Props and CofG

[stiknruda]

My prop is due for a Notice 75, so I've been having lots of propeller chats to various folk about 75's and overhauls and generally thinking about propellers quite a lot over the past week.

So, my gardener watched me struggle across to the workshop with my c/s Hartzell in my arms on Saturday. He remarked that it did look quite heavy!

I explained that it was off to the propeller hospital for a check-out at a cost approaching two grand, once I'd made up a crate for it. He appeared interested, so I then explained to him that the blades move and that it is quite a complex thing compared to a fixed pitch wooden prop.

He asked what would happen if a blade came off and I said well the imbalance would probably tear the engine out of the mount - and if that happened the aeroplane would develop the gliding characteristics of a house brick and that he'd not be paid ever again by me!

So.... yesterday, I'm back in the hangar and I need to move the aeroplane to position the engine under the hoist as I am about to remove it to perform various maintenance chores and install my new hi-comp pistons. The tailwheel was supported on a modified trestle and I attempted to lift it off. I can normally do this with one hand and with a bit of effort, hold it up whilst I pull the trestle out with my other hand. Well, I huffed and I puffed but yesterday I could barely move it - I eventually managed with two hands and kicked the trestle over so that I could place the now incredibly heavy tail back on the deck.

I took the engine out and the engine mount which needs painting and as I plan to renew the bungee cord on the main gear, I manually lifted the front of the aircraft to gauge the weight (with a view to supporting the a/c from a rope block and tackle as the 25T hoist was still supporting the engine, albeit that the engine was resting on a couple of trestles, whilst I get around to welding a stand for it or locating the one that I made 9 years ago!).

Without too much effort I had the main gear wheels off the deck so I feel quite comfortable using the lighter block to support the fuselage.......

So this started me thinking, without wishing to do any major CofG calcs, IF I lost the prop, the Cof G would be so far fwd that I don't think that she'd fly, BUT if I lost the prop and the engine the CofG would move rearwards and quite possibly be a safer scenario!

This obviously is hypothetical and I intend to renew both the engine mount bolts and the engine bolts, too!!

Your thoughts?

(I am aware that I do have a very vivid imagination and I ought to get out more!! )

Stik

[Genghis the Engineer]

You know roughly what it weighs presumably, easy enough to measure it's position relative to the CG datum.

You know what your normal flying W&CG are.

You know what the aft CG limit is.


After that, it's a 2 minute sum, just equivalent to removing a passenger or piece of baggage.

G

[DubTrub]

IF I lost the prop, the Cof G would be so far fwd that I don't think that she'd fly, BUT if I lost the prop and the engine the CofG would move rearwards and quite possibly be a safer scenario!
Not sure about your logic there, Stik...if the prop came off, the cg would move aft (a bit). If the prop & engine came off, the cg would move so far aft that it might well become uncontrollable, not safer!

[Cusco]

Thought notice 75s had gone with the new dawn.

A twin (small) made successful emergency landing in a field in Norfolk a few years ago with 3 pax on board after shedding one engine and destroying the other with debris from first engine, so there must be some leeway in out of balance Cs of G.

Cusco

[DubTrub]

some leeway Indeed, C, but the engine on the twin in question is (was!) closer to the longitudinal cg than in Stik's case, and of a smaller mass in proportion to the total.

[Brooklands]

Like Cusco I was under the impression that notice 75 had been withdrawn (a consequence of EASA?).
I think the 'small' twin that lost a prop in Nofolk was a Navajo - I've had a look for the report on the AAIB site, but can't find it.
As to loosing a prop on a single - didn't this happen in the mid 1990s to somebody, and was one of the reasons the CAA instigated the reqiurement for crankshaft inspections on all lycomings with fixed pitch props. IIRC the person it happen to managed to pull off a forced landing and got a CAA safety award for it.
Brooklands

[stiknruda]

Nope - I was under the impression that the requirement had been lifted but I spoke to several knowledgeable folk (JadeAir, H&S, Andy Brinkley and the 3 year 75 and the 6 year o/haul is still current!

[Phoenix09]

As to loosing a prop on a single - didn't this happen in the mid 1990s to somebody, and was one of the reasons the CAA instigated the reqiurement for crankshaft inspections on all lycomings with fixed pitch props. IIRC the person it happen to managed to pull off a forced landing and got a CAA safety award for it.
Brooklands

I attended this incident. If I remember correctly it was a Warrior being ferried back to White Waltham from the Channel Islands when it lost its propeller over Junction 10 of the M4. A very nice forced landing in a field alongside the M4 was carried out and by the time I arrived the pilot was very nonchalantly talking on his mobile phone. :)

It must have been in the early 90's. Is there anyway of accessing old AAIB reports? I don't seem to be able to go back further than 1996.

[Pitts2112]

"IF I lost the prop, the Cof G would be so far fwd that I don't think that she'd fly, BUT if I lost the prop and the engine the CofG would move rearwards and quite possibly be a safer scenario!"

Stik,

What you need, then, is not to renew the engine bolts but to install explosive bolts on the engine mounts, with the trigger in the cockpit. That way, in the unlikely but devastating event that the prop departs the airframe, you can immediately jettison the engine thus restoring the harmonious balance and handling characteristics of the venerable Pitts and glide safely to a soft landing...in a cushy field...near a cup of tea...and a phone.

Or, if you want to get clever, you could design a microswitch setup such that when the prop departs the airframe, it triggers the explosive bolts automatically so prop and engine all go at nearly the same time. Through this ingenious setup you spend virtually no time in the dangerous transitional "engine but no prop" phase of the sequence. You'd merely hear one wrench, one loud bang, and then complete silence, maybe even feel a bit of a shudder, as most of the aircraft weight hurls itself toward the nearest school/hospital/orphange/cute furry animal sanctuary.

I think you're on to something here. Properly designed and marketed, maybe a bit of Millo Magic stuffed in there somewhere, and you'd really have something. THE aviation safety system for the 21st century. You'd be laughing at Cirrus and their poncy "floating humiliatingly around the sky" parachute recovery system. REAL pilots will go this route and continue to fly their machines, not float, to the crash site...near a cup of tea...and a phone.

Just my .02 worth

Pitts2112 ;)
(Which of us needs to get out more?)

[White Bear]

Sorry Stick, I'd like to help but I just can't get past:
"my gardener watched me struggle across to the workshop with my c/s Hartzell in my arms".
My Gardiner!!:uhoh:

Regards,
W.B

[1972]

Sorry Stick, I'd like to help but I just can't get past:
"my gardener watched me struggle across to the workshop with my c/s Hartzell in my arms".

Me either! As soon as I read that, I got images of the master talking to Ted on the Fast Show!

[smarthawke]

Stik

AWN75 certainly doesn't exist. The only requirement is to adhere to manufacturers recommendations ie overhaul lifes.

Most Hartzells have an overhaul calender life of 6 years - can't remember what the hours are off hand.

If yours is on a 3 year AWN75 inspection I would go and get it back, someone is telling you porkies...

[stiknruda]

Smarthawke - it has gone for an overhaul, with a compulsory hub replacement that I am led to believe will be FOC.

Gardeners - WB and '72, don't you have them? His primary purpose is to ensure that the front garden is kept pretty, weed free and that the grass is suitable for landing my aeroplane on:p . As for the FastShow - too busy in my workshop to have time for anything so mundane!


Stik

[Farmer 1]

IF I lost the prop, the Cof G would be so far fwd that I don't think that she'd fly, BUT if I lost the prop and the engine the CofG would move rearwards and quite possibly be a safer scenario!
Stik

Stik, the engine is an essential part of the aircraft, even when it doesn't work, simply to keep the C of G within limits.

I heard the following apocryphal story many years ago.

A private pilot took a club aircraft for a spin. There he was, full of the joys of spring etc, when the propeller shed a blade. Out of balance forces then tore out the engine and one or two other minor bits and pieces.

The aircraft immediately went nose up, stalled, and started falling backwards. The pilot was now a passenger, and the aircraft fell to earth like an autumn leaf. It hit the ground while going forward, sustaining little further damage.

The pilot crawled out and saw the empty front end of the aeroplane. He found a phone, and in a high state of nerves, rang his flying club and did his best to describe the course of events.

"It's the engine!" he said, "it's - missing! It's missing completely!"

The chief pilot, not one to be excited unduly, tried to reassure him. "Sounds like you've got a bit of water in the electrics," he said.

[KZ8]

AWN 75 is no longer in existance, but it has been replaced by GR No.17 in CAP 747. It is all laid out in there.

KZ8

[fltcom]

2 things:

First, notice 75 doesn't exist anymore.

Second, your logis is unsound. If you lost the prop, the CofG would move rearwards not forwards.

[smarthawke]

Stik

I know the feeling, my propeller is away at the moment for overhaul (5 years). It's an ex Bulldog prop and was brand new. It has the Mk1 hub which apparently cracked round the front (visible) half. The Mk2 cracked round the rear (not visible half), Mk3 supposedly okay.

Mk2 is a compulsory change to Mk3, Mk1 is optional change if the aircraft is aerobatic, crop dusting or attached to more than 300hp. If you don't change it, it's an Eddy current inspection every 100hrs 'on the wing'. My machine isn't cleared for aeros in the UK so it doesn't do any... If it did it would only be gentle loops and rolls as it isn't cleared anywhere for flicks or gyro stuff. This means I don't have to change the hub in theory and 100hrs will take 2 years to do.

[Them thar hills]

A homebuilt "Owl" racer lost part of its metal prop because the prop had been shortened (at some rpm's this can cause the prop to resonate) The subsequent imbalance tore the engine (0-200) from the front of the aircraft, which crashed by the River Thames.
I believe the pilot did not survive.
To lose a whole prop would be preferable , just get on with the real forced landing !:E

[Zulu Alpha]

Stik,
I think DubTrub has the answer. In an single engine aircraft, lose the prop and the Cof G moves back a bit. Lose the engine and prop and it moves back a lot and is unflyable.
Twins are not affected as much because they have the engine roughly in line with the C of G so an engine detaching itself would make a lot less difference. I suppose there is twice the chance of it happening.

I did hear of a cable that could be looped between engine and fuselage. The idea was that if the engine came loose because of a prop blade failure the engine would still be attached and keep the C of G in flyable limits.

Its a sobering thought when you weigh the prop (I just re installed mine after overhaul) and think that it all whirls round at 2500 rpm connected to the noisy bit by a 1.5 inch diam tube with 150+ HP going though it.
The only good thing is that I don't have enough spare brain cells to think/worry about it when I'm doing aeros!!

[Andy_RR]

all this talk of aircraft turning unflyable on one makes one wish for a ballistic recovery system, eh?

[fu 24 950]

There way a case in New Zealand back in the 60/70 of an ag pilot (crop duster) who had taken his C180 in for a AD prop check, all ok but on the flight but to his home base the prop let go and took the engine with it. Back and forth like a leaf he went until he landed, I have seen a photo of the 180 undamaged apart from nothing fire wall forward sitting in a paddock.I think the pilots name was Don Ecreg. As the story goes he walked to a farm house and phoned his engineer,
MY ENGINE IS MISSING (Q) HAVE YOU CHECKED THE PLUGS
(R) I WILL WENT I FIND THE ********** ENGINE. true story

[ShyTorque]

If the C of G moves forward when you lose the prop, why not carry a spare one in the back, just in case? ;)

[stiknruda]

shytorque you have a point!


I've been looking at 3 bladed props because the mass must be more localised and I could fit one in the "boot" more easily!

Stik

[Barcli]

Stik,
is the weight issue why so many people are going to composite MV props ? :confused: been doing some research on them myself ( mainly import) as my Hartzell on the Eagle is on its last 100 hrs ( might be same MV replacement model as yours ) - be interested in what you find re cost ....::{

[Zulu Alpha]

This is what I was quoted for a new MT prop and spinner for a Lyc. AEIO-360-A1E engine
3-bladed hydraulic constant speed propeller with a diameter of 190cm.
9.930,00 Euros
2-bladed hydraulic constant speed propeller with the
diameter of 183cm:
8.530,00 Euros

I was very impressed by the whirlwind prop which all the aero boys are fitting in the US
See
http://www.whirlwindaviation.com
Its carbon fiber with a nickel leading edge I believe the blade is hollow and is made by inflating a bag inside the blade while the blade is in the mold Price is $8600 which compares well with MT and Hoffman.
Unfortunately its not certified and can only be used on homebuilts. The PFA have not yet approved it so it would take some paperwork to be able to get them to approve it over here

[DubTrub]

I'm not convinced that Stik , bless, has grasped the mettle regarding losing something "up front" and the subsequent aft change of cg.

Your nice new, light-weight MT wooden prop will reduce your MAUW, but might send the cg aft enough to exceed the aft legal limit. You could of course add a lump of swan-friendly lead to the firewall to compensate.

Stik: come to the fly-in that Pitts2112 is (hopefully) organising in Norfolk this summer: I will take you flying and demonstrate the effect to you (in fact I can only do it with you in the aircraft...how's the diet coming?:) )

[Onan the Clumsy]

Perhaps worse than the engine coming loose would be it hanging on by a cable or two, surrounded by splayed out, mangled cowling.

As if you didn't have enough troubles.