Any other Nerds or just me? (Airspeed calcs)

[Bob - S50]

Stall speed = SQRT(weight/gross weight)SQRT(1/cos(B)), where B is the bank angle.

 

Simple rule of thumb, on final, reduce stall speed by 1 knot per 100 pounds below gross weight.

Ahhh.  So I'm NOT the only one!

[M20F-1968]

Bob:

 

your "bottom line" is assumed stall speed of 58 knots adjusted by + 1.5(fuel weight + payload)/100

what assumptions provide the 58 and the 1.5 ?

John Breda

[Bob - S50]

Bob:

 

your "bottom line" is assumed stall speed of 58 knots adjusted by + 1.5(fuel weight + payload)/100

what assumptions provide the 58 and the 1.5 ?

John Breda

Actually, 58 is the assumed 1.3 x empty stall speed.

Here is the math I did: empty wt/max wt = empty stall squared/ max stall squared

1770/2740 = x^2/55 ^2

55^2 x (1770/2740) = x ^2

1954.11 = X^2

x = 44.2 KIAS (empty stall speed)

1.3 x = 57.46

I rounded up to 58 because I'd rather be half a knot fast than half a knot slow.  Ya right, like I can fly that precisely!

At full gross, stall of 55, 1.3 x 55 = 71.5 (approach speed at full gross)

71.5 - 57.5 = 14 knots difference.

14 /9.70 (hundreds of pounds difference in weight) = 1.44 KIAS/100# increase.  I rounded up to 1.5.  Again, I'd rather be .06 knots fast for each 100 pounds.  Plus the mental math is much easier for 1.5 than it is for 1.4.

In reality I ran the numbers for every hundred pounds from empty to max gross and then saw the pattern.

Sorry you asked?

[Danb]

I've been flying with my AOA for about a year and half. In theory it seems a no brainer but that said to really make it a useful tool it takes practice in differing configurations ie. wind etc. once used to it you kind of forget about the weight etc. at a Mooney PPP I had the good luck to have Major Mark as my instructor and after a few moments he said you can fly this can so let's learn how to fly the AOA indicator properly after an hour or so it all came together, my landings which weren't the best prior became quite easy basically now if it's not close to a squeaker my eyes screwed up.  I carry my speed almost to the threshold and let the energy dissipate then round out, by keeping the donut in the middle makes for good landings, yesterday gusting to 20 made little difference in the outcome.

[M20F-1968]

Bob - Thanks for the mathematical version of your thinking process.  No, not sorry that I asked.  Guess that makes me a nerd as well.

As my post states, I am a frustrated engineer, and as my plane suggests, I don't shy away from projects.

Danb - Your post makes me want to play with the AOA more.  Have it installed but still learning about the plane and its avionics.

John Breda

[M016576]

For those who don't want to read long entries, this is about airspeed on final.  I have started using yet another speed (involving mental math) and wonder if anybody else is doing something similar.

When we first got the J I flew 80 KIAS on final... too fast.

Then I started slowing to 75 KIAS, still floated forever.

Then I tried 70 KIAS, still float more than I like.

Here comes the nerd part.  Our POH only gives stall speed for max gross weight; full flaps it is 55 KIAS.  It does not give stall speeds at any other weight.  So I got out my trusty calculator app and did some figger'n.  Since lift is proportional to the square of the velocity, I used the formula W2/W1 = V2^2/V1^2.  Since I knew W1= 2740 and V1 = 55 I could enter any weight and come up with the stall speed.  I then took the stall speed at each weight and multiplied by 1.3 to come up with a target speed (no gusts) on final.

Bottom line, I now use the following:  58 KIAS + 1.5 x (fuel+ payload in hundreds).

So for example.  If I come back to the airport solo with 10 gallons on board that's about 190# for me and all my gear + about 60# for fuel = 250# total.  I round that up to 300.  3 x 1.5 = 4.5 so I would use 63 KIAS on final.  If I come back with 30 gallons, and 400# of people and bags I would use 58 + 1.5 x (400 + 180)/100.  Call it 58 + 1.5 x 600 = 58 + 9 = 67 KIAS on final.

So far I'm much happier with my landings.

So is it just me?

you could do all that... Or you could install an AoA indexer.  A wing stalls at the same AoA no matter what your gross weight.  Actually- your weight calculations are only as good as your last W&B and as accurate as you estimate the weights of everything else.  You should install an AoA gauge if you really want to nail it aerodynamically.  In fact, all those calculations you are performing are precisely why we used AoA (and not airspeed) for our landings at the aircraft carrier back when I was flying F-18's: it's the only way to really know for sure, no matter what.

[Andy95W]

You should install an AoA gauge if you really want to nail it aerodynamically. 

Wait, so closing my eyes and screaming as I flare isn't as effective as I thought?!?!?

[Hank]

Wait, so closing my eyes and screaming as I flare isn't as effective as I thought?!?!?

I've been forgetting to scream!    Usually I just close my eyes and flinch, more so when I have a passenger.

[Marauder]

Wait, so closing my eyes and screaming as I flare isn't as effective as I thought?!?!?

It is when a herd of deer run onto the runway as you are doing your flare!

Sent from my iPad using Tapatalk

[Bob - S50]

you could do all that... Or you could install an AoA indexer.  A wing stalls at the same AoA no matter what your gross weight.  Actually- your weight calculations are only as good as your last W&B and as accurate as you estimate the weights of everything else.  You should install an AoA gauge if you really want to nail it aerodynamically.  In fact, all those calculations you are performing are precisely why we used AoA (and not airspeed) for our landings at the aircraft carrier back when I was flying F-18's: it's the only way to really know for sure, no matter what.

Couple of things to respond to.

1.  Our plane was weighed about two years ago and we have not installed anything since then.  I'm comfortable with the basic weight.

2.  I would not mind an AOA except for the cost and the need to get approval from my three partners.  I figure probably about $2000 - $3000 installed but that's just a guess.

3.  I've flown planes with an AOA and know that they jump around with every little twitch of the hand or up/down draft.  If I had one, I would use it to determine the correct speed to fly on final and then fly airspeed, not AOA.  Airspeed does not dance around as much as the AOA.

4.  Having watched the video posted in another post, while I'm sure I would get used to it, I would not want the AOA yelling Too Slow! at me while I'm in the flare.  Especially if I have passengers with me.

Don't get me wrong.  I think they are a great tool but at this point, at least for me, not quite worth the cost.  If I was to get one, I would want one that provided more precise indication of AOA.  More like a gauge, less like; too fast, on speed, getting slow, too slow.  Of those that are available for sale, this is the one I like best because it does show more detail: AOA Pro.  Unfortunately, I couldn't put it in our plane because it is for experimental aircraft only.

[Bob - S50]

Wait, so closing my eyes and screaming as I flare isn't as effective as I thought?!?!?

Close.  Wait until the person in the right starts to suck up the seat cushion, then flare.

[gsxrpilot]

Close.  Wait until the person in the right starts to suck up the seat cushion, then flare.

Don't close your eyes! Keep them glued on Lead's wing out the left window. Flare when Lead flares, roll it on and keep it rolling to the end. No brakes, No flaps. :-)

[M016576]

Couple of things to respond to.

1.  Our plane was weighed about two years ago and we have not installed anything since then.  I'm comfortable with the basic weight.

2.  I would not mind an AOA except for the cost and the need to get approval from my three partners.  I figure probably about $2000 - $3000 installed but that's just a guess.

3.  I've flown planes with an AOA and know that they jump around with every little twitch of the hand or up/down draft.  If I had one, I would use it to determine the correct speed to fly on final and then fly airspeed, not AOA.  Airspeed does not dance around as much as the AOA.

4.  Having watched the video posted in another post, while I'm sure I would get used to it, I would not want the AOA yelling Too Slow! at me while I'm in the flare.  Especially if I have passengers with me.

Don't get me wrong.  I think they are a great tool but at this point, at least for me, not quite worth the cost.  If I was to get one, I would want one that provided more precise indication of AOA.  More like a gauge, less like; too fast, on speed, getting slow, too slow.  Of those that are available for sale, this is the one I like best because it does show more detail: AOA Pro.  Unfortunately, I couldn't put it in our plane because it is for experimental aircraft only.

The price tag on an AoA gauge can be (overly) expensive, I agree.  Certain gauges have desirable and undesirable features, also true.  some are more sensitive than others.

its the data that's the important piece.  We fly using an airspeed indicator because that's what the engineers at the factory installed for general aviation pilots. Angle of Attack is the most accurate way to measure where we are on the L/D curve, though- and that's what all the speeds in the PoH for stall and approach are ultimately derived from- as the instrumented test aircraft can simply fly any multiplier of stall by flying an AoA gauge.

A pilot can calculate their speeds for each weight on every flight, or (if you have a gauge) they can fly one angle of attack regardless of the loading.

some people really enjoy the extra math and go into detail. some people use the PoH numbers.  Some people just estimate and add a few kts for the wife and kids, it seems.

im not judging- just laying out the information the best I understand it.  I'm impressed you (and the others that have populated this thread) go to such detail to find your approach speeds more precisely on each flight.   And I have no doubt that going through the mental effort results in a shorter landing rollout: you're collecting a customized approach speed that best models your aircrafts parameters- not the one-size-fits-all numbers from the book. Nicely done

[M016576]

Wait, so closing my eyes and screaming as I flare isn't as effective as I thought?!?!?

you've got to fly it all the way into the crash!  Duh!  :)

[Danb]

Bob, I don't know about other AOA indicators but mine doesn't jump around and I agree you don't want one screaming slow etc, I didn't either figuring my passengers would freak out so I just turned off the voice. I really had doubted the usefulness of it until I flew with the F-18 pilot who taught my the proper technique to use when flying. Honestly my landings became much better once I used the device properly. I don't think one who never flew behind one could just jump into the plane and be able to utilize it properly, or I could just be a bad pilot since it took awhile for me to fly it properly.

Edited October 25, 2015 by Danb

[Mooneymite]

We can all agree to the math on determining proper appraoch speed.  But what about touch down speed?

Question:  do you try to touch down at 1.3 Vs, or close to Vs?

I believe a lot of Mooneys float, float, float on landing because of a mistsken belief that touchdown should be at "close to" 1.3 Vs.

Since most of us aren't  looking at the IAS, unless it's  very gusty, I  think on a proper landing, the squeeker should include the sound of the stall horn.

[Hank]

I agree, Gus. 1.3 Vso I a a good pattern speed, slowing on short final to 70-75 depending on weight. Flare, slow some more and touch down just after the stall buzzer squeaks. Works pretty well for me, and I only float if I'm faster than this. At my old obstructed home field, I would often be down between the second and third stripe; there is no VASI, no PAPI, no instrument lines, and you often can't see the numbers for the trees until short final. If you want to come in high and steep, goo luck, the field is only 3000' long, and the trees at the other end are closer and taller, it actually has about a 300' displaced threshold.

[WardHolbrook]

Bob, I don't know about other AOA indicators but mine doesn't jump around and I agree you don't want one screaming slow etc, I didn't either figuring my passengers would freak out so I just turned off the voice. I really had doubted the usefulness of it until I flew with the F-18 pilot who taught my the proper technique to use when flying. Honestly my landings became much better once I used the device properly. I don't think one who never flew behind one could just jump into the plane and be able to utilize it properly, or I could just be a bad pilot since it took awhile for me to fly it properly.

If you want to learn how to use AoA go find yourself a Naval Aviator and buy him lunch while you listen and take notes. I have about 10,000 hours in AoA equipped jet aircraft. In the beginning, I was like most pilots and never bothered with them. Then, about 20 years ago, I spent a couple of weeks flying one of our company bizjets all around the country with one of the manufacturer's certification test pilots. He gave me the pertinent AoA indexer references for the common V and performance speeds (like max endurance, LR cruise, holding, Max L/D etc and of course, Vref) and I could duplicate, at will and instantly, whatever speed I wanted for our given weight, temperature, altitude etc. without having to crack open the performance charts. We jotted down the conditions and after the flights he took me into the performance charts to verify the AoA derived speeds. It was eye opening. It's a great tool and useful for much more than figuring out your approach speed.

Mooneys demand the use of proper airspeed crossing the fence and there are a lot of Mooney pilots out there that fly their approaches way too fast and way too flat. They end up having to compensate for one poor technique with other poor techniques - too fast over the fence compensated by partial or no flaps. We've all seen it. Their flying is pretty sloppy and they'd have a hard time making book landing performance numbers and their tires and brakes don't seem to last as long as they should. AoA indicators are really helpful for those guys. It tends to make them more at ease when they're on final precisely at 1.3 Vso with flaps extended and their approach gradients are much better. It's amazing your landings improve when you're bang on the proper airspeed for your weight and existing conditions. No more guessing, no more fancy math in your head and no more fudge factors. Can you fly without AoA? Of course, nobody is saying otherwise, but never forget that most of the performance speeds that we use on a regular basis are not based upon specific airspeeds, but upon specific angles of attack. Having an accurate AoA indication available to you and understanding what it is telling you is a much better way to fly an airplane.

 

[Shadrach]

We can all agree to the math on determining proper appraoch speed.  But what about touch down speed?

Question:  do you try to touch down at 1.3 Vs, or close to Vs?

I believe a lot of Mooneys float, float, float on landing because of a mistsken belief that touchdown should be at "close to" 1.3 Vs.

Since most of us aren't  looking at the IAS, unless it's  very gusty, I  think on a proper landing, the squeeker should include the sound of the stall horn.

The goal is to touchdown just as you reach 1 x stall speed for your configuration; the nose can then be gently lowered. In the F model at least, there is ample elevator to hold the nose off after the wing has fully stalled. I sometimes like to practice T & Gs without ever letting the nose touch.

[Danb]

Ward..totally agree, I flew with an Air Force pilot who did numerous missions over the sand, and that is when I learned to use the indicator properly, I learned more in two hours than usually learned in the 3 day courses I take yearly.

[Bob - S50]

I agree, Gus. 1.3 Vso I a a good pattern speed, slowing on short final to 70-75 depending on weight. .....

I'm assuming that you misspoke.  I do not fly the ...pattern... at 1.3 Vso.  I fly the pattern at or above 80 KIAS and then slow to 1.3 Vso (63 - 72 KIAS) on final.  1.3 Vso gives you a 30% margin when wings level.  It gives you much less margin in a turn or flaps up.  No margin at 45 degrees of bank, steady state.

[Hank]

I'm assuming that you misspoke.  I do not fly the ...pattern... at 1.3 Vso.  I fly the pattern at or above 80 KIAS and then slow to 1.3 Vso (63 - 72 KIAS) on final.  1.3 Vso gives you a 30% margin when wings level.  It gives you much less margin in a turn or flaps up.  No margin at 45 degrees of bank, steady state.

You're right, my bad. My pattern speed is 90 mph; stall is 57 with full flaps, 64 with half flaps, less an unknown number for being below gross. So 1.3Vso is either 74 or 83 mph. I fudge for weight by reducing the target by 5 mph for every 300 lbs I estimate myself below gross for each landing.

I also never bank beyond 30º in the pattern, and rarely beyond 20º. Yanking and banking 45º when trying to land is asking for trouble. For a 40º bank, stall speed goes from 57 to 69 mph with full flaps, or 64 to 76 with half flaps.

[Shadrach]

My Pattern speed is what ever I need it to be, but 1.2Vso is where I want to be across the fence.