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Need help with Astro Hog crash cause

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Old 08-03-2009, 04:00 PM
  #1
DaveB
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Default Need help with Astro Hog crash cause

I built an Astro Hog and powered it with an OS70 4 stroke engine. Crashed on the maiden flight. Normal take off, handling nicely when without warning it turned sharpley left and down and subsequently crashed. Fairly significant damage, but repairable. My first thought was interference (shot down) because of the normal take off and fine handling up to that point. Rebuilt the plane, and crashed again. This time immediately after lift off, but same result; turned sharply left and down into mother earth. This ime, I am thinking something is wrong with the radio. Repaired minimal damage and this time changed the receiver and transmitter and operated on a different channel. Same result. I have been building planes for about 25 years with good results. Have been flying for as many years also, not an expert, but not a novice either. To my knowledge, pilot error was not involved. The wing is not warped as far as I can tell, but I will be checking again with my incidence meter. Also, I had plenty of ground speed before I rotated the airplane. Any thoughts appreciated.

Thanks

DaveB
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Old 08-03-2009, 05:14 PM
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WestCoastFlyer
 
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Default RE: Need help with Astro Hog crash cause

If the engine has plenty of power and the airplane was built straight, I'd say the next logical explanation is a wing washout problem. At the wingtips is the LE higher than the TE? If so, that's washin problem, or maybe the wings are warped.

But I don't know about that airplane. The last model I saw do this was a little cub and it had a washout/washin problem.

Edit to add: Look at the left wing. Is the angle of attack of the wing greater than the right side at any point? A wing stalls first on the greatest angle of attack.

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Old 08-03-2009, 06:57 PM
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Default RE: Need help with Astro Hog crash cause

my guess is stalling with CG too far back.
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Old 08-03-2009, 07:08 PM
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Default RE: Need help with Astro Hog crash cause

I assumed when I said built straight he had the CG right. This will be really interesting to see what he finds. I've only heard good things about that model so there's no reason his can't fly great. And take off! How frustrating this certainly is for him!
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Old 08-03-2009, 09:27 PM
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Default RE: Need help with Astro Hog crash cause

Hi DaveB
Where is the CG relative to the wing LE? What is the wing cord with ailerons? Are you able to take off into the wind? Can you build up much greater ground speed prior to take off? When you lift off, are you at full throttle? It sounds like a classic wing stall. Are you certain the prop is mounted correctly? If it is mounted backward, what you have experienced can result; the plane can appear to accelerate normally but the top ground speed will be severely curtailed. Are you using a prop that is recommended for that engine?
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Old 08-04-2009, 12:47 AM
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Default RE: Need help with Astro Hog crash cause

Besides the good points already called out, wash out, wing warp, stall speed, cg, checking lateral balance, etc I would check all of your covering on the wing. The multiple layers or stripes may have a loose leading edge creating an instant turbulent condition and reduction of lift on one wing panel. I had this happen before on a multi-color wing before. I heard a slight difference in noise during flight. I thought it might be a flutter problem at first so after landing and conducting a full inspection I found no problem. I took it up again and the sound returned. It took quite some inspection time to find the loose leading edge on one of the stripes. You might also want to check your rudder for slop, improper radio mixing, etc.


Dan[:@]
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Old 08-04-2009, 05:59 AM
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Default RE: Need help with Astro Hog crash cause

Thanks for all the responses. I agree the crash certainly sounds like a typical wing stall. I will be checking and rechecking the plane to determine the cause.

The engine is an older OS-70 4 stroke with plenty of power. I am turning a 13 x 6 Master Air Screw K series prop. The plane was balanced per the plan and laterally also. I really believe I had ample speed before rotating as really let it run at full throttle before lifting off. However, I obviously missed something. I will be taking a very close look at the wing next.

DaveB
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Old 08-15-2009, 09:59 PM
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Default RE: Need help with Astro Hog crash cause

Not to overlook anything....did you range check with both engine running and off?
Intermittent gremlins, such as bad connectors, antennas, switches, battery packs (battery solder joints), semi-defective servos, etc.....can all be hard to chase down, but I've experienced defects in electronics more than once.
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Old 08-16-2009, 09:06 AM
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Default RE: Need help with Astro Hog crash cause





Dave,



I maiden my Hog 2 weeks ago with a Saito 82
and a 13x6 apc. Upon lift off mine yawed hard left,
but managed to bring her in ok. I was flying on low
rates and my right aileron had little effect. A week later
I tried her on high rates and it was much better. I had
to add weight to nose area to get her to balance. She weighs
just under 8 lbs. The control surfaces are rather small on this
plane and I think I was rotating prior to obtaining flying speed.

I kinda felt like she was under powered, but not sure.

Hope this may help you,

Bob
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Old 08-16-2009, 08:11 PM
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Default RE: Need help with Astro Hog crash cause

I had a receiver switch that would go bad, caused the same thing, intermittently on my old LT-40, and I had a servo extension that I had a bad end on, but you really had to look for it to find it. You would be flying along, and it would flip hard right without warning. It took a number of looks to find it, one of the female connectors would pull back just a small amount when coupled with the male half. It wasn't a solid error, so you could just track it down, it was very intermittent and I would not fly it anymore until I found what the cause was.
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Old 08-17-2009, 06:29 PM
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Default RE: Need help with Astro Hog crash cause

Thanks to all who have responded with crash cause suggestions.

Since the last incident I have thoroughly examined the wing and cannot find any warps. Secondly, I double and triple checked the balance and it is right on per the plans, i.e. slightly nose heavy at the main spar. Maybe another ounce or two of lead in the nose won't hurt, but I really think the balance is O.K. Thirdly, I replaced the aileron servo and increased the throws to exceed the plan specs. As suggested by Red7fifty, I will range check the plane with the engine running at full or nearly full power. Also, in as much as I experienced the same symptoms as Bob, the next time I attempt take off I will not rotate until the plane has used the entire field at full power and is "screaming" down the runway (LOL). Maybe I didn't have enough speed to take off, but I will definitely rule that in or out the next time I attempt to fly the "Hog".

I am going to give it another try in the next week or two, in the meantime, the KAOS will keep me busy.

All the best to all,

DaveB
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Old 08-17-2009, 06:57 PM
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Default RE: Need help with Astro Hog crash cause

Dave,

You might check the engine thrust line. I once saw an experienced pilot maiden a friends Hog Bipe. The friend had followed the plans which he said showed no offset thrust. The plane was almost uncontrollable at more than 1/2 throttle even with full right rudder. After offsetting the thrust a couple of degrees, it flew well.

pmw
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Old 08-17-2009, 10:02 PM
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Default RE: Need help with Astro Hog crash cause


Quote:
ORIGINAL: pmw

Dave,

You might check the engine thrust line. I once saw an experienced pilot maiden a friends Hog Bipe. The friend had followed the plans which he said showed no offset thrust. The plane was almost uncontrollable at more than 1/2 throttle even with full right rudder. After offsetting the thrust a couple of degrees, it flew well.

pmw

Dave,

pmw nailed it.

I plan on putting a couple of washers on my engine mount.
In hopes to off set the Adverse Yaw.

Bob
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Old 08-18-2009, 04:30 PM
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Default RE: Need help with Astro Hog crash cause

Thanks for the suggestion to add offset. I built the Hog with zero offset per the plans, but I agree a couple degrees of right thrust is worth a try.

DaveB
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Old 08-19-2009, 02:07 PM
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Default RE: Need help with Astro Hog crash cause

wanted to add this thought.....I and I always teach full power on take offs and go arounds until a positive rate of climb is established. Then you can reduce the throttle.....better to have the power and not need it then to need the power and not have it......just in case it was a stall
Best of Luck
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Old 08-20-2009, 08:43 PM
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Default RE: Need help with Astro Hog crash cause

Look at your rudder servo wiring. Aileron too. Had a very similar, but it was a intermitent problem. after much inspection I found one of the 3 wires on the rudder servo was kind of partially cut (previous crash).
looking quickly it would not show any problem, but upon close inspection on the wire cover I could see it has a cut, which also cut the wire but they were still contacting, hold by the wire cover. I believe once in the air, engine vibration would make the two pieces of wire make or break conact.
To check , I started bending the wire and then servo started twisting back and forth. in fligth it would cause the scary glitch like behavior. replaced the servo, problem is gone
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Old 08-27-2009, 09:59 PM
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Default RE: Need help with Astro Hog crash cause

Make sure your CG is at the forward most position shown on the plans, you can change it later to do aerobatics. If it is leaning toward or over the furthermost rearward position, it could put you into an immediate stall and torque will roll you in at that point. Just be prepared to add some right rudder to compenstate any adverse yaw on takeoff, but the CG is the #1 place to start to check for the problems you are having. Good luck!
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Old 09-03-2009, 06:52 PM
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Default RE: Need help with Astro Hog crash cause

After increasing aileron throw, adding a small amount of right thrust, and adding a little weight to the nose, even though the plane was balanced beforehand, I tried again for a successful flight; NOT!

After using about the length of the field and holding her on the grass, I attempted take off. The plane lifted off but was very unstable and basically out of control. I was able to land without damage, but what a handful it was. In as much as I can't find any problem structurally, I have concluded that my "Hog" is under powered. I have an older OS FS70 4 stroke, which I felt would be O.K., but after 4 unsuccessful flights, I believe it needs more power. So..., I will be replacing the 70 4-stroke with a new OS-61 2 stroke in the coming days or weeks, or whenever I get around to it. In the mean time, it's back to the "Kaos" and "Super Sportster".

Comments appreciated.

DaveB
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Old 09-04-2009, 07:51 AM
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Default RE: Need help with Astro Hog crash cause

It seems you are satisfied that you have found the problem and I to am of the school that anything can fly with enough power (F-4 Phantom). So, I would like to say... What a beautiful plane! Is that SolarTex covering?
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Old 09-04-2009, 08:43 AM
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Default RE: Need help with Astro Hog crash cause

Mr67stang,

Thanks for the compliment. It is indeed Solartex, with a light spray of poly urethane.

DaveB
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Old 09-04-2009, 08:53 AM
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Default RE: Need help with Astro Hog crash cause



Good luck Dave,

Let us know how it goes with the 61.
I'm going to fly my hog again this weekend
with my Saito 82 again. I'll be sure and use
more runway before I rotate.

Bob
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Old 09-06-2009, 02:34 PM
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Default RE: Need help with Astro Hog crash cause

Dave,

I am very sorry to hear of your problems. I have an Astro-Hog too, and they are a lot of work to build and cover! Icannot imagine the frustration you are feeling. I wish Iknew what your problem is. Mine is powered with a Saito .91. 14x6 prop. I usually rotate around half-throttle and fly at half throttle or lower as well. Ihave no right thrust. Mine has always been docile like a trainer. Was your elevator overly sensitive that last flight? It seems like you may still be tail-heavy. The Hog is such a solid flyer that I would think it could fly through almost any problem except tail-heaviness. Good luck!
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Old 09-06-2009, 02:52 PM
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Default RE: Need help with Astro Hog crash cause

Sig says it will fly on a .60 - .70 4cycle engine. When you balanced this plane, did you balance it inverted or upright? Low wingers are usually balanced upside down on their CG. Double check your CG again inverted if you did not do this when you first balanced it. It just sounds like a problem with the balance point when you talk about it being almost uncontrollable, your .70 should have been able to pull it around smooth enough to enjoy some soft flying with it. This is a very predictable plane, that is why it is still around today after over 50 years, good luck with it!
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Old 09-07-2009, 05:07 PM
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Default RE: Need help with Astro Hog crash cause

Dave, any luck over the weekend?
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Old 09-07-2009, 07:27 PM
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Default RE: Need help with Astro Hog crash cause

I haven't had a chance to change engines and probably won't get around to it for a while. I do have other planes to fly so I am O.K. in that regard.

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