Project

West Wings Hawker Tempest Mk V

Monday, 3rd July 2011.  I had this kit as a Birthday present about 5 years ago. The original intention was to put a 120 cu mm twin cylinder CO2 motor in it, rather than use the foot of elastic band that came in the box, and fly it free flight. This summer (remember it?) I took it on holiday in the caravan and got the fuselage about half built.

The intention now is to electrify it with RC on throttle, rudder and elevator. This involved a bit of redesign. I opted for the “build then modify” approach, rather than think it out first and do some drawings. I am completely new to electric flight, LiPos, ESCs and all, so it’s a learning curve. I purchased a Mini Combo kit via Channel4 from TechOne Hobby. After obtaining a balancer to fit my Pro Peak charger, I did some tests on the motor and ESC. Eventually got it working, after finding on the web blogs that the Spektrum AR6300 (2 gram) is wired differently from all their other receivers. The JST ZXH mini plugs have the black neutral wire on the middle pin. Fiddly, aren’t they?

Back to the Tempest. These kits are good and not expensive (the Tempest can be had for £16.99), all the balsa sheet and stock you need, wire, rubber band, prop, tissue, canopy, wheels and good plans. Printed balsa for the formers etc., so a fair bit of cutting out. A 1/16” square file comes in handy to clean out the stringer notches.

Having finished the latest DIY job, and been granted a week or two’s “holiday”, after New Year I pressed on with the model.
The wing centre section and main planes are supposed to be built in one piece over the plan, including 1” dihedral at the wingtips. This would make it difficult to cover effectively, so I built them separately, to be joined after covering.

The tail and fin, of course, need hinging to provide rudder and elevators, and are designed as 1/16” thick open structure. To provide a bit more strength, I have added additional 1/16” sq struts and extra members at the hinge lines, either side of the originals, then sanded to an aerofoil section. There is now room for the hinges: I used strips cut from a ½” wide polythene hinge.

Photo Album

• Click to open image! Click to open image!
• Click to open image! Click to open image!
• Click to open image! Click to open image!
• Click to open image! Click to open image!
•  

The rubber powered model is supposed to come out at 35 grams with wing area of 75 sq inches. Wingspan is 523 mm (20.62”). The electric components add up to 12.5 gm plus 2 cell 120 mAh battery (7 or 8 gm). This means a target all up weight of just less than 56 grams. The C0-5-23 motor should provide 54 grams of thrust and take 18 watts. This is a bit of an inference: the spec sheet for the motor says it has a “pull” of 108 Kg! Recommended model weight for the motor, it says here, is between 50 and 110 grams.

Weighing the bits prior to covering, it looks like about 80 grams, including all of the two provided sheets of tissue, but sans dope, so probably balances out.

There is, as you will appreciate, quite a bit of finger crossing here. Is this tiny motor big enough? Will it fly without ailerons? Answers on the forum, please. If it takes off, turns and lands I will be content.

The attached pictures show the tail feathers with added timber showing the effect of sanding to section. You can also see the three part wing and fuselage with characteristic chin radiator of the Mk V.

It is now Friday, 7th January. Off to Cashmoor tomorrow.

Out of interest, the Tempest MkV became operational in April 1944, the month I was born. Whilst I was doing what babies do, the Tempests were shooting down some 800 V1 flying bombs and the occasional Me262. For a lot more information visit
http://www.hawkertempest.se/WorldWar2.htm

Monday, 10 January 2011

Another half day has seen the hatch cut out and the hole reinforced, hatch completed. Also, the servo tray has been cut and applied to two bearers, formed by filling in the 1/16” stringers and bulkheads with apiece of light 1/16” sheet, both sides.
I spent a while changing over the servo leads, to get black on the middle pin. One of the wires came out of the endie bit. With the aid of a magnifying glass, I re-attached the wire, soldered it to be on the safe side then inserted the pins into the JST pluglets. As a check, I fitted all the electric bits up and ran it all. Only the motor worked, both servos dead. So, the fiddling with the wires was a waste of time, but trying it all was not. Either I burned them out when I had them plugged in before finding that the leads are different on the AR6300, or they are duff. I suspect the latter. Any road, I had two Blue Arrow servos fitted in the Hawker Hart, so whipped them out and tried them. These were wired from new for AR6300 (they do two versions). This time, all worked.

Tuesday, 11 January 2011

Fitted a floor for the battery and one for the receiver, also put a stay in to keep the ESC in the airflow. The chin on the tempest lends itself to cooling the ESC. That just leaves the control surface horns and push rods, then get it all covered up. Should have that done by tomorrow night. Ho Ho.
Wednesday, 12 January

I have decided that it would have been only slightly more fiddly if I had built it in a bottle! The push rods are from 1mm carbon fibre rod, with 20 swg wire z bends heat shrunk to the ends. The rear wire has a V bend to allow a bit of adjustment. As the loads are light, I softened the piano wire so that the V will open and close without fracture.
Found I had to alter the elevators since they clouted the rudder push rod and horn. And somehow, the rest of the afternoon has been taken up with the odd bit of extra balsa here and there, like around the wheel mountings. Also a revision to the rear of the fus, to allow for the modified tailplane. So: no covering done today.

Thursday, 13 January

More bits of wood added. Weight still looks like 80 grams. I think I may have to lower the battery. The CofG is well above the wing.

Friday 14th January

I decided to make a better job of the wing roots than the plan suggests, which was paper cutouts glued on after covering. 1/32” balsa over some added stringers and bits of 1/16” made them look reasonable. The battery bay is now within the wing, inside the fus, so will lower the CofG quite a bit.Using the tissue supplied, I covered the tail bits. The tissue proved to have no wet strength whatever, probably intended to be applied dry with paste, then steamed.

On Saturday after a blustery half day at Gourds watching some clever people flying in 40 MPH wind, gusting 50, (and launching my Wildthing a few times, then walking down the fence to the gate, then back…you get the picture?) I decided to remove the tissue and replace with some stronger yellow stuff. Getting the weak white stuff off proved harder than putting it on! So, now it is a trainer, but no need for coloured paint. The strong tissue went on like it ought to, and you can unpeel it if it gets folded over and pull it tight before rubbing it down with dope and a finger end.

Preparation of the airframe by sanding and doping then sanding again is essential before commencing to cover. The shape and finish of the structure is what you will get on the covering. This website is a good source for this subject, and many more: http://airfieldmodels.com

Tomorrow, the three wing sections and the fuselage…

Photo Gallery

• Click to open image! Click to open image!
• Click to open image! Click to open image!
• Click to open image! Click to open image!
• Click to open image! Click to open image!
•  

Monday, 17 January 2011.

That turned out to be three wing sections and some of the fuselage. Finishing it today. The curviness of the fus means using a lot of small pieces.

Sunday, 23 January 2011

Well, some tiling and grouting later, the model is now almost ready. Just the elevators, fin and rudder to attach.
One or two things went wrong during this little project. I didn’t prepare the airframe enough before covering, so there are a few places where the balsa is pushing the covering out a bit. After I attached the wing sections together with balsa cement, I decided to put magic tape round for good measure: wish I hadn’t: won’t come off!. The canopy was trimmed to fit, then applied, also with cement. Went on first time, in the right place. Held it firm until dry. Looked from the front and found it’s slightly on one side. Also, the tailplane is a bit higher at one side than the other.

In the time it has taken, I could have built a proper plane. Why am I doing this?

Monday 24th January

All finished and connected up. Slight stickiness with the rudder servo, but repeated use seems to have free-ed it up. Dirt on the pickup??

The weight turned out at 85 grams, but the balance point is a bit aft of the ideal 1/3 chord. No indication on the plan, so try with a small nose weight to start with.

Will it fly? Dunno really. I might try it tethered for the first flight. That means attach a nylon line from one wing tip to a pole with a swivel on it. Set the rudder to be slightly outside the circle. Make sure no one is inside the circle. Put the model on the ground with the line straight. Switch on, do the flight checks then attempt to take off. This way, turns are removed from the flight until after we know the model is balanced, and the elevators are trimmed. The problem with this is that everyone else who is there has to keep out of the circle…

 
Thursday, 27 January 2011

Five days before the next indoor meeting.

I checked with West Wings. The C of G should be 32mm from the leading edge, way in front of where it is right now. I looked up a WW2 flight test report by two US pilots. The C of G was 27.3% of MAC. This means on the model, 31.5 mm from LE. Allowing for the elliptical wing form, it turns out that the MAC is 85% of root chord, at 53% of the span. This worked out to be the same, around 32 mm measured at the wing root.

I have hung pieces of solder on the chin of the model until it balances at the right point. I need to add 25 grams of lead, when using a 180 mAh battery. I could also take 6 grams from the tail, but that is a horse of an entirely different kettle of fish! Lead it is.

Where does this place the model on the flyability stakes?. With weight added, the AUW comes to 120 gm, or 0.267 lb, or 4.272 oz. Wing area is 75 sq in or 483.87 sq cm. The resultant wing loading is therefore 0.25 gm/sq cm, or 2.5 kG/m2, or 0.513 lb/sq ft, or 8.2 oz/sq ft.

A slope soarer should be about 14 to 16 oz/sq ft, a thermal soarer should come out at about 7 to 8 oz/sq ft. So, I am in the right ballpark, and it might just fly. But will it rise off ground?
From an interesting website, I find that to ROG from a smooth surface, I need 40 to 50 watts per lb. For this model, that means a wattage between 10.68 and 13.35. What do we have? Eighteen watts! Definitely in the right ball park.
So, it should fly, and it should ROG, but what will be its take off speed? Answers on the forum, please! I don’t know how to work that out. I don’t think it can be done, without a wind tunnel.

Next >