Urs_Wildermuth Posted October 12, 2016 Report Share Posted October 12, 2016 Folks, I am putting this here as it concerns newer and older models alike. I've had my share of discussions about take off and landing figures on our M20C. The POH gives distances only for hard surface runways and only up to 5000 ft. So what do I do if I am on a grass runway? What if my departure is at 6000 ft? What if there is wet grass or asphalt? There is no information about it whatsoever. I recently checked the POH of the M20J and it indicates a 7% increase for a dry grass runway. What if the grass is wet? And how about take off and landing on contaminated runways? As a former dispatcher I'd have to say, my C Model is restricted to operation from (dry) hard surface runways and the J to that plus dry grass. We all know in practice that is not what happens, we do fly in rain, snow, on grass runways which are not picture perfect. How do you guys deal with this? Is there more information available some place? Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted October 12, 2016 Report Share Posted October 12, 2016 Go out and do a landing when the wind is calm, do not use the brakes....note the distance required, I would use that number for slippery conditions and adjust as necessary for altitude, wind, or runway slope. Quote Link to comment Share on other sites More sharing options...
Raptor05121 Posted October 12, 2016 Report Share Posted October 12, 2016 You could fly it and make a really accurate note in your POH, but I'd say 15% increased ground roll for wet grass would be a good margin for error. Quote Link to comment Share on other sites More sharing options...
kris_adams Posted October 12, 2016 Report Share Posted October 12, 2016 You bring up a good point. I fly pretty much in the flat lands and rarely off pavement (would like to find more good places). In addition I guess I'd say I rarely go into a strip shorter than 3000'. The only one I can think of is 2300' but there is a big pond (actually the gulf of mexico) at the end of the runway. I guess when we get outside of the POH we just have to look at the situation and make sure we give ourselves more margin for error. Btw my brother has a '67 Darter 100. Talk about a skinny POH. It pretty much gives you instructions to preflight and start (cold of course). -Kris Quote Link to comment Share on other sites More sharing options...
Urs_Wildermuth Posted October 12, 2016 Author Report Share Posted October 12, 2016 Well, we do have some 1500 ft strips here, some gras some concrete.. and we do have airports up at 6000 ft. Quote Link to comment Share on other sites More sharing options...
201er Posted October 12, 2016 Report Share Posted October 12, 2016 I don't think it's such a great idea taking a retractable gear Mooney on wet grass. All of that dirt and mud is going to fly right up into the wheel wells. Quote Link to comment Share on other sites More sharing options...
Mooney in Oz Posted October 12, 2016 Report Share Posted October 12, 2016 This has been discussed before and I remember reading a post some time ago that in the early days, Mooney did not want pilots operating out of grass strips and therefore did not include grass strip operations into the FM until later in the game. I don't know whether that is correct or not. I personally like my gear doors too much and therefore don't like the banging sound coming from underneath when rolling over grass clumps while feeling the stress put on the undercarriage, plus stone damage on dirt strips, so I always stick to sealed strips. I know this isn't practical for everyone, but is one of my usage limitations. Park a Mooney next to a C182 or similar and you can easily see why. The lack of information in the FM regarding the rest of what you mention is not good, but it is what it is and we just have to mitigate as best we can as per everyone's advice. Victor Quote Link to comment Share on other sites More sharing options...
carusoam Posted October 12, 2016 Report Share Posted October 12, 2016 Summarizing some of the thoughts... Issues: Ground roll (rolling resistance) on various surfaces... 1) paved surface 2) grass surfaces and their care 3) wet grass surfaces Sources of data: (possible) 1) POH for your year plane. 2) Most recent POH for your plane. 3) Most recent POH for a similar plane. other sources of data may not apply directly... because of 1) Tire size dimensions are important here. 2) Tire pressure can make a difference 3) Weight of plane. 4) Power being generated by engine/prop. 5) Density altitude considerations. Actual T/O data based on your actual plane. 1) collect your own T/O roll data and compare to other resources above. Note conditions, temp, pressure, rh, alt.... 2) WAAS ADSB receiver and Cloud Ahoy app. I am a big fan of actual data produced for my plane. This way I know it is operating as expected before expanding into the lesser known areas... PP ideas, not a CFI. Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Hank Posted October 12, 2016 Report Share Posted October 12, 2016 Urs-- I've flown my C in a pretty wide envelope. To see the full range, check the YouTube videos of piperpainter in his red C model. I don't do that . . . I am currently based at a 3200' paved strip, and was previously based [for seven years] at a 3000' paved strip with trees at both ends. Grass strips are not a problem for our Cs, as we don't have the lower gear door that the J pilots above are so worried about. Going into a nearby 2000' grass field, landing was never a problem but I kept weight down to 2 people and half tanks for easy departure again. A 3500' grass strip is not a problem, even when the threshold is displaced at one end for trees. The highest DA I've heard on AWOS was 6600' at Rapid City [KRAP] in the afternoon; the highest elevation I've operated from is 5100' [KCOD]. These two fields were on a trip, loaded to the ceiling and at gross weight. There are people on this board who live on grass strips, and keep their Mooneys there. If you are concerned, test the waters at a known field; take someone familiar with it on your first trip for extra confidence. You will find the ride a little louder, a little bumpier, and you will stop faster on dry grass with no braking. Just keep the yoke full up and you shouldn't have a problem taxiing after allowing for the extra throttle required. Quote Link to comment Share on other sites More sharing options...
Pritch Posted October 12, 2016 Report Share Posted October 12, 2016 According to the 'Book' at 15'c 1500 ft pressure alt, 6 kt headwind, 2600lbs , ground roll is 1000ft. For same conditions on grass surface, roll is 1100 ft, for my M20K Pritch Quote Link to comment Share on other sites More sharing options...
Urs_Wildermuth Posted October 12, 2016 Author Report Share Posted October 12, 2016 Thanks for all the very useful inputs. @Hank, no I am not at all concerned. I've taken my C Model into 1500 ft concrete strips and I know it will behave as advertized on take off. Also, my C model was based on a 1800 ft grass runway for almost 40 years. The original Mooney dealership in Switzerland was based at Bad Ragaz, one of the shortest and most obstacle infested airfields I know. As a former flight operations officer (flight dispatcher) I have dealt with loads of airplanes much bigger and they do have book values for just about everything. Likewise, I've seen similar figures for some Pipers and Cessnas too. I just wondered why Mooney was so economical about this. Also, my only real concern so to speak would be that if I ever was challenged by a friendly inspector as to my take of calculation on such a field, I'd have to say it is a guestimate based on experience. If that would sell? The way I know folks around here, they'd say, if you don't have figures then you can't operate. Which means, Mooneys would be restricted to operate from fields for which data are available (that is dry concrete for the M20C and dry concrete and dry grass for the M20J) and nothing else. That is definitly not what I want. The M20J Manual states 7% increase on a dry grass field. Again, there are no indications on factors for stuff like wet grass, let alone slush or compacted snow. Looking at a table I received a few hours ago from the UK CAA, they recommend as a general rule: 20% increase for dry grass 30% increase for wet grass as well as compacted snow or soft ground on that, they will then once again add 30% safety margin. I think this is way over the top, clearly, it will increase safety but so does a 10'000 ft runway. What I'd like is something I can get a proper idea to calculate with for my airplane (and the rest of the Mooney fleet, as I keep advising people on them). So any experience values or if there are some test folks around here would be highly appreciated. Quote Link to comment Share on other sites More sharing options...
Seth Posted October 13, 2016 Report Share Posted October 13, 2016 According to Bob Kromer at Mooney Summit, every additional knot of speed on short final leads to 100 feet additional rollout. So 5 knots over = 500 additional feet. Just something to think about when calculating. Flying the numbers is very important. -Seth 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted October 13, 2016 Report Share Posted October 13, 2016 At ten knots over... Do you count the roll out distance from the first touch down or the ones that come after that? For a 1500' runway, Urs has got to be on the numbers! Always check ground speed to be more than airspeed on the down wind. Landing fast with a tail wind can use up 1500' before the first bounce occurs. Best regards, -a- Quote Link to comment Share on other sites More sharing options...
donkaye Posted October 13, 2016 Report Share Posted October 13, 2016 When Bob Goldin was teaching the Mooney PPP he spent some time discussing the Top Comp Computer. You can get one here. It is slightly more conservative than actual performance, so is very good to use. While it can be adapted for turbocharged airplanes, (Bob went over it with me many years ago) it was too complicated for that and I don't remember how to do it. http://www.sportys.com/pilotshop/takeoff-performance-computer.html 1 Quote Link to comment Share on other sites More sharing options...
Mooneymite Posted October 13, 2016 Report Share Posted October 13, 2016 Just now, donkaye said: When Bob Goldin was teaching the Mooney PPP he spent some time discussing the Top Comp Computer. I've had one for years. I operate off of grass quite a bit and find it generally pretty accurate. You probably won't use it much, but under certain conditions it is a great device. Quote Link to comment Share on other sites More sharing options...
carusoam Posted October 13, 2016 Report Share Posted October 13, 2016 Any idea who created that linear whiz-wheel? Is it based on science from a governmental body? They selected concrete, turf, grass, long grass and soft field... Leaves a lot to interpretation and experience. I don't recall seeing it in training, only in stores... Best regards, -a- Quote Link to comment Share on other sites More sharing options...
Hank Posted October 13, 2016 Report Share Posted October 13, 2016 1 hour ago, Seth said: According to Bob Kromer at Mooney Summit, every additional knot of speed on short final leads to 100 feet additional rollout. So 5 knots over = 500 additional feet. Just something to think about when calculating. Flying the numbers is very important. -Seth I thought it was an additional 100' of float before touchdown for every knot of extra speed. Five extra knots will push your touchdown an additional 500' down the runway. Need to study that there computer-thing, Gus. You may need to show me how it works one Friday at lunch . . . 1 Quote Link to comment Share on other sites More sharing options...
kpaul Posted October 13, 2016 Report Share Posted October 13, 2016 7 hours ago, Hank said: I thought it was an additional 100' of float before touchdown for every knot of extra speed. Five extra knots will push your touchdown an additional 500' down the runway. That is correct and what Bob Kromer briefed. Each knot of extra speed over the threshold will lead to 100' of float prior to being at touchdown speed. so 5kts = 500ft, 10kts = 1000ft. Quote Link to comment Share on other sites More sharing options...
Seth Posted October 13, 2016 Report Share Posted October 13, 2016 8 hours ago, kpaul said: That is correct and what Bob Kromer briefed. Each knot of extra speed over the threshold will lead to 100' of float prior to being at touchdown speed. so 5kts = 500ft, 10kts = 1000ft. What they said is correct! Every extra knot over touchdown speee over the threashold = 100 extra feet of float!! -Seth Quote Link to comment Share on other sites More sharing options...
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