cbarry Posted September 26, 2021 Report Posted September 26, 2021 (edited) Leaving out of Bentonville recently I had the gear not fully retract. The gear unsafe light was on and the gear circuit breaker tripped. I was solo and full fuel. I was 475 lbs under gross and was able to maintain a fair climb rate but nothing stellar. I was able to determine by way of the gear window in the floorboard, that the gear was maybe a third from being fully retracted. I cycled the gear breaker once to no avail, left if out, confirmed gear switch in the down position and cranked the gear into the fully down position and got a gear safe indication. This predicament started making me think about whether the drag component changes based on the position of the gear as it extends or in this case doesn’t fully retract. In other words, does partially extended gear (say about 30%) cause more drag than fully extended gear. For example, do the gear doors, tires, etc( with partially extended gear) create a wind scoop into the wheel well causing more drag especially on climb out? Edited September 26, 2021 by cbarry
Ragsf15e Posted September 26, 2021 Report Posted September 26, 2021 Yes, but tough to say how much. If you depart fully loaded at medium density altitude, that can be a real problem. It will climb like a -152.
Hank Posted September 26, 2021 Report Posted September 26, 2021 48 minutes ago, cbarry said: In other words, does partially extended gear (say about 30%) cause more drag than fully extended gear. For example, do the gear doors, tires, etc( with partially extended gear) create a wind scoop into the wheel well causing more drag especially on climb out? I had old, hard pucks and in the winter my gear would not fully retract for several minutes (the time varied but generally increased). One trip they remained partially extended for ~30 minutes. The floor window showed barberpole and my headset squealed. When they finally clicked up, the squeal stopped and IAS increased about 15 mph. I don't remember what climb rate was. Once I put on new pucks (Dec '12.), it hasn't happened again. And my landings improved immediately!
Mooney Dog Posted September 26, 2021 Report Posted September 26, 2021 3 hours ago, cbarry said: does partially extended gear (say about 30%) cause more drag than fully extended gear. Anything that interrupts smooth flow of air around the body of an aircraft is going to cause some drag. While its not totally (or easily) relatable, you can break it down to its basic physics form D = Cd * ( p * V^2 ) / 2 *A . Any change in area or the coefficient of drag, in this case the gear, is going to change the total drag on the aircraft.
cbarry Posted September 26, 2021 Author Report Posted September 26, 2021 I appreciate everyone’s replies. It’s fairly straight forward that gear down causes more drag than gear up. I’m just curious if there’s a point at which if the gear does not fully extend (hung at 30-50%), the drag will exceed that of fully extended gear—simply because of the airflow over the top side of the partially extended gear being funneled into the wheel well and acting like an air dam. I wonder if Mooney ever tested climb rates/performance impacts at various gear positions—25% down, 50% down as compared to 100% down at both Vx and Vy? If the impact is not linear, then that would be good piece of information to have in one’s pocket.
mike_elliott Posted September 26, 2021 Report Posted September 26, 2021 Typically this happens when your emergency gear is not latched and you try to raise the gear. On older planes that have squat switches, old landing gear pucks will lose resiliency and not expand, causing the retraction circuit not to open, but it wont pop the gear actuator breaker. 1
Shadrach Posted September 26, 2021 Report Posted September 26, 2021 (edited) 16 hours ago, Ragsf15e said: Yes, but tough to say how much. If you depart fully loaded at medium density altitude, that can be a real problem. It will climb like a -152. We’ll sort of. If you use clean climb speeds with a dirty airplane you’re going to be very disappointed with ROC. However, if you’re willing to pitch for a much slower airspeed, a Mooney will climb just fine with the gear down. I’ve personally tested this in my F Model. The day I tested temp was moderate and I was light. IIRC, my normal 120mph cruise climb yielded a bit north of 1100fpm with the airplane clean. (Likely north of 1300 at VY). With the gear down I could get ~1000fpm but that was pitching for ~80-85mph. Not ideal for visibility, cooling or power loss but it climbed just fine. Remember the early D models managed just fine with just fairings on the gear. They were 130mph airplanes (at best). Flying a fixed gear D at C model climb speeds would result in dismal climb rate. Edited September 26, 2021 by Shadrach
A64Pilot Posted September 26, 2021 Report Posted September 26, 2021 Without flight testing there is no way of knowing, I don’t why it would have been tested. Airplane will fly, and climb etc just fine with gear down even at max gross, but at much likely much lower airspeeds, it wouldn’t pass Certification if it couldn’t. Obviously it will fly faster and climb better gear up, but it will meet the min climb angle required gear down. Just as it will go around fine full flap and gear down. Due to the possible interaction of air being blown into the wheel wells from partially extended gear it’s logical that the drag could be higher than fully extended, but only testing would tell. 1
PT20J Posted September 26, 2021 Report Posted September 26, 2021 Ross makes a good point. Best ROC occurs where there is the maximum difference between power available and power required. The power available decreases nearly linearly with airspeed at low speeds, but power required due to parasitic drag increases as airspeed cubed. Skip 1
EricJ Posted September 26, 2021 Report Posted September 26, 2021 2 hours ago, Shadrach said: We’ll sort of. If you use clean climb speeds with a dirty airplane you’re going to be very disappointed with ROC. However, if you’re willing to pitch for a much slower airspeed, a Mooney will climb just fine with the gear down. I’ve personally tested this in my F Model. The day I tested temp was moderate and I was light. IIRC, my normal 120mph cruise climb yielded a bit north of 1100fpm with the airplane clean. (Likely north of 1300 at VY). With the gear down I could get 1000fpm but that was pitching for ~80-85mph. Not ideal for visibility, cooling or power loss but it climbed just fine. Remember the early D models managed just fine with just fairings on the gear. They were 130mph airplanes (at best). Flying a fixed gear D at C model climb speeds would result in dismal climb rate. I flew the last leg of a trip with the gear down due to an electrical failure, and it didn't climb very well at all. A friend who used to own a Mooney pointed out that one issue is the big hole left under the wing, which some airplanes, like Bonanzas, partially fill up by closing doors when the gear is down. A fixed-gear D model doesn't have that big hole in addition to the wheel pants and leg covers, so I think it's a pretty significant difference from a different model with the gear down. 2 1
Shadrach Posted September 26, 2021 Report Posted September 26, 2021 1 hour ago, EricJ said: I flew the last leg of a trip with the gear down due to an electrical failure, and it didn't climb very well at all. A friend who used to own a Mooney pointed out that one issue is the big hole left under the wing, which some airplanes, like Bonanzas, partially fill up by closing doors when the gear is down. A fixed-gear D model doesn't have that big hole in addition to the wheel pants and leg covers, so I think it's a pretty significant difference from a different model with the gear down. I appreciate that as a data point. I can see how it would suck to have to fly gear down in cruise and make ^ altitude changes under such a condition. I’m sure it would also suck getting to cruise altitude and may risk high CHTs on the way. Nevertheless, having made several circuits in the pattern with the express purpose of validating the claim that “Mooneys don’t climb well with the gear down”, I found the premise to be demonstrably false. One can certainly say that Mooneys don’t climb “as” well with the gear down as with the gear up, obviously that would be the case, but they still have more than adequate climb and certainly better than the aforementioned C152.
Shadrach Posted September 26, 2021 Report Posted September 26, 2021 5 hours ago, A64Pilot said: Just as it will go around fine full flap and gear down. I’ve done this as well and lifts off and climbs just fine albeit at what feels like a very flat pitch attitude relative to normal operations. My personal testing was inspired by numerous accounts and claims of dangerous degradation of performance with the airplane dirty. Is performance degraded with gear and full flaps? Of course it is, but the margins are more than adequate.
Hank Posted September 27, 2021 Report Posted September 27, 2021 7 hours ago, Shadrach said: I appreciate that as a data point. I can see how it would suck to have to fly gear down in cruise and make ^ altitude changes under such a condition. I’m sure it would also suck getting to cruise altitude and may risk high CHTs on the way. Nevertheless, having made several circuits in the pattern with the express purpose of validating the claim that “Mooneys don’t climb well with the gear down”, I found the premise to be demonstrably false. One can certainly say that Mooneys don’t climb “as” well with the gear down as with the gear up, obviously that would be the case, but they still have more than adequate climb and certainly better than the aforementioned C152. I did this once on an instrument departure when requested to make my turn ASAP. Went actual about 400 agl, climbing out of KFXE for 9000, and less than halfway up noticed my climb was well under 500 fpm. Scanned the gages, engine was fine. Then saw the green light, and saw the gear switch was down--moved it up, felt the thump and the airplane accelerated noticeably and began to climb as normal.
carusoam Posted September 27, 2021 Report Posted September 27, 2021 What a drag… partially down, or all the way down… When it is down enough to have airflow on both sides of the wheel… the wheel well is open to the apparent wind… and the gear doors work pretty well as speed brakes… and both sides of the wheel are generating drag… Speed limitation seems to be gear operating speed… because they are not down and locked… So…. If gear is halfway down…. And the electric motor won’t move it either way… the emergency extension can be used to put it in the down and locked position…. A Known way to fly… Known is much better than unknown… As far as why Mooney didn’t publish data on half stowed landing gear…. It isn’t required for certification…. But, if you know the test pilots… they probably know the answer… and don’t mind relaying the experience… PP thoughts only, not a test pilot… Best regards, -a-
Recommended Posts