Jab vibrations

[TechMan]

Just a thought, that if you are experiencing vibrations coming from the front of the aircraft, is to check the blade pitch on both blades of your Jab prop, as well as balance it. The prop angles must be within +/-0.2 degrees difference.

 

Chris

 

 

[Guest J430]

Chris,

 

+ or - 0.2 degrees from what?

 

Or do you mean 0.2 dgrees of each other?

 

J:thumb_up:

 

 

[TechMan]

+/- 0.2 degrees difference in blade angle to each other.

 

Chris

 

 

[jetboy]

A neat way to measure the pitch difference is by holding a laser pointer across the back of the blade at approx. 75% length so the beam shines on the floor. move next blade to same position and check beam shift on floor. I got 1" difference which equates to about 1.5 deg on a stock Jabiru prop (which is no longer in use)

 

Ralph

 

 

[motzartmerv]

Yea, just don't point the laser up at any aircraft... Saw on the news tonight some wankers targeted a rescue choppa ...i mean comon, there's dumb criminals and then theres just plain idiotic..

 

 

[TechMan]

A neat way to measure the pitch difference is by holding a laser pointer across the back of the blade at approx. 75% length so the beam shines on the floor. move next blade to same position and check beam shift on floor. I got 1" difference which equates to about 1.5 deg on a stock Jabiru prop (which is no longer in use)Ralph

Hi Ralph,

 

Did you notice vibrations on the aircraft when that props was in use, had it been damaged and repaired? What made you change props?

 

Thanks

 

Chris

 

 

[jetboy]

The Jabiru prop had no noticable vibration and was fitted new and run for 230 hrs with no damage no repairs black strip still intact with slight rain erosion and never run loose - just cleaned bugs off. I pulled it because the 701 needed a different prop to run properly.

 

I was about to fix the pitch differential and the tracking was out of tolerance also, both these errors could not be taken out by bolt torqing alone and I'd be reluctant to buy another for those reasons - I keep it as a spare. Its remotely possible that the pitch imbalance could have resulted in the poor performance, but I needed the extra diameter. I could see the difference between blades when flying with the sun behind - the lines were wobbly and divergent. New prop is by Brent Thompson and casts one sweeping curve - whatever that means it looks much sweeter to me. Engine is smooth as normal - both props showed some engine rocking around 1200 rpm, way less than a friends SK with new prop which i thought was so bad it was going to shake something off (actually it did - sheared his oil cooler rivets) he took it to a GA balancing place and they said it was OK - .09 IPS or something well I'm pleased he got a 2nd opinion but I won't be flying in it

 

Ralph

 

 

[Guest Fred Bear]

Another common vibration through the Jab dash could be the landing gear (wheels) spinning. I have experienced it and a quick tap of the brake should work. Avoid by applying brakes on climbout. Just don't forget to release them :ah_oh:

 

 

[Guest brentc]

I realised the imperfections in the Jab props a long time ago which is the reason why I changed to Carbon. I've heard of people going through 2 or 3 props to get one that is right with the same pitch on each blade.

 

Darren, your brake theory is brilliant until the front wheel starts spinning!

 

 

[Guest Fred Bear]

I realised the imperfections in the Jab props a long time ago which is the reason why I changed to Carbon. I've heard of people going through 2 or 3 props to get one that is right with the same pitch on each blade.Darren, your brake theory is brilliant until the front wheel starts spinning!

I have not had that one happen

 

 

[Deskpilot]

I was taught to dab the brakes once airborne and its surprising how much vibration disappears. I've never experienced vibs from the nose wheel. Can't explain why not.

 

 

[Guest ROM]

I have heard of front wheels spinning up in flight and causing a lot of vibration and all sorts of very worried reactions from the pilots until the cause was eventually worked out.

 

Have never experienced the front wheel vibration myself, possibly because I flew taildraggers almost exclusively for most of my GA power flying.

 

The worst wheel induced vibrations I ever experienced was in a Tiger which we were glider towing with a long time ago.

 

One of my fellow tuggies came down looking pretty white about the gills.

 

He claimed that the horizion and the instruments had disappeared in a blur just after lift off but it only lasted a few seconds.

 

General guffawing greeted this claim so yours truly did the next tow.

 

He was dead right! Just after lift off, the whole bloody aircraft just absolutely shook and vibrated and the horizon and instruments just dissolved into a blur for a few seconds.

 

It scared the hell out of me!

 

A short discussion and we decided to clean the mud out of the wheels.

 

End of problem to everybody's great relief and normal business was resumed.

 

 

[Guest Andys@coffs]

Adding green slime to prevent punctures is another fine way to have a back massage on take-off and landing in a jab.

 

The alternate approach of using 10ply tyres sounds good to me and is something I'll be chasing shortly.

 

Andy

 

 

[Guest ROM]

Andy, I have posted this elsewhere on the forum.

 

One of our guys has got some of the about 100 mm wide by about 10 mm thick firm sponge rubber stripping that is placed between concrete slabs to take up movement in the slabs.

 

You will often see this stuff between the blocks on footpaths.

 

A length of this very firm sponge rubber is placed right around the inside circumference of the standard Jab tyre and the tube is put back in as usual.

 

It has certainly stopped punctures from the bindii on our strip and costs almost nothing to get good puncture protection.

 

 

[Modest Pilot]

The Bearepaire guy at Narromine fixed my J230 "Burr Effected" tyre in much the same way, but used stuff call insertion rubber. It's the standard out West fix and very tuff.

 

100mm is fine any more and you risk chaffing the inner tube. I did the other tyres one at a time. I was worried about vibration, but turned out not a problem on the mains and needed over 60kt to start for the nosewheel; an area that you would not normally venture into.

 

Jabiru tried three props before a reasonable one was found. Tony Kerr's mob at Gympie measured it and it's not perfect (up to 1/2 deg pitch diff in some areas) but the results of the Dynmic Balance they completed just magic best couple hundred dollars ever spent.

 

 

[Guest Macnoz]

Good good good Vibrations?

 

 

Same topic different origin.

 

How m(any) of you experienced engine / fuel knock vibrations on the 2200 engine fitted with the tuning mod jets. I have just had an exchange engine fitted @ 404 hrs – read my post in the thread “did you r engine reach TBO”

 

Old carbie was retained – for ease of throttle etc fitting but new jets installed.

 

There is a noticeable vibration on full lean / full power and this was briefed to me by Jabiru, slight slacken off – maybe 50 / 75 RPM and it disappears.

 

My question to you is does it eventually ride up with wear as the old tailors used say?

 

 

[Modest Pilot]

More thoughts on props. I have a Sensenich Wooden prop on my other Jab powered aircraft. (Sonex). Hardwood but light with protection inlay. Beautifully made smooth running prop. Rod will approve them on all but the J160. The prop used on U S A Jab 250's is a bit underpitched so perhaps one should wait for Jab Aust. to recieve their shipment of some with a couple of inches more pitch. $A1400 plus GST. Not cheap but I don't think you could ship them yourself much cheaper. Depite the drawbacks I still think a well built wood prop runs smoother than a composite. The Sensenich is much more tolerant to rain than Hoop Pine; it's pretty well impossible to fly up here in QLD in summer without running into rain showers; so far so good with the Sonex.

 

 

[BigPete]

G'day Modest Pilot,

 

Did Rod say why he wouldn't OK it for the 160?

 

regards

 

 

[jetboy]

I doubt the vibration wiould wear in although I did see some wear on my needle / jet when last changed out for the revised economy tuning.

 

When you say full lean / full power do you really mean that? Should be leanest at around 2900 and richest at full power, not like the original jetting which was opposite.

 

So there is a possibility that with the prop load you have it is over rich or excessively lean at these settings, but more likely the air is uneven going into the carb, needing a cobra head and/ or straightener vanes. I'm posting a picture of these on the thread about this

 

Ralph

 

Good good good Vibrations?Same topic different origin.

 

How m(any) of you experienced engine / fuel knock vibrations on the 2200 engine fitted with the tuning mod jets. I have just had an exchange engine fitted @ 404 hrs – read my post in the thread “did you r engine reach TBOâ€

 

Old carbie was retained – for ease of throttle etc fitting but new jets installed.

 

There is a noticeable vibration on full lean / full power and this was briefed to me by Jabiru, slight slacken off – maybe 50 / 75 RPM and it disappears.

 

My question to you is does it eventually ride up with wear as the old tailors used say?

[Modest Pilot]

Cost; J160 is certified requires Reg 35 engineer. Factory built LSA don't.

 

 

[Guest J430]

Modest Pilot

 

Heard you this afternoon into GYMPIE as CM (ex 744 capt mate of yours) and I were into Noosa.

 

Hope you had a nice afternoon!

 

J