SFA Forum - Reason for inverted flying?

B.karthik

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i am beginner!!

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Reason for inverted flying?
Jun 23^rd, 2009 at 2:36am

hi friends i have built a catapult glider with the following materials:
1.fuselage:bamboo of 0.2cmthick
2.wings:biofoam of 0.4cm thick
3.tailplane:visitingcard of very tiny thickness
4.fin:visitingcard of same thick.
i testglided it near by ground at around hot 39celsius at 1.00pm with steady wind not wild.
problem:
1.it is climbing well but in inverted flying and reaches maximum height and lands with a nosedive straightly.
i dont know what could be the reason?please help this beginner
karthik

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« Last Edit: Jun 23^rd, 2009 at 2:42am by B.karthik »

glider.JPG (28 KB | )

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JoshuaF SFA Staff Offline MAXOUT Posts: 5543 Moncks Corner	Re: Reason for inverted flying? Reply #1 - Jun 23^rd, 2009 at 4:11am Keep giving it up elevator until it transitions properly. Move the CG forward as needed to eliminate stalling in the glide.
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staubkorb

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Bugs fly too!

Posts: 1063
Roedermark, Ger.

Re: Reason for inverted flying?
Reply #2 - Aug 28^th, 2009 at 4:00pm

This is a similar problem that I'm having with this mini-CLG that I had posted in another forum, but probably in the wrong thread. �The key words are "most of the time":

>built a "Round Tipper" CLG (6") by Billy Stiltner last night and had it at the field today. �I modified the design to make it a bit more suitable (read: ROBUST) for an 8 yr. old that I'm mentoring, using 3mm for the wing and adding 0.8mm doublers to the fuselage front going back to just behind the wing TE - weighs 2 grams with a coat of lacquer. �After trimming it to fly from a hand launch, I put it up with a 1/8 inch catapult. �Took a few tries before I got it to come off the top in a glide, but all I can say is that it has a rather unusual transition.

I CANNOT describe what happens as the thing is going up - it all happens too fast - but it goes STRAIGHT up and then BUNTS into level flight (MOST of the time). �It literally SNAPS FROM VERTICAL TO HORIZONTAL. �Sometimes this snap puts the model nearly inverted from which recovery occurs at 10 ft above the ground. �Really wierd but truly spectacular!!

Haven't tried a "full pull" yet, it got dark too early, but am up to 60% and averaging 30 seconds. �I am REALLY surprised at the performance of this tiny plane, and so were the RC'ers present.<

This thing is too small and fast on launch to get any idea of what's happening, and the slightest change in settings is usually too much. �A HLG launch goes well and I'm using stab tilt for glide trim. �We tried to get it on vid, but proved impossible, and the success rate is 8 from 10 launches.

Would u think a tiny bit MORE dihedral (three panel wing with 11mm at each tip - as called for) might be needed?

Pete

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Da Debbil made me doit!&&&&&&Pit (Peter Pan, Capt., 1st. Tinkerbell Support Grp., Angel Command)&&&&

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olbill Offline Forget chasing - fly indoor! Posts: 443 Decatur, GA	Re: Reason for inverted flying? Reply #3 - Aug 29^th, 2009 at 8:14am Pete Are you saying that it always bunts at 10' up? That's a pretty serious bunt! I'd add a little dihedral and a little incidence. Also make sure the boom isn't flexing too much and that the stab isn't cracked or loose or flexing too much. I think you just have to make it happier flying right side up than inverted.
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olbill

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Forget chasing - fly indoor!

Posts: 443
Decatur, GA

Re: Reason for inverted flying?
Reply #4 - Aug 29^th, 2009 at 8:21am

B.karthik wrote on Jun 23^rd, 2009 at 2:36am:

hi friends i have built a catapult glider with the following materials:

1.it is climbing well but in inverted flying and reaches maximum height and lands with a nosedive straightly.

karthik

The tail looks too small to me compared to the wing area. Also the card stock could be too flexible to stand up to catapult launching. I would maybe try a larger tail made from the same material as the wing but maybe sanded thinner.

As Joshua said more incidence is probably needed also.

Please realize that using these materials that are outside of normal model building experience makes it difficult to know exactly what is needed.

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staubkorb

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Bugs fly too!

Posts: 1063
Roedermark, Ger.

Re: Reason for inverted flying?
Reply #5 - Aug 29^th, 2009 at 2:12pm

olbill wrote on Aug 29^th, 2009 at 8:14am:

Pete
Are you saying that it always bunts at 10' up? That's a pretty serious bunt!

I'd add a little dihedral and a little incidence. Also make sure the boom isn't flexing too much and that the stab isn't cracked or loose or flexing too much. I think you just have to make it happier flying right side up than inverted.

Not 10 ft! �More like 60-80'!! �I was out again today with a �VERY brisk wind, so I only piulled about 10 inches - as opposed to the 30"+ yesterday - and was getting 40 seconds and a best time of 72 Shocked

! �I had added a buit of color to the wing so that I could a least find the thing with a bit MORE on the left wingtip. �Seems to have helped the transition Huh

Don't think there's enough area in the stab to crack at only 1/2"x1 3/4" and everything's rock solid. I had thought that flex was the culprit - could be, as I've not had a chance for a "full pull".

I have a fly-in tomorrow - generally RC - but I'm going to try to put on a small demo with a CLOUD TRAMP, �the ROUND TIP and my VIGGEN catapult jet to show the public where model flying came from, and that it must NOT be expensive.

Pete

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Da Debbil made me doit!&&&&&&Pit (Peter Pan, Capt., 1st. Tinkerbell Support Grp., Angel Command)&&&&

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B.karthik Offline i am beginner!! Posts: 33	Re: Reason for inverted flying? Reply #6 - Aug 29^th, 2009 at 6:54pm Well thanks my friends .how much should be the area of tailplane with respect to wingarea? How much should be the chord of tailplane with respect to wing chord? Tailplane span?
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tonymat

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F1B guy, but don't hold
that against me..

Posts: 415
Haliburton

Re: Reason for inverted flying?
Reply #7 - Aug 29^th, 2009 at 8:04pm

I suggest that for a catapult glider, the tailplane area be about 20% of the wing area. And I suggest that the distance from the wing trailing edge to the stab leading edge be close to 1/2 of the wing span.
The stabilizer aspect ratio (span^2/area) I like is about 3.5:1

From the pictures I think that your stabilizer area is too small, and your tail moment arm is too short.

I hope that this helps.

Regards,

Tony

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staubkorb Offline Bugs fly too! Posts: 1063 Roedermark, Ger.	Re: Reason for inverted flying? Reply #8 - Sep 30^th, 2009 at 1:49pm I've come to the realization that the problem with the tiny "Round Tipper" is boom flex. �Apparently, the more pull, the more the boom flexes. �On release, the boom whips (NOT all the time), forcing the model into a loop or dive. �I'll be gluing some carbon tow to the fuselage sides tonight. Pete
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