Taildragger configuration question

[duncan_rtfm]

Hi,
I assume that the further aft the CG is from the main gear, the more difficult it will be to keep a tail dragger tracking straight down the runway, and vice-versa. Are there guidelines for this? Raymer suggests an angle of from 16 deg to 25 deg from the main gear to the CG.

My undercarriage can be swapped left/right to convert the Fleabike from a tricycle to a tail dragger, so I'm looking for some real-world experience from guys who have flown well-behaved tail draggers.

Any advice?

Duncan

[Old Koreelah]

Duncan I can’t comment on the ideal CoG, but ground handling would benefit if you can slightly toe-out the main wheels. 

[facthunter]

Work on Projected Distance from the CofG not  an angle of the leg. Use of brakes requires the wheels position to go further forward and the further you go the more directionally unstable it is..Nev

[kasper]

Duncan- I hate to disagree with other posters but I will for you.  
 

facthunter is not taking into account the unique operating regime of a flea - they CANNOT raise their tail in a takeoff/landing.  They will AlWAYS be in three point attitude right up to liftoff and immediately after touchdown.  
 

the limit with the flea layout with a front engine is one of not tipping onto its nose when you get out.  You will have your mains further forward than many will suggest for Ideal because it’s a weight criticality issue to have the tail wheel stay on the ground with the engine forward and your relatively large weight not in the seat.  
 

irs going to come down to angles and empty mass. Do your estimate weight n balance calcs for flight then redo them all for empty with the moment arms adjusted back to the landing attitude and determine where you need to put the mains to stay tail down. 
 

on the hm290fb Fred followed the plans and once it was complete there is a very close balance to nil.  In tail down there are a couple of kilos weight on the tail wheel.  Pick it up to level fuselage and the weight is nothing.  Tip it nose down a few degrees and you have to hold the tail down.

 

Ignore books of ideal angles - a tiny flea is limited by geometry and practically not having it tip on its nose when the seat is empty. 

Edited August 31, 2021 by kasper