Van's Air Force
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Spinner Backplate to Cowl Clearance
- Thread starter McFly
- Start date
Kyle Boatright
Well Known Member
My experience is that you'll be hard pressed to remove the bottom cowl if you go with a 1/16" gap. Mine is 3/8" or so and I have to flex the cowl to get it to drop.
Why? Because the gear legs prevent the cowl from dropping straight down. This *might* be helped by going with very large cut-outs where the cowl is relieved to fit around the gear legs. In addition, you need to move the cowl forward slightly to disengage the airseal fabric which seals between the cowl and baffles and between the air intake and airbox. In addition, the cowl needs to slide forward a bit to disengage the hinge eyelets. The combination of these factors seems to more or less rule out a tiny gap.
If I had it to do over again, I'd go with a 3/8" - 1/2" gap and would oversize the gear leg cutouts in the bottom cowl. Note that the cowl fore/aft placement is a double edged sword, because the farther aft you position the cowl, the closer the cowl is to the starter and alternator. On the other side of the equation, a bigger gap makes it easier to remove the cowl
Why? Because the gear legs prevent the cowl from dropping straight down. This *might* be helped by going with very large cut-outs where the cowl is relieved to fit around the gear legs. In addition, you need to move the cowl forward slightly to disengage the airseal fabric which seals between the cowl and baffles and between the air intake and airbox. In addition, the cowl needs to slide forward a bit to disengage the hinge eyelets. The combination of these factors seems to more or less rule out a tiny gap.
If I had it to do over again, I'd go with a 3/8" - 1/2" gap and would oversize the gear leg cutouts in the bottom cowl. Note that the cowl fore/aft placement is a double edged sword, because the farther aft you position the cowl, the closer the cowl is to the starter and alternator. On the other side of the equation, a bigger gap makes it easier to remove the cowl
dan
Well Known Member
Mine has 1/4" gap at the top and 5/16" gap at the bottom and it's just peachy like that. I gouged out pretty big chunks of the lower cowl aft corners where it meets the gear weldments, since that area gets covered by the upper intersection fairing.
My lower cowl is easy to remove, but then again I don't have any paint!
If I had paint, every little precious 64th of an inch gap-wise would help that lower cowl drop out without scratching the front face or the spinner.
1/16" is too slim for my taste.
I know everybody tries to shoot for zero gaps all around, but in some spots the gaps are highly functional and make life a heck of a lot easier -- overshadowing any "aesthetic benefit" you might stand to gain from less gap. Case in point...my spinner and spinner bulkhead was a nice tight fit on my prop. So tight that it chafed. Had it been any worse it would have meant blade overhauls. Sometimes you gotta go with a little extra gap for the peace of mind.
My lower cowl is easy to remove, but then again I don't have any paint!
If I had paint, every little precious 64th of an inch gap-wise would help that lower cowl drop out without scratching the front face or the spinner.1/16" is too slim for my taste.
I know everybody tries to shoot for zero gaps all around, but in some spots the gaps are highly functional and make life a heck of a lot easier -- overshadowing any "aesthetic benefit" you might stand to gain from less gap. Case in point...my spinner and spinner bulkhead was a nice tight fit on my prop. So tight that it chafed. Had it been any worse it would have meant blade overhauls. Sometimes you gotta go with a little extra gap for the peace of mind.
RV7Guy
Well Known Member
Gap
Forget the 1/16". As noted, you'll never get the cowl off. I have about 1/8" at the top and 3/16" at the bottom and it is barely enough. I'd shoot for 3/8" and you'll be set, a 1/4 is the closest I'd go for. I've seen up to a half inch and it really doesn't detract from the appearance.
Another thought that hasn't been brought up, if the gap is close and your engine runs rough for any reason, there is a chance the spinner could contact the cowl.
Forget the 1/16". As noted, you'll never get the cowl off. I have about 1/8" at the top and 3/16" at the bottom and it is barely enough. I'd shoot for 3/8" and you'll be set, a 1/4 is the closest I'd go for. I've seen up to a half inch and it really doesn't detract from the appearance.
Another thought that hasn't been brought up, if the gap is close and your engine runs rough for any reason, there is a chance the spinner could contact the cowl.
petehowell
Well Known Member
I want an umpire with .....
a keen mind and cat like reflexes......... eagle-eyes would be good too..
FYI - Darwin's other passion is baseball - he is a big time Ump for College, High School and Little League.
I coach Little League and we are sworn enemies
It's playoff time - shop time is suffering for all the right reasons.......
a keen mind and cat like reflexes......... eagle-eyes would be good too..
FYI - Darwin's other passion is baseball - he is a big time Ump for College, High School and Little League.
I coach Little League and we are sworn enemies
It's playoff time - shop time is suffering for all the right reasons.......
tx_jayhawk
Well Known Member
I am fitting the cowling. As the plans suggest, I offset the cowl approx. 1/8" lower than normal to account for engine sag. Due to the offset, it appears as though I have approx. 1/8" clearance on the top, and up to 1/4" clearance on the bottom.
Is this sufficient clearance? I have drilled the bottom half to the firewall but not the top. I am thinking I might be able to "pull back" the top when drilling the firewall attach holes, effectively shifting the whole cowl up and back.
I am curious what others might have done in this regard.
THanks,
Scott
7A Finishing
Is this sufficient clearance? I have drilled the bottom half to the firewall but not the top. I am thinking I might be able to "pull back" the top when drilling the firewall attach holes, effectively shifting the whole cowl up and back.
I am curious what others might have done in this regard.
THanks,
Scott
7A Finishing
Jim P
Well Known Member
Same here...
Scott,
I just drilled the top cowl to the camloc strip tonight and have the same. From reviewing the forums, it looks like this is pretty common. I have .250 at the top of the spinner plate and .375 at the bottom of the top cowl. Depending on how bad this looks, most folks seem to build up this area with foam/ glass when closer to finishing.
Jim
Scott,
I just drilled the top cowl to the camloc strip tonight and have the same. From reviewing the forums, it looks like this is pretty common. I have .250 at the top of the spinner plate and .375 at the bottom of the top cowl. Depending on how bad this looks, most folks seem to build up this area with foam/ glass when closer to finishing.
Jim
RudiGreyling
Well Known Member
Hi Guys,
Ditto, I was going to place a post myself today, mine is a bit worse, see pictures below.
Everything aligned I get 1/4" difference top to middle. I am concerned how bad it will get when I fit the bottom cowl. The top is a 1/8" spacer which is the minimum clearance, then middle i get 3/8". I aligned the top of spinner and cowl ZERO difference to acount for eventual 1/8" engine sag.
I checked engine mount, rubbers, bolts etc, everything is in place as per plans.
I am baffled and sent an email to Van's last night, no response yet.
What you guys think?
Thanks, Rudi.
Ditto, I was going to place a post myself today, mine is a bit worse, see pictures below.
Everything aligned I get 1/4" difference top to middle. I am concerned how bad it will get when I fit the bottom cowl. The top is a 1/8" spacer which is the minimum clearance, then middle i get 3/8". I aligned the top of spinner and cowl ZERO difference to acount for eventual 1/8" engine sag.
I checked engine mount, rubbers, bolts etc, everything is in place as per plans.
I am baffled and sent an email to Van's last night, no response yet.
What you guys think?
Thanks, Rudi.
Dont screw it up. ;o)
I have to interject. If you don?t want to find out later your fit has gone to **** in a hand basket, do yourself a favor and make a nice stiff wooden back plate and use that to mock up your cowling fit. That back plate is flimsy and once mine was bolted on it was not true on the aft edge. Making a wooden one will allow you to clamp to it and maintain perfect alignment.
-Jeff
I have to interject. If you don?t want to find out later your fit has gone to **** in a hand basket, do yourself a favor and make a nice stiff wooden back plate and use that to mock up your cowling fit. That back plate is flimsy and once mine was bolted on it was not true on the aft edge. Making a wooden one will allow you to clamp to it and maintain perfect alignment.
-Jeff
RudiGreyling
Well Known Member
RV_7A said:
Hi Jeff,
Thanks, I was considering this but did not want to take out my nice prop yet out of its box or go the extra effort. But then last night I decided to do it right, I bolted the prop to the back plate, on the plane, now it is the way it will be in final fitting. Guess what...no significant difference in the cowl fitting and sizes for me, but at least know I now for sure...And I can also start on the spinner fitting while the prop is on.
Regards
Rudi
Last edited:
jsharkey
Well Known Member
RudiGreyling said:Hi Guys,
Ditto, I was going to place a post myself today, mine is a bit worse, see pictures below.
Everything aligned I get 1/4" difference top to middle. I am concerned how bad it will get when I fit the bottom cowl. The top is a 1/8" spacer which is the minimum clearance, then middle i get 3/8". I aligned the top of spinner and cowl ZERO difference to acount for eventual 1/8" engine sag.
I checked engine mount, rubbers, bolts etc, everything is in place as per plans.
I am baffled and sent an email to Van's last night, no response yet.
What you guys think?
Thanks, Rudi.
Rudi,
I'd try to get the upper and lower cowls trimmed and aligned together. You have to make small and repeated cuts to seak up on the final fit and trim. I had similar problems but no where near as severe. Getting every thing aligned and trimmed togther helped. I also ended up redrilling hinge holes.
Have you trimmed the rear edge of the upper cowl and settled it flush with the front deck skin of the fuselage? Otherwise it will be riding high. This coupled with the low setting at the front relative to the back plate will tend to tip lower edge of the front backwards. Having said that many builders end up building up the front face of the cowl with filler for a better look.
See earlier posts:
http://www.vansairforce.com/community/showthread.php?t=17902
PS - wait till you start the baffling!!!!!!
RudiGreyling
Well Known Member
Hi Jsharky...
thanks for your feedback, and no it is not riding that high at the back, maybe I just got the worst of the lot of cowls.
I will reserve judgment if I am going to fill-up with glass until I have fitted and mounted the bottom cowl as well.
Regards,
Rudi
thanks for your feedback, and no it is not riding that high at the back, maybe I just got the worst of the lot of cowls.
I will reserve judgment if I am going to fill-up with glass until I have fitted and mounted the bottom cowl as well.
Regards,
Rudi
Vern
Well Known Member
Cowl fit
Just remember that the closer the fit,the harder to install the cowl from now on and the more likely you will scratch your paint . The A's in particular will have a tougher time installing the lower cowl with the gear leg to deal with.
initailly I was determined to have a very tight close tolerance cowl to spinner fit but had to keep making minor adjustments. Now I almost wish I could do the whole thing over with about 3/8" clearance. {note I said 'almost' }
As I'm fond of saying: the next one will be better.
Just remember that the closer the fit,the harder to install the cowl from now on and the more likely you will scratch your paint . The A's in particular will have a tougher time installing the lower cowl with the gear leg to deal with.
initailly I was determined to have a very tight close tolerance cowl to spinner fit but had to keep making minor adjustments. Now I almost wish I could do the whole thing over with about 3/8" clearance. {note I said 'almost'
}As I'm fond of saying: the next one will be better.
vlittle
Well Known Member
RudiGreyling said:Hi Jsharky...
thanks for your feedback, and no it is not riding that high at the back, maybe I just got the worst of the lot of cowls.
I will reserve judgment if I am going to fill-up with glass until I have fitted and mounted the bottom cowl as well.
Regards,
Rudi
I have some bad news. When both halves of the cowl are mounted, you will see that the spinner disc on the cowl is not co-planar (the clearance to the spinner backplate is not even). I had to build up the disc quite a bit to get everything looking good and the clearances correct.
When you mount the lower cowl, you will see that the largest clearance will be at the separation line, with less at the top and bottom. Much grumbling, fiberglassing, sanding and filling will entail.
I trimmed the top cowling disc, filled the middle and bottom to get everything just right. See photo.
Vern
Similar cowling fit issues
Rudy,
My cowl looked very similar to yours and had a good 1/2" gap behind the spinner plate to the cowl on the bottom half. I mounted a 1/8" board on the back of the spinner plate to give the flat reference and bolted this in place. Mine also was not symmetric side to side on the top cowl. With the correct clearance on the right side, the left side had an additional 3/8". I ended up slicing the cowl top from the center outboard just forward of the foam core, pushing the sliced part forward and clecoing it in place with a couple of aluminum strips and then glassing it underneath. The top gap was then filled with an epoxy/micro fillers and sanded. The bottom cowl and top cowl were then assembled with the piano hinge pins in place, stood up on the floor, and an epoxy/micro filler laid onto the bottom cowl flange and then a flat piece of glass was laid on top with weights to make a nice even surface to give a uniform gap of 1/8" hehind the spinner plate. It seems like a lot of glass work, but it went fairly quickly. The time spent trying to avoid it was probably more than it took to do it. It will also make you more comfortable with your glass skills. Nothing was difficult leading up to this point in installing the cowling where sloppy work would account for the problem. The cowling is simply not that good a fit following the manufacturer's fabrication.
Good luck. I can post a couple photos of the process later, if you'd like.
Rudy,
My cowl looked very similar to yours and had a good 1/2" gap behind the spinner plate to the cowl on the bottom half. I mounted a 1/8" board on the back of the spinner plate to give the flat reference and bolted this in place. Mine also was not symmetric side to side on the top cowl. With the correct clearance on the right side, the left side had an additional 3/8". I ended up slicing the cowl top from the center outboard just forward of the foam core, pushing the sliced part forward and clecoing it in place with a couple of aluminum strips and then glassing it underneath. The top gap was then filled with an epoxy/micro fillers and sanded. The bottom cowl and top cowl were then assembled with the piano hinge pins in place, stood up on the floor, and an epoxy/micro filler laid onto the bottom cowl flange and then a flat piece of glass was laid on top with weights to make a nice even surface to give a uniform gap of 1/8" hehind the spinner plate. It seems like a lot of glass work, but it went fairly quickly. The time spent trying to avoid it was probably more than it took to do it. It will also make you more comfortable with your glass skills. Nothing was difficult leading up to this point in installing the cowling where sloppy work would account for the problem. The cowling is simply not that good a fit following the manufacturer's fabrication.
Good luck. I can post a couple photos of the process later, if you'd like.
Another Caution
I'm at my MIL's in PMD, CA, and plans are 600 miles away, but I can caution this point on cowl fit-up after building two 7's: Van's Lies.
Besides all the above discussion regarding a tapered gap which is molded into the parts,and you may want to deal with it by cutting/filling for evenness,the instructions make mention of using a spacer to simulate the prop hub. THE DIMENSION IS WRONG, at least as far as a constant speed hub. I think Van's says 2 1/4, when it really needs to be 2 1/8 for a nominal final 1/4 gap. Add up the washer and bushing dims and you will see the error. If you don't,you wind up with a 1/8 narrower gap when you bolt up the for-real prop.
John Siebold
Boise, ID
I'm at my MIL's in PMD, CA, and plans are 600 miles away, but I can caution this point on cowl fit-up after building two 7's: Van's Lies.
Besides all the above discussion regarding a tapered gap which is molded into the parts,and you may want to deal with it by cutting/filling for evenness,the instructions make mention of using a spacer to simulate the prop hub. THE DIMENSION IS WRONG, at least as far as a constant speed hub. I think Van's says 2 1/4, when it really needs to be 2 1/8 for a nominal final 1/4 gap. Add up the washer and bushing dims and you will see the error. If you don't,you wind up with a 1/8 narrower gap when you bolt up the for-real prop.
John Siebold
Boise, ID
RudiGreyling
Well Known Member
cytoxin said:
Hi cytoxin,
I don't have a fix yet, just started to mate the bottom cowl, will look what it looks like after the bottom cowl is on. I hate fiberglass so much currently I might just say stuffit, leave it, fly it like that. But time will tell. I think one will have to build it up similiar to what Vern did. I am currently in the grumbling phase, don't know what I am going to do yet.
Regards,
Rudi
cowl to spinner clearance?
Hey all -
i perused the archives, but thought i'd ask again here... I'm fitting the cowl on my RV-10, and so far i've got the upper half pretty much dialed in, but i've set the clearance from the aft edge of the spinner (MT prop) to the front of the cowl at 1/8". is that too small? I have seen where others have gone for 3/16 or 1/4", but I wonder if there's a reason for that. the RV-10 plans seem to indicate 1/8", and the instructions for the Sam James Cowl indicate 1/4". what say you all?
thanks
cj
Hey all -
i perused the archives, but thought i'd ask again here... I'm fitting the cowl on my RV-10, and so far i've got the upper half pretty much dialed in, but i've set the clearance from the aft edge of the spinner (MT prop) to the front of the cowl at 1/8". is that too small? I have seen where others have gone for 3/16 or 1/4", but I wonder if there's a reason for that. the RV-10 plans seem to indicate 1/8", and the instructions for the Sam James Cowl indicate 1/4". what say you all?
thanks
cj
CJ,
The plans call for 1/8". It is tight at an 1/8" but the top cowl lifts straight up it's not to big of a deal. Mine right now is at 1/4". It is a 1/4" because that was the only way to get the upper and lower nose rings to match flat acrossed the front and fit the lower cowl on the bottom. I plan to apply micro/epoxy to the nose ring and sand for a better fit all around of 3/16". Deem's just refitted the spinner on his because of some mismatch. Check out his latest post on kitlog
The plans call for 1/8". It is tight at an 1/8" but the top cowl lifts straight up it's not to big of a deal. Mine right now is at 1/4". It is a 1/4" because that was the only way to get the upper and lower nose rings to match flat acrossed the front and fit the lower cowl on the bottom. I plan to apply micro/epoxy to the nose ring and sand for a better fit all around of 3/16". Deem's just refitted the spinner on his because of some mismatch. Check out his latest post on kitlog
flickroll
Well Known Member
Prop Spinner / Cowl Gap Clearance
I purchased a previously flying, but disassembled when I bought it, RV-8. I am now close to flying it, having rewired the aircraft, completely redone the panel, changed out the gear to a Grove airfoil, and at this point have also reattached the wings and empennage. This weekend I will reattach the flaps, ailerons and prop. The airplane came with a Hartzell cs prop, however I sold that prop and am about to install a new Whirlwind 200RV prop.
There may be a slight difference in the gap between the spinner and cowl from the previous prop installation to the new Whirlwind installation. So my question is, what is the minimum gap that is acceptable, and what is the maximum gap that is acceptable? I know tighter is better, but it can also be too tight such that engine movement and/or sag could cause interference at times. Not good! Conversely, I may wind up with a large gap that I will somehow need to tighten. Any thoughts and comments appreciated. Thanks
I purchased a previously flying, but disassembled when I bought it, RV-8. I am now close to flying it, having rewired the aircraft, completely redone the panel, changed out the gear to a Grove airfoil, and at this point have also reattached the wings and empennage. This weekend I will reattach the flaps, ailerons and prop. The airplane came with a Hartzell cs prop, however I sold that prop and am about to install a new Whirlwind 200RV prop.
There may be a slight difference in the gap between the spinner and cowl from the previous prop installation to the new Whirlwind installation. So my question is, what is the minimum gap that is acceptable, and what is the maximum gap that is acceptable? I know tighter is better, but it can also be too tight such that engine movement and/or sag could cause interference at times. Not good! Conversely, I may wind up with a large gap that I will somehow need to tighten. Any thoughts and comments appreciated. Thanks
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So my question is, what is the minimum gap that is acceptable, and what is the maximum gap that is acceptable? I know tighter is better, but it can also be too tight such that engine movement and/or sag could cause interference at times. Not good! Conversely, I may wind up with a large gap that I will somehow need to tighten. Any thoughts and comments appreciated. Thanks
Hi,
I have had both Hartzell and WW props. Recently change my plane from a WW 151 to a WW 200. The hartzell spinner backplate is flat and a closer gap will cause no problem. Shoot for 1/4 to 3/16 inch. The WW is a different animal. The spinner back plate is conical and this causes the clearances from cowl to back plate to be closer. Not an issue until you do a high G maneouver, or when starting up the engine. It is possible for the back plate to contact the cowl . With the WW 200 I would try for no less than a quarter inch and maybe just a hair more. After flying for awhile, check the cowl to make sure there is no contact. Mine did, and i needed to perform the "shim the lower engine mounts" routine to bring it back into center.
Steve Ciha
So my question is, what is the minimum gap that is acceptable, and what is the maximum gap that is acceptable? I know tighter is better, but it can also be too tight such that engine movement and/or sag could cause interference at times. Not good! Conversely, I may wind up with a large gap that I will somehow need to tighten. Any thoughts and comments appreciated. Thanks
Hi,
I have had both Hartzell and WW props. Recently change my plane from a WW 151 to a WW 200. The hartzell spinner backplate is flat and a closer gap will cause no problem. Shoot for 1/4 to 3/16 inch. The WW is a different animal. The spinner back plate is conical and this causes the clearances from cowl to back plate to be closer. Not an issue until you do a high G maneouver, or when starting up the engine. It is possible for the back plate to contact the cowl . With the WW 200 I would try for no less than a quarter inch and maybe just a hair more. After flying for awhile, check the cowl to make sure there is no contact. Mine did, and i needed to perform the "shim the lower engine mounts" routine to bring it back into center.
Steve Ciha
flickroll
Well Known Member
Agghhhh.....not what I wanted to hear but really what I expected to hear. Will find out for sure tomorrow when the prop finally goes on. Thanks for the info Steve.
The minimum gap...
...is what is required to remove the cowl. If you are using the piano hinge solution, then the gap is 1/8 inch (depends on the hinge material you actually used; take two hinge segments, nest them together, and measure the distance that they have to move apart to get themselves free-and-clear of each other.) Remember, with the hinge solution, the top cowling needs to be pried away from the bottom cowling on both sides, and then moved forward (towards the prop) to clear the hinge segments across the top.
The minimum distance measurement that you come up with is just that. It also guarantees that as you are shoving the cowling forward to get free from the hinges, the cowl front will bang into the rear of the prop spinner and may scratch the paint. Additional clearance helps prevent this from happening.
Quarter turn fastener solutions eliminate this "clearance" requirement as described above...
What you are left with is somewhat of an unknown...a minimum gap still needs the clearance to accommodate engine shake.
...is what is required to remove the cowl. If you are using the piano hinge solution, then the gap is 1/8 inch (depends on the hinge material you actually used; take two hinge segments, nest them together, and measure the distance that they have to move apart to get themselves free-and-clear of each other.) Remember, with the hinge solution, the top cowling needs to be pried away from the bottom cowling on both sides, and then moved forward (towards the prop) to clear the hinge segments across the top.
The minimum distance measurement that you come up with is just that. It also guarantees that as you are shoving the cowling forward to get free from the hinges, the cowl front will bang into the rear of the prop spinner and may scratch the paint. Additional clearance helps prevent this from happening.
Quarter turn fastener solutions eliminate this "clearance" requirement as described above...
What you are left with is somewhat of an unknown...a minimum gap still needs the clearance to accommodate engine shake.
revenson
Well Known Member
Jim: Glad it worked out for you.
I want to start fitting my cowl (7A), but don't have the WW200RV prop yet.
Van's instructions say use PVC spacers of a certain length (2.25" I think) between the ring gear and the spinner backplate to simulate the prop to fit the cowl. But that's for a fixed pitch and a Hartzell.
Would that work for the 200RV?
Any advice out there?
Roger, 7A finishing, Tucson.
Hazebuster Aviation Sunglasses
Premium Hangar Coatings
I want to start fitting my cowl (7A), but don't have the WW200RV prop yet.
Van's instructions say use PVC spacers of a certain length (2.25" I think) between the ring gear and the spinner backplate to simulate the prop to fit the cowl. But that's for a fixed pitch and a Hartzell.
Would that work for the 200RV?
Any advice out there?
Roger, 7A finishing, Tucson.
Hazebuster Aviation Sunglasses
Premium Hangar Coatings
[email protected]
Well Known Member
You can make the cowl spinner as tight as you like if you split the bottom cowl. The bottom half will now come out sideways instead of having to drop it down. I did that on my RV10 and it is an easy one man job to pull the cowl and put it back on. I used the Skybolts at the back of the cowl and the hinge halves at the sides. I lowered to centerline of the hinges about 3/8 of an inch and use a 8-32 Allen head set screw silver soldered to the wire to hold the wire in. There is a piece of stainless steel bonded into the cowl that the 8-32 screw goes into, so there is a small hole slowing right at the front on both sides.
The joint for the bottom cowl was done with #8 counter sunk screws and nutplates. I used 5 layers of carbon fiber for the joint yo make sure it did not flex much.
The joint for the bottom cowl was done with #8 counter sunk screws and nutplates. I used 5 layers of carbon fiber for the joint yo make sure it did not flex much.
