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FT Racer Narrow Fuse/Speed wing

#41
No this does not sound like flutter, but it does sound like dutch roll. I have had bad luck with the tip plates you are using personally. They are not going to help the dutch roll since they are not aft of the center of lift. Purely drooped tips have helped my previous efforts but I think your fix might be a dorsal fin (see cessna 172 vertical stab) or a ventral fin or fins (see Citation XLS or Citation Latitude) these may help the stability and control.

All of these installations were to reduce dutch roll or yaw issues. The dorsal fin is the easy one the ventrals need to be angled so as to not cause pitch issues.

Once agin just thoughts on things to try.

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Thanks Jeff!

Yes my research had shown a ventral fin should help and probably is the easiest fix to try. I noticed the single fin like on the MIG-23 and various others vs double fins such as the Citations you posted. To keep things simple I was planning on trying the single fin. Are the double fins that much more effective and do you know why they are cambered out?

Steve
 
#42
So I ran a few more packs yesterday, I forgot my Gopro to record the flights to hopefully get a closer look at the wobble. But I'm sure its Dutch roll.
Another thing I noticed at moderate speeds I can't do a loop, as soon as the nose is vertical the plane starts rolling. I do remember my previous Racer doing this too but not as extreme as this one. Could be to do with the extra weight of the air frame and large motor. Perhaps I'll just have to use a little left aileron. At high speeds it rolls fine.
I put a EFxtra 7x6.5 prop on it and it certainly is faster. On the maiden with the 7x6 prop I only hit full power for 2-3 seconds, this time I held it for longer periods and it seemed quite a bit faster.
My maiden landing was much better than my last 2. Flaps are definitely needed, on one of them I thought I dropped them but I hadn't and man did it come in fast.

This plane performs spectacular at high speeds, it tracks so straight and is such a blast to fly. None of the above issues are present at 60-100% power. The last flight I used a 2500mah 4s and the flight was about 3 minutes at hight power settings. It came down at 3.7volts per cell.
 

jfaleo1

Junior Member
#43
Thanks Jeff!

Yes my research had shown a ventral fin should help and probably is the easiest fix to try. I noticed the single fin like on the MIG-23 and various others vs double fins such as the Citations you posted. To keep things simple I was planning on trying the single fin. Are the double fins that much more effective and do you know why they are cambered out?

Steve
In the case of the citations at least a centerline ventral fin was “blanketed” by the fuselage. Putting them to the sides is more effective. It has proven out many times on fuselages that slope upward at the tail. Beech King Airs had center fins for years and needed yaw dampers. With the newer left and right ventral fins it is no longer required to have a yaw damper.

If your issues are mostly low speed it is very much like the Citation XLS.

I would actually try the dorsal extension myself but a center ventral fin should work well on this airframe.

Just got the point of reference. I am a citation maintenance instructor on the Citation X and Latitude and had years of experience on King Airs as well.
 
#44
In the case of the citations at least a centerline ventral fin was “blanketed” by the fuselage. Putting them to the sides is more effective. It has proven out many times on fuselages that slope upward at the tail. Beech King Airs had center fins for years and needed yaw dampers. With the newer left and right ventral fins it is no longer required to have a yaw damper.

If your issues are mostly low speed it is very much like the Citation XLS.

I would actually try the dorsal extension myself but a center ventral fin should work well on this airframe.

Just got the point of reference. I am a citation maintenance instructor on the Citation X and Latitude and had years of experience on King Airs as well.
Thanks for the advise Jeff! it all makes sense.

Unfortunately I will have to try a dorsal extension and ventral fin on V2 of this plane. I managed to lawn dart it.:confused:
 
#45
So V2 will be coming soon, I pulled on the elevator too much on the down slope of a loop and the plane snap rolled and went out of sight behind some trees with a good thunk sound.
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The nose and leading edge foam are complete mush. way too soft to do anything with. The part that bothers me is that the motor bearings are now shot since it it nose first. I found new bearings but the cost is the same as a new motor. Anybody have a source on good ceramic bearings?

So on V2 I'll be making some changes:
- Wing will not be removable, just faster to make.
- Servos will be on top of wing.
- Redesign the spar so it follows the leading edge rather than the trailing edge, hoping for a more consistent airfoil and make it thinner.
- Reduce the dihedral, or perhaps eliminate it?
- Adding a dorsal extension and a ventral fin.

Certainly open to any suggestion or ideas. Let me know.

Steve
 

Arcfyre

Well-known member
#47
Sorry about the crash, extra sorry that your motor was damaged.

The downside of building fast stuff is that when it crashed, it's usually totaled. I just smashed an arrow into itty bitty pieces last week, so I feel your pain.
 
#48
Sorry about the crash. Regarding the bearings: For starters, make sure that you don't have a bent prop adapter or a bent motor shaft. It's possible that the bearings are fine and you've just bent the shaft.

Those Propdrive motors should be fine with any decent shielded steel bearing. What size bearings does that motor take? The more common sizes can be had from Innov8tive designs (US distributor of Cobra and Scorpion motors, https://innov8tivedesigns.com/parts/motor-parts?cat=53) or GetFPV (https://www.getfpv.com/motors/accessories-and-parts.html). For the less common sizes, search on eBay for the bearing size under the "Toys and Hobbies" category.
 
#49
Sorry about the crash, extra sorry that your motor was damaged.

The downside of building fast stuff is that when it crashed, it's usually totaled. I just smashed an arrow into itty bitty pieces last week, so I feel your pain.
Yes either fast or heavy, their going to get damaged when they hit the ground. its all part of the hobby. Luckily I enjoy building too.
 
#50
Sorry about the crash. Regarding the bearings: For starters, make sure that you don't have a bent prop adapter or a bent motor shaft. It's possible that the bearings are fine and you've just bent the shaft.

Those Propdrive motors should be fine with any decent shielded steel bearing. What size bearings does that motor take? The more common sizes can be had from Innov8tive designs (US distributor of Cobra and Scorpion motors, https://innov8tivedesigns.com/parts/motor-parts?cat=53) or GetFPV (https://www.getfpv.com/motors/accessories-and-parts.html). For the less common sizes, search on eBay for the bearing size under the "Toys and Hobbies" category.

Thanks! I was questioning if ceramic bearings were really necessary, I doubt that the motors come equipped with them.
The size I needed is 5x8x2.5mm which neither of those sites seemed to have, but lots on e-bay. Turns out Traxxus PN 5114 is the same size and the LHS had those. 2 in the package for $4, put it in and its now quiet. Not sure what these bearings were for so we'll see how they handle the higher rpms of a brushed motor.