Nameless V-tail -> 1 Sheet, V-tail 'stick' build as light as possible (Build Log)

[JasonK]

I checked my CG setup with the cgCalc
https://www.ecalc.ch/cgcalc.php?dee...75;0;0;0;0;2.5;0;0;0;.75;5.25;0;0;0;14;25;10;

photo shows were I had my CG (approx at the holes) and the lines are were the cgCalc says were my CG should be (way farther back) I tried test tosses without the battery which puts the CG between the indicated locations and were I have it and it glided great. The cgCalc also has my stability higher then that of a trainer, so If I am understanding this correctly, I have way more tail then needed (does that sound correct?).

At this point to get my CG between the 2 recommended marks from cgCalc, I would need to mount my battery behind the CG (or at least overlapping it).

 

[Sero]

I checked my CG setup with the cgCalc
https://www.ecalc.ch/cgcalc.php?dee...75;0;0;0;0;2.5;0;0;0;.75;5.25;0;0;0;14;25;10;

photo shows were I had my CG (approx at the holes) and the lines are were the cgCalc says were my CG should be (way farther back) I tried test tosses without the battery which puts the CG between the indicated locations and were I have it and it glided great. The cgCalc also has my stability higher then that of a trainer, so If I am understanding this correctly, I have way more tail then needed (does that sound correct?).

At this point to get my CG between the 2 recommended marks from cgCalc, I would need to mount my battery behind the CG (or at least overlapping it).

View attachment 172659

As a general rule of thumb, a regular tail surface area is 20-30% of wing area for the horizontal and 10-15% for vertical. For a v-tail I believe the surface area should be comparable to a regular tail, but I'm not 100% sure on that. Regardless you should be in the ball park.
In the video your plane looked quite agile but the tail will have more authority with it being nose heavy.
Moving the CG back and trimming it to compensate should help with the harsh climb.

 

[JasonK]

per the calculator:
Wing Area: 147.25 in²
Tail Area: 49.88 in²
which puts me at 33.9% effective horizontal stabilizer area. I am going to first work with the CG as it is the easiest to test (and easiest to revert) and see what it does.

 

[Sero]

per the calculator:
Wing Area: 147.25 in²
Tail Area: 49.88 in²
which puts me at 33.9% effective horizontal stabilizer area. I am going to first work with the CG as it is the easiest to test (and easiest to revert) and see what it does.

When I researched V-tail plane (was going to build one but I never did) I believe I read that you combine the vertical and horizontal surface area of a regular tail to get your V-tail surface area, which would give you 30-45%, so you're with-in spec if that theory is correct.

https://www.wattflyer.com/forums/sh...f you have a successful,of your V-tail panels.


I agree, play with CG first.

 

[JasonK]

When I researched V-tail plane (was going to build one but I never did) I believe I read that you combine the vertical and horizontal surface area of a regular tail to get your V-tail surface area, which would give you 30-45%, so you're with-in spec if that theory is correct.

https://www.wattflyer.com/forums/showthread.php?t=65215#:~:text=If you have a successful,of your V-tail panels.


I agree, play with CG first.

that is the 2D projection of the tail onto the horizontal plane that I was using there, just like the calculator asked me to.

 

[JasonK]

I moved the CG back to the indicated location (or as close as I could reasonable get it) based on the calculator. Got the plane up in the air today, it flew fairly good. Still had a some nose up tendencies when under power - unfortunately the location I was at didn't give me the space to get it level and trimmed under power to test speed + cut of motor. It definitely didn't take as much down pressure to keep it level when flying, still had very good control over the plane.

It did seem to get a possible new issue... the plane's glide wasn't quite as clean as before, I had to keep the nose down slightly to keep it from stalling and when I was coming in for a landing, I dropped one of the wing tips (I am still trying to remember to use the rudder at slow speeds to turn) coming in and the wing tip just dropped right out from under the plane - I think the wing stalled. It was fairly close to the ground and just came down and somersaulted slightly.


My re-maiden flight after the changes. Unfortunately the 'closest' park [which is still ~30 minutes] to me is fairly close to the beach and the wind always seems to be coming from the same direction as the sun. I don't know that there is anything useful in the video that would tell you anything about the balance/etc, other then that stall when I was coming in to land (my electronics hatch had came open, so I was coming in to land and it seems to have stalled.

 

[Sero]

With CG changes you'll need elevator trim before anything. Trim it out at 50% throttle and see how it reacts at full throttle and glide, from there you can decide what other changes need to be done if any.

 

[JasonK]

yup, that makes sense, big issue was were I was at, I couldn't get a straight line at 50% long enough to try to trim (at least at how fast I can trim). will definitely try that next. I think I still need down trim, just less then before moving the CG.

 

[JasonK]

I got back out with the changes at the air field. After multiple passes got it trimmed fairly good (down trim) at 50% throttle, however more throttle still goes up and cutting it now noses down. I can fly it upside down now, but it takes more down elevatator then I expected (probably at the 1/2 point between neutral and full down) when upside down). Was rather happy with over all - could do some really nice smooth lines/circuits, still did very tight loops and rolls, etc.

 

[JasonK]

well, the Vtail lived a wonderful life while it was working, but a bad crash from me (that I mostly repaired) and then a further crash from my son has made the tail boom so weak that it is questionably fixable at this time. It was a great LOS flying plane, but I am working on some other ideas now and am not likely to rebuild this again.