Idea high-lift camera foamie...

[highflier]

That may be right, You said it droped the nose with no throttle didn't you?

You may have just severaly underestimated the downthrust you need.

BTW I wish I was near you, would love to play with CNC machine.

Highflier

[rjarois]

the model trimmed at half throttle, when ya gave full, it would loop, and if ya chopped it it would go into a 45 deg, dive.....i built in a 2 deg. down and right thrust...randy.

[highflier]

It all makes sense.

If there is up trim in elevator holding up a nose heavy plane. When thottle is applied the elevtor gets more air and thus will cause climb.

2% down may not be enough either.

I would try 5% down thrust. Shift CG rearward abit try to fly it and then if it is still wacked you can change airfoil.

Trimed at half throttle what did the elevator look like, Up down or neutral?

Highflier

[Bilbobaker]

I've seen that airfoil in profili.
Did you build that cnc wing cutter?

[rjarois]

Originally Posted by highflier

It all makes sense.

If there is up trim in elevator holding up a nose heavy plane. When thottle is applied the elevtor gets more air and thus will cause climb.

2% down may not be enough either.

I would try 5% down thrust. Shift CG rearward abit try to fly it and then if it is still wacked you can change airfoil.

Trimed at half throttle what did the elevator look like, Up down or neutral?

Highflier

with the model trimmed at half throttle, the elevator was neutral. randy.

[rjarois]

Originally Posted by Bilbobaker

I've seen that airfoil in profili.
Did you build that cnc wing cutter?

i got the airfoil off of google, when searching airfoil images...it had no name or number is assigned to it..

yes, i did build the wing cutter...it is very ghetto, but works very well. randy.

[DiveBombDave]

Originally Posted by rjarois

with the model trimmed at half throttle, the elevator was neutral. randy.

1> Trim the elevator for a good glide (power off). Adjust CG until this elevator trim is neutral.

2> Now you can bring power in. Adjust thrustline until powering up gives a mild/moderate climb angle.

3> I'm serious, done this many times in many homebuilts. With a high lift foil and any incidence at all, you will need massive downthrust to compensate.

Dave

[rjarois]

Originally Posted by DiveBombDave

1> Trim the elevator for a good glide (power off). Adjust CG until this elevator trim is neutral.

2> Now you can bring power in. Adjust thrustline until powering up gives a mild/moderate climb angle.

3> I'm serious, done this many times in many homebuilts. With a high lift foil and any incidence at all, you will need massive downthrust to compensate.

Dave

Dave, thank you for the insight and knowledge....i already chopped down the fuse saddle to accept the clark-y...i can cut out a new fuse in 5 mins. and go at it again at a later date....i have no troubles building, but i lack the knowledge of aerodynamics you smarter fellas possess. thanks again. randy.

[DiveBombDave]

Hey no problem - hope I'm not coming across as a "know it all" type. Just been through these hoops before.

I really think you'll like the clark Y better - it has a good lift:drag ratio. The bad thing about undercambered wings is when you get downwind and have to "muscle it" back to you, it's like pulling an umbrella - and limits the speed drastically. The clark Y can still lift yet will hit a much higher airspeed under full throttle.

If you want to still use the first wing, you can cut a saddle in the shape of the pieces you cut off the fuse, and permanently attach them to the wing. This way you can swap out depending on wind. If the two wings end up needing radically different thrustlines, you can cheat and use a throttle-elevator mix on one.

My advice for maiden is to do your trimming in glide (no power). Adjust CG until you get a neutral or slightly positive elevator trim. If the optimum glide angle needs a negative elevator trim, then reduce/remove the incidence in the wing. THEN bring power into the equation, and adjust thrustline until you get what you want. I like the plane to climb with power, but if it pitches up into a stall under WOT (or worse, loops), then more downthrust is still needed. Some, few, pilots like to see power not change pitch angle at all, and use elevator to climb. In an AP ship I like to "set it and forget it" with throttling up and letting it climb on it's own, and not having to hold a little elevator stick the whole time.

Hope this helps, good luck with it!

Dave

[Real Ira]

I totally agree with Highflyer and Dave about the down thrust. You may need to add so much (10-15 degrees) that it almost looks silly sitting there with the motor pointing down. Even the Magpie is the same way if it is sporting monster P/W ratio.

[rjarois]

dave, ira, your advice is well taken...im gluing up the spar now...i used plastic banding instead of fiber...the fella at home depot gave me some free he cut from a pallet. randy.

[vpatron]

See my post #46 where I wrote "...you will already have pitch issues with the extreme undercamber."

The undercambered airfoil I use for my AP plane, my friend modeled in a computer sim for me and it works well.

Clark Y is very good but faster/less lift. Maybe you can use Clark-Y, but put in flaps when you want to fly slow. That's what I'm doing with my next design, tapered flaps.

-Vince

[rjarois]

yea Vince, you and a bunch of fellas warned of pitch issues....but i had the project started, and had to see it thru...since i changed the saddle, if i ever wanted to mess with the high-lift again, i could just cut a new fuse, or just cut a clark-y center section to adapt to the high-lift foil...with the cnc machines, its all just a breeze to do, not like when i first started to mess with the models, lols. anyhow the new clark-y is built and ready to fly. it came out at 7.2oz. with its 60in. span. also i programmed a 2deg. washout on the foil as i did with the smaller one. its a proven design and flies great. i still will see how much weight it will fly, hopefully i wont need a smaller camera. randy.

[vpatron]

This one will fly very well. I just know it...

-Vince

[DENHAMDULAKE]

Hi there, really looking forward to hearing about your test flight when it comes along and how the new wing will perform :-).

Just wondered about the packing tape.. I can understand how it would work on the underside of the wing but would have thought it would not work to well in compression on top of the wing? I suppose it depends on how well it is glued to the wing?

Denham