Sunset build thread for everyone

Wayne · Apr 10, 2023

Sounds like you are saying the PW likes a forward CG at only 22%, right? So the 140 may not be that far off?

thenated0g · Apr 10, 2023

PW likes cg 185mm from the nose and the guys in the thread say 135mm from the nose.

Wayne · Apr 10, 2023

It is a rather screwy planform..

I'll take real life test data over calculated.

Wayne · Apr 10, 2023

You saw my secret project for Sunset when you were here. The calculated CG does not match what I am seeing with some simple drop tests. I appear to be massively nose heavy in my drop tests. Calcs say I should be rather tail heavy. I need to run the calcs again just to double check.

thenated0g · Apr 10, 2023

Yeah good point. Ill make room for cg ballast adjustments.

jure · Apr 10, 2023

Wayne said:
...I'll take real life test data over calculated.

Agree !
in my experience, many times happened that a fine glide test in my neighbors front yard , produces a tail heavy model at the slope.

Red · Apr 10, 2023

thenated0g said:
Ill build up a a few of the starfires depending on how much time i have before sunset. Should just need to drop in servos, electronics, and put in control horns. What's weird though is the recommended CG in the build thread. I have been making pw51 airfoil planks for many years now and every single one of them i have used peter wicks 22% recommendation and it has been great every time. In this case the recommended CG in the build thread is around 140mm, but cg calc is telling me 185mm. Which is almost a 2 inch difference. Thats huge on a little wing like this. That would be crazy nose heavy if i do what they say.

CG i found is 185mm

Recommended CG: 137
Sweep: Inner cores = 30 and Outer cores = 15 degrees.
Inner core: Chord 280 & Wingtip 230mm, Span = 278mm
Outer core: Chord = 230 & Wingtip 143mm, Span = 330mm

I'm sure you already know this, but this isn't really a plank. Its swept, so the CG will be significantly further aft than a straight-ish wing. 22% of MAC not of the root correct?

Wayne · Apr 10, 2023

True that, this is a normal wing.

thenated0g · Apr 10, 2023

Yeah i did use a Cg calc that i have used before, it does multi panel. But ill try the numbers from rcgroups first.

Doc J · Apr 10, 2023

Red said:
I'm sure you already know this, but this isn't really a plank. Its swept, so the CG will be significantly further aft than a straight-ish wing. 22% of MAC not of the root correct?

I'm doing a 3M plank with Peter Wick at the moment.

It has a chord of 250mm (About10") and a tip chord of about 100mm (about 4")It has a straight trailing edge so its aerodynamically slightly swept and the CG is 74mm - around 33%. But it has to be said that the PW sections are all new optimized and smoothed ones. Think E180 series for the approximate profile types.

On a conventional X-Tail with this wing planform, which would work prefectly well - and of course different sections; I'd expect the CG to end up around 40% or 100mm.

7% is a fair bit of difference, and as Red says, on a flying wing plank or swept design, the further aft the sweep goes, the further the CG goes back, and for a FSW then vice-versa.

Cheers,

Doc.

thenated0g · Apr 11, 2023

Had to redo my hot wire bow with some better copper wire, wasnt getting enough amps out of my power supply for epp, but i finally got cutting some epp last night for the first time. Now i can try cutting out these starfires.

thenated0g · Apr 12, 2023

@Wayne Are you guys going to bring any of those Slope Monkeys? I want to see one in person.

Wayne · Apr 12, 2023

Now the count is up to 15! You are not helping!

thenated0g · Apr 12, 2023

Always looked like a nice bulletproof foam plane to toss in the back of the car and not worry about.

Wayne · Apr 12, 2023

Mine is VERY old now, but still flies. It has been at sunset the last couple of years. Usually other people flying it. Chris and Sean here both had their first slope flights on the plane as well as a number of other folks. She is well worn these days, but still kicking.