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Jul 09, 2016, 02:33 PM
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Discussion

Wing AOA, vs H stab incidence.


I modified my Hz super cub into this..





It looks great but fly's terrible. I had it in the air for 2.5 minutes and fought it the entire time.
Under power it wants to dive, the more power added the faster she dives.
I suspect the wings aoa is pointed down rather than up slightly.

I was hoping the scratch build gurus could confirm my suspicion.

For a fix I have no problem raising the wing AOA, but would prefer to shim the H stab.

Will adjusting the horizontal stab have a similar result as cutting into the fuse and adjusting the aoa?
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Jul 09, 2016, 03:31 PM
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Sounds more like way too much downthrust than incidence problems. I'd sort that out first.

BTW adjusting the H. Stab is equivalent to using the elevator. If elevator trim hasn't fixed it then that probably won't either.

Steve
Jul 09, 2016, 05:04 PM
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Down thrust didn't change at all. It flew beautiful as a high wing.
Only thing changed is the wing.
Jul 09, 2016, 05:44 PM
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So what has changed is that the thrust line is now above the lifting surface and before it was below the lifting surface. Are you really confident that doesn't change how much downthrust is needed?

Steve
Jul 09, 2016, 05:53 PM
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Quote:
Originally Posted by slipstick View Post
So what has changed is that the thrust line is now above the lifting surface and before it was below the lifting surface. Are you really confident that doesn't change how much downthrust is needed?

Steve
I didn't even consider that.. Thank you. Where would a good start point be? 0 degrees?
Jul 09, 2016, 07:13 PM
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Whiskers's Avatar
Where would a good start point be? 0 degrees?
Yes.
Jul 09, 2016, 07:34 PM
Retired CAD guy
birdofplay's Avatar
To me , from the pic, the H stab seems to follow the roof line.
As opposed to being in line with the CL of the Wing.

Now if it's an All flying stab then it wouldn't matter as it can be trimmed or adjusted to be better.

The Prop vs the cowl front does NOT look like there is any Down trust at all.

I mean its essentially tail dragger " Cherokee" it should fly just fine.

So something is not aligned quite right.

The wing should be no more than 3Deg but the h-stab should be zero
to ... say the bottom of the wing.

Motor down thrust will only fix a high lift situation.

Motor left thrust will fix torque issues.

my 2 cents
Jul 09, 2016, 08:06 PM
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Whiskers's Avatar

Negative incidence?


This photo seems to show that the wing may have much less incidence than the original.
I think my lower line should be a bit further negative.
Jul 09, 2016, 08:16 PM
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The motor does have 4 down and 3 left thrust angle or whatever the stock Hz s cub has.

Just sitting staring at the plane the wing looks tilted down com po are to the stab.
Jul 09, 2016, 08:23 PM
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Whiskers's Avatar
Take some vertical measurements from the leading and trailing edges to the estimated mating points of the original wing.
Jul 10, 2016, 07:17 AM
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vega07's Avatar
Sporty

My fun planes are two of these . They have the added ailerons and fly great .
Only alittle elevator down to fly level as is my original highwing cub.
Using the original down and right angles for the motor .
Mine are belly landers so the servos and horns are on top of the wing which allow me to show this pic of how the horizontal tail looks in relation to the wing . I would say this would be your problem. I run an Eflite Power 15 in one and a power 25 in the other . No issues at all throughout the power range . The link I got my measurements from https://www.rcgroups.com/forums/show....php?t=1184270
Hope this helps .
Jul 10, 2016, 09:02 AM
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Thank-you for all the input gentlemen. After taking measurements I discovered the leading edge of the wing was below the trailing edge 3/8".

Surgery is complete and the gorilla glue cured over night.
I will test fly her and report back.
Oct 17, 2019, 10:48 AM
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Well I never reported back...

After years of flying experience, and a low wing plane in the stable, including a mid wing, and several home brew designs... I have discovered I had way to much throw in the elevator, she was shorter coupled than before, and I was banging sticks too hard. After a massive reduction in elevator throw, she fly's on rails and floats like a butterfly.

Using a park 450, and 1300mah , or 2200mah batteries in the hatch, she balances out beautifully, glides better than expected and looks half way decent.



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