Skydive Pilots Around??

[bugchaser]

Huncowboy is right. Like Avbug said, there is a huge difference between a practice p. o. descent and a rapid descent from altitude. In my opionion, temp management is a skill that many pilots have not grasped. Another very important thing which Avbug touched on is the backlash damage that can occur when the engine is being driven by the air. You should always try to keep the prop pulling the airplane instead of being driven by the slipstream. This is important in all powerplants and is absolutely necessary with some.

 

[414Flyer]

I used to fly a twin bonanza for a DZO, and I always tried to make sure the engine was turning the props, and wasnt in a low power situation where idleing down, and having the airflow turn the prop.

Its not good for piston engines, especially if geared, like the twinbo and C-421 are.

 

[Sctt@NJA]

Good info on this thread.

I had a hard time keeping my boss happy when I did the jump pilot thing. Not only did he not want to be blasted by the prop but he didn't want to lose any altitude either. The strictest rule was "don't shock cool the engine" yet they would flip out over every tenth of an hour on the engine. It seemed like they wanted the impossible. Either too much prop wash, or just right but "we lost 50 feet of altitude, nobody likes to give that up".

I could come down from altitude fast and risk shock cooling, or I could take my time and be conservative, or something in the middle, didn't matter it was never right.

 

[avbug]

The idle cut on jump run does mean a descent and small loss of altitude, but it's inconsequential. There is no danger of shock cooling the engine during that cut. You're already slow and descending slow; the reduced relative wind means less push on the prop to drive it. It's also a safety issue; you stand a better chance of jumpers making a clean exit and not grabbing a reserve handle or cutaway by mistake. Safer for you, safer for them. You can decend at that airspeed all day long, keeping it slow, and it's easier on everyone. At that point, you end up having to power up for the descent, and you're already slow...you don't have to slow down to come down.

Door open and the drop is nothing more than getting the jumpers out while you set up the descent.

 

[MED]

britishguy,

any problems closing that door after the monkeys jump away?

 

[PropsForward]

Well, I see from the other posts that you have been fully briefed that cross controlling the aircraft is fine.

I flew skydivers for about a year and I would not pass that experience up for nothing. Most new skydiving pilots get many complaints the first few times up. Not getting the spot right, taking to long to climb, or having to fly back to the airport after reaching the assigned altitude, etc. You will learn quicky and in time be tearing your very own holes in the sky as apply your new flying skills to the demands on commercial aviation.

On word of advice though, the aircraft tend to be on the shady side of being airworthy and the operator does not give a s#!t about you. Protect yourself at all times and make sure the aircraft is airworthy. If something a "dumb" as the manifold pressure guage is broke, then don't fly it. It will be you that gets the ding on your record for flying it.

Happy Safe Flying!

 

[plattsburgher]

my two cents

British Guy,

I have a couple of summers flying a 182 for a DZ. The jumpers don't care at what speed you are flying, they don't like the prop blast. I used to reduce the pitch a bit to let the aircraft accelerate the last few hundred feet prior to the desired altitude (while still in a climb). This allowed me to keep the prop blast low (making the jumpers happy) and keep the airplane from stalling the right wing (keeping me happy).

The other advice about the rules is right on target. You are the adult and it is your ticket on the line. If it isn't VFR for your airspace the jumpers won't care--I guarantee you will be told that they "don't mind jumping through a cloud". Keep an eye on people as it gets later in the day, don't let them on board if they are drunk or high. Most of the planes will have only what is required for VFR as far as equipment goes. Know what you have to have.

Then go have fun. It is a great way to pick up some good PIC time and a lot of good memories.

 

[FN FAL]

Shock cool this...

This is an oldie, but this type of thing happens. In fact, it happened last week in Illinois with similar results. The more level and stress free you can make the jump run when you are flying, the less chance you are going to have of someone getting hurt while flying jumpers.

To the original poster of this thread, good luck and stick with it. I think you'll get the hang of it in no time. Consider this next time you go up and the door opens. Look at the ball...guess what, it's out of the dog house! Cross control it back to center. Then the jumpers get out on the step, look at the ball...guess what, it's out of the dog house! Cross control it back to center. You might be cross controlling the plane, but you are cross controlling it to get it back to coordinated flight...If you have enough control authority, that is. Oh, don't mind me, I only got about 1,200 hours flying jumpers and at least 600 jumps...and yea, as a jump pilot, I have had to dead stick twice and a jumper had an open parachute container in my plane once while the door was open. I had to pin that sucker to the floor to keep him from getting up and killing us all.

Seen it, done it, doing it tomorrow, got a closet full of t-shirts.

Be carefull out there...

14 CFR Part 91: General Aviation
Accident occurred Sunday, April 14, 1996 in HARTWOOD, VA
Probable Cause Approval Date: 5/13/1997
Aircraft: Cessna P206C, registration: N8682Z
Injuries: 1 Fatal, 2 Serious, 1 Uninjured.


The pilot stated that after climbing to 10,000' msl on a skydiving flight, the occupants began preparations for the fourth and final parachute jump of the day. The first parachutist (skydiver) of three was standing on the right wing strut preparing to jump, when his main parachute (that he had packed himself) deployed inadvertently. He (and/or his parachute) struck the right horizontal stabilizer; subsequently, the stabilizers (empennage) separated from the airplane. The second skydiver stated that he had one foot on the wheel step and the other foot in the door when the first skydiver's main parachute deployed. He stated that the airplane gyrated and that he was pressed against the lower side of the wing, but he was able to free himself. The pilot stated that shortly after the first skydiver had exited the airplane, he (the pilot) felt a 'thud' and the airplane started to react violently. The pilot tried to regain control of the airplane, but was unsuccessful. He stated that he and the third skydiver were slammed around inside the airplane as it continued gyrating. The pilot exited the airplane by pulling himself to the door. The third skydiver did not exit the airplane, and the airplane crashed. Examination of the wreckage did not disclose any preaccident anomalies. The National Transportation Safety Board determines the probable cause(s) of this accident as follows:

the inadvertent/premature deployment of the first skydiver's parachute, which resulted in contact with the airplane's horizontal stabilizer by the first skydiver and his parachute, loss of integrity of the empennage to the aft fuselage, loss of aircraft control, and subsequent separation of the empennage. The third skydiver was fatally injured when he failed or was unable to bail out of the uncontrolled airplane.


Full narrative available

 

[FN FAL]

I think there are a lot of books that could be written by people who profess to be experts on shock cooling. I'm sure they'll chime in as soon as possible with unverifiable stories about how they did or saw this and that. I say bunk! Write a book on it and get it published! DZ owners make their bread and butter off of that plane going up and down, not with it sitting in the shop while thousands of dollars a day in business gets turned away.



Giving the "cut" from 17 inches of manifold pressure, to just under 14 inches of manifold pressure, isn't going to shock cool sh!t. About the only thing I can think of being too cool is going to be your carb heat, in the case an engine dies on you during the "cut". And the "cut" is not done abruptly...it's done smoothly.



We run two 182's with the 0-540 conversion engines in them and we just got 1800 hours out of the one engine...it went out with a cracked case, but that was a problem of age, not shock cooling. You can only rebuild something so many times before it goes to the trash bin. And who hasn't replaced jugs on a Cessna? It happens.



We use specific procedures to "pre-cool" the engine before jump run and we use specific procedures for descent. Temperature monitoring of the EGT and CHT is done from take off to landing. And yes, the owner of the DZ doesn't want your monkey ass trashing the plane and he wants it up and down as fast as humanly and mechanically possible. For those of you who never worked at a real job before you got into aviation...it's the same at the factory, the same at the warehouse and it's the same at the fast food joint. They want you to do the job you are paid to do, without trashing anything and while being as productive as possible. Who would have imagined that concept.

If you want a job where there is no pressure to produce, I would look at government careers...specifically in the federal government. You can trash stuff there, maybe even get people killed and not have a care in the world, just ask Janet Reno.

 

[RedheadCFI]

Hey, I can vouge for the black eye flying divers. I swear to god the brake was on, the wheel just happens to spin when a complete as*hole that complains about the last lift w/you steps on it. Here is a tip from one jump pilot to another. Get a copy of the key to the aircraft and take it with you on every flight, and if the last guy out points out traffic at your 7 o'clock don't bother looking.

 

[FracCapt]

Hey, I can vouge for the black eye flying divers. I swear to god the brake was on, the wheel just happens to spin when a complete as*hole that complains about the last lift w/you steps on it.

I hope you're joking...because if any pilot ever does that to me, he'll have a lot worse than a black eye. That's dangerous, and could kill somebody...or even EVERYBODY in the airplane. I'm all for fun and games...but things like that(and taking the key) are going way too far.

 

[A Squared]

Backlash damage to engine accessory drives and to the engine itself, any time the slipstream is driving the propeller, is also a real factor to consider.

and

Another very important thing which Avbug touched on is the backlash damage that can occur when the engine is being driven by the air.

Guys,

this is a complete misconception. There is no "backlash" in the accessory drive during an idle descent. Before you answer, think it through, in order for there to be backlash, the accessory would have to be driving the crankshaft. The accessory gear on the crank is always driving the accessories.

Just as a side note, that is not "backlash". Backlash is the quality of the gears not meshing perfectly, i.e.: "slop" if you will. It exists in all mechanical drive trains in varying degrees. What is being described is gear tooth contact face reversal.

Follow mw through this:

You pull the plugs out of an engine and you begin turning the prop forward by hand. the magnetos turn, of course. Is the crankshaft driving the magnetos, or are the magnetos driving the crankshaft? Obviously, the crankshaft is driving the magnetos , the gear tooth contact is on the normal tooth faces, not on the reverses faces. Now put the plugs back in, start it up, and run it at 1200 rpm. Is the crankshaft driving the magnetos, or are the magnetos driving crankshaft? Again, obviously the crankshaft is driving the magnetos. Now, push the throttle in all the way, and take off at let's say 2700 RPM. Is the crankshaft driving the magnetos, or are the magnetos driving crankshaft? Again, obviously the crankshaft is driving the magnetos. Now get up to altitude and slow it up and pull the power all the way back, put it in a gradual, slow descent at 1200 RPM. The air is driving hte prop, but, is the crankshaft driving the magnetos, or are the magnetos driving crankshaft? Again, obviously the crankshaft is driving the magnetos. Now, push the nose over into a dive so that the RPM spools up to 2700 RPM (still with the throttle closed) The air is driving the prop, but, is the crankshaft driving the magnetos, or are the magnetos driving crankshaft? Again, obviously the crankshaft is driving the magnetos.

The *only* way to reverse the contact of the gear teeth on the magneto drive is to; a: turn the crankshaft backward, or b: slow the crankshaft so abruptly that the inertia of the spinning magneto causes it to momentarily reverse the gear tooth contact. In scenario b, the crankshaft is actually slowing the magneto, but the deceleration of the crankshaft has to be *very* rapid, much more rapid than you could possible achieve by yanking the throttle to the stop, and even so it would only be momentary. As a side note, this is one of the items you check on a sudden stoppage inspection, You check for damage to the accessory drive gears resulting from the crankshaft slowing more rapidly than the magneto.

Any time that the crankshaft is turning, whether it is being turned by the pistons, the air on the prop, or by your hand on the prop, the crankshaft is driving the magnetos, it's driving the oil pump, it's driving the vacuum pump, and it's driving the generator; not vice versa.

One exception to this, is starting, on many GA recip engines, (continentals mostly) the starter turns the engine through the accessory gears (the generator drive gear on the O-470) So during starting, only, ,the gear face contact is reversed from "normal" as soon as the engine fires and the starter disengages, the contact returns to normal.

I suppose that if you had a engine driven hydraulic pump, and you connected it to an external hydraulic pump (hand operated or powered, your choice), you could turn the crankshaft with an accessory gear by "motoring" the hydraulic pump on the engine, and the gear tooth face contact would be reversed.

Except for starting, and my far-fetched hydraulic pump example, the crankshaft will always be driving the accessory gears, and gear tooth contact will always be normal.

Now, on an engine on which the prop is driven through a gear reduction, it is entirely possible to reverse the gear tooth contact in the *gear reduction unit* by allowing the prop to drive the engine. This is a matter of concern for geared engines, *but* it is still impossible to get gear contact reversal in the accessory section during idle, regardless of whether the engine is geared or direct drive.

So, are there concerns for a *direct drive* recip engine in an idle descent?

Yes. There is the controversial "shock cooling". There is also "ring flutter" in which the piston rings move excessively up and down in their grooves when the combustion chamber pressures are very low. This may contribute to failure of the ring lands failure in the piston. Also there may be lubrication issues on the "big end" (i.e.: where the connecting rod attaches to the crankshaft journal) There's an interesting column on Avweb which presents one view of this and other issues.
http://www.avweb.com/news/columns/186778-1.html

One thing that is certainly not a concern is accessory drive gear contact reversal. It doesn't happen. It can't

 

[avbug]

It sure does. In fact, when setting the timing on the big engines you drive, as I have done many times, we set it through backlash, putting tension with a wrench and an assistant, not as the magneto sits on the engine. There is slop in there. I know what you're saying, but I disagree, and so does every other engine expert with whom I've ever worked...ones who know what they're doing.

I've read the avweb articles. I take exception to them. I've had discussions regarding them with the author, and I do disagree. It's been discussed here to death, and has been discussed here in the past, to death.

Allowing the prop to drive the engine is harmful; it's harmful on reduction drives, accessory drives (even though they're at the back of the engine), crank journals and bearing surfaces, etc.

Thermal issues are hotly contested, but are also an issue. I can vouch for that from personal observation and experience. And yes, in some cases, ring flutter may (I emphasise "may") be an issue.

The bottom line, and the point followed here, is that allowing the prop to drive the engine is unwise and bad airmanship for a number of reasons.

 

[A Squared]

Avbug,

You may have misunderstood what I said about backlash, I didn't mean to imply that it didn't exist, nor that it wasn't related to the subject at hand. Rather I was commenting on the semantics, in that it is not "backlash" when a gear train reverses tooth contact, but it is backlash that allows it to do that. I agree that backlash exists in any gear train, from aircraft accessory drives to Swiss watches. Even so-called "zero-backlash" drive trains (non-aviation) have backlash, they are merely spring loaded so that the gear contact is always on the same face. So, I don't disagree that there is "slop" in an accessory drive, any accessory drive. I've timed magnetos, (not on the R2800, so I don't know that specific procedure) so I am aware that in general, if it is done incorrectly you could set the timing with the "slop" reversed, on the "wrong side of the backlash", for want of a better term. That of course would result in an improperly timed magneto. I think that on all this, we agree, 100%.

Where we disagree, is that in a windmilling descent, the accessory drive gears reverse tooth contact, or operate on the "wrong side of the backlash". Now, instead of merely contradicting me, explain to me *how* the accessory drive reverses the tooth contact. I mean really, prepare a detailed explanation of how that happens, as if I were completely ignorant of the subject. If you are certain that it happens, it should be no difficult task to explain how it happens in a way that will be completely convincing both to me and anyone else who might disagree with you.

Just to clarify some of the other issues: I was not advocating windmilling descents, or trying to suggest that they a good thing, in fact, I mentioned that there were some reasons why they may harmful. I think you may have assumed that because I was disagreeing with you on one point, I was disagreeing with you on all points. I'm not. Rest assured, the only time the props are driving the engines on the DC-6 when I am operating it, is for a very brief moment in the flare. I posted the link to John Deakin's article as food for thought, not to "prove" something to you. I am aware that you disagree with Mr Deakin on most things. I don't agree with everything he says either. I do however find it usefull to read such things, and think through whether things make sense, and analyze why I do or do not agreee with them. Sometimes you can gain a greater understanding of something by reading something which is wrong, and thinking through *why* it is wrong.