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Javahawk


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  • 3 weeks later...

Hi Ady,

The Javahawk looks very nice. Do you happen to know what weight of silk ( g/m^2 or momee) you used for the covering? I'm thinking about doing something WWI and silk should look about scale for linen.

Regards,

Steve.

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Hi Steve, The silk used is 36g/sq metre http://www.beckfordsilk.co.uk/browse_465 (Using the add link button). It went on very like nylon does so the same techniques will work, and it does have a nice translucent look too. I water shrunk the silk after attachment to the airframe, and it did shrink a little but make sure that the covering is quite wrinkle free to start as the shrinkage is not much.

Hi Erfolg. The c/g is some 15mm forwards of the recommended point for free flight so for r/c work is at about at the aft limit. The tailplane isfixed at -1 degree incidence and the elevator position is just raised by a couple of degrees for level flight suggesting a slightly forward c/g already exists. The wing rocking is classic for angles of wing sweepback as used on this airframe and only becomes apparent at high alpha and at low airspeed. The next series of flights will have wing fences at around 40% half span, and maybe another set at 80% of half span if needed. It would appear that as the free flight versions flew at a moderate speed under power and gliding the slow speed regime woulsd maybe not be witnessed. The R/C version of the Javahawk (Evolved in to the Rapier) was single channel, so again would be trimmed and flown at a suitable cruise speed and glide, again probably outside of the wing rocking flight envelope.

Ady

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Hello Ady,

Thanks for the info. It looks like the stuff I ordered on fleabay might be a bit thin then (5 momme ~ 20g/m^2), still should be usable for freeflight and quite reasonable at £4/m http://www.silkcraft.co.uk.

Back when I was flying control-line I always covered with the nylon wet which seems to be what some also recommend for silk so I'll probably try that first.

Steve.

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Well, Looks like the weather has beaten me to the next section of flight tests. I've made two sets of wing fences, The first set are placed at 40% the half span, and if there is no appreciable changes then another set at 80% of the half span. The third test is to have just the fences at 80%. I've read several articles and certainly for the fullsize wings it seems the 40% span ones are most effective against wing rocking, whilst the 80% ones can reduce tip stalling tendencies. We'll see when I'm next able to test.

40% wing fences

40% Wing fences

40 & 80% Wing fences

40 & 80% Wing fences

Ady

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I can imagine that fences can do a lot of good near the stall, as long they are of sufficient length.

I remember reading of some trials undertaken by a student in the USA, as part of a college project. It started with the supposition that model wings, which were unsupported between ribs, performed better at and near the stall than those which were sheeted between ribs. Based on an observation that a models performance had been noted to deteriorate when a simple wing was replaced by a sheeted "D" section wing.

The results indicated, that the channelling of the flow, caused by the depressions, improved the stall angle. I assume with a reduction in flying speed that the stall occurred (not with standing BEB,s argument) in level flight or maximum L/D, steady state equilibrium conditions .

Assuming that the work was reasonably well done and the parameters are those applicable to models, I would assume that fences would have a similar affect.

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Hi I read several articles on the wing rocking issue and it is largely due to the spanwise air flow down the wing leading edges, and spilling around the tips to cause loss of lift and the wing drop. fences were the first method of stopping the flow, then more exotic methods were employed as dog tooth leading edges, notched leading edges and in the Vulcan's case a kinked leading edge. Most writings offered that the fences do little past the first 1/3 chord hence the short length. It will be interesting to see what is gained by them.

Ady

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  • 2 weeks later...

Hi Erfolg,

Sorry for not replying sooner.I was admitted to hospital on the 19th for knee replacement and still haven't got out yet due t some complications after. Fortunately my wife brought in a dongle that I can use. I wasn't making any statement against what you are saying, but just giving a bit more info for readers that may not know much about them.

Best regards Ady

 

Edited By Ady Hayward on 28/04/2012 18:51:12

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Hi Ady,

I hope the complications are not too serious, and you are on the mend, After my Heart problem I found the laptop and dongle a god send for keeping in touch with people. The nurses found the flight sim amusing as I spent hours playing on it and every time I made a dogs of the landings or crashed, the monitor gave a blip.

Get well soon,

Cheers, Chris.

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  • 2 weeks later...

Well, I tried to fly the machine and had a couple of issues.Trying to balance on the good left leg, steady with the new right knee and hand launch wasn't a good idea. The plane just went in to a left hand roll and cartwheeled along the grass strip. The first time I throttled back as she went down and no problems. The second time it did the same but shed 5 of the 6 blades off the fan as i didn't throttle back as it seemed to stop rolling but was too nose down, low and slow to do anything. Due to the wind direction coming from near the pits I had to launch with a bit of wind under the right wing, so probably not suprising it rolled left.

It did seem that the aileron response was much reduced, and no sign of any wing rock so it looks like the inner wing fences may be doing something. The next outing will be with more favourable winds hopefully and a stronger knee joint and upping the control throws a bit. Unfortunately previous attemps at hand launching by club members was not good as no one seemed to be able to launch it without launching it at extreme angles upwards or downwards as due to the wide fuselage the best launching grip is via the fuselage cockpit section, or pushing it from the rear. Furtunately it is proving to be a very tough plane.

Ady

Edited By Ady Hayward on 08/05/2012 21:39:56

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Hi Andy

I have just got my Delta into the air for the first few times.

I found that I could get the model rocking at high AOA and slow speed.

I also managed to tip stall in a turn at low speed.

From your experience, are these aver present problems with Deltas?

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Hi All,

Erfolg, unfortunately this is one of the issues with deltas, and a look at deltas through the aviation timeline you will see many have wing fences and/ or modified leading edges to reduce these tendencies. It was also prevalent in the early swept wing designs, especially noticeable in the MiGs which displayed quite huge wing fences.

BB thanks. The new knee is definately better than its predecessor, especially as my foot is now pointing in the right direction as well (Good stuff this computer alignment system). Along with favourable winds is a need for some nice weather which we all deserve for our new batch of vintage models.

Hi Bob. Yes a bungee has been considered, and may well be the ultimate solution. I had some good launches some time earlier, but with my new knee, my balance and therefore ability to launch it well was less than expected. All being well I'll be fit enough to hurl it skywards at the RCM&E fly in.

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  • 3 weeks later...

I have finally been able to test the wing fences and have good results with the mid span ones. Slow flight shows some wing rocking tendency if the aircraft is disturbed by gusts or thermic activity but it damps out within a cycle right down to the stall. The stall is quite sedate with a slow wing drop, but as soon as aileron is applied the roll stops so I'm quite pleased with the fences which will now become permanent fixtures. Hand launching proved to not be an issue today so all bodes well for Greenacres.

Ady

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  • 7 years later...

d991f369-39bd-4ee5-bc05-dba78ee9ef51.jpega53acb74-d028-4e75-a52a-0e92ec0a4fb0.jpeg0cc31252-00cb-4c46-8288-bd61e2495ae6.jpegAmazing to see this one come up after so long, I wonder if Ady still has it? It would be great to hear more about it.

Perhaps like a few others I remember when P E Norman designed this and it was published in I think AeroModeller. Incredible the way he made these designs work with a home-made fan on a Diesel engine so long ago. I imagine that he coined “Javahawk” from Javelin and Skyhawk, you can see elements of both in the design.

The Javelin fascinated me from the beginning and I have fond memories of being close to FAW9s for a week at ATC summer camp, RAF Waterbeach, 1961. They truly were “all weather, day and night” and you were forcefully reminded when they took off over your billet at 02.00! It was a mixed bag in some respects and there were handling restrictions throughout. (Can’t recommend too highly “The Quick and the Dead”, by Bill Waterton).

I recently put something about my “knock it together in an evening” profile Depron D/F Javelin on my indoors page, a bit of a joke really being not much more than a chuck glider with 24” span and weighing 58 gms. with a pair of Eric Strefford’s miniature D/Fs and 1S 300 mah Lipo. It has astonished me how well it flies. No wing rocking or odd stalling characteristics, dead stable in pitch and direction, yet responsive on elevon. It has surprising presence in the air, looking bigger than it is. af831c41-1813-4fd7-9e30-e075fc1d7490.jpegDefinitely a candidate for scaling up, although it is giving me a lot of fun as it is. Here’s hoping we will hear more about the Javahawk. Didn’t mean to hijack the thread, but I was interested by it. 

 

Edited By Colin Leighfield on 13/07/2019 15:56:07

Edited By Colin Leighfield on 13/07/2019 15:58:22

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  • 11 months later...
Hello friends, I have read the whole thread and I am putting together a javahawk
like this one, using the same plan, but fundamentally this post as a guide. I am
from Argentina, and I have some doubts: The EDF I have is 50mm, and with 3s it
delivers 480 grams of thrust at maximum voltage. Is that enough for this model?
Sorry for my English, I am using the translator.

 

Edited By Steve Hargreaves - Moderator on 25/06/2020 09:04:42

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  • 8 months later...

Hi Folks. I thought the thread had closed and was surprised to see it was stirring interest. The Javahawk is still airworthy, and on its 3rd fan unit. A 55mm unit  is the smallest I would suggest to allow the motor to be throttled back a little in flight.

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