scatsob,
maybe this might help;

http://www.djaerotech.com/dj_askjd/d...ntra-prop.html


Randy

Thanks Pilatus! I’m going to have me some fun with Excel tonight.

I also started sanding down the rear stators this evening. Only 10 minutes into it and the magnets barely rub anymore....promising.

chad do you have pics of those planes you mentioned

So I had some fun with math and pretty much got the same numbers as the person who wrote the article. Even more interesting was the trend as you increased velocity. The faster the plane goes the closer the ratio of the free stream velocity to slipstream is to one. So, the faster the plane goes the higher the pitch of the rear prop need to be. So in theory it will be massively inefficient at low velocities but do much better in flight.

Sounds about right. Then there is the magic of constant-speed propellers.

Finally took some pictures of the motor. You can see where I had to sand the rear stators to keep the magnets from rubbing. Honestly it was not that much sanding so it wouldn’t have been too much trouble for them to fix at the factory. Now that the rotor spins freely, it appears that the magnets are quite strong. The cogging is much more pronounced when compared to the 5065 SK motor that’s been a great performer for me.

Its a little hard to see but the gaps between the magnets are not filled with epoxy so that will be the next order of business. JB Weld has quick drying epoxy now and that’s what I will be using. Ill post pictures when I get started on that.

I ordered a 6mm collet from Tower yesterday along with the 4" Zinger spinner so once I get the those and the shaft material this week I can get the motor and props mounted up. That is if I have any time.

I did some test fitting of the motor and mount to see how this is all going to work. Luck was one my side and the left over e-conversion parts from the Phoenix Extra 330 I just put together are going to fit perfect. The front bell is just outside of the cowl. I think it will need to be a little farther out but that’s nothing some washers can’t fix. It should be an easy install; I just need to get some quality blind nuts and bolts for the whole mounting system.

Next order of business is to get this motor fixed up. Today I started putting JB Weld in between the magnets so I feel better about them not flying off. It actually ended ub being pretty painless once I got the hang of it. Basically you want to wait till it is a putty and then force it down with an exacto. The problem is it is not a putty for long so you have to work fast. I did four spaces at a time and that was manageable. Once it is set up mostly you simply cut off the excess with the same knife. Here are some pictures of the process.

Wow,

that's a great install. It looks like it will work. Good repair job, too. How's the balance? Any vibration?

Randy

I have not checked the balance yet. I really need to get one of those magnetic frictionless balancers but every time I make an order from Tower its low on the list and ends up getting bumped. Hopefully I can get the other rotor finished up this week and get it back together with the new shaft thats coming. If that happens, and my batteries arrive, and my prop adaptor arrives, I can run it up this weekend. But more realistically, two weeks from now.

After some initial trouble I finally got a new shaft fitted and the props mounted up to see how it will go together. The shaft is 6mm precision ground tool steel from McMaster Carr and is awesome stuff. It was really easy to work with once I figured out the nuances. I had some early trouble with the diameter of the new shaft being a little too big for the bearings and I ended up pretty much destroying a bearing trying to get it unstuck. After cutting a few more shafts I decided to chuck one up in the drill and spin it using 220 grit sandpaper to reduce the diameter and that did the trick. I only needed to take a couple hundredths off and it worked perfectly. As it sits the shaft can move axially and I will set the distance when I get the 4.5" spinner and I figure out how far apart they need to be. Here are some pics of the unit. It weighs 2lbs as it sits.

Once I get some new bearings from Boca, along with a much needed thrust bearing, i will button it up and get it mounted.

This is getting more interesting.

Good work Scott.
Looking foward to some test data.



FYI, I find that JB quick isn't as stong as regular JB.

Originally Posted by TripleW

FYI, I find that JB quick isn't as stong as regular JB.

I'm not too wrried about strength. It's really just acting as a wedge to keep the magnets from flying off while running. I would never use JB Weld in applications where there were tensile forces, there are much stronger glues for that. The reason I used the 5 minute stuff is because I wanted to be able to complete the job in an evening or two. I only get a little time here and there to work on airplanes.

Im sorry this is such a slow build but I think its going to continue that way. I cant really start on the wings until I get the retracts and TBM says that wont be till after the new year. Im also waiting on som S3102's for the elevators. It's going to be a long process but well worth it.

TBM is killing me to with nice stuff. The just added a 55" PC-21 to their linup that is due in around April. I have a HUGE soft spot for the PC-21 and its priced right at $200 for the ARF. CMP is also releasing an L39 soon and Ive been looking for one of those at a decient price as well. Needless to say whats left of my budget is going to be streatched pretty thin.

So you wont fly her without retracts? Till they come in of coarse.