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Old May 31, 2014, 11:06 PM
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United States, FL, Lakeland
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Question
Arc cessna trouble taking off

Have an old arc cessna with a 90 st engine,it gets up on the step ok,but doesnt want to lift off,untill i back off the throttle from full to 3/4,it doesnt want to break the suction of the water.now the float angle/set up is factory,could the engine thrust angle be off?the floats?once its in the air it flys fine and you cant mess up a landing.also i had to put a lot of up trim in it to take off and fly level
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Last edited by brownman863; Jun 02, 2014 at 06:01 AM. Reason: add pics
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Old Jun 02, 2014, 09:19 AM
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Hi Brownman,
There might be a couple of things for you to check. I would first locate the CG as the aircraft is now configured. It is generally recommended that the CG be slightly forward of the normally specified point, normally something like 3/8" to 1/2" for float-equipped aircraft of this size. However, if it is substantially more nose-heavy than that, it could be contributing to the lift-off problem and might explain the need for substantial up-trim on the elevators.
Following that, from the photos, it seems you could need a bit more wing incidence relative to the float decks. It sure varies with my aircraft, but the general suggestion is that the wing chord show an up incidence of about 1.5 to 2.0 degrees. I don't know if you have an incidence meter, but following the CG determination it is something I would check out.
Good Luck!
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Old Jun 02, 2014, 02:45 PM
Art Schmitz
United States, TN, Crossville
Joined Jan 2012
392 Posts
Try shimming the front struts 3/8 " to start with.
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Old Jun 02, 2014, 07:35 PM
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>>It is generally recommended that the CG be slightly forward of the normally specified point, normally something like 3/8" to 1/2" for float-equipped aircraft of this size.<<Never heard that before.
>>it seems you could need a bit more wing incidence relative to the float decks<< I agree totally. And while I almost NEVER disagree with my pal Art, It appears to me that 3/8" is about the minimum to try. It'll help, fershurr.
with the top of the float level, the chord line of the airfoil should be about 3 degrees positive. in your pic it looks about 2 degrees negative....Pictures can fool ya, tho'

Good luck with it!
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Old Jun 02, 2014, 09:21 PM
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United States, FL, Lakeland
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It will be a week or two unlill I can get back to the lake,I'll do some checks and adjustment and let you know how it does.thanks for all the advice
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Old Jun 03, 2014, 05:53 AM
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United States, FL, Lakeland
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I dont have an incidence meter,but with what i have,adding 1/4 in spacer to the front float mounts will put the wing at 3 deg.the cg is hard to tell where its at, but i can pick the plane up in the general area( 3 in back from the leading edge) and it balances ok and the step is aprox 3/4 in behind.so the plan is to give it a try with the shims and see how it does,thanks again for the help
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Old Jun 04, 2014, 12:14 AM
Art Schmitz
United States, TN, Crossville
Joined Jan 2012
392 Posts
Take some extra shims with you....
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Old Jun 04, 2014, 06:25 AM
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good idea.thanks
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Old Jun 04, 2014, 05:52 PM
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Cmon over to the Florida Float Flyers' pond on Saturday morning. We'll get 'er dialed in for you.
Not far from Lakeland. Just west of Plant city. pm me and I will give you directions.
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Old Jun 05, 2014, 12:01 AM
Art Schmitz
United States, TN, Crossville
Joined Jan 2012
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brownman863...life just got easier, Jim has been doing this for quite a while.
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Old Jun 05, 2014, 06:00 AM
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United States, FL, Lakeland
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thanks ive been to your club ,my work sch. makes it hard to make it there,great bunch of guys, ill see what i can do,sounds like fun
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Old Jun 05, 2014, 06:59 AM
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Is it possible that you have the front supporting legs fitted to the rear position on the fuselage ... and the rear legs at the front ... thus, altering the rigged angle of the floats, if the legs are of different dimensions.
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Old Jun 05, 2014, 02:15 PM
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had not thought of that, will check it out.thanks
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Old Jun 05, 2014, 08:57 PM
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You have the stock mounts, so they can't be inter changed .
Are you using the stock eng. mount ? I'm sure you are and if that's true there shouldn't be any problem with the mounting.
I did notice that it looks like you may not have much throw in the elevator , check your plans and make sure you have what they call for. Also, once on step, don't try to pull up to soon, let it get it's head .
You shouldn't be having any problems with that plane, I've had 3 of them and never had a problem with any when float flying. I did get in a little trouble when I pushed the aerobatics a bit to far. ( the wing started to fold )
I still have some parts for it (and some other ARC planes ) including a Beaver and 2 sets of floats. ENJOY !!! RED
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Old Jun 06, 2014, 02:03 PM
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United States, FL, Lakeland
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Ipurchased it a swap meet for $80 engine and servos,it does look to have the stock engine mount,its just weird, it looked like it was doing a 100 mph with full up would not lift off untill i was aborting take off ,it did fly.but i probably had backed off the up elevator. after it was in the air i was having to hold some up with all the trim gone.i re adjusted the elevator which helped taking off and flying level,but it still was half way across the lake before take off.i did get better and better, but it seems like somethings a little off on the set up,it couldnt be the pilot haha
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Last edited by brownman863; Jun 06, 2014 at 08:52 PM.
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