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Old 01-19-2013, 06:10 PM   #1
npowell28
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Default Low wing trainer dihedral - suggestions please

Hi,

I'm currently about half way through building my scratch built low wing trainer. It's mainly depron with a bit of balsa and ply. It is 60" span with a 13inch constant chord giving it loads of wing area. It should weigh about 55 ounces making it pretty light.

I'm not sure how much dihedral i should be going for. I'm thinking about 5 degrees but that looks loads on sketchup. I'm not bothered about doing anything extreme in it but i would like to do a few lazy rolls and loops.

Any body got any suggestions.

Thanks
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Old 01-19-2013, 06:59 PM   #2
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My old Dave Robelen's Pronto must have had at least 10 degrees in each wing, it was stable but you still could do loops and rolls. after a while I taught myself to fly inverted with rudder control (no ailerons) It was a great trainer. after about 200 nitro flights it fell apart.

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Old 01-20-2013, 12:09 AM   #3
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If it has ailerons then you don't need or really want much dihedral (I'm assuming this isn't a primary trainer). About three degrees (each side) should be ok
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Old 01-20-2013, 01:37 AM   #4
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For a 60 inch wing span that you want to do some ail rolls with i think about 1 1/2 inches under each wing tip would be good enough . Are you putting any washout in the wing tips ? Wildfire here is my scratch built pronto surpreme (ailirons) joe


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Old 01-20-2013, 09:26 AM   #5
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If it has ailerons it needs very little dihedral, about 2 degrees will make it look reasonable (low wing with no dihedral always looks a bit odd).

If it is intended to turn on rudder only then you'll need a load of dihedral to get it to turn properly. Could be anything up to about 8 degrees but I'd say at least 5.

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Old 01-21-2013, 03:15 PM   #6
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With ailerons, an inch to an inch and a half for a 60 inch wingspan.
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Old 01-21-2013, 03:25 PM   #7
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Originally Posted by Gary H View Post
With ailerons, an inch to an inch and a half for a 60 inch wingspan.
Yes thats what i thought for a 60 inch wing ,it would help on landings but not hurt rolls and such. I built my pronto with a little dihedral for ail ,i think around 1 1/4 under each wing tip (50 inch wing span )and balanced it upside down and it flys inverted hands off . The oringal pronto did have 3 1/2 under each wing but it still was a great flying plane and lots of fun to goof off with. joe


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Old 01-21-2013, 03:45 PM   #8
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Originally Posted by road king 97 View Post
Yes thats what i thought for a 60 inch wing ,it would help on landings but not hurt rolls and such. joe
Your right Joe. The 4 star 60 I'm building is considered a low wing trainer, has a 71" wingspan and calls for ~2* of dihedral or 1 7/8" +- 1/2". So a 60" wingspan, at least for me I would go 1-1/12" at the last rib bay.

The exact amount of dihedral is really not much of a critical thing for trainer type planes. A little more, a little more "self righting", but you lose a little bit of ability for rolls. A little less dihedral and you a little sportier plane with a little less forgiveness.
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Old 01-21-2013, 04:07 PM   #9
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Iam building a foam plane like this balsa canard and it had no dihedral so i put none in my foam conversion . Should roll very fast i hope . If it flys like its big brother i will make a 42 inch wing span one ,draw some plans and give them out free. This is a 38 inch wing span test plane.


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Old 01-21-2013, 04:49 PM   #10
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Originally Posted by road king 97 View Post
Iam building a foam plane like this balsa canard and it had no dihedral so i put none in my foam conversion . Should roll very fast i hope . If it flys like its big brother i will make a 42 inch wing span one ,draw some plans and give them out free. This is a 38 inch wing span test plane.

Looks great! Ill have to try building a foam plane one day. That's if I don't get fed up with building. Today I'm working on my Balsa USA Sopwith Pup and it's a tad of a challenge and sometimes, downright frustrating.
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Old 01-21-2013, 04:59 PM   #11
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Ha Ha Gary your not telling me anything i dont know already ,i scratch build with foam and balsa to break things up a bit . One thing i can say it gets easyer after learning the tricks and building alot more planes. joe


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Old 01-22-2013, 06:56 AM   #12
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Dihedral on low wing .. yep- I'd put 1" under each tip just for cosmetics in fact ... and for trainer - 1.5 - 2" under each tip to add a little stability.

You only have to see a Russian Airliner ... Tu, An etc. to see what flat or Anhedral looks like to the eye !! It just doesn't seem to look right.

And note that WW2 warbirds all had serious dihedral ...

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Old 01-22-2013, 04:31 PM   #13
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Cool. So about 1 to 1.5 inch. I've sized it up and that looks good. Yes my wing does have some washout at the tips. Just on the building with foam and balsa comments. It's still coming out heavier than i thought it would. I reckon i'll finish at about 65 ounces. I was hoping for about 55. Wing loading should still only be about 12oz per square inch though.
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Old 01-22-2013, 04:35 PM   #14
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Originally Posted by npowell28 View Post
Cool. So about 1 to 1.5 inch. I've sized it up and that looks good. Yes my wing does have some washout at the tips. Just on the building with foam and balsa comments. It's still coming out heavier than i thought it would. I reckon i'll finish at about 65 ounces. I was hoping for about 55. Wing loading should still only be about 12oz per square inch though.
Thats still a good wing loading . If you get a chance post us some pictures of your build . joe
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Old 01-22-2013, 04:39 PM   #15
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Originally Posted by road king 97 View Post
Thats still a good wing loading . If you get a chance post us some pictures of your build . joe
I will do once i've joined the wings. Wing loading is good but i think my motor will possibly be underpowered. 300 - 320W motor. It doesn't really hit the 100W per pound figure. We'll just have to wait and see i guess.
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Old 01-22-2013, 04:49 PM   #16
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Iam getting ready to order a motor about the same size you need for a different plane. I have it down to two choices here is one . http://www.headsuprc.com/servlet/the...ushless/Detail and this is the other one iam looking at. joe http://www.valuehobby.com/power-syst...30-1100kv.html I take that back Don has some great deals on motors too and great service also. joe http://www.strongrcmotors.com/Motors.htm
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Old 01-22-2013, 04:58 PM   #17
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Originally Posted by road king 97 View Post
Iam getting ready to order a motor about the same size you need for a different plane. I have it down to two choices here is one . http://www.headsuprc.com/servlet/the...ushless/Detail and this is the other one iam looking at. joe http://www.valuehobby.com/power-syst...30-1100kv.html
I'll see how it goes first. THe motor should produce 320w dropping down to about 300W. Even at 4lb that will give it 75W per pound. I know it's old data but the Shaw-Kopski values show that it should fly fine. It might not do mad acrobatics but for training it'll be fine. I think what i'm finding from experience is thats it's better to nearly complete the build and then buy the motor based on what i want the model to do. Saying that i was'nt too far off. I thought it would be about 55 to 60 ounces. So not too bad.

I could probably remove a bit of weight somewhere. I'd rather it was robust though. I think on my next foam build i'll be a bit braver and use less balsa. Probably save me some money aswell.
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Old 01-22-2013, 07:25 PM   #18
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Aren't you guys going a very small on the motor? A 74g motor is a bit weak for a 4lb trainer type plane, no? Consider that if you get 300W on a fresh pack you will be down in the low 200's by the time the pack is run down. That's going to leave you pretty marginally powered.

I just don't see the point in being stingy on the motor when you could put a bigger one in for near enough the same price. The bigger motor will also be more efficient when run at part power rather than thrashing a small motor at it's limit the whole flight.
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Old 01-23-2013, 08:04 AM   #19
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Originally Posted by JetPlaneFlyer View Post
Aren't you guys going a very small on the motor? A 74g motor is a bit weak for a 4lb trainer type plane, no? Consider that if you get 300W on a fresh pack you will be down in the low 200's by the time the pack is run down. That's going to leave you pretty marginally powered.

I just don't see the point in being stingy on the motor when you could put a bigger one in for near enough the same price. The bigger motor will also be more efficient when run at part power rather than thrashing a small motor at it's limit the whole flight.
Yeah i think i've missed a trick here. I was beginning to think along the same lines. Trouble is if i go down the lines of a bigger motor i'll have to fork out on new motor, 4s batteries and ESC. Plus theres another 6-8 ounces of weight to put on board. Food for though. Thanks!
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Old 01-23-2013, 08:41 AM   #20
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Originally Posted by npowell28 View Post
Cool. So about 1 to 1.5 inch. I've sized it up and that looks good. Yes my wing does have some washout at the tips. Just on the building with foam and balsa comments. It's still coming out heavier than i thought it would. I reckon i'll finish at about 65 ounces. I was hoping for about 55. Wing loading should still only be about 12oz per square inch though.
These might bbe of use ..... (old but good !)





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Old 02-12-2013, 05:54 PM   #21
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just thought i'd put a quick pic on of the build so far. wing and fuse both built. Quick pic of the fuse. I wasn't going to paint it but the weathers not good at the moment so i thought i'd waste a bit of time on it. Hope i don't crash is first time out.


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Old 02-12-2013, 07:41 PM   #22
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Originally Posted by npowell28 View Post
Yeah i think i've missed a trick here. I was beginning to think along the same lines. Trouble is if i go down the lines of a bigger motor i'll have to fork out on new motor, 4s batteries and ESC. Plus theres another 6-8 ounces of weight to put on board. Food for though. Thanks!
Where is the 6-8oz coming from?. You could put a motor twice the weight in and it would only add 2.5oz

You will almost certainly need the weight in the nose anyway.
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Old 02-12-2013, 08:08 PM   #23
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Originally Posted by JetPlaneFlyer View Post
Where is the 6-8oz coming from?. You could put a motor twice the weight in and it would only add 2.5oz

You will almost certainly need the weight in the nose anyway.
Yeah that might be a miscalculation on my part.
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Old 02-12-2013, 11:54 PM   #24
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Run a larger motor/battery for nose weight.

Tail weight is lighter, but i'd rather have the longer flight times, andhate just adding lead to add lead.

What is the motor you ended up going with? I'd personally recommend at least a 1:1 thrust to weight ratio, but i'd been told I over power things from time to time.

I went with a powerup 480 plus motor, and jeff advertises 55oz of thrust on 3 cells, and the motor only weighs about 3.6oz. If you find it under powered, you could run a 4 cell and get 450w out of that little motor, although I have not done that yet.
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Old 02-13-2013, 05:03 PM   #25
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Originally Posted by hayofstacks View Post
Run a larger motor/battery for nose weight.

Tail weight is lighter, but i'd rather have the longer flight times, andhate just adding lead to add lead.

What is the motor you ended up going with? I'd personally recommend at least a 1:1 thrust to weight ratio, but i'd been told I over power things from time to time.

I went with a powerup 480 plus motor, and jeff advertises 55oz of thrust on 3 cells, and the motor only weighs about 3.6oz. If you find it under powered, you could run a 4 cell and get 450w out of that little motor, although I have not done that yet.
The motors only rated for 3s. I'm pretty happy that it is going to fly. 75w per lb should be more than enough. I have a twin motor plane. Total watts is only 220. It weighs 3.5lbs. THats about 64 w per pound. Although i don't think is would do anything other than fly around in circles it flys high enough to drop my parachute bloke out the back. I only want my trainer to get comfortable with a low winger. If its really under powered then obviously i'll have a look at changing the motor.
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