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Building Tips and technical articles. => ARF'S => Topic started by: Marvin Denny on February 28, 2010, 08:11:00 PM
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I have finally got all the major work done to get my ARF Profile Pathfinder ready to fly. The weight checks out at 50 oz or 3#2oz.
Is that a decent weight? I have an OS LA 46 for power. So far the engine is unmodified other than a CL venturi installed in place of the throttle assembly. Venturi size is 0.275.
What prop would be a good starting place? I plan on running 10%nitro, 22% oil . This ought to be a good learning experience for me as this is the biggest engine I have flown in stunt.
Any other good advise???
Bigiron
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Marvin
I would try 11x5 zinger and if you are near sea level I would add a head gasket..
Willis
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Marvin,
Your not overweight. Seems to be fairly typical of most of them to end up somewhere around there. Mine is just about the same as yours. Box stock, OS46LA Zinger Pro 11/4, Nelson lite fab covering, Rustolium trim. It's several years old and has delivered lots of flying. It does a better pattern then I, but al I care about is the pleasure that it brings me.
Dennis
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What prop would be a good starting place? I plan on running 10%nitro, 22% oil . This ought to be a good learning experience for me as this is the biggest engine I have flown in stunt.
Any other good advise???
Bigiron
Marvin
Try an APC 12.24x3.75 cut down to 11.75 you won't be disappointed.
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Marvin, As you know I have a Pathfinder built from Brodak kit. Power is an LA46 with a .281 venturi and a ST needle valve. I have tried every prop that I have that would be suitable for this engine and the Thunder Tiger Cyclone 11x4.5 was the best by far. The APC 12.25x3.73 is also a very good prop for this engine but the Pathfinder does not have enough ground clearance to use it.
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Marvin, As you know I have a Pathfinder built from Brodak kit. Power is an LA46 with a .281 venturi and a ST needle valve. I have tried every prop that I have that would be suitable for this engine and the Thunder Tiger Cyclone 11x4.5 was the best by far. The APC 12.25x3.73 is also a very good prop for this engine but the Pathfinder does not have enough ground clearance to use it.
Thats why you trim it down to 11.75 :) worked for my Pathfinder
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APC 12.25 x 3.75 is a VERY solid prop for the LA 46.
we dont cut them down, if you need another 1/2 inch clearance, put on bigger wheels. The prop really works well, especially with the venturi size you are using, ( assuming you are using a ST style needle assembly?) 10-22 fuel is a good choice too. I launch mine around 9700 to 9800 depending on how your tank is configured as a wider tank will lean out a touch after flight speed is reached.
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Thanks guys. I got all this writ down so I 2on't fergit it. I made some more venturis today and will make some more tomorrow. I got some of the recommended props, but will get the others soon.
Tanks agin
Bigiron---
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Marvin
I would try 11x5 zinger and if you are near sea level I would add a head gasket..
Willis
Willis, May I ask what size Saito and 3 blade prop you are using on that nice looking Pathfinder?
Regards
Warren
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Warren
It is a Saito 50 with a 12x6 Master Airscrew and Longer landing gear. It is still flying today, good plane.
Willis
The Cardinal is another Saito 50 powered plane.
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Got all the props except the Thunder Tiger. Where do I find that one? Got two of the APCs so I can cut down one of them.
Now to get some good weather.
Bigiron
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Willis, I noticed you enlarged the elevator chord on your Pathfinder. Would you mind sharing your thoughts on that?
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John
That is a good question. Let me say the Pathfinder doesn't really need larger elevators this goes back to the red Cardinal. Mike Garmon built one of the first pre produced Cardinal kits and I used the planes to build me one. Mike and I agreed that the plane seemed to drop its nose or hesitate before square corners We thought that the flaps were to big causing this. ONLY OUR OPINION. Mike moved the push rod up one hole to make the elevator move more then flaps it made the difference from the worst plane that he ever flew to his most favorite. His words. On Mine I added half inch to the elevator and put the landing gear in the wing the plane flew great . I built several Cardinals after that and all had that modification. The pathfinder was built during this time that is the long winded reason the elevator is wider.
A few years ago I bought a ARF Cardinal and I thought it had the same problem so I cut about one third off the flaps and TO MY OPINION cured the hesitation. I gave the plane to Artie Jessup and for the two years he has cleaned house with it .
As for the Pathfinder the only weakness I see is the fuselage is week on the ARF and the stab will twist up and down in the maneuvers. I fixed mine at the field but the rear of the fuselage needs to have some one sixty-fourths plywood down each side. Just my opinion.
Willis D>K
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Good explanation Willis. I was aware of the need to reduce the flap area on the Cardinal, or use more elevator throw. I tend to use about 35 degrees max on the elevators, and about 26 degrees on the flaps for my Pathfinders.
The reason I asked was to answer some questions I've had. Originally, the Pathfinder had the elevator hingeline at 50% of the total stab-elevator chord. Gordy and I talked about some problems we'd seen, and he decided to go to 60-40 with the elevators at 40%. It seemed to help a lot, but I often wondered what going the other way might have done.
I'll bet that your plane is more comfortable with the flap and elevator throws equal.
Most Profiles will twist in the air. I b elieve that the problem is caused by the circular airflow coming off the prop, and affecting the stab and rudder, causing the twist. Believe it or not I built a Pathfinder with the stab tilted down, lower at the inside tip, about 3 degrees. It looked strange on the ground, but in the air, it was straight. I attached a pic of the plane, but I'm not sure you can see the tilted stab-elevator very clearly.
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John
Like I said I fixed mine at the field. I twisted the elevators opposite what the tilt was in the air. Don’t laugh it has worked for eight years.
Willis LL~
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Well, if it works....... y1
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John,
I did the same thing on my Gee Bee profile after a long talk with Pat about this. The Gee bee has a LOT of horizontal area and I thought it would be prone to twist. Ultimately, it didnt really twist all that much especially after I did your silkspan trick under the monokote. but I certainly didnt see any harm in that.