By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by CML

Fokker EIII Scratch build

For 2018 Indoor R/C Scale Nationals (Hopefully)

All Topics | Latest Posts

Search for:  in Thread Title in  

Martyn K15/12/2017 13:27:21
avatar
4612 forum posts
3227 photos

I have just started building my chosen model for the 2018 Indoor R/C Scale Nationals. I actually started the design work a few weeks ago but delayed the start while I was trying to get my 1/4 scale Foka 4 glider to a state of semi completion so I can actually move in the shed without breaking things.

The Indoor Scale Nats are next March so I don't have a great deal of time.

The plan looks like this. As usual it's laid out for my benefit and not really designed to be replicated. I have a few ideas and I don't know if they will work so detailed info is a little sketchy to say the least.

The full sized had all moving rudder and tailplane (both rather small but a longish moment arm). For roll control it used wing warping. I am going to cheat and alter each individual wing panel incidence to give me roll control. That will be fun, if nothing else, keeping the movement low enough (I wouldn't have thought more than 2deg up/down total would be required - in fact that is probably too much).

fokker plan.jpg

 

Details - Wing Span 835mm, Chord 157mm, AUW Target 100g

Last night I built one fuselage half

fus1.jpg

You can see the wing pivot plate and also closely a very small slot in the rear plate for the twist actuation.

This is going to be an interesting one to get working properly.

Hey ho...

 

more to come...

Martyn

Edited By Martyn K on 15/12/2017 13:27:45

Capt Kremen15/12/2017 14:21:37
avatar
213 forum posts
53 photos

Very nice Martyn.

Dare I say, don't forget the inset 'Compass' in the Starboard Wing! (Often missing from models).

Martyn K15/12/2017 14:23:37
avatar
4612 forum posts
3227 photos

Thanks

I didn't know it existed - more research required.

McG 696915/12/2017 14:39:43
avatar
2178 forum posts
912 photos

... already 'Subscribed', Martyn. yes

Cheers

Chris

Martyn K18/12/2017 10:55:25
avatar
4612 forum posts
3227 photos

A quiet weekend so a bit of progress to report.

The fuselage second half was completed and the two halved joined together.

fus2.jpg

and

fus3.jpg

This shot shows the wing swivel plates with ali tube to take the carbon tube pivot rods from the wing. The rear plate (both from 2.5mm lite ply) has the slot for the actuating arm and the pivot for the bell cranks. Weight of this so far is just less that 10g.

Who can spot the mistake?

While the glue was drying, I had a think about the spar. One thing I am a bit paranoid about this will be keeping the wing warp free and also free from bowing. The main spar is quite close to the LE leaving a huge area behind the spar effectively unsupported. Its quite a bit floaty wing.

To add some stiffness, I made up a composite spar - 1/8 sq hard balsa capped with 0.006" unidirection carbon sheet top and bottom.

spar1.jpg

This stuff is incredibly thin but strips quite easily. Use cyano to glue to the balsa. The spars weighed 1.2g each half

Wing rib cutting involved cutting a central hole for the spar. Quite simple, I cut the hole in the template and then made a little tube hole cutter out of an offcut of ali tube which was quite effective

So one wing wing went together quite well. No ribs were broken in the threading process

wing2.jpg

You can clearly see the composite carbon spar here

wing1.jpg

The TE is quite hard balsa as well and laid on extended tabs to support it at the correct angle.

Quite pleased with it so far.

I also cut the templates for the wing and tailplane tips and laminated them (3 x 1/32 tips and 4 x 1/32 fin). The rudder also has a strip of 0.006" carbon to help keep it stiff and hopefully warp free

templates1.jpg

and

templates2.jpg

More to come

Martyn

Bob Cotsford18/12/2017 11:27:55
avatar
7327 forum posts
419 photos

Nice work Martyn, my fingers shake at the thought of such delicate work. Have you thought about knocking up a quick Depron job to test out the wing twist mechanism and check just how much movement is needed?

Martyn K18/12/2017 11:50:31
avatar
4612 forum posts
3227 photos

Thanks Bob

Good idea but to be honest I really haven't got the time to do that. I have been thinking on how to get the servo rotary action down from about +/- 50 degrees to about +/- 2 degrees. A 25 x rotary reduction without slop..

I will get about 5:1 reduction in the wing twist actuation bell cranks but I think a second reduction bell crank will be required buried in the fus somewhere.

I'll get the calculator out later and draw some ideas up.

I am actually more worried about getting the all flying tailplane at the correct angle. The original has about +5 degrees positive on the wings so I need to fly the tailplane at about +3 and also get the travel reduction down for that as well. This will be challenging as the horns for the tailplane will be quite small unless I can find a way of hiding them.

The other challenge I have concerns the all flying fin. The side elevation of the fuselage comes to a point at the rear. There is nowhere to glue a vertical pivot tube. There is plenty of space for the elevator pivot though. The original had two tubes welded at 90 degrees for the fin and tailplane rotary bearing tubes. I don't have that luxury, but I do have a cunning plane involving the tailskid

Gordon Whitehead 121/12/2017 10:30:10
avatar
239 forum posts
120 photos

Hi Martyn

Back in about 1952 a chap published an idea in "Model Aircraft" for a way to get a free flight model to do aerobatics. He used an airdraulic timer pulling a shaped cam on which arms from the rudder and elevator rode. As the shaft of the timer pulled in as normal, it pulled the cam, the controls moved appropriately, and the plane allegedly did a loop, or barrel roll according to the shaping of the cam.

Perhaps you could use a similar system to work your EIII's rudder and elevator from separate servos. It could even work for your wing drive.

Here's a sketch:

fok eiii tail drive.jpg

It might be worth a bench-top experiment surprise

Gordon

Martyn K21/12/2017 10:43:43
avatar
4612 forum posts
3227 photos

Thanks Gordon

I can see how that would work and it would also get round the travel reduction problems - especially for the wing 'warp'. The only surface that I feel comfortable with (so far) is the rudder movement.. Yes - definitely worth thinking about

Martyn K02/01/2018 09:44:50
avatar
4612 forum posts
3227 photos

A bot of progress over the Christmas break..

Tailplane and rudder built. Nothing too exciting here. The spars are 2mm carbon tube. A bit heavy TBH.

tail1.jpg

You can see the three bearing tubes here plus the cross tube to support the all moving rudder. Assembling this will be fun..

and

tail2.jpg

With the fin/rudder and wing wing panels more or less completed, it was time for a dry fit

ass1.jpg

and

ass2.jpg

I started work on the wing warp mechanism and came up with this..

The horns are 1/32 ply pivoted on M2 bolts. The rear actuating rods are 2mm carbon tube.
A bit of calculation showed that I could get the reduction with a single horn. It seems quite slop free so hopefully it will be OK.
I have ordered micro servos and a tiny outrunner motor and ESC from Micron. I'll need those soon..
With that out of the way I can start finishing the fuselage
Added the upper deck and side cheeks
fus5.jpg
Balsa is 1/32 light sanded down to about 1/48 I would guess.
Currently working on the undercarriage using piano wire that refuses to be soldered to..
More to come
Martyn
Martyn K09/01/2018 09:24:34
avatar
4612 forum posts
3227 photos

A bit more progress. The micro radio parts have arrived from Micron.

The motor fitted onto a liteply boss then soft balsa standoff.

motor1.jpg

Apparently it will drive a 7x3 prop. Its a 2000kv motor running on 1s or 2s LiPos. ....looks a bit rough

Also working on the wing warp linkage. The servos are 1.4g each

Danny has suggested that I replace the pushrods with carbon. I will be dong that.
Next job is to make one of these.
gnome_monosoupape_9n_p1040425.jpg
That will be a challenge. I was originally thinking of making it out of paper with perhaps a thin balsa crankcase
...tricky one..
More to come
Martyn
Colin Leighfield09/01/2018 09:56:58
avatar
5438 forum posts
2229 photos

I was at the Old Warden engineering weekend last week and found out that that engine has 1,560 parts, so don’t leave any out. Good luck with that tiny tailplane, It looks as if you’ll need the c of g well forward if it’s not going to be twitchy.

Colin Leighfield09/01/2018 09:57:38
avatar
5438 forum posts
2229 photos

I was at the Old Warden engineering weekend last week and found out that that engine has 1,560 parts, so don’t leave any out. Good luck with that tiny tailplane, It looks as if you’ll need the c of g well forward if it’s not going to be twitchy.

Martyn K09/01/2018 10:07:07
avatar
4612 forum posts
3227 photos

Thanks Colin

Getting the CG forward - I think it will need to be about 15-20% will be a challenge. It has a long moment arm and a shortish nose... Ho hum.. Its quite a big aeroplane so I shouldn't have problems with wing loading although I am starting to worry about the weight. I could make the engine out of lead though..

Nick Cripps09/01/2018 21:19:07
38 forum posts
16 photos

Martyn,

Why don't you keep the tailplane fixed and use wing incidence to control pitch as well as roll?

Martyn K10/01/2018 14:19:49
avatar
4612 forum posts
3227 photos

Now... Thats an interesting idea. I would need two aileron servos but no elevator servo.

It would be a simple elevon mix wouldn't it..?

Martyn K18/01/2018 13:26:18
avatar
4612 forum posts
3227 photos

Working on the engine

This is what I am aiming for..

engine9.jpg

Starting with some balsa dowel wrapped with sea ranger fishing line.

engine1.jpg

Sprayed Grey and test fitted -its a push fit over the motor stand off box

engine2.jpg

The pushrods are stainless wire, crankcase bolts are pin heads

engine3.jpg

Looks a bit heavy on paint so cellulose thinners to remove the excess

engine5.jpg

First attempt at weathering. Engine sprayed silver then a dusting of primer then satin black rubbed into the cylinder and crankcase with my fingers. Lower rockers added - which admittedly are a bit crude.

engine6.jpg

Front of cowl added - 2 laminations of 3/16 balsa cross grained then hollowed out and glues to me engine - inside sprayed black first

engine7.jpg

The side parts to the cowl are 1/32 balsa glued to a dummy former near the firewall and butt jointed to the cowl front.. Rare use of cyano on this model

engine8.jpg

Another shot. Fairly pleased with it so far although the weathering looks a bit patchy

Need to make the lower hatches now then I can start covering it..

More to come

Martyn

Martyn K01/02/2018 11:35:51
avatar
4612 forum posts
3227 photos

An update. Sorry its all a bit slow..

 

wheels.jpg

Wheels done. Spin and sand blanks on the pillar drill to get the basic shape and the shallow cones from paper. The original used solid tyres and the cones are much shallower than those used on British WW1 aircraft.

 

The model is at the stage where I need to start adding some flying surfaces.

The rear rudder/tailplane hinge assembly looks like this.

hinges.jpg

Note the tailplane has been covered which subsequently warped badly when the strip ribs buckled. Hey ho.. So that was stripped and the faulty ribs replaced with solid ribs from very soft 2.5mm balsa then recovered. All while still attached to the fuselage

The lower end of the carbon fin post will be located - like the full size - in a pivot point on the tailskid quadpod but that will come after the model has been covered and painted.

linkages1.jpg

Fin covered - in situ and the rear linkages done. I couldn't cover the tailplane until after the tailplane had been mounted as the rudder pivot sits within the closed fin loop.

Carbon rods terminating in thin piano wire links into 1/32 ply horns. Nothing is adjustable..

linkages2.jpg

Linkages at the front. All seems to work remarkably well.

With all that done, I added the hooks for the wing rigging wires. Simple piano wire epoxied to the ribs

rigging hooks.jpg

Covered the wings. Esaki Jap tissue using thinned down PVA as adhesive. This was actually take 2. I used a Pritt stick first time and the tissue pulled aways from the undersurface..

wing3.jpg

Fuselage is now covered with Silver Esaki representing the metalwork area.

covered1.jpg

This has subsequently been watershrunk and 1 coat thinned dope applied

Time to see what it looks like fully dressed

dressed1.jpg

and

dressed2.jpg

and

dressed3.jpg

Maiden at the next Shawbury indoor in just over 2 weeks time

It's ready for war paint I think..

More to come

 

Martyn

Edited By Martyn K on 01/02/2018 11:38:14

McG 696901/02/2018 13:11:26
avatar
2178 forum posts
912 photos

Still following in admiration, Martyn.

... and still amazed by your 'wing warping' solution. yes

Now eager to see some "war paint" as well.

Cheers

Chris

Martyn K01/02/2018 13:43:18
avatar
4612 forum posts
3227 photos

Thanks Chris

Hope you are now fully recovered.

I can see the end now.. The photos don't seem to show just how big this beast actually is. Its just slightly less than 1/12 scale but the prototype was quite large being a monoplane

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E! 

Latest Forum Posts
Support Our Partners
Gliders Distribution
CML
Expo Tools 14 July
Wings & Wheels 2018
Airtek Hobbies
Slec
electricwingman 2017
Overlander
Motion RC
Advertise With Us
Sarik
Latest "For Sale" Ads
What is the main brand of transmitter you use? (2018)
Q: What is the main brand of transmitter you use?

 FrSky
 Futaba
 Graupner
 HiTec
 Jeti
 JR
 Multiplex
 Spektrum
 Other

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us