Dumb question about pusher props

[Spikey]

If I wish to build a model in which the prop is mounted behind the motor (i.e. a pusher) and the direction of motor rotation is immaterial, do I need a pusher/reverse prop? Or can I just turn an ordinary prop round on the shaft?

Edited By Spikey on 07/07/2016 15:04:39

[Pete B]

If it's a leccy motor, just mount a tractor prop facing forwards. Adjust motor direction to suit, if necessary.

Pete

[Don Fry]

Put a tractor (ordinary) prop on, facing forward as usual, and have the moter spinining so the prop is going anti-clockwise when you are looking from the front.

Two points, take care with pushers, they can drag hands into their arc. Second, fit a locknut, pushers tend to loosen their props.

[Spikey]

Thanks Pete. II just edited my post to read "pusher".

I knew my brain hurt from trying to work out why that might not be all I needed to do...

Good point about the locknut, Donald.  Thanks!

Edited By Spikey on 07/07/2016 15:08:55

[Rosco]

Yep, same as the above posts. Easy to remember - the numbers on the prop always face forwards direction of the model.

Also, If you need to make any after build thrust/motor alignment adjustments, remember its now opposite to a normal front mounted tractor design.

Rosco

Edited By Rosco on 07/07/2016 23:10:26

[KiwiKid]

What sort of model are you building Spikey?

As Donald mentions, it's important to keep the digits out of the prop arc. If you are hand launching, make sure you have a good gripping point on the model and do a firm javelin launch with full follow through so your hand drops away.

If you are using a high power system it's worthwhile to use some protection.

[Rosco]

Yes, agreed also.

A spot to give a good solid grip but also easy hand/finger removal on release.

Normally I find the best location for a hand hold spot around the balance point of the model. There are a few different ways to hand launch too.

Sorry if I'm telling you what you might already know.

I find that I do a sort of 'flick' at the end of my handlaunch. Maybe it's the natural unconscious tendency to keep my fingers away but it is something to be aware of.

[Steven S]

Posted by Rosco on 07/07/2016 23:08:56:

Also, If you need to make any after build thrust/motor alignment adjustments, remember its now opposite to a normal front mounted tractor design.

Rosco

Edited By Rosco on 07/07/2016 23:10:26

I am also building a model with a pusher prop. I thought that my motor [in the forward direction] should point down and to the right, or is that wrong [because it's behind the C of G].

[Rosco]

Hey Steven,
You may find that your models flies well without any adjustments needed.

I cannot say because down and right is not necessarily a requirement for the motor angle. It is generally what most setups use. How far down? How far right?

It all comes down to how you like your model set up, although, like I've mentioned, it is the general consensus that this (down and right) is the normal.


I try and build my models with no angles on the motormount bulkhead/firewall and add small washers to the appropriate mount 'legs' if I need too, just in case. It's better than building it in only to find it dosen't need it.

My post was about making the adjustment but remembering that if you need to angle it down then the spacers/washers adjustment is done by adjusting the bottom of the motor as opposed to the top when the motor is on the front pointing the other way.

Have I just made it more confusing!!?

Rosco

[Steven S]

Thanks Rosco - I have been reading phil 9's topic about "Down and right thrust". The comments there seem to also support building it square.

[Peter Miller]

Posted by Donald Fry on 07/07/2016 15:05:14:

Two points, take care with pushers, they can drag hands into their arc. Second, fit a locknut, pushers tend to loosen their props.

I agree!! over they eyars I have seen a number of really nasty accidents when the porp was in an unconventional location i.e Not right at the front.

I was off for a week with a sliced thumb, another member needed eleven stitches to put his finger together (He also ruined my hand carved beech pusher prop)

Seen a few others too.

The worst was a photo of a chap in RCM&E. He hand launched a pusher model with an IRvine .40. It took three fingers clean off!!

These days I refuse to even touch a model where the prop ins not right at the front (Call me chicken if you like)

Edited By Peter Miller on 08/07/2016 14:35:40

[Chuck Plains]

Theoretically a pusher prop should have it's thrust line pointing at the combined CG point. Or there about. But I have to add that I've only had Bixler. Even so, the web is great place to learn about all this aerodynamic malarkey!

[Chuck Plains]

Edited By Chuck Plains on 08/07/2016 15:38:00