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May 24, 2018, 08:33 PM
Disaster magnet
Well, I just got back from the test flight. The first few two flights did not really go well, it just seemed really twitchy and awful. Fortunately, I managed to land both times without too much damage. The third flight I had a feel for what to expect, and it flew for about two minutes before I tried to land it (I didn't have a voltmeter on it).

So all in all, I'm pretty happy with it, but it really seems to be exhibiting all the symptoms of tail-heaviness - twitchy, overreacting motions, always a bit tipped backwards, and always wanting to roll to one side or the other, seemingly on its own. I tried adding tail ballast to a sim plane, and it seemed to have somewhat similar issues, though without the random rolling part. Should I move the battery forward?

I did have someone take a video of two of the flights (of course they were the two flights that didn't work very well.......) and will try to upload them once I figure out how. Do I need a youtube account, or will dropbox work?
Last edited by Chelonian; May 24, 2018 at 08:46 PM.
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May 24, 2018, 08:37 PM
Disaster magnet
Quote:
Originally Posted by nuteman
Transmitter flaking out at a distance? The exact same behavior happened to my neighbor's plane. It was at mid/high speed in trimmed level flight when it suddenly rolled over and crashed. At first I thought it was him, but then he showed me that it did the same thing again with hands off the sticks. Sure enough we did a range check and it would intermittently move surfaces drastically even when not touching the sticks...
Ohhh, yes, that does seem rather similar. Also with the flights I just got back from it did seem to become more unstable at longer ranges... The voltage display on the transmitter says it's still fine, but I definitely will recharge the AA batteries before the next flight. Your idea here might explain quite a bit actually.
May 24, 2018, 10:41 PM
Kimbers Keeper.
BHOFM's Avatar
Do Youtube, it works for everyone. some don't.
May 24, 2018, 10:56 PM
flyin' fool
goldguy's Avatar
Strange? Thirty percent has always been the recommended starting point for the CG on a conventional airframe since I began this hobby over 7 decades ago.

Have I missed something?
May 24, 2018, 11:10 PM
flyin' fool
goldguy's Avatar
Quote:
Originally Posted by gpw
Tail feathers look a little small too … just saying …
Righteo!

The H stab should be 20-25% of the wing area and the V stab 7-12%, with the rudder being 30-50% of the V stab area.

Another rule of thumb that dates back to the stone age.
May 25, 2018, 01:11 AM
Build straight - Fly twisty
Whiskers's Avatar
Quote:
Originally Posted by goldguy
Strange? Thirty percent has always been the recommended starting point for the CG on a conventional airframe since I began this hobby over 7 decades ago.

Have I missed something?
No, nothing has happened in the intervening 70 years to invalidate that.
It's just that some people like to stop a model from being lively and responsive and opt to debilitate it with a forward CG.
May 25, 2018, 02:28 AM
Registered User
Quote:
Originally Posted by Whiskers
No, nothing has happened in the intervening 70 years to invalidate that.
It's just that some people like to stop a model from being lively and responsive and opt to debilitate it with a forward CG.
Seems kind of backwords. Reduce a planes ability to fly slowly on landing by loving the cg forward to make elevator less "twitchy" because there's no other way of making a model less twitchy.
May 25, 2018, 03:30 AM
Build straight - Fly twisty
Whiskers's Avatar
Indeed it does seem to be undesirable but that's what they do.
Personally I like planes to be "spirited."
I go for generous control surface areas with a heap of throw and a rearward (properly positioned) CG.
Then I'll tame it, if required, with a bundle of expo.
May 25, 2018, 04:18 AM
Registered User
Quote:
Originally Posted by Whiskers
Indeed it does seem to be undesirable but that's what they do.
Personally I like planes to be "spirited."
I go for generous control surface areas with a heap of throw and a rearward (properly positioned) CG.
Then I'll tame it, if required, with a bundle of expo.
whenever hear of a model being described as not wanting to slow down for landing, i think of nose heavy which is exactly not what you want for a beginner, i struggled landing with my wot trainer because it just kept wanting to fly until i shifted the CG back (and its still nose heavy damn wot trainer. once i shifted the cg back i was able to come in slower before loosing tail authority and now i can get the nose up witht he right amount of power applied.
May 25, 2018, 08:35 AM
Disaster magnet
Quote:
Originally Posted by goldguy
Righteo!

The H stab should be 20-25% of the wing area and the V stab 7-12%, with the rudder being 30-50% of the V stab area.

Another rule of thumb that dates back to the stone age.
The H-stab is 26% of the main wing area, and the V stab is just over 10%.
May 25, 2018, 09:25 AM
treefinder
springer's Avatar
Quote:
Originally Posted by Whiskers
No, nothing has happened in the intervening 70 years to invalidate that.
It's just that some people like to stop a model from being lively and responsive and opt to debilitate it with a forward CG.
That would be me!

As I inferred in original comment, It is a personal preference for me, but in watching a lot of guys fly their first planes, I find that their biggest problem is anticipating what the plane will do. A CG that works just fine for experienced pilots will generate movements that confuse and confound noobs, causing them to over correct and crash the plane. Hence the 25% aft of LE suggestion, which slows down the planes tendency to react to the air conditions and to control inputs. One can always move the battery aft if there's room (and scratch builders should always provide ample room for battery moves both fore and aft) to see if one likes the performance. I certainly agree that one can have the CG so far forward (and too far aft) as to make the plane unflyable. Every plane has a sweet spot, and it is seldom at the exact "recommended" location it seems. I have only built one kit since getting back in the hobby, and only a few from plans by other scratchbuilders, so can't comment with authority on how kits work, but in the planes I have designed and built, when one finds that sweet spot it makes the plane "work" and it's obvious.

Actually I wonder if that historic recommendation is why there have been so many balsa/monokote planes flown once then thrown in the trash barrel or taken home to sit on the rafters in the garage never to be flown again!
May 25, 2018, 09:35 AM
treefinder
springer's Avatar
Back on topic with the plane in question:
" I did all the checking that I could possibly think of, the CG is exactly 10" from the nose" So where is that in relation to the wing Leading Edge? The distance from the nose is essentially immaterial, as the location relative to the wing is the real key.

If you think you are having signal loss, I'd suggest having a friend hold the tx and you walking the plane as far as you can get ( max distance you might be flying at) to see if the plane responds correctly to inputs at the distance you may actually fly. (Range Check) If you get good response at the distance on ground, you should have no problems in the air. Additionally, when you are at the max distance, change the orientation of the plane relative to the TX (facing away, facing toward, both sides facing TX) to insure that the Antenna is not masked or pointing right at the tx. ( I suppose it would be useful to know what radio you have) All RC antennas (both TX and RX) work from the side of the antenna, so if either points at the other, signal strength is weakest. When flying, as a matter of habit, make sure you don't hold the TX so it's antenna is pointing right at the plane.
May 25, 2018, 09:37 AM
treefinder
springer's Avatar
Quote:
Originally Posted by Chelonian
The H-stab is 26% of the main wing area, and the V stab is just over 10%.
I suspect that the "small" tail empennage was an artifact of the perspective in the picture.
May 25, 2018, 09:59 AM
Disaster magnet
Quote:
Originally Posted by springer
Back on topic with the plane in question:
" I did all the checking that I could possibly think of, the CG is exactly 10" from the nose" So where is that in relation to the wing Leading Edge? The distance from the nose is essentially immaterial, as the location relative to the wing is the real key.

If you think you are having signal loss, I'd suggest having a friend hold the tx and you walking the plane as far as you can get ( max distance you might be flying at) to see if the plane responds correctly to inputs at the distance you may actually fly. (Range Check) If you get good response at the distance on ground, you should have no problems in the air. Additionally, when you are at the max distance, change the orientation of the plane relative to the TX (facing away, facing toward, both sides facing TX) to insure that the Antenna is not masked or pointing right at the tx. ( I suppose it would be useful to know what radio you have) All RC antennas (both TX and RX) work from the side of the antenna, so if either points at the other, signal strength is weakest. When flying, as a matter of habit, make sure you don't hold the TX so it's antenna is pointing right at the plane.
The CG is right about at the highest cambered part of the wing. When calculating the % back from the leading edge, do you include the aileron or not?

As for the signal issue, I am recharging the AA batteries in the transmitter, but will still make sure to do the range test just to make sure I didn't put the antennas in bad places or something. The TX I am using is a Flysky FS-i6.
May 25, 2018, 11:11 AM
flyin' fool
goldguy's Avatar
Aileron included.

The thickest part of the wing is not the CG. A good flat bottomed airfoil has the CG set at 30% where the thickest part of the cord it at 40%.
Last edited by goldguy; May 25, 2018 at 11:26 AM.


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