Insect debris on leading edge
Insect debris on leading edge
Pre-flighting I noticed a moderate splattering of dead insects on the leading edge. I wiped with a cleanish rag as much for aesthetics as anything else. But I am wondering how significant insect debris has to be before it impacts performance. I suppose a decent sized bug could in theory block the pitot, I have heard of wasps building mud nests in pitot tubes, but never thought about an in-flight 'dudu-strike'! Is this a realistic concern?
Thanks
Thanks
On high performance gliders with natural laminar flow wings it can be a significant issue, and there are in-flight "bug scraper" systems which have been devised to deal with it (eg this one from DG Flugzeubau).
PDR
PDR
Had an airspeed failure recently not long after takeoff. I tried pitot heat but no change. Afterwards the engineer removed the head of the pitot and we found a (quite small) (and quite singed) bug that had gone straight into the pitot tube.
Pretty much unheard of (hasn't happened to me in several thousand hours), but on an average light GA aeroplane the difference between clean and shiny, and covered in dead bugs, is worth five knots or so of cruise speed.
But, Jonkster clearly proves it's possible.
G
But, Jonkster clearly proves it's possible.
G
Gnome de PPRuNe
Join Date: Jan 2002
Location: Too close to Croydon for comfort
Age: 60
Posts: 12,618
Received 293 Likes
on
161 Posts
It was a major concern for the Voyager team for the round the world flight in 1986, with potential implications for absolute range, so the aerodynamicist, John Roncz, came up with a wing section that minimised bug contamination. I believe very few were found on the leading edges after the flight.
A pal of mine, who has a concours Porsche 911, uses a sponge covered in "netting" which is/was available from Halfords for bug removal. I've used one and it doesn't scratch the wing leading edge if it is used wet. Quite cheap at around £1.50. Best used before the bugs harden.
Join Date: Mar 2019
Location: French Alps
Posts: 326
Likes: 0
Received 0 Likes
on
0 Posts
Insect are usually encountered at low altitude. No problem when flying high.
Bugs slightly impair cruise speed on a standard GA airfoil, but are definitely a problem with 'laminar' airfoil on gliders, as mentioned by PDR1.
Twice had 'pitot anomaly' occurrences on a light airplane. No problem returning to base with engine parameters and attitude to assess correct AoA on approach. Pretty standard PPL exercice in my country.
Bugs slightly impair cruise speed on a standard GA airfoil, but are definitely a problem with 'laminar' airfoil on gliders, as mentioned by PDR1.
Twice had 'pitot anomaly' occurrences on a light airplane. No problem returning to base with engine parameters and attitude to assess correct AoA on approach. Pretty standard PPL exercice in my country.
Join Date: Sep 2002
Location: Australia
Posts: 1,082
Likes: 0
Received 0 Likes
on
0 Posts
Some aircraft have a warning in the flight manual regarding loss of performance due accumulation of bug debris on the leading edge.
They can also choke up oil coolers.
Yes, a bug, more often larvae can block a pitot head.
Also, less apparent, can block fuel tank breathers. Only warning often suction when removing a fuel cap.
They can also choke up oil coolers.
Yes, a bug, more often larvae can block a pitot head.
Also, less apparent, can block fuel tank breathers. Only warning often suction when removing a fuel cap.
Moderator
It is common for bugs to nest in small orifices. Pitot tubes make a favourite place. Happily, Cessna type static ports seem too small for them to bother. I've had a number of blocked pitot tubes due to nesting bugs - and this includes a number of occasions where the plane had been parked with a pitot cover for only two days since the last flight. So I got a better pitot cover! They've also nested in my fuel tank vents, once resulting in collapsing the side of my wing tip float aux tank when I pumped it into the main tank. Happily, it popped back, with only a minor wrinkle. I then drilled tiny holes around the periphery of each fuel tank vent tube (1/4" or 3/8" diameter), and threaded fine lock wire to form an X across the end of the vent tube - that was effective.
Generally, for GA planes, unless it's stated in the flight manual, the performance loss from hitting a swarm of bugs in flight will not create an unsafe situation for the plane, though yes, it may create a loss of a couple of knots in cruise speed. It is a good wash and wax before a multi hour cross country flight. Here, in Ontario, we do get clouds of bugs up to a few hundred feet. I was once landing on the lake, and hit such a cloud. It was so dense, that my windshield bugged over. I was just able to see enough to complete the landing, and I had to shut down, and clean the windshield, and as much wing as I could reach, to continue my flight.
A smear of bugs on the leading edge is ugly, but of a lesser concern than the top of the wing being contaminated. Frost or other sticking snow/ice on airfoils is taken very seriously in Canada. The rules are specific - none permitted for takeoff. A layer of thick frost can make a wing nearly useless, increasing stall speed by many knots (like 20 in some cases). A number of careless pilots in Canada have gone off the end of a runway, attempting to take off when the plane refused to fly due to frost or snow. A few made it into the air, to then stall. A clean wing is a good idea, and a legal requirement in Canada. The inspector won't stop you for some bugs, or chipped paint, but will for frost/snow/ice.
Generally, for GA planes, unless it's stated in the flight manual, the performance loss from hitting a swarm of bugs in flight will not create an unsafe situation for the plane, though yes, it may create a loss of a couple of knots in cruise speed. It is a good wash and wax before a multi hour cross country flight. Here, in Ontario, we do get clouds of bugs up to a few hundred feet. I was once landing on the lake, and hit such a cloud. It was so dense, that my windshield bugged over. I was just able to see enough to complete the landing, and I had to shut down, and clean the windshield, and as much wing as I could reach, to continue my flight.
A smear of bugs on the leading edge is ugly, but of a lesser concern than the top of the wing being contaminated. Frost or other sticking snow/ice on airfoils is taken very seriously in Canada. The rules are specific - none permitted for takeoff. A layer of thick frost can make a wing nearly useless, increasing stall speed by many knots (like 20 in some cases). A number of careless pilots in Canada have gone off the end of a runway, attempting to take off when the plane refused to fly due to frost or snow. A few made it into the air, to then stall. A clean wing is a good idea, and a legal requirement in Canada. The inspector won't stop you for some bugs, or chipped paint, but will for frost/snow/ice.
I spend a lot of time at low altitudes, towing gliders and in the summer time, this means a lot of cleaning of the leading edges of the prop blades and the wings. Probably not much impact in performance on a draggy power plane, but significant on gliders, as PDR1 mentioned. I remember reading about flight testing, where small squares of masking tape were stuck onto glider leading edges and the polar measured. Degradation was of the order of 10%.
I've had an ASI failure due to a mudwasp nest in a Cessna pitot tube. A tow pilot in my club had an instantaneous ASI failure due to a well-aimed bee strike!
I've had an ASI failure due to a mudwasp nest in a Cessna pitot tube. A tow pilot in my club had an instantaneous ASI failure due to a well-aimed bee strike!
Join Date: Jun 2007
Location: Milano, Italy
Posts: 135
Likes: 0
Received 0 Likes
on
0 Posts
The worst bugs for reducing performance occur on the backs of the propeller. Flying a tug aircraft usually gets a prop very dirty.
bug removal sprays are very effective but expensive. I use a dilute mix of bicarbonate of soda in water with a couple of drops of washing up liquid.Spray on to the propeller, wait a minute and wipe clean.
bug removal sprays are very effective but expensive. I use a dilute mix of bicarbonate of soda in water with a couple of drops of washing up liquid.Spray on to the propeller, wait a minute and wipe clean.
Join Date: Sep 2002
Location: Australia
Posts: 1,082
Likes: 0
Received 0 Likes
on
0 Posts
I shall attempt to remain polite.
During engine run up, one exercises the propeller pitch lever.
The funny noise you hear as the lever is moved rearwards?
Is the propeller cavitating.
Join Date: Nov 2016
Location: 57 North
Posts: 78
Likes: 0
Received 0 Likes
on
0 Posts
I believe vihai is correct in asserting that cavitation only occurs in liquids, specifically incompressible liquids, like water, so cavitation is a factor with marine propellers but not aircraft propellers.
As with any propeller there are pressure differences around a propeller in water. AIUI when the local pressure drops significantly the water changes state explosively (implosively?) with a release of energy creating micro cavities in the liquid. When the pressure relaxes the water changes state again back to liquid equally implosively. That energy release causes erosion to the propeller, but the cavitation happens in the liquid. Erosion of the propeller is not the cavitation, it's the result of cavitation.
Join Date: Sep 2002
Location: Australia
Posts: 1,082
Likes: 0
Received 0 Likes
on
0 Posts
No.
I believe vihai is correct in asserting that cavitation only occurs in liquids, specifically incompressible liquids, like water, so cavitation is a factor with marine propellers but not aircraft propellers.
As with any propeller there are pressure differences around a propeller in water. AIUI when the local pressure drops significantly the water changes state explosively (implosively?) with a release of energy creating micro cavities in the liquid. When the pressure relaxes the water changes state again back to liquid equally implosively. That energy release causes erosion to the propeller, but the cavitation happens in the liquid. Erosion of the propeller is not the cavitation, it's the result of cavitation.
I believe vihai is correct in asserting that cavitation only occurs in liquids, specifically incompressible liquids, like water, so cavitation is a factor with marine propellers but not aircraft propellers.
As with any propeller there are pressure differences around a propeller in water. AIUI when the local pressure drops significantly the water changes state explosively (implosively?) with a release of energy creating micro cavities in the liquid. When the pressure relaxes the water changes state again back to liquid equally implosively. That energy release causes erosion to the propeller, but the cavitation happens in the liquid. Erosion of the propeller is not the cavitation, it's the result of cavitation.
If not, it is the equation that explains lift, of both wings and propeller blades.
One of the factors of this equation is fluid density.
Because under about 260 kts, "air behaves no differently from water and is considered an incompressible fluid."(Modern Airmanship, Van Sickle)
The funny noise you hear as the lever is moved rearwards? Is the propeller cavitating?
The noise is probaly the air stalling around the blades. Some people call that cavitating but it's not.
But how really solid is "solid" ?
In atomic terms everything is mostly space with just a few electrons whizzing round a tiny Nucleus like a miniature Solar System.
It all depends on where the observer places himself.
In atomic terms everything is mostly space with just a few electrons whizzing round a tiny Nucleus like a miniature Solar System.
It all depends on where the observer places himself.
Cavitation is something that only occurs in liquids. While air and water are both fluids they do not behave identically in this respect. This can be easily seen by placing air into a cylinder with a close-fiting piston and then pulling the piston. The air inside the cylinder will drop in pressure and increase in volume. If you try the same thing with water you'll find that you can't actually pull the piston out AT ALL until you've applied enough force to overcome the surrounding air pressure. When you get to that point the piston pulls away from the water and leaves a vacuum* in the space - the water does NOT expand to fill the extra volume.
Air and water are both incompressible (Bernoulli), but air is elastic while water is not. Try filling a gass strut with water and you'll soon see the difference. That's also why Hydraulics are inherently safer than pneamatics. In high pressure pneumatic systems a heck of a lot of energy is stored in the pressurised gas, energy which leaps out and hurts people if there's a leak. But the fluid in a hydraulic system has NO stored energy, so a leak just goes "phut", dumpingt the overpressure with no great amount of movement.
PDR
* into which the water may boil, but only in certain ranges of temperature and pressure