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64 Thousand Dollar Question in Pattern Flying

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64 Thousand Dollar Question in Pattern Flying

Old 06-29-2014, 04:23 AM
  #26  
Malcolm H
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Apologies that the auto spell checker didn't catch my "here" "hear" mistake!

M
Old 06-29-2014, 05:45 AM
  #27  
Ryan Smith
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A larger fuselage isn't necessarily easy to see...there are a lot of factors involved. The Splendor is a big airplane and sometimes was invisible in the air. I'm not convinced that a gigantic fuselage is the answer. Seba's airplanes have been on the smaller side and it hasn't affected him at all. I think a well-balanced fuselage is the answer.

I think ink pertaining to this issue, having a "tight" airplane is key, so making adjustments as you've done to the strut mounts I see going a long way. As with most things related to F3A, I am under the impression that it's not one big thing, rather several small ones. I'm sure pilot technique is applicable to a degree as well. I'm very close friends with Quique Somenzini and was his caller for Argentina and Portugal. I've flown with him a bunch and built/wrenched on airplanes for him. I can tell you that he's quite particular with the build and setup of his F3A models and does a lot of things that seem ritualistic, but clearly have some merit as his airplanes were always settled in the air. I don't have the luck to fly with Andrew Jesky on a regular basis, but know that he tweaks and tunes models a lot. CPLR is a mystery to me, but is clearly quite skilled in this department as well.

I wish you all the luck in the world. I hope that as you try some things out, you report back here with your findings! Curious minds want to know.
Old 06-29-2014, 06:42 AM
  #28  
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Hi Malcolm,

Ryan makes a good point re 'several little things V one big thing'.

I put the shims at the toes and heels - it increases the chord of the contact points some and is easier to fine tune.
See the picture ;

Brian
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Old 06-29-2014, 06:59 AM
  #29  
Malcolm H
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Good point Brian! I didn't spot that one but I still think the work I've done today was worthwhile. Going to make me some stick on tip fences next.

Malcolm
Old 06-29-2014, 08:07 AM
  #30  
flycatch
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Originally Posted by Malcolm H
Flycatch,

You know its snide smartass posters like you that are gradually stopping people who genuinely want help and to promote informed debate to come on here and ask for it.

I posted this thread with a humorous subject line because I'm at a loss what to do with my expensive dud and all you can do is take a cheap shot.

Thanks for that,

Malcolm
Call me names for pointing out the obvious. You posted a question that you already knew the answer for didn't you? People do it all the time but just can't accept the truth. Go ahead and shoot the messenger but it does not change anything.
Old 06-29-2014, 08:57 AM
  #31  
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Originally Posted by flycatch
Call me names for pointing out the obvious. You posted a question that you already knew the answer for didn't you? People do it all the time but just can't accept the truth. Go ahead and shoot the messenger but it does not change anything.
How do you add ballast to a model that is already at the max,, allowable weight ?????
Old 06-29-2014, 09:03 AM
  #32  
Ryan Smith
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Originally Posted by flycatch
Call me names for pointing out the obvious. You posted a question that you already knew the answer for didn't you? People do it all the time but just can't accept the truth. Go ahead and shoot the messenger but it does not change anything.
Many more facets to his question than simply adding ballast, so no he didn't already know the answer to the question he was asking. Perhaps best not to come across as you did when it's clear you know little about the subject as it relates to the facet of modeling.
Old 06-29-2014, 12:14 PM
  #33  
em14
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Malcom I have learned much from this thread. Thanks for starting it and the best of luck in finding the answer to the question you ask!
Leo
Old 06-29-2014, 12:33 PM
  #34  
Jason Arnold
 
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Hi Malcolm,

I meant to say bobble in vertical rolls up or down. That probably makes more sense...

FWIW, flying a biplane in the wind is probably of no advantage. Do you think that may be why some have a mono and a bipe and swap between the two depending on conditions?

Cheers,
Jason.
Old 06-29-2014, 01:20 PM
  #35  
dwaynenancy
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Malcolm, thanks for the thread. I have no input but I like reading the output.
Old 06-29-2014, 06:33 PM
  #36  
Dean Pappas
 
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Hello Malcolm,
What is interesting is that you describe the airplane as becoming noticeably unstable in yaw with an aft CG adjustment ... I strongly suspect that you are simply less unstable in yaw now.
Add side area in the tail: and I don't mean a measly 10 square inches per side, but at least 25 squares per side. I had 15 square inches per side of extra side area glued to the underside of the stab of my ARIEL back in the early 90's. That's what that airplane required in my opinion. It looped nicely outside, but in lumpy or crosswind conditions, it would drop a wing on insides. I think you have a yaw-roll couple issue.
1mm Perspex will be invisible at 150m!
Cheers,
Dean Pappas
Old 06-30-2014, 12:02 AM
  #37  
Malcolm H
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OK Dean,

That is a very interesting point you make regarding yaw/roll couple. This model has other issues that I was deliberately keeping out of this thread because I didn't want to cloud the bobbling about issue but maybe they are related.

Over the last few years I have been used to being able to get a pretty much mix free model by using Bryan Hebert's trimming method. That is set the CG by the knifedge behaviour, forward if it goes to belly and backwards if it goes to canopy. Then add incidence to correct pull to canopy in uplines. When I installed the Contra in this model I knew it would be a little nose heavy but decided to fly it like that anyway. Lo and behold a strong pull to the canopy in knifedge. So I started moving the CG back and got way behind the designer's recommended position and still a slight pull to canopy but now slight directional instability. So I moved the CG forward to Suzuki's recommended point and started to add a rudder/down elevator mix to straighten the knifedge. But now I noticed proverse yaw/roll coupling and have a small rudder opposite aileron mix to correct this. So yes Dean, maybe what I'm seeing is that yaw/roll coupling causing the wings to move about and this is something else to investigate.

Looks like I need to make some tail strakes as well as tip fences!

Malcolm
Old 06-30-2014, 12:45 AM
  #38  
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Hi Malcolm,
Not having witnessed the issue makes diagnoses difficult but it is also likely that Dean's point has relevance here.
When we were discussing the CG position (offline) I suggested to move it back and then to address the yaw issue separately.

So if it were mine I would ;

-Set those wing incidences tight and correct re each other - good meter req'd - Cocked wing tips will have high drag and feed in as yaw as well as roll.
-Move the CG back - 20mm further back would be a good point to start, based on the Midrex.
-Add yaw stability - a decent rudder flair is what I would go with to start with - you say the model is slippery so it can wear some drag - the flair also helps with rudder control at centre.

Brian

Edit ; Malcolm, we posted at the same time !!

Last edited by serious power; 06-30-2014 at 12:48 AM.
Old 06-30-2014, 12:59 AM
  #39  
Malcolm H
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Brian/Dean,

Of course the Contra moves the NP forward, reducing the static margin so I'm leaning towards devices which recover that loss.

Malcolm
Old 06-30-2014, 07:49 AM
  #40  
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Malcolm,

Installing the rear fences will help the apparent yaw destabilization. But these add weight in the wrong place.

Another approach if it were a mono would be to move the wing forward. But as a bipe, it's triple the trouble so adding the fences may be about the only option.

Proverse-adverse roll couples can be changed considerably when adding wing fences near the fuse CL. Instead of orthogonal placement, the fences could be angled to either remove or add dihedral effect. The model may still need some mix (depending on area and angle of the fences) but it will be reduced and may not compromise the rest of the flight envelope
Old 07-01-2014, 08:21 AM
  #41  
Jeff Worsham
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Originally Posted by Dean Pappas
Hello Malcolm,
What is interesting is that you describe the airplane as becoming noticeably unstable in yaw with an aft CG adjustment ... I strongly suspect that you are simply less unstable in yaw now.
Add side area in the tail: and I don't mean a measly 10 square inches per side, but at least 25 squares per side. I had 15 square inches per side of extra side area glued to the underside of the stab of my ARIEL back in the early 90's. That's what that airplane required in my opinion. It looped nicely outside, but in lumpy or crosswind conditions, it would drop a wing on insides. I think you have a yaw-roll couple issue.
1mm Perspex will be invisible at 150m!
Cheers,
Dean Pappas
Appreciate very much the intricacies and some of the conflicts we experience in trimming that are being discussed in this thread. I hope not to derail that with a quick side question for clarification: how can one test to know if the side area to be added should be greater above the stab, below the stab, or equal? IE: the stab fences that BJ Craft included with the Prolog and Nuance are of equal area above and below while the ones that were installed on my Sebart Wind S Pro have more area below the stab.
Old 07-01-2014, 08:28 AM
  #42  
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Hi Jeff,
Maybe you're over thinking this. The side area I added to the ARIEL was all on the bottom because of aesthetics. Most people never ever knew they were there!
The 1" tall strakes or fences, that folks are adding to tails these days, could easily be 2" tall and hidden on the bottom. I also suspect that they are undersized, generally speaking.
take care,
Dean
Old 07-01-2014, 08:36 AM
  #43  
Jeff Worsham
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Thanks Dean! If there's a way to over think or complicate something, I'll usually find it!
Best regards,
Jeff
Old 07-01-2014, 08:44 AM
  #44  
Malcolm H
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OK had a very interesting day at the field today. Went to our airfield site which is a combination of paved runways and large grass areas. It was warm for Scotland, 23-24 C, and a light breeze. Perfect thermally conditions and big bumps when you fly over the paved/grass transitions.

Had a flight with the model as previously flown except for the work done tightening up the strut ends and realigning one end. Only difference noted was a couple of clicks of aileron trim due to the strut now not twisting the bottom wing slightly to enter the top fixing. Lots of wing dropping and bobbling about in the bumpy air.

Then stuck on the 6mm Depron fences shown in pics with double sided tape. Total transformation! Much steadier and virtually no wing rock! It would still drop the odd wing in the big bumps but so did my colleagues Mythos which is usually rock steady. It was a particularly bumpy day. Just can't believe the difference a few bits of foam make!

Now need to engineer something permanent. Not sure whether to make fixed or removable. I have some 3mm carbon/Herex sandwich but can't see how to radius the cut edge simply. Probably won't make any difference aerodynamically but esthetically not nice to leave square.

I'm sure Brian and Matt will have some ideas!

Malcolm
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Old 07-01-2014, 09:23 AM
  #45  
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Now that's interesting! Also good news ...
Dean
Old 07-01-2014, 11:27 AM
  #46  
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Good news Malcolm
I had similar results with 3mm depron as in my previous post.
I'm no aesthete, so I just cyanoed the depron to masking tape stuck on the (filmed ) surface, and left it at that.
Surprisingly little damage over about 70 flights so far---can't use wing bags though, so the wings are transported loosely wrapped in my dogs' duvet...
Old 07-01-2014, 12:07 PM
  #47  
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Malcolm,

It's good to hear the small winglets solved your problem. You might want to check these posts too:
http://www.rcuniverse.com/forum/elec...l#post11194747
http://www.rcuniverse.com/forum/elec...l#post11194764
http://www.rcuniverse.com/forum/elec...l#post11202318

Quotes from the posts above:
"I modified my wings with winglets like the Wind S Pro GFK version the bubble tips these seem to work better than the flat ones used on the Oxai Citrin. I also have them on the tips of the stabilizer for rock solid flight in windy conditions."
"I personally think that it has something to do with the aerodynamics since the bubble version is smoother compared to the regular thin fins wich are noticable nervous during turbulent weather. I tried different styles with the thin fins, toe in and out and straight. Also experimented with height and dept. Because I fly a bipe it is more work and harder to notice the differences.
The bubbles on the stabilizer give me a big difference in loops the tail of the plane tracks better."


I hope this helps.

Alex

Last edited by Alex Voicu; 07-01-2014 at 12:11 PM.
Old 07-01-2014, 05:43 PM
  #48  
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Great info guys. I'm currently trying to dial in a 150cc Extra and so far all the trips to the flying field has had wind and bumpy air. The wing fences are something that I may have a go at. I'm wondering if something like a tall teardrop shape would be effective. Being an IMAC airplane I'm not sure what I will be able to get away with let alone get into the wing bags. I think I will start carving on some blue foam and attach with double sided tape. If I come up with something that works it would be easy enough to make a mold and lay up some glass parts. Thanks again for some insight and please keep the info share moving.
Old 07-02-2014, 03:59 AM
  #49  
Malcolm H
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Alex,

Thanks for the links, all of which I have seen but somehow forgot!

The bubble winglets are attractive from a structural point of view because I think there is enough base area to attach them with double sided tape and no mods to the wing. I'm actually thinking of 3D printing them hollow and completely closed in one piece with a very thin wall so they will weigh virtually nothing.

What I don't know is how high they would need to be made to work. I arbitrarily chose 25mm high for my Depron ones but it would be nice to reduce this a bit for the bubble version. Also is the bubble the same width as height i.e. 1/4 circular looking on the rear? I don't have a lot of time to sort this so don't really want to have to do another Depron trial if I can get away with it.

Your help appreciated.

Malcolm
Old 07-02-2014, 04:50 AM
  #50  
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Malcolm,
When you get get past the R&D stage I'll have a couple of sets of those 3D printed super-light ones.
Just enough to do a couple of models
Thanks

Brian

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