HI all, how many would agree that a badly designed jet that porpoises on landing is caused by a scale tail ( too small, no 15% increase) or by the elevator getting blocked out.
Thanks in advance.
Rcpete

on touch down? Can also be a nose strut with a spring rate that is to "bouncy. I have flown a lot of planes with inconsistent approach due to dirty air and/or downwash over the tail. Very frustrating. A slight difference in speed can make a big difference in pitch force. I usually have to reduce flap angle. I haven't noticed any pattern relating to tail size.

Agree with Brad. I am not aware of anyone who makes noseleg struts, everyone uses a main leg strut with a spring rate and pre-tension suited to the weight put on a main leg. The result is a noseleg with a higher frequency than the main legs, often so hard as to have no give at all, and the result is a bouncing nose while the main legs are going downwards, which pitches the plane back up again. I have altered the springs in all of mine and it makes a difference.

Hi Pete
Just sell that thing and stop beating around the bush, you know what to buy.
Chuck

I can't speak to the areas you've mentioned, but on the two jets I've owned, that displayed that tendency, reducing the amount of landing flap cured the problem. Seems that getting rid of excess lift had a positive effect. Once it was down, it stayed down.

David S

In my experience, full scale and models, a porpoise is caused by poor technique of touching the nose gear first.

Make sure the nose gear strut is not too long. If the nose gear touches before the mains, then the dreaded porpoise is likely to occur.

Mike Danchak

HI all, just to clear my question, the porpoise is in the air on final. When the best Pilot in the world has trouble landing a *#!*^ and he has to land on the low of the porpoise, I think their is a design problem or like David says, reduce the flaps.
I was also thinking, the flaps
Rcpete
PS. on the ground, it is called the Kangeroo Hop

HI Chuck, not everyone has a fountain of cash.
Rcpete

I once had a large Mustang that had flap servos that were not up to the job and they moved depending on approach speed. It made for very inconsistent landings....

That can be caused by a lot of things besides design, technique, speed during the touch-down, flaps, CG, struts, type of tires, tons of stuff.

don"t you just like a guy that has a answer to everything, must be a politician.
Rcpete

Pete:

If the jet porpoises in the air only on final near the pavement then it must be "ground effect" and some interaction with some airfoil (like flaps, etc. as others have suggested and maybe airspeed) . If flaps were the issue, I would think the only way to be sure would be to land with varying degree of flaps to see if that cures the problem.

Nick

Pete I had a jet that did that, never got it fixed. Sold the jet. The only thing that helped was, if you could get it in the right angle of attack then do not move the elevator.