Building Options & Misc. 090708 page 10
Aileron Option: On the Poorboy you can remove the aileron deflection (angle
difference between the root and end of the aileron). This angle difference was
put into the Poorboy design to soften the stall characteristics, it also
increases lift if rigged in the inline outboard pattern. A builder can remove
the angle difference if he is aware that the stall character may change. The
plans call for an abrupt angle difference at the strut position on the aileron,
the PB-1 has an extra rib at the strut location and the angle difference is set
right at that point and it is fairly easy to cut the tube where these two ribs
angle difference occurs allowing a person to eliminate the offset by putting a
splice over or inside the tube and riveting in the changed angle (the new angle
being “no angle difference in the aileron”). If a person didn’t like the
results he could go back to the split angle style by redoing the splice tubes
position. We recommend using the split aileron on all models as that is what we
tested for, the suggested rigging position is to have the outboard position in
line with the rest of the wing, this puts the inboard section down five degrees
into the air stream (like a slight flap position). A reminder that improper
center of gravity is critical to stall behavior as is anything else.
Tail size: Tail control area. The size of the tail surfaces meet the design
and handling goals of this design. With the center of gravity at 29 percent of
the wing cord the size of the elevators do not allow an easy slow approach to a
full stall, the aircraft will buck and shake and resist stalling. For the tail,
the factors that effect control behavior are distance of the tail surfaces from
the wing, size of the tail surfaces, range of motion, and center of gravity
location to the wing. Additional factors effecting stall behavior is the main
wing area, airfoil shape, and airfoil modification devices such as flaps. PB-1
tail should use the 48” wide sections with 1” tube. The drawing is a PB-U 44”
wide tail. It is easy to increase the tail authority a bit on the PB-1 by
changing the horizontal stabilizer and elevators width to 48 inches on the horz.
stab. instead of 44 inches on the PB-U and increase the elevators by 4” width
for each one to match the stabilizer and using 1” x .058 tube where 7/8” tube is
indicated. A proportional increase in vertical stabilizer and rudder should be
included when resizing the tail. The PB-U should use the tail as the plans show
using a 44” horz. stab. and 7/8” tube, and the bow type tips on tail control
surfaces as shown in the web page pictures. (see diagram TL-19) The PB-1
should use ¼” bolt and larger matching Stainless Steel U-brackets to replace the
S2-SAB brackets. Note that when you are changing the tail to the larger version
using 1” by .058 tube this applies to the Vertical fin tube components as well
(vert. stab. & rudder), also build the tailpost to use 1 1/8 x .049 4130
material to accept 1” tail tubes. The flying protype PB-1 is using the 44” tail
size of the PB-U as in the plans and does fine but be sure to use the bow tips
on the rudder and elevators.
Center of Gravity calculations 090708 Pg-11
The Poorboy is designed and plans written for people who may or may not have
aviation experience. On the CG (center of gravity) topic we make it clear that
you need a proper and correct reference for calculating the CG. An incorrect
CG is a life threatening condition.
CG calculation on the Poorboy was done with half full fuel in the tanks, pilot
in the seat (flying configuration).
29% of wing cord balance point, about 17 ½” from Leading edge of wing.
I use the U.S. Department Of Transportation (Federal Aviation Administration) Pilot’s
Weight and Balance Handbook # EA-AC 91-23A. Formula for tail wheel type aircraft.
I used a plum bob line off the wing leading edge for a datum point, look at the correct formula for
your datum line application in the manual.
You cannot do an empty weight CG without the pilot because the pilot’s weight is too high a
percentage of the overall aircraft to exclude the pilot from the calculation.
Elevate the tail about a foot or so, so that the bottom of the wing is at the normal flying angle (angle
of attack is around 5or 6 degrees).
Don’t take my word for anything, there are several ways of figuring weight and balance.
I follow the instructions in the weight and balance handbook EA-AC 91-23A, there may be a
newer addition of this publication. See (FAA-H-8083-1)
Some handbook sources.
http://www.avshop.com/prodinfo.asp?number=163
http://www.amazon.com/gp/product/1560273771/104-0651358-687129?v=glance&n=283155
March 18, 2007 Aircraft weight and balance manual is available as a free
download at http://www.faa.gov/library/manuals/aircraft/media/FAA-H-8083-1A.pdf
Poorboy Construction 090708 Pg-12
Tube cutting is best done with a hacksaw, 24T blade. A tube cutter can be
used but it thins the wall at the end of the tube after de-burring and the
cutter can introduce small fractures or cracks that are hard to see so be
observant. A chop saw works well but the heat can effect some metals temper.
Tubes should be de-burred on the cut ends with a de-burring tool both on the
inside and outside of the cut surface. De-bur on the inside because anything
you insert into the tube could be scratched, on the outside to prevent scratches
on brackets etc., a round and flat files will do fine. A de-burring tool works
well. De-bur holes that are drilled into the tube with a larger drill bit,
file, or de-bur tool removing just enough material to make it smooth.
Hole location on tubes can be difficult to align when drilling a “through”
bolt hole, one way to get alignment is to use a piece of graph paper cut to make
a collar or “ring”. Align the paper on the tube and tape the circle seam, slide
the collar off the tube and flatten in half, use a marker to dot the creases.
When you slide the paper ring back on the tube the marked creases will be
exactly 180 degrees opposite each other and inline by the edge of the paper or
graph line. Slide the paper collar back on the tube and mark the hole location
and use a center punch before drilling.
Center punch all drill positions before drilling. Tube and brackets can all
be drilled undersize (1/8 bit) and then have some chance at correction if a
slight problem exists, this makes the larger bit easier to drill also. On
bracket or plate brackets that are identical try to match drill using one to
overlay the others and use the 1/8” bit first. Pin the first drilled holes with
a bolt, rivet, or drill bit to keep everything in alignment.
Tubes are shaped with a tube bender when necessary. If you haven’t done this
in the past you may want to get some inexpensive conduit and try a few times to
get the hang of it. Place the bender and the piece your bending on top of a
piece of plywood so you don’t scratch up the work piece. You need the plywood
and good foot pressure to give good support to the work piece or it may buckle.
A ¾” and 1” conduit bender are required for this project, these are conduit
sizes and do not match inch OD sizes. A ¾” bender is used on 7/8” and ¾” tube;
a 1” bender is used on 1 1/8” and 1” tube. Place your foot on the bender (foot
location) and keep good down pressure applied as you make the bend. You do not
need to make bends in steel to their final shape, you can make partial bends
repeatedly and slowly bring the piece to its final shape. You can reverse the
bender and make “minor” corrections in the opposite direction but if you get too
far out of shape it may be easier to discard the piece and start again, note
that repeated movement back and forth will weaken the piece. Aluminum hardens
as you bend it and if you wiggle it back and forth trying to get the right shape
it will weaken significantly, you can make progressive bends in the same
direction but a reverse bend should be very minor. When making progressive
bends put the tool in its original position with each increase in bend radius.
Hardware: All hardware needs to be “AN” quality aircraft hardware. In order to
keep from marking up the bolts and wearing the nylock nuts you can use generic
hardware during building, you must not keep any lower grade hardware during
final assy.
090708 Pg-13
The plans list bolt sizes by diameter and type (like drilled or un-drilled),
however length will not always be correct. You can expect some error in
lengths so it will be a good idea for you to double check what the plans are
telling you on bolt lengths. You can figure it by learning “AN” numbering
system as described in most aircraft hardware parts books. A bolt gauge is
included in the diagrams (need to correct for print scale) may I suggest that
you buy a better bolt gauge. Note the difference between bolt length and grip
length. A locking nut should have at least one thread showing past the end of
the nut.
POP RIVETS: We recommend stainless steel rivets as the first choice. An
example is P/N SS42-SSBS, at .09 cents each (cheaper in qty), steel rivets are
quite a bit cheaper. No aluminum rivets are used in this plane except as
“temporary” fasteners except where noted. Rivets are either stainless steel,
regular steel, or a special monel rivet. The stainless steel rivets can be
substituted with a steel rivet but the steel rivet tends to corrode over time so
if you are in a high humidity area they are less desirable (you can paint or
varnish steel rivets to control corrosion). The stainless steel rivets are a
pain in the neck if you have to remove them but they are strong and don't
corrode. Removal....of a rivet is done with a drill bit 1/64” smaller than the
rivet size, drill and remove the head with a chisel or wobble the stem of the
drill bit in the top of the rivet to break it off. If the rivet spins when you
are drilling it you need to rotate the drill angle and revolve around the hole
position (wobble) to remove the rivet. If the hole becomes two far enlarged you
would need to go to the next size rivet for a proper fit (exp..1/8 rivet to a
5/32 rivet). Rivets are 3/32, 1/8, 5/32, 3/16” diameter, there is a “grip”
length associated with any rivet, look at the “total thickness” of the items
that are being riveted and be sure the rivet minimum grip length meets or
exceeds the requirement. A few solid rivets are used on the controls they are
to be flattened or “mushroomed” on the end. Aluminum fabric rivets can be used
on droop wing tips.
* Each construction step is associated with a file numbering system that
matches construction with pictures, diagrams, parts list, and hardware list.
You will notice a two letter indicator on each of these files or portion of a
file. (exp. AF (airframe), MG (main gear), WG (wing) etc.)
* Diagrams are done on graph paper, if you have difficulty in finding some
dimension look at a known dimension for that piece of the drawing and count the
lines (boxes). exp. 1 box = 1”, 1 box = ½”, 1 box = ¼” etc.
Help: The plans are intended to give sufficient information to build a
PoorBoy if you have some shop or mechanical experience. There may be
builders in your area or people with aircraft building knowledge, they are
usually quite willing and helpful if you ask. Check your area for Ultralight
or general aviation clubs, many fixed base operators have a repair shop and I
have gotten a lot of help from their A & P mechanics. The Poorboy builders have
a forum http://groups.yahoo.com/group/poorboy/
Substitutions: Most builders have idea’s they want to try out, sometimes they
have better ways of doing things but please remember to check with others when
making changes for safety.
090708 Pg-14
Hinge construction using formed hinge sections.
A regular flat hinge as is standard applied piano hinge is acceptable in place of the rolled and
shaped hinge style you see explained here. The novelty of the formed hinge is perhaps a bit
stronger and I think is nifty however it does slow down the building process.
The Poorboy rolled hinge installation style. Start off by making the hinge press, this is done
with a ¾” x 6” bolt, cut off the head, the non threaded area (grip length) is 4”. Make a press cap
from 1” outside diameter gas pipe (nipple etc.) and with a 4” no thread area cut it in half
lengthwise, file it smooth and remove imperfections. Put a strip of duct tape on one 4” edge of the
press cap and tape it to the bolt so it is easier to handle when you are pressing the hinge pieces.
Position the piece of hinge with the factory curled hinge portion facing away from the bolt, squeeze
the hinge strip in the hinge press using a vise. You now have a hinge half that is contoured to fit a
¾” to 1” etc. tube for the tail feathers hinges, you may not want to use this on the ailerons as the
bigger tube limits deflection angles. Using two of these formed hinge halves rotate one half 180
degrees in position to the other half and insert the hinge pin, this gives a slight “S” shape to the 3
½” to 4” hinge segment you have just built. Take a look at the pictures, I hope this will make it
clear enough. Install the hinge with ½ hinge segment up (Leading tube) and ½ of the hinge
segment down (trailing tube) as shown. This hinge segment will give you about 50 degrees
rotation in either direction from straight in line position on a 1” tube installation (+ 100 degree total
rotation). Where a hinge strip requirement is greater than the 4" segments just put more segments
side by side and use a common hinge pin. Leave the hinge pin 1/2" longer than the hinge segment
on each end and bend the sticking out ends 45 degrees, using a drilled AN4 bolt (drill the hole to
3/32") bend the hinge ends. This style of hinge pin installation is a bit unsightly but it is very easy
to view for safety inspections and allows easy pin removal in case you want to remove a control
surface.
The description sequence of building can be altered, you can build any section first, hang-cage
(fuselage), tail, wings etc. The tail is one place to start that gives you some building time without
a lot of investment, I prefer the A-frame and hang cage.
A-FRAME 062807 Pg-15
A-Frame Bow.
Optional:: start by purchasing 10 ft of ¾ emt conduit, cut into two 4’ lengths, use these two pieces as practice before you bend the 4130 steel bow.
See DIA-AF-1 and PIC-AF-1.
The Bow is made of 7/8” x .058 x 4ft long 4130 steel tube. THIS IS THE HARDEST (most pressure required) BEND ON THE AIRPLANE. Mark and center punch both sides of a through hole position located at the center (24” from either end of the tube), use a graph paper ring to get the holes in alignment. Drill a 1/8” hole on both sides of the tube. Insert a ¾” x .049 x 3 ¼” long 4130-st piece of tube into the bow tube and center it to the 1/8” hole, slightly round the cut ends of the insert before installing. Drill 1/8 hole into the insert at one of the 1/8” bow holes, (be sure the insert is centered), (“or” drill 1/8 centered hole into the insert before you install it into the 7/8” tube being sure you can align it to one of the 1/8” bow tube holes).
Put a 2” sheet-rock screw into the hole to hold the insert in place, this screw is the bottom reference for the bender (parallel inline with the benders handle) and you want the screw to stick out straight as it goes through the bow tube and insert. Drill the opposite “top” insert hole with the screw in place so the insert does not loose alignment.
On top of the bow tube mark a line 1” on both sides from the top hole. On the bottom of the center screw position mark a line on both sides of the Screw 1 ½” to each side. Slide a bending support tube onto one end 8” of the tube you are bending (the back side “tail” of the work stock to be bent and place on a piece of plywood to prevent scratching when you make the bend. You will need this support tube for leverage, any 4’ long pipe that gives a snug fit will work for the support tube (a 1”x .058 x 4’ tube fits perfectly). Tape the support bar in place so it doesn’t move around when you make the bend. You probably will not be able to make the bends without the use of a support tube because the leverage will bring the work piece off the ground unless you have the support tube extended length sticking out the back side giving you the mechanical advantage for leverage, I even insert a big screwdriver in the end of the support bar and tie a rope around the screwdriver handle so I can pull at the same time I make the bend for additional leverage. You will need all of your weight on the foot position of the bender, if you are a light person you may need help.
Position the tube on the bender with the support bar attached (RIGID ¾” EMT p/n B-1678 Bender) so that the top 1” mark falls on the back side of the benders Hook, and the bottom 1 ½” mark falls on the body at the start of the bend radius support of the bender. The screw should be protruding straight out and parallel in line with the handle of the bender and on the bottom side of the benders hook.
This is a fairly hard bend so keep good foot pressure on the bender, the bend is about 70 DEGREES (go slightly less until you check everything). Bend the other side of the bow by reversing everything (including the bend support bar) and this also is about 70 DEGREES, “NOTICE” Pay particular attention to keep the bent arm in plane with the handle on the second bend or your piece will not be in-line on the legs of the bow. “Lets say that again!” Keep the two bent legs of the bow in line (in plane) with each other, (use the benders handle for reference compared to the first bend).
If you want this piece already made we can supply it.
042207 (See DIA AF-1 and DIA AF-2) Pg-16
The side legs are made of two aluminum (AL) tubes for each leg, a 1” tube inserted into a 1 1/8” tube. These are .058 wall and are 48” long. From the bottom of the side legs to the bottom of the seat support tube is 10 ½”. The first hole for the frame strut bracket is at 9 ½” (three holes are from the bottom of the leg at 9 ½”, 11”, 12 ½”). Use a graph paper circle to locate these “through” holes” that are 1 ½” apart to match the double U-bracket. The Rans W-WCL attach brackets are very nice piece of hardware and cost about $5.00 a piece, you can make your own from 1.25 X 1.24 X 1/8” 6063-T52 U Channel stock from Aircraft Spruce & Specialty, P/N 03-39150 at $3.75 a foot. Note.. the double U-bracket should be exactly 1 ½” hole spacing but double check and match everything to the double U-bracket holes (P/n W-WCL), use the double U-bracket as a pattern to check hole locations. Make the flat strut frame brackets that go under the double U-brackets and assemble on the side leg tubes (See Pic-AF-2 & DIA-af-2). Install bolts and assemble the brackets to the legs. **Note** The Diagrams for flat strut brackets and gear leg brackets list the aluminum material as 6061-T6, a stronger bracket can be made using 2024-T3 material and if cost is not a consideration this .125” is the better material. The prototype PB-1 is flying with the .125 6061.
Insert the steel bow tube legs (top of the “A” in the “A-Frame) into the aluminum side legs of the A-frame and with the crossover tube in position, set the bow to crossover seat tube height dimension for the pilot 42” (from bottom of the bow tube to the top of the cross over tube). The outside distance at the bottom end of the side legs should be 52” (outside), and at the seat cross support it should be about 42” (inside distance of the A-Frame tubes at top of the seat cross-over tube location).
Now is the time to decide how large your seat area needs to be for the pilot.
The distance between the bottom of the bow tube arch and the top of the cross-
over tube (seat rail) is 42” in the plans and is adequate for most pilots, you can increase this for a quite large pilot, this will not bother the instructions as the root tube is set by angle not by distance. You can lengthen the nose if need be also (see nose section) Make final angle adjustments to the 4130 steel bow tube and line up everything.
You should have two side legs with four frame (strut) brackets underneath four double “U” brackets. 3 ea. AN3 bolts (3/16”) hold the brackets together on each leg (use temporary hardware). These too side leg assembles slide onto the bow tube legs (do not drill yet, just tape in position). Now the cross over “seat support” tube is also two tubes, one inside the other like the legs (1” inside 1 1/8” .058 al. tube). Cut the cross over tube to 42” and position in the bracket and drill one hole only in each end matched to the flat plate bracket. The “A” is complete, insert a bolt in each end of the cross over tube.
After cutting the 42” seat support tube (cross over carry tube), check position and alignment of the A-frame assy.