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-   -   engine and prop (https://www.rcuniverse.com/forum/questions-answers-154/7969797-engine-prop.html)

BINGO4 09-19-2008 09:40 AM

engine and prop
 
I'm flying a Golden Skies Crossfire powered by a saito 120 using a 15 x 8 prop. the plane flies great. My question is the plane does not want to slow down to land so I'm wondering if I put a larger prop will that help and if so what should I use.

MinnFlyer 09-19-2008 10:17 AM

RE: engine and prop
 
Very often, a plane that doesn't want to slow down on landing is nose heavy.

Try moving the CG back in 1/8" increments and see if it helps.

BINGO4 09-19-2008 10:23 AM

RE: engine and prop
 
I have the plane balanced to the manufactures spec should I still move it back

Flying freak 09-19-2008 11:05 AM

RE: engine and prop
 


ORIGINAL: BINGO4

I have the plane balanced to the manufactures spec should I still move it back

Move it back in small incroments you wont go from flyable to unflyable when it starts to act tail heavy stop moing the cg aft,

Remeber that the specs are just to get you started they are there so that you can get the first few flights and than adjust to your own flying style.

MinnFlyer 09-19-2008 11:07 AM

RE: engine and prop
 


ORIGINAL: Flying freak

Move it back in small incroments you wont go from flyable to unflyable when it starts to act tail heavy stop moing the cg aft,

Remeber that the specs are just to get you started they are there so that you can get the first few flights and than adjust to your own flying style.
Ditto to both points FF made

BINGO4 09-19-2008 11:11 AM

RE: engine and prop
 
Thanks I will do that tonight and see how ot goes. You guys are the BEST.

alfredbmor 09-19-2008 12:16 PM

RE: engine and prop
 
Do you know your idle numbers?
Have you had landed the plane with the engine off?
Is there a difference?
Some new light airframes are difficult to bring them down because of the thrust of the props. You may want to try a bigger prop with less pitch but your plane will fly different than the way it flies by now so you must consider that option.
As Minnflyer mentioned, try to change the CG a bit, if that does not make any difference on landings, then check your idle numbers, and if your engine cannot idle on the lower 2,000 rpm then think on lowering the pitch of the prop, enlarging the diameter.

Alfred.

BINGO4 09-19-2008 12:40 PM

RE: engine and prop
 
I have flown this plane several times most of the time there has been a head wind but the plane still came in hot. Eng idles at 2050 rpm. I'm in the process of rebalancing it manual has a range of about 7/8 of an inch and I'm at the front edge of that so I'm moving the CG back about 1/4 inch and will try flying again. The more I think of it that must be the problem just plain to nose heavy. I will let you know what happens

JohnBuckner 09-19-2008 01:20 PM

RE: engine and prop
 
Agreeing with moving it back a bit. Remember when balancing an airplane at any given spot it is only balanced at that point when the airplane is perfectly level. In reality most people give the airplane a slight nose down when balanced at the desired point, Kind of like pushing another inch of manifold pressure for mother and country taking off high, hot and heavy.

That is fine as a little safety margin however since there is no way to quantify that margin and just a degree or two will alter the cg noticibly. In reality what we have done is balance the airplane an unknown distance forward of our target CG.

In other words while we think it is balanced at the forward most point (if that was the target CG)
Its is actually an unknown point even further forward than we thought depending on how much nose down was added for mother an country.

While not generally a safety of flight problem such as an excessive aft CG it can and does
contribute to problems in slowing down for approchs and landing too fast and so forth.


John


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