karolh

Well at long last the profile is finally finished and will post some pictures shortly. The specs are:

Wingspan 64"
Length 59"
Wing area 810 sq. ins.
Weight 8 lbs.5 ozs.
Engine Mintor 22cc gas
Prop Falcon 17x6

I am using a CG point set at 27% of the wing root chord for the maiden flight and hopefully the current very windy conditions will not last to long.

AA5BY

Good going Karol... looking forward to the pics and flight report.

karolh

Well at long last I finally got around to maidening my profile and it certainly gave me a feeling of satisfaction seeing my creation take to the skies and fly as I hoped it would. Weighing 9.0 + lbs. it is on the heavy side but it flies quite well, needing a couple clicks of right aileron and a similar amount of down elevator to fly straight and level. The CG is very close to my liking but the model needs some more trimming but that will be done in due course. It does not have unlimited vertical but it is adequate for my needs, hopefully when the engine breaks in it will improve. At present I am using a Falcon 17x6 but I intend to test a few more props to see which gives the best performance. I plan on increasing the right thrust and adding some down thrust to hopefully overcome the down elev. trim required for straight and level.

DaleD

Congratulations on a successful maiden Karol. We waited a while to hear the news and I must say your report maid it all worthwhile. Looking forward to an update when you take care of the required trimming at which time maybe you will bless us with a few pictures and by slim chance a video.

Wishing you many safe and happy landings

DaleD

karolh

I tried loading some pics but the system bounced them, but will keep trying.

speedracerntrixie

My Feedback: (29)

There are better ways to trim this out then using down thrust. If you can tell me what wing section you are using and what wing/tail incidences you have it set to I would be able to come up with some options. Adjusting the engine can lead to poor tracking on the verticals.

karolh

Thanks for the offer. The wing is set at +0.50 deg and the stab at 0.00 deg.

speedracerntrixie

My Feedback: (29)

Provided that the engine is at zero as well the down trim would indicate you are a tad tail heavy. I would adjust the CG forward until your elevator trims neutral. My guess is that it tucks to the gear in knife edge right now.

AA5BY

It seems to me that a mid wing if symmetrical should have been given a 0-0-0 setup so the down trim is likely required due to some positive in the wing. You can try to balance at the forward point of the balance zone. If not happy with that, try to adjust the ailerons up or down to get the elevator neutral then compare power on and power off trim. If they are not the same, then a mix to adjust either the power on or power off trim.

karolh

Most 0-0-0 setups tend to need a tad of up elevator to get the wing flying hence the positive wing incidence setting.

karolh

Sent you a PM

speedracerntrixie

My Feedback: (29)

I did get the PM. This one has me stumped a bit. There can only be two reasons for the down trim. One, the stabs are off in relation to the wing. You state 1/2 degree of positive and that is how alot of guys are setting up their aerobatic models. That little bit of positive should eliminate the need for any up trim and the need to fly the whole airplane at a positive AOA. The second reason would be an aft CG. There just really isn't any other causes. You have stated that you like where the CG is, could it be that you prefer an aft CG? What does the airplane do when you go hands off inverted?

AA5BY

I think Karol related that the wing has 1/2° of positive rather than 1/5.

speedracerntrixie

My Feedback: (29)

Thanks for pointing out the typo. 1/2 degree is what was ment. Howerver 1/5 degree would work just as well I think. I have just gone to setting everything with a symmetrical airfoil so that the TE center is 1/16" lower then the LE center. I'm still curious about where exactly his CG is.

AA5BY

The wing panels can also be trimmed as they are on a tube. Karol needed two clicks of right aileron and two clicks of down.. so the right wing panel might have a tad bit more positive than the left and causing both the need for right and down trim. I've shimmed the positioning studs on several wings using very small strips of 1/64 ply and in most cases improved flight trim with only one or two shims.

One option would be be to shim the right wing panel down very slightly.

speedracerntrixie

My Feedback: (29)

yes that would be a good option. I would suggest the measurements to be verified before adjustments but it does seem that it can be corrected by adjusting the one wing panel. Then the rest of the trimming can begin.

karolh

At present the model requires just a tad of forward stick when inverted straight and level, and when inverted on a 45 deg up line it holds the line fairly well before falling off, and IMO the model is certainly not tail heavy. As is the CG is at 27% of the wing's root chord and I am really stumped as to why the needed down trim.

Based on both your suggestions I plan on doing a thorough check of all incidences and thrust lines and will report my findings.

karolh

I measured all the incidences on the assembled model and they are as follows :

Engine ........... -0.25 deg. down thrust
Right wing ...... +1.00 deg.
Left wing ........ +1.00 deg.
Stab .............. 0.00 deg.

Based on the foregoing it seems reasonable to assume that the model would require some down trim for level flight.

speedracerntrixie

My Feedback: (29)

Ok your last two posts have given me some good info. Check your CG formula again, I doubt it is at 27% as what you are describing is more like what an airplane would handle like with a CG closer to 33% to 35%. We can take fuse lift out of it being that it is a profile. +1 degree is a bit much. You may want to cut that in half. I would also set the engine to zero. Now with the positive incidence you currently have the airplane should pitch to the ground more while on an inverted 45. This is why I still think your CG is farther aft then you think. Based on this info here is what I would do: Set wing to +.5 degree, set engine to zero and move the CG forward 3/8".

karolh

AT present the CG is set at 27% of the root wing chord which equates to approx. 34.5% of MAC, so if this is the CG location you are referring to then you are correct in your assumption. Thanks for your suggestions regarding the incidences which happens to be quite in line with my thinking.

karolh

Guys, I have been thinking, suppose I raised the ailerons just a bit to try and cancel out the unwanted +0.5 deg of wing incidence, would this have any adverse effect on the model's flight performance, for example when inverted ?

BMatthews

When you reflex the ailerons like that you both alter the angle of incidence as well as the airfoil's camber. So you'd end up with a slight amount of reverse camber at the same time you reduce the wing's angle.

The only way to find out if there's issues is to try flying it. We're splitting hairs when it comes down to this degree of trim and so many things that are all but undetectable can be contributors.

Certainly the model won't suddenly snap roll and crash. But on the other hand it may do some things in some maneuvers that make it a less than ideal solution. Or you may not notice anything at all.

Which brings us to another option. If you simply add in some down trim your -.25 degree stabilizer angle will be reduced so that it becomes 0-0 with the wing. Altering the angle and camber by adjusting the associated control surface works for the tail as well as the wing.

karolh

Thanks for all your help, however it seems to me that unless the model shows some real bad flying trait ( which it has not done so far ) the easiest thing to do is just fly the model with the wing incidence as is and add the necessary down trim needed for level flight.

BMatthews

Well you're the one that asked about reflexing the ailerons up a little in lieu of altering the wing incidence angle.

karolh

Yes I did, and sometimes an easy out or fix is never the best way, so yesterday I tackled the problem of adjusting the wing incidence and now it has been corrected. I have sent the engine in for an upgrade under warranty so it will be awhile before the model gets flown, but I will advise you of the outcome whenever I do.