Flight Trimming

[Brucester]

It was moved up and moved down, but with a measurement such as 1/16", 1/32", and 1/8", and those movements were relative to lines on the wingposts. Well thanks for clarifying.

Thanks,
Brucester

[jander14indoor]

The supervisor was just wrong, there is no definition of what a parameter is except the required three, and those are practically wide open. But he is the supervisor. If he's doing your regional or state contest, you'd better listen.

I think you are taking the right approach with far more than the minimum six. Do try to keep them numerical and relevant, but nothing says they have to be.

As to tail angle of attack, just because the tail is nose down wrt the boom DOESN'T mean it is negative lift. Curved surfaces like these can still have positive lift with very negative angles of attack.

And consider, its not really the tail angle of attack relative to the wing, but relative to the air that's important. Does your plane fly level, but nose high? If so, the tail angle of attack MAY be positive. Certainly less negative than you think.

One way to tell, where is your cg now? Is it at the back wing post or pretty near on a wide wing chord? If so, your tail is lifting positive, has to, to balance. Think about it. If the cg is behind the wing (on narrow wings it should be, may not be on wide wings), then your tail is definitely lifting.

Jeff Anderson
Livonia, MI

[StampingKid]

I have a problem in trimming flying on a big wing when I try to use the Ikara broad blade in that it throws off my cg. I fly real good (1m30 on a .080 half motor) with the regular 8 7/8 Ikara blade when the the cg is 5/8 in. behind the rear post but I keep getting ceiling bumps in a 24 ft gym. But with the broad blade I lose .4 gr of ballast and the cg goes forward. Moving the rear post down a 1/16 gets me flying but I also lose 20+ seconds.

[leetx]

I have a problem in trimming flying on a big wing when I try to use the Ikara broad blade in that it throws off my cg. I fly real good (1m30 on a .080 half motor) with the regular 8 7/8 Ikara blade when the the cg is 5/8 in. behind the rear post but I keep getting ceiling bumps in a 24 ft gym. But with the broad blade I lose .4 gr of ballast and the cg goes forward. Moving the rear post down a 1/16 gets me flying but I also lose 20+ seconds.

The broad blade should not weigh .4 g more than the regular blade if trimmed. Have you trimmed your propellers to 20 cm? If you have, then try trimming little by little the width of the broad blade.

[StampingKid]

StampingKid wrote:
I have a problem in trimming flying on a big wing when I try to use the Ikara broad blade in that it throws off my cg. I fly real good (1m30 on a .080 half motor) with the regular 8 7/8 Ikara blade when the the cg is 5/8 in. behind the rear post but I keep getting ceiling bumps in a 24 ft gym. But with the broad blade I lose .4 gr of ballast and the cg goes forward. Moving the rear post down a 1/16 gets me flying but I also lose 20+ seconds.

Leetx replied:

The broad blade should not weigh .4 g more than the regular blade if trimmed. Have you trimmed your propellers to 20 cm? If you have, then try trimming little by little the width of the broad blade.

The regular blade is 1.76 gr trimmed to 20cm. The broad blade is 2.16 gr. trimmed to 20 cm and with everything behind the spar trimmed away. Which is not right? I cannot trim anymore off the borad blade. But if it is the one that is not right I can get another to trim.

[blue cobra]

If the 8-7/8 blade works better why not just use that one

I haven't seen your plane, but what I would do in that situation is find the CG with the broad blade and move your wing around until the rear wing post is 5/8" in front of your new CG. Play around with wing position and Angle of Attack until you get it at its best.

[leetx]

StampingKid wrote:
I have a problem in trimming flying on a big wing when I try to use the Ikara broad blade in that it throws off my cg. I fly real good (1m30 on a .080 half motor) with the regular 8 7/8 Ikara blade when the the cg is 5/8 in. behind the rear post but I keep getting ceiling bumps in a 24 ft gym. But with the broad blade I lose .4 gr of ballast and the cg goes forward. Moving the rear post down a 1/16 gets me flying but I also lose 20+ seconds.

Leetx replied:

The broad blade should not weigh .4 g more than the regular blade if trimmed. Have you trimmed your propellers to 20 cm? If you have, then try trimming little by little the width of the broad blade.

The regular blade is 1.76 gr trimmed to 20cm. The broad blade is 2.16 gr. trimmed to 20 cm and with everything behind the spar trimmed away. Which is not right? I cannot trim anymore off the borad blade. But if it is the one that is not right I can get another to trim.

I have several of broad props laying around, trimmed and untrimmed. I found something interesting. One that I just bought a few weeks back weighs 2.75g untrimmed. Another one that I ordered earlier (2 months back) is 2.25g untrimmed. Another older blade that is trimmed as you described is 1.74g trimmed. Looks like the manufacturing of this blade has changed.

To the touch, it's obvious that the newer prop's blades are thicker. I have not flown this heavier blade personally, but I doubt that it would flair like it's supposed to, like the lighter one. Personally, I would not use this heavier blade, especially if .4 g is gained. What is the total weight of your plane with this prop?

Previously, I have lightened another broad blade (from 1.65g to 1.50g) by sanding it. It's not as much as what you have to do, but I believe 0.4g is do-able, BUT it will take a bit of time. It took me a good 20 minutes of sanding to decrease the weight by .15g.

Here is a description of how to sand the prop by Chris Goin

Code: Select all

Modifying the Ikara prop is perhaps the most time consuming part of the build. Starting with one of Harlan’s SO
props, the blades are reduced in thickness by sanding the underside with 400 grit sandpaper wrapped around a
soda can. I hold the blade cupped in my hand, with my fingers controlling where the pressure is applied. You
must work slowly to keep the blade from deforming too much. Matching the blades in weight is important, but
matching their flare characteristics is essential. The spar is blended into the surrounding blade, and the hub area
is lightened. The blade shape is easily changed with a pair of scissors, but it’s best to do this after sanding is
complete. The pitch is reduced and the distribution is checked. After all that sanding, it will probably be pretty
far off. The plastic can be persuaded into the correct shape with your hands if this is the case. I put a bit more
camber in the blades and several degrees of washout in the tips, knowing that both would nearly disappear at full
flare.

Here is the full article and plans on this airplane. It's very nicely done. http://www.indoorduration.com/ftp/DoubleTroubleSO.pdf

Others with experience sanding the prop please chime in.

[StampingKid]

Looks like I may be able to sand down both some and get usable ballast. With the broad blade the plane is 6.7 gr. without ballast. Flew it yesterday on a half motor and got 1m24 rising only to 12-13 ft. --so if I could get enough additional ballast to get the cg right I think it could do 3m + in a 24 ft gym. The plane will actually do 1m30 on a half motor with the regular blade but you get ceiling bumps in the gym and obviously would out fly the site on a full motor.

[SOCoach]

Could someone explain to me the method of creating wing wash? Am I correct in assuming that the left wing (by left, looking at the plane head on) should be tipped so that the leading edge is about 1/8th and inch higher than the trailing edge . . . while the right side of the wing is level. Is that correct? I just don't know how to teach my students how to create it.

[StampingKid]

Reading the Indoor Duration clip posted by leetx,

The spar is blended into the surrounding blade, and the hub area
is lightened.

I understand that I am going to be sanding down the gray spar and the center hub as well as the white blade.