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Old Apr 06, 2009, 07:37 AM
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carbondale il
Joined Jan 2007
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JWFinn, I Need Your Help

Joshua, Please bear with me on this one. I'm planning on building another Herr Engineering 30" F4U Corsair. You suggested 3 degrees positive incidence for the wing. If you look at a cross section of the wing at the root, the airfoil at the front bottom curves up some - the bottom isn't flat from the LE to the TE. If you draw a line, then, from the LE to the TE that line is at about 2 degrees positive incidence. If you consider the bottom flat part of the airfoil it is at 0 degrees incidence. My question is for the change to 3 degrees positive incidence do I measure the line from the LE to the TE, which would be a change of only about 1 degree, or use the flat 0 degrees incidence as a reference point and add all of the 3 degrees positive incidence?

Also, how did you manage using 1/16" stringers when the slots of the formers are cut to 3/32"?

Kev
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Old Apr 09, 2009, 12:24 PM
Free Flight rubber flyer
South Carolina
Joined Mar 2005
466 Posts
Kevin, just saw this. For the wing, I honestly just used what the plans showed for the wing, which I estimated to be about 3 degrees on the flat underside (yes, that's wrong) by eyeballing it, and just moved on from there. All pitch trimming was done using CG and shimming the stab. As for the stringers, I filled in the slots with 1/32" shims so they would accept the 1/16 sq stringers. Remember to leave the cowl stock except for building in down and right thrust, of which you'll need quite a bit.
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Old Apr 09, 2009, 01:38 PM
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carbondale il
Joined Jan 2007
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Thanks Joshua. Adding another 2 degrees positive incidence to the wing is do able without a lot of trouble. What do you think about this deviation from what you did? Did you cut the formers down? I drew up the plan to add 20% to the stabilizer area and am going to double the fuselage stabilizer slot so I can shim it with some negative incidence. I'm planning on using Easy Lite tissue - it comes in a dark navy blue. I won't paint it. That's a lot of work there changing the former slots. Is the average art store 1/16" balsa lighter than the 3/32" stock sticks? The stringers will have to be strong enough to span the large distance between formers. The 1/16" sticks I have from Easy Built Models are too soft. You get a variety though with an order from them. I've used up the harder sticks which seem about the same as the art store stock but I'm not sure about that. I have a Gizmo Geezer thrust button and plan to start with 5 degrees down and 5 degrees right thrust.

Kev
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Old Apr 09, 2009, 09:24 PM
Free Flight rubber flyer
South Carolina
Joined Mar 2005
466 Posts
Kevin, I'd leave the wing as is. It will work very well as per plans. Further incidence changes should be carried out with the stab. The main thing with the wing is to make sure you have plenty of dihedral. As mentioned elsewhere, jack the wingtips up level with the top of the fuse just in front of the canopy. This will not hurt the plane's appearance, and will pay dividends in improved performance. I did cut a lot of wood out of the fuselage formers, as they are much heavier than needed. The rear peg should be moved forward two bays from what's shown on the plans, by the way. Be sure to cover the center section of the wing that is enclosed in the fuselage with some heavy paper (computer paper will work fine) to keep the rubber motor from beating up the structure there. Don't ask how I know this. For the stringers, I used fairly strong wood. Light stuff is not needed, as it's a big airplane with lots of wing area. 3/32 is just overkill, though. Oh, and be careful about depending on the Gizmo to provide your thust offsets here. That cowl is really wide, and you have to make sure the prop will clear it. That's why I chose to shim the whole noseblock. Also, you might want to invest in that 11" Peck prop instead of the 9.5" that you have on the Gizmo. Corsairs like big props, and I'm pretty sure that the Peck 9.5 actually ends up being smaller than a scale prop would be. And that is a rarity in scale models.
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Old Apr 10, 2009, 08:36 AM
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carbondale il
Joined Jan 2007
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Thank you Joshua. Will do. I've worked on out paper how to add dihedral for the wing and built it in with the first Herr Corsair I made which had problems with other things so I'm planning on building another one. I'll make sure the propeller clears the nose using the Gizmo thrust bearing. I'm thinking two loops of 1/4" rubber is right.

Kev
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