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Thrust Ratios

Old 03-09-2007, 05:34 PM
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reyn3545
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Default Thrust Ratios

I've seen this discussed 1000 times, but now that I'm looking for it... can't find it....

What thrust ratios are generally best for sport, 3D, and Pattern flying? I've just put a Saito 180 in my 13 pound biplane and wanted to experiment with props to get the most thrust (don't really care about speed, but certainly don't want to try and 3D a biplane) for basic acrobatics...

With a 16x6... the plane pulls about 14 pounds, but spins at 11K on the ground... I think it would explode in the air.
with a 16x10, it pulls about 15 pounds, just shy of 10K RPM, still a bit too fast for me on the ground.

I'm thinking of going to a 18x6 or 18x6W, but I'll have to change spinners also.

Old 03-09-2007, 05:46 PM
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Default RE: Thrust Ratios

G'day Mate,
How does it fly with those props?
That is the only criteria, that I use, to determine the best prop/engine combination.
IMHO, Thrust & revs, only tell you so much, it's the aircraft & your flying style, that determines what is best.
Old 03-09-2007, 06:03 PM
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reyn3545
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Default RE: Thrust Ratios

yes, I guess that's certainly the best rule of thumb, but I was hoping to get a good thrust:weight ratio on the ground so the landing wouldn't be as difficult if I'm underpowered.

I guess as long as I'm over 1:1, it should be manageable, but I've spend a ton of time on this kit, and I wanted it to be as forgiving as possible the first few times up.
Old 03-09-2007, 06:27 PM
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Default RE: Thrust Ratios

G'day Mate,
I have always found that the takeoff is a problem, if underpowered, rather than the landing.
Old 03-09-2007, 07:20 PM
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BillS
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Default RE: Thrust Ratios

I guess as long as I'm over 1:1, it should be manageable, but I've spend a ton of time on this kit, and I wanted it to be as forgiving as possible the first few times up.
I find that a forward balance point and mild throws are the most important considerations to make an airplane mild on the first few flights. In addition some bi-planes glide like a brick with engine out so be mentally prepared. I usually only make two circuits on the first few shakedown flights. It is sometimes good to land and see if anything fell off.

Bill
Old 03-09-2007, 09:27 PM
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reyn3545
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Default RE: Thrust Ratios

Yep, I agree... I've got it set noticably forward, and very slight ailerons and elevator on low rates. I had a Saito 150 in this plane last season, took off like a wet sock. The motor was a little worn out. Now, with a saito 180, it spins a 18x6 about 9000 RPM, but at 13+ pounds, its going to have to come in with some speed.

I'll be fine, just a little paranoid. I put a lot of time into re-doing this plane, don't want to have to mess with it again for a while.
Old 03-09-2007, 10:27 PM
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alan0899
 
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Default RE: Thrust Ratios

G'day Mate,
Check out this Saito site, then think about how much speed you will need, & maybe think about a bit more pitch than an 18x6. You can throttle back if the overall speed is a bit fast.
http://saito-engines.info/prop_sizes.html
Old 03-11-2007, 02:53 PM
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daveopam
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Default RE: Thrust Ratios

I have been running a 17x6 APC on my 1.80. The 18x6W is to heavy for the 1.80. I have not tried a 18x6 non W blade.

David
Old 03-11-2007, 04:17 PM
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Ed Smith
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Default RE: Thrust Ratios

If you are truly interested in prop thrust then go here.

http://www.mh-aerotools.de/airfoils/index.htm

Click on "Propellers" then "Static thrust"

Ed S
Old 03-13-2007, 05:47 PM
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pilot727
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Default RE: Thrust Ratios

How do you determine the thrust point on the fire wall, what do i need to do to get this, thanks for a hope full answer, rollie

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