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Old May 30, 2012, 12:40 AM
Sittin' on my hands
depronair's Avatar
United States, WA, Seattle
Joined Jan 2005
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What are the specific challenges that come with building and flying airliners?

I read in the scale forum a thread that was entitled "what is scale flying?" and there was alot of good discussion about level of detail in the build, philosophy, and how flying scale is every bit as important as the build itself..

Im currently building an aircraft in CAD with plans to scratchbuild a 'liner after seeing so many awesome scratchbuilds on here. I can't help but notice after reading some build threads and watching some youtube vids, that there just seems to be certain problems and solutions for airliners and large transport. (trying to emulate slow graceful flight from a high wingload, dealing with instability, how to make one appear to fly like a 200 ton machine vs a rolly and tippy foam tube, etc)

And Id like to know what type of sacrifices you guys can tolerate to make on a build to help make it fly more scale-like...

Alright, discuss! Hopefully this will help generate a list of techniques to help us all build better flying airliners.. pooling info into one thread.. etc..
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Old May 30, 2012, 04:06 AM
ich bauen groß modell flugzeug
Keenan smith's Avatar
United Kingdom, London
Joined Dec 2010
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Me and airbuzz sacrifice some Strength to Build our planes light
Pros: Light wing loading and scale like apperance in the air and the ability to use less powerful cheaper Power systems (take Olles A340 for example he used GWS Brushed EDF75's)
Cons: there has to be almost no Wind to fly and the planes tned to be more vunerable to hangar Rash and usually end up becoming a Hangar Queen

Keenan...
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Old May 31, 2012, 07:56 PM
Balsa&Tissue
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United States, OR, Beaverton
Joined Jan 2011
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I have an extremely lightly loaded 80" DC-6B and it can be flown very scale like. The problem is the wind. A heavier version would be fine though as larger planes can tolerate a higher wing loading. It depends on the size you want to build and how much weight is just right.

The thing about liners and any multi-motor plane is you have to be good with your left hand. These planes fly by their throttles (more like real planes) and not elevator. They very often require good rudder control (coordinated turns). On my Six I use throttle to control ascent and descent and elevator only for minor corrections and at the very end as the wheels are about to touch the elevator stick comes way back (slight flare). Multi-motor planes will teach you throttle management unless you already learned it from a really twitchy tip stalling warbird.

Dave
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Old May 31, 2012, 08:44 PM
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demondriver's Avatar
United States, SC, Charleston
Joined Mar 2007
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Hi Depron-Air Both Keenan & Dave are right on the money! Airliner & cargo planes is designed to fly like any other aircraft it's just the overall design does no lend itself to aerobatics or really tight turns but other than that how you build & fly your airliner is up to you, the 6 most important factors to building a sucessfull RC airliner Are:

1 Correct CG location
2 A good airfoyle design for the wings
3 weight AKA light weight
4 control surface travel
5 enough thrust aka proper EDFs ESC's & batteries
6 structural strenght
7 scale design (trying to match the real thing)

if you stick to these rules you can do no wrong!
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Old Jun 01, 2012, 04:16 AM
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if you stick to these rules you can do wrong!
You mean no wrong?
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Old Jun 01, 2012, 06:12 AM
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You mean no wrong?
Ha-Lol Thanks Boss!
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Old Jun 01, 2012, 01:09 PM
Sittin' on my hands
depronair's Avatar
United States, WA, Seattle
Joined Jan 2005
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Haha, good stuff..

Payne- your 6 is amazing! It flies like its a much larger machine than it really is.

K, yup, building light to allow use of lower power systems is beneficial.. Neffwaffe's airliners teach us all about the benefits of "light"

DD- Sir, I learn from all your vids.

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if you stick to these rules you can do wrong!
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Originally Posted by MrADT View Post
You mean no wrong?
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Originally Posted by demondriver View Post
Ha-Lol Thanks Boss!
Rofl! DD, you should be a super hero named Captain Airliner
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Old Jun 01, 2012, 01:17 PM
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depronair's Avatar
United States, WA, Seattle
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Im totally with everyone that says airliners need to be built light, but I have a few other ideas/concerns that I personally would like to experiment with and tune into an aircraft when it comes time to construct one:


- ability to rotate slowly - if that means larger elevators so they can become effective before stall speed, its a scale sacrifice Im willing to make.. And of course delicate throttle usage helps this.. Jamming the stick to 100% probably wouldnt help acheive slow rotations..

- slightly rounder than scale leading edge - for higher AOA to help with nose high flares and being able to rotate the nose for a distance before mains leave the ground

-thicker airfoil at wingtips - for more effective lift at the tips, creating stability (winglets will help mask the thick airfoil at the tips)

- 3axis gyros to help keep rock solid attitude during climbs, turns and descents.. to help combat the dreaded foamy dance when there is slight gust

Of course these are all just goals and theories at the moment. If some of these ideas seem "lofty" please tell me what you think.
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Old Jun 01, 2012, 03:07 PM
Balsa&Tissue
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United States, OR, Beaverton
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Originally Posted by depronair View Post
Im totally with everyone that says airliners need to be built light, but I have a few other ideas/concerns that I personally would like to experiment with and tune into an aircraft when it comes time to construct one:


- ability to rotate slowly - if that means larger elevators so they can become effective before stall speed, its a scale sacrifice Im willing to make.. And of course delicate throttle usage helps this.. Jamming the stick to 100% probably wouldnt help acheive slow rotations..

- slightly rounder than scale leading edge - for higher AOA to help with nose high flares and being able to rotate the nose for a distance before mains leave the ground

-thicker airfoil at wingtips - for more effective lift at the tips, creating stability (winglets will help mask the thick airfoil at the tips)

- 3axis gyros to help keep rock solid attitude during climbs, turns and descents.. to help combat the dreaded foamy dance when there is slight gust

Of course these are all just goals and theories at the moment. If some of these ideas seem "lofty" please tell me what you think.
You hardly need elevator to rotate. As soon as the plane gets to a sufficient airspeed it will just take a bump of elevator to initiate a climb. Look at the videos of my six, it climbs too steeply. Once it gets to flying speed I just tap the elevator with a little "up" and once it initiates a climb I am at neutral elevator. If I want to climb slower I have to reduce throttle and feed in some down. My six has a fairly scale elevator and it is too much. I use about half stick on the elevator to make a last second stall on landing right before the wheels touch but that is the only time I use that much stick. In fact I have a fair amount of expo on the elevator to prevent porpoising. Some planes are different but I think a scale elevator will suffice in most cases.

Except with certain jet liners higher angles of attack are probably not needed either. On big heavy full size jetliners they do this so the AOA is high enough to fly level (maintain lift) and keep the nose level so the pilots are not looking up into the sky instead of where they are going. Most heavy aircraft are made this way. With my six it is just 2 degrees and the only time it flies nose up is when intentionally climbing or on the last bit of final approach. The full size DC-6 has 6 degrees of positive wing incidence.

The Concorde is a good example of a plane that needs high AOA in order to fly slowly enough to land. During normal flight (cruise) the nose/cockpit is in a normal position. During landing they had to design the nose/cockpit area so it could droop down just so the pilots could see. A light model of this plane would probably fly a little nose high on approach but probably not as severely as the full size plane.

A well made light liner does not really need gyros unless your area of flying is notorious for gusty winds. Scale may be a factor though because bigger planes can handle heavier wing loading and more wind. Park flyer sizes will be much more difficult to fly on a breezy day. My original DC-6 is 60" wingspan and 32 ounces (ready to fly weight), by these specifications it is a park flyer. My current DC_6 is 80" and 76 ounces and can handle the wind OK.

Dave
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Old Jun 01, 2012, 03:53 PM
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The idea behind the large elevator is to become effective before the wings- to raise the nose first... The idea is so that it doesnt lift off right away- I want the nose to lift off the ground and stay there for a stretch before the mains lift off- like a real airliner. And this is where perhaps a rounder leading edge might help too.

I agree that gyros are not needed, but the key phase where I think they are needed is near stall- the point where many rc model airliners get very tippy.

Edit: sorry this is my other account
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Old Jun 01, 2012, 06:02 PM
ich bauen groß modell flugzeug
Keenan smith's Avatar
United Kingdom, London
Joined Dec 2010
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thicker tip foil is a no no and trying to disguise it with a winglet will make it look worse!

Kind regards
the Overly scale purist...
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Old Jun 01, 2012, 07:49 PM
Up-Out-&-Gone
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United States, SC, Charleston
Joined Mar 2007
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Originally Posted by depronair View Post
Haha, good stuff..

Payne- your 6 is amazing! It flies like its a much larger machine than it really is.

K, yup, building light to allow use of lower power systems is beneficial.. Neffwaffe's airliners teach us all about the benefits of "light"

DD- Sir, I learn from all your vids.





Rofl! DD, you should be a super hero named Captain Airliner
Thanks Payne! More Like Captain Moron . . . . . . . .More "ON" than Off LMAO!
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Old Jun 03, 2012, 11:32 AM
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Ha-Lol Thanks Boss!
Any time.

Quote:
Originally Posted by depronair View Post
- ability to rotate slowly - if that means larger elevators so they can become effective before stall speed, its a scale sacrifice Im willing to make.. And of course delicate throttle usage helps this.. Jamming the stick to 100% probably wouldnt help acheive slow rotations..
I agree that this type of takeoff would look more scale, but as others have said, you can use less elevator, which is probably a better plan than making a non-scale elevator, if scale looks are what you're concerned about.
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Old Jun 03, 2012, 11:35 AM
ich bauen groß modell flugzeug
Keenan smith's Avatar
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BTW im offering up my cad work...
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Old Jun 04, 2012, 05:51 PM
ich bauen groß modell flugzeug
Keenan smith's Avatar
United Kingdom, London
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ohh and another advantage of light weight airliners is the need for a throttle Jokey approach is mitigated
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