darryltarr

My Feedback: (2)

Hello Gents, (and David, Mark, and Marc),

Both my Skygate Hawks use the original set-up (see photo's attached). However, here is some additional information:

1. Both servos have been perfectly matched, although with this system it is Not an absolute must as it does allow for a slight miss-match.

2. My Stabilizer has been statically balanced (CG slightly behind the middle join on the central box spar). A lot of lead was required here, 120 grams in the leading edge of each STAB (240 grams total).

3. Although Dubai is at the coast, we are fortunate that the climate is warm and dry (with low humidity), and does not encourage a lot of rust. Similar to Phoenix Arizona - I believe. And one of the best lubricators for my STAB bearings is Zefal Dry Lube (available from most bike shops). I also use this on my Turbine Helicopter's Swash Plate's.

4. Tailpipe Heat. As you know airflow will always travel along the path of least resistance, so if your Hawk utilises a full ducting system you need to ensure that enough air is entering the fuselage (apart from the inlet ducts), and can flow out the rear end (between the tailpipe and the fuselage). This will ensure adequate cooling for the Stabiliser mechanism.

Bob, looking at your set-up it appears that you STAB movement may be limited as your "full stabiliser travel" is defined by the limit of the Ball Links. Should you find the time please can you measure your STAB Leading Edge travel. Mine, for example, is HUGE, and the HAWK does need a lot of UP STAB when landing with full flaps.

David, I usually do JetPower every Two Years, so my next visit will be 2016.

Regards,

Darryl Tarr

darryltarr

My Feedback: (2)

Just another observation Bob,

I completely understand that on some applications we have to use a very long servo arm but remember, for maximum torque: the shorter the servo arm - the better.

Short servo arms and long control surface horns.

Darryl

Blancr

Hi Darryl,

Thanks for your input. It's a good observation of yours re the ability of the ball links to cope. In fact, I have full and free movement of the stab with no danger of binding. These are 3mm links and rod. I wanted to go to 4mm but I couldn't find ball links that would give the range of movement. Will give more thought though to the need for ventilation beyond the main inlet ducts
Bob

darryltarr

My Feedback: (2)

Hi Bob,

Okay, that's good to hear that you have full range of movement.

Here is a photo of the aft fuselage showing the small gap around the pipe.

DUCMOZ

Hi All

I first powered up the plane. Everything seem to be working as it should on the back. Then, I heated up the bearings to about 165 degree with the heat gun to the point that the glass started smelling. Still had easy and smooth movement. So in my case, the heat could not be an issue. Last, I took the servos out and individually cheeked. One is perfect and one has a chipped tooth which I mentioned earlier, as I am sure that happened at the impact as the tip of one stab is broken. So at this point. My crash remains a mystery. I was hoping to find something solid so maybe I would order a replacement.

Thanks

Behzad

lavi rider

My Feedback: (6)

Aluminum , the more one heat it up the more it expands ....it expands more than steel . So no matter how hot it gets there is no way the bearing will seize in this case ( I'm not up to melt down where nothing last anyway).

c_makhija

Now all you guys are scaring me, so far have had just 4 flights on my original SG hawk, with stabs balanced like Darryls Hawk.
So far, touch wood all systems function fine.
Are you guys balancing the stabs with weight in the leading edge on the compArf ones?

Regards
Chatty.

lavi rider

My Feedback: (6)

Mine are balanced .

jws_aces

My Feedback: (33)

Mine were not balanced and I am not going to on my new one. I hope Karma doesn't bite me..

lavi rider

My Feedback: (6)

Now that's the spirit ! Put your faith on luck !! He , he

jws_aces

My Feedback: (33)

Karma has overiden skill and luck many of time. Luckly my skill on the elevator was good just my luck on fuel filter ran out

DUCMOZ

I need to talk with Mike to see what happened to his. Last Sunday I was saying Never Again. But, I am recovering so like to have another one. What if we do one large strong servo?

Behzad

jws_aces

My Feedback: (33)

Behzad if you look at the Skymaster thread on there new 1.35 hawk. Anton is using a very simular set up to ours. He is using Sbus it appears. Most of the failures seem to be from a seesaw applacation that I feel like promotes the problem. Yours is the only one I know with the 2 servo's at the rear and connected directly that had a elevator only control failure. There may be more.

Oh yea I just missed the Deal of 10% off on Carf Kits now on there FB page. Good for this month so now you have to order one....

DUCMOZ

Hi Jeff, I know. A friend of mine has their smaller thank ours Hawk and has many many flights on it and that has the same set-up. I don't want to be special that way! I will dig in more for possible cause. I like that plane and with a discount, maybe I jump in. Last year they had a sale for 15% off and I bought a Marchetti. still needs to get built.

Behzad

DUCMOZ

Hi Darryl

could you please let us know that how much flap you have on the hawk?

Thank you.

Behzad

darryltarr

My Feedback: (2)

Hello Behzad (Gents),

Skygate details attached.

Just curious, for those of you whom have modified the STAB control set-up. Where is your horn (on the stab) located. You will notice mine is as AFT as possible to allow the correct relationship between the moment-arm and STAB center of pressure. It is also behind the STAB bearing pivot point.



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jws_aces

My Feedback: (33)

This it the location that mine came from the factory. Mine came with the servo mounts in the from the factory. It seems pretty close to your setup on location of the stab control horn push rod mounting hole.

Still behind the center pivot point but no as much as yours.

Blancr

Mine is still centred on the stab as per Jeff's but about 10mm further aft and with shorter rods.
Bob

DUCMOZ

Hi Darryl

Thank you very much for the details. My set-up was same as Jeff's which came from the CARF. But from the details from Skygate, I think I can see what happened. This detail is calling for 75 mm flap for short landing but 45 mm ideal. carf calls for 60 degree which translates to (in my case about 89mm) if we take it from the center line of the wing. So we basically are killing the air flow over the elevator by too much flap and this should explain it. The reason I started looking at this is that we were flying yesterday and I looked at my friend's Skymaster Hawk and noticed that the landing flap angle is much less than what I had. So I thought I would ask you. I wonder how this detail changed going from Skygate to Carf. What do you think about this analysis?

Behzad

Mike Haddox

My Feedback: (5)

Jeff,
Is this picture of your original Hawk or the new one?
Thanks, Mike

Mike Haddox

My Feedback: (5)

Behzad,

You might be on to something. I used 20 degrees flaps for take off. Elevator had lots of authority. I used 40 degrees for landing
and had no elevator at all. There is nothing wrong with the airframe. I believe that so much I ordered another one. Gonna do
things different this time. Mike

Blancr

[QUOTE=DUCMOZ;12088678]Hi Darryl

Thank you very much for the details. My set-up was same as Jeff's which came from the CARF. But from the details from Skygate, I think I can see what happened. This detail is calling for 75 mm flap for short landing but 45 mm ideal. carf calls for 60 degree which translates to (in my case about 89mm) if we take it from the center line of the wing. So we basically are killing the air flow over the elevator by too much flap and this should explain it. The reason I started looking at this is that we were flying yesterday and I looked at my friend's Skymaster Hawk and noticed that the landing flap angle is much less than what I had. So I thought I would ask you. I wonder how this detail changed going from Skygate to Carf. What do you think about this analysis?
Behzad.

Hi Behzad,

An interesting thought but I have not heard anything to date that would suggest the Hawk has an elevator blanking problem. I think we should remember that there are many hundreds of these aeroplanes flying successfully. Too much flap is rarely a good thing. In the case of this very 'draggy' airframe, too much flap is simply going to slow it down even more and possibly induce an incipient stall. Flight controls very quickly become ineffective as speed drops off. I can have no idea what happened to your plane but when we start to point to fundamental design flaws then I start to get a bit edgy.
Bob

DUCMOZ

Hi Bob

thanks for the note. I did not say anything about the functional design flaw. In fact, if our theory becomes valid. It would mean that I messed up by using a lot of flaps no matter where the source of my information was. My intention for posting the detail is two: first, to help others prevent going through what myself and other friends went through. Second, to find the reason for the experience and if preventable, get another one as I like the plane. Otherwise, I would kick, scream and cry and blame the world for doing it to me! ��

thanks again.

Behzad

Blancr

Hi Behzad,

...and I was a little clumsy in the way I expressed myself -sorry! Not my intention to criticize since I applaud your efforts to discover the cause. What I meant to say was that it's usually best to exclude the 'simpler' causes before getting into more technical questions such as loss of elevator control resulting from flap blanking. A 'simpler' cause might be that because the Hawk is known to be draggy, large amounts of flap will require a larger amount of thrust to compensate. So one question in my mind is -'when deploying the flaps, did you have sufficient speed and power to overcome the additional drag since stage 2 flap is the 'drag' stage'?

Not my intention to criticise your flying ability - merely trying to exclude this as a possible cause. It's important to me because, if this were the case, then it's something that I (and others) can guard against when I maiden mine!.

Thanks for your thoughts and help in working this through
Bob

marc s

Gents, not that its possibly relevant but the full size Hawk I understand did have issues with flaps blanking the elevator, the fix I understand was to add the inboard flap airfoil blade which allowed air to pass through the flap closer to the wing TE. Again not completely sure but this blade was later shortened to increase the airflow further too.

Models don't often mimick the FS in aerodynamic terms but those more in the know might see a correlation.

Those who do know the FS might be able to be more accurate in the flap design.....

marcs