How much tail wheel weight?    Gallery
View related threads: (in this forum | in all forums)

Logged in as Guest



Users viewing this topic: none
    Search This Thread  
 
Printable Version

All Forums >> RC Airplanes >> Aerodynamics >> How much tail wheel weight?
Page: [1] 2 3   next >   >>  

Tower Hobbies Get Coupon Codes Brands  
Login
Message << Older Topic   Newer Topic >>
How much tail wheel weight? - 3/15/2012 1:46 AM   
AA5BY


 

Posts: 1961
Score: 153
Joined: 9/7/2006
Last Login: 5/21/2013
From: White Oak, TX, USA
Status: offline 		Hi all... I'm just completing construction of self designed plane and am wondering if there is any rule of thumb about how much weight on the tail wheel is best. Though construction is finished, I could easily shim the gear to move the mains fore/aft perhaps an inch. With the plane balanced... where the gear are naturally yields 24oz on the tail wheel.... this for an estimated total weight of 15lbs.

Part of my concern is that the model has generous wing area and if there were too much tail wheel weight, it could get airborne before there is elevator authority.

I'll enclose pics.

Any thoughts?



Attachments
Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize


Hide Signatures
       Post #: 1

RE: How much tail wheel weight? - 3/15/2012 2:23 AM   
cfircav8r



Posts: 1156
Score: 218
Joined: 7/17/2004
Last Login: 5/20/2013
From: Hampton, IA, USA
Status: offline 		I have found on my aircraft flying off hard packed dirt or asphalt I move the mains to where when the plane is tipped onto the nose it just has enough weight to set it back on the tail. This makes it far easier to handle on T/O and landing. If you are flying off grass this could make it nose over too easy. I have not seen a good rule of thumb and have always adjusted it, when able, for the best ground handling. If you are flying off grass I would start right where you have it now.

Nice looking plane, you will have to give us a flight report when your done.

_____________________________

The three most useless things to a pilot, the sky above you, the runway behind you, and the fuel on the ground.

Hide Signatures

(in reply to AA5BY)
       Post #: 2

RE: How much tail wheel weight? - 3/15/2012 3:13 AM   
AA5BY


 

Posts: 1961
Score: 153
Joined: 9/7/2006
Last Login: 5/21/2013
From: White Oak, TX, USA
Status: offline 		All the way on the nose... it won't set back... but about an inch from being on the nose... it does settle back. It has fairly long gear, which plays a factor in that. It has abt 3 1/2" of prop ground clearance. We have a pretty rough field on a land fill and it is hard to keep it in good shape. When I ordered the gear... I wanted to error on the side of being too high rather than too low.

Will do on a flight report.

Hide Signatures

(in reply to cfircav8r)
       Post #: 3

RE: How much tail wheel weight? - 3/15/2012 3:56 AM   
speedracerntrixie


 

Posts: 2378
Score: 189
Joined: 6/7/2010
Last Login: 5/21/2013
From: San Jose, CA, USA
Status: online 		It looks like it is about perfect. On all my designs I place the wheel axles on the leading edge at the fuse. This has worked well on warbirds and aerobatic airplanes. Too far forward and the airplane wants to bounce on landing and too far aft promotes nose over and poor tailwheel response.


Hide Signatures

(in reply to AA5BY)
       Post #: 4

RE: How much tail wheel weight? - 3/17/2012 4:52 AM   
BMatthews



Posts: 11656
Score: 247
Joined: 10/4/2002
Last Login: 5/14/2013
From: Chilliwack, BC, CANADA
Status: online 		There's no hard and fast rules on this aspect. It comes down to a range of acceptable values.

On the whole a model intended for rough grass field flying should have more weight on the tail wheel by keeping the mains further ahead of the CG location than that for a model which will fly off smooth "golf course fairway" like fields or pavement.

A good way to set this is with the nose tip test. Models flown on rough fields should just balance on the main wheels when tipped to about 25 to 30 degrees nose down. Or if the nose hits first then it should not be able to sit on the nose and mains at the resulting lesser angle. For those models flown from smooth or paved runways most of the time I like to see them balance at around 15 to 20 degrees nose down.

But also keep in mind that in general terms the further forward the mains the more prone to ground looping the models will tend to be. So even with rough fields some give and take is needed. And on paved runway setups the closer to the 15 degree nose down balance you can get the more likely that it'll track during landings and takeoffs more nicely.

This also doesn't mean you can't take a "15 degree" setup and fly from rough fields. But it DOES mean that you'll need to hold more up elevator for the takeoff and until the model gets light on its feet then reduce it quickly to avoid a pop up sort of takeoff. Same on landing. You'll need to be ready for adding up elevator and maybe even some small bit of power to hold the tail down for a pavement tuned model flown on a rough field.

_____________________________

Witty saying to be plagarized shortly.....

Hide Signatures

(in reply to speedracerntrixie)
       Post #: 5

RE: How much tail wheel weight? - 3/17/2012 5:13 AM   
combatpigg



Posts: 16883
Score: 376
Joined: 11/22/2003
Last Login: 5/21/2013
From: arlington, WA, USA
Status: online 		There was an aircraft inspector I used to fly with who said that 10% of the aircraft's weight was typical for full scale.
I'll bet that figure gets less critical the smaller you get.
A "scale" imperfection in a model airfield runway would look like a moon crater to a full scale plane.


_____________________________

Blatantly corrupt umpiring at Yankee Stadium is an American tradition
It''s just part of the game.

Hide Signatures

(in reply to BMatthews)
       Post #: 6

RE: How much tail wheel weight? - 3/17/2012 11:44 AM   
AA5BY


 

Posts: 1961
Score: 153
Joined: 9/7/2006
Last Login: 5/21/2013
From: White Oak, TX, USA
Status: offline 		The model is exactly at 10% so I'm feeling ok about being somewhere in the range. I'll try to remember to offer report of how it does.

btw.. BMatthews, this is the design that recently the aircraft center of gravity calculator was used to determine where to mark the initial CG point. As one may have noted from the pics, the wings are surplus balsa covered foam cored and the plane built to incorporate them. This is my first effort at self design, though admittedly there was no straying far from the farm. The area that was strayed the most was the addition of three inches forward because experience has taught that more models require nose weight than tail but more nose weight is needed than tail to effect a balance. That decision seems to have been good. A preliminary balance before covering shows very slightly nose heavy and covering weight will favor aft. Battery placement should balance the plane.

< Message edited by AA5BY -- 3/17/2012 12:14 PM >

Hide Signatures

(in reply to combatpigg)
       Post #: 7

RE: How much tail wheel weight? - 3/17/2012 12:24 PM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/19/2013
From: , UT, USA
Status: offline 		keeping the tail wheel down in th e grass is often counterproductive .
The reason being that the craft stays at a high AOA which slows acceleration and the stalled wing panels are offering lots of forward drag but the tail group is offering no direction control -result is typically ground looping
the real fix is to add power as rapidly as possible and get tail UP so that it works and the wings can actually begin to add lift or at least offer reduced drag.
For the doubters - fly a Cub.

_____________________________

Libby is still watching you

Hide Signatures

(in reply to AA5BY)
       Post #: 8

RE: How much tail wheel weight? - 3/17/2012 1:17 PM   
da Rock



Posts: 10887
Score: 265
Joined: 10/11/2005
Last Login: 5/21/2013
From: western, NC, USA
Status: offline
quote:

the real fix is to add power as rapidly as possible and get tail UP so that it works and the wings can actually begin to add lift or at least offer reduced drag.


Very true, however..... if you think that firewalling the throttle is "as rapidly as possible" and the best way to do that, there is a good chance you'll take the sucker home in a garbage bag.

You definitely want the wing's angle of attack down so it doesn't stall, but keep that "as rapidly as possible" in mind. Cubs are a perfect example. The wing's AOA while sitting is WAY up into stall territory. And the engine/prop is pointed at the same place. Turn the motor loose and you might see the tail rising a touch after you see the airplane starting a snap roll to the left.

The advice is good so long as you remember the "as possible" and what that means.

I wish I had a dollar for every model I've seen go home in a trash bag because the pilot firewalled the throttle on takeoff.

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to rmh)
       Post #: 9

RE: How much tail wheel weight? - 3/17/2012 2:20 PM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/19/2013
From: , UT, USA
Status: offline 		I hesitated between possible and practical .
Real world shows that if the budding pilot cannot/will not abort power if control is not quickly established, the disaster simply takes place at a higher speed and in the air.

_____________________________

Libby is still watching you

Hide Signatures

(in reply to da Rock)
       Post #: 10

RE: How much tail wheel weight? - 3/19/2012 12:21 AM   
BMatthews



Posts: 11656
Score: 247
Joined: 10/4/2002
Last Login: 5/14/2013
From: Chilliwack, BC, CANADA
Status: online 		Much of what I described is based on reducing the takeoff and landing nose overs. Dick, I totally agree with what you typed but the reality is that low time model pilots will suffer far more noseovers if the model is set with the LG placed so far back that it takes very little to stick the nose down.

It's also been my own experience that quickly but SMOOTHLY adding power over the first 10 to 15 feet of the takeoff makes it a lot easier to catch and correct any angling off to the sides or even full on ground looping. That's a lot harder to do if the throttle is simply whacked open.

_____________________________

Witty saying to be plagarized shortly.....

Hide Signatures

(in reply to rmh)
       Post #: 11

RE: How much tail wheel weight? - 3/19/2012 12:49 AM   
AA5BY


 

Posts: 1961
Score: 153
Joined: 9/7/2006
Last Login: 5/21/2013
From: White Oak, TX, USA
Status: offline 		Strangely... I can name models that favor each method, though the greater amount have done better with the slower acceleration.

Hide Signatures

(in reply to BMatthews)
       Post #: 12

RE: How much tail wheel weight? - 3/19/2012 2:20 PM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/19/2013
From: , UT, USA
Status: offline 		small model, in grass?
slow acceleration is not desireable or even possible many times .
on hard packed or concrete - -different ball game that's ez

In either event - the idea is to get the tail surfaces working first -unles you have lateral control you are doomed
a noseover is natures way of preventing larger problems

_____________________________

Libby is still watching you

Hide Signatures

(in reply to AA5BY)
       Post #: 13

RE: How much tail wheel weight? - 3/20/2012 1:14 PM   
AA5BY


 

Posts: 1961
Score: 153
Joined: 9/7/2006
Last Login: 5/21/2013
From: White Oak, TX, USA
Status: offline 		Yes... the model that came to mind that demands fire walling the throttle is an old Honker bipe... a small .20 size with a tail skid. I've also an old Das Box Fly bipe with a Saito .30 and tail skid that prefers the slower acceleration however. And... yes again, all my flying is off grass.

Hide Signatures

(in reply to rmh)
       Post #: 14

RE: How much tail wheel weight? - 3/26/2012 7:17 PM   
mithrandir



Posts: 1089
Score: 110
Joined: 7/17/2003
Last Login: 5/10/2013
From: adelanto, CA, USA
Status: offline 		it is customary with taildraggers to hold up elevator, sticking the tailwheel to the ground until there is enuff airspeed for the rudder to provide steering....

ever notice how often people taxi with the elevator full backstick?

"a noseover is natures way of preventing larger problems"


nice.. I will remember that!!! lol



_____________________________

LOOKING FOR ENGINEERING WORK ON UAV''S?
http://search9.smartsearchonline.com/asi/jobs/adhocjobsearch.asp

Hide Signatures

(in reply to AA5BY)
       Post #: 15

RE: How much tail wheel weight? - 3/26/2012 8:15 PM   
da Rock



Posts: 10887
Score: 265
Joined: 10/11/2005
Last Login: 5/21/2013
From: western, NC, USA
Status: offline 		How fast the throttle can be opened really is about as simple as almost everything in modelling. In other words, it isn't simple. But some other things are.

Light wing loaded models can lift off as soon as you start the throttle forward, and if you were holding up elevator to keep the tail wheel down and waiting on the rudder to have authority you made a big mistake. Three of them actually.

All of my warbirds will lift off thanks to their power loading and 3-blade props if I am holding the up elevator I use while taxiing. I go to neutral on the elevator as soon as I start to roll the throttle forward. That's off grass. When I fly at the paved fields around here, which isn't as often as off my grass home field, I go to neutral and then hold a touch of up. As soon as the take off roll starts and the direction is established, the elevator goes to neutral.

My tiny little WWI electric warbirds get some up held until I start to roll in throttle. They always take off from our "fabric asphalt". No way to get 'em off any grass runway available around here. Nobody has grass those narrow wheels will ride. Pavement gets the same touch of up that's released quicker than the throttle is pushed. People very often say those things do more realistic takeoffs than bigger models. They do when I do exactly what the guys back in 1918 did. Rudder still matters, btw.

If you can taxi the plane at even a moderate speed, you can do a safe, rolling takeoff that doesn't need you to hurry the throttle. Can't you taxi somewhat fast? How slowly do you taxi out to the numbers? You can do that,right. Then once out at the numbers and lined up, start taxiing down the runway. About the time you realize you've just discovered that steering at the start of a takeoff roll isn't anything different than taxiing out, roll in a bit more throttle and you've just done what probably is your safest takeoff ever.

Will there be situations that firewalling the throttle is the best solution? Might be, but if you can taxi out, is there a real reason you suddenly have to firewall to get it off? Taxiing is a safe maneuver. It can start a takeoff just as safely. MOF, it'll make most people's takeoffs safer when they get over their firewall and pray.

_____________________________

Good flying wit ya today

Hide Signatures

(in reply to mithrandir)
       Post #: 16

RE: How much tail wheel weight? - 3/27/2012 2:21 AM   
kerwin50


 

Posts: 1225
Score: 100
Joined: 10/18/2006
Last Login: 5/20/2013
From: winston, MO, USA
Status: offline 		Guys there are 2 differnt cg's. The cg in the air and is determined by how far the balance point is ahead of the center of pitch.
Next is the CG on the ground and that is determined where the landing gear is located.
If the landing gear is right at your balance point the plane will nose over very easy. If it is far ahead of the balance point the plane will want to ballon and bounce up on landing.
Ideally you want your axles on your leading edge.
This way she will neither want to nose over or ballon on landing

Hide Signatures

(in reply to da Rock)
       Post #: 17

RE: How much tail wheel weight? - 3/27/2012 2:31 AM   
kerwin50


 

Posts: 1225
Score: 100
Joined: 10/18/2006
Last Login: 5/20/2013
From: winston, MO, USA
Status: offline 		BTW tail wheel weight has to do with your cg. balanced aft of the center of pitch and you have a tail heavy airplane that will be dynamically unstable . Too nose heavy an you will loose elevator authority.
Noticing you have a double tapered wing you will have to use a formula for figuring your center of pitch.
I use the 1/3 rule.
The forumla is a trig function for figuring area. Now it's been some years so I'd really have to pick my brains. But I'm sure if you reposted your question for figuring CG on a double tapered wing there should be alot of guys out here that can help you

Hide Signatures

(in reply to kerwin50)
       Post #: 18

RE: How much tail wheel weight? - 3/27/2012 3:25 AM   
AA5BY


 

Posts: 1961
Score: 153
Joined: 9/7/2006
Last Login: 5/21/2013
From: White Oak, TX, USA
Status: offline 		Thanks Kerwin... unless I'm errant in doing so, I used the calculator offered in the sticky for this forum. It ask for a good bit of data so am I correct in that it considers the double taper? It considers the horizontal stabilizer area and distances from the wing as well.

The plane is ready to cover but I've gotten busy with spring chores and yard and garden and am anxious to get back on it. There is considerably more mystery involved in a self design, which makes it really interesting wondering about how it will do.

When mocked up for a pre-covering cg check, it was very close and that is when the weight on the tail wheel was measured and then noted that if fell right on the ten percent rule that someone suggested, though I agree that a lot depends upon the surface one flies off from. I fly from grass on a land fill so it is a bit rough.


Attachments
Click to see fullsize image.
Click for fullsize


< Message edited by da Rock -- 3/28/2012 2:35 PM >

Hide Signatures

(in reply to kerwin50)
       Post #: 19

RE: How much tail wheel weight? - 3/27/2012 1:07 PM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/19/2013
From: , UT, USA
Status: offline 		FWIW- I just setup a 1/5 scale Mustang -using a DX8 radio and two rudder servos - one for the rudder - one for the tailwheel- The TX allows for mixing in the relative amount of deflection and the relative center position of the tailwheel.
great setup.
I have found thru much trial and error - that models such as this need very little wheel movement (relative to rudder movement) and the power on tracking CENTER needs real times experimenting to get best straight on tracking
As example -set tailwheel LEFT a bit and hold in a little right rudder . Typically you will be holding in right rudder as roll speed increases and too much tailwheel movement simply screws up the tracking.

_____________________________

Libby is still watching you

Hide Signatures

(in reply to AA5BY)
       Post #: 20

RE: How much tail wheel weight? - 3/27/2012 8:36 PM   
BMatthews



Posts: 11656
Score: 247
Joined: 10/4/2002
Last Login: 5/14/2013
From: Chilliwack, BC, CANADA
Status: online
quote:

ORIGINAL: kerwin50

Guys there are 2 differnt cg's. The cg in the air and is determined by how far the balance point is ahead of the center of pitch.
Next is the CG on the ground and that is determined where the landing gear is located.
If the landing gear is right at your balance point the plane will nose over very easy. If it is far ahead of the balance point the plane will want to ballon and bounce up on landing.
Ideally you want your axles on your leading edge.
This way she will neither want to nose over or ballon on landing



Kerwin, I get what you're trying to say but it's actually confusing to think of it that way. There's only ONE CG or Center of Gravity for a model. It's better to just simply say that the main gear axles need to be X amount ahead of the balance point and leave it at that.

The amount ahead is often given as an angle from the true CG. But that's not always obvious where it is. So it's often easier to say keep the axles ahead of the balance point by something like 10 to 15% of the chord for a low wing model operating off pavement. 20 to 25% ahead of the balance point is good for grass and low wing models. For high wing models add 5 to 7% to those numbers to make up for the true 3D center of gravity being somewhat higher due to the usual cabin style fuselage holding the wing up high and the mass of the wing being that high.

WIth this rule of thumb the axles will often end up at or just slightly behind the leading edge of a constant chord wing on a cabin style model just as kerwin suggests. That's also what I normally aim for. For a low wing model having the gear that far ahead produces too much tendency to ground loop and poor ground handling in stronger cross winds. But with the amounts I've suggested in terms of the wing chord I've had good success over the years.

_____________________________

Witty saying to be plagarized shortly.....

Hide Signatures

(in reply to kerwin50)
       Post #: 21

RE: How much tail wheel weight? - 3/28/2012 1:32 PM   
ZedHead


 

Posts: 21
Score: 100
Joined: 9/5/2004
Last Login: 5/17/2013
From: Quohog, RI, USA
Status: offline 		At the sod farm where I fly a noseover is nature's way of telling you that the grass is responding well to all the irrigation and fertilization. It's also a sure sign your gear is too far aft. This grass is not rough, it is very smooth. It is just so thick and lush and draggy that the gear needs to be moved forward. The rule of thumb I aim for is "the further forward, the better". On the Mad Dog and Venus pictured below, I simply reversed the angled gear that came with the ARF and mounted it backwards. The Gee Bee required much more creative modification. This gear forward location works equally well on the Mad Dog with wheels on grass and with the skis on snow.

Furthermore, I haven't seen any of the bad side effects mentioned by others above. Never any groundloops, and beautiful 3 point, "greaser" landings are the norm. Minor bounces are rare, and only occur if I dont get the plane slowed down enough before touchdown.

Attachments
Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize 		Click to see fullsize image.
Click for fullsize


Hide Signatures

(in reply to BMatthews)
       Post #: 22

RE: How much tail wheel weight? - 3/28/2012 2:44 PM   
HighPlains


 

Posts: 4596
Score: 152
Joined: 3/2/2003
Last Login: 5/21/2013
From: Over da rainbow, KS, USA
Status: online
quote:

The amount ahead is often given as an angle from the true CG. But that's not always obvious where it is.


But it is easy to find the angle that the wheels are ahead of the actual CG. Just turn the model upside down and hold it by it's main wheels. The angle will be quite apparent.

As far as the rest of the discussion, it's been pretty well nailed down, except for a few other factors like the thrust line and rolling resistance, multiplied by distances. Nothing amplifies scant piloting technique more than the ground handling of a tail dragger. Throw in cross winds and pavement and you usually want to stand down wind of the typical RC pilot.

< Message edited by HighPlains -- 3/28/2012 4:50 PM >

_____________________________

- Supplementary insipid innocuous inane vacuous proclamation

Hide Signatures

(in reply to BMatthews)
       Post #: 23

RE: How much tail wheel weight? - 3/28/2012 2:45 PM   
da Rock



Posts: 10887
Score: 265
Joined: 10/11/2005
Last Login: 5/21/2013
From: western, NC, USA
Status: offline
quote:

ORIGINAL: AA5BY

Thanks Kerwin... unless I'm errant in doing so, I used the calculator offered in the sticky for this forum. It ask for a good bit of data so am I correct in that it considers the double taper?


If by double taper, you're referring to both the leading edge sweep and trailing edge sweep being "double sweep" and therefore "double taper", the answer is yes.

If your wing's chord decreases (or increases) uniformly from the root to the tip, the answer is yes.


_____________________________

Good flying wit ya today

Hide Signatures

(in reply to AA5BY)
       Post #: 24

RE: How much tail wheel weight? - 3/28/2012 4:39 PM   
rmh



Posts: 12307
Score: 252
Joined: 12/12/2001
Last Login: 5/19/2013
From: , UT, USA
Status: offline
quote:

ORIGINAL: ZedHead

At the sod farm where I fly a noseover is nature's way of telling you that the grass is responding well to all the irrigation and fertilization. It's also a sure sign your gear is too far aft. This grass is not rough, it is very smooth. It is just so thick and lush and draggy that the gear needs to be moved forward. The rule of thumb I aim for is ''the further forward, the better''. On the Mad Dog and Venus pictured below, I simply reversed the angled gear that came with the ARF and mounted it backwards. The Gee Bee required much more creative modification. This gear forward location works equally well on the Mad Dog with wheels on grass and with the skis on snow.

Furthermore, I haven't seen any of the bad side effects mentioned by others above. Never any groundloops, and beautiful 3 point, ''greaser'' landings are the norm. Minor bounces are rare, and only occur if I dont get the plane slowed down enough before touchdown.

Ya can't beat experience and low rolling resistance .
and a good cat -
Libby loves cats -

Attachments
Click to see fullsize image.
Click for fullsize


_____________________________

Libby is still watching you

Hide Signatures

(in reply to ZedHead)
       Post #: 25

Page:   [1] 2 3   next >   >>  
All Forums >> RC Airplanes >> Aerodynamics >> How much tail wheel weight?
Page: [1] 2 3   next >   >>  




Jump to:


 
Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

RC Universe is a service of Internet Brands, Inc. Copyright © 2001-2013.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America


2.219RCU1