Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
August 07, 2020, 05:58:01 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: 1 [2]   Go Down
Print
Author Topic: Flat Wing P-30  (Read 1394 times)
0 Members and 1 Guest are viewing this topic.
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #25 on: June 12, 2020, 08:19:22 PM »

I have attached a picture of a prototype "flat wing" that I quickly built.  The soup can was included in the picture to give the viewer a better idea of the size of the wing. It measures 29 7/8-inches by 4 1/8-inches.  The tip plates have been tack glued on with generic glue similar to that sold under the Duco brand. They will later be easily removed with acetone before covering the wing with Esaki tissue.  When shrunk, that tissue will add a lot of torsional strength. I usually cover wings with the grain of the tissue extending span-wise.

The weight of the flat wing frame as shown is 10.40 grams.  That’s descent considering the heavy balsa wood I used to build it.
  
I purposefully used heavy balsa wood for durability and resistance to warps.  This wing will be a component of a beginner’s P-30 so there is no need to try to build near the 40-gram minimum set forth in the P-30 rules followed in the United States.  I used 9# wood for the 1/8-inch square leading edge (later rounded), and 12# wood for the 1/8-inch square main spar.  The two 1/16-inch square stringers were made of light balsa wood because that is all I had access to during my stay-at-home.  I am running low on 36-inch long sheets of 1/16-inch thick balsa wood. The ribs were cut from a sheet of 1/16-inch sheet balsa wood that had an overall density of 10#. Some of the individual ribs felt like they came from a lighter part of the sheet.

The tip plates measure 4 1/8-inches in length and have a maximum height of 2 5/8-inches.  They might be a bit tall. If test flights show that my beginner's P-30 exhibits good lateral stability, I may progressively cut down the tip plates with scissors at the flying field to see if they can be reduced in height without impairing roll stability and recovery from turbulence.  The tip plates weigh a combined 3.15 grams.  Reducing their height would reduce weight and drag.

The wing ribs have a Neelmeyer airfoil with a flat bottom.  Cutting, sanding and notching fourteen uniform ribs was time consuming.  A novice could easily assemble this wing frame in less than an hour with laser cut ribs. I purposefully did not build in any wash-out as I want to see if adequate lateral stability can be achieved without adding this complication for a novice.
 
For those who have been following this thread, you know my reason for using a flat wing on a beginner’s P-30 model.  To reiterate, novice builders often have difficulties properly inclining and joining built-up angled wing sections.  A flat wing with vertical tip plates is the easiest built-up wing to construct that can provide sufficient lateral (roll) stability.  The tip plates effectively provide the flat wing with dihedral.

As usual, your comments and suggestions are welcome.
Attached files Thumbnail(s):
Re: Flat Wing P-30
« Last Edit: June 12, 2020, 08:41:10 PM by calgoddard » Logged
applehoney
Titanium Member
*******

Kudos: 279
Offline Offline

Canada Canada

Posts: 3,181




Ignore
« Reply #26 on: June 12, 2020, 08:41:02 PM »

Cal, my only exposure to a 'flat wing' model was, decades ago, witnessing flights of a glider with this configuration - as published in a British magazine of the time.

It flew quite well in near calm conditions, was a little unhappy when towed quite fast in little wind; from what I remember of that far-off day  its stability was marginal and glide pattern easily upset.

With no more personal experience than this I would, with the greatest respect, not consider such a wing for a  P30 .. least of all for a beginner's design.  Had a flat wing have an advantage over dihedral/polyhedral then such would have long been seen in numbers on the flying field.  Other than general structural simplicity, stability is essential and I do not see a borderline level of such as fulfilling the requirement of intended  purpose.

Ultimate performance is not a requirement of a model proposed for youngsters, in particular. Easy to build, strong, easy to trim and fly proved ideal for my boys  (when they were boys!)  ... a robust model which briefly out-climbed  Coupes of the time ... no freewheel so a fast descent quickly returned the airplane to the flyer's hands. Novices do not seek ultimate performance ...  a stimulating power pattern,  a fair but fast glide ..and not far to walk to retrieve and return to wind up and fly again ... and again.

A strong ... if overweight ... dihedralled P30 with no freewheel would likely be good for up to a minute; given successful flights an upgrade to a freewheel would add some performance.  Hopefully the builder/flyer would be hooked by then  !

Cal, please appreciate  I'm not trying to wet-blanket your thoughts and proposition.  I hope you'll build and fly your flatwing airplane and would be  very interested in the outcome; I love  P30 and an improvement in layout and performance would always be welcome.

Respectfully,

Jim
Logged
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #27 on: June 12, 2020, 08:55:06 PM »

Jim -

Thanks for your input. Yes, I too have wondered why there are few outdoor models with tip plates.

My latest free flight endeavor could well be a waste of time.  But I currently have time to waste.

I really liked the Square Eagle as a beginner's P-30 but it is no longer being kitted.  The ONE NITE 28 has been re-named by the successor to Peck-Polymers but is currently out of stock.  Unfortunately that model did not accept a typical P-30 blast tube.

The old HOT BOX design by John Oldenkamp is a very good beginner's P-30 if you have to scratch-build. It uses a "Cracked Rib" design in the wing which eliminates the tedious job of cutting, sanding and notching wing ribs.

Jim - I really want to thank you for all your input on HPA over the years.  Among other things, I think you stressed the need to round the upper surface of the nose block plug on OTR models.  This tip probably saved my carved balsa wood props from breaking on a number of occasions.

« Last Edit: June 12, 2020, 10:13:16 PM by calgoddard » Logged
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #28 on: June 18, 2020, 06:17:39 PM »

I am attaching a picture of the fuselage frame of my beginner’s P-30 which I just completed building.  It borrows from the design of the Square Eagle P-30 fuselage.  I constructed the fuselage in the picture with two “slab sides” made of 1/16-inch sheet balsa wood.  As shown, the fuselage frame weighs 8.4 grams.  

Fabricating and joining the slab sides from scratch took a lot longer than building a conventional box frame or making a rolled tube for the fuselage.  However, if the parts were laser cut the assembly would take less time to build than the traditional P-30 fuselage designs.
 
The fuselage measures 28-inches long x 1 1/8 -inch wide x 1-inch tall.  It will easily accept a blast tube of sufficient internal diameter to accommodate a standard 6 x 1/8-inch P-30 rubber motor. The laminated nose block and 9 ½-inch plastic prop (not shown in the picture) will extend about 1-inch forward from the front end of the fuselage.  If a Gizmo Geezer prop assembly is used, two inches of length beyond the forward end of the fuselage will ensure that  the airplane does not exceed the 30-inch limit in the P-30 rules.
 
I cut the ¾-inch round holes in the slab sides to save weight using a segment of Aluminum tube filed to sharpen one end.  This tool is similar to a hole punch except that you do not ram it through the balsa wood. Instead, you manually spin it to cut out a circle of balsa wood. Filing one end of a segment of a Brass tube or a Copper tube would probably make a better cutting tool as the edge would stay sharp for a longer period of use.  I didn’t have Brass tube or a Copper tube of this size available.

The motor peg holes are located to achieve a 19-inch hook-to-peg distance. That’s the length of a conventional 6 x 1/8-inch 9.8-gram P-30 rubber motor.  The area on the inside of each slab side surrounding its motor peg hole is reinforced with a small vertical section of 1/16-inch sheet balsa wood and a small square of 1/64-inch plywood. A 1/8-inch hole was drilled in each vertical balsa wood section and plywood square to accommodate a segment of 1/8-inch outside diameter Aluminum tube which will serve as the motor peg.

¼-inch diameter holes were drilled in the tail section of each slab slide to reduce weight. 3-inch long tapered notches, 1/8-inch tall at their forward ends, were cut into the upper edges of the tail section that will provide negative stab incidence of 2.4 degrees.
 
The slab sides were joined with 3/32-inch square balsa wood cross-pieces.  The fuselage sides with all the holes and notches can be laser-cut if my beginner’s P-30 is ever kitted.
 
The 3 ½-inch long nose section is fully sheeted without holes in the sheeting. This is because the modeler will need to handle this portion of the fuselage while inserting the nose block. In the nose region the upper edges of the slab sides and the rectangular top and bottom pieces can have laser cut interlocking notches to facilitate assembly.  A beginner should easily be able to assemble this fuselage frame in less than one hour using laser cut slab sides, laser cut top and bottom nose pieces, along with pre-cut 3/32-inch cross pieces.
 
I will cover the fuselage frame with Esaki tissue with the grain extending perpendicular to the longitudinal axis of the fuselage.  This will add considerable torsional strength once the tissue is shrunk and doped.

Your comments and suggestions are welcome. P-30 is a great event! I am hoping my beginner's P-30 will inspire beginners to become involved in the free flight hobby. Test flights will be needed to validate that the flat wing provides sufficient roll stability.
Attached files Thumbnail(s):
Re: Flat Wing P-30
Logged
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #29 on: June 22, 2020, 05:17:07 PM »

I built a stab for my beginner’s P-30 as shown in the attached photograph. It mimics that of the Square Eagle P-30 except that I opted for twin 1/16-inch sheet balsa fins attached to the ends of the stab instead of a single vertical fin aligned with the center of the fuselage. Securely mounting a single vertical fin to the rear portion of the fuselage (common P-30 configuration) or the center of a horizontal stab in proper alignment can be difficult for a beginner.  In constructing the tail feathers of my beginner’s P-30, each fin can be readily glued in a vertical position to a corresponding outermost rib. In the attached photograph the twin fins have been tack glued onto the outermost ribs, and will later be removed to facilitate covering the stab with Esaki tissue.

The rear ends of the stab ribs are glued in notches in the trailing edge, to increase strength at these critical joints. These notches can be laser cut if my beginner’s P-30 is ever kitted. The span and chord of the stab (including its twin fins) measure 12 3/4-inches and 3 inches, respectively. The fins measure 3-inches in length x 1 ¾-inches in height x 1/16-inch thick.  Their combined area is more than double that of a typical single P-30 fin and therefore the twin fins should have enough area to provide sufficient yaw stability. The weight of the uncovered tail feathers as shown in the attached photograph is 3.31 grams.
Attached files Thumbnail(s):
Re: Flat Wing P-30
« Last Edit: June 22, 2020, 05:30:22 PM by calgoddard » Logged
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #30 on: June 24, 2020, 12:46:23 PM »

I made a mistake in constructing the stab of my beginner’s P-30.  It was supposed to have a 3/32-inch square main spar and two 1/16-inch square stop spars.  I simultaneously sanded notches in the lower side of a bunch of 1/16-inch sheet ribs for receiving the main spar using my 3/32-inch notch sander.  Then I incorrectly used the same sander to sand notches into the upper side of the bunch of ribs.  I forgot to switch to my 1/16-inch notch sander. When I realized my mistake, I decided it was too much work to make all new ribs.  Rough calculations using John Barker’s 2005 SHEET AND STRIP WEIGHTS IN GRAMS chart indicate that this error resulted in about 0.2 grams of additional weight.  This is still bad because even a small amount of unneeded weight at the end of a long tail moment is undesirable.  However, the upside of my mistake is that the stab will be less prone to warping with larger top spars.
 
If my beginner’s P-30 model is ever kitted, it will probably use a 1/16-inch x 1/8-inch main spar in the stab, with the 1/8-inch dimension oriented vertically.  It will use 1/16-inch square balsa wood sticks for the top spars and 1/16-inch sheet ribs. If the stab used 1/32-inch sheet ribs I fear it would be too delicate and too prone to warping with tissue covering.  Such a light construction would probably be fine with Mylar film covering.
Logged
flydean1
Platinum Member
******

Kudos: 25
Offline Offline

United States United States

Posts: 1,128



Ignore
« Reply #31 on: June 24, 2020, 01:01:59 PM »

Just an observation not necessarily negative:  Mylar covering requires a heat source to attach and shrink.  Many beginners won't have this.  Even domestic tissue, with all its' defects, will be easier to handle.
Logged
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #32 on: June 26, 2020, 09:58:45 AM »

flydean1 -

Thanks for your input. I agree that covering with Mylar film requires tools and skills that are very unlikely to be available to novices.

I intend my beginner's P-30 to be covered solely with tissue.

The comment at the end of my prior post should have said the following. Using 1/32-inch sheet ribs in the stab would require the use of Mylar film covering to avoid warps.  Therefore 1/16-inch sheet ribs will be used in the stab to permit tissue covering.
Logged
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #33 on: June 26, 2020, 10:01:18 AM »

A pre-assembly picture of my beginner’s P-30 is attached.  The weight as shown is 25.02 grams. I was not careful with balsa wood selection. The nose block and prop assembly will add at least 10 grams.  Adding the weight of the tissue and dope on the wing and stab, and the weight of the wing saddle will surely push the all-up-weight (less rubber) of the finished model above the 40-gram minimum set forth in the US rules for the P-30 event.  The finished model should come out less than 50 grams, and perhaps close to 45 grams. Nominal amounts of down thrust and right thrust have been sanded into the forward end of the fuselage.
Attached files Thumbnail(s):
Re: Flat Wing P-30
Logged
BG
Platinum Member
******

Kudos: 83
Offline Offline

United Kingdom United Kingdom

Posts: 1,713


Me with F1B - epic retrieval (flew 10km after DT)


WWW

Ignore
« Reply #34 on: June 27, 2020, 03:06:22 AM »

Looks nice. I agree with Jim's analysis though. I think she will fly but may be tricky in turbulence etc. In the end I think even rank beginners can handle a simple V dihedral wing with little trouble and the discussion regarding the particular need for more dihedral on FF models is an instructive one to have with any beginner in the hobby. The last thing we want to do is to give folks the impression that dihedral is optional.

just my two cents.

BG
Logged

F1B guy but its not my fault, Tony made me do it.
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #35 on: June 27, 2020, 02:20:19 PM »

Bernard -

I have great respect for your opinions based on your vast knowledge and experience in the free flight hobby.

You and Jim are probably correct that a flat wing P-30 is not be the best configuration for a beginner.

Right now I have the time to conduct this experiment.

At this time, I don't have access to a flying field and my winder, stooge, blast tubes, etc.

I will go ahead and finish this model in the hopes that I can do some test flights with it in the coming months.

Thanks for your input Bernard.  It is welcome.

Logged
calgoddard
Gold Member
*****

Kudos: 25
Offline Offline

United States United States

Posts: 982


Topic starter
AMA, NFFS & FAC Member



Ignore
« Reply #36 on: July 19, 2020, 05:59:56 PM »

The weight of my completed beginner’s P-30 model as shown is 45.5 grams (without rubber).  I was not careful with balsa wood selection during the build. Better wood selection would achieve a weight closer to the 40-gram minimum under the P-30 rules followed in the United States. By way of example, lighter 1/16-inch sheet balsa wood could be used for the tip plates on the ends of the wing and the twin fins on the ends of the stab. This would probably save a couple of grams.

I set the CG at a conservative 57.5%.  The CG is located 2 3/8-inches aft of the LE of the wing, which has a 4 1/8-inch chord. Right now, the down thrust is about 6-degrees due to the generous decalage. The right thrust is slightly over 2 degrees.
 
Low power tests flights in my small local park yesterday showed that this model exhibits sufficient roll stability in relatively calm conditions.  I wore a mask and stayed away from other people who were exercising their dogs.
 
I cannot launch this model at more than 300 turns and 2 inch-ounces of torque in that small park without risking its loss.

When I can test fly my beginner’s P-30 at a large flying field, I will gradually increase to 1000+ turns and 5+ inch-ounces of torque. I need to confirm that the model exhibits sufficient roll stability in windier conditions.  This may not take place for several months due to the ongoing pandemic.

Thanks for reading this post.  Your input is welcome.
Attached files Thumbnail(s):
Re: Flat Wing P-30
Logged
flydean1
Platinum Member
******

Kudos: 25
Offline Offline

United States United States

Posts: 1,128



Ignore
« Reply #37 on: July 19, 2020, 08:24:00 PM »

One way to test at higher torque levels without exceeding small field dimensions is to double the rubber cross section.  You will have to ballast the model to keep the CG the same as with the 10-gram motor.  If you double the cross section of your present motor, the 2 oz/in torque will come up at about 75 turns.  5 oz/in will probably require less than 200 turns.

This accomplishes several things.  First, the increased motor weight and CG ballast will inhibit the glide, shortening the flight.  The higher torque will bleed off very quickly.  Any dangerous tendencies will be revealed but will be of short duration; sort of like a short motor run at full power on a gas or electric model.

I used this to trim my Majestyk to be "safe" at 6 oz/in torque knowing it will be well able to handle the 10 gram motor (2-loops of 1/8).  Best flight was still less than 40 seconds, and well contained in the small field I had at my disposal.
Logged
atesus
Gold Member
*****

Kudos: 27
Offline Offline

United States United States

Posts: 724




Ignore
« Reply #38 on: July 19, 2020, 09:01:02 PM »

Went back to the correspondence.  Ding was flying with a club in the Sacramento area.  Searched the Endless Lift site.  No picture of the P30.

Ding Zarate is a member of Oakland Cloud Dusters. I'll let him know of this thread.

Our web site has one of his designs with tip plates, but it's a more conventional setup.

http://www.oaklandclouddusters.org/Resources/Documents/Plans/Rubber/DingZarate_equilibrium_P30.pdf

--Ates
Logged
Pages: 1 [2]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!