Naturally Aspirated GA Airplanes -- High or Low?

This is the place where we can all meet and speak about whatever is on the mind.

High or Low?

High. I like to play jet in my lawnmower.
7
21%
Low. I like to cut grass and smash bugs.
27
79%
 
Total votes: 34

Hook
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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by Hook »

Anyway, don't take my word for any of this. Go find some freezing rain and see for yourself.

Take notes, describe exactly what happened, then describe exactly what you expected to happen. There may be a way to fine tune the icing experience.

Hook

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AKar
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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by AKar »

Hook wrote:What we need to be able to model it is descriptions from GA pilots who have experienced icing to any degree while actually flying the aircraft.
I can ask specifically certain "Cargo CAVOK" old schoolers who used to fly professionally various things that would be considered GA airplanes, but from earlier discussions I've had about this issue, the most common statement is that slight to perhaps light-moderate icing one picks on the leading edges when penetrating some cloud or similar is not really noticeable at all at cruise/approach speeds, perhaps a knot or few lost to the drag. Obviously, they know to keep up some speed margin as it may very well become suddenly very noticeable at higher angles of attack. Also, note that you do not want to pick any significant icing on your propeller, so at least that should be ice-protected if fooling around any longer!

Mostly glider pilots who fly wing profiles that are sometimes notoriously sensitive to contaminants do note that the gliding performance is significantly affected as the laminar flow is disturbed and drag noticeably increased. Obviously, a glider is rather sensitive to any issues decreasing performance in the first place, and therefore it is easily noticeable.

I don't remember any personal accounts of severe icing encounters in small airplanes but could ask a guy or two who maybe have some experience. Though I'd consider them smart enough to mostly stay out of that kind of stuff, or steer out if encountered. Anyways, the results of letting things get worse are deducible from aerodynamic studies - or accident reports. How soon and what kind of performance effects first become noticeable certainly varies a lot from airplane to airplane and would depend on conditions. Flying is seldom sterile enough for subtle clues of trouble to be clearly noticeable.
Hook wrote:If you don't see actual ice, for example at night, how do you know you're getting airframe icing?
This, indeed, is a serious and somewhat grim consideration: you don't necessarily do at all when it still remains at mostly harmless level. That's why visual icing indicators are used in airplanes certified for flight in known icing conditions. Also, various common wisdom exists in different airplane models on where to look for the first traces of ice. Perhaps the most well-known for general audience is the one in DC-9/MD-80 series...
Hook wrote:There is something about FSX that you can get ice when you are not expecting it, and you might not get it when you are expecting it. Icing from clouds builds up slowly and you might never notice it before it dissipates. You might not even notice in freezing rain if you fly through it quickly. Unless you are watching the actual variable used by the sim to calculate ice effects, it is going to seem very random.
I have to test that some time for correlation with conditions where it should happen.
Hook wrote:Up to about 5% ice is difficult to detect. You notice somewhere between 5% and 10% and at 10% it is obvious. By 15% you know you are in trouble.
Of course, without a key a percent gauge is fairly meaningless as the effects of icing in reality are very non-linear. As an example, consider an airliner for a moment. Usually, most of the leading edges are not ice-protected. Only the ones that are most prone to pick ice and where its effects are relatively critical, do get ice protection. Often this is limited to as little as a few slat panels per wing. A relatively little amount of ice can perhaps, I suppose, have noticeable effects if ice protection is kept off. That's why those few selected areas are probably ice-protected. However, a greater residual amount of ice can be carried by the airplane even if the ice protection is on, with probably much lesser consequences in terms of airplane's performance. How would that translate into a linear %-scale? That's just one kind of problem one would end up trying to simulate it properly.
Hook wrote:[...] and I didn't have a chance to test if my flaps could freeze in a down position which makes attempting a landing in freezing rain interesting as this can happen in real life [...]
For this reason, in airplanes that have slotted flaps in particular it is a SOP item to stay from extending the flaps until necessary if in icing conditions. Further, one should leave the flaps extended after the landing to avoid damaging them by ice stuck in between the structure. Around here it is fairly common to have airliners taxiing in while keeping their flaps extended all the way to the spot - to much annoyance to the tankers, obviously.
Hook wrote:If you want to see what ice is really like, go find some freezing rain. You might get some in clouds, but you may not be able to tell before it dissipates. You will know for sure after a few minutes in freezing rain.
In my opinion, the issue should not be that much the simulation of extreme phenomena, but to properly simulate kind of conditions that tend to affect every day operations. Getting ice in proper amounts in right circumstances, and having proper consequences - and lack thereof where appropriate. Including some effects that may not be easily noticeable at all until reaching high CL, for instance during landing flare.

-Esa

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Oracle427
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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by Oracle427 »

Most of the "old timers" I have spoken to say that bad icing can take less than a minute to get very dangerous. You can get buildups measures several inches within a minute if you do not take prompt action to get out of the conditions. It all depends on the conditions you find yourself in.

I have had trace icing in cruise while going through the tops of clouds at around 0C. The ice looked like small spots probably smaller than 1mm all over the leading edges of the struts and wings and remained on the airframe for over an hour until descending to warmer conditions below. The ice accumulated in under 5 seconds of passing through the top of a cloud and exiting the other side. It was not accumulating because I wasn't continuously flying through a layer of clouds.
Flight Simmer since 1983. PP ASEL IR Tailwheel
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ClipperLuna
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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by ClipperLuna »

Regards the OP, for me it depends on terrain. If I can keep several thousand feet below me and the ground without going higher, I'll fly at either 8,500 (heading west) or 9,500 (east). This way I can cruise WOT with the engine still making a healthy amount of power. However, if there's going to be mountains under me I'll go 11,500 heading east and either 10,500 or 12,500 west. For the Spokane to Kalispell run (I've done this one a few times, it's one of my favourite flights in my greater local area), I fly in a straight line between KSFF and KGPI at either 12,500 or 10,500. My reason for wanting to keep some distance between me and the ground has to do with the engine--if it quits, I want some time to try and troubleshoot it and pick a forced landing area.

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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by Hook »

I have no interest in airliners, only GA planes. The larger guys usually have some kind of anti-icing protection. The stuff I fly does not, unless I "install" it myself, which I did on the Goose after nearly losing it that one time.

When I was doing a lot of sailplane simming and studying real world stuff, I remember reading that some sailplanes had problems with simple rain. Not surprising and you probably wouldn't want to fly in that anyway. The places I flew sailplanes and the times of year generally precluded icing. If you're doing wave soaring going for altitude records, then you might have a problem. I didn't try that as wave action wasn't modeled in CumulusX.

During any kind of normal flight you aren't likely to notice ice. The reason to look for freezing rain is so that you can see the effect quickly and dramatically. It won't be the "less than a minute" but you should notice effects fairly quickly.

The variable used to accumulate ice effects is not intended to be human readable. It is an abstract number. But two different aircraft will probably get similar effects at similar percentages. This is why I originally posted a formula to translate the ice percentage into effective weight gain. Unless you have a gauge to display it, you won't know what it is anyway.

I don't want deductions, I want first person descriptions. Otherwise I'd be working from whatever preconceived notions I had at the time. And I still need need to know the symptoms that tell you that you are getting ice if you can't check visually.
The ice looked like small spots probably smaller than 1mm all over the leading edges of the struts and wings and remained on the airframe for over an hour until descending to warmer conditions below.
Thanks. This will be useful if I ever get around to finding a way to display actual ice on the wings. I believe this may be possible as of Prepar3D 4.4 if you can display a 2D gauge in the 3D cockpit. Vehicle Simulator panel functions allowed you to add 3D objects to the model which was very useful for the ships I was sailing at the time.

Generally ice will slowly dissipate when you leave the conditions that cause it. I don't remember having it hang around simply because the temperature was still below 0 C, but has been a while since I did much serious ice research so I might be wrong. If there is anything wrong with the FSX icing model it is this.

Hook

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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by Hook »

I fly in a straight line between KSFF and KGPI at either 12,500 or 10,500. My reason for wanting to keep some distance between me and the ground has to do with the engine--if it quits, I want some time to try and troubleshoot it and pick a forced landing area.
What he said! :D

I checked out that route on Skyvector and decided it would depend mostly on what plane I was flying at the time. The A2A Cub I'd fly down highway 90 to Missoula and up 93 to the destination. The Stearman I may do the same (it has no IFR instruments but I can fly needle-ball-and-airspeed if I have to) or I may fly direct using dead reckoning at an altitude of at least 8000 feet and maybe 10 degrees south of the direct line so I hit the lake in case my calculations are off. For the A2A Cherokee and others with VOR I'd fly direct. The problem with that route is that you have to fly at 8000 feet or higher to avoid terrain, and especially this time of year you'll be dodging clouds. I don't assume I have oxygen. Following the roads I can go as low as I want to get under clouds or attempt to climb above them if necessary. Everything else depends on the weather, and I don't care about wind speed or direction for a flight like that except as it affects my dead reckoning. All my recent flights I've had to eyeball and estimate wind as I haven't been able to fly my original planned altitude anyway.

Hook

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AKar
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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by AKar »

Hook wrote:When I was doing a lot of sailplane simming and studying real world stuff, I remember reading that some sailplanes had problems with simple rain. Not surprising and you probably wouldn't want to fly in that anyway. The places I flew sailplanes and the times of year generally precluded icing. If you're doing wave soaring going for altitude records, then you might have a problem. I didn't try that as wave action wasn't modeled in CumulusX.
Sailplanes approach L/D ratios of around 50 these days even with rather modest spans of 15 and 18 meter classes. Open class gliders regularly glide 60 meters for each lost in altitude. In competitive gliding, it is actually a significant advantage to have a profile that is not overly sensitive to contamination. In real life conditions, this can be more important than absolute performance. Some otherwise competitive glider types have been let down by their sensitivity to wing contamination. Rain, yes...that's a problem, not so only because of aerodynamics but perhaps more because the air itself sinks in rain together with the water coming down. So does your frame of reference, in a glider. If we speak of a sensitive profile, bugs and dust are where the problem already becomes noticeable.

Icing becomes a factor in gliding when thermals are followed into the clouds (depending on local rules, this can be legal - with compass, airspeed indicator, altimeter, variometer and turn coordinator only, I remind...). Zero levels are surprisingly low in the early summer (the best gliding season!); if you are inside a Cu, you will eventually get some good amounts of ice in good lifts.

At very high altitudes, as in wave gliding, the icing is not that often a problem unless you push into the clouds there as well. Generally the cold air up there is too cold and dry for any significant icing.
Hook wrote:During any kind of normal flight you aren't likely to notice ice. The reason to look for freezing rain is so that you can see the effect quickly and dramatically. It won't be the "less than a minute" but you should notice effects fairly quickly.
During any kind of normal flight in winter conditions, you ought to notice icing in certain telltale circumstances. It should not need to be freezing rain that is the only hazard - that phenomenon gets international airports stuck (though for the biggest part due to issues on ground, not in the air). Icing hazards coming with reasonably planned GA flights are what I'm missing.
Hook wrote:I don't want deductions, I want first person descriptions. Otherwise I'd be working from whatever preconceived notions I had at the time. And I still need need to know the symptoms that tell you that you are getting ice if you can't check visually.
Deduction will be only thing we will ever have. This is the first rule of any simulation. :) First person observations will always remain a scatter plot all over the place, except in the most definable of circumstances. This is why they still hire test pilots to fly controlled and instrumented test programmes, instead of relying on the reporting system built into the industry, however magnificent on its own.

-Esa

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AKar
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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by AKar »

ClipperLuna wrote:Regards the OP, for me it depends on terrain. If I can keep several thousand feet below me and the ground without going higher, I'll fly at either 8,500 (heading west) or 9,500 (east). This way I can cruise WOT with the engine still making a healthy amount of power. However, if there's going to be mountains under me I'll go 11,500 heading east and either 10,500 or 12,500 west. For the Spokane to Kalispell run (I've done this one a few times, it's one of my favourite flights in my greater local area), I fly in a straight line between KSFF and KGPI at either 12,500 or 10,500. My reason for wanting to keep some distance between me and the ground has to do with the engine--if it quits, I want some time to try and troubleshoot it and pick a forced landing area.
Thank you! Any pics to share, either in sim or RL? :) One of my favorite short hops in the sim, I wonder how it looks in the real if you're locals.

-Esa

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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by Hook »

It is beginning to appear that your only real problem is that you can't predict when icing will occur. Welcome to real life. Go complain to Active Sky or whatever weather program you are using. The reason to seek out freezing rain is that it is a known source of severe ice. But if you're not going to do it, then you're not going to do it, which is fine. I was hoping to get your input on a possible enhancement.

At this point I suspect that icing is working exactly as intended and is good enough within the limits of the sim and there is no problem to address.

There seems to be a Murphy's Law going on here. I need some clouds at freezing temperatures to run a short test and even though the temperature on the ground is -12 C there is an inversion covering much of of Sweden and it is about +3 C up around 3000 feet where the clouds are. Go figure. Maybe on the next leg of the flight.

Another Murphy's Law seems to be that there will always be clouds at the altitude you planned to fly... unless you are looking for clouds to fly in.

Weather was absolute crud on the flight just before I discovered I need to do that test, but has been clear ever since. I've been saying for years that the random number generator is perverse and hates you. This might be why you aren't getting the results you expect. While it would be easy enough to use some historical weather that matched my needs, I only want a little of the bad weather, not another entire flight of it, and if I'm going to be flying I'd rather it be on the flight I've planned. I keep expecting some clouds that would produce ice, but not finding them. I should probably be careful what I wish for.

Hook

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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by BrianW »

I usually plan and fly the route in the sim the same as I would in RL. For me it depends on route length, airspace, terrain, and winds generally in that order. The deal altitude for most of the stuff I fly is between 5000’ to 6500’ MSL and I like to be above 3000’ AGL whenever I can.

My most commonly flown mountainous route in RL is between SEA and ELN. When flying VFR eastbound I’ll usually fly at 9500’, and westbound I use 8500’ or 10500’ depending on the chances for mountain turbulence. I got caught in a rotor wave once which was a wakeup call, so I like extra altitude when crossing mountains from the leeward side.


As for the Icing discussion, In RL I’ve had light rime a couple times when flying right around the freezing level. In all my cases the clouds were scattered and we had plenty of room to descend into air that was above freezing. The ice shed or sublimated pretty quickly once out of the cloud.

None of the current single engine A2A fleet are certified for known icing, so you should do your best to avoid it. This might mean staying out of the clouds or precipitation near freezing temps. As for freezing rain, it’s bad for all aircraft even the big ones because it can produce runback icing which even anti-ice can’t clear. Freezing rain usually grounds all aircraft when it happens at the surface.

I personally don’t think the default icing is simulated very well in the sim. I’ve never noticed any change to the stall AoA during any of my tests, which as Akar pointed out is the real danger.


The FAA has a pretty good video about it:

https://youtu.be/NBX84bF2d4U

Hook
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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by Hook »

Thank you BrianW, the video was helpful. It included exactly what I was looking for: a description.

So what were the symptoms?

Flying in a nose up attitude. Check.
Decrease in air speed. Check.
Buffeting. None. Talk to A2A; they're the ones who model stall buffet in AccuSim and AccuFeel. This is not part of FSX.
A sudden stall at something above expected stall speeds. Not modeled. May be possible with AccuSim and AccuFeel.
Tailplane stall. Not modeled in FSX.

Based on that video, FSX does not accumulate ice as fast as in real life. This is probably appropriate for the kind of flight sim that FSX is, where it has to be a good experience for the beginner as well as the expert. If someone strongly feels this needs to be addressed, ask A2A to add it to AccuSim and AccuFeel.

The initial description of icing in the video was exactly what I experienced the first time I encountered freezing rain the the Goose. While I had an ice gauge, I didn't keep it visible so I wasn't monitoring it. I was flying on autopilot. After a while I noticed my airspeed decreasing and I was flying in a more nose up attitude. When I turned on the ice gauge I noticed it was increasing rapidly, especially since it displayed in pounds rather than percent at the time. I think at the time 100% would have displayed 8000 pounds. I knew it wasn't adding weight but it was an easy way to visualize the effect.

I did not have an outside air temperature gauge at the time. At first I tried climbing to get out of the ice but it was higher than I wanted to go. I tried descending but it didn't help. When I tried climbing again I soon discovered that I couldn't even get to my original altitude. I descended to almost ground level (about 50 feet AGL) and was still accumulating ice. I climbed a bit and turned toward an airport I'd recently passed and tried to keep the plane flying. By the time I landed I could barely keep the aircraft above stall speed. It was only on the ground that ice accumulation stopped, and it took 2.5 hours (in time compression) for the ice to completely disappear.

Gone unnoticed at first. Check.
Not concerned about it when it was first noticed. Check.

Before that flight I was not worried about flying in icing conditions. The symptoms were mild and usually fairly short lived. After that flight I was a lot more careful about ice, even after adding deicing boots to the Goose. Now, with an OAT gauge and no deicing equipment, I avoid icing conditions completely unless I am running a test and actually want to fly in ice. To this extent FSX icing did exactly what it was intended to do: teach you to avoid icing conditions.

If you have never experienced freezing rain in FSX you are like I was before that Goose flight: not particularly worried about ice. If you think icing in FSX is unimportant then you haven't actually experienced it.

If you want the severity of ice increased, or the stall speed changes modeled, talk to A2A and see if they think it is worth adding to "the bucket", which is how they describe whether or not to add some new feature. The bucket only holds so much, and to add more to it something else would have to be removed.

Hook

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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by Hook »

On the next flight I was able to do my test 35 minutes in, then flew in and out of clouds and freezing rain for the next three hours. Ice got up to 26% at one point. The 15% point didn't seem near as bad going down as it did when going up. :) At 26% the plane flew about like I had added an extra 1/4 of the aircraft weight. No stall buffet and I was watching for it as I don't know if AccuFeel already models the stall speed differences from icing for their buffeting.

I saw fairly fast ice accumulation in a cloud without rain, something I hadn't seen before. Also I got ice while parked on the apron in rain, something I wasn't sure was possible. At one point I saw ice accumulating when I wasn't in clouds or rain. This doesn't happen often, but it does happen.

A lot of variables go into icing so it won't be possible to predict every time it could happen.

I suspect if we increased the severity of the ice to more closely match descriptions from the real world it would make a lot of areas totally unflyable, not something I'd prefer to do in my flight sim.

Hook

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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by ClipperLuna »

AKar wrote:Thank you! Any pics to share, either in sim or RL? :) One of my favorite short hops in the sim, I wonder how it looks in the real if you're locals.

-Esa
I took this on the Bald Mountain fire lookout a few years back. It's about 60 miles to the south of the line between Spokane and Glacier Park International, but the topography is similar. Gives you an idea of what it looks like RL.

Image

Also, and I can't get a link to work for this one, but someone posted a 360 image to Google street view on top of Scotchman Peak, just east of Lake Pend Oreille. It's closer to the actual place.

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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by AKar »

Thanks, at least summer representation of the scenery looks very decent in the sim. What I absolutely love to do when I've got some good time to allocate into a flight sim session is to take the flight in the sim, record it, and then review it in Google Earth, checking any Street Views or 360° images while finding out about interesting places. :)

-Esa

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Re: Naturally Aspirated GA Airplanes -- High or Low?

Post by Hook »

One of my favorite places for scenery is the long east-west valley between two ridges northwest of Mena, Arkansas. When the weather is right in the sim it looks just like the pics of the real area. It is a decent area for ridge soaring when the wind is right.

My last flight had fairly typical altitude limits for this time of year. I was flying from Norway to Longyear, ENHV to ENSB. Temp was -5 to -10 C over the water, cloud bases were 2000 to 4000 feet. I couldn't fly in the clouds because of icing and couldn't fly over them because of headwinds. The first hour of the flight included precipitation and the reports were of snow. I flew at about 3000 feet for most of the flight.

I figured I could avoid icing, but at one point I was flying in obvious snow, the gauge said snow, but I was getting ice. Mixed with freezing rain? I don't know. Shortly after that I encountered freezing rain, but ice never got bad enough to turn back as it was intermittent and I knew I'd be out of it shortly. It did cause some concern as the destination and travel time were right at the calculated maximums for the aircraft with no fuel reserve and the ice accumulation slowed me down. I shut down with 2.67 gallons of fuel remaining, enough for 8 minutes of flight at cruise speed after spending the last part of the flight on a more economical power setting.

Hook

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