Upper cowl inlet ramp plugs

Bob Axsom · #1 04-08-2006, 02:27 PM

I carved blue foam from Aircraft Spruce yesterday to plug the side openings of the upper inlet ramps after two years of flying with them open. The TAS has been just over 171 -173 kts all that time. I epoxy resin (EZ-Poxy 24 hr cure) "glued"them in this afternoon. Over thhe next few days I will be glassing them in and finish sanding. Hopefully it will add a little bit of speedby eliminating those two drag buckets.

Bob Axsom

Ironflight · #2 04-08-2006, 06:49 PM

I hope you get a speed increase Bob, 'cause that sounds like a pretty easy thing to do! (Easy even for someone like me that doesn't enjoy glass....)

How about some pictures when it's done?

Paul

Bob Axsom · #3 04-08-2006, 08:44 PM

I use the slow cure epoxy resin so it will be a few days coming but we plan to fly to Ashville, NC on the 17th so it will be done by then. I am photographing it as I go.

Bob Axsom

gmcjetpilot · #4 04-09-2006, 09:16 AM

Quote:

Originally Posted by Bob Axsom

I carved blue foam from Aircraft Spruce yesterday to plug the side openings of the upper inlet ramps after two years of flying with them open. The TAS has been just over 171 -173 kts all that time. I epoxy resin (EZ-Poxy 24 hr cure) "glued"them in this afternoon. Over thhe next few days I will be glassing them in and finish sanding. Hopefully it will add a little bit of speed eliminating those two drag buckets.

Bob Axsom

BOB please update with speed if you don't mind, it will be fun to see what diff it made. If anything when some one looks in the cowl at the airshow, they will go WOW! Darn this thing is plugged!

No really record your oil temp and cht, also. It may improve cooling?

Cheers, George.

Bob Axsom · #5 04-09-2006, 10:04 AM

I will honestly report the speed difference. The plane isn't instrumented to provide CHT. The oil temp is around 180 (under 200 anyway) all the time. The only time it went high was when the original LASAR timing from Lycoming was about 60 degrees off (85 BTDC). I will report that as well.

No one will see the plugs. They are up inside the upper cowl where the there is a very slick airfoil shaped ramp from the trailing edge of the upper part of the inlet opening to the inside surface of the cowl itself. I believe that the air comes in and is accelerated across the surface and drawn up into the plenum where it decelerates and follows the normal plenum outlet flow from there. The sides of the ramps are wide open so I am pretty sure that the air spills over the edges of the ramps and curls in and runs into the inside of the junction between the ramp and the inside of the upper cowl. My thought is, if I block off the access to the backside of the ramp in a manner that provides a smooth transition, the spillage will curl and rejoin the inflowing air to the plenum.

The only inputs I have received on this were from Mark Manda and the fellow from Colorado that finished 1st or 2nd in the RV Blue class (360 cu. in.) in the AirVenture Cup race last year. Mark had done his from the start so there is no comparative data there. The other fellow's achievement speaks infavor of the mod but there again, I have no before/after comparative data.

The mod is a little tricky because it should be done in a way the eliminates sharp corners and does nor interfere with the inner or outer baffle seals. At this point my plug shapes do not do a good edge rounding job but I hope to progressively improve it if the current configuration shows promise. One subtle thing that needs to be considered is some vent for pressure change with altitude.

Bob Axsom

Davepar · #6 04-09-2006, 07:00 PM

I thought everybody sealed the sides of the ramps. I did it a few days ago right after putting in the ramps:
http://www.dualrudder.com/rv7/2006/04/02/912

I didn't use a plug or anything. I just draped some fiberglass cloth from the ramp down to the cowl making it curve gently to avoid sharp corners as Bob mentioned.

Dave

Bob Axsom · #7 04-09-2006, 09:27 PM

The plugs are in and everything is filled and ready to sand but no glass yet. all of the baffle seal areas are clear but I'm not happy with the break off of the sides of the ramps. Dave not everyone sealed them obviously but certainly a lot of people did. I thought about it but decided not to at the time since it was not called for in the drawings (at least as far as I saw). I will be able to tell if it makes any difference in a week from now at the most.

Bob Axsom

Bob Axsom · #8 04-10-2006, 09:28 AM

Here is an early photoof one of the plugs. The edge radius is only about 1/8". A lot of sanding to do before the fiberglass goes on. You can see the markings on the cowl from the front baffle seal so that prollem area is clear.

Bob Axsom

[IMG]

[/IMG]

Kevin Horton · #9 04-10-2006, 04:14 PM

I'm having a hard time understanding why we should expect a speed increase from plugging these ramps. I can understand why the cooling might be improved, if air was leaking from the upper cowl area to the lower side through these ramps. Stopping that would force more air to go through the fins and oil cooler, and improve cooling. But it won't affect the amount of air coming into the cowl inlets, which is what affects the amount of cooling drag.

If the cooling is improved, then we could reduce the size of the cowl inlets. Reducing the amount of air coming in would reduce drag.

Enlighten me, please.

Note: my cowling work is not yet complete, so maybe I don't understand what we are talking about with these ramps.

Bob Axsom · #10 04-10-2006, 06:00 PM

Kevin,

I can't right now but in a few days I will get the mod finished and test it. I've been thinking about this for a couple of years and "thinking" just doesn't provide knowledge like testing does. S-o-o-o-o I decided to modify it and test it. I have an airspeed established under rigorous requirements for the Marion Jayne Air Race put on by U.S. Air Race, Inc. last year so I can repeat that if it is necessary (so close that a comparision standard is needed) but I want to know whether it makes any difference or not. Any time you have an air trap in the system there certainly is the potential for parasitic drag. Those open sided ramps just seem like a problem to me unless the pressure under (above actually) the ramps is such that no air coming through the inlets rolls off of the sides and impinges upon the inner wedge shaped junction of the ramp and the inside of the cowl. I put on the first layer of glass this afternoon so I have a few days of finish and cleanup before I fly it again. When I'm done I know I will be able to tell you if it is faster but I can only theorize about why. Inquiring minds want to know as they say - it's an easy mod and test with little risk.

Bob Axsom

[IMG]

[/IMG]