Prop Differences
 

Whats the difference between a 11x8 and a 12x7? I know one is longer and the other has more pitch,but what differences might I see when I stick them on my plane?

RE: Prop Differences
 

G'day Mate,
Try them & see for yourself, we don't know what sort of plane it is, high wing, low wing, fast, or slow flyer. What size the engine is, or if the engine will swing those props.

RE: Prop Differences
 

The plane is a low wing Hobbico Su-31 with an Evolution .61 in it. I have both props,just wasnt sure which I wanted to make its first flight with.

RE: Prop Differences
 

G'day Mate,
I would try the first flight with the 12x7, & go from there.

RE: Prop Differences
 

I would aslo go with the 12x7 in general more pitch=more speed more diamiter = more thrust this is a VERY general rule with lots of exseptions depending on what rpm the engine turns the prop and other factors.......

RE: Prop Differences
 

My OS61FX works great with a 13x6 on my Skybolt. It also does as well with a MasterAirscrew 12x6 THREE blade. Not supposed to by most "expert's" advice, but the engine must not have heard them.

RE: Prop Differences
 

I guess part of it is coming into the engines power band.... try and turn an os ax up at a good rpm [>:]

RE: Prop Differences
 

My Sukoi flew for the first time today,not by me,but my clubs pro. I screwed up on my post at first...the props in question are an 11x7 and a 12x6,not an 11x8 and 12x7. Same difference I guess. The guy that flew it for me said it was pretty darn fast and not under powered at all with a Evolution .61 in and the 12x6 prop. So,I dont know,it seems to be working pretty good I guess. It was very windy today,so we decided to call it quits after that flight. The guys at the field were all pretty impressed by my Evolution engine. Thought I should mention that. The Hobbico SU-31 definetly had some design flaws that became appearant today though(a whole nother topic).

RE: Prop Differences
 

Design flaws? in an ARF? nahhhhhhh........ ;)

The most fatal one is the bulkhead that the wing tab goes into, that holds the fuselage to the wing (or wing to fuselage if that's how you prefer to think of it) is ONE PLY OF LITEPLY! Or it was on the two Sukhoi's I've assembled. Both of them started to crush that bulkhead AND the two layer LITEPLY wing tab that fits into that little slot in the bulkhead.

I doubled around the bulkhead slot with real plywood and doubled the wing tab with real plywood.

If you haven't had that connection start to crush and crumble, there is a good chance you will. First thing you'll notice is that the front of the wing has some play. Once it has some play, it goes to hell in a handbasket pretty quickly. With my first, it took two flights the first time out. The second one started life with the doublers. No play yet, and that sucker sees some hard flying. Sometimes I think some of these flaws are just ignorance, but sometimes I think they're downright criminal. Fraud comes to mind.

RE: Prop Differences
 

Ya know,I'm glad you mentioned that about the wing tab bulk head thing. Now that I think of it,thats exactly how mine is and it would be a good idea to strengthen that area as well. I know the cowl mounting block system is a waste too. Had to fix that after the first flight. Flew it quite a bit today and it flew awesome though,but I still am going to stengthen that bulkhead just in case. Thanks

RE: Prop Differences
 

When I first encountered the wing/bulkhead connection loosening (the 1st Sukhoi's 2nd flight), I doubled the bulkhead. Next time out, the two layer tab started failing against the now strong enough bulkhead slot. So I sandwiched the two layer tab with layers of ply on either side. That worked.

With the second one, as I was putting the sucker together, I simply did both jobs right up front. It's still flying and shown no looseness.


I used AeroPly for the doubling. It's 5 plies of equal thickness wood. Think I used 1/8" behind the bulkhead and 1/16" each side of the tabs.