Author Topic: 25LA at altitude (Read 5220 times)

Brett Buck · « **on:** January 29, 2015, 10:49:37 PM »

  I had been wanting to try the 25LA in something other than sea-level conditions for a while to convince myself that it was a repeatable phenomenon. So, between that, and offering to let Bill Calendrella fly it, I hauled it down to Tucson for the Southwest Regionals last weekend. The answer is - it's still really good!

   The only change to my previous settings was to use YS 20/20 fuel - like I had been using in my RO-Jett 61 for the last few years when flying in Tucson. As per many previous discussions, I just kept adding nitro until the fuel consumption was the same as at home, and then it ran the same in the air.

The temperatures were in the upper 60's/Low 70's with little humidity and a pressure altitude of ~2200 feet (about the same as the real altitudes). I test-ran it on Saturday morning and got some RPM readings. With the YS 20/20 and no other changes I was just a *hair* down on RPM. The 50/50 point for the 4-2 break was about 13,200 RPM (compared to 13,400 RPM with 10% at sea level) and peaked at about 14,200 (compared to about 14400 at sea level). Very close to the same, just like the fuel switch on the RO-Jett.

   We flew it on Sunday after the contest, and it was very, very, good. I missed the needle on a few flights to begin with. I flew it with it 4-stroking in level flight, and while it was a little soft, it was certainly flyable and had the nicest 4-2 break ever, very gentle and the same on insides and outsides. Once we got it cranked up (about 13,400 on the ground) multiple people flew it and it was just dead-nuts, flight after flight. Tons of power - on my second flight I took off straight into a wingover and did the entire pattern without completing a lap, bolo wingovers, a dozen or so square 8's with no break, never slowed down or ran out of poop. Do that with an old ST46 airplane it and just gets slower, and slower, and slower until you have to give up.

   I think everybody who flew it was amazed at how good the engine worked, and what a good package it is. I know I did better triangles on my Skyray flight than I did with my real airplane. The only issue I have had is that the needle clicks are a bit too coarse, but it's so stable in flight that even if you get it a click too fast, it's still like falling off a log to fly with and you never feel rushed in the maneuvers. The fuel consumption was matched to the altitude by adding nitro, other than that, it ran about the same as it does at home.

   So, I have tested it enough to convince myself that the "new" 25LA is the best of the bunch of the small engines I have tested. The others are still good, but you won't likely do better for the money. Anyone else should be able to reproduce the same effect, just LEAVE THE ENGINE ALONE, run it STRAIGHT OUT OF THE BOX WITH *NO*, repeat NO CHANGES, bolt on an APC 9-4, and you are set.

   Brett

Brent Williams · « **Reply #1 on:** January 30, 2015, 03:07:16 AM »

Good info for us high altitude folks. I'm at 4300ft static and our summer DA's can be in the 7000+ft range here in Utah.

Would you consider changing the prop to a 10x3 or 10x4 for the extra 2000+ ft of static elevation?

Bill Calandrella · « **Reply #2 on:** January 30, 2015, 06:42:21 AM »

Just a quick comment here about Brett, the contest in Tucson and the people who attended.

Brett had offered to bring the Skyray to Tucson so I could fly it. Good offer. Even better was his offer to loan me a NIB OS LA 46 as I was trying to buy one and they were temporarily not available (got one now). This was after I had posted some comments on Stunt Hanger about getting back to it again.

So, on Sunday I arrived to watch the contest and saw Brett fly his ship with the RO-Jett 61. I was quite impressed with his performance, his plane and the engine. I had not met Brett in person prior to that day, so after a good look at the plane he had just flown, we walk to his car to look at the Skyray. I must say that for the type of plane that the Skyray is, it was quite impressive as well. Brett has covered the details of the engine and it's setup above, so I won't go on about it here.

Okay, after we looked at the Skyray the most humbling thing happen. Brett pulled out this container with many of his supplies, fished around for a second and came up with BRAND NEW OS LA 46 in it's box. What could I say... He didn't know me other than the posts here and he remembered his offer to bring the Skyray and the engine. That experience made me realize just what a wonderful bunch of folks make up the heart of this hobby.

Thank you, Brett. You are truly a gentleman!

Bill Calandrella

Brett Buck · « **Reply #3 on:** January 30, 2015, 11:28:19 AM »

Quote from: Brent Williams on January 30, 2015, 03:07:16 AM

Good info for us high altitude folks. I'm at 4300ft static and our summer DA's can be in the 7000+ft range here in Utah.

Would you consider changing the prop to a 10x3 or 10x4 for the extra 2000+ ft of static elevation?

Try it with the 9-4 first, but I would experiment. But be objective - one of the big mistakes that people have made with modern engines, based on 60's-70's era "stunt folklore", is try to max them out on the prop diameter to get more "power". That was a good plan with an ST46 or similar. On these engines, it is not always necessary or desirable to run larger props. Less load wakes them up, and less diameter makes the prop less efficient, allowing the engine to rev up more without excess speed, and release more power. With a Fox/McCoy/ST, it's not gaining any power as you drop the diameter so the loss of efficiency is just a loss. With engines like the 20FP/25LA/40VF/PA61, etc you can gain a lot of power faster than the efficiency drops, so you can be ahead of the game.

The other advantage is that the faster you spin the engine, and the more power you make, the more air has to go through it - making the "grossly oversize" venturi work perfectly well. If you slow the engine down (reducing the power) you are likely to have to choke down the venturi to get acceptable fuel draw. That's where people get into the cycle of rework, runaways, modifications, etc.

If I was going to make prop changes for altitude, I would increase the pitch before I increased the diameter.

Brett

Tim Wescott · « **Reply #4 on:** January 30, 2015, 11:54:34 AM »

Russel Shaffer usually flies out of Kalamath Falls, at around 4000 feet. When he comes down (literally) to fly with us in the Willamette Valley at less than 200 feet, he switches the prop on his LA 25 from a 9-4 to a 10-4 to calm his planes down.

So you may find that switching to a 10-4 gets you less power than a 9-4, or worse, less regulation. He's always after me to switch to a 9-4 prop on my LA 25, but it flies a Flight Streak on 60' lines with authority, so I don't want more power.

But like Brett says: give it a whirl and report back. You'll advance science if you do.

Balsa Butcher · « **Reply #5 on:** January 30, 2015, 04:18:14 PM »

One combination I have had good success with is the APC 9.5x4.5 on an FP-25. Lower RPM (11,000) than the LA-25 likes to turn but good power, line tension, and very repeatable fast 4 stroke run.

Garf · « **Reply #6 on:** February 02, 2015, 11:05:39 AM »

I find that a good prop for the 25 size engines is the MA 9.5-6. It's a little hard to find but it works well due to the nature of the Master Airscrew prop. Has anyone else tried this one?

Brett Buck · « **Reply #7 on:** February 02, 2015, 09:39:13 PM »

Quote from: Garf on February 02, 2015, 11:05:39 AM

I find that a good prop for the 25 size engines is the MA 9.5-6. It's a little hard to find but it works well due to the nature of the Master Airscrew prop. Has anyone else tried this one?

No, not that one, but similar . That is way too much pitch to run the engine in the desired powerband for stunt, at least for a 20/25FP or 25LA, TT25, even a Veco 19. if you are running your 25LA on a 9-6 you are giving up a tremendous amount of performance, not to mention run stability.

Brett

rustler · « **Reply #8 on:** February 03, 2015, 01:32:51 PM »

Quote from: Brett Buck on January 29, 2015, 10:49:37 PM

"new" 25LA - just LEAVE THE ENGINE ALONE, run it STRAIGHT OUT OF THE BOX WITH *NO*, repeat NO CHANGES, bolt on an APC 9-4, and you are set.
Brett

Brett - So, effectively the BB TuneUp for the 25LA? Reason for checking - I have one of Eric's Mosquito kits, originally two Fox 35's. At the moment I'm considering O.S. 26 or 30 4Str, or 20 or 25 FP. (Weight and power need considering! Maybe add the 25LA to the list.
Are we saying the 25LA-S + std. muff.?

Brett Buck · « **Reply #9 on:** February 03, 2015, 04:21:45 PM »

Quote from: rustler on February 03, 2015, 01:32:51 PM

Brett - So, effectively the BB TuneUp for the 25LA? Reason for checking - I have one of Eric's Mosquito kits, originally two Fox 35's. At the moment I'm considering O.S. 26 or 30 4Str, or 20 or 25 FP. (Weight and power need considering! Maybe add the 25LA to the list.
Are we saying the 25LA-S + std. muff.?

Everything in the box is on the airplane, except for the stickers. The only issue I have with any of it is that the needle clicks are a tad too coarse, which doesn't make much difference on a conventional airplane but would potentially matter on a twin.

Lack of power will not be an issue.

Brett

Steve Fitton · « **Reply #10 on:** February 04, 2015, 04:48:46 PM »

Thanks for reporting these findings Brett. I enjoy reading this stuff as well as the engine column in SN.

The discovery that the new LA-25 is good for stunt is such a boost for helping noobs. I tried an "old" LA-25 about 8-10 years ago and it was lousy compared to FP-20,25 engines. Now we know that if somebody shows up at the field with a new LA-25 that it *should* work. That makes troubleshooting much easier!

Brett Buck · « **Reply #11 on:** February 04, 2015, 06:20:23 PM »

Quote from: Steve Fitton on February 04, 2015, 04:48:46 PM

Thanks for reporting these findings Brett. I enjoy reading this stuff as well as the engine column in SN.

The discovery that the new LA-25 is good for stunt is such a boost for helping noobs. I tried an "old" LA-25 about 8-10 years ago and it was lousy compared to FP-20,25 engines. Now we know that if somebody shows up at the field with a new LA-25 that it *should* work. That makes troubleshooting much easier!

A good test seems to be - bolt on 9-4 APC, use 10%, tach it at the 4-2 break point (where it is cycling back and forth about 50/50 4 and 2), and at peaked out (max possible RPM). The 50/50 point should be about 13,100 to 13,400, the peak should be in the low 14000s. The old version wouldn't touch that.

As always, all bets are off if any of the following is changed:

venturi
spraybar (ST or Randy is larger and will reduce the choke area substantiall, although it works better in general)
muffler - any change, like reaming out the hole, not using the internal baffle, throwing it away and using a chip muffler to save weight, etc.
prop - only use a 9-4 APC for the test above, and don't complain if anything else doesn't work very well, my first sentence will be "what did it do with an APC 9-4 at 13400 RPM?" followed closely by "here's an APC 9-4" or "here's where to order an APC 9-4".
any internal modifications, or replacing parts with "better" parts. My first response will be "what did it do with the stock liner?" followed closely by "here's where you can get a stock liner and piston"

It may be possible to run it some other way, and it might even be better (I certainly haven't tried it with any sort of modifications), but I doubt it, and it's certainly an exceptional stunt engine as it comes. If it doesn't run that way, something else is wrong, not the engine setup. Note well the previous comments about break-in. It's safe enough to fly with straight out of the box, but the fuel consumption will be heroic at the beginning, and the engine will get richer and richer over the first 20 flights or so as it loosens up the front end.

Try it as it comes first, and I think it will do the job.

Brett

Robertc · « **Reply #12 on:** February 07, 2015, 09:05:24 PM »

I've built two of Sheek's Mosquito's (One that Eric is kitting) with Thunder Tiger 25s and it was plenty of power.

t michael jennings · « **Reply #13 on:** February 19, 2015, 10:52:21 AM »

Brett,

When you say "out of the box" did you include using the remote NVA?

If not, which NVA was used?

Thanks for the info.

T Michael Jennings
Knoxville, TN.

Tim Wescott · « **Reply #14 on:** February 19, 2015, 11:21:23 AM »

Quote from: t michael jennings on February 19, 2015, 10:52:21 AM

Brett,

When you say "out of the box" did you include using the remote NVA?

I'm not Brett, but I've read enough of his posts on this subject to know that when he said "out of the box" he meant "out of the box", not "out of the box, except".

Personally, I've had good experiences with remote needle valves. They're a bit worse at keeping the fuel pulled up to the venturi, but if you prime the motor correctly it'll run long enough to stay started anyway. They're a bit worse at handling bubbles in the fuel line, but you want to avoid that anyway. If you're still in the "crashes a lot" phase, and you fly a profile, then if you mount them correctly they're a LOT better in a crash.

I would repeat Brett's advice: out of the box. Straight out of the box. Do not pass go, do not collect $200 (or any needle valves). Just take the engine out of the box, mount it on the plane, and go flying.

If you absolutely cannot live with the notion of using a remote needle valve, then get a replacement that has a spraybar that's exactly the same diameter as the one that comes with the remote needle -- otherwise (as Brett points out) the engine will run differently.

The LA 25 and LA 46 are great stunt engines, unless your goal is endless farting around with engines rather than having a no muss no fuss run.

Brett Buck · « **Reply #15 on:** February 19, 2015, 03:09:43 PM »

Quote from: t michael jennings on February 19, 2015, 10:52:21 AM

Brett,

When you say "out of the box" did you include using the remote NVA?

  Yes, I used the rear needle. In fact, it was pre-set at the factory for break-in, and I used that as it was, too. It works fine. There are only two issues:
The response is coarse, in that one click borders on too much of a change. This is somewhat mitigated by the fact that the performance in the air is so predictabel that even if you get it a little fast, you never feel "behind" the airplane or rushed.
As predicted, if you crash inverted with a profile model, it breaks the backplate, too. I think you can safely turn it 90 degrees to avoid that, but I haven't run it that way yet. There is a flat on the inside of the backplate to clear the piston, but I tried it rotated and it does not hit at BDC. It *might* affect the performance.

  When I say out of the box, I mean, literally, exactly as it was delivered in all respects. That's part of the plan - find engines, and ways to run them, that require *absolutely no changes*, no real break-in, no "disassemble, clean, lube", no ANYTHING. Put on the right prop and fuel, and go fly it. As it turns out, almost any available engine these days works pretty well, particularly the smaller types (and then only because you don't need the full power of the large ones). The one change I permit myself is to replace a carb with a regular venturi. But even that is rarely really necessary for anything but the most critical applications, usually on two-strokes, the RC carb is fine, and offers another adjustment to get the right amount of power.

   Brett

Gene O'Keefe · « **Reply #16 on:** March 31, 2015, 08:10:46 AM »

Just a FYI -- Tower Hobbies has "discontinued" the LA-25 control line engine

Steve Fitton · « **Reply #17 on:** April 01, 2015, 12:48:03 PM »

Quote from: Gene O'Keefe on March 31, 2015, 08:10:46 AM

Just a FYI -- Tower Hobbies has "discontinued" the LA-25 control line engine

That proves that they read this forum. Once an engine has been identified as being suitable for Stunt, it must be discontinued at once!

Tim Wescott · « **Reply #18 on:** April 01, 2015, 01:04:53 PM »

We need to start looking for another good un', or resign ourselves to eBay scratchin' or frying electronics.

Geoff Goodworth · « **Reply #19 on:** April 01, 2015, 06:47:04 PM »

But the venturi and the front mounting NVA are still available and, if you want the rear mounted NVA, the necessary spiggot for through the venturi is still available. While ever the RC version is available, we can convert them—even using after market parts.

George Hostler · « **Reply #20 on:** April 08, 2015, 12:33:14 AM »

Quote from: Gene O'Keefe on March 31, 2015, 08:10:46 AM

Just a FYI -- Tower Hobbies has "discontinued" the LA-25 control line engine

Not only have they discontinued the .25LA-S, the .46LA-S is discontinued as well. The SuperTigre G-34 Dual BB Ringed Control Line w/Muffler is still listed, but has been under "Order Pending" status for a long, long time. Ditto with the G-51.

Author Topic: 25LA at altitude (Read 5220 times)

George Hostler