23-Eng.& cowling
Chapter 23 Engine installation Summary (doubleclick pics for larger size)
23-1
Pic #1: This is Bruce Turrentine. His shop is near Raleigh, N.C. He did the conversion of the Renesis to aviation use. The engine is new. When I add the EC3 and EM3 and redrive unit from Tracy Crook, then the core of the FW installation will be done. I have pics of the IVO Magnum adjustable prop at 23-6, later in this chapter.
Pic #2:
This is the Renesis rotary engine. Before being modified for aviation use, it's rated for 230 H.P. I expect 220 H.P. The stock intake manifold sets up a perfect situation for a downdraft scoop on top of the turtleback to add some power at cruise altitude, and this led to custom engine cowlings. A Featherlite cowling is the best choice for the Lycoming engine.
Engine Cowling and scoop lip
You may wonder why start the engine cowling before the engine is mounted. I flipped the plane over to finish the strakes and then the final finish of the lower side of the fuselage. Now is the best time to start the lower half of the cowling. Later, I will build the cowling,in part, like I built the nose of the fuselage and the landing lights in the LE of the strakes. I will place blue foam over the engine and cooling segments with some temporary support from the lower side of the engine mount and carve the blue foam to shape. I'll apply some epoxy and one ply of BID in sections, masking tape holding the sections up onto the foam. Then I will reinforce the glassed core, externally, like for the winglets in my chapter 20, but I will add a frame like for the canopy work (no bondo). When the lower cowling core is stiffened, then I will release the temporary internal supports and remove the core and then carve most of the blue foam. I will leave some of the blue foam for internal "rib" reinforcements and glass these ribs. It's a sure thing that I will not impinge on anything, since the foam was thinned down to make the ribs. After cure, I will add some temporary supports and remove the external temporary supports. Then the exterior is cleaned up and a 4 ply BID layup is done in overlapping halves. That is better to show in pictures, but that is for later.
The plans call for a partial lip (aka fuse lip) to be added to the aft of the fuselage and then complete this lip to fit the premade cowling. I made the full length of fuse lip, but only after making the first four inches of the cowling lip. I will have the plane painted before the engine is installed and later complete the cowling to match the engine setup and then have the cowlings painted. I will have to trial fit the engine and intake manifold prior to the painting to get the intake scoop constructed. See pics later.
23-2
The first step for making a lower cowling is to make the first four inches with the foam, before I place the fuse lip off the fuselage. The cowl lip is four inches wide, and the fuse lip is four inches wide, but two of those inches overlaps the fuselage. I microed on some foam blocks that overextended the contour. The scoop blocks are per plans and are added into this setup. I had already filled the bottom before this point so I sanded off the micro from the last 2.5 inches of the aft of the fuselage. I recommend this approach, because the final contour is already set and the sighting is much easier. I sighted down the sides of the fuselage to get a symmetrical taper of the cowling lip. I trimmed down and then looked from the nose of the plane, "peeking" left to right. Since a four ply BID layup (the main cowling layup) will be glassed on top of the aft two inches of the cowling lip, the aft two inches of the foam needed some additional taper. The last picture show the stepdown from the end of the fuselage to the foam. The cowling lip for the lower cowling was done as a 6 ply layup, on a plastic template (two ply BID-45 degree and two ply UND-in line-LT to RT, and then 2 more ply BID-45 degree). The fuse lip is a 4ply BID and so I trimmed to account for this. The addition of the UND on the cowling lip added some problem on the shaping, so you may choose to stick with the 4 ply BID. The second picture shows the gloss on the foam. I painted on epoxy and let it cure. The stiffening action is vital for the contouring of the transferred glass layup. I did this for the LE of the strakes also. Do not use blue masking tape. Use a premium tan masking tape and it will peel off. The tape is needed to prevent a dip in shape at the foam junctions, since micro is not used here and the outer lip would also have that dip with this technique. You have to clean the under side of the cowling lip to add some 1.5 by 2 inch 4 BID reinforcements for the nut plates. Later pics show the scoop lip and "upper part" construction.
23-3
In the first picture, the fuselage lip is on top and the cowling lip is below. I drilled the holes for the Ms24694-S51 screws before separating the two. The holes will be redrilled at several steps along the way, but the orientation will be set. The separation of the two layers was made easier by using the dremel to separate the part of the cowling lip that fit over the "wing root" rib from the main portion for the separation of the two pieces. I reattached it later. The extra glass that drooped down on the cowling lip is left that way to maintain shape until it is attached to the fuselage lip with the nut plates and machine screws (see pic below).
23-4
In the first picture, I had to "glass up" and so I used masking tape to hold the glass on the inner side of the scoop lip. Then I added a lip on the upper and side parts of the scoop "throat". The air will circulate through the cooling coils and then be directed to exit points at the aft of the wing root areas. The 200 m.p.h. wind must be directed to the coils and be made to slow down enough to do the heat transfer and then regain speed at the exit points. This involves pressure changes, ect. I read Tracy Crook's conversion book and I think that the Cozy platform can lead to better cooling conditions, since everything is forward of the propeller. To do all of that, I must contain the air flow in ducting along the whole way. Back to the pictures, there is a space between the sides of the scoop throat and the fuselage lip to allow the cowling lip to slide in place.
23-5
The last pic of the group shows the cowling lip screwed onto the fuselage lip with the MS21069L3 two lug anchors, aka nutplates. You may see the 4 ply BID reinforcement strips on the inner side of the fuse lip to the aft of the CS. The small bit of tan on that strip is some tan masking tape that has not been sanded off. I needed these reinforcement stips to lay down perfectly in the corner, so I placed masking tape instead of peel ply on the "bottom" side and with some ficro in the corner, I adapted the corner and then placed masking tape on the edge to the inner side of the fuse lip. After cure, I trial fitted the cowling lip again and it still fit well. I had a 1/4 space from the forward edge of the cowling lip to the CS/FW before these layups were placed. Also shown is the 1.5 inch wide 4 ply BID strips on the bottom of the cowling lip at the nutplate points. I used strips, because I wanted to maintain flexibility of the cowling lip to adapt to the fuse lip.
Now, back to the first picture. I clamped the two lips together. The original drilled holes were preserved in the cowling lip and redrilled after the reinforcement pads were placed, but the micro on the fuse lip obscured the holes there. So, I got out my 90 degree attachment for my drill and drilled from the inner side of the cowl lip to remake the holes in the fuse lip. I marked tick lines to exactly refit the lips back together. I trial fitted the machine screws through the two lips,and then I took off the cowl lip and attached the nutplates. See the second picture for that. I ordered the exact nutplates called for in the plans, but I chose to place 1/8th inch pop rivets from Lowes. So I screwed the nutplates onto the cowl lip and drilled the holes out to 1/8th inch and placed the pop rivets. They are very secure and it was easy to do.
In between the second and third pictures, I refitted the two lips and placed the machine screws (with the A3235-028-24A washers), but this time into the nutplates. I drew outlines with a pencil around the washers and took out every other machine screw/washer and recessed the fuse lip and replaced those and repeated the process with the rest. That's too much detail. But, if you use this method, then I don't want you to go astray and wish that you had done the work another way. At this point, I am ready to do some final touch up on the finish and then "epoxy coat" the micro and then prime the bottom. I will have an aviation painter finish the painting from there.
IVO Magnum adjustable pitch with constant speed governor
(Let the e-mails be sent to russellcozym4@att.net)
See notes below the pictures.
23-6
The first picture is of John Slade's prop on his Cozy, placed in 2006 with a 2.17:1 redrive from Tracy Crook and a turbo Mazda 13B. My setup is a Mazda Renesis and a 2.85:1 redrive from Tracy Crook. The difference, in the redrive ratio, is due to higher red line and higher compression ratio and power.
I am well aware of the three shortcomings of the IVO system.
1. The vibration of the Lycoming engines conflicts with the design of this type prop.
The solution is to match this prop to a redrive setup.
2. The second problem is related to that and it is cracks in the fiberglass bass of the blades.
The third picture shows the cam shafts protruding from the base of the blades. The pitch of the prop blades is changed by flexing of the fiberglass with the cam shafts. The IVO instructions speak of fore and aft movement of the blade during rotation. This oscillation and the flexing of the blade put stress on the fiberglass. All props have stress in their motion, and the solution here is to set the climb and cruise settings at 80% of what is available in flexing. The IVO folks do not give you any settings. The pilot/builder sets this by test flights. The pilot takes off and with full power adjust the prop from the neutral position to the pitch for best climb, leaves the plane at that setting, lands the plane and installs the correct number of limit washers for that setting. If the best climb setting is scaled back by one/fifth, then the stress is decreased by more than one/fifth. The additional flexing of the prop blades to gain that last one/fifth of performance is like the classic bell curve of with a steep curve.
3. The third problem is the human error factor on assembly of the prop. It looks to be simple, but the errors that creep in here have led to erratic performance. I will have some help on the install.