Older aircraft with MPH vs Knots

[gitmo234]

Anyone have any experience switching back and forth between knots and mph?

My cessna is MPH. Today I flew solo xcountry to Ocean City MD and back and on short final to my home airport I noticed the airspeed dropped to 60mph and added some power.

Came in a bit fast but landing was great...once on the ground I realized that 60 I was thinking knots, and let it get a bit low.

So I'm having some hiccups adjusting to mph as well as air frames with 40 degree flaps. The older cessnas (with 40 degree flaps or otherwise) seem to come in a bit faster (to me), and fly a bit like a rock.

Anyone else have similar experience?

 

[murphey]

If you own the airplane, simplest solution would be to replace the airspeed indicator. Older cherokees have airspeeds with mph on the outside ring and kts on the inside ring. Makes for interesting discussins with people not familiar with it.

 

[champ driver]

What are knots, are those what you find in fishing line and shoelaces?

 

[ChrisK]

For a 172 / 152, I've found that adjusting my speeds by 10 usually works well. Checklist in knots and plane in mph, add 10 to the checklist. It means I don't have to carry around two checklists

I switch back and forth pretty often, and tbh, flying approaches at 80 kts instead of 90 - particularly if they are precision approaches - is generally only annoying to ATC and the traffic behind me

Also considering how far under MGW you probably are and that most people approach too fast, coming in a little slow probably isn't a big deal (as you saw). Just fly by visual references and add power when necessary if you sink too fast. Landing is a visual makeover !!

 

[NJP_MAN]

I switch between a AA-5 , C150, C172N and a C208B. I don't get goofed up too bad because each checklist has approach speeds listed appropriate for the particular K/MPH-IAS. Getting the Vref for landing the 208 before takeoff makes that plane easy.


And flaps 30 on the C150/c172 makes for a better approach until you get comfortable with the nose down attitude at flaps 40.

 

[BiffJ]

Quit worrying about what the airspeed is measured in. Its makes no difference. Use the numbers for that particular airplane and the guage it has in it. If it reads in kilometers, arshins or inches per day it makes no difference. If the book or the check pilot says use 291 1/2 on the guage for approach that is the number you use. I've been flying since the mid 80s in rentals, loaners and my own planes and never had a single issue with the nomenclature of the guages. Use the number for the plane and you'll be fine. Try to convert to a number convenient to you and you'll waste enough time to be dangerous to yourself and others. Quit converting and just fly. You'll be much happier for it.

Frank

 

[gitmo234]

Is changing an airspeed indicator something I can do as "pilot maintenance"? I doubt it. How much trouble is it?

 

[Graueradler]

To convert knots to mph in your head, add 10%, then add half of the 10% again. Example - 100 kts + 10 + 5 = 115mph

 

[docmirror]

Yup, I get mixed up once in a while on that. I fly a really old plane with only MPH, no dual scale. Then I fly something from this century and have only knots. Hassle. Wish they would have simply stayed with MPH, and not sure why the change.

 

[ChrisK]

And flaps 30 on the C150/c172 makes for a better approach until you get comfortable with the nose down attitude at flaps 40.

150 with fill flaps and power out sure is a kick in the ass, isn't it?

 

[NJP_MAN]

inches per day it makes no difference.
Frank

Fun fact:

If my calculations are correct.

65KIAS(general approach speed for C172) = 113,760,000IPD( inches/day)IAS.

So OP please use 113,760,000 inches per day as a nice safe final approach speed.

 

[upstateny]

Fun fact:

If my calculations are correct.

65KIAS(general approach speed for C172) = 113,760,000IPD( inches/day)IAS.

So OP please use 113,760,000 inches per day as a nice safe final approach speed.

What is that in furlongs per fortnight?

 

[NJP_MAN]

What is that in furlongs per fortnight?

200,928 FpFN

 

[CTLSi]

Anyone have any experience switching back and forth between knots and mph?

My cessna is MPH. Today I flew solo xcountry to Ocean City MD and back and on short final to my home airport I noticed the airspeed dropped to 60mph and added some power.

Came in a bit fast but landing was great...once on the ground I realized that 60 I was thinking knots, and let it get a bit low.

So I'm having some hiccups adjusting to mph as well as air frames with 40 degree flaps. The older cessnas (with 40 degree flaps or otherwise) seem to come in a bit faster (to me), and fly a bit like a rock.

Anyone else have similar experience?

My glass panel can be user set to mph v kts and f v C. I have mine set to kts and centigrade.

 

[gitmo234]

Well, as a student pilot, I watch my gauges more than I go by feel. Watching airspeed on short final and shooting for 60 has a much more drastic effect than 110mph vs kias. So while I adjust a bit, I have 7 hours flying mph and about 45 flying KIAS, so I will worry about making sure I'm using the right metric

 

[gitmo234]

Fun fact:

If my calculations are correct.

65KIAS(general approach speed for C172) = 113,760,000IPD( inches/day)IAS.

So OP please use 113,760,000 inches per day as a nice safe final approach speed.

It's 113,744,882 inches per day

 

[flyingron]

All the V speeds in my plane are in MPH and the airspeed indicator is dual scaled (though the main scale is MPH). I live on Knots however and the GPS and the other avionics is all set up for knots and nautical miles. I've never really had too much of a difference. If I need to convert I just look at the airspeed indicator and read off the corresponding scale.

Never really have any difference in speed because i don't really look at the numbers so much as where the needle is with respect to the various arcs on the indicator. Amazing how useful those things are ...

 

[JoeSelch]

All the V speeds in my plane are in MPH and the airspeed indicator is dual scaled (though the main scale is MPH). I live on Knots however and the GPS and the other avionics is all set up for knots and nautical miles. I've never really had too much of a difference. If I need to convert I just look at the airspeed indicator and read off the corresponding scale.

Never really have any difference in speed because i don't really look at the numbers so much as where the needle is with respect to the various arcs on the indicator. Amazing how useful those things are ...

This.

 

[weirdjim]

What is that in furlongs per fortnight?

Similar conversion factor for fuel burn in hogsheads per gigasecond.

Jim

 

[weirdjim]

Aviation will be one of the last bastions of the English system and VHF AM when the entire rest of the world (U.S. included) has long since switched to the metric system and either FM or spread spectrum.

 

[gitmo234]

All the V speeds in my plane are in MPH and the airspeed indicator is dual scaled (though the main scale is MPH). I live on Knots however and the GPS and the other avionics is all set up for knots and nautical miles. I've never really had too much of a difference. If I need to convert I just look at the airspeed indicator and read off the corresponding scale.

Never really have any difference in speed because i don't really look at the numbers so much as where the needle is with respect to the various arcs on the indicator. Amazing how useful those things are ...

Mine has the original asi and doesn't have all the v speeds on it.

 

[CTLSi]

Well, as a student pilot, I watch my gauges more than I go by feel. Watching airspeed on short final and shooting for 60 has a much more drastic effect than 110mph vs kias. So while I adjust a bit, I have 7 hours flying mph and about 45 flying KIAS, so I will worry about making sure I'm using the right metric

Be careful. Usually the POH gives speeds in IAS knots. If this plane was built with MPH, read the POH and get those numbers down. I would hate to be flying final at 60 mph when i wanted 60 kts IAS. you will stall.

 

[TUPilot]

Anyone have any experience switching back and forth between knots and mph?

My cessna is MPH. Today I flew solo xcountry to Ocean City MD and back and on short final to my home airport I noticed the airspeed dropped to 60mph and added some power.

Came in a bit fast but landing was great...once on the ground I realized that 60 I was thinking knots, and let it get a bit low.

So I'm having some hiccups adjusting to mph as well as air frames with 40 degree flaps. The older cessnas (with 40 degree flaps or otherwise) seem to come in a bit faster (to me), and fly a bit like a rock.

Anyone else have similar experience?

Just learn and use the correct indicated speeds in MPH. In that regard it is no different than switching between different types of planes. Learn the right speed and use it.

Replacing the ASI is going to be more trouble and expenses than it is worth... do some studying, fly a few more hours, and you'll have it down!

 

[Jeff K]

Quit worrying about what the airspeed is measured in. Its makes no difference. Use the numbers for that particular airplane and the guage it has in it.

^^^ THIS ^^^

Further, in some aspects of flight, in particular emergency ops, you don't want to be doing the mental math in your head. You know the number for the gauge you have... fly it. Done.

 

[iflyvfr]

I just posted a video of a landing with 40* flaps and about 62 MPH on short final. Pointed the nose down and with power out, didn't have much elevator for the flare. Made a firm arrival but on this shorty I was going to stop in plenty of time. I love throwing the barn doors out.

https://www.youtube.com/watch?feature=player_detailpage&v=Jd3BlLeELz0#t=24

 

[flyingron]

Be careful. Usually the POH gives speeds in IAS knots. If this plane was built with MPH, read the POH and get those numbers down. I would hate to be flying final at 60 mph when i wanted 60 kts IAS. you will stall.

Eh? If the plane has a MPH airspeed indicator, it's almost certain that the V speeds are given in Miles Per Hour True Indicated Airspeed in the corresponding book.

Airspeed does not make you stall.

 

[flyingron]

Mine has the original asi and doesn't have all the v speeds on it.

It should have the green, white, and yellow arcs and the red line. That gives you most of them.

 

[poadeleted20]

Anyone have any experience switching back and forth between knots and mph?

I jump back and forth all the time with my clients' planes, and used to do it with my 1976 Cheetah which was mph versus the knots 172's at the flight school where I was teaching part-time. It's just part of flying more than one plane, just like knowing several different Vy's or approach speeds for the different planes you fly. If you learned on knots 172's and are now flying a mph 172, you'll just have to get used to it, as I don't think you're authorized to swap out to a knots-primary airspeed indicator without additional FAA approval.

BTW, my experience is the old 172's land slower, not faster, mainly because they have pretty much the same wing but are lighter and have slightly higher stall speeds at full flap. We used to fly mid-60's 172's at 65 mph (about 57 knots) on final with the full 40 flaps, but these days I'm flying late-70's/80's 172's at 60 knots (69 mph) on final with the full 30 flaps. Small difference, but enough to float you a bit or get a sink going if you go the wrong way.

 

[gitmo234]

I jump back and forth all the time with my clients' planes, and used to do it with my 1976 Cheetah which was mph versus the knots 172's at the flight school where I was teaching part-time. It's just part of flying more than one plane, just like knowing several different Vy's or approach speeds for the different planes you fly. If you learned on knots 172's and are now flying a mph 172, you'll just have to get used to it, as I don't think you're authorized to swap out to a knots-primary airspeed indicator without additional FAA approval.

BTW, my experience is the old 172's land slower, not faster, mainly because they have pretty much the same wing but are lighter and have slightly higher stall speeds at full flap. We used to fly mid-60's 172's at 65 mph (about 57 knots) on final with the full 40 flaps, but these days I'm flying late-70's/80's 172's at 60 knots (69 mph) on final with the full 30 flaps. Small difference, but enough to float you a bit or get a sink going if you go the wrong way.

Thanks! When I was flying the S model it seemed that I would sometimes balloon when flying alone. Now that I'm flying a 1957 172, it seems to come in like a rock. 40 degree flaps or not there is zero balloon...ever. So far I am liking the older models much better. Not quite as much power but I like the way they fly and feel on final

 

[CTLSi]

Eh? If the plane has a MPH airspeed indicator, it's almost certain that the V speeds are given in Miles Per Hour True Indicated Airspeed in the corresponding book.

Airspeed does not make you stall.

You should always be watching airspeed, not some color coded bar when turning base to final and final to landing.

Yes, speed leads to stall when you are too slow and low and you pull up and get critical angle of attack. That's the first reaction student have and he might do that if he is not careful and already knows EXACTLY what MPH number he needs to make a good approach.

 

[poadeleted20]

Thanks! When I was flying the S model it seemed that I would sometimes balloon when flying alone.

You were probably flying it at the "recommended" 65-70 knots, which really is too bloody fast, especially solo. In such a case, 60 knots is a lot better choice -- maybe even a couple of knots less if you're solo with no baggage/cargo and less than half tanks.

Now that I'm flying a 1957 172, it seems to come in like a rock. 40 degree flaps or not there is zero balloon...ever. So far I am liking the older models much better. Not quite as much power but I like the way they fly and feel on final

You can get pretty much the same feel in a newer 172S if you slow it down to the same speed relative to stall speed. Unfortunately, at training weights, the Cessna-recommended speeds of 65-70 knots are up around 1.5 Vs0, and that's way too fast with full flaps at that weight.

 

[AdamZ]

Quit worrying about what the airspeed is measured in. Its makes no difference. Use the numbers for that particular airplane and the guage it has in it. If it reads in kilometers, arshins or inches per day it makes no difference. If the book or the check pilot says use 291 1/2 on the guage for approach that is the number you use. I've been flying since the mid 80s in rentals, loaners and my own planes and never had a single issue with the nomenclature of the guages. Use the number for the plane and you'll be fine. Try to convert to a number convenient to you and you'll waste enough time to be dangerous to yourself and others. Quit converting and just fly. You'll be much happier for it.

Frank

This is exactly correct. You own a plane now so learn and get comfortable with what its speeds are! Don't mess with putting in a new ASI.

 

[brian]]

Quit worrying about what the airspeed is measured in. Its makes no difference. Use the numbers for that particular airplane and the guage it has in it. If it reads in kilometers, arshins or inches per day it makes no difference. If the book or the check pilot says use 291 1/2 on the guage for approach that is the number you use. I've been flying since the mid 80s in rentals, loaners and my own planes and never had a single issue with the nomenclature of the guages. Use the number for the plane and you'll be fine. Try to convert to a number convenient to you and you'll waste enough time to be dangerous to yourself and others. Quit converting and just fly. You'll be much happier for it.

Frank

Amen.

Gear flaps at the top of the white. Stay out of the bumps in the yellow. wing quits flying at the bottom of the white. Use the POH - MPH, KTS whatever...

Now, when comparing who is going faster - well, just talk MPH if the other guy is talking KTS and it all works out well

 

[docmirror]

Amen.

Gear flaps at the top of the white. Stay out of the bumps in the yellow. wing quits flying at the bottom of the white. Use the POH - MPH, KTS whatever...

If I may be allowed to make a gentle suggestion sir, I wait on the gear until down to 75-80MPH on downwind, or even in base if you are comfy with your plane. I know what the operating speed of the gear is, and I know that it will not do immediate damage to operate it that way, but your gear motor, sector gear, inner gear door extension shaft and bearings will appreciate a lower gear operating speed.

Of course, in the end, it's your plane and you may operate it however you see fit.

 

[brian]]

If I may be allowed to make a gentle suggestion sir, I wait on the gear until down to 75-80MPH on downwind, or even in base if you are comfy with your plane. I know what the operating speed of the gear is, and I know that it will not do immediate damage to operate it that way, but your gear motor, sector gear, inner gear door extension shaft and bearings will appreciate a lower gear operating speed.

Of course, in the end, it's your plane and you may operate it however you see fit.

Hey - I'm an imperfect person - all suggestions welcome

Might be interesting to meet up or talk offline (are you on BeechTalk?). I have no problem getting to the upper 90's on downwind, but any slower is kinda hard on that slick airplane. (Ok, I could pull the nose up.) No problem flying in the 80's - but I found it made my BPPP instructor very nervous. I didn't expect that one...

 

[BillTIZ]

When I was flying a lot of different make/model/years. I had a smart card for each airplane and put it in my pocket for the airplane I had that day.

Now I just keep the speed appropriately above the bottom of the white arc. 1.3 x Vso?

 

[docmirror]

Hey - I'm an imperfect person - all suggestions welcome

Might be interesting to meet up or talk offline (are you on BeechTalk?). I have no problem getting to the upper 90's on downwind, but any slower is kinda hard on that slick airplane. (Ok, I could pull the nose up.) No problem flying in the 80's - but I found it made my BPPP instructor very nervous. I didn't expect that one...

I am not on BT. I was, but got removed for not offering my confidential info to them. It's sad that your BPPP instructor got nervous at 80s in that plane. At max gross, your plane stalls at ~55MPH, and by advanced calculus I come up with 72MPH for the appr speed. I'm at 80MPH downwind abeam unless I"m in a big rush, and down to 75MPH or less over the fence. You must float quite a bit on landing with those high speeds.

One other suggestion to slow the plane, is to set your prop to high setting when you get to pattern. That big ole prop disk at idle power will help slow you down very well.

 

[NJP_MAN]

You should always be watching airspeed, not some color coded bar when turning base to final and final to landing.

Yes, speed leads to stall when you are too slow and low and you pull up and get critical angle of attack. That's the first reaction student have and he might do that if he is not careful and already knows EXACTLY what MPH number he needs to make a good approach.

Watch out .. We have a instructor over here.

 

[brian]]

I am not on BT. I was, but got removed for not offering my confidential info to them. It's sad that your BPPP instructor got nervous at 80s in that plane. At max gross, your plane stalls at ~55MPH, and by advanced calculus I come up with 72MPH for the appr speed. I'm at 80MPH downwind abeam unless I"m in a big rush, and down to 75MPH or less over the fence. You must float quite a bit on landing with those high speeds.

One other suggestion to slow the plane, is to set your prop to high setting when you get to pattern. That big ole prop disk at idle power will help slow you down very well.

Too bad. The good news is I seem to have a lot of early 35 owners in the area that have been helping me. (This is my first year with the -35.)

Once I get the gear down, slowing down to 90 (base), and 80 (over the fence). But some of the 35 owners push it like a BE55 - and plant the gear on the pavement. Works, but it can't be good on the tires...

I'll try a few more things to slow down on downwind...

(Sorry about the thread hijack - but I have something new to try/learn ...)

 

[docmirror]

But some of the 35 owners push it like a BE55 - and plant the gear on the pavement. Works, but it can't be good on the tires...

I see/hear this all the time. Lotsa Bo pilots drive it on around 70-80. I watched a guy giving rides in a M35 a few years back(at Cedar Mills no less) come in really hot, bounce on the nose gear once, then pull the power back and use all of the runway to get slowed. Pretty common in the type. If you put 30-40Lbs of weight in the baggage bay, or some fuel in the aux tank you can come over the fence at 75 with power near idle and stop in a few hundred feet.