Elliptical Vs Swept Wing
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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
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
#2


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
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
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.
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apereira (09-11-2023)
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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
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
Last edited by MurrJohnson; 09-03-2023 at 07:15 AM.
#4


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.
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.
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apereira (09-11-2023)
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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
Cheers
#6


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