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WonderousMountain

Well-Known Member
Log Member
Joined
Apr 10, 2010
Messages
2,663
Location
Bellingham, Wa
Hi All Again,

Three things I like about the Sorrell Guppy:

° Wood & Fabric construction, Free Plans!!!
° Makes a nice draggy single engine Mule.
° Aesthetically pleasing reverse staggar Bipe.

Some of the Modifications I am looking into are:

Constellation style tri-tail only central rudder moving.
Airfoil selection Munk-21 undercamber 12% section.
Interlocator strut Ailerons - plans call for full span lower flaps.
Clipped wing; removing one rib box (a side), reducing span by 3ft.
Other aero tuning such as smoothed canopy, turtleDeck
and Oversized spinner by personal preferance.

Vinyl Ester Resin will be used throughout and Ia m looking into CF strip compatibility. Engine may be Boxer - Twin or the industrial V, availability couldp lay a part, roundly ignore and use what all you like.

That's probably enough for a Thread start, my first
question is about aileron roll rate, with 35" length,
Flaps will make up 32% of the span @ 7/9ths span,
R (1).png
What I need to decide on is if I keep 4 & 1/2 inch flap chord or do I go to 6" on 37.5" airfoil (16%). Positive of small flap is that it will be light and affect airfoil character least, positive of half foot flap is deflection will be less to acheive the same roll weight. Sorrell had these in simple Nylon bushings, I'd likely use brass.

Sincerely,
CK LouPai
 
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Lars Odeen

Member
Joined
Oct 2, 2019
Messages
13
First let me say I'm really new to this airplane building thing. However, drawing on my background with modifying cars, if you change one thing you need to change another 10 or more it seems like. Are you prepared to deal with that?
I'm not trying to be discouraging at all. But I'm not really a fan of making a big project bigger for no reason. Are there problems with the design you are trying to fix?
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
16,822
Location
Memphis, TN
It’s always been a cool airplane.

Why the modifications to the wing? I don’t think the plane will like the M21 airfoil and shorter span. You might be trying to recover lift, but I imagine with such a large camber, it will not be a good handling airplane. It will probably be very sensitive to speed.

Except for a fuel tank, what would vinyl ester and CF be used for?
 

WonderousMountain

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Log Member
Joined
Apr 10, 2010
Messages
2,663
Location
Bellingham, Wa
So my thought on the Carbon is to use it as a trailing edge cap strip, that's flaps & empannage: & It is a bit odd to use VE with wood outside of marine structures, but I'm willing to do the prep work and atm. pressure bagged thermosets are not a new field.

As for the airfoil, It will likely get messed with. Flap settings need to be considered at least in cruise. Stub wing design is not as tough a challenge as it sounds, taking one bay out acheived my build goal.
A+ Gallery_5.jpg
Above: the 'plans' six bay construction.
Below: Stub wing with bay taken away.
IMG_20210912_181638.jpg
Yes, I am prepared to do a lot to get flying.

C.K Lou Pai
 

Lucky Dog

Well-Known Member
Joined
Aug 4, 2021
Messages
90
Before you mess with the Guppy's wing, consider that the Sorrel brothers' wing plans consistently out performed their class rivals. They came from an RC model background and were well respected innovators. If you feel you need an under-cambered airfoil, research the SN8 Hiperlite wing (UL derivative of the Guppy) it was designed to fly slower, but was vey efficient. Both wings used short-chord ailerons. I never found the coordinates for it, but I bet there is someone here who can produce them!
 

WonderousMountain

Well-Known Member
Log Member
Joined
Apr 10, 2010
Messages
2,663
Location
Bellingham, Wa
This one below inspired me,
the gear resembles that of a
J3 and was likely found locally.
photostudio_1631636481296.jpg
I guess it is really, so what, but
the internal guppy bracketry is
not to my liking.
 

Stephen Asman

Member
Joined
Apr 30, 2019
Messages
16
Location
Michigan, USA
Before you mess with the Guppy's wing, consider that the Sorrel brothers' wing plans consistently out performed their class rivals. They came from an RC model background and were well respected innovators. If you feel you need an under-cambered airfoil, research the SN8 Hiperlite wing (UL derivative of the Guppy) it was designed to fly slower, but was vey efficient. Both wings used short-chord ailerons. I never found the coordinates for it, but I bet there is someone here who can produce them!
From what I have read, the Guppy airfoil is based on the Grant X-10, which is a model aircraft airfoil. After some research I was able to download a copy of C. H. Grant's book (Model airplane design and theory of flight) and get the coordinates for it:

ABSCISSAS*OVER
CHORD LINE
UNDER
CHORD LINE
0.00​
0.00​
0.00​
1.25​
1.93​
0.93​
2.50​
3.00​
1.33​
5.00​
4.33​
1.87​
7.50​
5.40​
2.13​
10.00​
6.20​
2.20​
15.00​
7.27​
2.07​
20.00​
7.87​
1.53​
25.00​
8.20​
1.07​
30.00​
8.40​
0.73​
35.00​
8.40​
0.53​
40.00​
8.27​
0.40​
50.00​
7.60​
0.47​
60.00​
6.60​
0.67​
70.00​
5.33​
0.73​
80.00​
3.80​
0.53​
90.00​
1.93​
0.33​
100.00​
0.05​
0.05​

1631638329905.png

Which looks very similar to the Guppy wing rib template. Grant considered the X-10 "...most suitable for biplanes of light wing loading...."

I spent a lot of time over the spring of 2020 going over my downloaded copy of the Guppy plans and found a few problems with the wing rib template. The copying and scanning process had rendered portions of it nearly unreadable and also had changed the aspect ratio of the drawing slightly. So, I spent some time re-scaling/correcting the copy of the temple, transferring the dimensions to a CAD program and rendering it as a PDF. I sent copies to Ron Jones at Thunderbird Aviation and he approved of my templates. I'm willing to share them if anyone is interested.

The C. H. Grant book is in the public domain and I can share that as well, but it's about 60 GB in PDF format.
 
Joined
Jul 15, 2010
Messages
22
Location
Orient, Ohio USA
From what I have read, the Guppy airfoil is based on the Grant X-10, which is a model aircraft airfoil. After some research I was able to download a copy of C. H. Grant's book (Model airplane design and theory of flight) and get the coordinates for it:

ABSCISSAS*OVER
CHORD LINE
UNDER
CHORD LINE
0.00​
0.00​
0.00​
1.25​
1.93​
0.93​
2.50​
3.00​
1.33​
5.00​
4.33​
1.87​
7.50​
5.40​
2.13​
10.00​
6.20​
2.20​
15.00​
7.27​
2.07​
20.00​
7.87​
1.53​
25.00​
8.20​
1.07​
30.00​
8.40​
0.73​
35.00​
8.40​
0.53​
40.00​
8.27​
0.40​
50.00​
7.60​
0.47​
60.00​
6.60​
0.67​
70.00​
5.33​
0.73​
80.00​
3.80​
0.53​
90.00​
1.93​
0.33​
100.00​
0.05​
0.05​

View attachment 115601

Which looks very similar to the Guppy wing rib template. Grant considered the X-10 "...most suitable for biplanes of light wing loading...."

I spent a lot of time over the spring of 2020 going over my downloaded copy of the Guppy plans and found a few problems with the wing rib template. The copying and scanning process had rendered portions of it nearly unreadable and also had changed the aspect ratio of the drawing slightly. So, I spent some time re-scaling/correcting the copy of the temple, transferring the dimensions to a CAD program and rendering it as a PDF. I sent copies to Ron Jones at Thunderbird Aviation and he approved of my templates. I'm willing to share them if anyone is interested.

The C. H. Grant book is in the public domain and I can share that as well, but it's about 60 GB in PDF format.
Stephen, I'm interested! I don't have the computer know-how to do what you did and my plan drawing is incomprehensible, as well. My material 'scrounging is over, time to get busy. Bob
 

Stephen Asman

Member
Joined
Apr 30, 2019
Messages
16
Location
Michigan, USA
Stephen, I'm interested! I don't have the computer know-how to do what you did and my plan drawing is incomprehensible, as well. My material 'scrounging is over, time to get busy. Bob
Here are the corrected templates that I made. Let me know if you have any questions.
 

Attachments

WonderousMountain

Well-Known Member
Log Member
Joined
Apr 10, 2010
Messages
2,663
Location
Bellingham, Wa
Mucking about in CAD today after getting back to HomePort,
Leaving off the harder parts & Starting on the Spar Diagram.
My Wood isn't a preset so I used Douglass Fir in the Plys and
Poplar in the Caps, Holes are Center to the 18" Wing Bays. 90"
leaves off the 4.5" tips and no Cabin mounting Hardware as yet.
Spar Assy.pngSpar Assy (1).png
Also, I'm about 4/5ths sure on the Wheels and tires, sourced from
Karting. I won't really need them till the Osage & Yew flat spring gear
are finished. E-Mailing a Member about their ScullCap Nose Bowl.

Sincerely,

CK LouPai

P.S. Assy. Weight is an oz. under 4 Lbs, 3mm 5 Ply & 24mm sq. Caps
 
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WonderousMountain

Well-Known Member
Log Member
Joined
Apr 10, 2010
Messages
2,663
Location
Bellingham, Wa
Would someone be willing to scale up a couple airfoils at MH index to 10/9 ratio. They are needed to Draft A constant Dynamic Pressure prop. (outboard)
Part Studio 5 (2).png
Numbers 112 & 117:

There is a feature for scaling up to 2X on Airfoil tools,
So I was able to scale the two Sections, the data files
are fine but only PDF loads to HBA W/in hassel limits.

That leaves mapping it onto Twist helix in CAD studio.
Hub extension need wasn't fully solved, but confusion
has lessoned. Iam onto other problems, like the Spun
fuel tank spout/truss structural occupying same space.

Up next, Thorp Strips, on Wood D-cell!
 

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