I build, I crash. What am I doing wrong?!?

[Ketchup]

Hi Everybody -

Wow! Thanks for all the replies and the advice. So to answer a couple of the questions that have been posed:

• Crap! The dihedral on wind is not symmetrical. I used a dihedral on both sides when I built the wing and at the root they both have an angle of 15 degrees. However, the left side is straight and has a vertical height of 1 7/8" at the tip, but the right side is bowed upward such that its vertical distance is 2 7/8". Its obvious as I look at it now...
  So that results in the left dihedral generating about 4% greater lift than the right.
• Thrust angle is 2 degrees right and 2 degrees down. At least that is the starting point. All bets are off once I crash.
• I probably did launch it at too high of an angle. I wanted my friend to take a video, so I launched it by myself.
• I didn't think that the elevator could make that much difference. BTW - the control surfaces were all trimmed to be level and I didn't even have time to adjust the stick.
• The control rod is shorted than the original design. I didn't notice the bent rod, but again the control sufaces were all level at launch.
• I did a test glide and it flew straight and level.
• The one issue that I have with the CG is that I always end up tail heavy. Is there a concern that adding putty as ballast would make the plane too heavy? This is the primary reason that I increased the length of the nose.
• And yes - I thing my tweaks are causing too many unknowns. Since I need to rebuild, I am going to follow the plans to the T. Also the CAD model is just an aside, I teach CAD to sophomore mechanical engineers, so creating a solid model is just 2nd nature.

So thanks again for all the help and advice. I will post again after I build the new plane. I think that I should do this BEFORE I go ahead and try to build the duct tape plane!

All right! So good luck with the new build! Just a few tips for next time though. Make sure that the servo arms are perpendicular to the pushrod if possible. For example, it should be pointing straight up on your elevator instead of a bit forward. Also if your wire bends you can tie a zip tie around the wire, tight enough so that there isn't too much play but loose enough for it to slide around on the wire. Then stick the end of the tie into the side of the plane and glue it in place. Trim the end so that it is the right length. I do this on a lot of my planes to act as a guide for the pushrod so that it won't bend under pressure. I'm not sure why your plane would be so tail heavy especially with the longer nose. What size lipo are you using and where is it in the plane? Is it all the way forward?

 

[JasonK]

what foam did you use? (name brand) as some foam is about 2x as dense as the recommended foam. if you used one of the 'heavy' foams with the FT design, it would likely end up tail heavy because most of the foam is behind the desired CG.

there isn't a direct problem with adding weight to the plane, but it is better to move around the weight your plan already needs.

it would be good to see the controller + control surfaces together showing the movement, just so we could be sure they are all working correctly (the high 5 method). between were your servo is and the bend in that control rod, I have strong thoughts about that elevator control surface not working very well at all...

regarding 'all the control surfaces were level' comment -> once I get my planes trimmed out in flight, that isn't always the 'neutral point' for flying. but if your design is close to the FT design, they should be fairly close to that, it wouldn't be enough to cause what we saw in the video.

Of everything you listed out, the dihedral issue on the wing is most likely the issue, which was causing some serious rolling issue.

 

[Flite Risk]

i'm not the sharpest crayon in the box so input from other, brighter crayons will likely follow.

First, if you have not yet, get some stick time on a simulator. I recommend Picasim.

I bet your T.T. v2 will fly very well. just follow the instructions.

keep us updated.

where in the world are you? maybe there is a community member near by who can help if v2 does not cooperate.

 

[Piotrsko]

I'm going to add: take the prop off, and toss test it with the radio stuff powered on. A decent trimmed glide should get you maybe 50 ft in a straight line with a second base slide kind of landing. Adjust surfaces a bit at a time until you get there. That will help with launches. Start out powered with a click up trim, and a click of left turn. Rule of thumb on flite test stuff is it should balance somewhere forward of the high point of the wing. If you do full power launches, it gets crazy really fast unless the plane is underpowered. Yours was not underpowered. Add power slowly until it wants to pull out of your hand then use that for launching. Finally carry wrenches and a couple spare props to the field.

 

[Battery800]

Hi Everybody -

Wow! Thanks for all the replies and the advice. So to answer a couple of the questions that have been posed:

• Crap! The dihedral on wind is not symmetrical. I used a dihedral on both sides when I built the wing and at the root they both have an angle of 15 degrees. However, the left side is straight and has a vertical height of 1 7/8" at the tip, but the right side is bowed upward such that its vertical distance is 2 7/8". Its obvious as I look at it now...
  So that results in the left dihedral generating about 4% greater lift than the right.
• Thrust angle is 2 degrees right and 2 degrees down. At least that is the starting point. All bets are off once I crash.
• I probably did launch it at too high of an angle. I wanted my friend to take a video, so I launched it by myself.
• I didn't think that the elevator could make that much difference. BTW - the control surfaces were all trimmed to be level and I didn't even have time to adjust the stick.
• The control rod is shorted than the original design. I didn't notice the bent rod, but again the control sufaces were all level at launch.
• I did a test glide and it flew straight and level.
• The one issue that I have with the CG is that I always end up tail heavy. Is there a concern that adding putty as ballast would make the plane too heavy? This is the primary reason that I increased the length of the nose.
• And yes - I thing my tweaks are causing too many unknowns. Since I need to rebuild, I am going to follow the plans to the T. Also the CAD model is just an aside, I teach CAD to sophomore mechanical engineers, so creating a solid model is just 2nd nature.

So thanks again for all the help and advice. I will post again after I build the new plane. I think that I should do this BEFORE I go ahead and try to build the duct tape plane!

I don’t think there will be a lack of power a 2207 on 3s seems like more than enough

 

[navillus5]

All right! So good luck with the new build! Just a few tips for next time though. Make sure that the servo arms are perpendicular to the pushrod if possible. For example, it should be pointing straight up on your elevator instead of a bit forward. Also if your wire bends you can tie a zip tie around the wire, tight enough so that there isn't too much play but loose enough for it to slide around on the wire. Then stick the end of the tie into the side of the plane and glue it in place. Trim the end so that it is the right length. I do this on a lot of my planes to act as a guide for the pushrod so that it won't bend under pressure. I'm not sure why your plane would be so tail heavy especially with the longer nose. What size lipo are you using and where is it in the plane? Is it all the way forward?

Thanks for the tip about the control rods. I was using a 3S pack that had a mass of 80 g and it was up against firewall.

 

[navillus5]

what foam did you use? (name brand) as some foam is about 2x as dense as the recommended foam. if you used one of the 'heavy' foams with the FT design, it would likely end up tail heavy because most of the foam is behind the desired CG.

there isn't a direct problem with adding weight to the plane, but it is better to move around the weight your plan already needs.

it would be good to see the controller + control surfaces together showing the movement, just so we could be sure they are all working correctly (the high 5 method). between were your servo is and the bend in that control rod, I have strong thoughts about that elevator control surface not working very well at all...

regarding 'all the control surfaces were level' comment -> once I get my planes trimmed out in flight, that isn't always the 'neutral point' for flying. but if your design is close to the FT design, they should be fairly close to that, it wouldn't be enough to cause what we saw in the video.

Of everything you listed out, the dihedral issue on the wing is most likely the issue, which was causing some serious rolling issue.

I am using Elmer's brand foam board. I will be following FT build exactly so hopefully my push rods won't be all bendy...

 

[navillus5]

i'm not the sharpest crayon in the box so input from other, brighter crayons will likely follow.

First, if you have not yet, get some stick time on a simulator. I recommend Picasim.

I bet your T.T. v2 will fly very well. just follow the instructions.

keep us updated.

where in the world are you? maybe there is a community member near by who can help if v2 does not cooperate.

I have Real Flight RF7. It's old but then again all I am trying to do is become adept at taking off making a series of right hand turns and landing.
I live in Amherst, NH. About 30 mi west of Manchester.

 

[navillus5]

I'm going to add: take the prop off, and toss test it with the radio stuff powered on. A decent trimmed glide should get you maybe 50 ft in a straight line with a second base slide kind of landing. Adjust surfaces a bit at a time until you get there. That will help with launches. Start out powered with a click up trim, and a click of left turn. Rule of thumb on flite test stuff is it should balance somewhere forward of the high point of the wing. If you do full power launches, it gets crazy really fast unless the plane is underpowered. Yours was not underpowered. Add power slowly until it wants to pull out of your hand then use that for launching. Finally carry wrenches and a couple spare props to the field.

Thanks for this advice. This is exactly the types of tips I need. I will definitely do this before my next powered attempt...

 

[Flite Risk]

old or new any sim is fine.

 

[JasonK]

I am using Elmer's brand foam board. I will be following FT build exactly so hopefully my push rods won't be all bendy...

Elmer's brand is about 2x as heavy as Adam's ready board (DTFB), which will sigificnatly impact your over all weight/wingloading and ability to get your CG correctly.

 

[NickRehm]

Elmers foamboard is your biggest issue at the moment. Mount the motor as straight as possible on the next iteration, the 2 degree angles won't do anything noticeable for a novice. Make sure it will glide straight first, then try throwing at ~15 degree angle up with ~30% throttle, add throttle gradually as necessary to gain altitude

 

[Flite Risk]

Elmers foamboard is your biggest issue at the moment. Mount the motor as straight as possible on the next iteration, the 2 degree angles won't do anything noticeable for a novice. Make sure it will glide straight first, then try throwing at ~15 degree angle up with ~30% throttle, add throttle gradually as necessary to gain altitude

And two or three click of up elevator never hurts.

 

[navillus5]

Elmer's brand is about 2x as heavy as Adam's ready board (DTFB), which will sigificnatly impact your over all weight/wingloading and ability to get your CG correctly.

OMG! I never gave any thought to the type of foam board. Didn't give any consideration to the fact that the density might vary between different brands. I might have missed it but I don't think they've ever mentioned this in any of the flight test videos. Thanks for the tip and I'll be sure to get some of the board that you recommend.
I just search the site and found an article comparing Adams and Ross brand boards.
I just put an Elmer's board on a scale ... 240 g. At least this explains why my previous builds were much heavier than what was given with the build info. I had thought I was being too heavy with the glue!!!

 

[navillus5]

Elmers foamboard is your biggest issue at the moment. Mount the motor as straight as possible on the next iteration, the 2 degree angles won't do anything noticeable for a novice. Make sure it will glide straight first, then try throwing at ~15 degree angle up with ~30% throttle, add throttle gradually as necessary to gain altitude

I'll give this a try but everything I've ever heard is that people say it's important to throw the plane as level as possible. Is the upward orientation and advantage for flying high wing trainer?

 

[Ketchup]

I'll give this a try but everything I've ever heard is that people say it's important to throw the plane as level as possible. Is the upward orientation and advantage for flying high wing trainer?

You should generally throw the plane a little bit up, its just that when you did it the plane was pointing up but going more straight forward. You want to throw it about 15 degrees up, but you also want to keep the angle of attack very low, basically propel the plane in the direction that it's pointing in.

 

[navillus5]

You should generally throw the plane a little bit up, its just that when you did it the plane was pointing up but going more straight forward. You want to throw it about 15 degrees up, but you also want to keep the angle of attack very low, basically propel the plane in the direction that it's pointing in.

Ahhhh...that makes a lot of sense.

 

[Piotrsko]

Dang. For maybe 50 years I have been launching wrong. Well, that explains a lot. Wonder how I survived just letting go of my slopers and ROG 1/2A stuff.

 

[Ketchup]

Dang. For maybe 50 years I have been launching wrong. Well, that explains a lot. Wonder how I survived just letting go of my slopers and ROG 1/2A stuff.

I don’t have a tiny trainer so I don’t know if just letting it go will be enough, but I’m pretty sure that launching it with a very high angle of attack and low airspeed isn’t good. Just letting planes go usually works for me, but I was commenting on the type of launch, not lack of it (I feel like this post was directed towards what I said about launching a couple posts back).

 

[Intashu]

Glad everything I was going to say has been addressed. CG should be closer to 20% of the wing not 30% when learning. and that the Elmers board is way too heavy. When I started out I made the same mistake. almost every plane was tail heavy and they all flew terribly. Dollar-tree foamboard is MUCH lighter and makes all of our planes fly significantly better. I only use the Elmers board for motor pods and the occasional wing spar when I want something stronger and less likely to bend or crinkle.

The zip tie on the rod helps a log with long rod runs so it doesn't deflect when it shouldn't.

and of course from the short video we saw, make sure you throw it level, or maybe a hair up. too much up and you'll immediately stall. and too much throttle and it will roll over because it needs air speed. most prop plane models in the flite-test catalog can take off easily with 75% throttle and a gentle level toss. Planes need airspeed to really start to fly, so if it stalls immediately you'll crash, and if it's got too much throttle there isn't enough air speed to prevent the motor from just flipping the plane over. although normally it rolls LEFT not RIGHT in my experience.

I bet most of your problems will be solved when you swap to a lighter foam however. It was a HUGE life saver when we realized we were using foam that was WAY too heavy!