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Old Jun 27, 2001, 03:25 PM
Registered User
Tulsa, Oklahoma
Joined Oct 2000
26 Posts
The Twin Jet CG and Down Elevator Mystery - Part 2

I flew my Twin Jet for the first time yesterday and crashed it (that's the first time I have ever crashed a plane on the very first flight). The good news is the crash had nothing to do with CG or down elevator problems. Here's the story:

Kit motors and props, eight, 2,000 mAh cells, deflections by the book, balanced on the bumps, elevons at neutral. Tricycle gear with steerable nose wheel as described in earlier posts.

Dead calm at 7:30 in the morning. Plane refused to ROG after screaming down 400 feet of smooth asphalt with full up-elevator. Tried again with second fresh battery pack, same result. Bent mains up so as to increase angle of attack, still no fly. Nose wheel strut extension is (was) not adjustable, so further attempts to increase angle of attack could not be made.

I am satisfied that (lack of) angle of attack was the problem. If the nose wheel had been about an inch or two lower, or maybe even if there had been a 5 mph breeze down the runway, it might have been a different story. I welcome your thoughts.

Since the little jewell wouldn't take off, I had a friend hand launch it. I was immediately pleased (and a bit surprised, in view of some of the earlier posts) to find the plane to be quite docile, not the least bit twitchy, and, most interestingly, needing NO down trim to fly straight and level at full throttle.

Now the bad news: At the time I was flying, about 8 o'clock in the morning, the sun was high enough that it was well above the bill of my cap, so being blinded by it was not a possibility. But as I flew under the sun about 25 feet off the ground, the plane suddenly became a silhouette and I lost the sense of attitude that the yellow top and black bottom otherwise gave me. Well, I saw a wingtip go up, guessed that it was turning right (bad guess), gave it a little left and the next thing I knew it was in the ground. The plane is fast! Extensive EPP damage, a broken receiver crystal. Fortunately, the EPP is easy to stick back together with slow CA.

The crash completely destroyed my steerable nose wheel assembly. I did not re-create it, but will hand launch for a while to learn more about how the plane handles. Maybe later.


Back in the hangar after the crash. Depressing isn't it?


After about two hours of reconstruction work it's almost ready to paint.

At the time of this writing the plane is once again ready to fly.

Bob

[This message has been edited by rltucker (edited 06-27-2001).]
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Old Jun 27, 2001, 05:22 PM
Fish & Fly
DaJudge's Avatar
Tyler, TX USA
Joined Jul 2000
1,406 Posts
Ahhh. You found the weak spot in the TJ fuselage. Mine has suffered there as well, but I hadn't broken it completely in half as you did.

Now is the time to replace that silly balsa spar with an aluminum hunting arrow or CF.

I'm betting that you'll eventually get this plane to ROG with a longer nosewheel.
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Old Jun 27, 2001, 05:37 PM
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Joined May 2000
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RL,

I crashed my first one as well, I think primarily from painting it sky cammo and loosing orientation. I have been flying my 2nd one (the new version) for probably 100 flights, and I keep that rascal as high as possible and have orange and yellow graphics on the wings and I can see it way better. I think you'll see a lot of TJ crash posts until everyone gets used to this higher performance stock foamie.

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Old Jun 27, 2001, 05:56 PM
EDF all the way!
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Gilbert, Az
Joined Jun 1999
7,983 Posts
I noticed the you have the canopy attached to the aft foam piece. I glued mine in place per the instructions. A friend did not on his, first flight you could see the wing flex under high "G" manuvers. After landing we quickly glued it in place and the flexing disappeared. Did you notice any wing flex in yours?
Bob Ruff
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Old Jun 27, 2001, 06:16 PM
Registered User
Tulsa, Oklahoma
Joined Oct 2000
26 Posts
No, I didn't see any flex, but I didn't attempt any aerobatics, either. Thanks for mentioning it... I will watch carefully next flight.

Bob
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Old Jun 28, 2001, 07:37 AM
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St. Paul, MN
Joined Feb 2001
337 Posts
I was wondering about the aft piece of the canopy as well. When I first saw yours, I thought 'cool, he can get at his components easier than me!'. Let us know about the flex. Mine is glued in tight.

Flew mine (stock setup with reciever aft of battery) for the first time this weekend. A little intimidating with the weight of 8 x 2400's, but flys great. Still feeling her out - not doing anything crazy. My test pilot did some great-looking low rolls on her maiden flight so I know a lot is possible.

Chad
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Old Jun 29, 2001, 06:53 AM
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Virginia Beach Va
Joined Oct 2000
217 Posts
I'd like to see more on the steerable nose wheel assembly, haven't found the posts on it.....
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Old Jun 29, 2001, 01:48 PM
Registered User
Tulsa, Oklahoma
Joined Oct 2000
26 Posts
You can see and read all about it at the following ezone address:
http://www.ezonemag.com/disc/Forum12/HTML/002371.html

Thanks for the inquiry.

Bob
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Old Jun 29, 2001, 02:21 PM
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St. Neots, Cambridgeshire,UK
Joined May 2001
13 Posts
Quote:
Originally posted by rltucker:
I flew my Twin Jet for the first time yesterday and crashed it (that's the first time I have ever crashed a plane on the very first flight). The good news is the crash had nothing to do with CG or down elevator problems. Here's the story:

Kit motors and props, eight, 2,000 mAh cells, deflections by the book, balanced on the bumps, elevons at neutral. Tricycle gear with steerable nose wheel as described in earlier posts.

Dead calm at 7:30 in the morning. Plane refused to ROG after screaming down 400 feet of smooth asphalt with full up-elevator. Tried again with second fresh battery pack, same result. Bent mains up so as to increase angle of attack, still no fly. Nose wheel strut extension is (was) not adjustable, so further attempts to increase angle of attack could not be made.

I am satisfied that (lack of) angle of attack was the problem. If the nose wheel had been about an inch or two lower, or maybe even if there had been a 5 mph breeze down the runway, it might have been a different story. I welcome your thoughts.

Since the little jewell wouldn't take off, I had a friend hand launch it. I was immediately pleased (and a bit surprised, in view of some of the earlier posts) to find the plane to be quite docile, not the least bit twitchy, and, most interestingly, needing NO down trim to fly straight and level at full throttle.

Now the bad news: At the time I was flying, about 8 o'clock in the morning, the sun was high enough that it was well above the bill of my cap, so being blinded by it was not a possibility. But as I flew under the sun about 25 feet off the ground, the plane suddenly became a silhouette and I lost the sense of attitude that the yellow top and black bottom otherwise gave me. Well, I saw a wingtip go up, guessed that it was turning right (bad guess), gave it a little left and the next thing I knew it was in the ground. The plane is fast! Extensive EPP damage, a broken receiver crystal. Fortunately, the EPP is easy to stick back together with slow CA.

The crash completely destroyed my steerable nose wheel assembly. I did not re-create it, but will hand launch for a while to learn more about how the plane handles. Maybe later.


Back in the hangar after the crash. Depressing isn't it?


After about two hours of reconstruction work it's almost ready to paint.

At the time of this writing the plane is once again ready to fly.

Bob

[This message has been edited by rltucker (edited 06-27-2001).]
I had the same problem with my tricycle gear. You have to have the mains right on top of the centre of gravity or the elevons just dont have enough grunt to rotate. It has to rotate (lots) before it'll take off so you need to make sure the props cant touch the ground by changing the balsa strip for something stronger and extending it out the back about an inch. I can get mine to lift off in the length of an asphalt tennis court (400s 7 cells, standard props). Extra weight extends the run a lot so dont make it too heavy unless you have lots of room.
DG.

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Old Jun 29, 2001, 10:26 PM
Registered User
Tulsa, Oklahoma
Joined Oct 2000
26 Posts
You make a very good point, Dave, when you say put the mains on the CG. That would certainly make it easier for the plane to rotate. Now that you mention it, I'm wondering what I was thinking when I put my mains four inches from the tail end. The plane never had a chance of rotating, especially with the nose wheel strut set so that the fuse was parallel with the ground.

Still, even with the mains four inches from the tail end, I think the plane would take off if the nose wheel strut is long enough to give a high enough angle of attack. It might even do so with the elevons at neutral. The downside may be that the nose might have to be so high that the plane would look ridiculous. I'll check it out if and when I put a steerable nose wheel back on my TJ.

Thanks for your input.

Bob
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