RFFS-100 Bristol Brownie

[Dave Robelen]

Hi Folks,
It's time to share a bit more. I finally got an airplane wrapped around that modified set of RFFS-100 actuators. I chose the short wing version of the Bristol Brownie for a variety of reasons. Nice and roomy for a small model, it also has a respectable wing area for it's size. I did kind of "rewrite history" just a bit as all of the original Brownies were silver overall. I chose yellow for better visibility in such a small model. Sorry, Mr. Bristol.
The structure is almost all 1/32" balsa sheet, with one thin spray coat of auto trim paint. The numbers are cut from black tissue and attached with Elmer's white glue. The complete finish and markings added .4 grams.
Some stats are: Wingspan 14.2", area 40 sq. in. weight 26 grams, power E-Charger motor geared 6-1 driving a 5-4 prop. The Li-Poly cell is a 170 mah from Dan Hurd.
It really flies super. The cruise is around 50% stick, and I was able to keep it in a real tight area. It handes the breeze quite decently, adequate penetration, just a bit of bouncing.
Cheers, Dave

[Dave Robelen]

And another view

[Dave Robelen]

Look Ma, no coils

[Dave Robelen]

And Finally, the "guts"
Note the absence of balance on the controls. It seems to work fine, and the magnetic centering is nice and crisp.

[FLB]

Say it and Dave will do it...

Four days ago it was question of a Bristol Brownie and here is this little jewel... Congratulations for this nice work ;)

Regards

Frederic

[Mike Taylor]

Beautiful detailing. The dummy motor, pilot and wheels really set it off! Also, the buried actuators are very trick. My hat's off to you...

[FLB]

Hi Dave,

I'm really considering buying a RFFS system with Bob Selman actuators as soon as I get enough time to do a project. As I see your monoplan, I was wondering if a Dewoitine D27 could be conceivable. I have already posted some photos of a real one in Ghmbo Scale Quizz Thread (not the radial engine version, the other one).

What do you think about it? Maybe the landing gear system will be too complexe and weighty. I plan to use carbon rods (if I find some) or something else to do it. What could be the appropriate wingspan?

Frederic

[FLB]

Is the landing gear fixed on the wing?

Frederic

[Dave Robelen]

hello Frederick,
The Dewoitine would be a fine subject. Iwould choose a span that will give a wing area between 40-50 sq. in. My approach to the landing gear issue is to make the functional struts from .020" dia. wire, and use stiff balsa or basswood to make whatever dummy struts are needed to mock up the scale gear.
One thing to consider about the actuators from Selman is the weight. There are several different versions sold by him. The Gary Jones versions are bit large and heavy for a small RFFS-100 model. The actuators made by Rujinsk or Leichty are a bit more of a match for the miniature models.
The actuators sold with the RFFS-100 are still a good match for the small models, and the price is right. The modifications I made are really not all that difficult, and you would not damage the device by fitting the bits of aluminum to make linear style device.
Regards, Dave

[Dave Robelen]

Hi,
The landing gear is a .020" wire that is glued in a sandwich of two layers of 1/16" balsa that is glued in the fuselage as a bulkhead. The wire is covered with strips of 1/16 balsa to create the scale appearance.
Regards, Dave

[t-turley]

Wow, nice job, Dave! One of these days, I'm going to get one of those systems and build a true "front yard flyer". I have a tree-free area in front of my house that is about 40' x 70'. If you consider a decent size maple to use as a pylon, :rolleyes: that flying area goes to about 80' x 70'.

Tony Turley

[GHMBO]

Very nice Dave. I am always impressed with models that look like airplanes and this one certainly does. A true microflyer with some details, inovative controls and design considerations - a real gem. I enjoy your craftmanship and logical approach - a master builder.
Jim

[MINIRCPLANES]

Dave,

She is a beauty! Thanks for inspiring us with all your fine models.

Regards,
Felix

[FLB]

Hi Dave,

Thanks for all this info especially about the landing gear.

Concerning Selman's actuators, I was thinking to those sold in option by Dynamic (selling the RFFS-100 system), weighting 2.1 gr. I read that they are twice the weight of DV ones but 5 or 6 times stronger.

I don't not know much about this tiny scale so I will follow your advice.

Now I will have to "translate" the 40-50 square inches in metric unit... ;)

Regards

Frederic

[Dave Robelen]

Hello Frederick,
Weight is our common enemy. The Selman actuators were originally designed for models with as much as twice the wing area of the Brownie. This is also why the extra power was important in their design. There is another manufacturer of small linear magnetic actuators named Leichty. Bob Selman sometimes sells his units which come in several sizes including very small ones.
The steps I took to modify the RFFS-100 actuators were not complicated, and I only used hand tools. Perhaps you could find a way to duplicate what I did, and have the lighter units at an attractive cost. Meanwhile, if there is enough interest, I fully expect other manufacturers to offer similar light equipment suitable for thse ultra micro scale models. With the currently available motors and batteries, there is ample power to fly many designs, and the RFFS-100 receiver will fit in quite an abunce of tiny planes.
The testing and research will go on, but the future certainly looks bright for those who would enjoy a tiny scale model.
Regards, Dave

[FLB]

Hi Dave,

I've just finished my first "calculation". You said a wing area between 40-50 sq. in. So I took 45 sq. in. (metric: 290 sq. cm.) as goal.

I've done a drawing of the right wing (see picture, not scale). And here are my first results:
wingspan: 16.53 in. (42 cm.)
wing area: 45.6 sq. in. (294 sq. cm.)

Does that make sense? I find that the wingspan is a little big in comparison with your Bristol Brownie... and other tiny models I've seen before.

Do I have to increase the width of the wing? I didn't take the tail surface and the curvature of the wing into account.

And another question. Do you suggest to buy special light balsa as I've read elsewhere? Or for a first try, I can use standard quality?

Thank you very much for your advice and your patience :)

Regards

Frederic

[Dave Robelen]

Hello Frederick,
That wing design should give fine results. Virtually every airplane has slightly different dimensions in the wing chord/span relationship. I do not take the tail into consideration when calculating the area. The airfoil I used is a section of my French curve that gave an airfoil depth of about 10%.
As for the wood selection, my sheets of 1/32" balda weigh about 6 grams for a 3"X36" sheet. Considering that many sheets are actually thicker than the .032" (and some thinner) just using the density of the balsa may not give a desired weight value. I generally go to a LHS that has a rack of wood, and keep selecting from the available wood until I am satisfied. It would be better to order wood from a source like Lone Star Balsa or Superior Products and get really nice wood of the proper weight than to use material that is overweight or warped.
Good luck, Dave

[FLB]

Hi Dave,

Can I find somewhere a drawing of the airfoil you are speaking about?

Regards

Frederic

[FLB]

Hi Dave,

In fact, I should have ask another question before my wing area doubt. Which is the maximum and decent weight of a micro plane, the RFFS system could handle?

Regards

Frederic

[Dave Robelen]

Hello Frederick,
I am attaching a scan of the airfoil I used. The maximum size and weight of a model for the RFFS-100 is basically determined by the ESC. Being limited to about 1.0A current, and at low voltages, the available motors are limited to the small Mabuchi series. N20LV, M20LV, KP-00, etc. If the wing loading is kept very low, these motors can fly a model of 150 sq. in. however, the structure would be quite light and delicate. There is a club in Canada with Tom McCann, (mr. Skyhooks and Rigging) Jack McGillivary and others who fly such models regularly. For a model with sturdier construction, I would stay within 40-80 sq. with the larger area going to a biplane. Please note that these are my estimates, and have not been proven in all cases.
Regards, Dave

[FLB]

Hi Dave,

Thanks a lot for sharing your experience and some of your " secrets" ;)

Well I think I have enough information to do something... Need just to find the time now :rolleyes:

I just browsed "Mr Skyhooks and Rigging" microRC website. Very interesting but a bit pricey. The RFFS system looks not so expensive after all. :D

Regards

Frederic

[bmutlugil]

Hi Dave,

You have done it again - produced a wonderful model in short time, and as a bonus we get the simple internal actuator design :)

In the time I need to cover and paint a model, I guess you can create two new ones.. I am still struggling to find a suitable masking material- the ones I find keep tearing the covering after final painting - I am getting really bored..

Maybe I should switch to building from kits..

Best regards,

Bulent

[GHMBO]

Hello Bluent
I have had the same problem. I now use "drafting" tape. This is almost like masking tape except it does not stick as well. It is used to hold paper to the drafting surface and not damage the corners of the drafting paper. Since I like to use tissue covering, I usualy apply a 50% thinned dope after masking and before the color. This stops the color bleed under the tape. I have given a lot of thought to printing the covering with an inkjet printer. I realize that alcohol will have to be used as a cover tightener rather than water. I will probably try some of the new "water proof" inks. Maybe Dave has a better answer.
Jim

[FLB]

Hello Bullent,

I hope Jim's tip will help you to finish your "work of art" :D . I'm impatient to see the color scheme you choose. These last weeks, we have seen some nice works on that forum...

Hi Dave,

One more question :rolleyes: What do you use as pushrod material? thin carbon rod or simple music wire?

Hi Jim,

How is the Curtiss Junior going?

Regards

Frederic

[Dave Robelen]

Hello Frederick,
My pushrods are .016" music wire except for the front 2". I made the front of the rods from .020" stiff copper wire I found in Radio Shack. It turned out that the steel wire was causing all sorts of problems with those strong magnets. I used fine copper wire and solder to splice the two wires together. I am sure the carbon fiber would work fine, but I am still a bit of a "low tech" modeler regarding materials. Besides, I really believe that the .016" wire is as light as would be possible with carbon fibre and splices. But then--maybe not.
Cheers, Dave

[FLB]

Dave,

Thanks for the info...

Frederic

[Dave Robelen]

Hello Bulent,
I had almost gone to bed when I remembered a technique that worked well for me on a similar tissue covered project. I painted the wings and fuselage with the base colors, and put some white tissue on frames where I then shrank and clear coated it. I then sprayed the trim colors of the panels of tissue. When these were dry, I cut the colored markings out using patterns, and glued them to the wings and fuselage. Either a light coat of contact cement, or pvd glue spread thin will work fine. The lettering on the Brownie is black tissue, glued in place with pvc glue spread thin on the back of the letter, and then positioned on the model. They go on reasonably, and there is too little weight gain to measure. Maybe it will work for you.
Regards, Dave

[GHMBO]

Hi Dave - what is pvc or pvd glue? If you can give a brand name I will run to the hardware store. I think that I may be missing a good technique.

Hi FLB - the Curtiss has been set aside for a while. I have to be somewhat domestic for periods. The building season will start when the first rains come, and I am putting together the project que. I will probably have another quessing game and maybe I can get by Dave and his great knowlege of airplanes.
Jim

[bmutlugil]

Hi Dave, Jim, Frederic,

Thanks for your encouraging words, I guess I will get through this difficult period. A few days ago I also broke the finished cowling to pieces while removing it, and had to remove the paint, apply glass cloth, and refinish it - with around 0.5 gm. weight and two days time penalty. I hope things get better soon, or the flight season will end.. I will go to a simpler shape on the insignia, being well off scale already..

I will give a try to the colored tissue method, but I guess this should be done while covering the model, to save time. Getting the new tissue finished will take some time also. There is also the problem with finding the right glue.. I was wondering if it would be possible to find a low weight type of self adhering computer cut plastic - the type used for advertisement lettering purposes? but even if it was possible, color match would be difficult.

Jim, I guess finding drafting tape would be as difficult as finding spray contact cement here, unfortunately.. Masking tape is acceptable for me, maybe I will try finding wider masking tape or joining tapes.. I used to apply the dope around mask edges method on older models - I rediscovered this at the first masking of the Sperry :)

Frederic, the colors are dark blue fuselage, chrome yellow wings and stab, silver wheels and cowling, white and red trim on rudder and insignia.. As you may guess, the electrostatic plastic was of no use for masking.. I had problems with the dark blue (Kingfisher blue), as it turned our to be semi matte, which I found only after drying :mad:. I had to polish and process it with polyvinyl alcohol to get some gloss..

As a summary, I guess I had lost my modelling touch, having all these problems; I hope I get it back soon. A positive side effect may be that the model will look more scale, with a lot of patches on the wings before the first flight; it might give a seasoned look :D

Best regards,

Bulent

[Dave Robelen]

Hi GHMBO,
pvc is the generic name for Elmer's white glue. I was trying to put it in terms that might have been more useful to Bulent, but I may have bombed out. Most any glue that will not get the tissue soggy would work fine.
Bulent, The colored tissue would probably be the most useful to you, but yes it does take a little longer, although the results are nice. Sorry to hear about the cowl. I too have suffered through handling disasters in building delicate models. Good luck with the finishing process.
Regards, Dave

[FLB]

Hi Bullent,

I use sometimes the same method that Dave describes (colored tissu panels glued (?)). Works well for me (Nieuport 11). Sure that working with tissu is better for mat finish...

Felicitations for your seasoned look :D Such planes can be called "old wings" and maybe you could be more confiant for the first flight :p ;)

Regards

Frederic

[Mike Taylor]

Excuse me, but my undestanding is that PVC is generally considered to mean Poly Vinyl Chloride - like used for plastic plumbing; it contains a strong solvent to fuse the plastic pipe together as well as contains lots of heavy disolved solids...

'White' glues are PVA - Poly Vinyl Alcohol; they are also called "Aliphatic" White Glues or Resins. These are Elmer's, TiteBond, Yellow construction glues, etc., and these are all water soulable.

If there are differences in terminology due to geography, pardon me...

[FLB]

Hi Jim,

By "quessing game", you mean a new "scale quizz"? If I have understood well, I will try to be better this time :D

Regards

Frederic

[Dave Robelen]

Hi Mike,
Thanks for setting an old man straight.
Regards, Dave

[bmutlugil]

Hi Mike,

I presume you mean Poly Vinyl Acetate or whateveter, unless this alcohol is used as the solvent for the glue. Polyvinyl alcohol is used as a mold release agent; it is a thickish fluid that dries to a thin film, to which resins used in composite structures do not stick.. I had read that this was the mold release agent used during the construction of Burt Rutan's around the world plane, as the others were found to be useless at high temperatures - during the autoclave curing of the carbon spars.

By the way, I made a mistake saying that I polished the matte paint using polyvinyl alcohol, it should be isopropyl alcohol - which I use as an all purpose solvent - a remnant from silicon technology research days.. I noticed that rubbing this solvent to the paint surface did remove the matte effect quite easily..

Hi Dave,

White glue is probably the only name that can be translated word for word to Turkish, so it would be very clear.. The Turkish name also describes the glue using the color.. Do you think this glue will stick to the cellulose based paint below? Doesn't it "give" by time?
or do you use this method without doping the area to be colored?

Another question related with this thread: Are the spoked wheels on the Brownie hand made, and how much do they weigh? I have seen some articles on constructing very light spoke wheels in MAN..

Hi Frederic,

The weathered look on the plane would match the weathered look on my face, by the time I get the model finished (if ever) :D This would produce a "weathering matched" plane - pilot combo, if not color matched.. In fact there is temporary - partial - color matching also, as long as the painting process is under way..

Best regards,

Bulent

[Dave Robelen]

Hello Bulent,
Well, finally we seemed to have sorted out what I meant in identifying "Whie Glue". As far as I can determine, it is quite permanent in the application of paper to various surfaces in such a low stress environment. I have models at least 10 years old with markings applied this way, and they are still quite permanent. As far as applying to a smooth or slick surface, I would not expect a problem with an electric model as long as the surface is quite free of contamination.
The wheels that I have on my Brownie are commercial, sold under the name Fulton Hungerford. I bought these some years ago from Peck polymers, and have passed them from model-model. Peck Polymers was still carrying a line of these spoked wheels the last time I looked. Mine are 1.125" dia. and weigh .75 gram for the pair. There have been several articles detailing construction of this type of wheels, I am guilty of being lazy when it comes to getting busy and building wheels. I guess I would rather spend my time carving props. :)
Regards, Dave

[Chris]

Another beautiful model, Dave. Your attention to detail (I'm noticing those gorgeous wheels) continues to humble me. Before I finish one plane, I'm usually thinking about the next, and just slap on some crummy round disk wheels. And your modified internal actuators really improve the scale appearance.

Is the removable part of the fuselage carved solid, or 1/32? There's a few planes I'd like to build, but am stalled on how to capture some compound curves. I may end up having to resort to carved solid blocks...

[Dave Robelen]

Hello Chris,
The top and nose are carved from block. I used a Dremel tool with a fine round stone to do the hollowing. Working with blocks does give a lot more freedom to capture those dificult shapes. And frankly, with the right tools, it just is not that hard.
The actuator situation is a large improvement over stock. Not only do you get clean flight surfaces, but the centering is crisp and positive when the two actuators are mounted with the magnet ends facing each other. It is especialy nice that I do not need any mechanical centering to rob the actuator power. Take note that thee is no aerodynamic balances on the Brownie tail, and the control is solid and positive at the highest speeds.
Regards, Dave

[FLB]

Hi Dave,

Today I went to my previous compagny I was working for. I help them solving a little problem. The important thing is that I was thinking earlier to contact them because I wanted that they "lend" me one of their precise balances to go further my D-27 project. A balance seems to be essential :D for this tiny scale...

And what happens in an ideal world? They gave me one (for the help), two decimals after the dot. So this evening, I weight my balsa sheets I bought last saturday. Not premium balsa but some I choose carefully to do my first tests in a near future. And then I really understood the gap existing between my idea and the reality. I appreciate even more your clean and light work ;)

6 grams for a 3" x 36" sheet is a very good result. I bought a 10 sheets package of 5" x 36"sheets. They weight around 12 to 16 grams... Then I bought some .020" and .015" music wire. So small... I'm affraid that the .015" as pushrod will bend too easily. It's really a "feather weight" category!

I've not too much time for the moment but I've already modelized the plane with my 3D software. Looks very nice. When all will be completed, I will transfer the 3D data in 2D at the wanted scale. Well it's my first try with this personal technique, but it's a good way to see where I will encountered problems and how to solve them.

Another technical question, if you don't mind:
Can you recommend me a wing incidence for the airfoil you gave me? And same thing for the motor mount? Thanks for the help.

I don't post 3D pictures now. I prefer to do it later when I will have more of them. I'm also awaiting for my 3D software update because there is a new tool in it which could be very interesting... But it's a surprise ;)

Best regards

Frédéric

[Dave Robelen]

Hello Frederick,
As you are finding, a light grade of balsa can be difficult to find "from the rack". I have been known to carry a scale to the store and wear out their patience while I weigh balsa sheets. And then I don't buy very much! After a while you can get a "feel" for a good weight and stifness in a particular piece of wood.
I used 3 deg of positive incidence in the Brownie wing, and 0 in the stabilizer. The prop has no down thrust and 2 deg of right thrust. If you can find small magnetic actuators that will buckle a short length of .015"wire, I want to know your source. It is all a matter of perspective, the control surfaces are small, and the actuators have limited force. The control horns on my controls are about twice as long as the arm on the actuator,so that does double the force at the surface. This is another advantage of remote actuators, you can use leverage to get more control force.
Take care, Dave

[FLB]

Re Hi Dave,

Thanks for your infos.

I still haven't bought the RFFS sytem. So I don't no what to expect...

I went on Peck-Polymer website to see their wheels. Very nice and not expensive. For the D27, I was thinking to the Golden Age wheels or the vintage wheels 1" diameter (respectively WB147 & WB125). They don't give their weight and it's the same picture for both. Did you used them?

At this scale, it's not modelling but surgery... Seems very promising. I'm impatient to begin the collages. Maybe I will be less happy after the first crack in my balsa sheet with this round fuselage :rolleyes:

By the way, if you think I ask too many questions (too detailed ones), don't hesitate, tell it to me and I will put a brake on my curiosity :D

Regards

Frédéric

[Dave Robelen]

Hello Frederick,
The vintage wheels have a more narrow tire than the golden age type. The weight is about the same. When it comes to bending the balsa, wetting the balsa on the outside of the curve will be a big help.
Regards, Dave

[accipiter]

Hi Dave or anybody else that can help.

Just how do you guys get perfect warp free sheet wings, I just tried to make a pair and found a small amount of warp. Figured id spray with H2O and tack the wing to the board, Big mistake the panel is now terribly contorted and unuseable. This was 8+ lb wood which I know is to heavy to fly with but I was simply trying to get the feel. Whats the secret.

Robert

[Dave Robelen]

Hello Robert,
My "secret" is to leave the ribs oversize and flat on the bottom. I pin these to the board in the desired locations, and then glue the skins to the ribs. I use Elmer's wood working carpenters glue for this to get the extra working time. The last three sets have come out flat, so something must be working. Once the glue is dry, I lift the panels and trim the ribs so that their length matches the chord, and there is about 1/8" of rib below the airfoil curve.
I hope this help, Dave

[accipiter]

Thanks Dave I will give that a try. I tried making the ribs the same size as the sheet so that was one of my errors, I was also using CA ( You know, trying to cut the time dowm a bit ). Thanks for wour good designs ive so far built the Pond Baby and the Pixie, But I cut a foam wing using the 6356 airfoil and it worked great. Im building the AVAIA BH-7b racer.

Robert