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Old May 22, 2012, 12:17 AM
Hawk Fanatic
SkylineFlyer's Avatar
United States, KY, Louisville
Joined Jul 2008
7,583 Posts
Quote:
Originally Posted by CRCJA View Post
I had the same problem with the strut when I used them on the Fly Fly Hunter. The solution was to turn the scissor around on the strut so that it was facing towards the back of the plane.

Ralph
Nice
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Old May 22, 2012, 08:59 PM
Registered User
Brisbane, Australia
Joined Oct 2004
1,167 Posts
Quote:
Originally Posted by NickM91 View Post
Looks good blizards!

Updates on mine:
Top layer of wing is glassed, bottom still waiting
Wing tip missile rails added
Nose is more or less complete, awaiting glassing and paint.

Don't think I'll be able to finish it before work commitments take over indefinitely.

Cheers
Ah no, MickM91!!!

Damn that work getting in the way of fun

I've just got a hawk kit off Biggles51 because you inspired me to get going on this one, but I'm opposite to you right now were I've been flat out at work for the last 2 months and it should really quiet down in about 1-2 weeks time. So in the interim I'm busy collecting all the parts I need to make this build go ahead!

I have the retracts, servos and ESC either here or on its way here. I can rob the fan out of my F-86 until I get in the fan/motor that i'm going to run in the Hawk, but I am heavily leaning towards the CS 90mm with the typhoon motor in it at 8s In my flyfly sabre, I have the flyfly housing with the wemo rotor and an ARC 36-75-1 motor on 8s and it's a pretty decently powered model

I am trying to find 3-views of the hawk that show rivet detail???

Thanks

dave
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Old Jun 02, 2012, 08:01 AM
Registered User
Brisbane, Australia
Joined Oct 2004
1,167 Posts
All quiet on the western front??

My bits have arrived so I am ready to start the build but I've just bought a new turbine so am busy installing that and I have to get a few minor issues sorted out on my sabre before the "Jets over the fraser coast" event at the end of the month before I look at starting on the hawk.

Any more progress Mick?

Thanks

dave
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Old Jun 09, 2012, 02:26 AM
Glow? What is that?
South Africa, FS, Bloemfontein
Joined Apr 2009
140 Posts
HI guys. My Hawk mk120 was maidened on Sat 26 May 12. First I did a highspeed taxirun diring which we found out that the elevators were set too much "down elevator". We reset the servo to be more "neutral". Then the flight went uneventful.

I flew her on 7s for 5:00 and put 2600mah back into the batts.
She handled very docile and landed at a jogging pace. Easy.
I was very impressed by her characteristics and awesome handling.


The saturday after that I was ready to try her on 8s but decided to go with 7s still due to insufficient charging time. ( wanted to do multiple flights)

Again initial part of the flight was uneventful so I decided with 1:30 left on my tx timer for a highspeed run.
It was a slight dive directly for me with WOT for approx 6-8 seconds already.

Thats when it all went wrong.

I could see The left hand elevator was fluttering heavily. And slowly but deliberately reduced throt to idle. I then just touched the elev to raise the attitude and reduce the speed, but at that moment the left hand stab separated from the rod.

She pranged on the centreline of our club's tarmac rwy.
Luckily she impacted perfectly level. But destroyed the cockpit area.

The wing is perfectly intact and totally undamaged. I am in process to rebuild the fuzelage.
But learnt quite a few lessons:

1 Do not use foam all flying stabs.
2 The servo driving the elev should be set to use maximum mechanical advantage. (first hole in arm)

I have cut the elev @ 50% chordline.
I attatched balsa LE and TE to both the stab and the elev.
Gonna cover them again with tissue and pva/glue combo.
I have drilled out the plastic elev fuz fittings to fit a 6mm CF tube.
I am fitting 4 hinges either side and want the gap as tight as possible.

Lets see. Hopefully she will fly again.
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Old Jun 09, 2012, 02:42 AM
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jacojet's Avatar
South Africa, Free State, Sasolburg
Joined May 2010
205 Posts
Same-thing happened to my my hawk, even fully glassed and reinforced stabs. I flew her on 8s with stumax fan, and on the first WOT run both stabs came of and she went in nose first. It looked like a real crash since both lipos caught fire on impact! Next one, I will make the stabs fixed!
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Old Jun 09, 2012, 08:08 AM
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NickM91's Avatar
Australia, WA, Perth
Joined Jan 2009
250 Posts
G'day guys,

Apologies its been a while since I've been able to do any more work on the plane due to work commitments (I'm moving interstate next week!)

Sorry to hear about your crash blizards!

With the gear I was reluctant to merely spin them round as that would result in the centre of traction (for lack of a better term) ahead of the strut... asking for bad news IMO I'll have a look at the mod to move the torque link to the rear while still keeping that trailing link

I managed to gain an extra week and a bit of leave to sort everything out, and of course do a bit more building, so here's where things stand.

*Power system has been tested (not to full power as of yet) and installed in the aircraft. Smooth and sounds good... at 1/3 power. I'm a bit anxious that 5S will not be enough though.

*Fuselage has been joined together, spackled, and coated with WBPU (not glassing it at this stage as I cannot source any light weave cloth in time, and I don't really need the extra weight as its only 5S powered.

*Experimented with paint on the wing I'm quite happy with the results however the finish wasn't terribly smooth so I sanded it back and will apply it again.

I mocked it up as I wanted to see how it looks, enjoy!











Cheers

Nick
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Old Jun 09, 2012, 08:16 PM
Registered User
Gold Coast Australia
Joined Sep 2010
263 Posts
Hi Guys,
Read with some concern about the two crashes with the stabs parting company.
I am just at the assembly stage with the rear fuselage sides to go together and the wing
on. Left the nose as standard for the time being.
Blizard and Jaco, what would you reccomend re the stab /elevators?
Ditch the fully moving stab and go for a fixed unit with rear hinged elevator ?
Would appreciate your thoughts.
Regards
Tony
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Old Jun 09, 2012, 11:12 PM
6 months to finish a rtf
pulsery2k1's Avatar
upstate ny
Joined Jun 2003
1,861 Posts
Well knowing this is a problem I made a stronger mod that I used on my
brothers F-100
he didn't like the flimsy tail set up , so I made a new one for his
and mine .

I made it from very light weight aluminum the arms are 6 mm
total weight is 34 Grams
it uses a single servo and the arms are held in place with set screws
very nice, strong ,secure , no slop or play
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Old Jun 10, 2012, 03:50 AM
Glow? What is that?
South Africa, FS, Bloemfontein
Joined Apr 2009
140 Posts
@Biggles:

I have already cut the elevators @ 50% chordline. To make it fixed with conventional elev.
I will not fly it with all moving stabs if I was you.

I dunno bout anyone else, but I built this hawk to have composite like looks and certainly be fast.
The stabs are way too flimsy stock to allow for any decent speed setupss. Its way too dangerous!!!

@pulsery:
How far does that rod go into the stab?
Mine went in 150mm and then turned through 90 and fixed to the balsa TE.
IT CAME OUT.....

All Im saying......
Dont risk it.

Its not so much work to change to conventional elev.
I will post a pic later...
Cheers
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Old Jun 10, 2012, 04:23 AM
Registered User
Gold Coast Australia
Joined Sep 2010
263 Posts
Thanks Guys,
Would appreciate that pic Blizards.
Did you leave the servos in the original place ?
Cheers
T
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Old Jun 10, 2012, 08:34 AM
Glow? What is that?
South Africa, FS, Bloemfontein
Joined Apr 2009
140 Posts
Elevator Mods Suggestions

Ok here goes some pics...

I have included some of the construction pics of my elevator modifications.
I have stuck balsa leading and trailing edge on both the stab and the elevator.

I plan to use 4 hinges on either side to ensure stability.

As for the servos, I plan to use the original servo locations, but obviously use TWO micro servos.. I am also thinking about using a micro DIGITAL servo.. But not dead neccessary I guess...

I installed a 6mm CF Tube through the balsa stock on the original location of the rod. And I am in process of covering the rod with filler.....

Also plan to put another CF rod through the Fuz close to the Leading Edge of the stabs. (Obviously only once assebled, and correct angle has bee attained)

Hope this helps...

PS
In the 2nd pic you can see the rod which I initially had in... It was 3.2mm piano wire. AND IT CAME OUT....
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Last edited by Blizards316; Jun 10, 2012 at 08:36 AM. Reason: Adding detail to second pic..
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Old Jun 10, 2012, 12:32 PM
Registered User
jacojet's Avatar
South Africa, Free State, Sasolburg
Joined May 2010
205 Posts
This is the way to do it, I will not be using full moving stabs again. If you fly with mild set-up and slow speed then it is fine.I have seen the stabs come of on a big turbine hawk that used a 10mm steel rod on the stabs and big digital servo. It was fine on milder speeds, but as soon as he opened the throttle for high speed pass, of they came! Flutter happens at higher speeds, the system can be as strong as you like, at high speeds it will rip them of!
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Old Jun 11, 2012, 12:17 AM
Registered User
Brisbane, Australia
Joined Oct 2004
1,167 Posts
umm, interesting.

Blizards316, firstly,sorry to hear about the damge to the model!

Full flying stabs can me made to work and work very well, but you have to make sure you are doing it properly. There are heaps of LARGE turbine powered hawks that have full flying stabs with no problems.

The first problem is to make sure that the pivot point is in the correct place. In basic terms, flight controls employ surface area forward of the pivot point to reduce the force required to move the flight control. if there is equal or greater surface area forward of the pivot point, once the surface has been moved from the neutral position, you will require far greater force to re-center it.The pivot point must be selected so that there is greater surface area aft of the pivot point. I have attached a picture of the SM Hawk for reference. you can see that it's almost at the 25% MAC position, and might be a little forward of what the flyfly's location is?? not sure, I might have to go crack out my kit to have a look. to be 100% honest at first glance it looked out, but it might be closer in reality than I'm thinking.

Second problem is that you have added a balsa leading edge. You would need to re-balance the flying surface to compensate. Flight controls are normally balanced neutrally along the pivot line. For full flying stabs there are a few schools of thought, but generally they are either setup to balance on the pivot point or slightly aft of the pivot point. your's would have balanced out very forward of the pivot point adding load to your servo and linkages which could have also lead to the in-flight failure.

Third, It's foam, so the area where the 3.2mm wire point turns 90 degrees and heads to the rear of the stab is carrying a lot of load, I would have added some form of load spreader. i.e. additional glass in those areas, some very very thin ply or maybe even balsa. Foam is great, but in order for it to survive the loads you have to spread it out over a larger area.did you glass the stabs?

And lastly, was there ANY slop in the control surfaces, and were the linkages strong? having the servo powered and being able to move a surface of that size a few mm up and down can lead to flutter. flutter can happen at ANY speed!!! it is just more devestatingand you have far less warning at higher speeds. I have a training video somewhere which shows the wings of a glider that have had flutter induced!! full size gliders are not exactly speed deamons either! this has also unraveled a few larger turbine powered hawks as well, and a stab in the dark would be that that is what happened to the turbine hawk jacojet saw go in....

So Jacojet is partly correct, if the surface is not setup correctly then regardless of strenght it will eventually fail. but if setup correctly it's perfectly fine!
Thanks

dave
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Old Jun 11, 2012, 07:40 AM
Glow? What is that?
South Africa, FS, Bloemfontein
Joined Apr 2009
140 Posts
Dave

Your comments are partially correct.
Here is some comments to clarify:
1 the balsa LE was installed after the accident. It is a set of CONSTRUCTION pics.
2 the pivot point was as per kit. And was balanced prior to the servo being connected.
3 the servo had ZERO slop.
4 the surface was not glassed but covered with tissue and pva/glue.
5 I hear there are full flying stabs that CAN work.
The point Im trying to make is : DO NOT USE THE STOCK METHOD OF THE FLYFLY KIT. thats all... I will shut-up now...
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Old Jun 14, 2012, 09:29 AM
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Brisbane, Australia
Joined Oct 2004
1,167 Posts
Quote:
Originally Posted by Blizards316 View Post
Dave

Your comments are partially correct.
Here is some comments to clarify:
1 the balsa LE was installed after the accident. It is a set of CONSTRUCTION pics.
2 the pivot point was as per kit. And was balanced prior to the servo being connected.
3 the servo had ZERO slop.
4 the surface was not glassed but covered with tissue and pva/glue.
5 I hear there are full flying stabs that CAN work.
The point Im trying to make is : DO NOT USE THE STOCK METHOD OF THE FLYFLY KIT. thats all... I will shut-up now...
Hey Blizard316,

Sounds like you had nearly all the points covered One area of interest for me, was there any damage to the pivot (mounting) point on the fuse?

If there was none, I will try to go ahead with the full flying stabs, where I will go down a different path is i'll be adding a carbon spar to the stab, reinforcing the connecting rod area, and glassing the whole stab.

I'm almost ready to start on this one.. the re-engine of the turbine model is nearly complete and the Ju-87 is also very close, the bench should be clear soon!

Thanks

dave
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