Prop Questions

[pylon500]

I figure this is the place to put forward technical/maintenance questions, so herfe goes.This question is aimed at people using Brolga props.Many of you would have read my thread about the cracked Brolga (Ultraprop)hub we had.Prior

 

to finding the crack, we had begun to notice an annoying vibration we

 

werew getting at some airspeed/rpm combinations, typically at 60kts

 

with around 4500 rpm in level flight with our GR-912 LightWing.Initially

 

we put it down to an unbalanced prop, but it proved to be within

 

limits, so we then suspected an imbalance between the carbis'.We also looked at timing and gearbox backlash to no avail and ended up doing the GA fix and said "Don't fly at that RPM!"About then we had the prop hub crack and figured problem solved!But

 

this was not to be, as once the new hub was fitted, and the prop

 

balanced, we took off, only to have the same vibration come back. We then found that a nearby GR-912 with a Brolga prop was doing the same thing.We

 

have an 80hp 912 with a three blade prop running 14 blocks, the

 

vibration does not actually occour at just one rpm, but more at a range

 

of 'Loads' on the prop.

 

As mentioned earlier, we can get the vibration anywhere from 60kts and 4500rpm up to 70kts at 5200rpm.If

 

we had a manifold guage, it may show the vibration occouring at a

 

certain pressure which would represent the amount of load the engine is

 

under (a relaxed cruise?)My theory is that when the prop is not under a high load (like climbing or flying fast), some form of resonance is exciting the blade tips and getting a 'tuning fork' effect going which feeds back as a vibration?I would like to hear from others runninng Brolga props, if they have had similar vibrations?From there we can try to determine the actual cause of the vibration and find a way to control it.As

 

a side note, back in 2002, I was in Germany and had a fly in a Technam

 

Golf, and although the translations were interesting, when the

 

instructor pointed to the tacho, which had a yellow arc between 4200

 

and 4700 rpm, and said "Nein, nein", I got the idea.And

 

he was right!, after joining circuit I slowly reduced power and as the

 

engine came down through that rpm range, a very strong vibration ran

 

through the aircraft before he grabbed the throttle and closed it

 

quickly!Arthur.

 

 

[Guest TOSGcentral]

Hi Arthur,

 

I cannot comment on the 912 as I have very little to do with them but I can broaden discussion out to include the Jab 2200.

 

Recently the Brit Thruster factory had discovered cracking in the large web engine mount on the Thruster T600’s (which can have that engine equipped in UK). The cracking was attributed to probably a vibration band on the engine at about 2200 rpm.

 

Accordingly they produced an AD for inspections and advice not to

 

cruise in that rev range due to consequential damage to flywheel

 

mounting bolts and the crankshaft.

 

I put a copy of the AD in the TOSG Bulletin as we have a few J2200

 

engined Vision 600s in Oz and sent a copy to the RAAus Tech Manager.

 

But a few things are worth airing!

 

Vibration band range is common on a lot of types of engine but I have

 

not heard of them on either the R912 or J2200. You would have thought

 

this to be common knowledge with the amount of the engines there are

 

about!

 

Vibration bands are a nuisance as they usually occur at a rev range

 

where the engine is certainly working but is not especially loaded. A

 

particularly annoying one was on the Limbach 2000 engine of a Dimona

 

motor glider I flew a fair bit. The range was just at the spot where

 

you wanted to cruise the aircraft under power on cross country. Slower

 

and you were wasting time and fuel; faster and you got a very rough

 

ride cutting through the thermals.

 

Personally I would like to see RAAus Tech Air mandate the standard

 

colour arcs on ultralight tachos so we can get more education and

 

awareness out there!

 

With the Brolga I have always found them to be very smooth props which

 

is why I like them so much. So I would opine that your problem is in

 

the motor Arthur.

 

 

[Guest babs1aus]

Props How I love em.

 

Well they do keep you going forward. I to have found my Brolga a very reliable durable and smooth operating prop.

 

They are easily cared for and inspected. Providing you have quality tools. ( eg A torque wrench that works)

 

Anyway back to an interesting point about maybe it is the motor. We

 

have an associate that has spent a great deal of time on theories for a

 

similar sounding problem with a 912 and a different prop. Not knowing

 

the complete working of a 912 gear box is it possible for the output

 

shaft to be out of balance causing the vibration.

 

\kind Regards Brett Wright

 

 

[Admin]

(Posted on behalf of a guest)

 

It might help if you let us know how many hours the 912 has done..........

 

Gearboxes in a 912 only go around 1,000 before needing work if they are not cared for fully.

 

By cared for, I mean, by not being run continually at low RPM. Eg. Like

 

when a Rotax 503 "chatters" at low RPM because there is little wind

 

resistance on the blades to take up the slack in the gearbox; same with

 

the 912.

 

As an example, a Skyfox requires higher RPM to taxi because of the

 

tailwheel, whereas a Gazelle with 912 requires less because it "coasts"

 

well and as a result is usually run at very low RPM to slow the

 

aircraft down. This is detrimental to the 912's gearbox, but that being

 

said the 912 gearbox components are not particularly expensive. An

 

overhaul for parts only could range from $250 - $1000.

 

That being said I flew in a Gazelle last weekend that at 4,800rpm had

 

an airframe vibration and it was fitted with a 2 blade carbon warp

 

drive (illegal on a Gazelle)...

 

it's been there for the last 5 years with that parcicular propellor,

 

didn't vibrate with the timber prop and the gearbox has been overhauled

 

byt Bert Floods.

 

As for the output shaft being bent, anything is possible, especially on

 

a second hand engine that you don't know the full history of.

 

 

[barandbrew]

Hi

 

I have a two bladed Brolga prop on my Gazelle which runs much smoother

 

than the wooden prop that was on the aircraft however at 4800 rpm in

 

cruise I have noticed some vibration but its not there all the time I

 

had put it down to the prop unloading in gusts. Maybe there is another

 

reason if other people are having simular problems.

 

REgards

 

John

 

 

[Guest ozzie]

some possible causes and some suggestions

 

Have you checked your blades tracking?lazar pointers are great for this.

 

vibration may be caused by matching harmonics between prop, g/box and engine. try altering rpm +- 50 see what happens.

 

balance. if there is a rotary wing engineer on your airport next time

 

he is doing a tail rotor balance. sling him a few dollors or six pack

 

and do your prop. i did this on a 182 and ended up putting 6 penny

 

washers around one side of the spinner. took the rumble out of the old

 

jumpship on the way to hight. they do it with a strobe and stick on

 

reflector a bit like a wheel balancer but a bit more techie.

 

 

[Admin]

(posted on behalf of a guest)

 

Take care if you are fitting a Brolga Prop to your Gazelle... A Gazelle

 

is not legal if fitted with anything other than the original "all-size"

 

branded propellor. These propellors are now produced by Tony Kerr of

 

Gympie Aircraft Maintenance who bought the business several years ago.

 

Vibrations at different RPM ranges are not standard on the Brolga and

 

912 combination and can he inherited from the airframe as a Brolga on a

 

912 may not vibrate the same on a different aircraft.

 

If the aircraft is being operated on-line you should immediately remove

 

the propellor as you will not be covered by the $1m RA-Aus insurance

 

policy, nor any other policy that you may have taken out on your

 

aircraft or passengers. You may as well not be registered!

 

Sorry to be so blunt, however I have known of someone who got hauled

 

over the coals when his aircraft was involved in an accident with glass

 

non-standard prop!

 

 

[pylon500]

Given a choice between using the GSC prop supplied with the aircraft, or a Brolga, I'll take the Brolga!

 

 

[Guest micgrace]

Hi.

 

Should look up the problems at least three of us were inflicted with on a Gazelle under skyfox etc.

 

The solution was very simple, change prop. to carbon fibre but illegal.

 

Micgrace

 

 

[Guest TOSGcentral]

This is why a 'User Support Group' can be valuable!

 

Getting approval for a Brolga would be neither difficult nor expensive.

 

It requires an Engineering Order from a CAR 35 engineer and Daffyd

 

Llewellyn would knock one up quickly enough.

 

Using a support group as a focus Gazelle owners could each chip in a

 

few bucks each to get the E.O. and then lodge a copy with the RAAus

 

tech manager - job done and all legal!

 

I have gone down this track several times with now unobtainable parts

 

for Thrusters but have paid out of my own pocket and slowly get the

 

money back through low royalties. At least that is what I tell the wife

 

- but it is bloody slow!

 

 

[Guest danda]

You know as a fairly newcomer to ultralighting to get a lot of information on props is a little difficult to say the least.

 

I have the Super Diamond (love it) however I wondered how well it would go with a 3 blade brolga, it would seem that everyone I spoke to had a different opinion one friend told me that the only prop to put on was a sweet apple sounds good except I have no idea what a sweet apple is or where you get them from. Then yet another said “Bull S---“ I had a brolga on my plane and I wouldn’t put anything else.

 

You know for us just starting out it is hard to get a greater understanding of the finer points of propulsion if there is so many different options but gee its fun investigating all the facts.

 

So hear goes this little diamond of mine has a 503 in it goes ok however I was thinking of putting a 3 blade brolga prop on would it make any difference?

 

Don

 

 

[Guest joe]

Mate, a Sweetapple is a wooden prop designed & manufactured by Richard (Dick) Sweetapple who has his workshop at Capalaba in Brisbane QLD. Top bloke & world renowed to the best of my knowledge. I recently had my prop serviced by him & he was maticulious & knowledgable to say the least. highly recommended (i have the prop on a 503)

 

Dick'scontact no is 07 32452579; he does not have a website as he says he does not need one as he gets enough business by wordof mouth. he often gives presentations etc tolocal aviation groups SAAA etc.

 

all the best. cheers, Joe

 

 

[Paul Willett]

Related to this thread, and for my own interest and benefit, what is involved in balancing the carburettors on a 912?

 

 

[pylon500]

Re your prop for the Diamond.

 

While a well carved wooden prop (Sweetapple, Catto, Allsize, Prince, etc..) will be a nice, light and realatively inexpensive prop, once made, that's all you get.

 

In your situation, with a unique (at the moment) plane, finding the best pitch and diameter settings will take some trial and error.

 

As such a ground adjustable is probably better.

 

As the diamond is fairly low, you need a smalll diameter prop, this is where a three blader would help.

 

You would have to talk to Brolga about what small diameter they can provide.

 

That is not to say that the Brolga is the 'best' prop to buy, but they are a bit cheaper than any others in that class.

 

If money is no object (ha ha ha ha ) you could talk to Bolley or look at a 'Warp Drive', these can be trimmed to length (the Warps), where as other composites are usually hollow, and take a lot of work to modify. (best not to!)

 

Arthur.

 

 

[Guest danda]

I have found the contact number fpr Bolly but can anyone giv me the contact for Brolga

 

And Joe Thanks for the contact for sweepapple

 

Don

 

 

[pylon500]

Brolga Props C/-

 

AEROFIBRE INDUSTRIES PTY LTD

 

17 SWAN STREET

 

BEERWAH QUEENSLAND 4519

 

(07) 5494 6604

 

 

 

Arthur.

 

 

[Guest danda]

Thank you Arthur you are a welth of great information I trully APPRECIATE your kindness.

 

Don