RedBarronBen

Is anyone else out there using folding props - probably most popular on e-powered gliders?
If so, did you/are you still frustrated with the parts combinations and selections?
I have been trying to put together a prop/yoke/spinner combination from aero-naut and I am not having much luck. My last attempt was though HobbyLobby and it seemed they have finally figured out that modelers need some help with this and therefore made a kind of buying "flow-chart" that helps one select compatable parts. However, upon recieving my order of a 10x6 CAM prop, a 47mm yoke, and a 45mm spinner, I found that the prop fits a little tight in the yoke, the yoke doesn't fit on the spinner without trimming it, and that the prop when installed with yoke and spinner appears to be allowed to "hyper-extend" to about 25 deg. forward of "flat." Maybe this is normal? Personally, I would expect more from German engineering.
Any comments appreciated.

Jim Finn

My Feedback: (2)

I use folding props a lot on my electric warplane belly landers. The swing frward of the blades is normal. Not a problem at all. I have even made my own center yoke for this Corsair from alum. channel I got at home depot.

RedBarronBen

Excellent looking Corsiar! Might you get me a close-up pic of your folding prop/yoke with the blades thrown all the way forward showing what it is that stops the forward swing? The aero-naut design seems to use the spinner as the stop. I think I may try getting the next size spinner up and modifying it to experiment with different stopping angles. I figure there must be a good reason for all other props being designed to swing in plane, probably a structural issue with the blades more than anything else. Hmmm... if the prop swings fast enough, will the inertia of the blades have more force to hold them in plane than the lift pulling them forward? I'll bet not, but I'll see! (Don't believe anything until you've tried it yourself.)
Thanks for your reply, Jim.

d_wheel

I can't believe anyone would land something that beautiful on it's belly! Nice job!!!

Later;

D.W.

Jim Finn

My Feedback: (2)

Here is the photo you asked for. The prop can swing all the way forward or backwards. THe centrifugal force keeps it in the proper line. This force is much stronger than the forward or backward force is on the prop. As you see in the photo I have tightened the bolt that holds the blade on for this photo. When doing this kind of thing it is a good idea to run it as I have to check for amprage draw and for vibration. The reason for the belly lander is that I want to fly this in a tall grassy field across the street form my house so I plan to bungee launch it. This plane is a modified Great Planes Corsair.

RedBarronBen

Jim, thanks for the photo and info. I wouldn't believe it, but I tried it and you are right. The prop's inertia keeps it true in plane while rotating at any speed my hacker brushless can spin it at.
To sum up for others: Folding props come in 4 parts: 1) the shaft adapter, e.g., on my direct drive hacker, the output shaft is 3mm. I used a 3.2mm shaft adapter which is held on by tiny allen screws (allen wrench is usually included in the package). This adapter then is the right size for the yoke and spinner which are installed over it and secured to the threaded shaft by a single nut and washer. 2) the prop; choose a prop of appropriate size and pitch for your motor/application. 3) the yoke; the piece that holds the two separate prop blades so that they can swing freely - folding backward and forward! - and holding this assembly to the shaft adapter. Don't worry, about the forward swing (see discussion above). 4) the spinner - usually in two pieces, one piece is a hub and the other the nose cone. The hub mounts on the shaft adapter along with the yoke and is bolted down with the nut and washer. In my case, the spinner had to be trimmed slightly to clear the arms of the yoke. Note that some spinner hubs that I have seen actually block the forward swing of the prop blades when installed, but this is not necessary. Then the nose cone is put on to clean things up. And whala! A folding prop is ready for flight. Now that is how the parts work, the trick is getting those parts to play nice with each other. Here I don't have much experience, but I was able to put the right pieces together easily enough with the recently modified Hobby Lobby web site. The choices are mind boggling, so I wouldn't expect your local hobby shop to carry all the combinations - too much inventory for a small business. Best look for what you need via Internet stores. This is why understanding this is so important, you can't trial fit the parts together before you buy. And this can be frustrating as hell, which is why I took the time to write this, for others. Where's the guys that get paid for writing these kind of articles in the magazines?!? Never mind, we figured it out without you.
B
P.S. I'll try to post some pics soon to help with the visualization of all I just wrote.

HoboDog

My Feedback: (1)

I just put my first folder together. I used the Hobby Lobby flow chart and managed to get one of every part I need. There is still confusion, at least for me, where it says to order the middle part to be long enough so that the prop will fold fully. Having never assembled or seen one of these assembled I just ordered the middle size middle part. Now it looks to big so I'm going to order the small size middle part.
I wish there were a better way then trial and error.
Regards,
Doug

Jim Finn

My Feedback: (2)

The size of the "Middle Yoke" is determined by the size of the fuselage near the nose. You want the prop to fold and lay alongside the fuselage so the yoke must be long enough to give the blades clearnce when folded. The dimensions of the yokes are in the cataloge.

HoboDog

My Feedback: (1)

Thanks,
I'll know what I'm doing next time. It really isn't that hard if you've seen one together.
I'm putting it on a Slow Stick with an AXI 2808/20 brush less motor and 3s2p LiPo.
Just one of those crazy experiments. How many RPM do these folding setups handle?
Regards,
Doug

Jim Finn

My Feedback: (2)

The folders will take any speed your AXI will deliver. Out runners are not all that fast I understand. Some props are rated at only 4000 others at 9000 and some at 12000. Need to check with manuf. I have never had a problem with one myself.

HoboDog

My Feedback: (1)

With the 9x5 I put on it the charts predict about 8000 to 9500 RPM. With a smaller 8 x 5 the charts say about 10,000.
Now I'm new to this, but those numbers seem high. The numbers come from the ModelMotors web site that has the AXI specs.
I used to fly a full scale Cessna 152 a long time ago. If I remember we flew around 2000 to 2800 RPM. It makes 10,000 seem odd. Did I get my numbers wrong?
Doug
Here is the chart I referred to;

http://www.modelmotors.cz/index.php?...id_odkazy=m_ac

RedBarronBen

OK, I'm finally back and I have pics! To answer a question posted since my last - what size yoke to use? Jim answered this question about how to determine how big the yoke ought to be, but didn't say how to determine the size yoke to order. The yoke measurement is the distance from one center-line prop connection pivot to the other (see pics).
Thanks to all the others posting additional info. Happy flying!

RedBarronBen

Here's a new question that maybe someone can answer about 'folders.' When you go to pick out the yoke, you will notice that some yokes have a choice of angles. I have always ordered ones with 0 deg. since I don't understand exactly what this means. I assume it is additional or negative pitch on the prop, but why would one want to do this? I would think that the prop is designed with the optimum pitch-angle/length/width across the entire section. Why wouldn't one just buy a bigger or smaller prop if they need more or less pitch?
Anyone care to expand upon this?

Jim Finn

My Feedback: (2)

I have never used these twisted yokes but as I understand it they just change the prop pitch to a higher number. I just get a different set of blades to increse pitch myself.