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Samuel117

Drifter Shake up!

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Hi every one, Happy new Drifter owner with a problem.

 

My Drifter is an AustFlight Drifter modified with a Rotax 912. Beautiful job done by the previous owner, the problem very subtle while flying!

 

Caught with help from the Go-Pro camera. on start and while the engine is cold and at idle the engine vibrates a bit and the engine bangs the air filters from both carburators on the flaps lever that are very close to the engine, only noticeable while starting and turning off the engine gives airplane vibrations. When reviewing the videos from the flight I found vibrations that at first I blame the poor camera and changed the position to the right side and then struck me that this subtle issue it is not so simple and at the last approach of this flight while decreasing RPM it looks really bad on video. the airplane loves to fly around 50 and more power and power changes while flying gives a very "mild" vibration.

 

1- I would not fly it again until I modify somehow the flap lever or even to get rid of a Fancy pair of flaps!

 

2- lucky me this shaking did not developed in to a Flutter with the result of me going prematurely to the ranks of "The 1000 miles high Drifter rider's club". I look forward to join but still would like to enjoy earth for a little longer if I can.

 

3- I am posting the video for your review. Consider that during the editing the computer slows down the vibrations and it looks better than the raw video.

 

thank you and every input about how difficult this task will be will be appreciated.

 

Sam

 

 

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Hi Sam! Excuse my ignorance! I wasn`t aware that the Austflight SB Drifter was ever fitted with a Rotax912.

 

One thing you can do without much trobule is to tighten your rear seat belt so that it doesn`t flap about.

 

Frank.

 

 

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Hi Sam! Excuse my ignorance! I wasn`t aware that the Austflight SB Drifter was ever fitted with a Rotax912.

One thing you can do without much trobule is to tighten your rear seat belt so that it doesn`t flap about.

 

Frank.

Farri, it's the one Justin Hawkins converted. Read about it here: http://www.recreationalflying.com/threads/converting-sb582-to-912uls.49166/

 

 

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In my note I mentioned it is a "modified" Austflight Drifter and thank you for your recommendation about the seat belt. Your right about that.

 

 

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Samuel the problem with using a camera (and I assume it is digital) is that you will get interference from the engine and vibrations that distort the video...usually comes in waves.... then also, how do you know that the movement is not actually in the camera mount and strut.

 

Looking at what I think is the 'shaking I think you are talking about (looks like the wing it self moving back and forward) this might explain it. You will also always get some sort of harmonic resonance at different RPM that will cause vibrations, some worse than others whether 503 582 or 912. You need to be satisfied about it though just making some observations AND Of course hard to tell from the other side of the world!

 

 

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Hi Tex,

 

Thank you for the nice video and yes there are vibrations in your video. while I was starting the engine last time there was a terrible bout of shaking that actually made me do a preflight again, then there are the deep indentations marks on the air filters in both sides against the actuator of the flaps. I have to lower the flaps before I start to mitigate it, these vibrations of the engine with changes of power settings should be absorbed normally by the airframe but I am not so sure this banging on the flaps would cause even failure of the bolts that attach the wing. I have to admit my experience with full scale airplanes is very limited but, with my extensive experience with RC models I have run across episodes in which a loose or vibrating engine or a loose connection of the tail plane caused a flutter on flight and it is so crazy it looks like an explosion with sudden destruction of the model. I love how this airplane flys and I would like to fly it without the fear of the thing coming apart without my input. I'll check for pieces of the video that shows this I have describe. I will check again the bolts that hold the engine and try to make a plan to see what I could do to stop the banging from happening in the first place. I have other videos in which the shaking in flight make you think it is a helicopter and not a sweet Drifter. thank you again and I hope you are completely right about it.

 

 

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You will also get what is often described as the "Drifter Waffle" at certain angles of attack, especially in climb I have found, when the air over the wing and then into the empannage cause the aircraft to get a real wobble coming through from the tail... I don't recommend looking back... as when you see jut how much the tail is wobbling around it is quite disconcerting!! 022_wink.gif.2137519eeebfc3acb3315da062b6b1c1.gif

 

If it is just the air filters hitting as you seem to be describing... perhaps a different shape of brand of air filter will fit better?

 

 

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Hi Tex,

 

Oh!! I ate that "waffle" already and yes it is quite an eye opener ! Great to hear that it is something associated with the design. I have being wondering if it was my fault when I put the tail back together even when there is good tension on the wires. You are absolutely right and this could be the easy fix that I have being praying for. I will look for a different shape of air filters, a more tubular design as the ones the rotax has are actually quite bulky. In any case I could maybe fly the airplane to your home base for a quick look over! 080_plane.gif.36548049f8f1bc4c332462aa4f981ffb.gif002_wave.gif.62d5c7a07e46b2ae47f4cd2e61a0c301.gif. Thank you again.

 

 

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Sure bring it over would love to have a look at it, you would break some records on the way! 011_clap.gif.c796ec930025ef6b94efb6b089d30b16.gif

 

 

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One of the first things I was taught on a Drifter, is to set the rpm at a fast idle immediately after starting, to the spot where it smooths out, let it warm up there. Never let it sit on the idle stop, shaking like a bastard.

 

 

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M61A1, That is a good point. I have being doing that out of necessity. Really on start if you don't do it that way it really look like it wants to destroy itself but was not sure it was proper way to treat the engine. Question:

 

How to know when the horizontal stabilator is tight enough. They told me to turn the upper wires three three complete revolutions before connecting them but how tense it should be. IMO my tail does not have enough tension but I am afraid to increase the tension and to crush the thing! Any advise about how you do it?

 

Thank you for your help guys.

 

 

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M61A1, That is a good point. I have being doing that out of necessity. Really on start if you don't do it that way it really look like it wants to destroy itself but was not sure it was proper way to treat the engine. Question:How to know when the horizontal stabilator is tight enough. They told me to turn the upper wires three three complete revolutions before connecting them but how tense it should be. IMO my tail does not have enough tension but I am afraid to increase the tension and to crush the thing! Any advise about how you do it?

 

Thank you for your help guys.

According to the manual, the wires should strike a low bass note when plucked. Additionally, if you can get the nut on the bolt you' re not going to crush anything.

 

 

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Oh, definitely I need to retention the tail!Thank you very much.

I should be clearer there, you can re-tension the cables by twisting them in the direction of the existing twist, until you can just get them on the bolts. Do not just tighten the bolts in an effort to tighten the cables.

 

There are limits as to how much you should twist your cables, I cannot remember just what they are.

 

When adjusting, it helps also to have some sort of inclinometer, so that you set it up all square and true, it can get a little fiddly, but worth the effort.

 

 

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Thank you for your help. I will try it on saturday and will get ahold of an inclinometer to try and do it right. I will let you know of the results

 

 

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Sam, I can help here------002_wave.gif.62d5c7a07e46b2ae47f4cd2e61a0c301.gif

 

Here's the start procedure:

 

Lower flaps

 

fuel pump on

 

full throttle

 

hold prime switch on for 8-10 seconds. When you release the prime switch, fuel pressure will increase slightly.

 

Throttle Idle, then crack open a bit

 

Start

 

Verify oil pressure in green

 

Immediately set RPM higher, around 2000-2200 for 1-2 minutes, then close throttle and it will idle smoothly. If the engine starts shaking and won't immediately build rpm right away, close the throttle and it'll shut off. This happens when the start sequence isn't quite right and it's pretty much unrecoverable. Try again with more primer and maybe a touch more throttle.

 

fuel pump off

 

This will minimize or eliminate the shaking on startup. Once the engine is warm, it'll idle very smoothly down to 1500rpm. It's not really an issue with the install, it's an inherent trait of the 912s, made worse by the unavoidable install design (no conventional firewall / mount. In flight, it's always been SUPER smooth, so if it's not, there may be another issue.

 

MAN, I miss that airplane. So sorry I've delayed sending your other stuff, I promise to get it in the mail ASAP

 

Justin

 

 

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Hi Justin. Thank you for your help. if the weather holds tomorrow morning i will try the proper way to start the drifter. I have nothing but good things to say about your airplane and you have my respect for the great job you did with the modifications. Thank you again and I'll post a small video on this site so you can enjoy the airplane until you decide to come to Miami and fly it again.

 

 

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Hi Justin. Thank you for the tips about starting the 912. I have nothing but good things to say about your help with the airplane. Really grateful. I posted a short video last night. Come to fly the Drifter any time.

 

 

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