Yetti Posted November 14, 2019 Report Posted November 14, 2019 So the F has straight cowl flaps and it looks like the J has a bump for the exhaust pipe. The cowl flap is a pretty simple piece of sheet metal. Would it be worth making a new one that included the bump for the exhaust pipe? Quote
ArtVandelay Posted November 14, 2019 Report Posted November 14, 2019 I think the J flaps with exhaust bump is longer, because of the bump, Im sure it’s costing you a knot or two. ;-)Tom Quote
EricJ Posted November 14, 2019 Report Posted November 14, 2019 2 hours ago, Yetti said: So the F has straight cowl flaps and it looks like the J has a bump for the exhaust pipe. The cowl flap is a pretty simple piece of sheet metal. Would it be worth making a new one that included the bump for the exhaust pipe? The entire cowl and engine airflow is different between Fs and Js, so I wouldn't assume it would be an improvement unless you changed all of that. What problem would be solved by adding the bump? Quote
Yetti Posted November 14, 2019 Author Report Posted November 14, 2019 18 minutes ago, EricJ said: The entire cowl and engine airflow is different between Fs and Js, so I wouldn't assume it would be an improvement unless you changed all of that. What problem would be solved by adding the bump? External skin should see improved airflow with less things sticking out. Quote
PT20J Posted November 14, 2019 Report Posted November 14, 2019 Early Js didn’t have the bump on the left side. Quote
Ragsf15e Posted November 15, 2019 Report Posted November 15, 2019 58 minutes ago, Yetti said: I need a wind tunnel Yes, so did the factory. 2 Quote
Yetti Posted November 15, 2019 Author Report Posted November 15, 2019 7 minutes ago, Ragsf15e said: Yes, so did the factory. Orville and Wilber built their own. 1 Quote
EricJ Posted November 15, 2019 Report Posted November 15, 2019 I can supply the wind. Well, some of it, anyway... 1 Quote
carusoam Posted November 15, 2019 Report Posted November 15, 2019 If copying a good design helps... Go O, no cowl flaps, and great CHT control... Best regards, -a- Quote
ArtVandelay Posted November 15, 2019 Report Posted November 15, 2019 If copying a good design helps... Go O, no cowl flaps, and great CHT control... And better looking from the front compared to the exceedingly large inlet vents of the Acclaim.Tom Quote
Yetti Posted November 15, 2019 Author Report Posted November 15, 2019 6 hours ago, carusoam said: If copying a good design helps... Go O, no cowl flaps, and great CHT control... Best regards, -a- https://www.airmodsflightcenter.com/advert/mooney-n904hs So that would be the question are the bumps more aerodynamic than the flat open flaps. Air volume wise I can see the bumps on an O moving as much air as as an open flap. But since you can close the flap and only one exhaust pipe an F with closed flaps would be better at least on the port side since there is no exhaust pipe. Does the O have the Always open flap in the center? It does not look like it in the picture. But then there are screw heads holding the "no flaps" with bumps in place on the O. Are the O no flap flaps aluminum or fiberglass? Not sure if it happened, in the Howard Hughs movie they made one of his race planes. He flew it and then told them to rebuild it with flush rivets for more speed. Should we start talking about countersinking the screws? Quote
Yetti Posted November 15, 2019 Author Report Posted November 15, 2019 It looks like they put a Nacel vent thingy on the middle cowl. I would guess this is used to create a vacuum in the low pressure area of the cowl? Or is this ducted to the accessory case area? Quote
Yetti Posted November 15, 2019 Author Report Posted November 15, 2019 Oh thank NASA I don't have to build a wind tunnel and my guess about cowl flaps is correct. " Exit location showed a large effect on drag. By adding a diffuse to the inlet,pressure recoveries of up to 95% were demonstrated. That improvement alone can eliminate most of the need fora cowl flap and thereby save up to 3 % of total aircraft drag." https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19980214918.pdf Next topic cooling drag Quote
jetdriven Posted November 15, 2019 Report Posted November 15, 2019 8 hours ago, Yetti said: It looks like they put a Nacel vent thingy on the middle cowl. I would guess this is used to create a vacuum in the low pressure area of the cowl? Or is this ducted to the accessory case area? On the R model? It’s the filtered air intake for the engine. 1 Quote
Yetti Posted November 15, 2019 Author Report Posted November 15, 2019 1 hour ago, jetdriven said: On the R model? It’s the filtered air intake for the engine. There is one on the front and one on the side. Quote
PT20J Posted November 15, 2019 Report Posted November 15, 2019 10 hours ago, Yetti said: It looks like they put a Nacel vent thingy on the middle cowl. I would guess this is used to create a vacuum in the low pressure area of the cowl? Or is this ducted to the accessory case area? NACA Quote
carusoam Posted November 16, 2019 Report Posted November 16, 2019 O Cooling Airflow... in through the nostrils... down through the cylinder fins... out around the exhaust pipe bumps... No additional airflow control beyond good silicone seals... one mod... fairy/pixie hole in front of cylinder #5... co pilot side nostril opening... O minimized drag... Smoothly curved fiberglass construction, carbon fiber in the more modern versions... nostrils sized for airflow control... not too much excess air to handle... all fasteners are quarter turn and flush machine screws... A proper spinner is tightly fitting and smooth lines with the cowl opening... (not a TopProp spinner yet) Is there room for improvement...? There is plenty of excess cooling in the winter months at altitude... altering the cooling exit to close down the amount of air flowing through the cowl would hold some promise... Would the added complexity net any speed gains? Would it be worth it? Want to go a few knots faster in an O..? Raise the step... test the theory, by removing it... then visit with Takair regarding building a retract step... PP thoughts only, the O is plenty fast for me... sort of... maybe... Best regards, -a- Quote
skykrawler Posted November 17, 2019 Report Posted November 17, 2019 Notice the cowl openings in the picture..... Sitting on the ground the airplane is sort of in a climb attitude thus opening is normal to the airflow for better cooling in climb. Transitioning to cruise there is a less effective opening because the angle of the opening is more down. So adjustable cowl is not needed. This is the modern cowl design also used by Cirrus, Diamond and others. Also notice the how deep the 'tube' is in the opening. This keeps the airflow smooth as it goes into the cowl (as the air slows down) resulting in better pressure recovery and more mass flow. As for the side duct..don't know but maybe a cooling duct for fuel pump or magnetos. NACA ducts are not about scooping but smooth airflow and pressure recovery for intakes. Quote
MikeOH Posted November 19, 2019 Report Posted November 19, 2019 I see barely 1 knot when I close the cowl flaps on my '70 M20F. Frankly, I just leave them open most of the time and don't have to monitor CHTs as closely. What do you other M20F guys see for speed delta? Quote
FastTex Posted November 19, 2019 Report Posted November 19, 2019 3 hours ago, MikeOH said: I see barely 1 knot when I close the cowl flaps on my '70 M20F. Frankly, I just leave them open most of the time and don't have to monitor CHTs as closely. What do you other M20F guys see for speed delta? I see a few knots. In the summer I pretty much do what you do (...keep them open). I have seen an impact in the oil Temp if I close them at the wrong moment. In the winter I usually follow the POH and close the cowl flaps when at altitude. Quote
Marauder Posted November 19, 2019 Report Posted November 19, 2019 I see barely 1 knot when I close the cowl flaps on my '70 M20F. Frankly, I just leave them open most of the time and don't have to monitor CHTs as closely. What do you other M20F guys see for speed delta? Do your cowl flaps have a speed restriction? Mine do. 150 MPH (75F). Sent from my iPhone using Tapatalk Pro Quote
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