Kitehawk

[Peter Miller]

I do like to have a powered gliderc for occasional relaxing flying and when my Spektra batteries gave up I decided to go witha smaller i.c. powered design.

This is based on a very old model powered by a Cox .049 Texaco called Sunbeam and an electric powered model called Easter Eagle. Both very nice models

The Name Kitehawk comes from my days in Aden. There used to be large birds of that name or similar. They used to be fascinated by our models, It was not uncommon to see them circling over our control ine circle and on one occasion being hit by a combat model. The bird shook itself and flew off. The model was a write off!!

WEused to fly free flight out at an ababnoned airfield in txhe deseert. The kite hawks used to circle over our launch area and then they would folow the model until itlanded after which they would come back and wait for the nexy=t model to climb into the blue

On one amazing occasion when it was flat calm some one had a KK Caprice which had circled ner us for 37 minutes. In the end a Kitehak actually hit it and just tipped it and it musthave lost the trim and landed.

So, now to building

[Peter Miller]

I have used a V tail as this works well and prevents damage when landing in rough grass etc. Span is 60" with a two piece wing

Contruction is ultra simple. I cut out all the parts for a start. well most of them.

The Vee shape by the tailplane is the assemly jig.

Fuselage sides are 3/32 with 1/16" sheet doublers set at an angle, an old and effective technique.

Then 1/8" sq. is glued to the sides.

The sides are assembled to the formers flat on the board over the plan view.

The rear end has a 1/2" sheetinseer that has to be carefuly shaped to take the Vee tail. It is important that the bottom of the V is parallel with the bottom of the fuselage.

The wings follow my standard warp proof method. I had chosen to sheettheleading edge to get a better airfoil.

I oce read an article in Flying Models. This chap had glider which was winning all the competitions, Everyone wanted to know what wing sectio he was using. Thye were using Epplers and Seligs etc. They got rather upset when he told them he was using good old Clark Y!! That is what I am using.

The root rib is set at the dihedral andgle. The centre section is flat. It is a two piece wing.

I did remember to draw the tip root rib as thicker to allow for the angle.

The top sheetis applied to the tip but not the inner panels until the tip is joined to it.

The outermost rib is not fitted until the tip as joined to the panel, This makes for a perfect fit.

The tip has 4" dihedral whch is about right for a 60" span model

[Dai Fledermaus]

I'll be following this with interest Peter.

When I built David Boddington's Super Rookie, an ic powered glider, recently a number of people on this forum thought it strange because, as they saw it, electric was a more sensible choice. They were asking `why`. I was thinking `why not`.

[Peter Miller]

My reasning was two fold.

1) I once made a flight with an electric powered model which lasted 1 hour, 16 1/2 minutes. and I could have gone on for at last another climb.The real challenge is how long on about a 1 minute power run.

2) I could have bought new batteries for the Spektra. They would have cost as much as my 1 cc engine and would have had to be replaced. eventually as I only used the model about twce a year. THis way don't have to charge up before I go, I just grab the model and go fying.

3) I like engines. The model will be lighter.

[Peter Miller]

Oh, I forgot to mention one very important thing. This model has been designed so that it can easily be built of electric power. The space for txhe battery etc has been designed in.

[FilmBuff]

Each and everyone to their own - but a noisy oily engine in a glider makes no sense to me.

Just saying - without prejudice.

[Peter Miller]

Grob 109, Falke, Tandem Falke. Several Fourniers ASK er 14 I seem to recall,

I could go on but I trust the point has been made

[MattyB]

Posted by Peter Miller on 12/08/2016 12:58:40:

My reasoning was two fold.

1) I once made a flight with an electric powered model which lasted 1 hour, 16 1/2 minutes. and I could have gone on for at last another climb. The real challenge is how long on about a 1 minute power run.

2) I could have bought new batteries for the Spektra. They would have cost as much as my 1 cc engine and would have had to be replaced. eventually as I only used the model about twice a year. This way don't have to charge up before I go, I just grab the model and go flying.

3) I like engines. The model will be lighter.

I don't have a problem with an IC engine on a glider providing it is only used as a launch mechanism then shuts down completely; based on the usage pattern Peter outlines above I can see it makes sense in his case. What I don't get is why anyone would fit an IC engine to a glider and then fly it around like a powered plane, or throttle it back to tickover so it can "thermal". IMO if you want a true powered aircraft then build/buy one, or if you want to thermal choose a powertrain that can be shut down completely so you can really test and improve your thermalling skills.

Assuming you are in the latter camp electric is much more suitable for the majority of people because of the ability to relight - it can get you back from downwind and avoid a damaged model. That ability to get back helps to improve your skills quicker, as you will learn to go downwind with confidence earlier knowing that if it all goes wrong you can relight and get back. You can also fit a folding prop which is that much less draggy once the power is shut down, plus there is no cylinder head sticking out into the airflow. The proof here is in the competition scene - I don't believe there are any RC soaring classes with any significant participation that utilise IC any more, whereas electric launch sailplanes continue to become ever more popular and now often compete alongside winch, bungee and hand launched models in the same class.

Edited By MattyB on 12/08/2016 18:56:17

[MattyB]

Posted by Peter Miller on 12/08/2016 18:19:25:

Grob 109, Falke, Tandem Falke. Several Fourniers ASK er 14 I seem to recall,

I could go on but I trust the point has been made

I have flown in a couple of those. The 109 was ok with the prop feathered, but the Tandem Falke in particular thermalled... badly!

[Peter Miller]

Well. what ever turns you on.

And, as I said, it is designed to use about a 100 watt motor and 2200 MaH battery for those who want it.

Oh! And someone else suggessted the elecrtic power set up.

[MattyB]

If you are going for a 100W motor the AUW should be no more than ~20oz - that sounds doable, but your battery is over 6oz of that if it's a 2200 3s. I would try and design it around an 1800 or 1300 3S instead; this should give more spritely thermal and climb performance and still give plenty of climbs to the height a 60" model is comfortable to fly at.

Edited By MattyB on 12/08/2016 20:04:11

[Peter Miller]

Don't ask me! I am only going by other suggestions.

I designed the space to suit that battery so there should be plenty of room for the smaller on.

[PatMc]

What size ic engine is it intended for ? What's the estimated aprox weight & wing area ?

Edited By PatMc on 12/08/2016 21:04:30

[Peter Miller]

The engine range wouldbe Cox .049 or an AP .061. Wing area just over 400 sqin. Weight will be about 25 ounces or might be a little higher as the wings have a wire joiner and some extra sheet.

[PatMc]

In that case a 3s 800 - 1000mAH lipo, 900 - 1100 KV motor weighing about 55 - 70g, 15 - 25A esc & prop that will load to around 10A at WOT (probably 9 or 10 x 6 folder depending on motor size & KV) should fill the bill for 7 or 8 by 30 sec climbs to thermal searching altitude per charge.

 

Edited By PatMc on 12/08/2016 22:29:09

[Peter Miller]

I accept your figures. I really do not have a clue when it comes to electric power. My electric flying was all done with Speed 400 and 600 motors and NiMH and Nicads.

[Peter Miller]

Well now I have some more pictures of the construction.

Once the complet tip has been added the top sheet of the centre of the wing as glued on. This ensures that there are no warps in the wing.

The wing joiner tubes areglued in place, Leace them slightly proud of the root rib to allow for the 1/332" ply facing rib.

If you are happy with a 60" one piece wing the flat part can be built as one unit . This will save some weight.

With the centre section sheet, capstrips and tips added the wing is ready for covering

The wings are held together with tape and are bolted down at the training edge. Then the holes for the dowels in the leading edge are marked and the wing removed. The holes are drilled. This holds the wing together and holds it in place on the fuselage.

The holes are drilled in the top hatch. These can be lined with 3/16 brass tube if required. These locate the rear of the hatch

For my ic version the front of the hatch is held down with a short dowel that locates in a hole in F-1

For an electric powered model a small latch can be fitted instead for easy access to the battery area.NOTE F-2 would be ommitted for a battery.

[Peter Miller]

A bit more work on the tail end.

The V tail is glued together using the V shaped template. The top "V" is filled in with scrap sheet carved to a good fit

Under side of the joint showing the dovetailed and. On the final plan F8 is moved forward so that cut away is not needed.

First layout of the hardware. The engine is mounted on a cut down .15 size mount. A Cox would just be screwed to F-1 as would an electric motor. 800 MaH battery and a fuel tank go jusy behind the engine, three Turnigy 9 gram metal geared servos behind that.Only two needed if a cox engine was used.

Simple brass tank is used with my AP .061 Holds just under 20cc

Dry run to check fit etc

[Peter Miller]

With the model covered with Solarfilm Supershrink I used the same material to make the old "Clothes horse " hinges.

These are cheap, light, and easy to make.

They have the advantage that they are gap free but moved very freely and are easy to keep an eye on for serviceability

Start of by cutting two strips of film and joining them over a strip of 1/8" sq. stock. adhesive surface to adhesive surface.

If you have a different colour between top and bottom use the two colours.

Cut the strips into roughly 1/2" strips as shown and then iron them on to the control surface (or tailplane) alternately placing them top and bottom.

Then position the control surface in the correct position and iron the hinges down as shown and you ahev an excellent hinge for slighter models.

You can use this method with Solartex as well. We used them with ordinary fabric tape and balsa cement on control line models .

[Peter Miller]

Well Sunday was perfect so test flying was started.

Due to getting totally mixed up with V tail programming (No. I won't go into the gory details but at least no damage was done) things got a bit hairy at times.

However the test flights did prove that Kitehawk climbs like a homesick angel and has a superb glide. Well she would with an all up weight od 24 ounces and a wing loading of 8 ounces per sq.ft

Some pictures taken by club member Michael Morris show the shape in the air.

Edited By Peter Miller on 01/09/2016 19:05:20