Prop change or not? If so, recommendations?
08-06-2008 | 11:47 AM
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From: Oklahoma City,
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Prop change or not? If so, recommendations?
I use an 8x6 APC prop on my little stik like airplane that has an old OS max 25 on it. The plane is heavy, and I'm gonna work on that. I want a little more airspeed and thrust if possible. I have to fly it at WOT to get it to do anything outside of just pattern circles.
08-06-2008 | 12:34 PM
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From: Garland, TX
RE: Prop change or not? If so, recommendations?
A lot of combat pilots use these on the OS 25FX (if that's what you have) for 2548 scale planes:
APC 10x3 $2.49
http://www3.towerhobbies.com/cgi-bin...?&I=LX1544&P=7
Master Airscrew 10x4 $2.39
http://www3.towerhobbies.com/cgi-bin...?&I=LXZ963&P=7 (square tip)
http://www3.towerhobbies.com/cgi-bin...?&I=LXNGU0&P=7 (scimitar)
If you got one of each, and hated them, you'd be out less than $10.
APC 10x3 $2.49
http://www3.towerhobbies.com/cgi-bin...?&I=LX1544&P=7
Master Airscrew 10x4 $2.39
http://www3.towerhobbies.com/cgi-bin...?&I=LXZ963&P=7 (square tip)
http://www3.towerhobbies.com/cgi-bin...?&I=LXNGU0&P=7 (scimitar)
If you got one of each, and hated them, you'd be out less than $10.
08-06-2008 | 01:49 PM
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RE: Prop change or not? If so, recommendations?
I would also try a 9 x 6 as Opjose has mentioned, the one that you are using by now is in the lower side of the range of that particular engine.
08-06-2008 | 08:39 PM
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RE: Prop change or not? If so, recommendations?
I wasn't aware of the 10x3, sounds like a good choice. What your plane needs is to shift into a lower gear, not flat out speed. The .25s that I have run get bogged down pretty easily. I would have suggested a 9x4.......you might find that the .25 likes to fly your plane with less load instead of more load.
08-06-2008 | 08:46 PM
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RE: Prop change or not? If so, recommendations?
Props are cheap enough at the small sizes that it can be fun to experiment a bit. Buy some different sizes/brands and see how they perform differently. You might find some surprising results!
08-06-2008 | 09:25 PM
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From: Rhinelander, WI
RE: Prop change or not? If so, recommendations?
I woldn't do too much with the props unless you have a tach to check RPM. You can't get power and speed from the same prop. Depending on what you intend to do, change the pitch. More pitch (within RPM limits) more speed, less pitch more power.
08-06-2008 | 10:47 PM
#8
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RE: Prop change or not? If so, recommendations?
Really need more information, but I do agree with MikeL. Props are cheap and in many cases the wrong prop will make an airplane/engine combination a complete dog. Small 2-cycle engines need to turn rpm to make power, and I suspect your OS just doesn't have the stones to perform well on a 9-6. I would try the following: 8-5, 9-4, or 9-5.
08-07-2008 | 12:20 PM
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RE: Prop change or not? If so, recommendations?
ORIGINAL: combatpigg
I wasn't aware of the 10x3, sounds like a good choice. What your plane needs is to shift into a lower gear, not flat out speed. The .25s that I have run get bogged down pretty easily. I would have suggested a 9x4.......you might find that the .25 likes to fly your plane with less load instead of more load.
I wasn't aware of the 10x3, sounds like a good choice. What your plane needs is to shift into a lower gear, not flat out speed. The .25s that I have run get bogged down pretty easily. I would have suggested a 9x4.......you might find that the .25 likes to fly your plane with less load instead of more load.
10x3 is not recommended for the .25 as it will produce only about 35mph airspeed at full throttle, which is only marginally above stall speed for the stik and does not meet the recommended prop diameter to pitch ratios.
O.S. recommends a 9x5 or 9x6 prop for sport flying and if moving up to 10" a 10x5.
08-07-2008 | 07:34 PM
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RE: Prop change or not? If so, recommendations?
His plane is already a dog with a 8x6, moving up to a 9x6 will only make it worse. I've run enough .25s to know that a 9x6 is an overload.
Are you saying that you have already tached his engine with a 10x3 and clocked the plane? Even if you haven't, 35 mph would be a doable cruise speed for any normally loaded model. I will bet that 40 mph is a more realistic actual speed.
I've spent 90% of my ".25 time" using 9x4 props on typical sport models and have gone up and down the ladder in the past looking for a better working prop, but always return to the 9x4.
Are you saying that you have already tached his engine with a 10x3 and clocked the plane? Even if you haven't, 35 mph would be a doable cruise speed for any normally loaded model. I will bet that 40 mph is a more realistic actual speed.
I've spent 90% of my ".25 time" using 9x4 props on typical sport models and have gone up and down the ladder in the past looking for a better working prop, but always return to the 9x4.
08-07-2008 | 09:45 PM
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From: Poolesville, MD
RE: Prop change or not? If so, recommendations?
I have a couple of those engines.
He stated that his plane is "heavy".
Thrust and pitch speeds are both an issue.
The 9x6 keeps the engine in O.S.'s recommended optimum operating range, which, for a heavier plane, tends to crank out more power, this comes from O.S. not me.
However given all he has stated he may be better off moving to a larger engine anyway, and leaving the engine for a plane where he could do exactly what you are saying.
He stated that his plane is "heavy".
Thrust and pitch speeds are both an issue.
The 9x6 keeps the engine in O.S.'s recommended optimum operating range, which, for a heavier plane, tends to crank out more power, this comes from O.S. not me.
However given all he has stated he may be better off moving to a larger engine anyway, and leaving the engine for a plane where he could do exactly what you are saying.
08-08-2008 | 12:18 AM
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RE: Prop change or not? If so, recommendations?
It really sounds like a bad case of engine constipation. I see cases of this all the time, especially when people load up their engine with too much load. So they put on a bigger engine, again with too much prop, only now they have also added extra weight. So the airplane still flys like a load of cr@p. There are two reasons that engine makers recommend heavy props. One is to make the engines quiet, and the other is pure marketing. 'This engine make suggests bigger props than that one, so it must be more powerful.' With the heavier prop, the mixture is much more critical, and the range between rich and lean is much much smaller.
Now CP only has about a quarter century of modeling, so perhaps he still has a few things to discover, but his suggestion is spot on.
Now CP only has about a quarter century of modeling, so perhaps he still has a few things to discover, but his suggestion is spot on.
08-08-2008 | 09:28 AM
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From: Chesnee,
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RE: Prop change or not? If so, recommendations?
Just an idea.... check your control surfaces.... primarily the elevator an rudder, to see if you have any up/down, left/right trim in it. You might have a CG or engine thrust line problem.
08-08-2008 | 10:04 AM
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From: Oklahoma City,
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RE: Prop change or not? If so, recommendations?
ORIGINAL: spiral_72
Just an idea.... check your control surfaces.... primarily the elevator an rudder, to see if you have any up/down, left/right trim in it. You might have a CG or engine thrust line problem.
Just an idea.... check your control surfaces.... primarily the elevator an rudder, to see if you have any up/down, left/right trim in it. You might have a CG or engine thrust line problem.
08-08-2008 | 10:15 AM
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From: Chesnee,
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RE: Prop change or not? If so, recommendations?
Yea, I don't doubt that she flies straight.... Lemme explain:
If your CG is too far back and your model is nose heavy with correct engine down thrust.... You'll have to give it up trim to keep the nose level.
If your engine thrust is high or low you'll have to add down or up elevator to keep the nose level.
If your engine thrust is left or right you'll have to add right or left rudder to keep your nose on course.
All these add drag to an airframe and depending on the severity, things can get pretty bad especially if you have multiple problems. What you want is an efficient plane. When I started this stuff, I put a plane in the air extremely nose heavy. The plane would fall at anything less than about 60mph (no kidding) and loops, inverted.... the fun stuff was impossible. The landing didn't go so well either.
I said just an idea, because once you have your plane flying straight and level (which you do) take a quick look at the elevator and rudder to see if neutral, or where the plane flies straight, is actual 1/4" down elevator, 1/4: left rudder etc. Some big trim problem.
If your CG is too far back and your model is nose heavy with correct engine down thrust.... You'll have to give it up trim to keep the nose level.
If your engine thrust is high or low you'll have to add down or up elevator to keep the nose level.
If your engine thrust is left or right you'll have to add right or left rudder to keep your nose on course.
All these add drag to an airframe and depending on the severity, things can get pretty bad especially if you have multiple problems. What you want is an efficient plane. When I started this stuff, I put a plane in the air extremely nose heavy. The plane would fall at anything less than about 60mph (no kidding) and loops, inverted.... the fun stuff was impossible. The landing didn't go so well either.
I said just an idea, because once you have your plane flying straight and level (which you do) take a quick look at the elevator and rudder to see if neutral, or where the plane flies straight, is actual 1/4" down elevator, 1/4: left rudder etc. Some big trim problem.
08-08-2008 | 11:46 AM
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From: Oklahoma City,
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RE: Prop change or not? If so, recommendations?
ORIGINAL: spiral_72
Yea, I don't doubt that she flies straight.... Lemme explain:
If your CG is too far back and your model is nose heavy with correct engine down thrust.... You'll have to give it up trim to keep the nose level.
If your engine thrust is high or low you'll have to add down or up elevator to keep the nose level.
If your engine thrust is left or right you'll have to add right or left rudder to keep your nose on course.
All these add drag to an airframe and depending on the severity, things can get pretty bad especially if you have multiple problems. What you want is an efficient plane. When I started this stuff, I put a plane in the air extremely nose heavy. The plane would fall at anything less than about 60mph (no kidding) and loops, inverted.... the fun stuff was impossible. The landing didn't go so well either.
I said just an idea, because once you have your plane flying straight and level (which you do) take a quick look at the elevator and rudder to see if neutral, or where the plane flies straight, is actual 1/4" down elevator, 1/4: left rudder etc. Some big trim problem.
Yea, I don't doubt that she flies straight.... Lemme explain:
If your CG is too far back and your model is nose heavy with correct engine down thrust.... You'll have to give it up trim to keep the nose level.
If your engine thrust is high or low you'll have to add down or up elevator to keep the nose level.
If your engine thrust is left or right you'll have to add right or left rudder to keep your nose on course.
All these add drag to an airframe and depending on the severity, things can get pretty bad especially if you have multiple problems. What you want is an efficient plane. When I started this stuff, I put a plane in the air extremely nose heavy. The plane would fall at anything less than about 60mph (no kidding) and loops, inverted.... the fun stuff was impossible. The landing didn't go so well either.
I said just an idea, because once you have your plane flying straight and level (which you do) take a quick look at the elevator and rudder to see if neutral, or where the plane flies straight, is actual 1/4" down elevator, 1/4: left rudder etc. Some big trim problem.
08-08-2008 | 01:00 PM
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From: Oklahoma City,
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RE: Prop change or not? If so, recommendations?
The battery is against the back of the tank, and the reciever is against the battery which butts up against the servo tray.
08-08-2008 | 01:15 PM
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From: Garland, TX
RE: Prop change or not? If so, recommendations?
It would 'look funny' on a stik, but you might be able to strap the battery pack to the engine mount and get rid of the lead weights.
08-08-2008 | 01:53 PM
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RE: Prop change or not? If so, recommendations?
ORIGINAL: carrellh
It would 'look funny' on a stik, but you might be able to strap the battery pack to the engine mount and get rid of the lead weights.
It would 'look funny' on a stik, but you might be able to strap the battery pack to the engine mount and get rid of the lead weights.
08-08-2008 | 03:17 PM
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From: Laurel, MD,
RE: Prop change or not? If so, recommendations?
I agree that you should try a 9x4 and 9x5 prop sizes.
The OP said "old OS MAX .25", which may or may not be a .25FX. In fact, it probably isn't an FX. Like some of the other guys here, I've run a lot of .25 size engines over the last 20-odd years, and a 9x6 works ok on light, fast airframes, but I think in this case a smaller prop is the way to go.
Also keep in mind that these engines aren't linear. Somes you actually pick up airspeed when you go to a smaller prop. I've seen planes fly faster on a 9x4 than on a 9x5, and the 9x5 was faster than the 9x6. The reason is that the engine makes so much extra RPM that it more than makes up for the drop in pitch, while the airframe's drag prevents the engine from really unloading with the 9x6.
You might try a 10x3 as welll, but honestly, that prop was picked for LimB and 2548 combat to keep the engine performance down. If you put a 9x4 on the same airframe/engine, you get better climb and speed and a lot more RPM.
The OP said "old OS MAX .25", which may or may not be a .25FX. In fact, it probably isn't an FX. Like some of the other guys here, I've run a lot of .25 size engines over the last 20-odd years, and a 9x6 works ok on light, fast airframes, but I think in this case a smaller prop is the way to go.
Also keep in mind that these engines aren't linear. Somes you actually pick up airspeed when you go to a smaller prop. I've seen planes fly faster on a 9x4 than on a 9x5, and the 9x5 was faster than the 9x6. The reason is that the engine makes so much extra RPM that it more than makes up for the drop in pitch, while the airframe's drag prevents the engine from really unloading with the 9x6.
You might try a 10x3 as welll, but honestly, that prop was picked for LimB and 2548 combat to keep the engine performance down. If you put a 9x4 on the same airframe/engine, you get better climb and speed and a lot more RPM.
08-08-2008 | 03:23 PM
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From: Oklahoma City,
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RE: Prop change or not? If so, recommendations?
It is a bushing engine, so it is a weaker style. I guess the fx would be a bearing engine?
08-08-2008 | 03:29 PM
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From: Laurel, MD,
RE: Prop change or not? If so, recommendations?
Yes, the FX is the current Bearing .25. Do you have the .25LA or the older .25FP? They are both good engines, but a 9x6 is certainly on the large side for either one.
