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General control line discussion => Open Forum => Topic started by: Kafin Noe知an on August 01, 2023, 06:59:19 AM
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My XEBEC is almost finished. Currently waiting for the epoxy at the elevator to cure then will do the pushrod setting. I知 going to put OS LA-S 25 at the nose and 3oz uniflow tank.
The wing area is 500 sq. in. and the weight target is around 35-37oz dry.
What prop should I use? 9x4? 9x5? 10x3?
(https://i.postimg.cc/DZTr7rzz/184541-A4-0-F5-D-4650-8-B18-575-B7082-FF4-B.jpg) (https://postimg.cc/DWxJgbLV)
(https://i.postimg.cc/4NN1KQQ7/229-A5-D99-D1-CB-4558-86-F0-0-BE3-A74-D59-E8.jpg) (https://postimg.cc/5jTzTvGb)
(https://i.postimg.cc/LsfkdC27/BBF56-C65-EB33-4-F62-99-F5-03-D9-C2-B66-B03.jpg) (https://postimg.cc/f3zSmv3j)
Best,
Kafin
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Kafin,
I would suggest an APC 10x4. As an option a 9x4 might work but I have had better luck with the slightly larger prop with larger airplanes. Airplane looks nice. Have fun and enjoy.
John
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As stated start with 10-4. Myself with 25 size engine(LA) i would start with a 9-6 or 9-5. Use what makes the plane happy. The plane looks great. Now don't bruise the grass or pavement. H^^
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9-6. Be prepared to go to a 10-4 or 10-5. I am not a fan of high rpm low pitch. Always seems to fly the plane too fast for me.
You building skill are improving at an alarming rate. What is on the wing?
Ken
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I'd start with an APC 10-4, then make sure to at least try an APC 9-4. That should be a good size plane for a 45LA.
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9-6. Be prepared to go to a 10-4 or 10-5. I am not a fan of high rpm low pitch. Always seems to fly the plane too fast for me.
You building skill are improving at an alarming rate. What is on the wing?
Ken
No way on the 9-6, way too fast. 9-4 to start, 10-4 as an experiment once you have the 9-4 working properly.
Brett
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9-6. Be prepared to go to a 10-4 or 10-5. I am not a fan of high rpm low pitch. Always seems to fly the plane too fast for me.
You building skill are improving at an alarming rate. What is on the wing?
Ken
9-6 is good on a 40FP for sport carrier, so it's going to be too much for a 25LA. If you want to go the low RPM high pitch route, use a bigger, spindly engine (like a Fox 35) and struggle with the 2-4 break.
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Hiya Kafin
Looks pretty cool.
I concur with prop advice so far. y1
You have fuel proofed the engine bay I assume.
You may need a heavy prop (APC) and a spinner to bring CG forward?
Waiting to hear how it all goes!
Have some great fun.
John Carrodus
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A Brodak 40 would be a nice engine for that plane. For an LA25 on something that big I would use a Master Airscrew 9-4. It has less pitch, less load and more blade area than the APC. You'll want the engine revving close to it's peak HP in manuvers. Another good prop would be the APC 9.625 x 3.75N report is it works good on the LA25 / Nobler.
That's a nice looking plane, is it original scratch built?
MM
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One that I like is the APC 9.5x4.5.
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That's a nice looking plane, is it original scratch built?
MM
MM;
Looks like the Xebec is available as an ARF: https://www.powers-international.com/aero/craftline/xebec19-35arf-en.htm
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First of all, I'd like to say thank you all for your inputs on the prop size to start with.
The total dry weight turned out to be 28 oz, I was actually surprised when I found out. I thought the final weight would be around 35-37oz.
Given that I have a very light ship, I decided to go with 9 inch prop diameter, even though the wing area is quiet large for the 25 engine size.
I tried two props, 9x5 and 9x4.
And here's the details of my every flights:
1st flight (Maiden):
OS LA-S 25
APC 9x5
12,500-ish launch RPM
Avg 4.9 sec lap times
0.015 60ft lines
https://youtu.be/bTjk-3yRTdE (https://youtu.be/bTjk-3yRTdE)
2nd flight:
OS LA-S 25
APC 9x4
13,400-ish launch RPM
Avg 5.1 sec lap times
0.015 60ft lines
https://youtu.be/nw0Lr8cKxFs (https://youtu.be/nw0Lr8cKxFs)
3rd flight:
OS LA-S 25
APC 9x4
12,400-ish launch RPM
Avg 5.45 sec lap times
0.015 60ft lines
https://youtu.be/bs0wUD5jSrA (https://youtu.be/bs0wUD5jSrA)
4th flight:
OS LA-S 25
APC 9x4
12,900-ish launch RPM
Avg 5.30 sec lap times
0.015 60ft lines
https://youtu.be/JvE7TV5-DPg (https://youtu.be/JvE7TV5-DPg)
At the end of the day, I felt that my 4th flight was the best one (in terms of engine setup). Please advise if it still sounds too lean or not.
However, even though I like how the engine ran on the 4th flight during upright level, wingover, and inside loops, it showed some oddities when I was trying to go a full lap of inverted flight. The RPM seemed to drop and it flew slower yet the tension was decreasing. The moment I flipped the ship back to upright level, the power was restored. And after couple of upright level laps, I could do another inside loops easily.
I suspect this had something to do with the fuel tank height and the long lines I had.
(https://i.postimg.cc/3JXGMNTm/IMG-4751.jpg) (https://postimg.cc/Wh4zg2t1)
It seems I need to move the fuel tank a bit higher and change the in-line filter so I can shorten the fuel lines.
Does it sound like a plan?
Looking forward to hearing more feedback from you guys!
Best,
Kafin
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Shorten the fuel and don稚 change anything else before flying. Tank might need adjusting but the fuel line length is a problem
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Shorten the fuel and don稚 change anything else before flying. Tank might need adjusting but the fuel line length is a problem
Like Dan says, reroute the fuel line under (behind?) the muffler. Make sure it is attached to the spray bar nipple securely and get it as short as possible. If it still goes rich inverted, raise your tank where the peak of the tank is just above the center of the engine as it is sitting on the ground. The center of the tank needs to be about in the center of the bypass port on the engine. Refly and see how it goes. Have some one get lap times for both upright and inverted, and that tells you which way to go with the tank.
Type at you later,
Dan McEntee
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I like the transparent spinner.
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Sealing the needle valve with a short length of fuel tubing is an easy thing to implement. It will help prevent air leakage around the needle valve and give you more consistent engine runs and needle settings.
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First of all, I'd like to say thank you all for your inputs on the prop size to start with.
The total dry weight turned out to be 28 oz, I was actually surprised when I found out. I thought the final weight would be around 35-37oz.
Given that I have a very light ship, I decided to go with 9 inch prop diameter, even though the wing area is quiet large for the 25 engine size.
I tried two props, 9x5 and 9x4.
Shorten the fuel line, but that is not really causing any problems. It sounds marginally close on the last flight, but richening it up any more is likely to make it too slow. I think you might try the 9-5, see if you can get a good setting at faster lap time. You really only need a slight tweak, if it was me, I would probably twist in about 1/4" more pitch but I think you should defer that to later.
Brett
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Hiya Kafin
Just chop both ends of tubing to shorten and toss em in your tool box - it's never wasted, you'll use em sometime for something. Make sure your tank is level with centreline of the plane. I'd suggest you try that first for inverted without messing with the tank height. Change tank later if still not happy, change one variable at a time. 9x5 sounds good.
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It sounds marginally close on the last flight, but richening it up any more is likely to make it too slow.
Do you mean it痴 still a little bit lean on the fourth flight video?
The needle setting on the third flight video was actually 1 or 2 clicks richer than the setting on my fourth flight?
Does that sound happier?
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-Hi Kafin
As others have said, make the fuel line as short as possible. Also, if possible, locate the fuel filter such that it is not in direct contact with the hot engine or muffler.
I have three OS 25 LA engines on various models, and below is my personal experience.
- Stock engine with rear NVA and stock OS muffler. (I do have an OS replica front NVA on one engine but don't notice any performance difference compared to the OS LA stock rear NVA setup)
- Profile-mounted engine
- I run muffler pressure and use metal uniflow fuel tanks
- 5% nitro / 22% total oil (50/50 castor/syn)
- 9-4 APC sport prop (One of my models, a very light Flite Streak, uses an APC 9-3 combat prop as it was flying too fast to my liking with the 9-4 sport prop)
- For equal lap times, the centerline of the fuel tank is approximately 1/8 inch above the center of the spray bar/venturi centerline.
- The 25 LA seems happiest running fast. Just like the OS owner's manual says, I first find approximate peak rpm (i.e.: just before the engine sags), then open the needle (richen) around 20-30 degrees. That is where the 25 LA likes to run. I don't pay particular attention to ground rpm. And don't go any leaner than the 20-30 degrees.
- I run the engine as noted above, then test-fly the model and adjust model lap speed with prop pitch. I don't normally try to adjust lap speed with ground rpm. I run the 25 LA engine where it likes to run, which is fast, and adjust prop pitch as needed.
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Do you mean it痴 still a little bit lean on the fourth flight video?
The needle setting on the third flight video was actually 1 or 2 clicks richer than the setting on my fourth flight?
Does that sound happier?
#3 sounds about right to the extent I can tell, but is clearly too slow. Doing a few loops in good conditions, it is fine at that speed, but I think you will have problems trying to do much more than that, at that speed. So you need about that "setting" but more speed - so, more pitch, to first approximation. If it was me. I have the means to repitch the prop and I would go to about 4.25-4.5" to solve this. If you only have a 9-4 or 9-5, use the 9-5.
I note that this appears to be (and sounds like) the "old" 25LA, not the new one that I have been using, so, you might well wind up with something different from me.
I also note that I might also try more nitro, if you are running 10%, try 20, that will increase the speed at the same "setting" and/or richen the setting at the same speed. I understand that this might be more problematic for you than for me. That will at least tell you if you are on the right track.
Brett
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Is that right $314 shipped to west coast?
MM 8)
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Is that right $314 shipped to west coast?
MM 8)
Yes, that's about right.
I paid $295 to get it shipped to where I live in Indonesia.
Best,
Kafin
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#3 sounds about right to the extent I can tell, but is clearly too slow. Doing a few loops in good conditions, it is fine at that speed, but I think you will have problems trying to do much more than that, at that speed. So you need about that "setting" but more speed - so, more pitch, to first approximation. If it was me. I have the means to repitch the prop and I would go to about 4.25-4.5" to solve this. If you only have a 9-4 or 9-5, use the 9-5.
I note that this appears to be (and sounds like) the "old" 25LA, not the new one that I have been using, so, you might well wind up with something different from me.
I also note that I might also try more nitro, if you are running 10%, try 20, that will increase the speed at the same "setting" and/or richen the setting at the same speed. I understand that this might be more problematic for you than for me. That will at least tell you if you are on the right track.
Brett
Great, thanks Brett.
Yes, my LA is like 20 years old now.
I had 9x5 on my maiden flight, but I set it too lean. NV position is at 1.75 turn ; got 12,500 RPM ; 4.9ish lap times ; it sagged when going into loop.
So, putting the 9x5 back and going a little bit richer to NV position at about full 2 turn (just like the NV position in the third video), I guess it will put me at around 11,900-12,000ish RPM and lap times in between 5.1 and 5.2 sec (still good lap times, I believe).
Will try it this setup on my next flying session, and I'll keep you updated!
Best,
Kafin
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I guess it will put me at around 11,900-12,000ish RPM and lap times in between 5.1 and 5.2 sec (still good lap times, I believe).
Sounds about right - but don't get obsessed with the launch RPM, set it based on how it sounds when going from level to a maneuver - medium 2-stroke in level flight, leaned out in the maneuvers, but never "over the top" like in the first video. Once you get it working, then, measure it to give you a starting point for next time.
Brett
p.s. on closer inspection, I note that you are running what appears to be about a 2" wide suction tank, with open vents. Proceed as you have been, but when you get something pretty close, I strongly suggest running muffler pressure from the tap to the upper tank vent, and blocking off the lower tank vent with a plug after you fill the tank. This will raise the fuel delivery pressure, which is marginal at the ends of the flight, because it has to suck the fuel "uphill" about 2" to the spraybar. You will also have to close the needle a lot, but by that time you should have a pretty good idea what the launch RPM should be.