trimming a low wing model

[star73gazer]

I have had success with high wing models such as the Porter and Aeronica Champion. I have tried three low ming models and have had the same problem with all three that resulted in unrepairable crash damage The problem: even though I was very careful about diahedral and balance point all three rolled hard left, lost all lift and fell sideways and suffered destroyed wings or the fuselage flexed enough that the rubber motor broke their spines. I want to build the GUI405 P40. How do I test and trim a low wing model?

[Jason K]

I am also interested in what all of you have to say about it to.Being I am building a low wing myself.Plus it is my very frist time ever tring to build a model airplane..I am really enjoying building it is really relaxing to do.

[joecrouse]

Build them bottom heavy and top light.
Trim them with LOTS of Practice Glides first

[Wildpig]

Someone with practical experience with low-wing model flight is Mitch. I think he is out sailing on the ocean right now.

You didn't say which low-wing models you built. The 500 series Spitfire and Stuka are notorious for difficult flight characteristics.
Hellcat, T-28, Avenger, do o.k.

Are they stalling during glide or is this during powered flight? Joecrouse is right, you must get them to glide properly before powered flights.
Small warps or twists in the wing can cause a wingtip stall and roll.
The low wing planes will fly o.k., the exception being the Stuka.

[star73gazer]

The rolls during glide test were very gentle. The hard rolls were during powered flight. The models I had problems with were not from Guillows. One was a P51-B with a 28" wingspan. The reason I switched to Guillows was because I could see from images of the non-papered models that the Guillows models had more robust frames.

[Wildpig]

28" span Mustang should fly fairly well. You should get the rolling tendencies ironed out the best you can for the glides.
Look at Mitch's threads. You can use the forum search feature to find his threads. He flew some 400 series P-51,FW190, and Me109 models. He was able to get good glides by adding trim tabs.
Guillow models do tend to have more balsa in their structure than other kits. That does mean more strength but, more weight also. Keeping the weight down is critical to good flying performance. (You probably knew that).

[atesus]

I'm not an expert on the subject by any means but I'll chime in since I built the 400 series P-40 and got it to fly half respectably by following the advice of fellow models .

Major things I pay attention to are below - of course a straight and true structure is the first critical step. Trying to lighten the structure up doesn't hurt either .

1. Dihedral angle: Usually the plans show less than adequate dihedral possibly for fear of not looking scale if too much dihedral is used. The rule of thumb I learned from the experts is to add enough dihedral so that the wing tips are above the thrust line, even raised up to the bottom of the canopy.
2. Washout: I add some washout to the wings, for a plane of the 400 series I would use 3/32" at the wingtips. Smaller than 20" w/s I use 1/16", larger than 30" w/s I use 1/8" (Don Ross' recommendations).
3. Stab: I make the stab opening large, so that I can play with the stab incidence while trimming. If I'm not mistaken, in the P-40 I ended up using a 1/32" shim under the trailing edge of the stab. I covered the stab-fuse intersection after I finalized trimming. BTW the wing was mounted as shown on the plans.
4. Nose block: I build a decent nose block which will allow me to adjust the thrust line and hold the adjustment properly.
5. Rear peg: I try to install additional peg locations, usually forward of the one shown on the plans. If the structure turns out tail heavy (which was the case with the P-40) I use the forward one, shifting the CoG forward, thus minimizing the need for nose weight.

After these, I follow the "10-step trimming" method of John Koptonak. Here's the link to what I suspect is the original version. There are some variations of it out there but the basic ideas are the same. The trimming method is not low-winger specific but becomes more valuable for those models as the trimming is more critical for them. The high wingers are less capricious and usually one can get them to fly decently with less effort .

http://www.gryffinaero.com/models/ffpag ... 0step.html

And here's my P-40 in the air (two best flights of that day). Unfortunately a short while ago she lost her last battle. She was damaged beyond repair as a result of a full power dive into the ground. I was trying to get her to fly longer by installing a looooong motor which bunched up in the rear and caused a stall followed by the fatal dive. RIP .

http://youtu.be/8ilwRVJ1rKM

I hope this helps. Best,

--Ates

[Wildpig]

Really nice flights with that P-40, Ates.
That gryffinaero trimming link ought to be a sticky on this forum.

[star73gazer]

Thanks to everyone for their help and hints. I can say from experience that high wing models are easier to trim. I built a Guillows PC-6 Porter and once I had it balanced at the indicated point was able to achieve good flights just by adding about
1/16 downward adjustment to the rear of the flying stabilizer. I built it striclly according to the plans. I have four other high wing types that fly well. One is scale, the other three are designed for endurance, the largest of these being a Gollywock.

[Mitch]

Thats a really great flight. Raises the bar for me. I cant wait till spring... got to get back to my ship... All my 400 series I think need to be trimmed better for that slow turn to the left. GREAT JOB!!! Mitch

[WIDDOG]

http://youtu.be/SWxwE9XKpD8


I’m testing a Peck Polymer propeller, My “Hat Cam” and messing with Windows Media Maker. BTW this is my experimental 500 series plane I do tests with it a lot. After I find something I like I try it on one of my better looking models.

[WIDDOG]

http://youtu.be/2YW4d3p3a1s

This is just a trim flight but I think that the Rufe built as a Zero with no landing gear should be considered a good flyer.

[Mitch]

Great Job!!! Looks like that first flight the model almost flew out to the street After looking at your post and others I realize I need to trim my models to fly in that left turn. I think I was just happy to get some successful flights this summer... Mitch

[WIDDOG]

Thanks Mitch, I started experimenting with longer motors. I’ll post if I come up with anything interesting. BTW I am very impressed with your WW l planes.

[WIDDOG]

http://youtu.be/_WqeQrpGdxQ

http://youtu.be/jzMBo2mYTFo

Still needs more trimming but the longer motor is definitely helping.