DA 170 shakes

[jamesrxx951]

Instead of continuing off topic on the other DA thread http://giantscalenews.com/forum/showthread.php?1011-DA-1-Customer-Service I figure I would continue on a new one. My 09 170 really shakes my plane in my opinion. There have been several vibration related repairs done already on a plane with just under 100 flights on it. The JR8911 servos are still in great shape and has the expected back lash of a JR servo and not deemed excessive at all. In fact in the video (which the volume seems really amplified) I am tapping on the ailerons (sounds like im beating on them) just to show they do not jidder and are rock solid. This engine has been rock solid over the years and no engine related problems at all. However the vibrations are really worrying me to the point of possibly selling it off. I don't know if the RE3's have anything to do with it but I really like the power of them. 14" headers by the way. The low end is leaned out to the point that I need to warm it up before it will transition. It has all the updates to the best of my knowledge. It was sent in to them about 2 years ago. Any suggestions on correcting this would be appreciated.



https://www.youtube.com/watch?v=hzrGdMDdCsw

 

[mbacosa]

I have the same airframe but with a DA-150 on Jtec pipes. Mine shakes just as bad. I honesty feel that it is the nature of the airframe itself. It it is built very light (even in the motor box area) I have toyed with the idea of really cross bracing the fuse from the motor box back to see if I couldn't make it more rigid but I haven't tried it yet. Honesty I have thought about upgrading to a 170 but I was worried about it being too much vibration for the air frame. The only repair I have had to make is to the top cowl center cowl mount.

 

[IMAC FANATIC]

Ive heard that re3's require servicing after a few years/seasons to remove any carbon back up on the baffles, robs power and causes back pressure requiring leaning of carb.

Maybe a back plate behing firewall to spread the load is remedy, white rose i think,was for me.went through 2 mufflers before I stopped the shaking. Also replaced the bolts/ nuts, oversized washers, because they would back off slightly no matter how much thread lock or tightening. Using a vess balancer ring also. Still shakes my elevators more than I like but calmed it down quite a bit.

 

[jamesrxx951]

http://whiteroseeng.com/products/rst.html I assume the plate on this page is what you are referring to? If so thank you for the information and my have to pick one up.

 

[IMAC FANATIC]

Thats the one, use the backplate together with the zero degree or 2 degree firewall depending on your thrust and spinner gap it'll calm down alot. Ties the whole thing together quite well. Im sure youve balanced your prop two ways also.

Lil triangle stock or carbon cloth to inside motor box couldnt hurt either. Problem is. .. you strenghten the motor box and then you find the rest of the weak areas in the airframe. Im not familiar with yours, I have a comp arf , but ive noticed some diagonal stringers added in a few of those sukhois at field.

Also, putting the 3 blade took the rest of my vibration issues away.but thats an expensive fix if you dont have one already. Hope it helps, keep us posted on the good news... or bad.

 

[IMAC FANATIC]

Forgot to mention.. have you ever seen the chip hyde soft mounts? Like to have one someday, heavy but makes good sense.you tube em', kinda cool.

 

[jamesrxx951]

IMAC FANATIC;19988 wrote: Forgot to mention.. have you ever seen the chip hyde soft mounts? Like to have one someday, heavy but makes good sense.you tube em', kinda cool.

There is a thread on the IMAC website forum about them with the 170's. I love the idea but it would require me to cut back the engine box. The engine bolts directly to the motor box and the hub is already out quite a bit.

 

[jamesrxx951]

IMAC FANATIC;19987 wrote: Thats the one, use the backplate together with the zero degree or 2 degree firewall depending on your thrust and spinner gap it'll calm down alot. Ties the whole thing together quite well. Im sure youve balanced your prop two ways also.

Lil triangle stock or carbon cloth to inside motor box couldnt hurt either. Problem is. .. you strenghten the motor box and then you find the rest of the weak areas in the airframe. Im not familiar with yours, I have a comp arf , but ive noticed some diagonal stringers added in a few of those sukhois at field.

Also, putting the 3 blade took the rest of my vibration issues away.but thats an expensive fix if you dont have one already. Hope it helps, keep us posted on the good news... or bad.

There was another post about beefing up the motor box. I think I will give that a try and see how that works. Keeping my fingers crossed on that idea.

 

[Vern.Smith]

Pardon me for butting in on this thread but I might be able to shed some light on the vibration issue. Nothing really dampens cyclical vibration like mass. Unfortunately mass and light weight are difficult to achieve together. Since we need to keep our airframes as light as possible the next best thing we can do is to get the power pulses from the engine to the center of whatever amount of mass we have with minimal distortion on the way. Beefing up the motor box is half of it but the section of fuselage from the firewall to the wing tube is just as important.



Soft mounts like the Hyde mount and some of the beautifully made systems I have seen pictured on European GS planes work well but the price you pay is power (torque) loss. When the piston is driven down by combustion this energy is transferred into the crankshaft/propeller and ideally you want all of it to go into the propeller. Keep in mind that engines can be made were the crankshaft is bolted to the firewall and the entire engine with an attached prop rotates. There were engines on WWI fighters with this type engine. The point of all this is the engine is just as happy to turn as the prop is and is only restrained from doing so by the firewall. Any soft type mount by nature allows some of the combustion energy to be transferred into the vibration absorbing mechanism with a direct resultant loss in the amount of energy devoted to the propeller.



Unfortunately there is no free lunch. The best way to stiffen the motor box as well as the fuselage area from the wing tube to the firewall is diagonal cross bracing they moves from former to former in a top right to bottom left fashion. Of course this complicates the hell out of installing things like fuel tanks, etc. You can also throw the quarter inch thick marine plywood at it but now we are back to adding substantial amounts of mass. Half to three quarter inch square hard balsa seems to be the best compromise unless you really want to get exotic and expensive and go with some of the super thin super expensive CF tubing.



I'm sure there will be a physicists in the crowd that will scream about my simplistic explanations but this works.



Vern Smith

White Rose Engineering

 

[DATech]

All of the above.