• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

Scratchbuilding a EPP Gentle Lady for a friend

cdfigueredo

Well-known member
#1
Some time ago I was approached by a person interested in the hobby with a lot of desire to have and fly his own plane. Considering that we don't have the possibility to buy a Tx or other parts, I thought that I could build an interchangeable module containing my Rx and a couple of servos and use my own Tx.
Thinking about which model to build for him, that would be easy to fly and entertaining, as well as simple (without motor), I came up with the idea to make a tribute to Carl Goldberg and build this beautiful model. As I can't get balsa, then we'll try it in foam.

The wings were cut from a solid block and have a totoal span of 2m and are divided into 4 sections.
IMG_20200829_092001.jpg IMG_20200829_091955.jpg IMG_20200829_091950.jpg IMG_20200829_104022.jpg

Each section has been reinforced with two 5mm wood strips. Wings and reinforcements are 158g.
IMG_20200831_090255.jpg

The gendle lady has only two channels, rudder and elevator, so my swappable pod will only have two servos and the Rx. We will use 4 AAA batteries connected directly to the Rx, this should help to get a good balance without adding extra nose weight.
 

cdfigueredo

Well-known member
#2
This is my first glider, so I have no previous experience. I have read a lot and I know that the gentle lady is a great model for beginners. I hope everything goes well.

So any help or opinion is really welcome!! :rolleyes:
 

quorneng

Well-known member
#3
Those foam wings look very nice.
Thin wood strips top and bottom are a very effective way of giving considerable bending strength for minimum weight. It is a principle I have used many times on foam wings.
How do you intend to join the sections together, particularly the centre join which carries the greatest bending load?

The rear fuselage, fin and tail plane requires as much attention to providing stiffness and light weight otherwise you will find your 4 AAA batteries in the nose may not be enough! ;)

I will follow with interst.
 

cdfigueredo

Well-known member
#4
Those foam wings look very nice.
Thin wood strips top and bottom are a very effective way of giving considerable bending strength for minimum weight. It is a principle I have used many times on foam wings.
How do you intend to join the sections together, particularly the centre join which carries the greatest bending load?

The rear fuselage, fin and tail plane requires as much attention to providing stiffness and light weight otherwise you will find your 4 AAA batteries in the nose may not be enough! ;)

I will follow with interst.
U are rigth, those wood strips made the job really well! i have used this method in almost all my planes.

i am planing to join the wings using 2 plywood reinforcements per join as a sandwish. look this diagram... it is not so clear, it is a bad representation, the best i can do form linux. :ROFLMAO::ROFLMAO::ROFLMAO:
1111.png
The blue pieces in the center part of the picture are the plywood reinforcement with th right dihedral angle. And the last part is a top view.

I will take spacial care abut the weight on the tail! thanks for the adive.
 

quorneng

Well-known member
#5
Using a pair of plywood "dihedral braces" is the conventional way of doing it and should work well.
Just be sure the plywood is of a good quality and the glue used is strong enough to transfer the load from the wood spars to the plywood.
The strength of your whole wing is going to rely almost entirely on the strength of a single joint.
 

cdfigueredo

Well-known member
#6
Using a pair of plywood "dihedral braces" is the conventional way of doing it and should work well.
Just be sure the plywood is of a good quality and the glue used is strong enough to transfer the load from the wood spars to the plywood.
The strength of your whole wing is going to rely almost entirely on the strength of a single joint.
I will do it! thanks!!!
 

cdfigueredo

Well-known member
#7
Is it possible to fly a glider with this in the plains? Where I live there are no elevations to fly on, only one but it is not very high and it is surrounded by trees everywhere.
When the model is ready, we will do glide tests, but I am sure we will want more. We plan to tow it by hand. Let's hope this works so we can get a decent height that will allow us to glide smoothly until landing.

I just want to know if the glider could gain height using some thermals? or even lift itself on very windy days while pointing into the wind.
My experience with gliders is zero, so any help would be greatly appreciated. :rolleyes::rolleyes::rolleyes:
 

cdfigueredo

Well-known member
#8
Last night I was looking closely at the plane and I realized that they are no more and no less than 2 meters in wingspan. :eek::eek::eek:
And I realized that I was thinking of joining the half-wings permanently. But if I do this I probably won't be able to get the model out of the room. No, I'm kidding, but it would really make it difficult to get it out on the field. Therefore the solution is to build the wings in such a way that they can be detached in two halves.

then I have two solutions:
  1. Either I divide the wing into 3 parts: Central section and the two wing tips,
  2. or I divide it into 2 halves.
The first option makes me confident that the union of the central parts of the wings is more secure because everything is glued in place, but also results in a wing formed by three pieces where I have to make two mechanisms to join the external sections. On the other hand the second option results in only two pieces and only one joint, but that will be exposed to high forces.

Personally I like the second option more, using a steel rod bent according to the angle of the dihedral to join the two parts.
But I really don't know what to do. Any suggestions? I wouldn't want a wing to come off in mid-flight. :oops:
 

cdfigueredo

Well-known member
#9
In either case, the options I have for attaching the wings are as follows:
Use a plywood key or use a steel key. With only 7mm of separation between the reinforcements of the wings, I believe that a plywood key would be very weak and could break or bend.
V1.png
Instead, using a steel wrench, and a rolled up cardboard sleeve to enlarge the diameter to 7mm would work better.
v2.png
what do u think?
 

cdfigueredo

Well-known member
#10
I finally decided on the second option. A steel rod, bent to the required angle, serves as a support for the wings.
IMG_20200913_113049.jpg IMG_20200913_113044.jpg IMG_20200913_112609.jpg IMG_20200913_112854.jpg
All that remains is to join the external sections of the wings and add some reinforcements to the central area. I hope that everything resists.
 

quorneng

Well-known member
#11
dcfigueredo
You have two steel rods, one above the other?
It will probably be adequate but be aware that under bending the top rod will also be under compression so will tend to stay in place but the bottom rod will also be under tension so will try to pullout.
If you look at almost any wing joiner it uses a single bigger diameter joiner, usually a tube as it is less than half the weight of a rod for virtually the same stiffness. As a single element it has to resist all the bending forces so has no tendency to pull out under load.

Note if you set the dihedral angle in the wing tubes the joiner can be straight.
WingJoiner.jpg
 

danskis

Well-known member
#12
Carlos - this looks good. It will definitely thermal and be a great beginner plane. You could put a small motor on it which would help balance it. You can also put a hook on the bottom about 5mm in front of the CoG. With that you could tow it up or use a high start. Both can be done with rudder and elevator. Without the motor just remember to keep it up wind. If you build it to plan you will probably have to add extra nose weight....I have a 3 cell lipo and a motor in the front of mine and it balances well. You might consider extending the nose about 40-50mm so you don't have to add too much weight. Also, can you get aluminum or fibre-glass arrow shafts in Cuba? They would be a big help in building spars - you're rolled paper looks good though! Since the plane should be very light and the wing is large the wing loading should be low. Are the airports open yet?

edit: the high start will definitely increase the wing loading.
 

cdfigueredo

Well-known member
#13
dcfigueredo
You have two steel rods, one above the other?
It will probably be adequate but be aware that under bending the top rod will also be under compression so will tend to stay in place but the bottom rod will also be under tension so will try to pullout.
If you look at almost any wing joiner it uses a single bigger diameter joiner, usually a tube as it is less than half the weight of a rod for virtually the same stiffness. As a single element it has to resist all the bending forces so has no tendency to pull out under load.

Note if you set the dihedral angle in the wing tubes the joiner can be straight.
View attachment 179035
quorneng,
thanks for the advice!I'm not using two bars, in the previous picture it was one wing over the other and made it look like two holes in the same wing. I'll post more pictures tomorrow.

I understand what you mean by the diagram, the problem is that my wing is not thick enough to receive a reinforcement like the one shown in the photo.

I made some calculations and the maximum length of the tube is only 14 cm and 5 mm in diameter. Given the stress it has to withstand it is necessary to use carbon fiber, fiberglass or some aluminum, and I really can't get any of that where I live.

Edit: this picture is not scale but mensures are.
IMG_20200914_191840.jpg
IMG_20200914_195817.jpg
 
Last edited:

cdfigueredo

Well-known member
#14
Carlos - this looks good. It will definitely thermal and be a great beginner plane. You could put a small motor on it which would help balance it. You can also put a hook on the bottom about 5mm in front of the CoG. With that you could tow it up or use a high start. Both can be done with rudder and elevator. Without the motor just remember to keep it up wind. If you build it to plan you will probably have to add extra nose weight....I have a 3 cell lipo and a motor in the front of mine and it balances well. You might consider extending the nose about 40-50mm so you don't have to add too much weight. Also, can you get aluminum or fibre-glass arrow shafts in Cuba? They would be a big help in building spars - you're rolled paper looks good though! Since the plane should be very light and the wing is large the wing loading should be low. Are the airports open yet?

edit: the high start will definitely increase the wing loading.
I'm glad to know that I'm on the right track! This glider is not for me, I am building it with a friend who wants to start in the hobby but does not have the means. For now I do not plan to add a motor, only two servos to control elevator and rudder. I plan to lend my Tx and Rx for him to fly and practice while I am around to correct it.
I will certainly add a tow hook, I think it is the only way I have so far to get him to a descending height. Later I will add the engine.
I will consider extending the nose to improve the balance, thanks for that!
Unfortunately I can't get arrows here. I think we'll have to give the rolled up cardboard a try. It really looks good and pretty strong.

If all goes well, after my friend masters it in flight, we will add a motor to the nose.
The airports are still closed, I think we will crash like this at least for another month. Hopefully everything will get better soon.
Un abrazo mi amigo, Carlos.
 

danskis

Well-known member
#16
The spar looks good is certainly strong enough to tow up with a string. It is probably good enough to high-start. You could reinforce the center of the wing with fibre-glass or perhaps just some paper glued on with thin glue....maybe multiple layers (like the cardboard tube) in a strip about 100mm wide.
 
#17
The rudder and the elevator are finished. In the plan they use a 5mm thick balsa, instead I have used 1cm foam for mine. The elevator is huge, so I have decided to reinforce it with a 5mm wooden rod. It is never good to sacrifice structure to lose weight.
3.jpg 2.jpg 1.jpg 4.jpg

The wings and tail group weigh about 190g and the electronics about 70g. This gives me a total of 160g. Not bad for the foam version.
5.jpg
6.jpg

I am working on the fuselage now. I will upload more pictures later.