RC Groups

RC Groups
    R/C Blogs
        Discussion Giant super sportster pitch up problem

#1 33champ Aug 04, 2012 10:45 AM

Giant super sportster pitch up problem
 
My giant 82" super sportster has a problem. At full throttle the plane pitches up uncontrolably. Trimming doesnt help, plus i dont want to strip out the servos. So i pitched the engine down to balance out the lift, and it still pitches up majorly. I have to fly it with 80% of the elevator down just to keep it level. How can i fix this problem? Would i have to cut out the stab and adjust the stab trim? I need some advice

#2 jwellsy Jul 20, 2013 07:57 AM

Did you ever get this straightened out? It sounds like the CG is too tail heavy. I just acquired a Giant Super Sportster and this thread has me wondering if the CG in the manual is off.

#3 33champ Jul 24, 2013 10:17 AM

I am still having this problem. I have come to some conclusions-

1. Whoever built the plane messed up on the wing. The fuse length is 57" but the wing is 82". The way it sits when mounted is like an up elevator instead of just the diheydral. This causes wayyy too much lift for the elevator to balance. at half throttle and full trim, the plane actually fly's straight, but when i gun it, it shoots straight up.
2. I have no clue.....:p iv put on weights, and everything to try and get it to fly straight. They helped, but still no good. It doesn't fly tailheavy, i believe its just a wing building problem.

Do you have the giant great planes one?

#4 jwellsy Jul 24, 2013 11:46 AM

I just bought one unmolested new in the box, and was looking for info. That's how I found your thread.

I would check the wing and horizontal stab with an incident gauge.

I've noticed several planes that require different trims at different speeds. Do you have a 2.4 radio? See if your radio can mix in elevator with throttle, so the the higher the throttle the more down trim you have. That's kind of a work around, but should work.

Have you tried adding washers to the engine mount for more down thrust? That might increase your trimmed out level flight speed. But, if you get too much down thrust when you back off the throttle it will balloon up because it won't be being pulled down as much.

Do you want any measurements from this unmolested kit?

#5 33champ Jul 24, 2013 10:21 PM

I have tried the downward thrust, i truely believe the wing is too big for the fuse and it causes an uncorrectable amount of lift.
And yes, what are the specs on your giant sportster?

#6 jwellsy Jul 25, 2013 10:57 AM

The specs out of the manual say:

Wingspan: 82 in [2085 mm]
Wing Area: 1293 sq in [83.4 dm2]
Weight: 13-14.5 lb [5850-6575 g]
Wing Loading: 23-25 oz/sq ft [70-79 g/dm2]
Length: 72 in [1820 mm]
Radio: 4-5 channel transmitter, 6-7 servos
Engine: 1.60-2.00 cu in [26-33 cc] 2-stroke,
1.20-2.00 cu in [20-33 cc] 4-stroke,
2 cu in [32 cc] gas

#7 33champ Aug 07, 2013 08:10 PM

My wing is 82"
the length is 59"

something's not right!

#8 jwellsy Aug 08, 2013 10:05 PM

Mine is not put together, but I can give you some numbers for you to think about.
Fuselage length from firewall to aft vertical trailing edge : 56"
Rudder at widest point : 6"
Cowl length : 8"

Mine didn't come with a spinner, but if you figure the spinner is 2" long plus the cowl/firewall overlap, then that would all add up to 72".

#9 WILLIAM M Sep 04, 2013 09:38 PM

4 Attachment(s)
Hi guys

Someone gave me a giant super sportster wing. so I ordered the rudder/ stab ,cowl, cockpit cover and spinner.
I am making the fuse myself of balsa covered foam. today I was working on the wing cutout and the plane specs. say that the Incidences are 1" up on the leading edge, and 0" for the stab.
this is a lot in MHOP. I bet this is the reason for the pitching.

http://www.greatplanes.com/techsupport/technotes.html
The giant super sportster is down 44 planes in the list. check it out.

I will be finished in a week or so. I will post here what I find out on my build.
my power is electric, 3300 watt Motor, that is 4.25 HP. I did not put any down or right thrust in the motor mount. we will see!!!:D

Bill

#10 WILLIAM M Sep 06, 2013 07:06 PM

Bills Giant Super Sportster
 
2 Attachment(s)
Hi guys
I am coming along good on the plane. Today I mounted the stab and rudder. and cut out the turtle back from foam, and glued it on.
The wing is 1 " incidence. Since the wing is 16 " wide that is 1/16" per inch.
I raised the stab LE up 3/16 to reduce the wing to .5" incidence.
I built the stab and rudder, removable so I can make any future adjustments.
I hope this corrects the problem of pitching up.

CG: you can figure the CG here. http://adamone.rchomepage.com/cg_calc.htm

The CG at the max. and min. are 6.91" and 5.31" from LE.

The manual say's it is 5 1/4" ?????? something is not right, this will make it nose heavy.

your comments please.

Bill

#11 WILLIAM M Sep 22, 2013 06:39 PM

4 Attachment(s)
33champ

Yesterday the Giant Super Sportster I built had it's maiden flight. In the air It needed trim to 56 on the down side of the elevator. and small amounts on the other trims. There was no pitching up at full power.
It flew beautiful. upon landing it made the picture perfect landing.:D

As I said in a prior post that the specs. call for a 1" incidence, and I reduced it to 1/2" after seeing your pitch up post.
It could have been even less because I still needed a lot of down trim.:(

If I had your plane, I would recut the rudder mounting surface to give it more down.
I moved my stab on the traiing edge down 3/16" and could have done more.
I have made the rudder and stab removable so I can make any future adjustments, also I can transport it easier.

I hope this helps

Bill


All times are GMT -5. The time now is 03:40 AM.