Bill Tews Tips

Someone was asking me about inlets and wires and stuff so here is how I did it for all interested. Under the little polished AL cover hides the hinge pins. I bent the tip of the pin 90 deg to make it easier to grab with needle nose pliers to yank it out. It's still a bit stiff to put in but getting easier as time goes on. Some people have suggested painting the cover rather than polishing the AL. I still might paint them red to match the flames but it seems a minor thing on my list of stuff. I had a real poor fit where the upper and lower halves mate when starting the fitup on the cowling. It took LOTS of milled fiber and grinding to reshape the mating areas to get this look. Making sanding blocks from various sizes of PVC pipe and sticking PSA 80 grit disks to them helped a lot. It still isn't perfect, but it's as good as my sanity would allow. Of note, I had a seemingly endless nightmare trying to get a consistent gap between the upper and lower edges until I broke the code. Ended up using a tiny rectangular jewelers file about 1 mm X 4 mm in cross section. The narrow edge of the file had teeth, and in about an hour, I cut the little rectangular groves you see between the upper and lower parts. I spent 2 weeks doing and redoing the joints, all of which was wasted until I figured out the file thing. I bought the file in a set of jewelers files from Harbor Freight for a couple bucks. Even after getting it mated up, the cowl still had a mind of it's own, and when the clecos where removed, the two halves twisted into whatever bizarre shapes they felt like.I was so bad, I needed two people to shove the corners around to get it lined up enough to get clecos in. I cured this by cowling it up, running the engine until 'till HOT, then shutting it down and blocking the inlets with rags. This got the fiberglass REAL hot (160 deg F plus) at which time it becomes somewhat thermosetting plastic. The fiberglass saw "the light" and was permanently reformed in the shape I wanted. Now the two halves line up very nicely without fasteners. Warmest Regards, Bob Gross

If my cowl looks as good as Bob's after I get done painting it, I'll be quite pleased. I'm filling pinholes this week. Gack! I hope to have the final paint on it soon. I also am using a polished plate to retain the hinge pins. I didn't have any particular problems fitting my cowl halves together. Luck or skill?.... I'll claim it was skill, but take luck every time. Here's a link to the cowl info section: <http://www.usi.edu/science/chemistry/vfrazier/page1.html> FWIW, I didn't follow Mark's assembly order. Not that it won't work, but I thought it would be easier to trim the horizontal hinge lines and install the piano hinge LAST. Completely different than the manual. (I hope Mark's not rolling his eyes too much as he reads this.) YMMV, but I was able to fit the entire cowling in TWO evening works sessions. Then I spent two more installing the Skybolt camlocks (which are nice, but have their own problems) and riveting on the hinges and nutplates. I did use a heat gun to mold the front lip of the removable airbox part of the cowl. Works great. I've spent WAAAYYYYYYY more time sanding and filling pinholes than it took to fit the darned thing. For those who haven't got to this point yet.... you're gonna love it...NOT! My advice is to use a two part (epoxy type) glazing putty to fill the pinholes BEFORE you prime anything. Then plan on spending an evening or two wet sanding 95% of it off. Then prime, sand again, and refill as necessary. It will look like crap while you're doing this but you really will be making progress nonetheless. BTW, for those who haven't had this heart attack yet: I am using PPG basecoat/clearcoat DBU process. Three gallons of paint, epoxy primer, a few pints of trim colors, and the necessary reducers, sandpaper, etc.... get ready.... take a deep breath.....>>>>$1800+. Just for materials. I already have the spray guns and other equipment, including paint shaker, HVLP, Hobbyair mask, etc. etc... I guess what I'm saying is that if you can get your plane painted professionally for $5000 then maybe that's not such a bad price after all! Vince

When installing the cowl, does anyone have some tips regarding spacing/clearances on the front of the engine? Also, there is mention of a template, I assume for this purpose? Do you need to have a prop and/or spinner for this task so you have something to check against? Also, I remember something about having the spinner set 1/8-3/16 above the cowl so as the engine sags over time you have a little to work with?? So many questions, so little time.... Thanks guys, and happy Thanksgiving. Scott Roth #93

Scott There is a jig that you bolt to the crankshaft and then cleco to the cowl that gives you the proper distance from the engine. I believe that Mark has one. I am currently using Tom Martin's. I am being extraordinarily slow at this right now. The jig is on the engine and I still have to rivet the top halve hinge to the cowl and then I can fit it to the fuselage. You can get the entire cowl ready prior to getting the jig and probably only need it for a day or 2 to finish the process. Loren Harmon s/n 76

I used the Team Rocket Cowl Jig and it seemed to work well, I installed the cowling before having the prop and all went well. The spacing came out at about 1/4 inch at the top. My install was a MT. The only problem that I had was the spacing was not even from top to bottom about a 1/4 to 1/2 inch in places. I just built it up with micro balloons as desired. I think positioning the cowling down a little is a good idea as the motor will sag over time. John Wach #96

It's nice to make your own jig or find on some one else made that you can keep awile. It comes in handy when you are making the baffles as you can position the top cowl properly without the bottom cowl installed. Don't be surprised if the front of the cowling does not come out square. I had to take 1/4" off the top front of mine to get 3/8" clearance to the spinner all the way around. Jack #70

I have 5/16" at the top and 7/16" at the bottom. This is needed to leave room for the air scoop to escape. You'll see what I mean when you try to install/remove the air scoop wtihout enuf room at the bottom. Happy Thanksgiving to all! Warmest Regards, Bob Gross

Mark† The air tube exiting the air box is tapered from a large to a small diameter. I assume it is cut off so that the scat tube just†fits outside. Is there any reason to leave it longer and smaller?Blue skies Bob

Bob I would leave it as long as possible for a couple of reasons.† It will be easier to install if it is longer and of more importance it will provide some support for the hose to reduce the possibility of the hose collapsing.† The hose is cut long and makes a tight seal by compressing itself when the filter is in place. Tom Martin

Not really. We made the cone so it would fit the SCAT tubing for both the Bendix (3") and the Airflow FM200 (3.25"), so it's longer than it needs to be.

Make the end so you can fit it into the correct sized SCAT tubing easily.

Hey -- if you make it smaller than necessary, you'll be slower than me (NASCAR restrictor plate style)....in that case, I retract all the above.....

Seriously, I hope everyone understands that the SCAT attaches to the injector with a clamp, and simply slides onto the cone. In order to get the hose to compress a bit (for a good seal), leave the hose about 1 1/2" longer than required for use with a clamp. Carry on! Mark

Since I am not using the stock air box I may not be fully understanding the issues but one bad thing about having that tube taper down is that it is acting as a convergent duct.† Three characteristics of a convergent duct are: 1) airflow speeds up (same number of air molecules trying to go through a smaller opening),† 2) temperature goes up (the molecules are pushed tighter together causing more friction), and† 3) the air pressure drops (venturi effect from Bernoulli's principle).††† The first one isn't as important as the last two.† You want the air to be as cold as possible because it results in a denser fuel/air charge entering the cylinders, and you want as high a manifold pressure as you can get so a drop in air pressure is a move in the wrong direction at this point in the induction system air flow.† Another thing is that if the outlet of the glass flange is not the same size of the ID of the SCAT the air will basically fall off a cliff into the larger diameter SCAT.† This causes lots of turbulence and disruption to clean airflow, further affecting MAP.† One parting shot before I step into my asbestos suit is that SCAT tube by it's very design causes lots of turbulence to the airflow.

Now I guess I would be a real pessimist if all I did was point out the issues and not offer any suggestions, so here goes (for what it's worth):

Bond in a flange that is the same size as the I.D. of the Fuel Injection inlet.† Wicks has different size "Air Duct Flanges" on page 153 of the 2002 catalog that could easily be mounted to the airbox.† A 3 1/4" flange may have to be fabricated if you are using the FM-200.
Maintain the same I.D. from the airbox flange to the FI inlet to maximize flow.
Don't use SCAT.† If possible, reduce the distance from the airbox outlet to the F.I. inlet to 1" or less and make a flexible connector tube out of wetsuit material.† You can by it at dive shops on-line and if you ask for the wetsuit repair glue the stuff literally melts the rubber together and makes a stronger joint than the parent material.† I just cut a 2.5" wide strip long enough to wrap around the flange and bond the ends together.† Add a clamp on each end and you have a very smooth flexible connector between the airbox and the F.I. inlet.† The wet suit material will not stand up to heat or chemicals as well as SCAT but three things make this a reasonable material to use IMHO:† 1) During flight there is very cool air constantly pulled through the tube, keeping it very cool, 2) At shutdown it is at the bottom of the cowl so it gets the coolest air available as the convective cooling of the engine compartment is taking the heat up and out of the oil filler door and cooler air is coming in the exhaust area of the cowl, 3) They are very easy to make so you can change it at annual or even at oil change if you are concerned about it as it is very easy to change.† By the way, if anybody knows of a rubber material with similar flexibility but better heat and chemical resistance please let us all know about it.

Sorry for the "Stream of Consciousness" response but I was in the groove and just couldn't stop myself.
Fire suit is in-place so Flame on,† Scot

Didn't we lose a HRII a couple years ago when his SCAT collapsed?† Or was that an RV???† I can't remember.† I'd hate to be the one to have an "Oh shit" moment.†I'd get the Wicks flange and use SCAT. Vince...It's just my opinion, I could be wrong.Oops, make that SCEET if possible... whatever you feel absolutely won't collapse or delaminate.

Like Scot said NEVER use SCAT, use SCEET. SCAT will kill you.† Warmest Regards, Bob Gross

I like it....EXCEPT... what do you do if your clamp comes loose and the floppy wetsuit material gets sucked into the intake?†† Or if the heat deteriorates it and it rips with the same result?

Like Bob sez, SCEET is the tube to use here, so it doesn't collapse under suction. I am concerned that wet suit material won't hold up to the rigors of an intake and will collapse. (This has happened in the past with less than optimal results.) This goes under the category of bad. You are correct that smoother and more uniform intake is good, though I'm not sure how to easily achieve it. Scott Roth
Didn't we lose a HRII a couple years ago when his SCAT collapsed?†> Or was that an RV???† I can't remember.†

Yep -- that was Steve Jacksons' HR2. Had been in for service about a week before, and the tech didn't put the clamp on. The hose came off the filter, and stuck to the inside of the cowl.
This ship had an aft-facing servo, with the accordingly long hose run. Ugh.

So, I set up a system on the F1 that doesn't need any steenkeeng clamps, and has a very short hose run
!
In addition, because the distance from the cone to the adapter on the servo is minimal (3-4") -- doubtful if a collapse there could cause a shut-down...but, for the belt-and-suspenders types out there, making the cone longer -- to within 1/2" of the adapter collar -- would minimize possible engine stoppage from a collapse further yet. Gotta allow some room for the engine to jiggle, remember.
As for drag inside the SCAT, remember that the inlet in the sump is about 2 1/2" or so -- kinda small -- so it might be that a† larger sized SCAT tube of about 3" length max wouldn't reduce MP very much.
The 2-layer stuff CAN de-laminate and collapse (it was designed for pressure applications); the single layer hose could possibly hold a vacuum a bit longer (can't delaminate). BOTH can collapse completely under a vacuum, if the end is plugged up for a very short time -- but, barring a completely iced up filter, this is not likely with our filter system. Further, Bob Gross is working on a bypass for the filter box that will likely work very well. Cheers Mark
The airbox needs some sort of bypass.† In the current configuration if the†intake gets packed with ice the engine will suffocate, maybe even if it got pretty wet (flying through rainshowers).† And where you'd find out that your filter is completely iced over is on short final with low MP--not a good time to be diagnosing the problem.† Its happened to a number of RV's supposedly.† An automatic†door on the†top of the airbox†that operates off a†magnet would work.† When the filter ices up, the door which swings down and in the airbox would be pulled open by intake vacuum and stay open.† In normal operation the door would be forced closed†by ram pressure and the magnet would hold it there.† Van's has a SB for this on the RV's and they have provided their builders with the parts kit free of charge, it surely could be adapted to our airbox.† Regards, Bob

Bob,I just sent drawings to my laser metal cutting guy an hour ago for revision 2 of just hat type of device. This one works on a IO-540! Warmest Regards, Bob Gross

Hey Bob:
Let's be practical here: the ship is not approved for flight into known ice, or unknown ice either! Stay the hell out of that stuff, and snow for that matter. Period. I've done enough missing man formations for a while.
BG is working the bypass issue -- he'll actually have an imitation FAA approved do-hickey, sort of...problem solved. Unless the do-hickey decides to come apart...
I guess you could fly in snow if you had the bypass installed.
Rain isn't an issue, unless it rains hard enough to put out the fire. The filter won't clog with water. Carry on! Mark

I built a Christen Eagle yrs ago and it had an automatic alt air, which as I recall was inop and held that way by a spring until the engine created a vacuum, via a blockage of the incoming air, then opened to allow it to inhale. I thought it kinda silly, as the plane had no way to fly in IFR conditions. Bob

All of these are good feedback. One of the reasons I kept the gap between the flanges to 1" or less was so that even if a clamp came loose and the tubing material got sucked into the gap and over the intake there wouldn't be enough material to cover more than about 1/3 of the intake diameter. However, you do need some gap, at least 5/8" IMO to allow for engine movement. My main points were to have a continuous path diameter and a smooth inside surface. Thanks for the various refining ideas. scot

Hi Builders, this message to all that ordered a LOUVER panel. I shipped them
out to all, thurs. May , 09. You'll should recieve them by Monday. I still
have panels for immediate shipment. Any one wanting to place an order order , contact
me ..... thanks billy waters....jones15183@aol.com..

Hey, you guys who have already attached the engine cowl.......or Mark (Chairperson of Group W): It sez in
instructions that the "technician marked the area of the doubler on the attach flange" so as to know where it
was. Well, I assume ( we have established this as dangerous) that this means NOT to put attach screw thru
doubler. Is that the caution that the above statement is conveying, OR does it mean that one should go there??
Thanks, Tom

PS to my original post: What is final ideal gap between cowl and boot cowl skin? Tom

Tom Fit the cowl as tight as you possibly can, complete all the attachments, fit the spinner etc. When it is all
done and you are satisfied that the cowling is where you want it then file/sand a gap that is a little less than
1/8". This might sound like a lot but after you have removed your painted cowl from your painted plane a
few times you will understand why you need some room to move. As for the mentioned spot, it is just to draw
your attention to is so a screw is placed in the correct spot. I used this spot but if you are off a bit it could get
into edge distance problems. Tom Martin

Has anyone used Camlocs as rear cowl fasteners? If spacing was reduced to 3", would these provide adequate
support? I would love to use something besides screws at least on top cowl to make removal more user-friendly.

That work for me! You really don't have to reduce the spacing, but you might consider adding layers of
cloth to the fastener areas. This type of fastener won't work very well at the front of the cowl --
put up with the screws there. Cheers Mark

Would piano hinge work on lower Cowl (a la RV-4) ? Looks like hinge would probably provide a stiffer support.
Tom Hall

I wouldn't do that -- the lower corners are subject to a lot of shear loads, and the hinge just ain't up to the job.
Cheers mark

Aren't we adding cloth there anyhow to make the rear cowl edge to the boot cowl? Doubting Tom

Correct, but those fasteners have less bearing sfc than we used -- might add 1 extra layer past what we did.
Cheers Mark

Hey How many layers do you typically add? On mine I added a 2bid everywhere. That was a little too much in a
few areas, but generally not enough in most. In some places I have added an additional 3 bid (total 5) but most
are 3 or 4 layers total. Also, the fuse radius at the cowl boot/fuse side interestion seem to be less than the
natural radius of the fiberglas top cowl. Is this typical? A LITTLE heat and bending?
Vice Chairman, Group WGuys,

I used .063 shims for the cowl attach rather than the .040 supplied with the kit so I can have a few
more layers of glass there for the camlocs to have a good bearing surface. Bob #80

PS to last post....Wouldn't the flusk camlocs have more surface area than none flush?Tom

I put the cs camlocs on my harmon top cowl along the back, standard pattern, and have had no prob (190 hrs)
Makes it a lot easer to take the top cowl off. I still have the hinge connecting top to bottom. Craig Lefever

I'm considering using Skylocks (Skybolt's type of camlock) instead of piano hinges for joining the cowing
halves and attaching the bulkhead flange. (for long term durability and ease of single handed on & off.)
Has anybody had success or experience with this type of fastener? Skybolt's RV kit (with a few more fittings)
would appear to be suitable for our birds. The stiffening system for the cowling used on display example at
Fun-n-Sun would appear to work well with our cowling. They also suggest a 0.62 attachment flange -
anyone used this thickness rather than .042? Bill #81

Bill, a bunch of us here in Indy ordered camloc kits from Skybolt on Monday...there was sale going on last week
(30% off) and they honored the sale price. You may want to call them soon and ask if they'll still honor the
discount. Jim W. ordered us the RV-8 firewall kit for the firewall and the smaller fasteners without the
grommets (10 of them) for around the scoop. Cost was ~$200 for the whole deal. Not too bad. My hangarmate
has camlocs on his 6A cowl and they are worth the money. Skybolt recommends .063 because their adjustable
receptacles are drilled for #30 rivets. If you use the 1097 rivets (flush) to attach them to the .040 flanges
you'll be fine. Those 1097 are a close second favorite to mine (the first one being a big-assed hammer).
Regards, Bob #80

Here is a link on the Skybolt web site of Dick Martin's plane with the setup you are suggesting.

http://www.skybolt.com/Products/Vans.html

The installation is on a RV-8 but should be close enough. If you look at the pictures carefully
you will see clearance issues between the side cowl fasteners and the valve covers. It looks like Dick
solved the problem with a piece of rubber hose to hold the cowl away from the valve covers. I believe you
would face the same issues with the Rocket. scot

You are correct, you will certainly have clearance issues to the valve covers. The hinge pin works nice for the
halves anyway, quick and easy to pull and put in. Greg Nelson

Skybolt... I used them and would not use them again.. My thinking was that I
would take the cowling off more often with skybolt because it would be
easier.. Wrong!! When I replace my cowling I will use a hinge pin at least along the
horizontal.. Theyare expensive too....Whew!! Larry #001

Scott - I used 3.5" spacing for my Skybolt camlocs - recommendations were between 3" and 4" - found
the 3.5" worked out better and avoided a fastener at the extreme cowling curvature at the longerons.
Made my flange from .062 - mighty strong - but perhaps a bit of "overkill". Will be happy to send or post
photos if you wish. Bill --

Glacier To All On page 347 of the manual it says in the second paragraph upper right side
"The dimension from the middle of the radius of the lower aft corner to the cut line is 15 3/8".
" Make a mark here and lay out a straight line forward to the attach flange at the forward
corner. This is a good cut line for the bottom cowl. I don't know how to locate that mark with
the description above, any help or lessons learned are appreciated. After locating my plan is to
overlay the top cowl and scribe cut lines. Thank You in Advance Safe and Happy
Memorial Day Howard

Let's see: This area is on P379 of V2.25. The lower cowl, at the firewall, or where it will be cut to match the fwd skin line, is a radius, not a sharp corner, but is cast to match formed raduis on the lower area of the fwd side skin. Use the center of this radius to start your measurment to the aft location of the lower cowl horizontal trim line. The fwd end of this trim line is, of course, obvious at the cast-in tabs to be used at the fwd corners.
You can use the embossed trim lines cast into the cowl too, but it looks like our mold man has the left and right lines at two different locations on the bottom cowl mold, with the average being about 15 7/16". The top cowl mold does not appear to have this anomaly. The embossed trim lines can be used successfully -- this procedure was used on the new demo ship. The cowl should be fully assembled before any attempt to use the cowl installation tool is made, tho using the big plate to make sure the spinner opening is round is not a bad idea. Any 15" dia plate can be used here. SHOP TIP: Time your requests for the cowl tool so it arrives after the cowl is assembled. There is a waitng list for this tool, and all involved will appreciate a minimal stay at each stop.
Early fit-ups of the cowl will display a very small exhaust opening. Don't worry -- this will get bigger when the cowl is trimmed, and fits onto the attach flange, and is not forced over the boot cowl skin and side skins. For this reason, you will not want to drill any of the cowl attach fastener holes until the cowl is trimmed to lay onto the attach flange, and the required additional layers are added to the aft edge of the cowl.
Follow the manual very closely at this stage! Cheers Mark

Bob Do you have any tips on how big of a hole to start with on the cowl exit ?? I have one or 2 but wanna see what the flyin` guys have to offer .I sure as hell ain`t going to try to re-invent the wheel now.
Bill A

The exit area on mine is stock with the cowl hanging below the lower fuselage skin about 1/8" near the outside edges. This gives an opening that had about 3/8" above and below the 1.75" dia exhaust pipes. About. I'll measure it later today. Warmest regards,
Bob Gross

Hi Fellas:

Yes, I do have some of that going on. I took some pics this AM for the
manual, and now I'll order some of the stick-on aluminum from Van's and apply to
the affected areas (basically under the pipes where the back cyls join to the
tailpipes, at the aft corner of the scoop on the rt side, and about 4" aft of
the corner on the left side.

I'll put photos in V2.26 if I can get the sheilding quick enough. Any ideas from you fellas?
thxMark

I just finished the miserable job of fitting the cowling. Got everything to go together
nicely but I'm now concerned about the clearance between the exhaust system and the lower
cowling. There is only about 3/4" clearance between the lower cowling and the ball joint
on both sides. Does the lower cowling sag a bit in service? Should I consider some for of
heat shield here? What do other have for this clearance? Don't want to blister my
expensive paint job!! Thanks Bill

The lower right cowling is close to the exhaust on my ship. A simple AL heat shield, Glued
to the cowling with little blobs of HI temp silicon so that there is a 1/4 inch space
between the AL and the fiberglass is working great on my plane. I also needed two cowl
blisters at the cowl exit, to get a little more clearance to the pipes there. Greg Nelson

Bill My exhaust system may not be typical since it is ceramic coated, but the aft portion
of the pipes virtual touch the cowl and they have no ill effects. The only bubbles that I
have experienced have been on the right mid, bottom cowl. The clearance there is close
and headers are much hotter near the exhaust ports. I have had no problems on left. Tom

Bill, I used some stuff called Fiberfax from aircraft spruce to make heat shields that run
the length of my lower cowling just below the pipes. I cut strips about 5" wide and they
run from below the front pipes all the way to the aft edge of the cowl No problems with
heat or heat damage on the lower fiberglass and don't expect any. Got this tip from an
EAA tech adviser that specializes in glass airplanes. Real neat stuff. It's a matt spun
form ceramic. You can put a torch to it and it glows bright orange but doesn't burn. Fun
to show your friends. It installs using high temp sealant you can get at home depot. This
is the orange stuff that comes in a caulking tube that electricians use to seal vapor
tight electrical connections. Cleans up with water. You can find it in the electrical
dept. Warmest Regards, Bob Gross

The go-fast RV's that go 230-240 at the races have a bump molded into the inside bottom
of the cowl to act as a venturi which reportedly speeds up the air exiting the cowling,
relieving the low-pressure area behind the exit. There is also a rounded piece of
stainless sheet that eliminates the sharp corner at the cowl exit (look at a RV-8 with
the cowl off, that mod is incorporated into the kit.) I talked to one of these guys at
SNF and he invited me to crawl under the airplane and have a look at the evidence. The
oil definitely streams differently around the cowl exit, than it does on mine. I am
going to put one in my cowl after I fly the airplane without it, so I can tell if it
does anything. I wouldn't do this permentantly on the F1 without a cowl flap, which

may certainly help the cooling in the pattern and on the ground. Bob G, you could
tape a curved piece of alum. to the inside bottom of your cowl to try it. I can send
you some pics of different variations of th! is if you'd like to see them. Those guys
are also using a custom pitch on their hartzells to break a wall they hit around 220.
So the same thing may be happening with us. Other than a plenum, the round inlets, and
what I mentioned in the first paragraph there is nothing else special about the cooling
systems. On the airframe, they have the hinges faired, and use sailplane gap seals on
the control surfaces, and tape up every gap or seam for the races. Regards, Bob #80

Yep -- Butch Milani walked over and sold me one of his S shaped pcs for fixing the cowl
exit shape at Reno, but we couldn't get it installed before the race -- order one ($20)
on the helping hands page on our website. Looks like the ticket, but tough to fit with
the exh system on there. Our 'exit bump' will be an extension of the cowl lip, if I
understand you correctly. Dave Anders has his exh outlet inside the cowl by about 2"
or so -- not much! The NACA reports show the augmenter should be substantially longer
-- 14" or so. They were pulling 5" of vacuum pretty easily. No mention of a venturi in
front of the inlet of the aurmenter duct, but it did have a belled/flared inlet
shape....the exh energy accelerates the exit stream to about 75% of ship velocity if
done correctly. Carry on! Mark

Oh yeah, I forgot about that detail. They are cutting off the exhaust stacks inside
the cowling, the pipes are cut at a 45 degree angle to help pull the air out of the
cowl. I'm not an aerodynamicist but the way I understood it speeding up the air on the
outlet side is the way you help eliminating cooling drag. He did tell me that he cut
them off straight and the vibration on the floor was unbearable, so he rewelded the
piece back on but cut the angle at 45 degrees and he did not get nearly the amount of
noise or vibration. Regards, Bob

The go-fast RV's that go 230-240 at the races have a bump molded into the inside bottom of
the cowl to act as a venturi which reportedly speeds up the air exiting the cowling,
relieving the low-pressure area behind the exit. There is also a rounded piece of
stainless sheet that eliminates the sharp corner at the cowl exit (look at a RV-8 with
the cowl off, that mod is incorporated into the kit.) I talked to one of these guys at
SNF and he invited me to crawl under the airplane and have a look at the evidence.
The oil definitely streams differently around the cowl exit, than it does on mine.
I am going to put one in my cowl after I fly the airplane without it, so I can tell if
it does anything. I wouldn't do this permentantly on the F1 without a cowl flap, which
may certainly help the cooling in the pattern and on the ground. Bob G, you could tape
a curved piece of alum. to the inside bottom of your cowl to try it. I can send you
some pics of different variations of th! is if you'd like to see them. Those guys are
also using a custom pitch on their hartzells to break a wall they hit around 220. So
the same thing may be happening with us. Other than a plenum, the round inlets, and
what I mentioned in the first paragraph there is nothing else special about the
cooling systems. On the airframe, they have the hinges faired, and use sailplane gap
seals on the control surfaces, and tape up every gap or seam for the races.
Regards, Bob #80