Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Prop selection, .91FX on Vortex

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Old 05-22-2008, 06:57 AM
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Lomcevak Duck
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Default Prop selection, .91FX on Vortex

I'm finishing my BTE Delta Vortex in the next few days and I'm hoping to fly it this weekend sometime. Power is an OS .91FX and I'm not overly familiar with the engine so I'm asking for some prop recomendations for the engine/airframe combo. I know this isn't a true speed plane, but I've seen several guys in here had one.

I'm not really seeking max top speed or 3D capability, just a good middle ground that'll make the engine happy. I've got a three blade 12x6 (looks great on this triangle airframe) and some wood 14x4s, master airscrew 12x8s APC 13x4 sport and 15x4 wide blade (worried about ground clearance with this one). Anything other recomendations?

Thanks, Steve
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Old 05-22-2008, 07:54 AM
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Default RE: Prop selection, .91FX on Vortex

If that’s a 12X6 Master Airscrew 3 blade, go with it. It will have a bit less top speed than the right two blade, but some other fun factors can make up for it. Three blades typically pull harder in climbs, re-accelerate faster after hard turns, better air braking and not having about trimming the blades at landing is definitely a plus in your case. Think about an 11X 8 (3 blade) if your plane’s not too dirty.
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Old 05-22-2008, 10:14 AM
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Default RE: Prop selection, .91FX on Vortex

Id try the 12x8 2 blade.

The Vortex is a bit big. You are ok up to about a 13" prop.
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Old 05-22-2008, 12:51 PM
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Default RE: Prop selection, .91FX on Vortex


ORIGINAL: Lomcevak Duck

I'm finishing my BTE Delta Vortex in the next few days and I'm hoping to fly it this weekend sometime. Power is an OS .91FX and I'm not overly familiar with the engine so I'm asking for some prop recomendations for the engine/airframe combo. I know this isn't a true speed plane, but I've seen several guys in here had one.

I'm not really seeking max top speed or 3D capability, just a good middle ground that'll make the engine happy. I've got a three blade 12x6 (looks great on this triangle airframe) and some wood 14x4s, master airscrew 12x8s APC 13x4 sport and 15x4 wide blade (worried about ground clearance with this one). Anything other recomendations?

Thanks, Steve
Forget about your 4" pitch props with this bird. Go with the other suggestions.
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Old 05-22-2008, 07:29 PM
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Default RE: Prop selection, .91FX on Vortex

.....I use a 12-7 on mine at 12,900 RPM using a clone engine on 5% nitro.
The plane is surprisingly fast for how thick it is. A 12" prop is about as big
as you can go on the Vortex. [sm=teeth_smile.gif]

FBD.
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Old 05-23-2008, 07:37 AM
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Default RE: Prop selection, .91FX on Vortex

Thanks guys, I'll try to snap a couple of picks and let you know how it goes with the maiden. I don't expect any troubles.

FBD- Is that the old ARF version? I like the cowl.
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Old 05-23-2008, 07:52 AM
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Default RE: Prop selection, .91FX on Vortex


ORIGINAL: Flyboy Dave

.....I use a 12-7 on mine at 12,900 RPM using a clone engine on 5% nitro.
The plane is surprisingly fast for how thick it is. A 12" prop is about as big
as you can go on the Vortex. [sm=teeth_smile.gif]

FBD.
That's a 13X7 in the picture Dave, did you try that too?
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Old 05-23-2008, 09:54 AM
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Default RE: Prop selection, .91FX on Vortex

....whoops....yes, that is the original prop I tried on the plane....too big.
The engine detonated with it. I had too much nitro in it as well 15% in
the clone ASP engine which is a high compression European engine. I
blew two plugs on the first two runs, a Fox Miracle plug, and it blew a
cold Rossi plug. I went to 5% and it was OK. I didn't fly it with the 13" prop.

Any of the 12 inchers should work fine, the 7 pitch gives better than expected
performance....I suspect the 3 blader would work Ok too. A 12-8 would be
a good bet too in a Zinger.

Yes, that is the ARF version. I have the rudders rigged up to work as air
brakes using the retract switch....pretty cool.

FBD. [sm=regular_smile.gif]
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Old 06-08-2008, 08:31 PM
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Default RE: Prop selection, .91FX on Vortex

I flew a Delta Vortex for 4 or 5 years with an O.S. 91 FX running 13*8 or 14*6 props. It was a wonderful airplane. It is not a high speed plane. Bruce Tharpe designed it to fly well not to go exceptionally fast. The one trick I have learned recently about it is in landing in high wind watch out with increasing angles of attack as the induced drag will slow the plane rapidly with lift increasing slightly causing it to drop suddenly. It will suddenly loose lift on landing in a high wind. All deltas do this with high angle of attack. Despite this minor ideosyncracy, it is a wonderful plane, but it is not a speed plane.
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