eye, 5.3 lap times. I'm going to try a cut down 12.25 x 3.75 to 11.75 x 3.75 next time out. I find the faster speed of 10K plus gives a lot less wind up in the wind. I use a 6 oz clunk tank and get about 6:50 to 7:00 engine run. I ran a RO-Jett muffler with the stinger drilled out and an OS 762 with it's stinger drilled out too.

All,
Thanks for your input. I trimmed the one 12.25 x 3.75 I have down to 12 inches. I will try it in the next couple of days and report back. I am thinking that my lap times will be a bit slower - which isn't a confidence builder, but I will try to let it show me what it can do rather than assuming it is going too slow to keep the lines tight. We'll see.
Regards,
Monty
Note: measured my venturi this evening = .285

Phil,

I know you've told me before, but I'm a lousy note taker-how big is the fuel tank on the Model air?? I'm putting an LA-46 in my new Time machine 50 and right now I'm thinking about a 4.5 ounce tank. I seem to remember you saying that your model air took 4.25 ounces for the pattern, but I might be wrong there.

Thanks!
Steve

Hi Steve, The tank on the Model Air is a 5OZ. Uniflow jobby from which I draw .5 to .375 OZ'S depending on the weather. My engine also is equipped with an OS FP .40 (etc.) NVA. For some dumb reason the settings I get on this arangement are better than those I obtain with an ST NVA even though the opening in the ST set up has to be larger to allow for appropriate choke area. Phil I believe that the magic number for choke area is 13mm2. That's 13 square millimeters! Phil

That is what makes the LA 46 such a great engine, as I posted before. While at Brodaks I saw an LA 46 run the nicest 4-2-4 I had ever seen. Then a couple of flights later another LA was running low pitch hi-rev and it sounded like it was on a pipe.. Both runs were perfect and both engines were stock except for prop and venturi.

I am running a 293 venturi with ST needle and Bru Line Green filter in the low pitch hi-rev mode and like it because it seems to be a little better when the wind comes up. With my engine I found the 293 venturi a tad large for consistent fuel draw but adding the air filter fixed it.

Bob,

Just imagine how nice that engine is going to perform in my 50 ounce 55" wingspan 635 Sq. In. Continental whenever I get around to building the thing. For a picture of how mine will look - just pick up a copy of the March 1971 Model Airplane News, but change the AMA number on the wing to 68146!

>That is what makes the LA 46 such a great engine, as I
>posted before. While at Brodaks I saw an LA 46 run the
>nicest 4-2-4 I had ever seen. Then a couple of flights later
>another LA was running low pitch hi-rev and it sounded like
>it was on a pipe.. Both runs were perfect and both engines
>were stock except for prop and venturi.

Exactly what we have been saying. Much more versatile than its predecessors. On the cheap too. Frankly, why anyone would use anything else for Intermediate or Advanced levels is a mystery.

It would probably be awesome with a pipe.

I failed to note that I was using a Big Art muffler, big difference.

This question might deserve its own heading, but to those of you folling this thread: How does a LA46 compare to a Super Tigre .46? In a 2-4-2 set up, I don't know how much more power, ease of starting, etc. could you improve upon, but then again I've never had a S.T. 46

I was able to try the APC 12.25 x3.75 (cut down to 12") on my
Vector40 this evening.
It had been a windy day and even though it calmed down there still must have been a stiff breeze at the top of the circle - so conditions weren't ideal. But, that prop works as advertised. I thought lap speed would be a problem but it wasn't. I actually overdid it on the first flight, launching around 10,500.(What is it about that prop that allows it to turn so easily, yet develop so much thrust?). I made two more flights, the last of which was in four stroke mode most of the time. I didn't time any laps but the speed seemed just about right to me.
Now as for the rate of turn - no it doesn't turn nearly as easily as it does with a 11x5 Zinger. (CG with the APC is as per plans)But I might be able to fly a bit slower and still keep good line tension.
More testing required!
On a related subject - this prop is fairly large diameter and about 42 grams. It is turning rather fast. It is possible that it is a bit much for a 520in2 airplane. Would a larger airframe, like the 630in2 Vector handle the gyroscopic forces more easily. I would like to build that plane - looking forward to building season.

Regards,