|Sep 25, 2007, 02:16 AM|
Following the Guillows Stearman
Primary Goal of This Thread
To convert a Guillows PT-17 Stearman (Kit #803) into a scale-like, four-channel, electric powered flying model.
Design Goals for the Construct*
• All Up Weight (AUW) – 10-1/2 oz (298g) [Final AUW = 9.35oz]
• Himax Outrunner Motor HC22121180
• Direct drive
• Propeller – scale-like 2-blade [APC 8x6]
• Batteries – 2-cell lithium polymer [Thunder Power, 2-cell, LiPoly 730mAh/7.4V]
• Radio Receiver – micro 4-channel, Berg 4L
• Electric Speed Controller - Thunderbird 9 Brushless Controller, 5V BEC
• Micro Weight Servos – 6grams or less [Cirrus CS101/STD 4g Coreless MIcro Servos x2 for rudder & elevators; Cirrus Ultra Micro 4.4 for ailerons]
• Elevator & Rudder – single servo pull-pull system for each surface,
• Wheels – foam rubber 1-3/4” dia. Mains [Dubro Micro Lite 1-3/4" dia], ĺ”dia. Rear [Perfect #P61 3/4" rubber balloon tire alum. hub]
• Steerable Tail Wheel – wire steering linkage connected to rudder,
• Ailerons - single servo on lower wing with 3/64” torque rods [1/32" wire control horns with 1/8" aluminum torque rods]
• Re-enforcement of various “high tension and compression” components and joints (landing gear, wing struts, motor mounts, etc.),
• Rigging - elastic thread,
• Reduced weight in stock fuselage, wing, and tail components (accomplished by sanding, scalloping, boring, and sectional removal),
• Stock Balsa stringer replacement with 1/16" sq. basswood stringers,
• MicroLite plastic film covering with US Army Air Corps markings,
• Cockpit detail & pilot figure (if below limits of final assembled weight),
*(I’ll update this list as I select specific components, and finalize my power system. Look for the actual components listed in brackets "[...]" above.)
This will be my first attempt at constructing an R/C airplane. Excluding three crudely constructed Guillows balsa models in the early 1960s (a Nieuport 11; a Spitfire; and a Zero) and a partially completed Carl Goldberg Gentle Lady in 2005 (given away prior to my move to Denver) I have no significant R/C modeling experience. I suppose there are easier kits for a newbie to assemble, but I’m partial to Stearmans, and there’s something appealing about leading off with a trainer.
I’m not an experienced pilot. In March 2001 my kid sister sent me a 2-channel electric Firebird. I put it to use chasing resident Canada Geese from the public golf course behind my house in Alexandria, VA.
Since 2001, I’ve collected some R/C books and spent time surfing R/CGroups. I’ve assembled a modest collection of modeling tools, equipment, and supplies. I’ve picked up a half-dozen kits on sale at the local hobby shops or on eBay. Now it’s time to start building!
I have several objectives for this thread, including:
• Creating incentive to complete this project by posting it on the Web.
• Accelerating my skill level through online modeler comments.
• Encouraging other newbies to start projects; sooner than later.
My Current Shop
My modeling area is relegated to a corner of the basement. I’m starting with a small model that doesn’t require a lot of space or stationary tools like vises, scroll saws, drill presses, disk sanders, etc. Two cheap knock-down utility tables (purchased at Office Depot) and a little rolling kitchen utility table (purchased on-sale at Home Depot (HD) for about $80.00) comprise my working platform. A 2’x4’ ceiling tile from HD, cut down to fit the top of the rolling table is my building surface. I checked the flatness of the tile - it’s less than 1/64” across a diagonal of 37”.
I chose the little rolling table because it was easy to assemble and had the benefit of being portable. I can easily move it around the house. It’s reasonably stable. The two storage shelves need some work to better accommodate my tools and stuff. The working height at 33” is a little high for my 6’-1” height, but it’ll do for now. The rolling table also allows me to adjust my location to take advantage of whatever light is available at the current work location. If you go this route, consider using something to protect carpets and flooring (I use a small tarp), and cheerfully volunteer for some extra time with the vacuum cleaner.
During the past few years I’ve assembled all of the essential tools for building small balsa kits. Nevertheless, without much practical application or skill, it should be amusing to the veterans, and instructive to the novices, to watch my experiences. I’ll try to document my narrative with photographs, but using the digital camera during this assembly is going to be a “learning experience” too.
Before starting, I went to Kinko’s and ran full-size copies of the plans and photocopied a dozen 8-1/2”x11” sheets of the fuselage formers and wing ribs.
I’ll use the photocopies for building the model and save the original plans for reference. I learned with my Gentle Lady, how quickly original plans were damaged from tears, cuts, pin holes, and glue leaks. The photocopies weren’t cheap! Kinko’s charged $0.75 per square foot for the larger plan sheets. [If you want to make copies of your original plans, look for an architectural/engineering/blue printing firm in your area. Their prices will most likely be substantially less expensive than FedEx/Kinko.]
(Note: You might be able to use a flat bed scanner, computer, and printer to duplicate parts of the plans at home, like wing ribs, but I ran into distortion problems when trying this on my HP Photosmart C4150 flatbed scanner, Gateway computer, and HP Laser printer. My test wing rib scans were all slightly distorted by about minus 2%. Until I work out the details in my hardware and software, I’ll stick with the commercial photocopies.)
I cut the plans into sections to better fit my small work surface.
I purchased a small professional pocket-sized weighing scale on-line from Old Will Knots Scales ( http://www.oldwillknott.com/ ) for my weighing chores. There are many quality vendors out on the web, I just happened to choose this one; and was pleased with their prompt service. The make and model I selected was the ProScale XC2000 - Digital Pocket Scale / 2000 x 0.1 Gram Scale. Since I was building small models, I wanted a scale that was accurate in measuring small and very light components, and had a small footprint. The total price, including shipping, was $65.84. I didn’t order the 2000g calibration weight. I saw comparable scales for as low as $35.00 from this vendor.
Construction - Phase 1 – The Upper Wing
It seems most kit instructions recommend starting with the tail feathers or fuselage. I chose to start with the upper wing. It seemed like the least complicated part of the plane - I was wrong.
I mounted the upper and lower wing plans and wax paper on my work surface with thin half-inch long pins. They don’t seem to get in the way very much and I’m going to try them in place of masking or painters tape.
A 24” steel straight edge checked for flatness across the rule (Don’t’ assume that rules are flat!) was aligned with the back of the trailing edges on the plan. This created my horizontal reference line for building the upper wing.
The rear center wing edges that form the cut-out over the cockpits were sanded and glued to the trailing edges. Next, the wing tip pieces were sanded and glued to the trailing edge; working sequentially forward, from rear to front. These required some sanding to approximately align them with the plan form. Each of the wing tip pieces were sanded until the front edge of the E6 sections aligned with the back edge of the leading edge, when laid flat on the plan.
The wing tips will have to be raised up about ľ” off the plan (slightly warping the tip into a helix shape) when glued to the rear of the leading edge. To create a tight fit, the front edges of the E6 sections were sanded with a small vertical block so they will lay flat against the vertical back face of the leading edge when it comes time to glue them together.
I cut the upper wing ribs – F1 through F6 - from the stock sheets and removed the stringer notches. I lined up the notches and leading edges as best I could, and then sanded the leading edges and took a flat file and gently filed out the stringer notches to a width and depth of 1/16”.
In the photos, you can see that my rib notches didn’t’ align very well; some being off as much as the thickness of the 1/16” stringers. Some of the rib tops broke off next to the notches. The tops of some of the ribs were a bit low also.
Rather than use the stock ribs, which would require filling in the voids around the stringers with small bits of wood and gluing 1/16” filler strips onto the top of the low ribs, I’m going to re-cut all of the ribs using 1/16” sheet balsa and an Exacto knife. I’ll use photocopies of the ribs from the plans, glued to 1/16” sheet balsa with rubber cement.
|Sep 25, 2007, 03:32 AM|
Wonderful first post, Jugjock! Your work area looks like it should be quite servicable, and I suggest you upgrade the lighting before any other upgrades; it makes a huge difference in lessening "bench fatigue". A hint on the spar notches - cut and match all the ribs without the notches, then stack the ribs firmly together, aligned with pins or a wrap of tape, and then cut all the notches at once in the stack; they HAVE to align then.
|Sep 25, 2007, 06:03 AM|
Well done that man.
I have one of these I built ages ago. Its flown a few times, but now hangs from the kids bedroom roof. They fly great, but really need to be lighter than stock.
I wouldnt advise learning to fly using this as a trainer though. Get a high wing 4ch foamy and play/break it first. I can assure you that the Stearman is a challenging plane to fly!
|Sep 25, 2007, 10:19 AM|
JugJock, not sure if you know this but a biplane aircraft has issues with wing incidence.
Both wings must be set to a very close tolerance to fly right. I'd have to agree with Barry that this plane is NOT a good choice to learn with. Also remember that bigger is better ! The bigger it is the easier is to fly. I would listen carefully to what is written in these posts for succesful attempts to fly rc. Theres nothing worse than putting in alot of hours and watching it tip stall and crash on the first take off.
|Sep 25, 2007, 11:05 AM|
A Guillows kit, especially a biplane, is not a good choice for a free-flight rubber kit conversion by an inexperienced builder and flyer. There are a number of nice kits intended for electric power and designed to be easy to build, survive maiden flight and rough landings. Mountain Models 48" w/s Cub for example. The PT-17 is a relatively small model with a lot of drag, critical wing and stabilizer incidence settings, and need for correct down and right thrust and adequate power requirements.
If you must proceed with the PT-17 as a first electric R/C conversion project by a beginning flyer, here are my experiences with this model:
My PT-17 was a "tip stalling fool", I tried various wing incidence changes, cg changes, and elevator trim settings with many repairs. I made a saddle for the top wing, both wings were held on with rubber bands. The N struts plugged into slots in the wings. I also had hooks in upper and lower wings with rubber bands to hold wings and N struts together firmly. I went through a number of too-heavy-insufficient power setups finally settling on a Medusa 12mm motor in a GWS DXA "gearbox" , 8x4 slow flier prop, and 3S 400MA lipo packs. The battery pack was mounted next to the motor with a slot in the firewall to achieve proper balance. With adequate power, it finally settled down to being controllable for ROG takeoffs, decent climb, and scale- like cruising. It would also do decent large loops. I used rudder, elevator and throttle, no ailerons. Rudder and elevator are very effective, use small throws.
The dummy motor did not survive first flight. I made a ring cowl from an ABS calcium supplement container. If nothing else, building this model will be a real learning experience for you .
|Sep 25, 2007, 05:13 PM|
Too bad you don't have two kits, one to be pretty and one to fly.
If you're not aware of it, the strip wood and balsa for this kit is WAY too heavy for a small model. I have a N17 from Jim Wikerson's plans that's about the same wing area and it's flies nicely at 7 oz. I'm not sure the airframe alone in this kit will end up being under 5 oz. with the included wood. Contest balsa for the formers and maybe get a Master Airscrew balsa stripper for lighter wood?
The other issue with this model, being a former and stripwood design, introduces lots of complexity in the conversion from a rubber powered FF model to RC scale model. You'll have to make hatches and mounts for the batteries and servos, RX, ESC, etc.
I don't mean to discourage you, it's been done before, but for it to be your first build and model for learning on, it maybe sort of frustrating. One thing in your advantage is that the power systems available now are much more liely to get this ship flying than they would back when small Nimh packs were the rule.
I'd at least try to build a simpler, laser cut Biplane micro RC kit which has a proven thread record here on RC groups.
|Sep 25, 2007, 11:05 PM|
I have to agree with everyone's input on this matter. If I didnít coordinate every turn it would fall
out of the sky. Although it did fly what I thought very well before I painted it. Just reinforces
the idea of keeping it light.
Whatever you decide to do good luck.
|Sep 26, 2007, 02:38 AM|
Is this a great hobby filled with wonderful people?
Thank you, to all six of you, who graciously took time to add your comments and gentle advice to my first posting and thread. I've read your replies several times and will incorporate your suggestions into my planning; and yes, if the final product turns out to be flyable, I will look to several of the local clubs for an experienced micro-biplane pilot/instructor for a maiden voyage. I have a feeling that flight may be a ways off given my schedule as of late.
Brad Trent - You're the very first in line. Thank you for the solution on the rib notches. You'll see your suggestion put to use in my next post. BTW, my wife and I cancelled a week of riding our tandem up in Lyndon this past June. If we reschedule for next year, perhaps, I could stop by to take a look at that beautiful Fokker biplane in your avatar.
RCMiniman - The Web is truly incredible - all the way from the tip of the Highlands! Thank you for your kind words. Peter Townsend's BofB book is on my nightstand; I'm just through the part where his squadron is leaving John O'Groats for 11 Sector and convoy duty. If you have a picture of your Stearman, I'd love to see it. (Correction: A slight error in my quote from Townsend - he was actually based in Wick, with 43 Squadron. I wonder, if anything remains of that old RAF base?)
CaptAhab - Thank you for confirming one of my principle bete noires about the Stearman: the wing incidence. I keep staring at the plan side view and section and wondering if I can make a jig of some sort to hold the wings in proper relation while I gluing them. I'm also wondering about those plastic struts and if I should replace them. And yes, I have my own copy of Moby Dick, staring Gregory Peck, and hopefully, this little plane will not lead me in a self-defeating chase after my own little white wale. I'm envious of your RC experience and skill, and also that you live in the land of Blue Bell Ice Cream. (The unwashed will not understand this last comment.)
E-Chanllenged - You are truly one of the reasons why I embarked on this build. About 5 years ago, I stumbled across an Internet article that you'd written about converting Guillows planes to electric flyers. You included pictures of that Stearman and a bright yellow Piper Cub. I copied it into an MSWord document and must have read it over a half-dozen times. It's in an unpacked box in the basement. I'm going to go find it and read it again. You were a real source of inspiration for me when I first started thinking about taking up the hobby; and a sustaining factor later when I had no time for modeling and could only snatch a few moments for reading day-dreaming now and then. Thanks again!
Looooeeee - Thank you for your comments on the weight of the stock balsa in this kit. I must admit that I'm just becoming aware of the fact that balsa comes in some significantly different grades, weights, density and hardness/softness. I've reviewed pburress' Stearman build (IMHO he's a superb craftsman) and he makes a big deal about replacing parts with lighter balsa and cutting out a lot of material. I'm planning on copying his weight-loss techniques in my build. You're suggestion to go simpler and bigger is duly noted - I have a 3-year old Goldberg Mirage kit that may get started in parallel with the Stearman.
SVX - Hmmm, the names of Alice Cooper and Eric Clapton come to mind... Thank you for those great pictures of your Stearman. Very handsome! How did you hinge your control surfaces? What did you use for your rigging? Gee, I could really be a pest...
Again, many thanks to all of you.
|Sep 26, 2007, 10:34 AM|
Small, lightweight, yet powerful motors and lipo battery packs have made small light weight scale models much more flightworthy than in the days of round cells and heavy geared brushed motors. There are a number of great laser-cut kits and short kits designed by the likes of Pat Tritle and produced by Manzano Laser Works and sold by Dumas and Tower Hobbies. The only problem is that many of these kits are intended for experienced builders with minimal instructions and only basic details shown on the plans. The Guillows PT-17 wing has no actual spar, it is held together by brittle 1/16" square stringers and the leading and trailing edge. I added sheet balsa to upper and lower stringers to form wing spars. The airfoils in Guillows kits are intended to look scale like but are not necessarily good for RC flying. The incidences are intened for short rubber-powered gliding flights. Some experienced rubber kit converters enlarge Guillows plans and modify airfoils and incidences etc,. etc., to produce really nice flying scale models. This is more work and challenge than building a larger purpose-designed scale electric R/C plane. Still there is a strong compulsion to convert Guillows, Sterling and other rubber kits to electric R/C I finally got over it , I think!
|Sep 26, 2007, 11:40 AM|
consider trying something similar to this for immediate success using a trainer cord with help from an experienced rc pilot. Also if you buy one of the rc computer simulators it will help you immencly.
That little Stearman is really kool but I think you're headed the wrong direction to learn to fly rc.
|Sep 26, 2007, 11:58 AM|
No problem, I'm just being an echo chamber for what was already said, I hadn't quite read through your whole thread and was assuming that you'ld already started with the stock wood.
Actually as you become more familiar with the properties of the balsa we use, you'll find uses some for the heavier density stuff. I've been using quite a bit of the heavier balsa for stuff I'd normally use basswood for, like interplanes/cabanes, leading edges, and (or) spars on the bottom wings of biplane models that might encounter rough landings, ( something my home flying area specializes in..) as sometimes the heavy balsa is also quite resilient and tough.
Properly chosen and sized you can also use this wood as longerons in stick built fuselages.
One technique that's invaluable to learn is the "laminated outline" technique for making lighter tails and wing edges/tips, basically it involves getting some light 1/32"~1/16" strips, soaking them until somewhat flexible, and then laminating them using some aliphatic glue around a properly undersized water proof form using pins and clamps.
Not quite on subject, I do have a few WWI and pioneering sim models at RC-Sim.de that are made for the freeware R/C sim Flying Model Simulator, that are modeled as small light electric aircraft. I can't vouch for their complete fidelity to small flight modeling, as I'm a bit biased in that opinion, but I think they do behave like my real models do. I've even got a few models done by folks here that have online builds, Like Mr. Hooper's Armstrong Whitworth FK10 Quad and Edi's Wight quad. I like multiple wing oddities.
You mentioned tandem bikes. I have a close friend who co-owns a tandem making company in Eugene OR.
|Sep 26, 2007, 02:35 PM|
Having converted a few rubber free flight models myself, Iíll toss in my dos centavos.
The number one goal during construction is weight reduction. The wood in the Guillows kits might be good to enough to build a table out of but is no good for a flying model. Get some decent, less than 8lb balsa and cut your parts using the patterns on the plans. It sounds like you already have a good idea what will be required to do this conversion.
Here are a few suggestions based on stuff I learned doing these conversions.
I have used the kit airfoil (Clark y?) on my conversions and it works fine for my flying style. Enlarge the top and bottom spar strip wood size to 3/32 and add a 3/32 shear web out to the dihedral break then 1/16 out a couple of rib bays then 1/32 out to the tip. Plan your aileron installation and add structure as needed. Plan wing attachment scheme and add structure as needed. Plan dihedral modifications to the center section and determine if fuselage mods will also be necessary for the wing to fit. Laminate tips if possible. Sheet the center section with 1/32. Build washout into the wing panels.
Make the formers aft of the wing trailing edge from 1/32 sheet. Remove as much material as possible from the remaining formers. The horizontal keels can also be cut from 1/32. Remember the fuse was designed to withstand the tension of a wound rubber motor. We donít need that extra strength or weight aft of the center of gravity. Adjust the horizontal stabilizer incidence as needed. Adjust the wing incidence in the wing saddle area and modify the structure as needed. Add structure for removable wing mount if used. Plan control linkage routing and servo placement, add structure to mount servos and radio. Pull/pull controls will help reduce weight aft of the CG. Short nosed radial engine models are tough to balance. Tail heaviness is always a problem so plan on mounting the equipment as far forward as possible. On this model the servos and RX could end up on the firewall to get the CG correct. Add motor mount structure with provisions to adjust down and right thrust. Insert plank or sheet the forward fuselage back a couple of former bays. Strengthen the landing gear mounts and structure as needed. Use Bass for the stringers. I know, itís a little heavier but it really suks when you break stringers just handling the model.
Laminate the outlines; this saves weight where we really need to, at the tail. Get rid of anything else back there that is not needed like the rubber motor peg mount.
Two things you can add as much as you like to the structure, sandpaper and lightnessÖ.
You might want to consider a CDROM sized brushless outrunner like this one
for this project. That speed 280 is a heavy lump, and remember weight is our biggest enemy. You can shove the battery forward to make up for the lighter motor.
These conversions are not easy, thatís what makes it so satisfying when one actually flies. I keep telling myself, if were easy everybody would be doing it. So as E-Challenged suggested you might want to look at a kit that has already had the design work done. Then you can see how other designers have done things and when you do that Stearman conversion it wonít be as steep a learning curve. Look here for a nice free plan.
Also have a look at Charlieís laser cut kits for stuff designed for RC.
|Sep 27, 2007, 02:13 AM|
Jugjock, if you make it up here to Canada, you'll get to see a lot of the structure of my 75" D VII, as it's sitting in my shop awaiting extensive repairs after an ESC failure caused an unplanned crash landing in the top of a hazelnut tree, over a year ago. It was a delight to fly, for the 4 years I managed to keep it one piece, though. Repairs are planned, but timing is iffy. In the meantime, being a confirmed biplane nut, I'm really enjoying flying the Great Planes ARF SE5A, which is a little bigger than your Stearman, but much smaller, and therefore more convenient, to transport than my scratch built monster.
When you mention cycling at Lyndon, I assume that you mean Lynden, WA., which is about 40 min. from my home, not counting possible border crossing delays, which are getting to be a real hassle this last year or so. A couple of times, the line-ups have delayed me as much as an hour and a half, while other recent crossings have been only 10 min. The Lynden area is pretty flat farming country, while most of the cycling I've done is of the single-track mountain variety. Although the mountains surrounding the Fraser Valley area where I live are only about half the elevation of CO. peaks, they're every bit as steep! The al. frames for Kona mt.bikes are made right here in Surrey, and the choices at local bike shops are excellent, for all types of biking, though I don't often see tandems, except at the rental shops serving the tourists in Vancouver.
All of the advice in the above replies is excellent; now you have some decisions to make. ;-)
|Sep 27, 2007, 09:15 AM|
The base you refer to, RAF Wick is still there, but alas not an RAF base any longer. There are a few remaining buildings, like two C hangars, and the original wartime control tower. It is now simply a domestic airport, mainly used by private pilots and island hopping commercial operators.
Im a 43 Sqdn fanatic, and have built models of both Pete Townsends Hurricane (FT-A), and also Frank Careys Hurricane (FT-Y).
Im yet to read Pete's book though. Im sure it would be an amazing read.
I will look out a few pics for you and post them here with your permission?
|Sep 27, 2007, 11:35 PM|
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