project pattern
C
Redux
ontinuing with the attachment of hatches, my priorities for the at- tachment of Yuri’s chin pan were a lightweight and clean appearance. Electric power systems rarely need to be ac- cessed, so I was willing to incur a bit of in- creased time to remove the chin to gain some appearance points.
For the ultimate in clean appearance, I used a slotted/bolt capture method at the front of the chin pan (similar to the front of the canopy) and a pair of bolts to secure the aft section of the chin pan. When installed, the fastening mechanism(s) for the chin pan is completely hidden.
Starting with the slotted/bolt capture, the front flange of the fuselage is reinforced with a piece of 1⁄8-inch five-ply birch ply- wood. The ply is then drilled and tapped to receive an 8–32 nylon flush head bolt. The decision to place the bolt in the chin pan or fuselage flange (or canopy or fuselage flange) is dictated by the contours of the hatches and natural direction of motion to remove/attach the hatches. The bolt could be attached to the chin pan, but doing so would require the chin pan be slid into place at an angle (so the rear of the pan would clear the fuselage), and a snug fit of the bolt/slot would not be possible without tightening the bolt after the chin pan was installed. Placing the bolt in the fuselage pan allows the chin pan to be slid onto the fuselage without any angle and a snug fit of the bolt/slot.
Front retention slot of chin pan reinforced.
Moving aft to the rear attachment bolts, they will be installed from inside the fuse- lage, pulling the chin pan flange directly against the fuselage flange. This bolt orien- tation is very secure and virtually elimi- nates all rattling and wear between the flanges. The flanges of the chin pan at the lo- cations of the bolts are reinforced with small pieces of ½ inch long, 1⁄8-inch lite ply (the full width of the flange). The chin pan is then se- curely taped to the fuselage (with the front bolt/slot capture fitted snugly).
by dave lockhart with algirdas ungulaitis You can reach Dave Lockhart via e-mail at
davel322@comcast.net
any 2- to 5-ounce fiberglass, Kevlar®, or car- bon fabric could be used.
After the pilot holes have been drilled, the
holes in the fuselage flanges are opened up to be a slip fit for 4–40 bolts. The holes in the chin pan flanges are opened up to accept 4–40 blind nuts, which are glued into the lite ply reinforcements. Securing the chin pan is now complete, but a little bit of optional (but high- ly recommended) work remains.
Rear
retention screws for the chin pan are installed/removed from the inside of the fuselage.
Chin pan securely taped to allow accurate drilling of rear screw locations.
Using a long 1⁄16-inch drill bit, pilot holes are drilled through the fuselage flange into the chin pan flanges. This is a bit of a deli- cate process as it is possible to pierce the sides of the chin pan if the drill bit is allowed to “plunge” after going through the lite ply reinforced chin pan flanges.
PHOTOGRAPHY: DAVE LOCKHART Retention bolt for front of chin pan.
The slot in the chin pan was easily made with an 1⁄8-inch carbide bit in the Dremel. The flange area of the chin pan was suffi- ciently strong enough to not need reinforce- ment (as was done on the fuselage flange for the canopy bolt/slot capture). However, be- cause of the proximity of the air inlet hole (pre-cut by RC-Composit) and the capture slot, I did add a bit of cloth reinforcement be- tween the two areas. I used a scrap piece of 5.4-ounce carbon fiber/Kevlar® fabric, but
44
While the electric power components se- lected for Yuri are quite robust and do not specifically need aggressive air cooling, ESCs and motors run more efficiently and last longer at lower operating temperatures. I have personally seen particularly ineffi- cient installations that run as much as 50° F hotter than those that are nearer ideal. On hot windy days when the equipment is being run hard, exceeding critical temps (variable depending on the component and brand) can generate crispy bits and a release of “magic smoke”, both of which are bad indeed, espe- cially if combustion of the airplane (ex- tremely rare) occurs when a component fails.
As general rule of thumb, ESCs and mo- tors should not exceed 180° F, as measured on the hottest part, using either infrared or direct contact thermometers. Li-Pos should not exceed 130° F. In the absence of a ther- mometer, most people will describe a 130° F Li-Po as hot to touch, but have no problem holding it. Most people will find it uncom- fortable to firmly grasp a 130° F for more than a few seconds.
Pilot holes for rear retention screws are drilled through the fuselage floor flange into the chin pan flange.
At 140° F, most people will find discomfort with any prolonged contact and OSHA (Oc- cupational Health and Safety Administra- tion) requires protection for workers ex- posed to equipment above 140° F. The next couple of construction steps for Yuri will substantially increase cooling for the motor, ESC, and Li-Pos. Starting with the chin, air enters through the front face, and left undirected, the major- ity will pass by the motor, out the back of the chin pan, into the lower fuselage, and out the
MAY 2013
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