Desert Aircraft vibes

[CatalinaWOW]

Full scale aircraft designers spend quite a bit of time tuning designs so that airframe natural frequencies don't match sources of vibration (engines, wing vortexes, etc.). It isn't surprising that moving an engine from one airframe to another changes results. Since few, if any, of us have the resources to measure all of this and predict results, building a database here of combinations that work either well or badly might be really beneficial.

 

[49dimes]

Full scale aircraft designers spend quite a bit of time tuning designs so that airframe natural frequencies don't match sources of vibration (engines, wing vortexes, etc.). It isn't surprising that moving an engine from one airframe to another changes results. Since few, if any, of us have the resources to measure all of this and predict results, building a database here of combinations that work either well or badly might be really beneficial.

Really like your thinking on this. I think you just may have NAILED it.

 

[3D-Joy]

Lighter airframes shake more than heavier ones.
Transferring all that vibration to the wings will dampen it quite a bit.
The Beast is light and also has extremely light wings which don't do much to absorb vibrations. I have yet to see a Beast that does not vibrate like crazy. I have yet to see a comp-arf (or similar) vibrate too much. Composite planes have dome type motor box which is crazy strong and also quite heavy wings due to their composite construction.

 

[stangflyer]

The thing that really confuses me the most about the vibration mystery is that the mystery in itself really is never consistent. Example, Three identical airframes from the same exact manufacturer setup precisely the same in exact detail. One is fairly smooth, one is "VERY" smooth with nearly no shake or vibration. The final third one has more vibration than the previous two combined. Not sure if anyone else has noted this, but something we discovered last summer. Makes ya go hummm....????

 

[ExtraNuts]

Mabey prop balance vibration or just that different props were used as no 2 are actually totally identical since I think they are hand finished.?? Slight difference in timing, compression?? Mabey more or less glue in the airframe?? hmmm....????

 

[ExtraNuts]

I wonder if the vibration is the same in the air as on the ground? I cant recall any of my planes shaking noticably while in the air..... even the ones that shook bad on the ground.

 

[Ohio AV8TOR]

Flying yesterday with Herve and his DA120 Edge and in low harriers I could still see the wheel pants shaking on the low side of throttle bursts.

 

[stangflyer]

Mabey prop balance vibration or just that different props were used as no 2 are actually totally identical since I think they are hand finished.?? Slight difference in timing, compression?? Mabey more or less glue in the airframe?? hmmm....????

Hmm...now that you mention it, you might have something there. All three using exact same props. Falcon CF 23x8. As we all know, Falcons are pre-balanced before they are shipped. But I still check them to be sure. So probably not the issue. But.... (and here's the good stuff) The smoothest running one, least amount of time with Bowman ring. Next best one... a little more time with Bowman. The least smooth one? Massive compression like a 3w and about eight gallons through it. Needless to say, it runs like a scalded dog.

 

[Spats]

I am not an engineer but I would think the shaking in the air would be more than on the ground since no one is holding the plane for support absorbing some of the vibration.

 

[bigblueswope]

I am not an engineer...

But did you stay in a Holiday Inn Express last night?


BJ Swope