Question for Current and Ex Meat Bombers

[Dupre]

I was reading somewhere today that a jump plane descends from 12,000' to landing in 90s.

What on earth happens to your ears when doing this? My ears pop when descending from 8000' cabin alt. relatively slowly in an airliner!

Also, what is the shock cooling effect on the pistons - I can't imagine a worse scenario!

Cheers,

Dupre.



p.s. Has anyone thought of cutting the ignition and feathering the prop/s just after the load jumps? Can then glide back down without running up expensive tacho/hobbs time!! (better not need to go around though...)

pps. Has the Whenuapai skydiving gig moved to Parakai?

[Cypher]

Dupre...

I'm guessing that 90 seconds from 12000 ft is a turbine aircraft... no way I'd do that in a piston!!!

I'm flying a piston on jumper dumping and usually I'm heading to about 9000 ft. I take it pretty sedately, probably around 5-6 minutes roughtly for the descent. I'm limited by the door off Vne, if only we had a door... :(

Constant val Salva usually helps in the ears.. usually one at 7000 ft, then around 2000-3000 ft.. I do it often enough so I can still hear the radio clearly.. which is my biggest concern.. obviously no flying with a cold.. been there, done that.. never again!

Shock cooling is a biggie, I was taught to descend with power on, so in the C206, I'm descending 22" MAP @ 2200 RPM, cowl flaps closed, mixture fully leaned.

The boss has installed a really good cylinder head temperature gauge, so we can select certain pistons. Our procedure is to monitor the rear pistons on the climb, as that theortically will be the hottest part of the engine due to lower flow of cooling air, and we monitor the front pistons on the descent, to make sure we're not descending too fast, as to shock cool the front pistons.

This is all hooked up to a piezo buzzer, so when the rate of cooling is too quick, the buzzer goes off and a light flashes.. it's pretty invaluable when your about to go power off to let the jumpers out. It's not the engine itself being cold that damages it, but the rate at which the engine cools which damages it.

Jump planes have a bad rept for being badly looked after and abused.. with the right operator, this is not the case. Properly looked after, a jump aircraft engine should last as long as it's design cycle.

Cutting the engine and feathering the prop isn't probably a very good idea on an aircraft such as the C206/C185/C180/C182s,
The thermal shock would be pretty bad...

Just ask the Air Force what happens when you repeatly cut power half way downwind in a big six cylinder engine, without the gradual power reduction that these engines need....

I have heard of jump pilots though doing the stop the engine and glide it in when flying a C172, but call me chicken, I ain't keen to do it...

[Master of the House]

I would have thought that the skydivers ears would have been of more concern than the pilots, they come down pretty quick!

[Boney]

Cypher

You know your obviously know your stuff.

Having a CHT that you can bounce between front and rear cylinders a a "ditter" when you are getting too carried away - brilliant.

[Cypher]

I can't take credit for that.. that was the boss's invention...

He taught me everything I do and know about parachute flying.. so it's really him that really knows his stuff... :ok:

[currawong]

SOP where I worked was keep the power up for the cyl heads and enter an approx 2g spiral dive. Descent is rapid, airspeed is ok, temps stay ok and is quick. This was on a 206.
A 172 was also used, with a different method. Small power reduction and pole back into the white range, full flap, trim forward to stay in the top of the white range.
206 on high loads, 172 on low static line jumps.
Either method, if memory serves, put the aircraft landing with the last jumpers.
Good for the boss, bad for the logbook!
Yeah, not with a cold, it will write you off for days probably.

[Torres]

Master of the House: "I would have thought that the skydivers ears would have been of more concern than the pilots, they come down pretty quick!"

I would have thought if a meat bomb "descends from 12,000' to landing in 90s" the stop at the bottom could be far more painful and his ears would be the least of his problems.

Could take a fair bit of digging out as well!

[OpsNormal]

At first I thought he meant landing back in the 90's!

I was about to say "wow", skydivers and their drivers can now time travel too..... :uhoh:

[Continental-520]

Yeah,

Likewise to that of OpsNormal.

Still chuckling...

I think the power on descent is pretty much the most common method in 6cyl engines, no?
I used to go up to 10,000 AGL in a 182 (only got about 18" MAP up there) and just let it increase to 22", where I'd 'peg' it till late downwind. Cowl flaps closed and mixture gradually richening. Got about 1500 - 2000 fpm.


520.

[Menen]

Yeah - shock cooling is a real problem. There are reports coming in every day of Cessnas crashing due engine failures caused by shock cooling. Maintenance organisations are making a killing with all the cracked cylinders they find.
Operators are going bust every day at the costs of new cylinders.

If you fly through rain, the shock cooling on the front cylinders is so lethal that chances are the cylinders will crack on the next take off where after being cold at idle power the application of full power will also cause shock cooling with associated engine failure not far off. Can you just imagine all the damage done if you throw buckets of ice cold water over the cylinders in flight - because that's what happens if you fly through moisture laden clouds or just ordinary rain.

The worse type of shock cooling is when you cut the mixture control at the end of each flight. Now that really is a change in CHT!! Terrible thing is shock cooling. I know one of one CFI who is so frightened of shock cooling that he tells his students to fly long wide circuits to allow the engine to cool down after take off gradually before throttling back on base leg. His theory is that the students pay for the extra flight time and with the money they pay it pays for repairing the cracked cylinders. Nice work 99.

Maybe its all a myth?

[OpsNormal]

Menen, if anything, the temps go up inside the cowls after shutdown, for there is no reasonable airflow passing along and forcing the heat out and down through the cowlflaps. Because of the radiated heat (coming off the cylinders, and also being stored very well in the cast iron engine case/block), being mostly contained within the cowls, the thermal shock after shutting down should be almost negligible. The heat in the engine case will slowly dissipate into the cylinders and into the air, originally through conduction into the cylinders, and then through radiation into the air surrounding the cylinders.

Also meant to mention that in the C185 we used to maintain 18 inches and 2000 rpm all the way to base/final, with cowl flaps shut, mixture gradually enrichened all the way down and airspeed pegged about mid yellow arc until in the cct.

We used to see 0.4 times just about every sortie. :ok:

Regards,

Ops. :)

[0tter1]

Interesting article in regards to shock cooling and engine management...

http://www.avweb.com/news/columns/183094-1.html

[Kiwi Flyer]

Used to fly a dog of a jump plane out of Charing Cross near CHCH.
The old 300hp PA32, it wasnt bad for the job. Used to do jump run at 20 squared, and then straight into the spiral descent at same settings. It came down like an aerodynamic man hole cover! Cooling was okay as well, except in the climb it would get a bit hot.

Oh, and yes the big 6's do actually get hotter after shut down.

[Gravox]

DUPRE it would have to be a turbine jump ship to descend that quickly, but I think it will take a little longer than 90sec. The new Cresco, PAC750xl, can carry 17 jumpers up to FL120 and and back down in around 15 minutes. A full load of 10 in a navjao is around 35-40 minutes. Boney might tell you it is less, but hey the battery in his watch is a little slow.....

Boney are you getting a hard on over Cyphers CHT ditter? Perhaps you should get your outfit to install one, nah two for you. Whats the bet you could have both ditters going off at once!

Cypher how's it all going mate, hope all is well, any plans to move over this way, to the better climate. Perhas Boney will let you loose on a Navajo, if you ask nicely, and are prepared to bend over and grab your ankles.:p

Boney you know you love it. HAHAHAHA

JTB would never have placed a ditter in their planes, cos they don't understand the value of longer sorty times, especially when crossing hire someone else aircraft

Hope all it going well for you both I'll chat to you guys later.
2C1SD:

[Cypher]

Bend over and grab the ankles? Isn't that standard operating practice in G.A ???? :}

Yeah things aren't bad... still got long term plans to move to Oz..

If you can't beat em.... join em!!!

[Boney]

Hey, anyone see the front page of "the thinking persons paper" (The Daily Telegraph, Sydney) today. This poor excuse for a paper must have ran out of stories about granny's having a cat stuck up a tree or something. The front page is HUGE picture of some poor pommy dude who had his main and reserve parachute sabotaged. It happened in the land of the great unwashed (UK) and the police are treating it as a murder investigation.

Poor buggar, but "thinking persons paper", is it really worthy of a front page. Typical Murdoch!

Boney

[Transition Layer]

I thought exactly the same thing myself Boney - is it really front page worthy? Did you notice it was half way through the article before it mentioned that it happened in the UK? Tragic story nonetheless.

Whilst on the Daily Telegraph bashing, I heard a rumour once that the estimated reading age required to read this paper is around 6 years old? I'd believe it!!!

TL

[Boney]

TL ..... um

Don't get me started!

I read an interesting article last month about the blatant Murdoch support for America's illegal, immoral invasion of Iraq in search of oil, sorry, weapons of mass distraction.

All his mass media outlets here and abroad have been very pro war. Not surprisingly, ownership rights for media outlets is being debated in earnest in the states at the moment. No doubt, Murdoch will be looked after for his unwavering propaganda and support for the United States of Aggression.

The United States of Aggression murdered 800 civilians, injured 4,000 and killed an estimated 20,000 troops. And Murdoch is willing to promote this as a way to solve the worlds problems so he can increase his income from say, $10,000 per hour to $11,000 per hour.

What a low life - how does he sleep at night?

Ahhhh ..... I have had my two bobs bit worth.



"All we are saying, is give peace a chance", J Lennon, 1969

[gmallard]

a pc6t will do it if not come very close to the 90sec from fl120 but joining the ct slows it down quicker descent then crescoe as porter uses beater.

[bush mechanics]

hey Ops,Cast iron engine blocks?????I flew c182 for a little while meat bombing and company policie was 2200rpm and when the M/P reached 24inches hold it there all the way into the circuit.cowl flaps closed all the way.now engine baffles are placed soo all cylinders get the same amount of cooling air as the others within reason.When you shock cool a engine you crack the alloy cylinder head which is connected to the steel cylinder which is then conected to the alloy crankase.Soo the head cools quicker than the cylinder due to the dissimalar metals.
Most engines have baffles infront of the 2 fwd cylinders nearly all the way up the head wall to disapate rain or keep ice off the cylinders and off course stop ram air striking the front of the cylinders,the air has to go over and down thru the cooling fins of all cylinders.

[FelixInk]

I used to jump in NZ back in the late 80's, out of a 206 mostly. Most pilots did a high a/a spiral descent back then. Jumped with a bad cold once, very painful after opening and left me with a small scar on my eardrum.

[the wizard of auz]

I used to use around 20"MAP (all I had at 14500) and 2300 rpm, 60' AOB and around 120KIAS. I was able to get to the ground about the same time the jumpers were landing without hurting anything. that was in the C206.

[OpsNormal]

You are absolutely right, of course. The only thing I'll admit to being (that night I posted that), is under the affluence of incohol. I know what I meant, and yet it still never came-out as it was meant to..... "Iron" tends to follow "cast" for me, if you know where I'm coming from..... ;)

Ahh, the joys of being pished..... :ok:

Can I swap yer a S/E/M (in two weeks time) for the two after that? :) :D

Regards,
Ops.