| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1065.1 | Shock absorbing gear... | WRASSE::FRIEDRICHS | Never trust a premi! | Mon Jul 31 1989 14:28 | 59 |
| OK, again I am starting this because I have a problem to solve..
On the 4th landing yesterday, the Bristol pushed one of its landing
gear blocks up through the bottom of the fuse. The fuse was made of
very light ply, I should have reinforced it while I was building it.
Oh well, no major damage.. Easy fix...
My concern is that the landing gear is VERY stiff. There is no give in
any direction so all forces are transmitted to the plane itself. To
give you an idea of the setup... The gear is made of 5 pieces of
5/16 (??) rod. 4 pieces make up 2 "V"s and the last piece is the axel
and runs between the 2 "V"s. Each "V" is soldered together and to the
axel with copper windings around it. 2 hardwood blocks are attached to
the fuse, one forward and one back, so that each block houses 2 struts.
Looks kinda like this:
| | \ |
| | \ |
| | \ |
| | \ |
| | \ |
| | \ |
| | \ |
| | \ |
--------------------- \O|
Front Side
To avoid damage to the plane, I want to absorb some of the shock in the
gear itself. I am thinking of cutting the axel off at base of the
"V"s. Then, use a new piece of rod as the axel. This new axel would
run along ABOVE the old axel, and be held on by rubber bands. I plan
on making guides for the base of the V. It would look like this...
| | \ |
| | \ |
| | \ |
| | \ |
| | \ |
|1 2 1| \ |
|V V V| \ |
--------------------- \ O|
------------- \O|
Front Side
Rubber bands would be placed at #1 positions above. I have also
thought about making the new axel 2 pieces and joining/hinging them at
#2 above.
Comments or suggestions.
Thanks,
jeff
|
| 1065.2 | I think you should think some more! | LEDS::HUGHES | Dave Hughes (LEDS::HUGHES) NKS1-1/E3 291-7214 | Mon Jul 31 1989 15:08 | 11 |
|
It looks to me that if you came in for a hard landing, the rubber bands
would stretch, the wheels would move up, and the cross wire would bottom
out on the ground and dig in. This isn't the kind of "retracts" you want
- I would think it could damage the plane more than the original setup
which would at least keep the wheels in contact with the ground. I would
suggest you think of a way to let the wheels spread apart to absorb
shock, like cut the cross bar in the middle and put some rubber bands or
shock absorber between the wheels.
Dave
|
| 1065.3 | Hmmmm | WRASSE::FRIEDRICHS | Never trust a premi! | Mon Jul 31 1989 15:36 | 13 |
| I have been thinking about that, but I have not come up with a good
way yet. I refered to using a guide in my note. This guide should
also limit travel so that .2 does not happen. Also, the rubber will
be bound very tightly, as, like with holding down a wing, I don't
want it to move unless it is really needed.
Like in cars, the shock absorbers will/should only do so much. I
expect to pay the price for very very hard landings.
Interesting idea about cutting it from the center...
jeff
|
| 1065.4 | has to be better | ROCK::KLADD | | Mon Jul 31 1989 15:38 | 9 |
| jeff,
sounds good to me. you might try soldering the 2nd axle (containing
the wheels) to the orig at the center only (#2). that way the wire
is acting as spring and you can add rubber bands to endpoints (#1)
for whatever help seems necessary. the guides prevent side-side
movement and you could use them to bottom out before the wheels
go so high the vee hits the ground.
actually, that center solder joint might take too much punishment,
maybe use wire instead?
|
| 1065.5 | | SA1794::TENEROWICZT | | Mon Jul 31 1989 16:03 | 12 |
| I was a fokker set up thatmight help.
Landing gear was normal except that there was an 1/8 inch piece
of wire soldered between the two gear as a cross piece. Where the
original design had wanted the wheels the gentleman cut off the
axle to app. 1/2" in lemgth. Next he had a piece of 5/32 wire that
ran parallel to the 1/8" cross piece that was wrapped and soldered
in the middle of the cross piece app.1". As the wire passed where
th normal axles were he used "O" rings to act a a bungy cord.
Tom
|
| 1065.6 | dog toys | K::FISHER | Stop and Smell the Balsa! | Mon Jul 31 1989 17:30 | 53 |
| Timely discussion. I need to enhance the landing gear on my BJ.
Looks OK for static then when I actually fly the beast I break up
the gear bad. Then I'm doomed to fill and paint before the next static
again. Mine is simply just two wires soldered together at
the bottom. Then each music wire is covered with balsa then sanded
to contour shape then each balsa cover is fiberglassed and sanded and painted.
I need to create two cross braces when viewed from the front (to be scale).
and would like them to function as shock absorbers. I would also like
to permanently shed the balsa cover for something that can take a licking
and keep on ticking.
I've been looking at god toys with a raised eyebrow lately. Yes - DOG
toys. They are a hard rubbery substance and if I could find one long and
straight then I could form a cross brace made out of this stuff.
Along those lines I am presently searching for luggage rack straps (the
rubber ones - not elastic cloth ones). But haven't been able to come
across any since I was turned on to dog toys. Anybody know where I
can find luggage rack straps? Can you sand and form this stuff?
Paint?
In case you come up with an elegant solution let me make it more difficult.
One cross brace is suppose to pass thru the other. That is one brace
should have a hoop in it.
Front view
-------------------
/ \ / \
/ \ / \
/ \ / \
/ \ / \
/ X \
/ / \ \
/ / \ \
/ / \ \
/ / \ \
/ / \ \
/ / \ \
/ / \ \
/ / \ \
/ / \ \
/ / \ \
/ / \ \
========= =========
Side view is just like Jeffs.
Bye --+--
Kay R. Fisher |
---------------O---------------
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| 1065.7 | basic questions for a tail-dragger | ABACUS::RYDER | perpetually the bewildered beginner | Fri Dec 08 1989 09:00 | 10 |
| Can some one point me to some basic texts or opinions on the placement
of the main gear of a tail dragger? (Other than according to the PLANS.)
I can see that the tendency to nose over will be a function of the
angle between CG and vertical as seen by the axle, but I have no
idea of the rule-of-thumb for this angle.
I have read in the current issue of RC Report that forward placement
tends to adversely affect yaw stability on the ground. But the
statement was terse and made no mention of left-to-right spread.
|
| 1065.8 | | SA1794::TENEROWICZT | | Fri Dec 08 1989 09:41 | 13 |
|
I've seen gear raked at extreme anglesforward and backwards
and still work fine. What does matter is the relationship of the
axle of the main gear to the CG location. A general rule is to
place the axle of the gear at the leading edge of the wing. The
wheels can be used to some extent as a tolerance. I wouldn't go
forward with the axles any further than one half a wheels diameter.
Than is to say place the back end of the hweel at the leading edge
of the wing. The reverse is the same. As the front of the wheel
gets close to the leading edge stability wanes.
Tom
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| 1065.9 | HOW WIDE CAN YOU GO........?? | PNO::CASEYA | THE DESERT RAT (I-RC-AV8) | Fri Dec 08 1989 12:37 | 25 |
| I concur with what Tom has said. I always set the axle in line with
the leading edge as viewed from above. The forward/rearward angle is
far less important than the position of the axle relative to the CG.
As a case in point, the struts on the MiG-3 emanate quite far back from
the leading edge and angle forward radically, placing the axle in line
with the LE. It _looks_ plenty treacherous but is really very
manageable...If I had more rudder throw, I doubt I'd ever blow a
takeoff.
And _that_ brings up an important point; get all the rudder you
possibly can for a taildragger...this is _much_ more important than on
a tri-geared plane. As to track (width), I know of no particular rule-
of-thumb on this; within reason, set the gear as wide as possible
within practical and aesthetic limits...the wider, the better! Take a
look at the _extremely_ wide stance of the P-47...this is, without
question, the easiest ground-handling scale ship around owing to this
feature.
Hope this helps........
|
| | 00 Adios, Al
|_|_| ( >o
| Z__(O_\_ (The Desert Rat)
|
| 1065.10 | no fixed rule on gear width | PERN::BRET | Crazy Hawaiian DTN 289-1604 | Fri Dec 08 1989 12:38 | 7 |
| There seems to be no set rule to tread (the distance between the two
wheels) in the real world. It's related to the wing structure, the
size of the center section (the strong part of the wing) and the
ability to contain the strut and wheel. For example, the P-40 retracted
straight back, the TBM retracts outward, the T-6 goes inward. The
Me-109 had a very narrow gear, the P-51 had wider gear. I would say
that the choice is yours if you are designing from scratch.
|
| 1065.12 | What about 1 wheel landing gears? | K::FISHER | Stop and Smell the Balsa! | Fri Dec 08 1989 13:36 | 48 |
| > <<< Note 1065.7 by ABACUS::RYDER "perpetually the bewildered beginner" >>>
> -< basic questions for a tail-dragger >-
>
> Can some one point me to some basic texts or opinions on the placement
> of the main gear of a tail dragger? (Other than according to the PLANS.)
In Al Casey's magazine "RCM" the column called "Cunningham on R/C" has been
having a sequence of design articles using rule of thumb stuff rather
than math and formulas for sever issues lately. I can dig up an old
one (3-4 months back) that covers the landing gear position if you want
but...
Tom and Al and Eric all seem to be in the agreement and I'll bet a Coke
that Cunningham's article matches.
Speaking of Cunningham. In his latest issue there is a picture of a
motor glider built by Marvin Reese that has a 18 foot wing span.
Check it out. I saw a reference to it in another magazine a month ago
and wrote to Marv about it.
The bad news is - it is not a scale model - it is a sport plane and the
plans won't be available for about a year.
The good news is it flys great. I had asked Marv a dozen questions so
let me quote out of context most of his reply.
A friend is building #2. It will stay up as long a you want after
the engine shuts down - 30 minute flights are common - spoilers
are an absolute must. 2 piece wing at about 102" each.
Fuselage is 10" wide and about 95" long. Horizontal stab is 40" long.
Around 2500 sq inches (17 sq feet) at 17 lbs. Eppler 197 airfoil.
Flaps and spoilers. Powered with an OS .61 four stroke (not a surpass)
with a 12x6 prop.
One belly wheel and a tail wheel. Quite maneuverable on the ground
as with only the slightest ground roll you can level the wings.
"I took the sailplane, my Mooney, and my Ligeti Stoator (which is suppose
to be on the cover of Model Aviation soon) to the Council Bluffs, Ia. fly-in
and by far the greatest interest was in the glider. It is awesome in the air
and a real pussy cat. I call it 'Ultimate Solitude', which pretty well
tells the story."
Bye --+--
Kay R. Fisher |
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| 1065.13 | Don't forget toe-in | CURIE::ANKER | Anker Berg-Sonne | Fri Dec 08 1989 15:53 | 18 |
| With tail draggers its also critical the the wheels have
toe-in. Without this it will be very susceptible to ground roll.
The effect of toe-in is that if the plane lifts a wing the wheel
remaining on the ground will tend to steer the plane towards the
lifted wing, which will cause it to settle down. With toe-out
you get the exact opposite effect, wing lifts, plane pirouettes!
Fun to look at, but not for takeoffs.
_
/ |
_----____/==|
/__====-------
|-
/
/
Hang in there!
Anker
|
| 1065.14 | | CTD024::TAVARES | Nuke Christmas Music! | Fri Dec 08 1989 18:48 | 21 |
| Now you're talking Anker! I've been getting very little flying
time in lately because Son of Quick Stick suddenly developed an
adversion to straight takeoffs. It likes to do doughnuts on the
runway. I followed the advice at the field and moved the gear
back (it was even with the leading edge per CC) that did nothing
but make it worse. Then I changed to an aluminum gear, from the
old 5/32 wire one, thinking that the rough runway was throwing it
off. Nope.
My latest was to measure the incidence which I found to be
a whopping 4 deg. I don't know how it got that way but I
theorized that the wing must be lifting off before the tail and
causing it to go crazy. I reset it to 1 deg. But nothing really
cured the problem. The local wags allowed as to how it was a
small plane and was too hard to fly, why don't I get a big one,
etc...
All the while I remembered the Sage Cunningham's advice to toe in
the gear, which he said the reasons for were too complicated to
explain. Now you come along and say it in one sentence. Ok.
Tonite I bend the gear in.
|