Hello Ken,

I don't know the name of either of your gliders, but the picture of the one that is not covered is both mind blowing and very inspiring to a relative newbie to this great hobby like myself. The craftsmanship and construction techniques look outstanding.!!!! The plane appears to have at least a thousand pieces of wood in it and so beautiful just like it is, I would never cover it, no less fly it...

Thanks for taking your time for sharing your story and your planes with us. Good luck with your new trainer. I sincerely hope you and your grandkids thoroughly enjoy building and flying it. Please keep us posted.

David

David,

Thanks for the kind words. A couple more pictures and some additional info, and then I'll tell you everything I did wrong with that design.

The first shot shows the gull dihedral which I've always liked. In the second, you can see that both the stabilizer and vertical fin are full flying surfaces with no hinge lines. The flaps are also seen, but the spoilers are hard to see. They are two bays ahead of the flap hinge line in the second quarter of the span. The airplane was covered, with three colors of silk. The deatil photo shows that all the fillets are formed by bulkheads and longerons. It was one royal pain to get the silk to adhere and be wrinkle free on those compound curve, concave fillets.

Now on to all the dumb things I did. There indeed were a lot of pieces of wood. Too many. I built it to withstand winch and bungee launch loads, but I overdid it. It was too heavy. I also didn't provide a long enough nose moment for something with no engine. When I was done adding lead, it was even heavier. Then on the first landing, that slug of lead shot right out the bottom of the fuselage's nose. A sheet wood box to contain it would've helped, but I didn't want to do that because it would spoil the all bulkhead and stringer look. I learned my lesson and moved utility higher up the importance scale. The other sailplane came later, was lighter and structurally sound, and flew really well.

Sorry folks. I know this is a pattern thread, so I'll shut up about sailplanes now.

Ordered wood for the trainer. Targeting first flight for no later than Fourth of July.

Okay, now I'll shut up about trainers!

Regards to all,
Ken

Found some photos of the very first Brushfire with a younger Steve Rojecki. This is the balsa and foam original that Steve and I built and Steve flew. This ship was used to cast the first set of molds for a fiberglass fuselage. The vinyl letters transferred to the molds and had to be sanded off if you didn't want them.

The line drawing is the trainer I'm building for the grandkids. Everything framed up but the fuselage so far. Hopefully, it'll be happy to fly straight and level if you just let go of the controls. Rejoined the AMA and the local club so I'll have a place to fly it when the time comes.

Back to the work now. The yard awaits.
Ken

As someone who spent a number of years in SAM and the NFFS I can really appreciate your trainer. The polyhedral, single wheel and skids on the stab are reminiscent of of old timers like Shulman's Zomby, for example, which used that setup.

Thanks for the Brushfire photos. Is this the one shown in the FM article, or was that a later one?

David

David,

The construction article was in Model Builder and had pictures of the second Brushfire, the first with a fiberglass fuse.

By the way, there is a German flight simulator program called Reflex that has modeled the Brushfire. You can find the info package here: [link]http://time.fh-augsburg.de/~erd/Modellflug/textDownloads.shtml[/link]

I flew in SAM quite a bit, too. At one time or another I had a Record Hound, Super Dolphin, a couple Goldberg Clippers, and a few others. One of the Clippers is sitting in my basement with a 4-stroke 40. My dad made an R/C sailplane by putting a Comet Sailplane wing, tail, and vertical on a simple sheet balsa fuse. Boy did it ever fly great!

Ken

I get MB and FM confused for some reason. I actually have the issue of MB with the Brushfire.

Henry Struck is one of my favorite free flight designers. I have an .020 Replica Record Hound that was a rocket. I built his KGS (still in the garage) and started, but never finished his Apache (similar to the New Ruler). There are no big, open FF fields where I now live, so I've drifted away (no pun intended) from FF. But, I miss the challenge of trimming new ships. My favorite build was a Megow Jap-Slapper (war-time pylon). Obarski's Fu-Too-U (sp.) was another that translated well to .020.

Thanks for the sim link.

David

Ahandful of pre-covering shots of the Relic. It's mostly covered now with just the wing to go. Then painting. Haven't weighed it yet, but it feels about right. Fourth of July deadline looks doable.

Ken

Ken,

very nice looking Relic! I'm sure your grandkids will enjoy it.

I'm looking forward to the day my boy is old enough to fly. I think a year or two. Ihave to get him on the sim more often though.

Speaking of looking forward, thanks to you and Raindave's suggestion, I've pretty much decided to build a 40" span Brushfire around a little Webra 12 REjewel that I picked up recently. Ithink I can make it work with the engine inverted and the header running in the nose gear retract bay (no retracts on this one) and out through the forward wing belly pan former. The 10" pipe would run under the wing and end just aft of the rear pan former where the exhaust would be diverted downward. Unfortunately the belly pan would be built as a tunnel rather than keeping the nice round contour of the original fuse bottom... some compromises. I think the pipe would be concealed for the most part though.

If you have any suggestions on such a project they would be very much appreciated. It would also be great to read the original MB article if you happen to have it.

I do have a few questions if Imay:
<ul>[*]the fuse side view shows 3/4 sq (3/8" sq at 60% scale) along the bottom and along the canopy base. The section views however show a round profile to the fuse as if triangle stock was used rather than square stock. I though about using tri stock but it would provide little support for the "strip formers" at the base. Am Imisinterpreting something or do you think either one would work?[*]The 3/8" ply firewall is shown to be cut with round contours all around. How does the square stock in the retract bay intersect F1? Does one shape it to contour around the former? Likewise for the square stock beneath the canopy at the F1 junction? Do you think that cutting F1 with square angles at these intersections and providing a square slot for the stock to enter would work equally well? I'm thinking of something analogous to the way spars enter notches in balsa ribs; the square stock would meet and join F1 flush with the front of it.[*]Did F4 interfere with the flap servo or were notches just cut into the base of the former to allow the pushrods to pass back to the torque rods? I was thinking of omitting F4 on my little version. I don't know whether it makes any sense to install flaps on a model this size (a wet AUW of 33 oz is my goal).[*]The 3/32"balsa flap ribs are marked F1 through F4 with F4 being the largest rib. The wing plan shows these ribs as running from root to tip on the flap F1-F4 which would produce a wider flap at the tip than the root. Does this make sense or should the ribs be inverted running F4-F1 root to tip (flap would taper in thickness toward the aileron junction)?[*]Any suggestions on how to secure the round aileron servo covers? Simple 4 screws or did you guys do something clever? I was thinking of mounting the micro servo's with foam tape to the covers.[*]I really like the wing and stab planform as well as the wing core design. It would be really cool to use a flying stab! Any suggestions on how to do this (what hardware) at this scale?Maybe it would be simpler to just use elevators and a fixed stab.[*]Was the height of the landing gear as shown suitable for an 11" prop? I'm able to get a 7" prop to swing clear on the reduced plans but would have to raise to allow an 8"prop. Do you foresee any problems with a higher stance?[*]Last ones: what was the wing span and weight of your first wood/foam model? Did your glass ones come out lighter or heavier?[/list]Thanks in advance for any help you can provide.

David.

Corrupt post.

Ken,

Ihope you don't mind my uploading the reduced plan to a thread Istarted on the subject a few days ago (let me know if you'd like me to remove the plan):

http://www.rcuniverse.com/forum/m_8798063/tm.htm

I added some further comments and pictures there.

David.

David,

I don't mind the plan being posted. The original plan from the MB article appears several places in RC Universe.

Now on to your questions: Wow, you're asking me to remember back 31 years for details of a one-off building project. I'll give it my best shot.

- Yes it was square stock, but it had to be carved on the outside and hollowed on the inside to the contours shown in the fuselage cross sections on the plans. I spot glued them on initially, then carved and sanded the outside. I then popped them loose and carved and gouged the inside so that about a 1/8 to 5/32 wall thickness resulted. Then they were glued back on permanently. It was never an easy airplane to build in the balsa version. You can use triangle stock, but you'll have to extend the fuselage sides up to the top of the canopy rails and down to the bottom of the lower rails or you'll have nothing to glue the triangle stock to. As I recall, I contoured the fusealge and canopy separately and finally glued them together only after sanding. If you don't do that, it's very hard to carve and sand the concave discontinuity between the fuse side angle and the canopy side angle (See Section B on the plans).

- Yes, everything was contoured to fit the around the firewall shape shown (See Half Section A on the plans). I believe the firewall was glued to the flat fuselage sides first. Then the 3/4 square was shaped as described above and glued to the fuse sides and the firewall. Finally, the top block and bottom sheet were shaped and glued to the fuselage and firewall. You can put square or triangular notches in the firewall, but make sure you have plywood firewall wherever a motor mount bolt goes.

- I think I cut away the lower cross member of F4 to make room for the flap linkage.

-The flaps are a constant chord, but the wing is highly tapered. This makes the inboard end of each flap a smaller percentage of the local wing chord and the outboard end of each flap a larger percentage of the local chord. The result is the outboard end of the flap is thicker than the inboard end. The plans are correct - the deepest rib goes outboard.

- Our aileron well covers were Trim Monokote. The servos were mounted to a plywood floor in the well.

- The first Brushfire had a flying stab using a Giessendanner (sp?) mechanism. The nylon control arm that came with it didn't fit inside the narrow fuselage at that location. So we drilled a hole for a threaded rod control arm in the square aluminum bar that was the spar for the two stab halves. It worked great until the stab came off in flight and totaled the airplane. The aluminum bar broke right at the small hole we drilled. You're never so stupid as when you're being smart! I haven't been following the hobby as of the last 20 years and have no idea what kind of flying stab mechanisms are available these days. Can someone else help out here?

- Yes, we ran 11 or 11 1/2 inch props. The Brushfire was very solid on its gear. You should have no trouble lengthening it some as long as the wire diameter isn't too flimsy..

- Balsa Brushfires ranged from 8 1/4 to over 11 pounds. It all depended on how much hollowing you did, whether the wing was built up or foam, and if it was foam, whether or not you you included the lightening holes in the cores. Fiberglass versions with cut out foam wing cores could come in at less than 9 pounds. The span was 65 inches.

Good luck with your project. That engine and the size you've settled on should be a show stopper.

Ken

Ken,

your reply and answers to my many questions are invaluable. Many thanks for taking the time to go back 31 years in cadid detail!

Ithink Ican see a little clearer now on how to go about things on the reduced scale version.

I'll be sure to inform you of the results of my project when the time comes. Hopefully, I'll manage to get a build thread in.

Best regards, David.

The Relic is ready to fly. I'll let everyone know how it went sometime within the next week.

Ken

Beautifully done Ken!

Happy flights with your grand kids!

David.

The first two flights of the Relic happened Thursday evening. It flies very well. Not quite docile, but still very well behaved. It will putter around holding altitude at 1/3 throttle. A little more juice opens up mild aerobatics like loops, wing overs, etc. I suspect it will climb like a free flight on full power, but I didn't try due to a low ceiling. It does level itself if you release the stick, so it should make a good trainer as hoped.

A storm blew in during the second flight and it got quite windy and gusty. I had to quickly retrieve long dormant flying skills to get it down safely, but it helped me out by being crisply responsive to control inputs. It came home in one piece and unscathed.

Thanks for your interest. It was a fun build, and the flying yesterday evening, although a bit more than I bargained for on the first time out of the chute after 15 years or so, was a joy.

Ken

Here's the picture I promised four months ago of a new old guy design, with both the old guy and the new design. And it did fly before the Fourth of July.

Congratulations Ken! I think the best threads on these forums are ones seeing projects make it from beginning to end. Which is something I really need to do.

David

Is this the beast Ken?

Ray

The mind is a wonderful thing to lose. I don't remember that ad, but that's definitely the "Big Zlin."

Ken

Bump, just as a point of contact:

Triggered by a [link=http://www.rcuniverse.com/forum/m_9961187/tm.htm]thread about trimming[/link] in the Aerodynamics forum, I revisited my Brushfire simulator models. Recently, someone had posted a high-resolution plan where all specifications are readable, especially rudder throws. Apart from trying Triangulation Trimming (to no avail for this model), I tried the setup and trim exactly as recommended in the plan and in the build article.

What I noticed only now is the flap setup. It's not at all mentioned in the build articles. The plan shows a flap mixer (a piece of hardware in the late 1970s) in the fuselage. The flaps are beveled for up and down deflection and recommended throw is ±1/2" at T.E. (± meaning up and down) what is only 11.5 degrees. So while I had thought the flaps are intended to give a stable trim and moderate pitch attitude for landing, they really seem to be intended as snap-flaps only.

I'm surprised not by the fact that snap-flaps have been used even in the late 1970s, but by keeping that secret in the articles describing the Brushfire. Was it common to use snap-flaps but kind of a business secret for competition pilots? Or was it just natural for someone interested in a competition model like Brushfire? Seems I'm a bit slow on that, but after all Brushfire had several features not yet common back then.

Maybe an expert here can explain this conundrum or even Ken Bonnema could be so kind again and fill us in on that.

Happy New Year to all!

P.S.: For those owning the Reflex flight simulator, look [link=http://time.fh-augsburg.de/~erd/Modellflug/textDownloads.shtml#Brushfire]here[/link] to download the model.

Nice post UStik.

So how does that Brushfire fly? It almost is worth getting a hold of that simulator just to fly it! [8D]

David.

Yes David, might be well worth it since Brushfire flies so well (as far as I can tell with my limited pattern skills). It's a very "centered" design avoiding most couplings in the first place. It's big and if built light can be flown slowly and close-by (sort of turnaround style), what Dick Hanson attributed only to his Hippo Tipo, the EU-1A, and the Brushfire in the other thread. And that's what attracted me.

It's said that swept-wing airplanes do rolling maneuvers especially well, and that is true for Brushfire. It's said that they don't track well in looping maneuvers and I find that's as well true for Brushfire, at least a bit. But the snap-flaps seem to make up for just that, so I suspect the flaps were a (another) clever trick by Ken Bonnema. I'd just like to be sure.

By the way, the simulator is good enough to render the relevant characteristics. I take it the other way around: I don't need to build several models in reality to try them out since I can do it virtually. Even if I sometimes doubt if it's less work to build a model virtually...

Sorry this isn't very timely.

The flaps were maneuver flaps and moved down with up elevator and up with down elevator. They were intended to make square corners sharper. They worked, but the second Brushfire built without them squared corners almost as well. Since they added weight, we dropped them.

They were never for snap rolls. Snaps were enhanced by using a thinner percentage airfoil at the wing tips and by sanding a much sharper leading edge on the outboard third of the wing.

Congrats on your rendering of the original paint scheme. Very nice!

Ken Bonnema

Seems it was simpler than I thought and the second model built was the better version because it was simpler with the conventional elevator and without the maneuver flaps. You must have done tailskid landings, though, since there are only 5 degrees pitch up left for flare.

Thanks so much for your help!

The Brushfire didn't need much flare. With that big wing, you just slowed it down and flew it onto the ground. But we did make the tail skid deep enough so it would hit the ground before the aft tip of the rudder, just in case.

KB