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Noob prop question

#1
Hey guys. I am a total noob to RC flight. Until FT, I was way to worried (and broke) to think about trying to learn how to fly a $100 (or more) RC plane. But now I have no problems tossing a dollar worth of foam into the air while my thumbs learn their way around the controls. I understand the prop numbering system. 8x4 means an 8 inch long prop that will move (theoretically) 4 inches forward for every revolution. My question is about the styles of props. What are the advantages and disadvantages or similarities and differences between an 8x4 slo fly and an 8x4 direct drive prop?? Is one better than another on the swapables?? Is one better than the other for a noob like me?? I built a nutball and had a few 30 second flights and broke a few props until it took a dirt nap from about 30 feet up. I have another nutball cut out and a FT flyer about 2/3 glued up but only one prop left. I am going to order some more but was wondering if I could/should order something different.
 

xuzme720

Dedicated foam bender
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#2
Right now I'd say stay with the cheap ones. They have more flex but as you're learning it won't matter much. As you learn and get more airtime and less repair time, then go for the stiffer APC or carbon props.

To answer your question though, The slow-flys have a different profile more suited to lower Kv motors, where the Direct drive do better on higher RPM's. At least that is the way I heard it...
 

Craftydan

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#3
On prop type, Xuzme is right here.

8x4 prop can be turned by a tiny 24gm motor consuming 85W at 1300KV*2S battery, or it can be turned by a beefy 90gm consuming 560W 1300Kv*4S battery (2 times the RPM, burning 6 times the power!).

The 24gm motor will happily throw either, but will LOVE the SF. The 90gm motor would HATE the SF at WOT, and would proably flatten the prop at 3/4 throttle. Probably won't break the prop, but you'd be robbed of power at the higher RPMs.

Now for which props, If you're using a collet adaptor it doesnt matter -- you're gonna break a prop wiht any less than fair landing. If you're using a prop saver adaptor, buy cheap, but not too cheap. If you get above the bottom tier, you should get a prop strong enough to break the band on the prop saver. The botom tier, however, will "save" the rubber band :(

Only measure I've found of not-too-cheap is cost (brand is unreported/unreliable at the lower levels). If they're selling a 5 pack for $2.50, expect them to be fragile (one of these broke when I put the prop-saver band on!). If they're 2 pack for $2.50, you might have a better chance. Of course, YMMV
 

rcspaceflight

creator of virtual planes
#4
The nutball isn't the best first plane. Fly your FT Flyer first.

I've had bad luck with prop savers. Either the bands are too fragile and break at full speed, or they are too strong and don't save the prop. Slo Fly props just seem too weak for the prop saver to do much good. But that's just my opinion.

No matter what you're going to break props. I'm debating whether or not I should suggest that you buy some of the cheapest props because you're going to break them regardless, -OR- if I should suggest you buy stronger props and use a prop saver. I currently use carbon fiber props and a prop adapter and I don't break props as often as I did with cheap plastic props and a prop saver, but I'm also more experienced since then. Maybe buy one, or two, Master Airscrew props and try it out to see if that works better. I really don't know which way to recommend.
 

Craftydan

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#5
. . . I dunno about that . . . MAS props are really nice and tough, but they're notoriously unballanced off the shelf. Last one I got, I had to switch to aluminum tape to get enough weight on the light blade to get it to balance. Ran smooth as silk after that, but needs a bit more skill than I'd reccomend for a first time.

Wrench, If you know how to balance props, Master Air Screw makes nice props. BIG, but nice. At 8x4, though, it'll shake your plane apart if it's as far off balance as my last prop (I know -- it was shaking my plane apart!). Try to get the "Electric Only" versions if you can. They've got smaller hubs (more likely have a good balance) and are easier to work with than the more common G/F series. Install the prop, and slowly run up the speed on the bench (hold on to it but watch the fingers and toes). If it's got a bad vibe to it, chop the throttle and research how to balance a prop.

I have gotten Gemfans from HK before, and they're cheap/nice props, but it's not advertised which ones are those. They're sold by name elsewhere.

APC does make a nice prop, but IMO, still a bit fragile for the cost.

Never used a GWS above 6", but the plastic they use is on the flexy side -- should survive a crash well, but inefficient at full power. If you're motor is on the small side (24g 2730's or similar), it'll work just fine, but expect to find another prop if you want a motor with more power.

Carbon, carbon mix, fiberglass reenforced, or composite blades should be stronger than the pure plastic blades, which means a better chance for durability.
 

FlairFan

Junior Member
#6
To reiterate some of the points Crafty Dan makes... You can visualize what happens a bit by just lifting your plane up by the prop. A slow-fly prop is going to bend at least a little bit no matter what's attached. It's not meant for "heavy lifting". The "E" props are meant to keep a lot of the rigidity but with less weight (when weight on an electric powered plane meant everything). Less weight takes less torque to get moving, so you gain a bit of efficiency.

Also, I've always felt that 'prop saver' was a bit of a misnomer... props are easy to replace. But a bent motor shaft... now THAT'S a problem. If the prop pops off, there's much less chance of bending the motor shaft. I guess 'shaft saver' didn't catch on.
 

Craftydan

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#7
Hey, anyone who starts his first post as "Dan is right" is OK in my book ;)

Welcome to the forum Rick.

Completely agreee about the prop/shaft saver -- when everything's sized right the rubber band breaks first, but it always ensures the motor shaft is the last part to get stressed.
 

rcspaceflight

creator of virtual planes
#8
Wrench, listen to them. I don't have much experience. I will also add though, I should have said it earlier, but Master Airscrew Props seem too thick at the hub to be used on a prop saver. And it is more of a shaft saver than a prop saver. And it is far better to break a prop than to bend a shaft. A thicker prop would probably be better. But somewhere along the medium lines. Not the cheap thin ones, and not the expensive thick ones. Somewhere in the middle.
 
#10
Thanks for the input guys. Instead of the direct drives, I think I am going to get some of the SF props. I am not at all supprised nor upset about breaking props. I did expect it. I do use the prop saver (shaft saver LOL) that came with the motor and I did break one band. Of course I never had the foresight to order extra bands so I had to get some o-rings at the hardware store. As for the Nutball, a guy I work with is an experienced RC pilot and he did say it was a handful in the conditions we were flying in (5-7 MPH winds with gusts up to 11 or 12 MPH) and with the high rates on. I also had my linkage in the wrong holes in the control horns. Either way, I have the Flyer just about done so I will give that a try next. Thanks again for the explanation.
 
#15
Well, I got the slofly props I ordered and now I have another problem......I think. The first set of props I ordered had a molded in hex that nested nicely on the prop saver. The new props came with bushings to fit on various size shafts but even without a bushing it will not sit square on the prop saver. Do I need to drill a pilot in the prop to fit the prop saver or is there some other method to secure the prop to the motor? Seems like it should be simple enough to attach a prop to a motor so what am I missing??
 

Craftydan

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#16
Wrench,

Have you checked both sides of the prop saver? If not, flip it over -- most will have two different size mounts, one on each side.
 
#17
Yes, I noticed the prop saver looked different so I tried flipping it over. No joy. My micrometer and dial calipers are at work so I cant measure but the diameter on both sides LOOKS the same. One side is slightly shorter and with less taper on the end. If I grind off the one of the raised portions of the prop saver (that sat in the recessed hex on the original props) the bushing in the prop would keep it concentric with the shaft and still allow the o-ring to hold the prop in place. That would defeat the purpose of the prop saver though because the prop would not be free to pivot off axis. Delays, delays. :(
 

Craftydan

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#19
About 1 in 5 props I've tried (I go through a lot of props :( ), I've had to bore out a bushing to get it to fit. I've bored out 1 hub successfully, but it was pretty thick. If the hub is thick enough (in diameter), you can get away with using a good reamer. If you go this route, take care that there's a lot of material left in the hub -- you do *NOT* want a prop disintegrating at WOT.

Xuzme's suggestion of a bushing to lift the prop is good, but make sure the prop is tightly centered on the shaft (another tapered bushing above the bushing?). If the prop can move in any direction but twisting laterally, it will get off balance and badly off-balance props tend to break the bands at inopportune times.

I think is should go without saying, every time you use a prop saver the bands should be *TIGHT*, but I'm gonna say it anyways. if it's easy for you to get it on/of, you'll be surprised how easy it is for the motor to sling it off.
 

xuzme720

Dedicated foam bender
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#20
Sorry I should have been more clear. I don't mean that the bushing rides on the taper or cone, but that it just bottoms out at the flat. So it keeps the prop dead center and rests on the flat part of the prop saver. The hub should always be flat against the prop saver and should only be able to rock but not slide.
I'm not sure I'm being any clearer...
 
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