Scratch build a Trike

[ystervark7]

Boet, gaan jy nou begin trikes bou ?

Cloud Warrior

I will not be using any standard to build this - it is an experimental home build so I will try and use as much commonsense as possible. I am not sure what CAA requires but I know they want a static load test which I will do with sandbags up to at least 4g's.
I am still considering the FE (finite element analysis which means doing a lot of modeling and calculations on the computer). I might do FEA for the pylon only but note that I am not a mechanical engineer, electronics are more in my line. Furthermore the software is prohibitively expensive for a hobby project (in the order of R100000 for Solidworks with FEM, I use Alibre for my drawings which is much cheaper but the FEM is still in the order of R10000 and I do not know of anybody using it) The pylon I know can hang 3 tons without deformation so I think that I am at least in the right ball park.

---- Warning: do not read if you are not interested in maths -----
I have done some thumb suck calculations on the pylon but these are done with a lot of assumptions (so no criticism please, I know that they are not accurate but if they are totally stupid you can say so):
If I assume that the pylon only hangs on the inner side of the rectangular tube ( this is very rough because some of the stretch might be transferred to the back or there might even be compression on the back in which case I have underestimated it)
The MAW without the wing hanging on the pylon is about 450-60kg = 390kg
using a 80x40x1.5mm rectangular tube the inner metal area is 1.5 x 40 mm = 60 mm2
The yield stress (stress before permanent deformation) of 304 is about 220 N/mm2
This gives a yield of 60x220 = 13200 N or about max of 1350 kg at 9.8kg/N. This gives about 1350kg/390kg = 3.5g before deformation. Not quite enough so I might have to use 80x40x2mm rectangular tubing which gives:
a 80x40x2mm rectangular tube the inner metal area is 2 x 40 mm = 80 mm2
This gives a yield of 80x220 = 17600 N or about 1800 kg. This gives about 1800kg/390kg = max g's of about 4.6g's
the max tensile strength of 304 is 515 N/mm2 which means the g's before the pylon breaks is about 10.7g (you should have passed out by then)
A cable under tension might also be added inside the pylon.
The max stress on the pylon is just above the brace (between the top and the bottom section). I will look at strengthening it there.

The hang point is easy, I know more or less where it is supposed to be and will design around that. The pylon I will make last when everything is fished and adjust the hang point position after I have done the weight and balance.

Fatigue is an issue, but to be honest, I do not have a clue how to take it into account. Any advice welcome. I plan to over design a bit to counter this and do early detection, e.g. pylon pressure leak detection. I will also minimize vibration where possible. The engine mount will be Chromoly and will be the same as the one used on oupG's trike. If resonant frequencies are a great risk I might consider measuring these when the trike is finished but I do not think that this is is a problem on a trike if everything is build relatively stiff.
Advice is always welcome Cloud warrior and if you know of a way that I can do the FE in an affordable way, please let me know. I have tried to find free ones but they are to complicated for me.

[Oupa-G]

The saying goes teach a man to fish etc. In our workshop give a man apiece of metal and he builds an aeroplane, I like the project I saw Vliegvark in the making and to make sure the project maintains momentum I will donate the powerplant it does not have to be a 1200GS anything new that inspires the creative mind I will support. Go for it Ystervark.


Cheers Oupa-G

[ystervark7]

Dankie oupsG but I think that this is to big an offer to accept. Your moral support and help is more than enough.

[Lieb Liebenberg]

Hi all,everyone that wants to have plans,can pay a R100-00 and this money can then be used to buy the GS-motor.I would love that motor in this trike!

[Cloud Warrior]

From what I can see the calc looks good. I have never really gone into the engineering of my trike until now. But you have got me interested. My feeling was that you could really optimise the design by doing some analysis upfront but maybe that is over complicating things. Simple hand calcs should so the trick. Does the CAA require a design package for the design to be approved?

[Cloud Warrior]

From what I can see the calc looks good. I have never really gone into the engineering of my trike until now. But you have got me interested. My feeling was that you could really optimise the design by doing some analysis upfront but maybe that is over complicating things? Simple hand calcs should so the trick for the basic design. Does the CAA require a design package for the design to be approved? I have a contact at Technip who has access to FEA software who owes me a favour. When you are ready with drawings / load cases / etc let me know - maybe he can run an analysis for you (during his lunch break of course!) just to prove that it all works.

I would be very interested to hear on how you came up with your front suspension design - is that a straight copy from a DTA trike?

[Tailspin]

Hi all,everyone that wants to have plans,can pay a R100-00 and this money can then be used to buy the GS-motor.I would love that motor in this trike!

Hi Lieb

You have a Deal.
banking Details ?

[Lieb Liebenberg]

Money to be paid to Ystervark to test his trike with the GS-engine.We can then get sertified plans from him after showing that you are paid up!

[Miskiet]

Remember that fatique is liked to the number of cycles. You get S-N curves for material that you can use to estimate the number of cycles a material can withstand. If you know the stress in a member you can use this curve to estimate how many cycles it will take before failure. How often will the trike be loaded to 4 g? - Probably never.

Also remember your pylon is not straight - The kink will mean that a moment is developed around it which will add to the stress on the inner surface of the tube. The sides will also contribute to the strength.

I think If it passes the 4G load test it will be strong enough for fatique not to be a problem (So lang as you don't do aero's 3 times a day!). Remember even 2 g in a trike is scary.....

[ystervark7]

With all the talk about fatigue I just had to read up on it a more, so Friday night I spent most of the evening on the net doing some research. Thinks Miskiet and Cloud Warrior for pointing me in the right direction.

The way I understand it I think that Miskiet is correct, if it is designed for 4G's fatigue will not be an issue. You must really push it to at least more than 40% of its limit (1.6G in this case) on a regular basis before metal fatigue will even start to come into play.

I also quote from this link http://www.msacomputer.com/FlyingBoats- ... esigns.htm
"If an airplane is designed to the usual 3.8g normal category limit load factor (5.7g ultimate)
the entire structure will be at quite a low stress level during normal operation. It can be shown that if the most versal of +2g once per minute – let us say along the beam can angles, 2014T6 extruded material would have a life expectancy in excess of 15,000 hours of airplane operation. Critical 4130 steel components would experience a considerable greater life expectancy.
Considering 300 hours annual use, an abnormally high rate for a small personal airplane, such an airframe would have a life expectancy of 50 years; if not properly maintained, the structure would corrode away long before any critical fatigue could occur."

I therefore think that this will be well within the limits.

Having said this the question that pops up in my mind is why metal fatigue has resulted in several airplane failures in the past? The best know is probably the Comet of which 3 disintegrated in one year before they realized what the problem is. More recent cases, Angeles Airways Flight 417 and China Airlines Flight 611. I can understand why planes that are pushed to their limits, such as fighter planes or acrobatic planes or helicopters, suffer from metal fatigue but I am not aware of any light airplanes that suffered metal fatigue? Why commercial airplanes?

I think that I can guess but if anybody knows better, let us know. Here is my explanation: Light airplanes are normally designed for at least a 3.8g and most of the time to 4g's limit, commercial passenger aircraft are designed to about 2.5g ( e.g. see http://www.b737.org.uk/limitations.htm). If I can assume a limit of 40% where fatigue will make a impact, what this imply is that light aircraft rarely reach the point where fatigue cycles play a role. On the other hand commercial aircraft with a design limit of typically 2.5g can regularly surpass the limit .

My 2c

[ystervark7]

Thanks for the encouragement and offers on the GS motor!
If you guys have some spare money after building your planes, maybe we can spend it better on more testing. I am not sure what CAA will require but as I understand it the requirements are more difficult if you want to sell a kit or plans. It might be that they will require more tests if several people wants to use the same plans. Maybe somebody got some inside contact at CAA to try and find out. I have not had a lot of dealings with them yet but their response time is not that great if you do get an answer I understand. Personally I am still waiting for a build number.

[Miskiet]

I have not investigated these failures - It probably has to do with dynamic loading/cycles on some critical surface (tail). This normally only happens to fast aircraft. It means some part got exposed to high frequency loads (Like flutter)

The other factor is that commercial aircraft normally does gazzilion hours instead of the 8000-12000 of typical light aircraft. Way, way more than a trike ever would. They also routinely fly in rough, turbulent weather which we never do !!!

[ystervark7]

Monday evening I have spent time with a friend looking at the pylon strength. He did a quick FEM analysis (quick is 4 hours later) and he thinks that it is not strong enough. I will do some more calculations but for that I need a new computer (mine is still running windows 2000 and the software wants to run on 64-bit)

Regarding the suspension Cloud Warrior, yes it is based on the DTA. It is a trailing link suspension and has been used on at least one other trike and on motorbikes as well. I have decided on using it because the construction is easy and it works very well. The only negative that I can see it its aesthetic appearance

I have also assembled the first parts (not welded). I would have liked to do some work this weekend but I am having trouble with getting the stainless steel. The place I have ordered it from only wants to supply me with 6m lengths. I will therefore order it from somewhere else but that will only happen next week.

Fist assembled part: foot pedals

[freetoadventure]

Congratulation Otto on getting started, cant wait to see it coming together!

Cheers
Mark

[ystervark7]

Thanks Mark, (Mark has graciously offered that I can put the design on his website http://www.freetoadventure.com/ from where people will be able to download the CAD files and images)

Today I will discuss the frame and explain my ideas around it. As usual feel free to disagree.

The frame is used mainly to mount all the other stuff on. You do not really have a choice what you are going to mount on it, just where and how. Furthermore it must be strong enough to carry all the weight.

The main part of the frame consists of 2 rectangular stainless steel tubes of 80x40x1,5mm joint at an angle of about 140 deg. An upright that serves a engine mounting is welded to the back of this.

To strengthen this frame, 2 tubes runs from the engine mounting's top (red oval) to the bottom (red circle) Note the important function of these tubes on most trikes: with the engine 'hanging' on one end and pilot in command 'hanging' on the other end of this frame it takes most of the strain of the frame. This also forms a frame around the passenger. (On most trikes the this these tubes run from the red oval to the orange circle. The bottom mounting point was moved forward in this design to 'carry' more of the forward weight and to leave more space for the fuel tank.)

The front part is strengthened as well with 2 tubes running from the blue circle to the blue oval. These 2 tubes have the additional function as mounting points for the front seat. The front seat is easily adjustable by sliding the front seat on these to tubes.

In contrast to most other trike designs, the tank hangs underneath the frame in this design (same as the DTA). Hanging the tank is a bit tricky. In the old DTA's there is a pipe running from the one side of the tank to the other on which the tank hangs in rubber mounts. This is difficult to manufacture and difficult to mount. The new DTA's use a plastic tank that is strapped to the frame. I have moved the tank hanging point to the top of the tank. Two plates welded to the tank act as hanging points. A pipe of about 35mm aligned with the holes is also welded to both sides of the tank. See detailed drawing with pipes and bolt removed. A rubber of 35mm with a hole for a bolt is inserter into these pipes. Large washers will be added to both ends of the bolt and the bolt tightened. The rubber should expand on compression and give a nice tight fit. The front of the tank will rest on a mounting at the blue oval. As an alternative or as a safety a strap can be used running underneath the tank. Straps that can carry 3 tons are easy to find but would need regular replacement.

Until next time.

Frame layout

Tank hang point detail