Adding flaps during the descent

[poadeleted20]

Any strut, fixed gear Cessna is draggy enough that a throttle pull back and nose lift will slow the airplane appreciably in moments.

When you're traveling at 150 ft/sec, "moments" covers a lot of ground, especially at the MDA in low vis.

 

[dmccormack]

When you're traveling at 150 ft/sec, "moments" covers a lot of ground, especially at the MDA in low vis.

Then don't fly fast when the weather is at mins, especially inside the OM.

I reject the contention that we must fly fast all the way to 200' AGL. I've flown to mins into fairly busy airports and once 2 miles out or so the power comes back, the flaps go to 20, and the airplane is configured for landing.

 

[ScottM]

So....110 and 10* is an AFM/POH operating limitation but NOT a type certificate issue...20* or greater and 85kts IS a type certificate limitation.

In your conversation with Cessna did they mention anything about how one could get the AFM modified to include the 110knot limitation or is it once published it is there for the life of the model?

I am just wondering if, for example, that the 172N can be updated to have the limitation changed.

 

[Pilawt]

Interesting note is the change in total flap travel from 40* to 30* I believe after the 1979 models

This was done to allow a gross weight increase from 2300 to 2400 lb. The limiting factor had been the balked landing climb gradient with full flaps. By reducing flap travel 10 degrees, they were able to make the climb gradient while 100 lb heavier.

And that happened with the introduction of the C-172P for the 1981 model year -- s/n 17274010 and up.

 

[poadeleted20]

Then don't fly fast when the weather is at mins, especially inside the OM.

150 ft/sec is only about 90 knots, which is a typical approach speed for many light planes. However, you may recall that I recommended flying final in a 172 at 80-85 with 10 flaps in order to avoid this problem. The other problem is that during IR training, if you vary the approach speed depending on conditions, it's harder to get the fundamentals down. That's why I try to get folks to fly one speed/configuration that works for them and their airplane until they can do that consistently well before playing with other speeds/configurations.

 

[dmccormack]

150 ft/sec is only about 90 knots, which is a typical approach speed for many light planes. However, you may recall that I recommended flying final in a 172 at 80-85 with 10 flaps in order to avoid this problem. The other problem is that during IR training, if you vary the approach speed depending on conditions, it's harder to get the fundamentals down. That's why I try to get folks to fly one speed/configuration that works for them and their airplane until they can do that consistently well before playing with other speeds/configurations.

Exactly -- one of the most basic instructional principles: Master fundamentals, then add complexity.

 

[DutchessFlier]

In your conversation with Cessna did they mention anything about how one could get the AFM modified to include the 110knot limitation or is it once published it is there for the life of the model?

I am just wondering if, for example, that the 172N can be updated to have the limitation changed.

I didn't ask that question..but I have been under the impression, maybe incorrectly, that once the AFM-POH is printed, the only change can be an approved modification to the document from the manufacturer.

 

[ScottM]

I didn't ask that question..but I have been under the impression, maybe incorrectly, that once the AFM-POH is printed, the only change can be an approved modification to the document from the manufacturer.

I was thinking that too. It seems as though no structural changes were needed for this, just a new procedure. Could Cessna do that by sending a new page out for the AFM? Sort of an STC type procedure?

 

[azure]

Any strut, fixed gear Cessna is draggy enough that a throttle pull back and nose lift will slow the airplane appreciably in moments.

Yes, I proved to myself today that this is a non-issue. Today we tried having me reconfigure at DH and landing, from the ILS 27 at FNT (actually about 30 feet above DH because I was a little worried over how quickly/safely I could remove the hood without sending my headset or glasses askew). The trick is to throttle way back, pull the nose up and add the flaps. I managed 20* of flaps in two steps before landing, and I did it twice, both times successfully. One of the landings was slightly side-loaded but the other was perfect.

I didn't do so well landing downwind from a mile final and 500 AGL back at home base. This was to be a straight-in landing from the RNAV 9 with a 4 knot tailwind. The tailwind was much stronger at MDA, and even with power to idle soon after going visual we came barreling in too fast. It also took too long for my airspeed to bleed off once I passed into the weaker tailwind near the ground. I was in ground effect by the numbers but at 65 KIAS, with the tailwind, the 3550 foot runway just wasn't long enough. I just don't have enough experience landing in tailwinds and was too slow in the uptake of just how fast we were coming in -- I neglected to check GS on the GPS. I think it might also be a better technique, in that situation, to add flaps at the FAF to allow a steeper descent rate at a slower airspeed.

It's looking as if I'll have to learn both the method Cap'n Ron teaches and my CFII's (minus the going below glideslope) in order to handle all possible situations.

 

[dmccormack]

It's looking as if I'll have to learn both the method Cap'n Ron teaches and my CFII's (minus the going below glideslope) in order to handle all possible situations.

I'm all for thorough training but don't get too wrapped up in mastering every possible eventuality before the IR practical -- after all, after you pass, all you have is a "License to learn."

 

[azure]

I'm all for thorough training but don't get too wrapped up in mastering every possible eventuality before the IR practical -- after all, after you pass, all you have is a "License to learn."

That's not the only situation where I might need the other method, though. To land straight-in on the RNAV 18 into 1D2, you have to lose 1700 feet in 4.2 miles. Even in calm winds, I wouldn't want to fly that one clean, I'd need about a 700 fpm descent rate the whole way. Reconfiguring anywhere along the descent would risk not making it without slipping or diving.

That's a nearby field and one the DPE could very well ask me to do.

 

[dmccormack]

That's not the only situation where I might need the other method, though. To land straight-in on the RNAV 18 into 1D2, you have to lose 1700 feet in 4.2 miles. Even in calm winds, I wouldn't want to fly that one clean, I'd need about a 700 fpm descent rate the whole way. Reconfiguring anywhere along the descent would risk not making it without slipping or diving.

That's a nearby field and one the DPE could very well ask me to do.

Right, though any sort of headwind will simplify the issue.

700 FPM isn't all that bad -- most non-precision approaches you'll want to drop fast (800-100 FPM) to MDA so you have time to look for the runway (and some runways with NP approaches are tough to spot in low vis conditions!)

 

[azure]

700 FPM isn't all that bad -- most non-precision approaches you'll want to drop fast (800-100 FPM) to MDA so you have time to look for the runway (and some runways with NP approaches are tough to spot in low vis conditions!)

That was part of my problem tonight on the RNAV. I didn't get down to MDA until I was less than 1.5 miles from the runway, and things were moving too quickly for me to get slowed down and fully configured in time for landing. I don't like long >500 fpm descents because I have trouble clearing my ears, but sometimes they're necessary.

I might not actually need to use flaps on the descent so I will try it both ways, but they would definitely help slow things down and allow a less rapid descent.

 

[TMetzinger]

That was part of my problem tonight on the RNAV. I didn't get down to MDA until I was less than 1.5 miles from the runway, and things were moving too quickly for me to get slowed down and fully configured in time for landing. I don't like long >500 fpm descents because I have trouble clearing my ears, but sometimes they're necessary.

I might not actually need to use flaps on the descent so I will try it both ways, but they would definitely help slow things down and allow a less rapid descent.

That's one of the times the "dive and drive" (get down to MDA as quickly as possible) has an advantage over the "stabilized descent" (maintain a constant angle of descent to the MAP) on non-precision approaches. Getting down earlier gives you more time to compensate for wind changes and adjust for tailwind, as well as spot the runway environment sooner. I always "dive and drive" if there's a tailwind or significant difference in winds aloft and at MDA. And on non-precision approaches "for real" I'm always in the landing configuration at FAF. It's not likely that there's another airplane in trail on the approach, and I want all the "wiggle room" - which translates to time - I can get.

 

[dmccormack]

That's one of the times the "dive and drive" (get down to MDA as quickly as possible) has an advantage over the "stabilized descent" (maintain a constant angle of descent to the MAP) on non-precision approaches. Getting down earlier gives you more time to compensate for wind changes and adjust for tailwind, as well as spot the runway environment sooner. I always "dive and drive" if there's a tailwind or significant difference in winds aloft and at MDA. And on non-precision approaches "for real" I'm always in the landing configuration at FAF. It's not likely that there's another airplane in trail on the approach, and I want all the "wiggle room" - which translates to time - I can get.

Exactly.

I've flown some NP approaches to new-to-me airports at mins.

It's truly amazing how far off the nose a runway can be as you're correcting for the shifting winds present in layered clouds.

Add in low vis due to rain and most NP runways lack of lights and poor markings and you need all the time you can get to actually look for the runway.

 

[azure]

It's truly amazing how far off the nose a runway can be as you're correcting for the shifting winds present in layered clouds.

Not the same thing, but that reminds me of another problem I had last night on the RNAV descent into VLL -- an old problem. I was right of the course line, and trying to bank left to get back to it. I would put in (what I thought was) about a 5* left bank, verified it (so I thought) with both the AI and TC, noted the DG was starting to turn left, glance back at the GPS, and then the next scan of the AI/TC/DG showed that not only was I no longer in a left turn, I was actually slowly turning right again... without any control inputs that I was aware of.

The only clue that I have is that the ball was definitely off to the left. This I know to be the rudder trim tab biting me at low RPMs. I needed left rudder and tried to add it. What I can NOT decide is whether my butt was fooling my eyes (i.e. I felt myself to be in a left bank but had never really established a turn), or whether the DG initial leftward motion was due to the rudder alone and, again, I was throwing myself off by not sustaining steady left rudder pressure.

This one really bothers me. I'm trying as hard as I can to turn left back to the course line, and all I can do is drift right. Even stranger, the crosswind was from the right.

 

[TMetzinger]

Now I WILL say that for non-precision approaches to a runway (as opposed to circling approaches like VOR-A) the WAAS GPS does alter my thinking on "dive and drive". The advisory glidepath provided on LNAV/VNAV or LNAV+V gives a constant smooth descent to the point where you should be able to land if you have the runway environment in sight. But even then, I'm in the landing configuration at the FAF, as I don't have all the built in advantages of an ILS or LPV working for me.

 

[azure]

Now I WILL say that for non-precision approaches to a runway (as opposed to circling approaches like VOR-A) the WAAS GPS does alter my thinking on "dive and drive". The advisory glidepath provided on LNAV/VNAV or LNAV+V gives a constant smooth descent to the point where you should be able to land if you have the runway environment in sight. But even then, I'm in the landing configuration at the FAF, as I don't have all the built in advantages of an ILS or LPV working for me.

The airplane I'm training in has a non-WAAS GPS and I've never flown an approach with a WAAS GPS. (Later I'll transition to our 182, which does have a WAAS GPS.) So for now, I have only LNAV guidance. But I thought that WAAS was sufficient to to get the vertical guidance on a LPV approach? Not true? If not, what more is needed?

 

[dmccormack]

I would put in (what I thought was) about a 5* left bank, verified it (so I thought) with both the AI and TC, noted the DG was starting to turn left, glance back at the GPS, and then the next scan of the AI/TC/DG showed that not only was I no longer in a left turn, I was actually slowly turning right again... without any control inputs that I was aware of..

This is often called "the hand of God" and it's your hands causing control inputs your mind did not command.

Release the yoke when this happens, then put just two fingers on it, no grasping.

It will help.

 

[dmccormack]

The airplane I'm training in has a non-WAAS GPS and I've never flown an approach with a WAAS GPS. (Later I'll transition to our 182, which does have a WAAS GPS.) So for now, I have only LNAV guidance. But I thought that WAAS was sufficient to to get the vertical guidance on a LPV approach? Not true? If not, what more is needed?

You'll need a certified WAAS receiver and an LPV approach as well as a glideslope indicator slaved to the GPS.

 

[Doggtyred]

I know, I'm going to hear from the "FAA is always right" crowd that "oooooh, you shouldn't make any major changes to anything inside the FAF or you will DIE!!!" Whatever.

.

Once you are visual in a slow spam can, you are visual... whether its 200 feet of 1000 feet agl..

 

[bbchien]

Pseudafed (pseudoephedrine, not neosynephrine)!

 

[azure]

This is often called "the hand of God"

Ha! That's exactly what it feels like!

and it's your hands causing control inputs your mind did not command.

Release the yoke when this happens, then put just two fingers on it, no grasping.

It will help.

I'll have to pay more attention next time. I usually fly with only two fingers once I have the airplane trimmed, and have been trying to develop the habit of relaxing them when I fiddle with the radios or the GPS. This usually happens in the bumpy layer about 1000-1500 AGL where I'm too busy trying to keep the wings level to remember to do that. So yep, that makes a lot of sense. Thanks.

 

[azure]

Pseudafed (pseudoephedrine, not neosynephrine)!

?????

 

[dmccormack]

This usually happens in the bumpy layer about 1000-1500 AGL where I'm too busy trying to keep the wings level to remember to do that. So yep, that makes a lot of sense. Thanks.

I didn't make up the "Hand of God" phrase -- read it in Gene Hudson's book ( a good one, BTW)

A good exercise is to take the airplane up on a really bumpy day and fly without the hood for a while and see how long you can fly without control input.

Most (many? some?) pilots immediately pull the dropped wing back up when often the next bump will right the airplane.

The purpose of this exercise is to help you gain confidence in the airplanes' stability in IMC.

 

[azure]

I didn't make up the "Hand of God" phrase -- read it in Gene Hudson's book ( a good one, BTW)

I glanced at the blurb on his site... so why is the light grip "pretty much worthless"?

A good exercise is to take the airplane up on a really bumpy day and fly without the hood for a while and see how long you can fly without control input.

Most (many? some?) pilots immediately pull the dropped wing back up when often the next bump will right the airplane.

The purpose of this exercise is to help you gain confidence in the airplanes' stability in IMC.

It's not so much lack of confidence in the airplane's stability as... well, you're maybe 1000 feet above DH and the needles are getting more and more sensitive, and all of a sudden you have no idea of what your average attitude is because all the gauges are bouncing around every which way. How do you hold heading within 1-2*? My instructor says you just have to do your best to keep the wings level. I don't see how to do that without a firm grasp on the yoke.

 

[gismo]

I glanced at the blurb on his site... so why is the light grip "pretty much worthless"?


It's not so much lack of confidence in the airplane's stability as... well, you're maybe 1000 feet above DH and the needles are getting more and more sensitive, and all of a sudden you have no idea of what your average attitude is because all the gauges are bouncing around every which way. How do you hold heading within 1-2*? My instructor says you just have to do your best to keep the wings level. I don't see how to do that without a firm grasp on the yoke.

The problem is that if you grip the wheel tightly you will apply force whether or not your conscious mind is focused on making attitude adjustments, and if you aren't deliberately making correct (conscious or subconscious) attitude corrections you will be making undesireable attitude changes. You want to force yourself to do two things (and eventually make them subconscious habits).

1) Keep your grip very loose except when making a deliberate correction. IOW, unless you perceive a discrepancy between the aircraft's actual attitude and your intended one, relax the grip. But when you need to change bank or pitch, tighten your hand as necessary to make the correction and then relax the hand again. This is especially important whenever you temporarily shift your focus on something besides attitude such as tuning a radio, checking a chart, or even just talking on the radio.

2) When the aircraft is headed in the correct direction, resist the futile temptation to force the wings to remain perfectly level. All you need is for the wings to remain level on the average and it's physically impossible to prevent some rocking in turbulence. So when a wing drops a little wait a short time to see if it corrects the heading change by itself on the next bump because the chances are much greater that this will happen than the chances that you will manually apply the necessary correction to both disturbances (the first that rolled you away and the next that rolled you back). At the very least you will have half as many corrections to make. Another technique (which I usually attempt to employ) is to make any correction precipitated by turbulence as close to half of what seems necessary. This could be thought of as averaging the effort required to make the correction necessary if there was no opposing turbulence induced roll with that needed if the next bump completely negated the first one. If you can manage this I think you'll find that things smooth out noticeably.

 

[dmccormack]

I glanced at the blurb on his site... so why is the light grip "pretty much worthless"?


It's not so much lack of confidence in the airplane's stability as... well, you're maybe 1000 feet above DH and the needles are getting more and more sensitive, and all of a sudden you have no idea of what your average attitude is because all the gauges are bouncing around every which way. How do you hold heading within 1-2*? My instructor says you just have to do your best to keep the wings level. I don't see how to do that without a firm grasp on the yoke.

It's very hard to distinguish between "light grip" and "tight grip" and "death grip."

Hudson advocates a two finger flying technique (one index on each side of the yoke).

This discipline forces lighter control inputs.

I'll confess I don't always fly that way. But I will ungrip from time to time and do the one or two finger method for a while to force myself to lighten the grip.

This is similar to horse riding, where newbies tend to pull on the horse's mouth (through the reins to the bit). A good rider's inputs are so light that they are invisible.

 

[azure]

Hudson advocates a two finger flying technique (one index on each side of the yoke).

This discipline forces lighter control inputs.

I'll confess I don't always fly that way. But I will ungrip from time to time and do the one or two finger method for a while to force myself to lighten the grip.

I had a chance to practice this today on a short trip, VLL -> FNT -> DET -> VLL. I flew two ILS approaches and one RNAV. On the ILS 9 @ FNT I was somewhat off due to the "Hand of God" problem, but still was able to land from DA. This confirmed to me that it usually happens in bumpy conditions. For the ILS 15 @ DET I resolved to let go of the yoke briefly when I found myself getting bumped around and I did much better. There were fewer bumps this time, but I started to lose the localizer anyway at about 400 AGL but recovered nicely and went visual at DA and landed easily. On the RNAV back into home base, the HoG again forced me to the right, only this time I beat it by letting go and then with two fingers, applying firm pressure to the left and making sure that I had really turned the amount I wanted before relaxing at all. Yes!!

All in all it was an interesting day. There was an airmet for moderate icing so I filed for 3000 to keep us below any forecast clouds, but we ended up in them anyway, my first actuals since starting IR training. (Only for seconds at a time though, so I had to don that darn hood again.) On our FNT -> DET leg departure told us to climb to 5000 and I objected because of concern about icing, and asked for 3. The controller uttered the dread words "unable 3000" and queried some recent arrivals, whereupon finding no reports of even light icing, apparently he worked out a compromise with Detroit Approach to keep us at 4000, which worked out okay.

It made me think a lot about my personal minimums once I'm rated... not sure I would launch at all on my own now, since there could well have been ice in clouds that were at my filed altitude but unforecast, and a denial of lower or higher could leave me stuck with my only out being the "E" word.

 

[EdFred]

?????

I think the doc was viewing by new posts and not by thread, and replied with the correct answer to the wrong question.

Hey, how come you aren't out practicing now? I bet it would be a lot less busy right now.

 

[dmccormack]

I had a chance to practice this today on a short trip, VLL -> FNT -> DET -> VLL. I flew two ILS approaches and one RNAV. On the ILS 9 @ FNT I was somewhat off due to the "Hand of God" problem, but still was able to land from DA. This confirmed to me that it usually happens in bumpy conditions. For the ILS 15 @ DET I resolved to let go of the yoke briefly when I found myself getting bumped around and I did much better. There were fewer bumps this time, but I started to lose the localizer anyway at about 400 AGL but recovered nicely and went visual at DA and landed easily. On the RNAV back into home base, the HoG again forced me to the right, only this time I beat it by letting go and then with two fingers, applying firm pressure to the left and making sure that I had really turned the amount I wanted before relaxing at all. Yes!!

Outstanding!!

As far as personal mins.... that will come with experience (I know, I know )

Your weather sense will also improve with more exposure to IMC, so don't sweat it -- focus on the Instrument PTS and after you pass the checkride spend some more time practicing with a safety pilot or a trusted CFII.

I scared myself a bit my first encounter with Towering CU (was all I could do to keep the blue over the black -- ATC yelled at me for altitude, but I had power to near idle and was still climbing 700 FPM).

I avoided IMC for a while, then finally told a trusted friend who happened to be a CFII. We went flying on a low stratus day and I regained my confidence.

 

[azure]

Outstanding!!

Thanks... my instructor didn't think so. He said, "You did fairly well."

Me: "Yeah, but really, only fairly." I felt my flying left a lot to be desired, especially the last landing.

Him: "No, you flew really well, but you're still getting behind the plane."

He then proceeded to bust my chops for not having FNT Tower dialed in until Approach handed us off to them. The truth is, I got distracted by the bumps that hit us before I'd had a chance to get the airplane trimmed after we were descended while being vectored toward the localizer, and I just forgot to do so. Not a good excuse, I know... in my defense, though, that was the only time this flight that I forgot to set something up well ahead of time. So things are starting to come together a little.

I guess it's a good sign that the standards are getting higher.

I scared myself a bit my first encounter with Towering CU (was all I could do to keep the blue over the black -- ATC yelled at me for altitude, but I had power to near idle and was still climbing 700 FPM).

Yikes! That kind of weather scares me even more than icing. I assume that cloud was embedded? Big CB buildups are common around here during the summer months but VFR, at least I can give them a wide berth, and I do, religiously. I will never forget going up in the pattern at PHN as a solo student just as a dying TS cell brushed by us about 5 miles away. Suddenly I found myself on the widest, most extended downwind I'd ever flown -- almost clear into Canada. It was a wild but fortunately short ride. Never again.

I avoided IMC for a while, then finally told a trusted friend who happened to be a CFII. We went flying on a low stratus day and I regained my confidence.

I think it will probably be "gentleman's IFR" only for me for a long while. I did get a taste yesterday of skimming the tops between layers, and mentioned to my CFII how I couldn't wait to be able to fly in that kind of weather (but only above freezing, of course). I realised later that I had a camera in my car that I could have brought along. It would have been so neat so get some pictures of that.

 

[dmccormack]

I assume that cloud was embedded?

Nope -- I was flying Victor airways to a VOR. In my newbie-ness I plowed right on through the towering CU in order to keep the needles centered.

Now I know to ask for 5 or 10 degree deviation for "buildups" (very common around here, too).

 

[gismo]

Nope -- I was flying Victor airways to a VOR. In my newbie-ness I plowed right on through the towering CU in order to keep the needles centered.

Now I know to ask for 5 or 10 degree deviation for "buildups" (very common around here, too).

It's too bad the IR syllabus doesn't cover much in the way of practical means of dealing with weather. Prior to the IR I was always concerned with staying clear of what I considered to be "weather" and once I was rated I found that I still needed to avoid weather but no longer had the means to do so visually. Another way of putting it is that pre-IR you have to deal with weather from the outside, post IR you must deal with it from the inside.

 

[dmccormack]

It's too bad the IR syllabus doesn't cover much in the way of practical means of dealing with weather. Prior to the IR I was always concerned with staying clear of what I considered to be "weather" and once I was rated I found that I still needed to avoid weather but no longer had the means to do so visually. Another way of putting it is that pre-IR you have to deal with weather from the outside, post IR you must deal with it from the inside.

Very true, and half my IR training time was spent in actual -- it still wasn't enough.

 

[azure]

It's too bad the IR syllabus doesn't cover much in the way of practical means of dealing with weather. Prior to the IR I was always concerned with staying clear of what I considered to be "weather" and once I was rated I found that I still needed to avoid weather but no longer had the means to do so visually. Another way of putting it is that pre-IR you have to deal with weather from the outside, post IR you must deal with it from the inside.

So how do you avoid the stuff you can't see? Other than being aware from forecasts that you might encounter it, and staying VFR or not launching at all?

I can think of two tools that are very useful, but also very limited: XM weather and a stormscope. (Onboard radar is... well, just a dream for most of us.)

 

[ScottM]

So how do you avoid the stuff you can't see? Other than being aware from forecasts that you might encounter it, and staying VFR or not launching at all?

I can think of two tools that are very useful, but also very limited: XM weather and a stormscope. (Onboard radar is... well, just a dream for most of us.)

A couple of ways. First if there is a risk of flying through embedded thunderstorms, stay on the ground. Or one can find where the tops are and see if they can get up to do some see and avoid. Third, storm scope, XM radar, help a lot. 4th having actual radar on board.

 

[dmccormack]

Liz -- anyone daring to fly in IMC with embedded CB should have those two tools at a minimum. Quite frankly I'll fly on top or underneath if I don't have them both.

XM provides a ready view of the unfolding situation, and the stormscope can confirm or deny where electrical discharges are in relation the the airplane. Together you can be in IMC and know where not to go.

I supplement those two on board tools with queries to ATC. During bad weather days they are always helpful.

 

[gismo]

Liz -- anyone daring to fly in IMC with embedded CB should have those two tools at a minimum. Quite frankly I'll fly on top or underneath if I don't have them both.

XM provides a ready view of the unfolding situation, and the stormscope can confirm or deny where electrical discharges are in relation the the airplane. Together you can be in IMC and know where not to go.

I supplement those two on board tools with queries to ATC. During bad weather days they are always helpful.

Exactly. Onboard Radar is more useful tactically, i.e. working your way through an area of not so widely scattered embedded TRW or finding your way through a line. The combination of a SS, XM, and ATC is IMO quite sufficient to avoid the unexpected or widely scattered TRW in IMC. It's also often the case that you can remain visual enough to avoid the cells as long as ATC and the nearby SUA gives enough wiggle room and you're flying with an IFR GPS (this is one of the often untouted advantages of IFR enroute GPS capability) so you aren't stuck on airways that haven't managed to avoid the nasty weather themselves. Even in the clouds you can see the difference between a benign light grey type and the nastier black and green ones, you just can't see them from far enough away to avoid the need to make a hasty 180 retreat at times.

One time when I was flying along in and out of clouds near Chicago with no onboard wx equipment beyond my eyes and the comm radio (ATC) I was given a vector that was about 90 degrees from my direct path and I asked ATC why the big detour. He came back with, "You see a big dark cloud off your left wing? I can turn you into that if you want but everyone else has been going around it." Sure enough it looked a lot worse in that direction and I happily continued along my current heading where the clouds were mostly scattered and definitely of a more pleasant shade of grey.

 

[Ted]

So how do you avoid the stuff you can't see? Other than being aware from forecasts that you might encounter it, and staying VFR or not launching at all?

I can think of two tools that are very useful, but also very limited: XM weather and a stormscope. (Onboard radar is... well, just a dream for most of us.)

You've got a good sum of it right there. Look at the forecasts (and there's a lot that goes with that). If you can, stay in VMC (even if flying on an IFR flight plan). Remember that there's a lot of IFR flight that is done in VMC.

I have XM weather and on-board radar. I plan on adding a stormscope at some point. Remember the limitations of any device you use. XM is nice, but it has a delay. It gives you a good idea of where the developed thunderstorms are, but not necessarily where they will be. On-board radar gives you a good idea of where thunderstorms are right in front of you (including developing ones), but it has a limited field of view, and thunderstorms or weather ahead of you can sometimes hide other weather behind it. The best thing you can do is get some experience by flying with someone who knows the tools and how to use them, and has experience tangling with bad weather. Remember that no two weather days are alike, but you can start to get a good idea of what you need to do to stay safe.

I've tangled with thunderstorms using those tools, including embedded thunderstorms, but wouldn't recommend it for anyone who's new without sufficient training.