15 replies to this topic

[Terry]

I flew my new Twinstar today which was a great success, the only problem was damage to the props on landing as was expected due to the fact they are 12" long.

I can add an undercarrage but to keep drag to a minimum I was thinking that if I can get the props to park horrizontal then I could avoid it. So anyone got any ideas of how this can be done ?


Terry

[W3FJW-Ron]

Have you considered folding props?

[Terry]

Yes Ron and I suppose I should keep them as an option but I hope to fit LH and RH props at some point and I dont think I can get them in folders. The other thing is that I find it harder to balance folders properly.

Terry

[Kilrah]

I'd just use smaller props with higher pitch... or motors with a higher Kv suitable to use smaller props... 12" seems huge on a twinstar, I was used to something like 9" for that kind of plane.

[Terry]

Hey Kilrah, your starting to sound like all of the experts that keep telling me I've got the wrong motors and should use outrunners. I know it's a simple way out but I want more performance, I had a pair of AXI2808/20 with 9" props on my last Twinstar.
My new one can launch vertical with a digital camera and all the wireless gear no problem and still do over 30min flights

I'm not going to share the setup just yet as it's still eary days but so far it looks good, fingers crossed. I may well put some folders on for now and see if I can balance them ok.

Terry

[Kilrah]

Well, it all depends what you want, of course if your goal is to go vertical with a heavy plane you might have the right setup for your usage, I personally don't see the point so wouldn't bother with that

[Terry]

Well my goal was not to go vertical but to be able to hand launch at 45 deg to allow me to fly from tight areas and have a good flight duration. As it turns out the performance is even better that expected and the big props work great as airbrakes and give it a steep approach ability too. Each to his own Kilrah

Terry

[Mr.RC-Cam]

Finding a way to cog a big prop to a landing position has been a question that has come up before on other forums. I have yet to see anything electronic or mechanical that would save the day.

[Kilrah]

Hm I've had 1-pole brushless motors that would have only 3 "holding positions" over the full revolution, so modifying an ESC to keep some current to one phase for example when putting the throttle a bit lower than the minimum would ensure the prop always stays at the same position when engaged... But those motors are usually higk-Kv inrunners that wouldn't be most suited for that app...

But still, my first idea holds, keep same power but with higher Kv motors to use smaller props... Keep the 9" but spin them faster.

Edited by Kilrah, 03 March 2009 - 02:22 AM.

[Terry]

I'm going to use folders for now as Ron said but I live in hope of another solution.

Kilrah, I don't want to use smaller props as I want duration as well as the odd burst of power. All the outrunners I have tested that can deliver the thrust for vertical performance are way down on efficiency when on cruise power. What motors, props and battery would you surgest ?

Terry

[W3FJW-Ron]

I think you may have to look at a motor/gearbox combination if you want the motors to run at their most efficient point. We have some good sailplane buffs at HC forum whose info could possibly help you, although we lost all the forum posts two weeks ago (crappy forum host. Forums now on HC servers) and we're still in the process of rebuilding the forums.

[headhunter23]

I know it would look a little ugly but why not cut mount off bottom and put it on top or make a new mount on top of wings to get that extra couple of inchs clearance?

Can you even use folding that big? I would have thought they were too big and would catch wing if stopped for any reason.

Edited by headhunter23, 03 March 2009 - 03:02 PM.

[Terry]

Guys I think we are going off at a tangent here, I have a motor / gearbox that has already flown with 12" props and flys great. If you look at my first post you will see I was asking about ways to stop the prop so it would not break on landing.

[Terry]

OK I had a go at balancing some folding props today but they are not as good as I would like, they seem to change balance every time I run them.

My options are :
1 To perceiver with the folding props in hope of getting them up to standard.
2 To fit an undercarriage.
3 To find a way of parking the prop horizontal.
4 To fit a prop saver.

My favourite is to go with a prop saver but I'm not sure if any of them are up to the job of holding a 12x8 at 200W, what do you guys think ?


Terry

[W3FJW-Ron]

they seem to change balance every time I run them.

Hmmm. That seems unusual. What brand of props and hubs are you using? Hope they're not Hobby City brand.

I would think that a prop saver would work in this application. i.e., no 3D or wild maneuvers, no 0 to 60 in 4 sec.

[Terry]

I must admit they are not the best make, in fact I have never heard of them before but I have had the same problem with Graupner but I am VERY fussy as I like to take pictures with the motors running.
I'm going to modify the folders a bit and see how they go if they are no good then I will make or buy some prop savers.

Terry