Scratch build a Trike

[AndyCAP]

Ystervark, I have only now come across this thread and have scanned though the main points. i am by no means an expert on fatigue, however delving into my Maties Mech eng. background as well as experience in the field, there are to main variables to fatigue life of a component:

1) Magnitude of the load
2) frequency of the load

You can fatigue a component by loading it with a large load for a few cycles (low frequency) or a small load for many cycles (high frequency). Generally components in aircraft and other machinery break as a result of the latter. Vibration is the biggest killer here - i.e. very low load, but high frequency.

Another aspect to consider is the natural harmonic frequency of a component or assembly. When the source of your vibration (primarily the engine in the case of a trike) generates a frequency that is close or equal to the natural harmonic frequency of the component, it will be excited to a state where it will fail (just like the soprano's singing breaks a glass)

there is a classic case where a suspension bridge was built in the USA over a canyon where they did not take the effect of the wind into account. The bridge could easily handle the maximum loads that it was designed to carry, however on one fateful day the wind blew out of just the right angle and strength which caused the cables of the bridge to vibrate. This vibration was close enough to the harmonic frequency of the bridge system and this caused it to start vibrating in unison, gradually growing bigger and bigger until the whole bridge was twisting from side to side. the film that was taken at the time (it must be on youtube!) showed a guy walking on the centre line of the road with the sidewalks twisting up and down in a sinisoidal manner. Shortly thereafter the bridge failed completely.

So just a word of warning dont just look at the ultimate loading at a relatively low frequency - the vibration from your engine is always (hopefully!!) there when you fly probably the biggest portential problem that you may face from a fatigue perspective.

You can ensure that this is overcome by allowing sufficient flex in your structures and isolation of vibration (engine mountings etc.) look closely at how other similar trikes are built (you clearly have) - particularly the commercially available ones to get clues as to how the brackets etc are designed. be careful of using too small a radius on bracket corners since this is where cracks start.

As another side example. A riveted structure often provides better fatigue resistance than a welded structure. as an example welding has replaced the use of riviting in most steel structures (ships & civil structures) post WW2, however you will still find rivits are used in the ladderframe chassis' of trucks. the reason is that it can carry the load but allow sufficient flexability to absorb vibration and twisting loads without succumbing to fatigue failures.

Hope this helps and that I dont have it horribly wrong !

Good luck with your project - its very exciting and necessary to get to make aviation more affordable!

[ystervark7]

I have been quiet for a while, mainly because I have worked on the trike and I had to do a bit of flying as well. I also replaced my old computer with a new one and installing all the software and configuring it takes quite a bit of time.

Since my last post I got most of my stainless steel and I have started on the fork. All the metal has now been cut and drilled for the fork and it must now be welded. Here is a photo of all the pieces.

I have also worked on the CAD drawing. I have added some detail and added some of the major components. An engine (a genuine box engine) and a wing was added just to get a better idea of what it is going to look like. Currently the engine and wing are attached to the frame with "sky hooks". I will add details of both "sky hooks" in future since I will have to make these parts. I am working on a new hang point actuator design that will be a bit different from existing ones and I hope will be easier to make with just some basic tools and easier to operate. As soon as I have all the niggles sorted out I will put it on the forum for comment.

One thing that I have not mentioned before is that I have made the trike about 150mm longer than a 'normal' trike. The reason for that is mainly to make more legroom for the passenger. I do not take a lot of passengers but normally they complain that it is a bit tight at the back so I thought that it is a good idea to make it a bit longer. Here is an image of the latest model.

Trike with wing and engine

[Bullseye]

Hi Ystervark

Stel al lank belang om n trike te bou,Het al na n klomp planne en tipes gekyk, baie geintriseert wat in wat jy bou, ek wil graag n sterk rugget tipe trike bou, vir die veld ens land , is n boer.Ek wil kyk na n sterk struktuur, groter wiele , ordentlike suspensie, plein harde sonder fiterjasie trike, iets soos my cruizer maar net in the air , as jy weet wat ek bedoel, het n klaar omboude BMW enjin ,Rotax ratkas,Deul feul sistem , deul ignition, wat uit n bushbaby uitkom, wat ek dink net die ding kan doen, ek het al iets gesien waarvan ek baie hou, ek sien jy verstaan al baie van ontwerp en bou af, sal graag wil kom kers opsteek met die ontwerp ens. hoop ons kan gesels dat jy my hier en daar kan touwys maak.Sterkte met jou trike , dit lyk goed

Bullseye

[ystervark7]

Bullseye

Ek dink die trike is die ding vir jou. Dit work gebou om rowwe terein te kan vat. (Dit is gebaseer op 'n DTA as jy al een gesien het)

Met die wiele is die plan om ses duim rims op te sit, waarskynlik met vliegtuig wiele (selfde as 'n Cessna dink ek) Dit is aan die swaar kant maar daarmee sal jy enige plek kan land.

Die engine sal werk.

As jy naby die Kaap is moet jy 'n draai kom maak en ons sal jou kan wys wat die plan is. Ek stuur vir jou 'n private mail met my kontak details. Daar is ook 'n moontlikheid dat ek binnekort 'n draai in Gauteng gaan maak as jy daar rond is.

ystervark

[Oupa-G]

Bullseye
Die engine wat uit die Bushbaby kom is dit die ou tipe engine wat ons na verwys as die airhead. Stuur 'n foto

Cheers Oupa-G

[Cloud Warrior]

Ystervark

What prevents the control bar (& wing from flying up) from going too far forward without the front strut there?

Cheers

Sebastian

[ystervark7]

Ystervark

What prevents the control bar (& wing from flying up) from going too far forward without the front strut there?

Cheers

Sebastian

Sebastian

Good question. It can actually go forward all the way. On the DTA they have a bracket at the top of the pylon that stops it. Below is a photo of one (black bracket that looks like a boomerang) This one is in the down position to remove the wing. The stop needs a bolt through one of the three holes to act as a stop. The position where it stops is determined by which hole you use.

I have seen at least one DTA flown without the stop so I do not think it is really necessary for the stop but it does make you feel safer.

You might also want to know how you tie it down without the front strut: the bar is normally tied to the seat.

[Cloud Warrior]

Aaaaah ok!

I thought it might be something like that. What if the bar is snatched out of your grasp during turbulence?

[Wargames]

Aaaaah ok!

I thought it might be something like that. What if the bar is snatched out of your grasp during turbulence?

You don't need to worry about that. The bar will always return to the neutral position. It is easier to fly turbulence in that position, so the bar would actually go nowhere.

[Cloud Warrior]

So the weight of the trike would not allow the wing to move to a high angle of attack? Bar would be forced to neutral?

[Wargames]

So the weight of the trike would not allow the wing to move to a high angle of attack? Bar would be forced to neutral?

Its all about the hang-point position. Not about the weight. Move the hang-point forward, and you will fly faster with bar automatically closer to you. (So you do not have to pull in as much.) Reverse also true. That s the beauty of electric trim. You can change your hangpoint in flight and thus your speed.

You need to remember that a trike is not a fixed wing where the placement of weight directly influence your balance. As you indicated, it is all about angle of attack, but in a trike, this is not affected by where you put what on the undercarriage. It is only affected by the setting of the hang-point.

[Cloud Warrior]

I hear you but what if the wing is violently flung up by a gust of wind in turbulent conditions. The bar is wrenched from your hands and is out of reach because there is no front strut. The wing is say now nearly 70 to 75 degrees from the horizontal? It is no longer flying and you are starting to fall. Would the wing recover from that position with the air flowing nearly straight up? If most of the wing area is in front of the hang point I can't see that happening or have I got it wrong?

[Cloud Warrior]

And apologies to Ystervark for the hijack. We were just talking about this issue in the hangar over the weekend and I would really like to understand how this arrangement is made to work safely.

[Wargames]

I don't know how to better describe this, but to do some calculations. You need to remember that your wing is always in balance, and that a trike wing is set at a certain angle of attack at the hang point, which you can alter by pulling or pushing the bar, which in turn will have a effect on your speed.

Now, on turbulence, you need to know that air, like a fluid, move from a high pressure to a low pressure, and if it passes an obstacle, it will create turbulence. Heat creates turbulence as well, aka thermals. Lets discuss this issue with thermals, as it is vertical movement, which is your biggest concern. Now we need to look at flying into a thermal head on, and then flying along a thermal, with one wing penetrating the thermal slowly.

Flying head on into a thermal at 80km/h, means that you are flying 22.22m/s. your wing is approx 3m from nose to a line connecting your wingtips, which mean you will enter a thermal in 0.13 seconds. That is way to quick for the bar to be bumped out of your hands and the wing flipping backwards into a complete stall. You will feel the thermal more than the pushing and pulling on the bar. Flying along a thermal with one wing slowly penetrating, will have a wing drop effect to try and kick you out of the thermal. This is only because the time for entering is longer with one wing rising in the thermal, rather than the other one stalling and dropping.

Ask all experienced pilots, and all will tell you that the best way to fly turbulence, is to relax or arms, or even to let go of the bar. They will not suggest this, if it was dangerous.

Hope this helps.

PS: Sorry to high JACK this thread. Maybe mods can move it to own topic, although this is something to consider, or not to consider when building your own trike, although ystervark is only building an undercarriage and not a wing.

[ystervark7]

I am glad your guys are sorting this out because I would not have been able to answer the question.

I do not worry about it because it has never been an issue that I feel as if the bar might be torn from my hands, not to the front anyway. It is also true that it even if I leave the bar it will always return to the neutral position.

While I am only building the frame and not the wing the stop at the back is part of the frame not the wing. I will therefore have to consider this.

Also note that I will leave the option open to add a profile tube in front, in fact I will have a bracket at the front of the frame on mine just in case I change my mind.