|Chris Walby||17/07/2017 07:51:12|
259 forum posts
Hi, the web seems to be full of old and sometimes contradictory guidance!
Looking to build a slow fly Depron delta about 40 inch so no speed records, but slow stable platform.
Thinking of using 3S800 lipo, motor 1200KV 85W max
So for slow flying (not ultra slow!) is it better to have a tractor and push some wash over the control surfaces or pusher?
Sort of need to nail this before progressing, so advice welcomed.
+ going to try profile HS522, unless there is a better recommendation?
|Tony Bennett||17/07/2017 08:55:58|
4761 forum posts
tractor prop would work better in my opinion.
|Engine Doctor||17/07/2017 10:21:21|
1787 forum posts
Plus one for tractor prop. It give better air flow over control surfaces.
|ron evans||17/07/2017 10:26:00|
309 forum posts
A clubmate and I have the same foam delta. Mine is a tractor, his a pusher.
The tractor is much quieter in flight, but does suffer from a quite severe torque/propwash reaction if the throttle is opened suddenly at very low speeds, the pusher does not react this way.They both have a central fin.
I would still prefer the tractor, and safer to hand launch too
|Chris Walby||17/07/2017 11:50:52|
259 forum posts
Thanks guys, based on flight characteristics, launching, noise and I need to get the weight up the front I'll go with a tractor prop and get on with drawing things up
Last call for any pro pushers out there?
|Old Geezer||17/07/2017 19:25:04|
|459 forum posts|
If you're going for a Pusher you need more kV and a nice small prop - opening the taps abruptly with a big prop can produce a serious torque roll and with barely any breeze over your elevons to help you counteract this - you can be in trouble. (Inverted at negative altitude.) Further, to keep things reasonably quiet try to keep the clearance between the prop and the T/E as great as possible.
|McG 6969||17/07/2017 19:41:09|
1608 forum posts
I'm a total 'apprentice' as I only have one plan build Hybrid - Depron, liteply & composites - Ballerina 'under my belt'. So, you've been 'warned'.
My first reaction was "why is this guy building a delta if he wants to fly slow"? Deltas are 'speedy' flying machines and are the same for landing, even at 'high alpha'.
From full size experience, tractors have a superior 'efficiency'. Period. The comments above tends to share the idea of the same 'fact'.
But for slow flying you don't need the max efficiency, are you? And pushers can have some nice advantages in relation to stability and ease of control.
Yes, they are obviously more 'noisy' as with the rotating impact to the flying surfaces nearby.
Now not that sure if a tractor gives a better control over the surfaces. It just depends were your prop is situated. Meaning by that, it is evidently so if your prop is situated behind all surfaces but not if it is situated in front of them. And a mid-motor/prop is really easy to build with a delta wing. Even adding a 'bow tie' type opening for the prop allowing a lot less noise from the screw.
The other advantage of a mid motor/prop is the enclosure around it guarantying safety for launch as well as prop protection for landing.
By the way, your "need for weight at the front" becomes a lot less important with a mid motor and Lipos are a nice remedy for that.
If you really want to fly a 'delta' at a slow pace, why shouldn't you consider a 'very low' wing loading? And why not? > a delta biplane could deliver that... this is one of my next projects anyhow > a mid engined delta bipe, central Lipo and an Mobius or Redcam up front. As slow as possible, I hope.
Sorry for the long post.
|Simon Chaddock||17/07/2017 20:27:06|
4985 forum posts
It depends on the configuration but there can be CofG advantages in a pusher configuration.
A long nose on a delta puts the motor along way ahead of the CofG so the battery has to be moved aft to compensate with resulting long wires.
Slow flying is all about wing loading and a delta is easy to make structurally strong so it is possible to build it much lighter for a given area than a conventional wing.
Just out of interest if a pusher is inefficient how come the Cessna Skymaster has a better (slightly) single engine climb rate on it rear pusher than its front tractor?
It all depends on the layout.
Edited By Simon Chaddock on 17/07/2017 20:27:32
|Dave Bran||17/07/2017 20:39:14|
1782 forum posts
Re: Deltas are 'speedy' flying machines and are the same for landing, even at 'high alpha'.
No No No No No No Noooooooooooo
|ron evans||17/07/2017 21:26:20|
309 forum posts
On my foam delta with the motor up front and three servos at the back, the battery sits on the CofG.
Different size packs can be used without having to move them about, and the model starts and stops pitching easier with the heaviest lump on the CofG.
It is a "speedy" model, but if I get it right will also land at zero speed.
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