prop advice

[snakeyme 0]

hi all i have a dilemma,

And here it is.

 

Im puting a .91 2-stroke on my plane and the following are useable prop sizes;

13x10-11

14x6-8

15x6-8

 

Now even though those are recommended for use with the engine, i have worked out that i have enough clearance for a prop upto 19" in diameter.

 

So im wondering if its possible to put a larger prop on the engine, as im thinking of using a 17x10 3-bladed wooden propeller but i really dont know what the consequences of doing such a thing.

 

If anyone could advise on this it would really help me in a massive way.

[Jimbo 0]

The sizes recomended for the engine are the ones to go for.

 

You do seem a little obsessed with the idea of a 3 blader - there's no big advantage with doing this, and they cost more and are generally less efficient.

 

Just because you can get a 19" prop on, doesn't mean that its a good idea for the motor.

My advice, stick with what th designers of the engine recomend.

[snakeyme 0]

thanx jimbo, thas what i thought with the sizes.

 

As for 3 blade props, i like them simply because, when you watch red bull air racing, all of there stunt planes have 3 bladed props and as the plane im talking about is a stunt plane, im trying to match it so it looks more "realistic" so to speak.

[arun 0]

2 blades are generally more efficient than 3. However, 3-blades can handle more torque which is one of the reasons they were found on warbirds to absorb the insane amount of power produced by their engines without risk of the tips hitting the ground (I imagine there were other design reasons too). Same might be true of the Red Bull planes you mention... which doesn't mean it applies to a scale model of the same with a different type of engine

 

One interesting use of 3+ blades is that it may improve downline braking effect from the propeller, so this might be a consideration for a precision aerobatic aircraft, but this is a fairly specialised use.

[snakeyme 0]

thanx arun.

 

The plane that its gunna be mounted to is an extreme 3d plane, specailly designed and built for aerobatics and when it comes to flying the plane i dont wanna risk an accident as its also extremely fast aswell so i think the extra braking will be good.

 

Also 1 thing i found interesting about this plane, is that on reviews online, people have said that its almost impossible to stall it and itll glide through the air with only 20% throttle, however i aint gunna find out how true this is until im comfortable and know how well the plane actually flies.

 

I will eventually use it for stunts and i want to set it up for this (equipement wise) now rather than having to spend a fortune on re-equipping it later on (if that makes any sence), this is why im fiting it with a .91 instead of the recommended engine size which is .40 - .50 2-stroke and its already got the .91 mounting on it and a P.A.D.M.A.C. Passed sticker on it (what ever that is for).

 

Just so u got an idea of it, its a topmodel kabriolin with the leading edge of the wings being back-swept.

[arun 0]

P.A.D.M.A.C. passed means it passed the noise test for the Portsmouth club I imagine.

 

The Kabriolin is a pretty standard 3D/fun-fly type design. You will not want 3 blades on this per Jim's advice.

 

The gentle (not impossible!) stall characteristic comes from the very thick wing section. Probably all this means in people's reviews is that it will stall from the centre resulting in a clean drop, rather than an aggressive wing drop...

 

Just being pedantic, but I assume by stunts you mean aerobatics? Stunts conjures up images of something inherently unsafe which isn't ideal...

[snakeyme 0]

yh lol arun, i did mean areobatics lol.

 

There are some i really wanna try when im ready to, these are;

Prop hang (when i figure out how its done)

Tail flip

Inverted g spin

 

but the plane will also be an advance from the trainer that i got (even though i managed to stall 2 already during take off and ended up totalled which were the white sunbeam i had at the field (turned out to have a major fault with its tail fin) and a tutor 40 mk1 which suddenly power during the take off) and ironically i havnt even managed to get the current trainer to take off yet due to various problems including it veiring off during ground tests.

 

So the hobby hasnt gotten off to a flying start for me but ill persist and eventually get there as i aint 1 for giving up with the things that i love.

[arun 0]

Good man... the manoeuvres you've called out should keep you busy for a long while to perfect! There are lots of exercises you'll need to do to get there - and I'd recommend practices core aerobatics first; cubans, stalls turns, in/out loops, knife edge etc.

 

As you say, stick at it, but be safe and progress at a slow and steady rate or your credit card will feel it...

 

Highly recommend the range of books by David Scott to give you guidance:

 

http://www.amazon.com/Precision-Aerobat ... 0981722636

[Trevor 25]

I would also suggest lots of practice on a simulator first, much cheaper than all the planes you seem to be getting through learning to fly. Good luck with the next one.

 

Sent from my MB525 using Tapatalk 2

[snakeyme 0]

yh i agree, i desperately need a simulator but im gunna get my kabriolin perpped for the air before i get a simulator and as for my current trainer, only cost me £10, so if it falls short, then its no big loss.

 

Also funily enough, ive had several goes of a simulator at shops and i seem to fly perfectly on them its just put it into practice that i seem to fail at lol.

 

Hopefully by or during next weekend, you will all hear of a successful flight by me but we will soon find out.