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Dr.J Bipe Pics - 8/29/2003 6:17:32 AM   
mc71



Posts: 173
Joined: 3/17/2003
From: Wollongong, AL, AUSTRALIA
Status: offline 		c'mon it's friday here already.

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Dr.J Bipe Pics - 8/29/2003 11:00:45 PM   
Jeff-RCU


 

Posts: 349
Joined: 3/8/2002
From: columbus, IN, USA
Status: offline 		Ok, got four short flights today on the biplane. And all you guys that said there would be strange couplings..................we're right (kinda)! Actually the only noticeable occurence is rolling and diving in the direction of rudder application. The first flight scared me to death on rudder, then I mixed in the wrong aileron direction and things got worse the second and third flight! Finally with Steve Maxwell's calm advice, I got the right mix direction in. It's better, but still not good (with 15% aileron mix). Also had some elevator vibration where you could see the whole stab oscilating. I"m going to stiffen up the rear end of the plane before I fly it again. SHould I change the dihedral of the wing to fix this or just mix it out? If I do change dihederal, which way and on what wing?

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Dr.J Bipe Pics - 8/29/2003 11:10:03 PM   
JWN



Posts: 4954
Joined: 3/26/2002
From: Florence, TX, USA
Status: offline 		If it rolls to the right with right rudder, you have too much (effective) dihedral. Since decreasing the dihedral on the lower wing will decrease your wing tip to ground distance (more likely to tear up the tips on a bad landing) I'd suggest changing the top wing. Another reason for adjusting the top wing is that it is the one causing the coupling. It's larger than the bottom wing and above the center line. Don Lowe showed a picture of an EZ Citabria several years back where the owner actually turned the wing upside down, since it was symetrical, and the resultant anhedral resolved almost all of the roll couple. But, I'd take care of the rear of the fuse first as it could very well change the roll coupling (if the tail is twisting) and give you a better feel of how much to change the wing.

Keep working on it! Trimming a pattern plane is one of those processes that can take a while, but well worth the efforts once you get everything dialed in.

John

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Dr.J Bipe Pics - 8/29/2003 11:21:26 PM   
3dUkidding!


 

Posts: 148
Joined: 2/27/2003
From: rugby, UNITED KINGDOM
Status: offline 		Jeff

Stunning plane!! sounds like that stab vibration could get interesting....could it be flutter? with all the tubulence off two wings?

Bla Bla

Regarding your earlier comment about unscrewing the pump on the OS140. Do you mean anticlockwise viewed from the back of the engine?

I really could do with a little more duration on a tankful as over here it is costing me about £3 to £4 per flight in fuel!!

My current set up is standerd header and hatori pipe with about 1/4 inch gap between header and pipe (Sorry don't know the length) OS F plug (fantastic move that!) and running on 18% oil and 18% nitro.

What fuel are you guys running as 10% nitro is sooooo much cheaper here. I'm thinking of 15% oil and 10% nitro and maybee unscrewing the pump 1 turn. Does this sound lik the right direction?

Thanks in advance

Rich

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Dr.J Bipe Pics - 8/30/2003 12:46:37 AM   
Jeff-RCU


 

Posts: 349
Joined: 3/8/2002
From: columbus, IN, USA
Status: offline 		Evidently its somthing about a biplane that is causing the effective dihedral as both wings were built with no dihedral. I would assume it would be better to cut the top wing and add anhedral than try to mix it out with the radio?

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Dr.J Bipe Pics - 8/30/2003 1:06:12 AM   
JWN



Posts: 4954
Joined: 3/26/2002
From: Florence, TX, USA
Status: offline 		If you can mix out the coupling with the radio, and the model flies clean at all airspeeds with the mixes, personally, I'd leave it at that. In many cases, the mixes change a bit with different air speeds and this is where modifying the air frame comes into play. You're going to need to get the mixes close and compare the behavior at different flight speeds. Then, decide if the difference, if any, warrants cutting into the air frame.

John

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Dr.J Bipe Pics - 8/30/2003 2:26:12 AM   
Slow Rollin'



Posts: 47
Joined: 6/9/2002
From: Columbus , IN, USA
Status: offline 		It looks great Jeff. Your paint jobs are getting better too!

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Dr.J Bipe Pics - 8/30/2003 4:01:25 AM   
turbo-RCU


 

Posts: 29
Joined: 12/17/2001
From: West Tx
Status: offline 		Several years ago (like 1990), Don Lowe discussed the modifications he had done on a Ultimate bipe. He used annehedral on the top wing and positive incidence on the horizontal stab to eliminate the roll coupling. all this info was in the Flying Lowe RCM column.

I built my own design ultimate using his recommendations and it flew very well with much less coupling than other bipes I had flown. I will try and find the exact numbers for you, but I am hoping this might 'jog' someone else's memory.

I have really enjoyed following this project of yours.

Good luck,
turbo

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Dr.J Bipe Pics - 8/30/2003 4:04:40 AM   
JWN



Posts: 4954
Joined: 3/26/2002
From: Florence, TX, USA
Status: offline 		I forgot about that!

The Precision Built Ultimate bipe (originally flown in the TOC by Chip) has positive in the stab. IIRC, it's +3 degrees. I always thought that was a lot, but apparently it works out quite well.

John

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Dr.J Bipe Pics - 8/30/2003 9:04:04 PM   
Cdallas2



Posts: 547
Joined: 2/7/2002
From: Kamloops, BC,
Status: offline 		I did here that Christophe was in the area of %15 rudder mix on the Suxxess - so that doesn't sound too far off.

You are also probably getting some downwash off the top wing which isn't helping matters any.

Looks good though. Keep us updated after you fix up the tail.

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Dr.J Bipe Pics - 8/31/2003 2:11:48 PM   
bla bla


 

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Joined: 9/19/2002
From: Oslo, NORWAY
Status: offline 		[QUOTE]Originally posted by 3dUkidding!
Jeff


Bla Bla

Regarding your earlier comment about unscrewing the pump on the OS140. Do you mean anticlockwise viewed from the back of the engine?


Yep, anti clockwise, did it in half turn steps.
Now at 1.5 turn from the factury setting.
I followed exactly what was beening said in the Jim Oddin article.

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Dr.J Bipe Pics - 8/31/2003 6:32:25 PM   
Jeff-RCU


 

Posts: 349
Joined: 3/8/2002
From: columbus, IN, USA
Status: offline 		Thanks for the advice. I'll fix up the tail first and then fly it to see if I can get the rolling mixed out on aileron. I now know why pattern people don't mess around with biplanes! Lot of work to get one to fly right.

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Dr.J Bipe Pics - 9/2/2003 1:34:47 PM   
mrbonk



Posts: 600
Joined: 2/18/2002
From: BundabergQueensland, AUSTRALIA
Status: offline 		[QUOTE]Originally posted by Jeff
Thanks for the advice. I'll fix up the tail first and then fly it to see if I can get the rolling mixed out on aileron. I now know why pattern people don't mess around with biplanes! Lot of work to get one to fly right. [/QUOTE]

Just about all the 'top' pattern guys are going for biplanes at the moment. Chip's flying one, as is Christophe (sp?), the Japanese team and the UK team (sorry, can't remember pilot names there). Bloke in my club made his own design bipe recently......I got a test flight and it's sweet to fly, but did take some mucking around with mixes to get right. Worth it for the looks though I reckon......there's nothing that looks as good as a bipe in the air


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Dr.J Bipe Pics - 9/4/2003 8:29:14 PM   
Jeff-RCU


 

Posts: 349
Joined: 3/8/2002
From: columbus, IN, USA
Status: offline 		Put three more flights on it last night. I have managed to stop the tail flutter by stiffening up the fuselage just in front of the stab. Some observations:
1) it doesnt fly tail heavy, but it climbs slightly in knife edge.
2) the rudder is incredibly sensitive at speed, so much that a knife edge looop is about 20 feet in diameter.
3) I've got 50% mix in the aileron and it still rolls slightly on rudder application.
4) I've got the dual rates down to 25% on rudder, but of course it won't stall turn with that, so to fly the schedule, I'll have to go back and forth between rates (or mix it into the throttle).
5) except for the rudder, it flies exactly like a Dr J. The extra wing area really doesn't slow it down for landings like I thought it would. Evidently this is a very low drag configuration.
6) Oh yeah, ailerons are also extremely powerfull. I may disconnect the bottom wing ailerons and just have them come on for the rudder mix.

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Dr.J Bipe Pics - 9/4/2003 8:46:32 PM   
JWN



Posts: 4954
Joined: 3/26/2002
From: Florence, TX, USA
Status: offline 		#1 - Could this be related to #4? You might be breathing a little hard on the rudder causing the climb. If not, you could always move the CG forward just a little to see what it changes.
#4 - I'd mix the rudder to the throttle. I don't remember what radio you are using, but it more than likely has a high/low throttle auto rate for the rudder as one of the options.
#6 - You might want to consider going to less throw instead of disconnecting the lower ailerons. I would expect your rolls to barrel a bit trying to use just the top wing ailerons.

Ahh, the joys of trimming a new design

John

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Dr.J Bipe Pics - 9/4/2003 11:13:30 PM   
Jeff-RCU


 

Posts: 349
Joined: 3/8/2002
From: columbus, IN, USA
Status: offline 		Thanks for the input.

1) It climbs slightly in knife edge without any rudder input! Which means slow rolls are incredibly easy. That's why I thought it was tail heavy, but up and down lines are almost perfect (no tuck or pull). and stalls are slow and easy.

4)I've got the futaba 8channel, so of hand I'm not sure of what throttle mixes I have.

6) Without serious work, about the only thing I can do now is use the ATV to reduce throws as I'm maxed (minned?) out mechanically. Doesn't take much throw with 4 ailerons!

Jeff

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Dr.J Bipe Pics - 9/4/2003 11:20:39 PM   
JWN



Posts: 4954
Joined: 3/26/2002
From: Florence, TX, USA
Status: offline 		Jeff,
What type of control horns do you have on the ailerons? Would it really be that much work to replace them with something longer?

Climbs on knife edge without any input? Wow, I could have used that when I was flying in competition. Heck, it would be great to have that just farting around

John

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