Engine shudder at liftoff

[Peter T]

93 J has a shudder right at lift off that lasts a second or 2. Produces full manifold pressure and RPM and runs smoothly in all other phases of operation. I seem to remember reading something about something similar here but cannot find it. 

[Fly Boomer]

1 minute ago, Peter T said:

93 J has <engine> shudder right at lift off

Why do you think it's the engine?

[PT20J]

Are you sure it is the engine? An out of balance wheel can create a short vibration as it slows down through a resonant speed.

 

[Yetti]

Run baby jar test.   Have fuel servo rebuilt along with fuel divider and injectors.   Assuming you leaned for takeoff.   Our 300 ft airport had a DA of 2500 feet the other day.

[buddy]

Sounds like a wheel out of balance, that’s exactly the time your going to feel a vibration right after rotation.

[Guest]

Engine monitor data to check engine performance?  Although a tire issue sound more promising.

Clarence

[ArtVandelay]

To check if it’s a main wheel out of balance, next time tap the brakes as soon as you feel the vibration, if it stops immediately you’ll know its a main wheel.

[Peter T]

I thought that someone had a client with a twin where one engine shuddered and it was finally remideed with a certain brand engine shock mounts.

[MikeOH]

9 minutes ago, Peter T said:

I thought that someone had a client with a twin where one engine shuddered and it was finally remideed with a certain brand engine shock mounts.

I’d sure try ArtVandelay’s test waaay before going there!

[Shadrach]

2 hours ago, Peter T said:

I thought that someone had a client with a twin where one engine shuddered and it was finally remideed with a certain brand engine shock mounts.

That sounds like urban legend not reality.

Ask yourself, why an engine would vibrate at lift of? And then ask yourself why it would only last a few seconds? It is likely that what you are feeing is a wheel vibrating that was previously dampened by the ground.  If you are feeling it up front, it is likely the nose wheel but it could be the mains. If your quick on the brake, you might try a quick jab on lift off to see if that stops it.  If it does then you can alternate on the next take off to isolate the wheel. In any case, I would check all three wheels and bearings before further flight...

Edit: I see Mr. Vandelay beat me to it.

 

Oh and maybe hold off on the complete fuel system overhaul until after you've checked the obvious issues that make sense.

 

 

[jaylw314]

I suppose there could be a engine/prop vibration only at takeoff, since that's one of the few times you'd have prop p-factor at high power....

Then again, you could test that theory just by doing some power-on slow flight.  Chances are, it's the wheels anyway, though...

[jetdriven]

Do a flaps up takeoff get it up to about 85 or 90 miles an hour and then lift off and if the shudder  is worse you found your problem, and as other people said if you brake and it stops that’s your problem but we had this too and it was out of balance  tire

[Guest]

3 hours ago, Shadrach said:

That sounds like urban legend not reality.

Ask yourself, why an engine would vibrate at lift of? And then ask yourself why it would only last a few seconds? It is likely that what you are feeing is a wheel vibrating that was previously dampened by the ground.  If you are feeling it up front, it is likely the nose wheel but it could be the mains. If your quick on the brake, you might try a quick jab on lift off to see if that stops it.  If it does then you can alternate on the next take off to isolate the wheel. In any case, I would check all three wheels and bearings before further flight...

Edit: I see Mr. Vandelay beat me to it.

 

Oh and maybe hold off on the complete fuel system overhaul until after you've checked the obvious issues that make sense.

 

 

I’ve read before that Twin Comanches have been known to vibrate more with Barry Mounts than with Lord Mounts, but that was in cruise flight.

Clarence

[jetdriven]

I had a client who bought a twin commanche and it had two fresh engines, props, and new Barry mounts in it. The aircraft would resonate and shudder so bad you might think it was coming apart.  Lord mounts fixed it. 

[Peter T]

That is the post that I was looking for. Will check out wheel balance thoroughly. Thanks for the replies. 

[Shadrach]

4 hours ago, M20Doc said:

I’ve read before that Twin Comanches have been known to vibrate more with Barry Mounts than with Lord Mounts, but that was in cruise flight.

Clarence

Perhaps that’s true, but a two second vibration upon lift off that quickly resolves does not read like a motor mount issue.