West Wings BAe Hawk EDF

[Tom Foreman]

Picked this kit up at Woodvale the other weekend, with the crap weather this weekend and all my models repaired and ready to go, I thought I'd open the box and find out how an inexperienced modeller would cope

According to the blurb you get;

Electric Ducted Fan Traditional Builders Kit

Scale: 1:11, Wingspan: 890mm, Length: 1010mm, Weight: 1200g

I'm planning on using a Wemotec Mini fan, Typhoon 2w-20 motor and a 60A ESC, probably a dualsky one as it comes with a 5A BEC. This combo should be good for 650W on a 4s1p LiPo or more on 5s1p A123. So if we come out near the target weight (as if) we should be looking at 250 W per lb!

Oh it needs a Bungee to launch as well, haven't tried that before so will be a new learning experience as well. On with the build!

When you open the lid you get a big pile of balsa, ply wood and some vac formed mouldings. A nice big rolled plan, some instructions, diagram sheets and some waterslide decals, RAF Valley ones.

You first have to trim the ducting by cutting off the waste and then sand down to the parting lines.

The instructions recommended varrious glues for gluing the ducting halves together, RC modellers glue, polystyrene cement or plastic magic. I toyed with the idea of cynao, but with visions of disaster (you only get one chance) I popped down to Wilko's in Lancaster to see what they had. I came home with a large tin of evostick contact adhesive and some kids paint brushes. As you can see from the picture the first go was a disaster. I followed the instructions of pegging the ducting and then running glue into the joint, but this just made a sticky mess.

The2nd duct, I looked at the contact adhesive instructions, they said to leave it to dry first, so I had to leave it for about 25 mins. True to their word, the duct stuck together pretty much instantly. Much happier

[Tom Foreman]

Next up came the tail nozzle, here are the two halves after cutting and sanding (takes forever using 180 grit wet & dry)

Getting good at this Evostick thang!

You then had to cut out some ply stiffeners from 1/64th ply and stick them to the inside of the ducting with the grain running vertically. Not sure why they need stiffening, perhaps to stop them collapsing under suction?

[Tom Foreman]

With all the ducting gluing happily, we can start on the fusealage proper, hope it gets easier now! The first bit is the nose cone framework. this is built seperately to the main fuse and stuck on to the fuse later in the build. All the CNC cut parts have to be identified and marked up with pencil. Some of my bits were labelled up wrong, either I got confused or the numbering sheet is a bit mixed up. Some of the bits needed a bit of fettling with the trusty scalpel but it went together eventually. I toyed with using alphatic resin, but in the end went with cynao. Using cynao means you can position the bits and then just let the thin stuff whick into the joint. I used the medium stuff to fill any gaps.

The second half of the frame work is built on top of the one you built from the plan, this seemed a bit of a farce, so will have to find a better way of doing it. I think Gordon Whitehead, who helped develop the model reversed the plan and made it translucent to make it easier. Don't want to spoil my plan, so might have to make a visit to the copiers.

Well I've had enough now and the dining table is wanted for dinner. Don't seem to have built much in 8 hours. Oh well I've got till xmas I suppose

Hopefully build some more later this week.

Cheers,

Tom

[Tom Foreman]

Oh I thought I'd add a photo of what it should end up looking like, in about 4 months time

[birdy]

Looks nice, if complicated! Luck to you!

[Alex Hasell]

will be watching keenly the same kit is on my wish list so will be joining you quite soon i hope good luck

Alex

[Tom Foreman]

Well have been away to Korea of all places on business, plus been building A123 battery packs. But have been enjoying some time off work, but with the crap weather thought I would do a bit more on the Hawk. Got to keep chipping away at her .

10 Nose skinning with vacform skins

11 Fuse framing LH side

12 Trial fit of nose to fuse

13 top & bottom keels pinned to plan, formers sorted out.JPG

[Tom Foreman]

Here is some more, lots of intricate parts to stick together and lots of twisting and bending of balsa to get it all to fit in the right place.

14 Nose glued together

15 Internal shot of nose

16 Formers, stringers, doubler and snake in place

17 Inlet skin on, planking to finish end of day 2

Today I have to attempt to plank the whole fuse in 1/16" balsa which will be quite tricky, especialy as I have to try and keep it all warp free. Lots of heavy weights are the order of the day and damping the balsa with water to get it to curve around the formers and stringers.

The next problem after that which I could do with some help and advice from you expert builders out there is that to build the RH fuse side, the instructions tell me to build it onto the already built LH fuse. But this is very difficult as it does not lie flat and there will be no building board to pin down to. This was the same way I built the RH nose framework, but it was very difficult and fiddly. The ony options I can think of is;

1. Build some sort of cradle to hold LH fuse level while I build the RH fuse onto it in the horizontal.
2. Reverse the plan, and build the RH side onto that and hope it all lines up with the LH side.
3. Build the RH side upright with the LH side, again needing some sort of support.

Any help would be welcome.

Cheers,

Tom

[Richard Sharman]

Tom,

I suggest option (2). You built a very nice LH side on the plan, so you should be able to build a nice RH side, and then they MUST go together?!

I'm building the WW Hunter, which seems to be very similar construction methodology. I've got to the fuselage stage, but I've got stuck, so no help there! I might finish it by Xmas ?

best wishes, Richard

[andy watson]

Assuming the LHS is straight, then you could make the RHS by using this as your template.

I assume you have a matching set of formers for the RHS as you had for the LHS.  By firmly clamping 2 pieces of scrap to one of the formers on the LHS you will naturally form a straight slot for the opposite former to slide into place.

It might be slow going, since you will have to allow the glue to set well before removing the struts.

The other possible help could be to add a single stringer to give each former something to grip when you put it in place.

[Tom Foreman]

Richard - looking good, you have got farther than me . Are you saying that you reversed the plan to build the RHS of the fuse of the Hunter?

Andy - will have a look at your method, if it isn't too difficult then that might be the way to go.

Cheers both of you for your help, however it is a flat calm outside today so I'll be flying today instead of building.

Found planking quite difficult yesterday and didn't get very far, have only managed the front part, and am concerned that I am inducing a small warp. Hopefully I will be able to correct it when it is joined together.

18 front planking on

Cheers,

Tom

[Richard Sharman]

Tom,

 I didn't reverse the plan -- West Wings did! The LH and RH sides are both given on the plan (in my photo look just to the right of the fuselage where there are 2 profiles given).  I built 2 shells, L and R, and put them together -- fitted perfectly!  

 With a ruler could you measure off former positions and plot on a separate piece of paper? You wouldn't have to draw the entire side plan, just former positions relative to some datum, such as centreline or thrust line?  You have the formers etc cut to shape already.  It's a thought!

Also, the skin of the Hunter is curved balsa sheet, not planking.  Once you get the hang of measuring the right size for the sheet, and then glueing the underside that you can't see, it's quite an easy process, and I don't think I've introduced any warps. Quicker than planking, and no need to sand much either.

I'm stuck on a number of questions now, that I can't decide on, and I see from your last photo that you've got the same issues:

1. is the fuselage strong enough around the fan housing? In order to make the fan removable they have designed a hatch which is HALF the fuselage.  Therefore the only thing holding the tail on is the other half!  I'm not happy with this as I think it will lead to fuselage flexing, and therefore aerodynamic faults like "tuck under".  I don't know what to do about it, but have been considering strengthening the fuselage with carbon fibre strip etc. What do you think?

2. Is the air intake geometry adequate?   As you can see from the photo of the Hunter, the duct inlets are larger than scale, but still not large enough IMHO.  I can't quite tell from your photo, but I would be worried.  I have been doing extensive testing on a Mig, and also fluid dynamics calculations of pipe flow, and I don't think the ducts are big enough, so a lot of potential thrust will be lost overcoming duct losses.  I don't know what to do about this -- what do you think?

3. Is the fuselage strong enough at the rear end of the canopy where it meets the duct entry?  The Hunter is also weak in this area.  If your model noses over on landing (and let's face it, even the best of us do this sometimes!) it will stress it at this point, and I predict a serious crack!  The fuselage is much stronger both in front and behind this point.  Again, I don't know what to do about it, what do you think?

So, I'm stuck! I hope you're proceeding ok!

Richard  

[Tom Foreman]

Hi Richard, I'm no expert but will attempt to answer your questions as best as I can;

1. Fusealage stresses around the fan housing will tend to be longitudinal due to the fan pushing the model, so as long as the fan is attached to two sturdy longerons it will be ok as there will be little bending and just compressive forces which is OK. The rear stab, will induce some bending on the fuse, but nothing significant.

2. Air intake Geometry is a black art which i don't fully understand so leave it to the experts. Things I have picked up are that the frontal area is bigger than the fan, boundary losses are reduced by aerofoiled intake lips. The nozzle outlet can be fine tuned for higher thrust or faster efflux speed, but 95% of fan seems to be a good starting point. Of course smooth ducting helps. Also a dynamic balanced fan and motor always help to improve efficiency.

3. I had a Rivington Hawk PSS which was weak in exactly the same area, it is very flimsy at the moment, but the model isn't complete yet so it is too early to judge. I guess if you nose in at speed somthing has to break, perhaps it will be asy to fix

Anyway had a great day flying today, the only damage I did was snap a tip tank off my Twister jet foamy EDF when the battery went on an overshoot aborted landing. I didn't notice until I had walked half way across the field and then it was impossible to fnd the small piece of foam in the grass. People reckon that its better to cut them off the wing and sand to an aerofoil section so I'll probably do that instead.

Anyway, I can hear batteries beeping so better go, got to get ready for tomorrows day of flying, got to make the most of the good weather!

Tom

[Erfolg]

Regarding, the production of a reverse half from a one view.

A very old but simple method is to tape the plan to a glass window on a very sunny day, with the plan facing out. Attach to the plan a translucent drawing film or tracing paper and then trace the outline onto the attached paper.

These days you can get reversed copies, from coping shops.

Erfolg

[Richard Sharman]

Tom,

 Erfolg and I have been working (offline) on the theory and practice of duct design.  Too early to say anything definite, but calculations and observations we've made recently would suggest this is a very contentious aspect of model design. This only comment I can make at this stage is that ducts are usually a lot worse than you think they are!  So, I'm not so sanguine as you.

Hope the building is going well! we look forward to seeing some more nice pictures!

best wishes, Richard

[Terry Whiting]

Tom,

I'm also building the Hawk. My method of obtaining the oposite fuselage drawing is with carbon paper,  I lay the C/paper face side up on my building board, place the plan on top and carefully draw.               All  I require is an accurate line drawing of the spines, and former positions, and nothing else. Turn the plan over and build.

Because I'm using an AP700, I have had to re-profile F12 & F13 and strengthen to take the slightly larger EDF., and F12a will be of 1/8"  (3mm) birch ply from F12--F14  as one continuous length, I know it means cutting through each former, but the kit F12a I think inadequate. I feel the hatch  is a weak area.

[Tom Foreman]

Sounds good Terry, my Hawk is on hold at the moment as I have been building a bathroom and breaking and fixing my other models. Will hopefully get back on track soon. Will be interested how the AP700 works out. What motor and battery are intending to use?

Tom

[Terry Whiting]

Tom ,

 I started with the Wimotec, and after  trying a few different motors I was advised  to use a  Mega 16/15/2,, this gave me about 25oz static. on a fresh charged 3s 2300ma 25C then settled down to 21-22 oz thrust.  I had then just purchased a AP700  so I tried the Mega, the same battery fully charged gave 32oz, settling down to 27-28 oz .  .I only use 3s batteries on all me models. Even with this set up my own design DH Vampire goes off with a hand launch, and is plenty fast enough for an old fossil.  (Myself)  

[Tom Foreman]

Excellent, sounds like the AP700 is more efficient or does it work the motor harder? Did you manage to measure the wattage on both setups?

Cheers

Tom

[Terry Whiting]

Yes I did Tom, and this is where I found that relying just on  Watts alone can be very misleading.

The Wimotec  gave a reading of 25oz  static settling down to 21-22oz  @ 350W, ...now the same motor with the AP700  gave 32oz settling down to 27-28oz  @ 370W.

Now if i hadn't made my own thrust testing rig I could have said there's only 20W difference why bother.   I know my theory could be wrong, but without a thrust test rig a high Wattage reading could be saying you have a mismatch motor / impeller and not  thrust  .

 Maybe one day EDF maufacturers will produce a varity of impellers for their fans.  

[Tom Foreman]

Cheers Terry, perhaps I will have to do some thrust testing with my current Wemotec Mini fan and HET 2W-20 in my MPX Twister Jet, which after a battery upgrade from 4s1p 2600 to a 4s1p 3700 now pulls 750W! Perhaps its just hot air!

[Tom Foreman]

Will post some more photos tonight of the build, have finished skinning the left half fuse (nightmare) and have started assembling the right half fuse onto the left, as per instructions. Its also a nightmare as its not looking very straight at the moment, but I'm hoping when I eventually join the two halves I will be able to true it all up. Also decided on a fan and ordered it last night. After much searching and umming and erring I went for an HET6904 as it seems to have a bit more thrust (more amps) than the Wemotec mini. I did have my heart set on a DS30 carbon fibre beauty but the small performance increase didn't justify the 5 times increase in cost!!! Still it would have sounded nice and probably has higher effluec speed, but I am more interested in aerobatic ability rather than top end speed. Over specced the ESC as well as I am concerned about cooling as the esc isn't in the duct so its going to get hot. List of bits below.

Tom

1x HET EDF 2W-20 () - HET2W20

1x HET 4 Blade Mini Fan () - HET4BF

1x Tornado U-BEC 4.8 or 6v Switchable () - TORNADOUB01

1x Tornado Gold OPTO 80A ESC () - TGOPTO50

4x Hitec HS-55 () - HS55

[Tim Mackey]

Hmm good luck with the Tornado stuff

[Terry Whiting]

Tom,

Why West Wing took that route  for building the fuselage is beyond me.

I used carbon paper under the plan with 'carbon face up', and with the use of a french curve I carefully drew in the fuselage spines and all the formers , when the plan is reversed you have your mirror fuselage image, then just build side two.  You then have you left and right  halves. .

[Richard Sharman]

Terry's carbon paper trick is neat! I must remember that for next time!

Still stuck on my Hunter. I'm still planning Wemotec fan with KMSQ380/10 motor and XTRA BL45HV ESC with 3s Lipo. Perhaps a bit old-fashioned nowadays, but I'd already bought the stuff when I got the kit.  Now the flying season is effectively over I must get back to building soon!

Tom -- how's the Hawk looking for weight? or is it too soon to tell?

Richard