@Peter ‘s problem of initially not wanting to use the engine to get out of his parking spot makes me wonder how big of a problem stones striking the prop really and, and under what circumstances. In mountain flying, you have stones on the altisurfaces most of the times, and sometimes you need almost full power to taxi up the landing strip after touching down. But you don’t really see a lot of issues with stones striking the prop in a Jodel D140 for example. I suppose that the high ground clearance of the prop helps to avoid this kind of issue:
I reckon that for a stone to be sucked into the prop, you would have to have a plane that sits sufficiently low, you need stones that sit in front of it (and not just directly underneath), and they need to be small enough to be able to be picked up.
On our airfield, there is a spot for doing the runups that has some grass with a few stones underneath, and even though it makes me feel uncomfortable to do the runup there and I try to position the plane as best as I can to avoid the stones, I have never seen anything happening to the props there. I wonder who has seen dented props and if you could trace this to a certain set of circumstances, and in which type of plane you have had this?
My old CH701 oinly had about 10" of prop clearance, but the nose wheel was a prime culprit by picking up mud and stones and slinging them at the prop when taxiing at low revs. I always had Krepairs to do after landing on one local muddy gravel bar. In the absence of mud, small stones can get stuck in the tread of a ribbed tyre and then flick into the prop, which is why bushwheels have no tread grooves.
My Maule has 28" of prop clearance, so even lofting the tail with power against brakes doesn’t seem to suck stones into the MT prop. However, it can blast quite large gravel at the tail, causing some fabric damage. But lifting the tail is a useful technique and one can’t make an omelette without breaking eggs…
Other than that, I’ve done hundreds of landings with nose-dragger Cessnas on gravel runways. I always do power checks on the move, and never more than the odd nick in an aluminium prop.
The runways at Andreas are in terrible condition (covered in stones, small to large). We don’t have any stone damage problems with our prop, I don’t think we have quite as much clearance as Jacko’s Maule but we’ve got a reasonable amount. There’s a Cherokee 180, a Robin and a C42 which get flown frequently from Andreas, and they haven’t complained about stone damage. The stone damage seemed to be more of an issue for aircraft with wheel fairings.
I would agree there is not a direct obvious 100% correlation between departing from somewhere with stones, and getting nicks in the prop.
But I certainly noticed it happening more at some places. For example at Elstree (where I flew out of a lot c. 2008, doing my FAA CPL) the start of the runway was covered in stones and I got a load of nicks in the prop. I also got a big one departing from Spanhoe which was covered in massive rocks (I kicked away the ones in front of the prop, as far as I could).
For sure, one needs to keep moving, but sometimes one is bogged down in grass (like e.g. last weekend at Friedrichshafen) and needs pretty well full power to get out, and then you just need to make sure there are no stones in front of the prop. The alternative is to get a fire truck along and a rope to go around the main gear (Southend, c. 2007, in front of the long-defunct WillowAir).
The problem is that if you get a large nick, say 10mm, this cannot be filed out and the prop may well be scrapped because if one blade is below overhaul limits then all the others are also, and with some types (e.g. my Hartzell 3B one) there is an outrageous “airworthiness” con that if you need to replace 2 or more blades, the hub has to be replaced too, and that scraps the prop. So one just needs to do all one can…
Stones are the reason that you don’t use reverse on King Air propellers below about 40 kts.
I dread to think how much the composite blades are on those big props, and I doubt you could just file any dings out….
Neil presumably on long taxying you are still using beta?
RobertL18C wrote:
Neil presumably on long taxying you are still using beta?
Yes, we’d be getting through some brakes if we didn’t. Actually we rarely use anything more on landing either, even at somewhere relatively short like Fairoaks.
Peter wrote:
I would agree there is not a direct obvious 100% correlation between departing from somewhere with stones
I find that the worst nicks appear after having operated at bitumen strips! Gravel on a gravel strip is normally well weathered and round. However the stuff embedded in bitumen is nasty sharp stuff.
Plus also the false sense of security when doing runups on a bitumen strip tends to make people use higher power settings, and stationary runups etc.
I have flown many entirely loose gravel runways, and with great caution and awareness (following one bad tiedown lesson), never damaged a prop. Keep it rolling with minimum power as much as possible. But, an important trick for Cessna high wing tricycle pilots: At all times while taxiing, have 15 flap extended, and apply full nose up elevator. You’ll find that this configuration will keep the nosewheel several inches higher, and with power even more. In some Cessnas, you can lift the nosewheel off the surface in the first few feet of takeoff ground roll (being careful to not bang the tail on the ground), and after that erosion to the prop is unlikely.
The prop on my 150 was “close to limits” when I bought it 29 years ago. Not wanting to afford a new one, I simply used caution, and it has lasted me all these years, from a lot of unimproved runways, with no damage. As I stated in the other thread, I minimize run ups over a loose surface – as I know the engine well.
My stone chips bigger than yours! This one scrapped the prop. I only fly the aircraft, don’t own it and another pilot was unfortunate enough to encounter this one.
