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Old Apr 21, 2007, 02:32 PM
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Park Hawk II First Flight NOT good -(But Now Resolved!)

My maiden flight on my brand new Park Hawk did not go well - must have received second hand parts on this bird (my 5th Kincade orni).

About 80' up at just under half throttle the wings folded straight up and the bird came down like a lawn dart - just missing my truck. Turns out the spar broke at the alum. ferrel mid flight. If it flapped any slower I would have lost altitude so I'm guessing it was a poor quality spar or too small of a diameter for the bird.

Also my fuselage cracked in half, HS56 carbonite servo gears stripped and the wing ripped almost in half along the edge of the heavy nylon band that runs down the middle of the center cord of the wing. It looked as though it were cut with a razor! There was no fraying at all. Anyways, my $270 kit is now a net loss until I can figure out how to repair everything.

Any ideas on how to fix and IMPROVE these parts?
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Old Apr 22, 2007, 01:11 AM
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Anybody???
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Old Apr 22, 2007, 01:54 AM
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Was it the stock setup?
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Old Apr 22, 2007, 09:56 AM
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100% stock, yes. Any ideas on how to upgrade and fix the spars - how about that wing membrane as well - looks too thin to sew. Also just noticed that the grub screw was missing that holds the 1" long pinion in place onto the center gear. That explains why it was flapping so slowly - and yet the spar STILL broke!!
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Old Apr 22, 2007, 12:10 PM
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The spar must have broke on impact,amd yes that sounds like why it would start flapping so slowly. The only thing you can do is ask Sean if he has replacement parts for sale. Sure bites,thats why i try to buy 2 of everything I get for replacement parts.
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Old Apr 22, 2007, 02:29 PM
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QuietRiot,
Were the bolts that bolt the ballinks to the aluminum ferrules still intact? If not this is probably where the wing broke and the spar broke on landing as helifann suggested. I have had these bolts snap or ripped out from the aluminum ferrules 3 times now. I ended up putting a thicker bolt and now it seems fine. Also another "weak" spot is the bolt the runs through the large gear (on the right side). I have had that bolt snap twice now and this has also happened to Tres a few times. Tres is using a cotter pin instead.

The parkhawk 2 is an excellent bird to fly. When it flys it fly beautifully. Sorry to hear about your maiden flight. Thatís got to hurt. But part of the hobby is tinkering to get it perfected. I hope Sean will have parts soon.

Hope you can get your bird up in the air soon.

i.
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Old Apr 22, 2007, 03:24 PM
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The spar did not break on impact, it broke mid flight which is the only way the wings could have folded straight up against each other - hence the lawn dart effect. The bolts and all hardware were all fine. I have broken spars before on every Kincade orni I have owned - some on impact others mid flight (none on first flight though).

This is why I'm asking if anyone has done their own improvement/modification on the spar system. This seems to be the weakest point of all Sean's ornis in my own experience which covers 5 birds over 4 years.
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Old Apr 22, 2007, 04:13 PM
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Thats just wierd,i have 2- slowhawk2's,2-parkhawk's and the yard hawk. The only time i had ever broke a spar is after i crashed my yardhawk several times,i replaced, and its as good as new. Ive had rough landings w all my birds, a few somersaults from the wingtip hitting the ground first but nothing broken. Were you at WOT,i never use WOT even when launching. Ive heard you might have part failure w some birds a WOT for too long of a time.
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Old Apr 22, 2007, 07:08 PM
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I always launch at half throttle, maybe a tad over if there's no wind...
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Old Apr 22, 2007, 08:04 PM
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Wow! That is an unbelievable amount of damage, sorry to hear it! It must have hit HARD to strip a carbonite servo! I can't think of anything that could be done to improve the spar strength, it may have just been a bad spar. I would just replace it with a new spar and hope for the best. Since you've broken spars before I'm sure you've noticed they break at the aluminum ferrule, there's not much that could be done to improve that short of fabricating some longer ferrules. I've broken a couple on my Yard Hawk due to hard impacts, but I've never lost one in the air. I wouldn't try to sew a repair, instead get some ripstop nylon and use contact cement to glue a reinforcement repair to it. The fuselage repair is going to be tough. I broke the head off my YH and used thick C/A and kicker, that has held fine but there's no pressure there. Good luck!

Oops, forgot to mention, you can get ripstop at a fabric store in basic colors (white, black, blue usually). If you need an unusual color you might try Aeromicro.com.
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Old Apr 22, 2007, 10:48 PM
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I'm working on a spar modification now that will be bullet proof - guaranteed to never break in any condition... will have everything up and flying soon - along with some other improvements. -QR
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Old Apr 29, 2007, 12:32 PM
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Quiet Riot,

If I'm not mistaken, you are Kelly Kendall, right? If I recall correctly you were extremely nasty to me in the past and gave me a really hard time and said you were "getting out of ornithopters" so in a way I see what's happened here as poetic justice. So let me me savor that thought for just a moment....... aah....

Okay now...in SPITE of the past I'm willing to move forward.

You did buy my product again and considering the RARE spar failure incident I am willing to bury the hatchet and help you out. I have no idea what happened and have to take what you say at face value but I am willing to apply warranty status to the event and look at the in flight spar failure as a defective part. Since the defective part led to complete destruction I will fix you up. Consider it like a "lemon law".

Oh, and once a wing tears like that it's toast unless experting repaired by me so don't even try repairing it.

If you pack up the carnage and send it to me I will replace what is needed, test fly it, and send you back a flying bird for just the cost of return shipping, so please throw in a $10.00 bill or so.. I'm at 5000 ft above sea level now so if it flies here in Wyoming it will fly anywhere. I will video my test flights of your bird as evidence that my product is sound.

Now I don't want everyone now to go claiming defective spars to get a free bird(!) but I trust most folks are too honest to do that. These cases are rare but when they do happen I try to make good. I know my birds aren't cheap so when things like this happen....as Clinton said "I feel your pain".

Send carnage to:

Sean Kinkade
52 Rolling Hills Drive
Cody, WY 82414
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Old Apr 29, 2007, 01:04 PM
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Concerning spar ferrules.....

I have done considerable research and testing and have found that no matter how much you extend the ferrule, the point where the ferrule terminates is where there is an abrupt gradient and stress riser point.
So if the ferrule is extended a 1/4 inch,3/8 inch, 1/2 inch..no matter, that's where the spar will still break on impact.

The flex of the spar along the span is also an important part of the wing flapping and flight dynamics and as you increase the length of the rigid spar ferrule the overall rigidity of the spar increases over its span and this is something to consider.

Excluding other factors that may lead to a spar breaking tat the end of the ferrule, the best way to prevent this from happening do to pure stress concentration is to reduce the stress gradient. This would theoretically be done by having the spar ferrule become more and more flexible as it extend out along the spar. I tried this in the past on the SkyBird by having a two piece ferrule...the inner part aluminum and the outer part a more flexible plastic. This had limited success.

The more likely cause for a spar failure in flight is:

1) the fit of the spar into the hole of the ferrule. The ferrule hole tolerances are held pretty close. The carbon spar diameters are held by my supplier and sometimes vary batch to batch, so it is possible the spars may be slightly smaller in diameter and this looser in the ferrule. The ferrule set screw holds the spar but any excess slop can lead to fatigue. I will scrutinize this possibility more carefully.

Also,

2) The screw that holds the spar in place MAY have been tightened too tight.
Excessive tightening of this spar keeper screw can crush the spar and start split. The split can then run out through the ferrule to the stress point and fail. One might say that a nylon tipped set screw would be better. This is a thought but I doubt the nylon tip would be soft enough to make a difference.
Some type of softer small insert for the set screw to screw down against the spar and disperse the stress but still grip would be optimal.

Even with the above possibilities, the occurences of in flight spar failure on my kits with the exisiting ferrule designs are very rare so from a manufacturing perspective no changes are really required.

Sean
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Old Apr 29, 2007, 01:19 PM
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I have found that the HS-56 servos do strip and much easier than Hitec suggests. They are okay but I stripped a bunch of them in crashes and then could only rebuild them with the aid of a lathe because the only way to extract the fragile main gear ball bearing without destroying it was to chuck the plastic gear in my lathe and machine the plastic down until the bearin came free. I didn't like that. HS-55's are much easier to rebuild.

My experience so far has been the BEST with the new Hitec HS-65 servo.
It fits right in my orni's servo cutouts.
I haven't even tried the metal gear version which I'm sure is excellent, but I have several of the plastic gear version and the gear train is smooth as silk and tough.

I now recommend HS-65's in all of my birds for at least rudder function...SH2, PH2, Shrike, and Yard Hawk. ( maybe a metal gear version in the Yard Hawk) I think this is Hitec's best micro servo yet.
You can either go with an HS-55 in the elevator servo slot and the HS-65 for rudder, or use two HS-65's for both functions.

I sell them all day for $25.00 each.
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Old May 04, 2007, 08:15 PM
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Quote:
Originally Posted by Kinkade
2) The screw that holds the spar in place MAY have been tightened too tight.
Excessive tightening of this spar keeper screw can crush the spar and start split. The split can then run out through the ferrule to the stress point and fail.
Sean, Yes, hatchet is buried and the good news is I completely forgot where I even dug the hole!...After close scrutiny, this is exactly what happened (set screw split the rod). I discovered this after my bulletproof modification however and have not had a failure yet, even after a pretty nasty nose dive from 50 feet or so - question on this later btw.

My rod mod:
I purchased a hollow shaft spar approx 10-15% thicker than stock. I then CA'd a 4" snug fitting brass rod inside the hollow rod beginning at the root of the carbon rod (ferrule end). I then drilled out the ferrule using 5 graduated drill bits so as to keep the hole true and centered.
I then CA'd the rod into the ferrule - using no set screw. Extreme heat can be used to remove the rod if necessary.

My wing repair: Applied two layers (one top, one bottom) of 2" wide nylon (thick, but not as thick as stock pocket nylon) and applied using super thin 3M laminating tape.

Servos: Replaced HS56 gears and will play the odds that they won't strip again.

Motor Replacement: Switched to E-Flite 380 Outrunner using 29 tooth pinion

Fuselage: CNC routed my own from G10

Glide lock mod:
Extended length approx. 3/8" (less dihedral - comes down slower but more parachute like glide)

Flight Test: flys beautifully with a 3 cell 960 with 30 minutes plus of relaxed flight. Will maintain altitude at less than half throttle with flap rate so slow they can actually be counted.

Only known existing and chronic problem that I need help with:
When I attempt to glide, and it doesn't lock into the sweet spot (7 out of 10 times like most folks) The bird goes immediately into a BAD nose down spiral. The CG is almost perfect so I'm really puzzled - please advise!
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