Author Topic: Help designing/building a foam-wing F2D airframe (Read 12750 times)

Bill Ervin · « **on:** August 12, 2016, 12:44:39 PM »

About 20 years ago a couple guys in our club designed a neat little FP15 plane called the Maxibat. It was very popular among the local flyers. About 50 kits were made and it seemed we each had two or three. We used them for basic training also by installing the prop backwards and slowing the motor down. Special tooling was created for cutting wings, molding bellcranks etc.. The project was a huge success.

All that's left are a set of plans and (hopefully) here is an image of them.

A couple of us in the club want to try this again but tweak the design so that it could (also)legally fly in F2D. It won't neccessarily have to be competitive just compliant to the rules. Guess I should mention that I'm not a combat flyer so some questions might seem silly or obvious.

First question that comes to mind is should the wingspan be stretched from the original 30" to something over 40"? At work right now so can't take a measurment til I get home. Hope the image gets posted...

Thanks for any help, sincerely, Bill

Bill Ervin · « **Reply #1 on:** August 12, 2016, 12:55:40 PM »

I have an old Cyclon with mounts to help when redesigning the nose.

Bill Ervin · « **Reply #2 on:** August 12, 2016, 01:39:50 PM »

Among the glass-filled, molded nylon parts was a stab mount that simply plugged into the end of the fiberglass boom. The back edge already had holes molded in, all the builder had to do was sew the stabilizer on and he was done. Those super nice molded parts are no longer available, how could the same thing be done with low-tech materials? 1/8" ply with a slot in the boom?

kenneth cook · « **Reply #3 on:** August 12, 2016, 03:00:14 PM »

Bill, you could also fill the end of the boom with a dowel, drill through it about 5/16" from the end and install a piece of brass tubing about 1 1/2" long. Wrap the tube and boom with carbon two and coat with thick CA. On the elevator, you glue two pieces of brass tubing onto the leading edge of the elevator spaced slightly wider than the boom tube and use a piece of wire to slide through the tubes to hold the elevator on. I like to use a piece of silicon tubing on the end of my hinge pin to prevent it from sliding out. In the event of impact, slide out old pin and plug new elevator on.

Dane Martin · « **Reply #4 on:** August 12, 2016, 03:04:43 PM »

Quote from: kenneth cook on August 12, 2016, 03:00:14 PM

Bill, you could also fill the end of the boom with a dowel, drill through it about 5/16" from the end and install a piece of brass tubing about 1 1/2" long. Wrap the tube and boom with carbon two and coat with thick CA. On the elevator, you glue two pieces of brass tubing onto the leading edge of the elevator spaced slightly wider than the boom tube and use a piece of wire to slide through the tubes to hold the elevator on. I like to use a piece of silicon tubing on the end of my hinge pin to prevent it from sliding out. In the event of impact, slide out old pin and plug new elevator on.

Cool! Thanks for the info Ken
Bill, I think I have a plane with a similar elevator as Ken is describing. I'll bring it out also. Joey had two Viko f2d planes and a Mejzlik (sp?)
Can we use that for some measurements?

Bill Ervin · « **Reply #5 on:** August 12, 2016, 03:21:40 PM »

Thanks Ken, got it, like a section of piano hinge. L bend on the inboard end of wire and tubing for the retainer. Great!

Joey Mathison 9806 · « **Reply #6 on:** August 12, 2016, 03:51:35 PM »

seek and destroy

phil c · « **Reply #7 on:** August 12, 2016, 06:21:32 PM »

Bill- almost all the current F2D planes are 45.5 in. span in order to fit into a shipping box. Many/most countries limit boxes to 46in. Otherwise the construction has been optimized to death so all the planes are virtually one design and between ~410-430 sq.in. The foam wing will build heavier so if you're not planning to ship finished planes to Europe add a little extra span and narrow the chord to better carry the weight but keep the wing area in the same range to minimize any speed loss. Also, if you go for a typical F2D mount with aluminum beams(it makes the engine run much better), extend the boom nearly to the front of the motor block so crashes won't break the block. Mount the engine back close to the leading edge and shorten the boom to balance.

Bill Ervin · « **Reply #8 on:** August 12, 2016, 07:13:17 PM »

Okay thanks Phil, got home from work and measured the root and tip chords and we're at 10.5" and 8.5". When the span is extended to 45" the area is right in the ballpark. The sections seem a little thick at 1 3/4" but I'll just use them and worry about optimizing later. Anxious to make a couple formica templates this evening and cut some wings over the weekend.

Every time your name comes up Phil my first thought is about the times we flew peanut scale together with the MMAC in the Brooklyn Center Gym back in the mid-seventies. Great memories.

Howard Rush · « **Reply #9 on:** August 12, 2016, 08:10:42 PM »

I'd do what Phil says, lighten the hinge by getting the brass out (I copied Phil's tail hinging method in 1978 and used it for a couple decades thereafter), and keep the airfoils. I'd sand off the little kink in the airfoil aft of the spar, though.

Bill Ervin · « **Reply #10 on:** August 13, 2016, 08:04:44 AM »

I believe that kink in the airfoil serves as an invigorator...

Fredvon4 · « **Reply #11 on:** August 13, 2016, 11:21:44 AM »

Bill

I get it...cutting the foam is or can be relatively easy

BUT If I wanted to get a fleet of many for the club again I would seriously consider asking Phil Cartier for the best closest wing he already has cut.... and how ever much SLC needed....
Production cutting the nose blocks, spars, bell crank support, and tails is too easy once you have the CG formula

I personally think the micro grams difference between sewn and very small brass tube/music wire stab hinge is insignificant for a training, fun fly, club set of birds

Bill Ervin · « **Reply #12 on:** August 13, 2016, 02:11:28 PM »

Thanks Fred, that's exactly what intelligent men who value their time would do. I, on the other hand, hacked out a pair of Formica templates last night.

Fredvon4 · « **Reply #13 on:** August 14, 2016, 09:35:49 AM »

Hummm...Sloan canyon
Las Vegas
Henderson
Combat playing
Club involved
Maybe some Big Block fast planes considered???
Certainly sounds like .15 F2D is planned
I see Fast 1/2a happening

Perhaps a excuse to fly to Las Vegas in the near future???

Hopeful Phreddy

Phil Krankowski · « **Reply #14 on:** August 14, 2016, 10:31:14 AM »

Quote from: Bill Ervin on August 13, 2016, 02:11:28 PM

Thanks Fred, that's exactly what intelligent men who value their time would do. I, on the other hand, hacked out a pair of Formica templates last night.

Doing something because you WANT to is not unintelligent. At the least it is a learning experience.

Those are nice looking templates. Some care can produce superior quality templates.

I do notice the spar pockets are missing. Those are a bear to put in if they are not cut with the core.

Phil

Fredvon4 · « **Reply #15 on:** August 14, 2016, 10:54:44 AM »

Hey Phil...I have no idea how Bill plans to do it

My first efforts at foam cutting WITH spar slots was a pain
My next templates omitted them and I got pretty good then with cutting the core without a bunch of grief

I managed to build a jig for each blank to hold the position for the spar slot on my router table

Before I fussed with routing them in: my much preferred method now
I positioned a guide and used a shaped 150 grit home made sanding bar...tedious and I did not like my method of depth control... but a doable method

For many of the wings I did wide by shallow horizontal spars and then some were narrow by deeper vertical spars and some where one method top and other method bottom...no evidence any method was better or worse...just me experimenting and learning

I settled with the wider 1/4" shallow 1/8th" spars with carbon TOW under and thinned TightBond II as my preferred easy to repeat method

Paul Smith · « **Reply #16 on:** August 14, 2016, 01:07:40 PM »

I prefer a template with some lead-in and lead-out so you don't have to hit the LE & TE exactly. Also, spar slots on the opposite side so the spar slots don't interfere with a smooth airfoil.

The center point cutter gets the taper right with no finesse needed. The wire is held tight with an old EX Just handle.

Bill Ervin · « **Reply #17 on:** August 14, 2016, 05:26:08 PM »

Thanks fellas, I read an article about that center point cutter, great idea, it looks like you have it working well Paul.

Thought there should be a little lead-in too and filed a little ramp at the front. At the rear there are a couple notches on the templates for the wire to fall into at the end of the cut. I'll be using a home-made drop-arm cutter.

Bill Ervin · « **Reply #18 on:** August 15, 2016, 09:52:31 AM »

After one failed attempt a usable wing was finally had. White Fang gave her stamp of approval, it passed QC.

Fredvon4 · « **Reply #19 on:** August 15, 2016, 10:47:59 AM »

Bill

you may know this but....

To make the wings nearly bullet proof I use Kevlar cord (or Carbon TOW) around the wing tip back to center of TE and wrapped around the arrow shaft set with thick CA....

I start the cord just in front of the Tip on the LE, set into a shallow slit in the wing tip to "bury" the cord, then along the outside of the TE to the center...In a direct nose plant this lash up keeps the foam wing from torquing forward and breaking

I also use .75 fiber glass cloth on each wing tip as well as engine mount area... generally glued on with thinned White glue...makes the tip and glue area of the engine mount tougher

I also fix flattened carbon TOW Under each spar top and bottom....layer of tinned White glue...TOW set in the glue... fresh glue, set spar, light clamp, when dry, razor plane spar to taper at wing tip

1 inch and 2 inch wide strapping tape is also used...the 1 " is folded over equally above and below TE perimeter

The 2" a strip on top and bottom of wing near 1/2 chord out about 10" either side of center, ironed down and then covered with SLC on the whole wing

These planes will take a direct full speed nose plant and survive with the only issue being digging all the dirt out of the broken prop engine

each of these ....carbon TOW, Kevlar thread, and strapping tape have very good tension strength vs weight

virtually impossible to fold or break a wing this way

Bill Ervin · « **Reply #20 on:** August 15, 2016, 10:49:22 AM »

Foam work done for now, enough for a couple prototypes. The plans call for a 1/8"x3/8" spruce spar on the original 30" span Maxibat, I've increased the span to 45.75", will that size spar still be okay?

Bill Ervin · « **Reply #21 on:** August 15, 2016, 10:53:32 AM »

Okay thanks Fred, I'll incorporate those ideas. Knew about the TE lashing but not the other areas. Good to know!

Bill Ervin · « **Reply #22 on:** August 16, 2016, 10:01:55 AM »

Here's one of the original center section/boom assemblies we used 20 years ago. It's set up for an OS FP15 and the engine bearers are the typical 1/2"x3/8" maple rails that have been standard for almost every sport C/L model since the 1950's. I will be using a modern F2d set up seen in reply #1. Would 3/8" sq. maple rails separated by some kind of hardwood be the norm? Maybe even slap some 1/16" ply on both sides?

Fredvon4 · « **Reply #23 on:** August 16, 2016, 11:38:02 AM »

Bill

I have cut my nose blocks from 1/2" or 3/4" thick bass wood about 2.5"~3.25" inches long and as tall as the rib profile after the motor mount area.... I prefer the 1/2 wide stock but trying to slice the "on hand" 3/4" thinner was a problem...obviously the 1/2" stuff is slightly lighter...a good thing

the very front top to bottom width is perfectly parallel and square Keeping same as spacing for the motor mounts

One arrow shaft diameter hole centered from aft to front, just shy of where motor mount bolt hole(s) will be

One side to side arrow shaft short spar hole...also aft of where motor mount bolts will be

The horizontal spar is in the center of the foam wing about 4"~ 6 " either side of center...spritz of water and gorilla glued

The total length, nose to rear, is such that the Bell crank bolt is in the motor mount.... but far enough aft for BC to swing free and this bolt is a secondary hard point for the arrow shaft to nose block gluing

Hope this makes sense...my camera will not upload to computer for some reason these days

Bill Ervin · « **Reply #24 on:** August 16, 2016, 11:58:33 AM »

Thank again Fred, it sounds like I should make the center rib/ mtr mount from just a one-piece block and not mess maple rails. Size it appropriately and bury the boom into the back end.

Bill Ervin · « **Reply #25 on:** August 21, 2016, 07:43:34 PM »

For good or bad a 3/4" clear pine block was chosen with the grain running vertically.

Bill Ervin · « **Reply #26 on:** August 21, 2016, 08:09:19 PM »

Two images seems to be my limit.

Bill Ervin · « **Reply #27 on:** August 21, 2016, 08:32:55 PM »

The forward part of the block needs to accomodate the engine and aluminum mounts, the rear needs to have a hardpoint for mounting the BC and have a socket for the tailboom. I slapped some 1/32" ply to the sides.

Bill Ervin · « **Reply #28 on:** August 21, 2016, 08:39:08 PM »

This seems like how the center rib needs to be configured.

Bill Ervin · « **Reply #29 on:** August 21, 2016, 08:45:55 PM »

Pine was chosen for weight and strength considerations. We'll find out soon enough if it works.

Bill Ervin · « **Reply #30 on:** August 21, 2016, 08:58:44 PM »

First airframe glued up with a slurry of epoxy and cotton flox. The groove for the spar will be sanded in. Decided on a 1/8" carbon tube for the stab mount, these have since been lashed with kevlar.

Dane Martin · « **Reply #31 on:** August 21, 2016, 09:17:23 PM »

Quote from: Bill Ervin on August 21, 2016, 08:45:55 PM

Pine was chosen for weight and strength considerations. We'll find out soon enough if it works.

It might need to withstand a figure 9 or 2.... lol

Bill Ervin · « **Reply #32 on:** August 22, 2016, 12:30:08 AM »

A figure 9 or a figure 2? I can do a figure 9, you'll have to show me a figure 2.

Phil Krankowski · « **Reply #33 on:** August 22, 2016, 06:25:52 AM »

Quote from: Bill Ervin on August 22, 2016, 12:30:08 AM

A figure 9 or a figure 2? I can do a figure 9, you'll have to show me a figure 2.

I think that is similar to an inverted pancake.

Phil

Dane Martin · « **Reply #34 on:** August 22, 2016, 08:08:20 AM »

I've been practicing,
I can show you all kinds of ways to crash! Lol

Fredvon4 · « **Reply #35 on:** August 22, 2016, 09:47:07 AM »

I personally like the craftsmanship of the pine nose block and think I would harden the engine mount and BC through holes with CA or Brass tube to prevent wallering out from figure 2 and 9 events

There is an argument for a horizontal short arrow shaft spar through the block into wing AND a thin ply piece the height of the nose block in front or at rear... set in a slot in the foam

Tedious to describe and wish my stupid camera would upload to this pc ..... I have tried EVERYTHING

Also ...once nose is set it is a good idea to use .75 FG cloth and reinforce the nose ...I don't fuss with epoxy and use slightly thinned white wood glue (Elmer's) or Tight Bond II (ugly yellow but combat so who cares)

Bill Ervin · « **Reply #36 on:** August 22, 2016, 11:36:36 PM »

Two airframes gettin there, need to do the fiddly bits now. Thanks for all the great ideas Fred.

Phil Krankowski · « **Reply #37 on:** August 23, 2016, 06:45:16 AM »

Can you tell me about those metal engine bearers please? Where they came from, what brand?

Thank you
Phil

Dane Martin · « **Reply #38 on:** August 23, 2016, 07:25:32 AM »

Quote from: Phil Krankowski on August 23, 2016, 06:45:16 AM

Can you tell me about those metal engine bearers please? Where they came from, what brand?

Thank you
Phil

Bill probably bought his many moons ago, but there's a couple places they can be purchased from.

http://aerohobby.ca/store/index.php?main_page=index&cPath=9&sort=20a&page=2

Bill Ervin · « **Reply #39 on:** August 25, 2016, 05:47:42 AM »

TE reinforcement is 80 lb. Dacron braid from Bass Pro Shop. Soaked the braid in epoxy, stuck it down. Wear gloves.

Paul Smith · « **Reply #40 on:** August 25, 2016, 06:38:44 AM »

Quote from: Bill Ervin on August 21, 2016, 08:09:19 PM

Two images seems to be my limit.

The limit is 1000 K, not a number of pitchers. You seem to be close to the limit every time.

Modern engines are A LOT more power and MUCH higher RPM than in 1950. Some of the old design norms have gone by the wayside.,

Paul Smith · « **Reply #41 on:** August 25, 2016, 06:42:10 AM »

If you have the technology, tapered spars are best.

More wood in the center where you need it.
Less mass outboard. Outboard mass puts stress on the center.

Bill Ervin · « **Reply #42 on:** August 25, 2016, 07:20:51 AM »

Thanks Paul, I'll install tapered spars on the next batch.

Bill Ervin · « **Reply #43 on:** August 26, 2016, 09:42:39 PM »

happy with the results. I suspect they'll be heavy but they're straight and seem sturdy enough. Left plenty of room for improvement! Still need to figure out a method for a bladder compartment, cover wings and install controls.

Dane Martin · « **Reply #44 on:** August 27, 2016, 11:31:03 AM »

Very sharp looking there Bill. It's very impressive what you did considering what you started with

Bill Ervin · « **Reply #45 on:** August 27, 2016, 11:50:28 AM »

Thanks Dane, hope our little scheme works! Already found better methods for producing just about every part on the plane.

Rich Perry · « **Reply #46 on:** August 27, 2016, 12:58:38 PM »

I have templates for bladder compartments so I cut them out with a mini hot wire bow. Just simple ply sheets top and bottom of wing held in place with t-pins that have been CA glued permanently to the templates.

Also, my favorite method for fuel proofing the compartment is to use white silicone caulk. Pure 100% silicone. It is flexible and is a nice soft area for your bladder, helping them to last.

I have also found round rubber grommets are great for creating a good exit in your covering, keeping it from tearing.

I am in the same boat as you, in that I need to design a good .15 powered "fast" design, as I want to start flying the .15 fast or F2D fast class. I need to get an engine, and finish up with this current flying season. But I lane to have them for the Nationals next year.

I understand the motivation to wrap Kevlar on the leading edge, but when flying a "kill" event, the bare foam L.E. is a huge advantage, that the Ukrainian FAI models do not share.

Your work looks great! Good job.

Rich Perry · « **Reply #47 on:** August 27, 2016, 01:09:54 PM »

Some pics

Rich Perry · « **Reply #48 on:** August 27, 2016, 01:10:56 PM »

More....

Fredvon4 · « **Reply #49 on:** August 27, 2016, 01:28:11 PM »

Always a good idea to fix two or three bladders and train them...then fill and measure height and width averages with typical expected fuel load

Make the in wing bladder cut out slightly larger so no false pressure

probably camera perspective but Bill's look a tad marrow to me

I use squares of strapping tape for bladder insert and bottom drain---- two pieces in both places one turend 90 degrees and under the final covering...then I burn a bladder insert hole in the top close to center line with dremel cone shaped stone and slightly smaller fuel drain hole in bottom.... that one outboad towards wing tip