MurrJohnson

Hello Everyone

After being out of the pattern game for a few years I have recently been bitten by the bug...again. Once more things have changed with the current design of airframes.

I am specifically looking at the purchase of a BJ Craft Anthem. My question to you guys is what, if any, differences are there in performance and/or handling between the elliptical and swept wing versions. I will start with the FAI A25 Advanced schedule with a potential move-up to FAI P25.

I would also like to ask if there are any glaring advantages pertaining to a contra vs a single propeller setup. I really like the concept of simplicity and less weight of the single prop but could be swayed.

As always your opinions are valued.

Cheers

Murray Johnson

barnowljenx

I have been flying an Anthem swept wing.with a Debowski contra. Theory says that the swept wing is more stable in yaw. In practice, in comparison with my Element, the Anthem does seem to be more stable in the upline in yaw. An ellipitical wing does not possess the same yaw "stability" but gives an ideal lift distribution. IMHO, there is less difference between a single and contra prop but a bigger difference in airframe effect. For example, with the same contra (CRS) my Element was better than my Agenda. The Anthem was another step up from the Element albeit it had a different contra setup. I'm sure with a single prop it would be just as good. The only difference is that the rolling speed for a contra is the same either way whereas for a single prop the roll is slightly faster with torque than against it.

MurrJohnson

Thank you for your feedback.

Do you notice any yaw-roll couple with the swept wing? There are many references to "Dutch Roll" in the full scale world with swept wings. Wikipedia has a good description. I am curious to know if this trait carries over to the model world.

Interesting to note your comments on the contra drive. In essence was it worth installing or not so much?

Cheers

barnowljenx

There is a huge difference between the angle of sweep and the inertia and mass between an F3A model and an airliner size airframe - the type of aircraft most likely to suffer from Dutch Roll. I have not noticed this at all with the Anthem - the wing sweep is quite modest so even in full size I wouldn't expect Dutch roll to be a problem. The other problem with yaw/roll coupling is that most full size aircraft, apart from aerobatic machines, tend to have the entire fin/rudder above the centre line of the aircraft. Application of rudder will then always induce roll especially as most full size have dihedral. Our F3A designs have half the rudder area above and half below the fuselage centre line so yaw does not produce roll. With a swept wing any yaw induced by rudder is counteracted by the swept wing - at least that's the theory. For the Element, moving the CG aft eventually cured the roll/yaw /pitch issue. For the Anthem, I still have a small knife edge mix to prevent roll and pitch when flying KE. I have moved the CG to the neutral point but didn't like the way the aircraft felt so I have a slight push force needed when inverted.

I have to say that I rather like the sound of a contra and, certainly, with the Debowski TMCR, the power. I have recorded a maximum of 3,600 watts with the TMCR in a vertical climb starting at a very slow speed. The Hacker Q80 in my Citrin could only manage 2,850 watts in the same situation which is fine as the motor is rated at 2,800 watts. The other problem is that it is so quiet I cannot hear it in the air - probably means my high end hearing is shot as well! The contra at least gives some sound to throttle movement. I may well revert back to a single prop solution in due course as I think there is little that a contra has over a single prop.

MurrJohnson

Thank you for your comments barnowljenx. I had suspected as you have stated with the model vs full scale swept wing performance but had to ask. All your points are very valid and not to mention the huge difference in Reynolds numbers and relative wing loading. I have decided to go with the elliptical wing Anthem with single drive.

Cheers

barnowljenx

The other thing is that the sweep back is quite small for the Anthem(10-12 Deg) unlike the 30+ degs for most modern jet airliners and subsonic military aircraft.

Be interesting to hear your experiences with the elliptical wing in due course.

kevenoco

My Feedback: (1)

Barnowljenx,
Have you flown the Anthem with elliptical wing? How do you like it? I’m interested in it as well.

barnowljenx

Hi Kevenoco, no, I have not flown the Anthem with the elliptical wing. Quite frankly, unless you are in the top 50 in the World, then flying almost any good quality F3A airframe will be as good as any other provided you do 2 things. First, you trim the airframe so that it is as perfect as you can make it - not well that's OK but wow that's spot on now. Second, that you practice the right things until you are really good at flying the manoeuvre in a cross wind. You can chase a lot of different latest and greatest, including a contra, but if you don't do the above two things then you are not making the best use of the equipment you have. Once you are at that level, then you can start to pick up that one airframe is better than another. Till then, the pilot's skill, or level of practice, will be the determining factor. You cannot buy yourself a good performance - unfortunately.

UKpatternflyer

Hi,
Not sure where you are up to with the Elliptical Anthem. I haven’t flown the SB version but have had two trimming flights on the Anthem E. it looks and feels great. Very little mixing with CofG at the recommended point. This was a monoprop version using an R210 outrunner and 21x 12 prop. Motor aligned to the nose ring. Vertical up perfect, vertical down slight pull to canopy, which can be fixed with throttle to elevator mix, though may yet be dealt with by moving cg further back slightly. Rolls really well, very Epilogue like in its character.
Not sure if I’ll ever get another go with it but definitely recommend this for any level of pilot.
Thanks
Keith