Soar-Jet - old school 2 meter flyingwing

[Mucksmear]

Planning for my next build - Grahm Jones' 1972 Soar Jet (https://outerzone.co.uk/plan_details.asp?ID=9235)
I'll be making some aesthetic adjustments to the top of the fuselage for reasons of personal taste.
Here's the specs:
Span: 72"
Airfoil: unknown symetrical
Root: 19.75"
Tip 6.5"
LE sweep: 28.8 deg
Twist: none
Elevons are a little less than 1/2 span and 1/4 chord at the wingtips.
Elevons are set with about 11 degrees up or 3/8" at the TE.

Question for you aero-gurus: IF one of you were building this, would you bother to change up the airfoils to something "better"? On a "vintage" sport design like this, would there even be any noticeable improvements from using reflexed airfoils given the old-school construction (built up balsa D-box wing with capstrips)?

 

[Red]

I would for sure update the airfoil, if for nothing else to get rid of the trim drag associated with all of the up elevon required in the original section. Something like an MH60 (might be too thick) at the root transitioning to an MH62 at the tip would be great. If you don't want to go through the hassle of transitioning the airfoils, just use the 62 all the way and add 1 degree of washout. PW51 would also be a good choice. It will be a sweetheart. Cool looking plane!

Please post build pics.

MH 60 10.08% (mh60-il)

Details of airfoil (aerofoil)(mh60-il) MH 60 10.08% Martin Hepperle MH 60 for flying wings

airfoiltools.com

MH 62 9.3% (mh62-il)

Details of airfoil (aerofoil)(mh62-il) MH 62 9.3% Martin Hepperle MH 62 for flying wings

airfoiltools.com

PW51 (pw51-pw)

Details of airfoil (aerofoil)(pw51-pw) PW51 Peter Wick. Airfoil for plank model gliders

airfoiltools.com

Red

 

[Wayne]

Totally agree with Red! Update the airfoil!

Looks like a neat project.

There are a range of airfoils that could be used. It is basically a chevron flying wing with a fuselage.

 

[Mucksmear]

Thanks for the input guys!

The most that I’ve played with flyingwing twist angles with anything beyond just guessing, is to compare root and tip profiles at an a given Re number and then measure the angular diff between the stall AoA based on the graphs generated by AirfoilTools… so that the wing tip stalls at the same time or later than the wing root.

I have not been able to wrap my brain around the issues of pitching moments.

I’ll check out your suggested airfoils

 

[Wayne]

Better hurry up so you can bring this one to Sunset.

 

[Mucksmear]

Edit - I posted the wrong combo of foils, ok fixed now:

Ok I just spent some time playing with the suggested airfoils plus a few others in the family on AirfoilTools, so as a followup, what do you guys think of the following?

Just guessing a typical airspeed of about 33 mph +/- gives the following Re for the root and tip chords:
Root Re: 530,020
Tip Re: 174,210

MH44 is not excessively thick at a root chord of 19.75" (from a purely aesthetic/practical standpoint)
MH62 at the tip

Is building in 1.5 deg soley to prevent tipstall the right thinking here?
Im assuming a linear transition from root to tip airfoil

Also, any thoughts on the original design's outboard elevons, vs outboard ailerons and inboard elevator? Sparating the controls could allow me to play with flaps by countering pitch changes with the ailerons.

 

[iti20090]

Regrets the belated reply. If you would like to stay with a symmetrical section, friend Russ Conradt built us eyeball knockoffs of the 1985 Pharaoh delta from cores computer cut by Dave Schaller, using the SD8020 thinned to 8%. All three of the Pharaoh's fly magic, including in the mildest of conditions.

Flying 20% mean average chord CG, the aerie barely needs 1mm reflex in light conditions (zero in blow) and is obviously equally happy inverted.
Swept wing may a bit of challenge though.

Cheers
Dave

 

[Mucksmear]

Scott and I are moving along with our first dual build in decades. The build log is unfolding on RCG and Instagram. The build techniques are

Much the same as I’ve done in the Coyote, Obelix and Midjet so I’ll spare the Aloft forum the detailed redundancy, and focus more on some of the problem solving we had to do and periodic progress shots.

First snag we hit was severely rippled hotwire test cuts on a scrap stand-in for the wing core. Problem turned out to be the 1:0.26 taper ratio. The hotwire at the tip would stutter as it struggled to glide smoothly along at less than 1/4 the speed of the root. Scott nailed it suggesting we subdivide each wing half. This reduced the ripples to an acceptable minimum.

 

[Mucksmear]

Next challenge: The root rib is 19-1/2” long … approximately the diagonal of my laser cutting bed. This makes for some inefficient parts layout on the 1/8” plywood sheet.

Lightburn to the rescue - a feature called “print and cut” lets you cut jobs that are longer or wider than your laser cutting bed by splitting the job into bite size segments to be cut in successive passes with the help of registration marks and the red dot laser. The key is to get the red dot laser precisely lined up on the registration marks. I was within about 1/100” on my first attempt (good enough for me). My second attempt looked perfect.

1st pass:

2nd pass:

Success!

Here’s a decent walkthrough of how the Print and Cut tool works:

 

[Mucksmear]

I was trying to figure out a way to cut clean, vertical slots into the wing core for the stub ribs without a complicated jig or other monkey biz.

I set up the hotwire above and parallel to the workbench and then stood the wing core vertically on its root face so I could feed it through the hotwire. After cutting in from the LE, turned off the hotwire while raised the core with a balsa shim to create the necessary offset for the return cut. The stub ribs are 1/8” and to account for the hotwire kerf, I used a 3/32” thick shim.

Wire mounted across the workbench (with a raised board to clear the barclamps):

 

[thenated0g]

Hurry up, almost sunset

 

[Wayne]

Think they have been working on it.

 

[Doc James Hammond]

Thanks for the input guys!

The most that I’ve played with flyingwing twist angles with anything beyond just guessing, is to compare root and tip profiles at an a given Re number and then measure the angular diff between the stall AoA based on the graphs generated by AirfoilTools… so that the wing tip stalls at the same time or later than the wing root.

I have not been able to wrap my brain around the issues of pitching moments.

I’ll check out your suggested airfoils

Hey Mucker - Basically if your aerofoil is reflexed it will have an upward pitching moment and if undercambered, the opposite. Obviously you dont need an undercambered section.

Since the flying wing has no rearward stabilization in the form of a tailplane, there will probably be no actual "Up and under" (Love rugby terms) stall but more likely a loss of forward speed and a waggling mushiness as the model pancakes - normally with little or no damage. I did know one guy years ago who had a "Delta Lady and regularly pancacked it for landing. Just gently pull in up elevator until the stall ocurs and down it comes like a Harrier jump jet.

With the right aerofoil you dont need any wing twist. Look at some of Peter Wick's sections - he is the wing aerofoil guru.

Great project by the way.

Doc.

 

[Mucksmear]

Thanks Doc, funny you mentioned the Delta Lady as that was originally what Scott and I were going to build before I settled on this Soar-Jet.

Made a simple jig to bore holes into the root face of the wing cores of the wing joiner sleeves. Happily, the bored holes lined up pretty well with the plans-accurate holes in the stub ribs (I had expected a little more error). We had been prepared to cut vertical channels in the cores so the brass tubes/ribs could be dropped into place, with the brass tubes back filled/packed in with balsa afterwards.

 

[Doc James Hammond]

I think you'll fnd that the Soar Jet has a lot more gliding performance than the "Delta Lady"

As I remember, the Delta Lady (Thanks to Joe Cocker RIP) had a roll rate like a DeWalt drill, but little else to recommend it unless you count the "Alien" looks it had when soaring - In a good wind mind you - it was NOT a light wind model. For some inexplicable reason it always looked like it had anhedral when flying - even though it didnt.

Nice choice for an oldie.

Doc.