Question: rc propellers
Hello everybody, this is my first post on the forums.
I've been reading a lot about RC for a few months now, very interested in the hobby, have bought my first plane and itís an FMS Cessna 182 V2 (1.4m)( http://www.xtremehobby.ashop.com.au/...o-fly-kit.html ).
I have been out flying once and it was a far too windy for my skill level (of zero), still I tried my luck but with no skill I crashed within seconds.
Anyway, The stock prop had been ruined in the crash and finding another one from FMS, or any other brand that is the same size is almost impossible without paying $8/per prop, and I'm not about to do that for a very brittle plastic item that Iíd need multiple of.
I'm looking to find a spinner/cone/thing to attach to my motor shaft so Iím able to pick and choose whatever prop size/number of blades I want, but Iím not 100% how to do this, so I thought Iíd ask on here first.
I've taken photos of my motor so Iím giving all the info I can to make this as painless as possible.
Motor: FMS 3536-KV850 - Shaft diameter: 6mm / Bore needed: 8mm
Photos of current setup that is limiting me to one type of prop: https://www.dropbox.com/sh/ga694blae04dd78/Taim6hNWJr
What I think I need from looking a around is one of these, http://www.hobbyking.com/hobbyking/s...t_collet_.html
But Iím not 100% sure.
What I'm trying to do is be able to buy other branded 2/3blade props for my motor.
If any more questions are needed to answer this I'll try and be as quick as possible answering as I'm wanting to try flying again lol.
Thanks in advance for all the help
You have options.
The simplest thing would be to ditch the spinner entirely. Add a spacer of some sort to the adapter shank (between motor and prop) to make up for the loss of the spinner and then just bolt on your new prop. It won't look quite as pretty, but it solves the problem and won't affect performance. You'd also be able to change to props with different blade counts without worrying about different spinners.
Next possibility would be to trim down the molded bits on the spinner backplate until you can fit other props. As long as it's balanced it'll be fine. This would let you keep using the spinner, but it's a little more work.
If you went with the first option, you could also buy an aftermarket spinner and use that. You'd have to settle on a certain number of blades, though.
The HobbyKing prop adapter in your link is useless in this case. It's meant to be attached directly to a motor's output shaft. The setup you have uses a bolt-on prop adapter which performs the same function but simply bolts to the motor's can rather than being attached to its shaft.
Note that you cannot just slap any ole prop on there and expect everything to be ducky. The prop determines performance and, even more importantly, current draw. If you put on a prop that loads the system too much, you could fry the motor, ESC, or both. This is where it's very important to have a wattmeter for keeping track of changes in electrical vital signs when you start experimenting with different props. Even props with the same stated dimensions (e.g. 11x9x3) can have very different characteristics.
Just not 100% sure what you mean by "Add a spacer of some sort to the adapted shank"
I'm guessing just some sort of light metal tube with a hex nut on the end of it to sit around the start of the shaft?
Then I could just use my current screw on nose bolt to tighten it all in correct?
Or maybe do you mean just a normal plastic placer like this one:
But wont that be spinning around loosely because its not pushed over the hex bolt on the shaft?
First off, great first post asking for help - pretty much all the info needed is there.
The sort of prop adapter you need if you can't modify or space the existing driver is like the one in this pack. Note that your motor is bolted direct to the aluminium box - the x-mount in the pack wouldn't be needed. Trouble is, I don't see the equivalent adapter on the FMS site, and not just any old adapter will fit. You might want to ask in a specific thread if anyone knows a source for a plain rear mount prop adapter for your FMS motor. If you could get a suitable adapter, then you'd probably need to bring the motor forward from the firewall to have the prop clear the cowl, and that would affect balance - you'd need a small amount of weight in the tail to compensate. Another option if you can't get a suitable adapter is to change out the motor while you try to learn. A suitable choice might be this NTM 3536 that takes the adapter I linked above. The Kv is near enough as long as the weight is similar to your motor. 11x8.5E APC prop would be a good choice, but the HK 11x7 is a LOT cheaper.
Now for the bad news. You're not going to want to hear this, but if you're going to self teach, you're going to find the Cessna an expensive and frustrating proposition. For its size, it's much heavier and thus faster than a more appropriate trainer, and is much more vulnerable to damage with its fiddly scale bits, as you've already seen. And flaps have no place on a primary trainer, just extra weight, cost and complexity.
For example, the Bixler has the same wingspan & nearly the same wing area as the Cessna, but weighs only 650g ready to fly. There's no gear to knock off on a rough landing, the prop is protected, and the wings are designed to separate and pop out, with no bolts or plastic mounting lugs to tear out of the foam. Another option is the Floater Jet
You could use the receiver and ESC from the Cessna in the Bixler, and once you've got the Bixler beat, move back to the Cessna. I know the Bixler is out of stock in the Aus warehouse at the moment and you're rearing to go, but maybe you could spend the time waiting for the Bixler on a simulator. It's time well invested. If you can't source a simulator cable for the tx that came with your Cessna, you can do a lot worse than a PC gamepad and Clearview
A couple of left field options if you're desperate for quick results that trades off space vs wind handling is firstly the eRC MicroStik. They claim to be tough enough to survive long enough for a beginner to learn the basics. If you stay over grass and away from obstacles and restrict to VERY light wind, the claim is accurate - A mate flew successfully after only sim time and only damaged it by dropping onto concrete nose first. But order 5 or 6 of these: LHS prices are murder
Then there's the Champ. More expensive, but a true success story.
If you go either micro, make sure you order one with the Tx same mode as your Cessna.
All the best and welcome to RC Groups
Hello and thanks for the warm welcome.
Haha at the Cessna had been a pain in the leg. I've had nothing but problems since the day the money left my wallet, from waiting for shipment to building to sourcing parts.
I am looking at the Bixler 2 actually, I already have a shopping list ready to go just waiting for HobbyKing to restock and I will snatch one up. I donít want to beat up my Cessna182 any more than I already have. :(
But either way I do want to rebuild and change this on my Cessna to make it a simple chore to change problems at a later stage.
I went into my garage and looked for a makeshift spacer to see if what i took from reading your post is what you actually meant.
So i got a random bolt large enough and did this (refer to pictures): https://www.dropbox.com/sh/y6kc1n2nntzeh3s/NEKxhRBQFc
And it seems by just tightening the nose cone bolt enough it locks everything into place and nothing is spinning freely.
I hope this is what you meant. If somebody would confirm this I will go out and look for a light plastic spacer and be ready to rebuild.
I think you're on the right track, but you'll want a spacer that has a close fit on the shaft so the prop mounts properly perpendicular to the shaft, and looks like it needs to be thicker than the nut. My concern would be whether you're going to get enough friction to drive the prop with a spacer just resting against the shoulders of the hex shaped part of the shank. Normally you'd have the driver face and a washer on the front face about the same diamter as the hub.
But if you're going to learn on a bixler, you'll not break any more cessna props;) - is changing props worth the hassle?
Changing the prop is really needed for multiple reasons.
The only shop I've been able to find is on China, and its $8 per prop, plus shipping.
They are rather brittle plastic so they crack easy. :(
I will go to the shops tomorrow and see if one of the guys will be able to fabricate me a spacer/hub with a hex nut on the end to push over the 'shank'(?).
Oh also, the one I have already on is ruined. sort of why I started this quest to find a good solution. :)
Needing big props is one other big reason to learn on something else. I suggest you get an eFlite Apprentice. You still have big props, but you aren't likely to break it, even as a beginner.
Otherwise, you need to scale down to something where a prop saver setup would be appropriate, like <1m WS planes. You can't use a prop saver with the kinds of power required to fly a huge plane like the FMS 182.
Otherwise you'll be going through props like crazy.
Really, get a trainer, and save this plane for later. Trust me, my first plane was a C182 as well, and it didn't turn out well... even when fixable.
Just came across this post -- to adapter other prop's to the Paep 3536 kv850 - simply cut the hex sleeve on bottom of spinner. That will fill space, then use any prop you want - use 1" bigger then 3 bladed ( 11x 6-3) I use a 12x6E flies great could also use a 11x7
I have been looking for research on propellers that would be applicable to much of our RC experience. One thing that came out repeatedly was the importance of RE (Reynold's number) for performance. Most studies show that as the RE goes below 100,000 the drag starts to increase significantly. "The results showed significant Reynolds number effects with degradation in performance with lower RPM’s." (Brandt, Selig)
Since the power requirement increases as the 4th power of the diameter, but only as the 3rd power of RPM, it is possible to increase RPM and decrease diameter so as to maintain constant power - and have an overall increase in RE. However, probably the best way to increase RE - especially for low speed applications - is to increase the propeller blade chord.
The decrease in drag from doubling the the RE from 75,000 to 150,000 by doubling the blade chord would probably more than make up for any increase in frictional drag and decrease in efficiency due to a lower aspect ratio. One possible way to test this is would be to take a larger propeller (larger chord) and chop it down - maybe by 25%. This would result in a smaller propeller with a relatively large chord. Maybe I'll try this when I get back to Canada :o)
A quick calculation for the case of a propeller shortened by 25%:
P = 1, V^3 x D^4 = 1 Let V and D be 1 to get a proportional answer.
(1 + x)^3 x (1 - .25)^4 = 1
(1 + x)^3 x .32 = 1
(1 + x)^3 = 3.125
(1 + x) = 1.46
x = .46
So the RPM would be increased by about 46% to maintain the same power output. This means that the RE would increase by about the same. So if the original prop was operating at about an RE of 70,000 then the cut down prop would have an RE of about 100,000 - a potentially realy significant improvement.
Of course cutting the ends of the propeller off is going to increase the effective pitch - so the previous calculation is for ballpark purposes only. However, you could start with a propeller with a lower pitch so that the modified propeller has about the desired pitch.
Oops - I made a mistake folks. Didn't account for the diameter change. The change in V is going to be the change in diameter (-25%) x the change in rotational speed (+146%). This gives a total change in V of only about +10%. Not nearly so impressive. So if the starting RE was 70,000 then after cutting down the prop and changing the power system to maintain the same power output at a 46% increase in RPM, the RE would be about 77,000. Some improvement - but not much.
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