Guillows Messerschmitt BF-109 kit 401 RC electric conversion - RC Groups
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Aug 18, 2009, 01:04 AM
Balsa Phil
Build Log

Guillows Messerschmitt BF-109 kit 401 RC electric conversion

I've been reading Smokin' Beaver's list of conversion threads over the summer with great interest. I thought it would be fair and hopefully fun to contribute to the forum.

I've been working on this kit on and off for the last 6 weeks and, being a slow modeler, am about 1/2 way through it. I also wanted to use the thread to discuss various ruminations about RC modeling as well, however I've chosen the build log category for simplicity. I hope to continue this thread to the very end. The list of Guillows conversions has a number of disappointments, captivating threads that simply stop without even a farewell. I'd rather this not be one of those.

So why convert a Guillows kit?
Well, I'd built a number of them as a kid and have get a nostalgic excitement when I paw them at the hobby store. Plus I've flown RC electric GWS ARFs and a couple of fommies over the last several years. Then last year I converted a simple balsa free flight to great success (RET 28" 'One Night' by Peck Polymers). Ebay lists about 200 unstarted Guillows kits each week, many sell cheaply. The electric RC hobby has experienced great advancements and with, it's cheaper than ever. It just seems like a natural next step.
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Aug 18, 2009, 01:16 AM
Suspended Account
Welcome to the Guillow fold.
6 weeks makes you one of the lightning builders! My builds take 2 to 3 years!
Please take a lot of photos and post detailed descriptions of what you are doing. Also ask a lot of questions. With the photos and question we may be able to help you avoid some of the pit falls of these conversions.

All the best,
Aug 18, 2009, 07:47 AM
Suspended Account
Good point about these threads just stopping. This is a good indication of just how difficult it is to build these gummy band conversions and to build them to a successful conclusion. Even though I have been doing these for years I often find myself in a trap by some issue. I try to point these out in hopes that the next guy can avoid the problem (also to often ask for help). I need to state that these are not beginner models! There is a lot of reengineering that needs to be done to these kits to make then viable for R/C.

For my part I know a lot of folks get frustrated reading my threads as I don't seem to finish a model. I apologize for the long time frame of my builds but rest assured none have been abandoned. I leave my threads open to encourage anybody wanting to start a build to ask questions. My posts are not a one way discussion or cold set of directions. So I hope they never end. I too wish I could finish a model soon!

All the best,
Last edited by Konrad; Aug 18, 2009 at 09:56 AM.
Aug 18, 2009, 11:21 AM
Fly, dangit!!!
Led Zepplin's Avatar
Phil - You are definitely right about the threads, I'm as guilty as any. I started a 500 series Hellcat that is still sitting on top of my cabinet. I think I got a little rattled when I started thinking of the WL and gear, so I opted to start another project of similar size, but greater WA. I'm a super slow builder, but I'll finish it someday although I'll most likely start over. I didn't use any of the kit balsa, but the stuff I used is still pretty heavy. I think I've learned a little bit with my current project, an 18" WS SE5a, that will help me in revising the plans a bit.

There is still something fun about these kits, even if it is only using them for the plans. Good luck on your BF-109, it's a great looking plane.
Aug 18, 2009, 04:40 PM
Or current resident
glewis's Avatar
I 'converted' this model to 3 channel rc. I didn't use any of the kit wood and the plans were used primairly for patterns. It was constructed like a Ryan warbird and all that was left of the original Guillows was the canopy and cowl. The airfoil was changed to more of a Clark Y section and the model is fully sheeted with 1/32nd. It's a nice flying model but is very sluggish in roll. If I were to do it again I would extend the ailerons inboard one rib bay to improve roll response and do a better job of sealing the wood before the color coats were added. The wet grass has caused some buckeling of the wing sheeting due to the poor surface prep. I can post pics if you would like to see my rendition.

Nov 15, 2009, 10:18 PM
Balsa Phil

A Start

High all! Please pardon me for 2 1/2 months of no response. I honestly didn't realize anyone had even noticed this build log. I was thinking that I would develop the log for a little while and then bring it to the group's attention. I would have been much more active in writing responses otherwise. Plus I'm not used to this blogging environment. I didn't get the memo.

Good news, I've essentially completed the model so there should be few barriers to completing this build log aside from my own snail's pace. I've quite a number of pictures and the build should offer something positive to the group.

Starting the build, I intend to use the Guillows wood from the kit in this build but I'm going to process it a little.

Guillows recommends carefully sanding the die cut sheets which lightens the structural pieces and makes them easier to remove from the sheet. In fact, the die cutting rarely goes completely through the plank. The builder often must complete the cuts with an xacto knife.

For this model, I took a standard belt sander with medium grit paper, inverted it on a rubber mat base, locking it on run, and sanded the die cut sheets the fast way. The builder must execute top notch care, constantly checking the work one part at a time. I allowed the plank to float above the sanding belt while pressing down -lightly- on select formers and ribs until they all but popped loose from the sheet. Keels and other parts shouldn't be thinned much or there will be assembly difficulties later.

This is a before and after wing rib (before - 1/16, after - very thin and light). OK, I went a little too far on this one but I still used it in the build, it was wing rib 12, the last one, and I made a solid carved wing tip around it.

Now that the formers are thinned, I'm also going to carve out some interior excess wood further lightening them. This wood was pretty dense and is still pretty strong even though I've scrapped 50-80% of it away. However, this wood is also brittle and easily snaps along the grain so I'm going to glue some tiny thin cross grain pieces to the structure, making a fly-by-night plywood and adding greatly to the strength while keeping things light.

3 lightened formers and 6 cross grain strengtheners for the tops and bottoms:

As you can see, I reduced the width of the keels but kept them about 1/16 in thickness. I don't usually sweat the weight of my RC models too much, well, not as much as some, but the BF-109 has a very long tail, compared to the nose, and I'll need to keep the tail section extra light or I'll have trouble balancing the model later. If I can save 5 grams in the tail, I might be able to save 20-30 grams in the nose.

I don't really know how much weight the nose will need until after the model is built but if I'll be able to use a lighter motor and battery if I can keep the tail section light.

Builders note the cross grain pieces glued to the top and bottom of the formers. This adds mucho strength without much weight. I noticed that some builders will drill lightening holes in their formers. Holes are OK for a metal and cross grained plywood but can promote grain splits in ordinary wood structures.

Nov 16, 2009, 10:35 AM
Balsa Phil

Aside 1. Ruminations on Guillows kits

The main complaints are that the kits are over engineered, too heavy, have hard heavy brittle balsa, poor to fair die cutting, and only average of rubber, propeller, and tissue quality.

Over engineered and heavy balsa

I would agree that Guillows kits tend to have much structure and hard grade heavy balsa, but that might not be such a bad thing. From an enginerring perspective, one wants to match the airframe's strength and weight to the engine's power and the expected stresses of flight. A free flight rubber powered model will have low powered thrust from the engine and low speed airframe stresses, however the tightly wound rubber band puts a special compressional stress along the length of the fuselage.

Personally, I'm OK with heavy wood and over engineering. The structure can be easily lightented for free fiight models yet is naturally sturdy enough for high powered U control or heavy duty RC applications. I've build light balsa free flight models that ended up being too easily crushed by simple handling. I prefer sturdy.

5-10 watt rubber power - lighten structure to optimize flight performance.
20-30 watt .020 Cox free flight - plenty of power for a heavier durable model.
40-60 watt .049 Cox U control - plenty of power for a heavy durable model.

For RC use, most successful 400 series conversions have 5-7 watts per ounce of flying weight. My guess is that 3,5 watts per ounce is a minimum requirement while 9+ watts per ounce would be stressful to the unreinforced airframe.

Poor die cutting

I've always been able to use Guillows wood. The die cutting was poor only for stringer notches but that is easily corrected by cutting tiny shims from left over stringer stock. A builder can write to Guillows for replacement wood but I've never come acrossed stock wood that was so awful that I couldn't fix on the work board from scraps. Now I've come across a Comet kit that was so bad I abandoned the kit however Comet doesn't have former and rib templates printed on the plan. With Guillows at least a builder can fashion replacement parts.

Poor rubber and propeller

I'll assume this is true. Of course a free flight modeler could use upgraded rubber and propellers. Of course a free flight modeler could focus on other model manufacturers. Peck Polymers and Herr Engineering have some pretty good free flight model offerings. I picked up a Herr Engineering 28" P51 on Ebay which had nice light lazer cut balsa. At first I wanted to convert it to RC but then felt it was a little too flimsy. I set the Herr project aside but I might well finish it to rubber power soon. My guess is that the Herr P51 would make a 2-3oz rubber flier vs a stock Guillows P51 which would make a 5oz rubber flier. The Herr kit would fly better but the Guillows kit would be much stronger and have better scale details. Easy Built models are also a good choice for free flight kits, thier 'scale' kits often have larger tail planes 25% of wing vs 17% for Guillows. The larger tails offer much needed stability for free flights.

Poor tissue

I think Guillows tissue worked just fine on the kits I built as a kid. These days I use polyester tissues like Coverlite or Litespan and Aleene's Flexible Fabric glue (Wallmart craft section). They apply about the same, are much stronger, and you don't need to stink up the house with dope applications. I've also used Solite which is light and self adheasive but I found difficult to work with and tends to sag after a time. Tissue is just too delicate for my taste.


In summary, Guillows kits build to robust and highly detailed if heavy models, but I think that is a good thing for electric RC planes that use fairly high thrust engines. The old Cox .049 engine had about a 50 watt output. Today's 25-30 gram brushless outrunners can exceed 100 watts in output plus us RC fliers often yank our planes roughly around the sky. We need that naturally engineered Guillows robustness and perhaps even more.
Nov 16, 2009, 10:49 PM
Balsa Phil

More on the fuselage

Just as I took some care to lighten the tail section, I hurled caution to the wind on the nose and added structure with little concern for weight. Mainly I just wanted some decent sheeting where the wing mounts and around the nose. At some point this model will probably take a few good front end wacks and I want it to be pretty tough. Additional weight from the nose to the wing root could helpfully offset the leverage of this model's long tail.

I used whatever scrap balsa was handy as planking, mostly 1/16 but also 3/32, 1/8, and 1/4, just whatever scrap was handy and hardy. Most was medium grade but some was darn hard and some soft grade. I've probably added about 10 grams to the fuselage from planking alone, but at least it was mostly to the front of the model where weight will be needed.

The air scoop, bottom of the front end, has a sharp curve that would normally require several separate planks to cover. Instead I used some soft and light 1/4 sheet. I also used it on the lower sides here as well. The bottom half of this models nose has no stringers, just blocks of 1/4 sheet glued between the formers and shaped to order. The upper half has stringers and traditional between stringer planks.

The motor mount is built up of 3 soft 1/4" pieces with a hard 1/16 plank on top and on the sides. The 1/6 is tough enough to take screws. The mount fits well onto the firewall. Note the firewall is also rimmed by 1/4" pieces that protrude and slop slightly inward thus offering significant support for the molded styrene cowl which slides snugly on over these rim braces.

Another view. Note the position of the tail feather servos (4.3g Hobby City $3.50 cheapo's, they chatter a bit). These servos are lightly glued into place and heavily braced with balsa beams on most sides for support. Mild surgery is needed to remove them so I hope they hold up.

I just happened to have black 'LW' tissue (litespan?) and white Coverlite so I'm using them. I'll likely use acrylic paints over this base.

I'm taking the route glewis did, mainly using the wing be a removable battery and electronic access hatch. The wing will be held on with rubber bands as opposed to magnets on glewis' model. Hey, rubber bands have attached wings to flying models for centuries, if not decades, and I've got those things handy. An upper front fuse clam shell access would have been difficult because of the gun trowels on this model, the wing access offers simplicity and fair if cramped access.

Here's a better view of the cavity for which the battery and other electronics must fit. It looks more roomy here than it actually is. The small servos were a tight fit, slightly larger ones were too big. I'll be limited to lipos of about 500 mah, my 1000 mah lipos didn't look to fit.


So here we have met some challenges of the BF 109, kit 401. For one, the long tail acts like one hell of a lever toward a tail heavy model. Two, the nose is short and very busy with molded plastics complicating the design of an electronics access hatch. Third, the forward fuselage is rather cramped thereby complicating the layout of the electronics and the possible size of the batteries.
Last edited by Balsa Phil; Nov 17, 2009 at 07:09 AM.
Nov 18, 2009, 12:20 AM
Balsa Phil

3 times the fuse

The elevator and stabilizer are built up to the Guillows FF plan using the kit balsa. The plans call for making these out of solid balsa when using engines but I wanted again to keep this model's tail light and I probably saved 2-3 grams. You can even see through the yellow covering to see part numbers.

Looking pretty good with the tail feathers installed and finally covered. Even though the black and white covering was simply on hand and were intended only as a base for later painting, the look is growing on me. I may not paint over it right away.

A view of the completed tail. The elevator was laid out and built on the plan with a strait hinge. Only after it was built did I notice it could have been built with 25% more control surface and a cooler appearance if it had that V shaped feature at the ends. Since it was already built, I just kept the strait hinge line.

A big motor cavity in the cowl, several screws to hold the cowl, and the motor, a smallish 10g, 25 watt outrunner, the 1811-2000 from Hobby City.
This motor is a bit small for the BF-109 but I've used it to great success in another 6 oz. model. I'll give this motor a try and then, if the model is one of the survivors, I'll probably drop in a more powerful one later.

Long and thin, well that's a BF-109.

Well, the fuselage front end is stuffed full of receiver, speed controller, battery and padding. The fuse is all up ready to fly, but you know, darn, it's still a little tail heavy! the balance point is 1 cm aft. I'll need another 10-15 grams in the nose somewhere. I'll need a bigger battery or perhaps just a good 1" spinner will do. After the wing is installed, I'll use fishing sinkers to refine balance for testing flights.

OK so here is a generally accurate weight breakdown of the fuselage currently pictured.

30g fuselage frame (~10g of which is front end sheeting)
7g rudder and elevator frame
11g covering (LW tissue black, yellow - Coverlite white)
13g pair of 4.3g servos plus linkages to tail
25g motor, base mount, prop, small spinner, speed controller
25g 2S 460 mah lipo battery
10g GWS receiver
10g Cowl, screws, motor base

131 grams or 4.6 oz. is the measured weight for the fuselage as pictured (ARTF). Add to that some extra weight for the spinner, canopy, styrene parts, paint job, details, bigger battery or ballast, we could easily see a weight gain of 1-2 ounces and we've not included the wing yet.

I predict this model will weigh about 8 oz. but will be powered by a 10 gram 25 watt brushless outrunner with about 4 oz. thrust. Yes, it'll fly, but at the lower end of practical power. It's time to think about upgrading the motor.

Soon, we'll talk about the airfoil.
Nov 18, 2009, 01:08 AM
Suspended Account
I often find the the scale counter weight/ aerodynamic balance tab cause enough flow disruption as to make the added area ineffective.

"The elevator and stabilizer are built up to the Guillows FF plan using the kit balsa. The plans call for making these out of solid balsa when using engines but I wanted again to keep this model's tail light and I probably saved 2-3 grams. You can even see through the yellow covering to see part numbers."

Thanks for this insight! I often wondered why so many of these conversion had solid tails. It made no since to me. But as you have mentioned the plans show this. And as these conversions are often attempted by low time builders, I now understand the practice. I also didn't understand the practice of multiple inlayed balsa fillers until I read that the plans again called this out for the gas powered ships.
Nov 18, 2009, 11:59 PM
Balsa Phil
Thanks for the support Konrad. The current elevator size should be fine assuming the plane is dead on balanced. I seem to recall reading that the BF-109 had simple control cables so flying required good pilot strength and that fatigue was common after 15 min or so of combat flying. I suppose the aerodynamic balance tabs were essential in the real plane.

Planking the front end isn't essential. The Guillows plan recommends planking as insurance against rough landing damage. It does make the plane much tougher for < 5% total increase in weight. Without it the plane invariably develops snapped stringers around the firewall. At least I've experienced snapped stringers, which are repairable but quickly end a flying day.
Nov 19, 2009, 06:58 PM
Suspended Account
I agree with planking (long strips) or sheeting for strength. I question if little inlays are the best way to add strength. I think the plans show the inserts as it is easier for Guillow. Otherwise Guillow would have had to show the removal of the former between the stringers to use planking, or the removal of the stingers for sheeting.
Nov 19, 2009, 07:09 PM
Or current resident
glewis's Avatar
131 grams is a good weight. If you can finish the wing around 30-40 grams you'll have a good flying model.

What are you planning to use for the spinner?
I used a copy of the kit spinner on mine. It would be easy to add a bit of weight in the tip if you have to.

Nov 20, 2009, 09:11 AM
Balsa Phil
The little inlays are tedious and certainly weaker than planking with long strips. I suppose the inlays are efficient if you're just reinforcing a few select areas. I've seen a number of interesting sheeting and planking techniques here on the boards and might try them in future.

P.S. I took just a moment to glance at your build logs, well the Cherokee anyway, and was impressed at how detail oriented they are. I'll give them some focus as time permits.

As it turns out the wing is a rather heavy 68g+ thanks to all sorts of things ... well I'll detail that monstrosity soon enough. I plugged everything together last night with a larger 42g battery and 6+ grams of clay in the cowl plus a few tweaks and had an all up balanced RTF weight (still without paint or true spinner) of 232 g or 8.2 oz.

Of course 8.2 oz. isn't too terrible a loading with a full square foot of wing area and I'll be running the little 10 gram 1811 motor now at 3s which will offer a more reasonable 6+ oz. thrust. I know your BF-109 is running quite light in the 6 oz range but some other 400 kits are flying well at the 10 - 11 oz. range so I don't feel too bad at the moment.

At 8.2 oz., the plane does feel a little heavy and difficult to grip. If you hold behind the wing, behind the balance, you need a good stringer bending grip to keep the nose up. A grip in front of the wing doesn't feel natural for a toss. I now understand why dziedrius, in his BF-109 video, held it from the top, just in front of the canopy, at the balance, with the nose pointed up 45 degrees, and launched it with an up toss. The grip just feels natural and sure there.
Nov 20, 2009, 04:14 PM
In Unusual Attitude Recovery
MPP's Avatar
Hi Phil,
Your Guillows 109 looks great. I like your "inlays", I did similar with a couple of my conversions. This kit has always scared me off with that small wing surface. As far as hand toss, I strategically placed one insert on each TE where I grip the fuselage. With the Mustang, and the FW190 both have to be tossed fairly aggressively as the high wing loading makes them fast flyers. My Mustang came in at 11 Oz.'s and the FW 190 came in at 9 Oz.s AUW. I think as long as your under 10 you should be OK. Remember that it will fly fast and gets small really quick. Good luck look forward to your maiden report.

Here is a link to my hand toss of the FW 190 if you are interested

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