Loverrly legs

[Tim Mackey]

I have decided to go for some DSR units for my 11lb+ Seagull PC9.

I like the look of the E-Flite units, but not the price.

The Lander all metal units look and read like the same units, but I have no hands on experience of them, although another club member has some of the smaller sized ones, and rates them pretty high. I can get the lander ones complete with trike set oleos for quite a bit less than the E-flites cost with just simple wire legs.

However, the lander main leg oleos are too long at 115mm from unit to axle hole, and my maximum available length is 90mm, with 85 being even better.

So, has anyone experience of the .120 size lander all electrics, and more importantly, where can I get some quality mains oleo legs of 85 -90mm length.

[andy watson]

I can dig out the tape measure when I get home, but I had exactly the same problem with the vulcan- and went for the same solution.

 

In the end I went to himodel.com

 

They are so cheap I just bought 3 different sets and decided which were best when they arrived!! I can check later and possibly send you some of my "rejects" if they fit your requirements

[Tim Mackey]

Sounds like a plan Andy, meanwhile I have contacted unitracts, but they are a bit pricey!

Thanks mate, I ook forward to hearing from the tape measure

[Alan Cantwell]

OY, you dont get much engineering for that money, cheapskates if you need them shortening. let me know, see what i can do

[Tim Mackey]

Cheers Alan - I could turn em down on my likkle lathe, but not sure how I would refix the solid barrel bits back in to take the con rod.

I might PM ya, if I get stuck.

[Tim Mackey]

Right, have found some decent strong oleos in my bits box , but these too are 115mm long. I obviously need to retain the 16mm sprung travel, but somehow need to chop 'em down to 85 -90 mm from axle centre to top end. The picture shows the setup at the mo.

If I removed the brass insert, Im not sure I could guarantee getting it back in securely enough. It looks like it has a sort of fine ridged /serrated edge to the outer surface, which was probably pressed in under high pressure. The set screws then go right through the leg wall ( 2mm ) and then through the barrel to clamp the con rod, which in turn obviously fits into the retract unit.

Although heavy, these legs do seem strong and are nice thick walled, hard looking aluminium so could be just the job.

[Tim Mackey]

Any engineers out there fancy advising me as to how to do this job?

Obviously I need to remove around 25 -30mm from the insert end, and then refit the insert.

1) I'm thinking ( I am NOT an engineer ) that maybe the strut is heated up, and the brass insert then releases easily?

2) I assume aluminium expands more than brass?

3) How will I know where to exactly drill and tap for the repositioned set screws? I'd rather use the existing holes in the insert, but maybe I need to re-drill and tap through the leg and into the insert.... once re-positioned?

4) Should I loctite or similar the insert in place rather than just relying on friction and the set screws? If so which loctite is best for brass+Aluminium

5) I will need a shorter compression spring - and it needs to be tough to support 11+ lbs without compressing too easily IYSWIM - where can I get a couple of such springs - or should I cut down the existing ones?

 

I have made oleos before from scratch, but not for a model as heavy as this so it needs doing right.

 

Any advice welcomed

 

[Brian Parker]

I’ve recently successfully fabricated crankshafts for model steam and IC engines trying both Loctite 262 and Truloc 231 (using a light press fit and then pinning).

If you need to reduce the length by 30mm and the brass bush is 30mm then it’s probably easier to make up and fit new brass bushes. Drill and tap after fitting.

 

If you cut the spring then it will be less ‘springy’ but the working load will not be altered. A spring is a length of bar in torsion (although it behaves slightly differently when a helix), a shorter bar twists less than a longer bar for the same load (ie. more turns, more spring).

You need a springs with the same spring rating (force/mm deflection) as the original but at the new free length to maintain the correct working length.

Or you could pop the springs in the oven with the Sunday roast for 15minutes to alter temper. Be careful whose temper you alter.

[Tim Mackey]

Thanks Brian, very good info

Can I take it that I am correct on questions 1 and 2 ?

[Brian Parker]

Expansion rate of Aluminium and brass is very similar ( Al. slightly higher). As expansion is linear the brass will loosen.

[Tim Mackey]

Well I removed the first brass insert - removed the two set screws and without heat, it drifted out quite readily. Its actually 17mm long, but as suspected, its serrated all around the circumference which obviously makes a tight interference fit, probably inserted with a press - and is then located by the two set screws.

Is this serrated brass rod available to buy then?

Or should I revert to plan A and try to relocate it accurately and reuse the tapped holes already in the insert

[Alan Cantwell]

no problem, new knurled bush, shorten leg, put brass bush on peg, press in with tailstock, drill and tap through, do you want to try it? or send them to me

Edited By Alan 4 on 07/07/2011 18:28:46

[Tim Mackey]

Well, I have pressed the old knurled bush back in, and heated up the work, and then pressed 25 mm further in using a 6mm bolt as drift. Now all I have to do is drill and tap two new holes. However, the amount of travel left for the "piston" section is now seriously limited, and chopping the spring in half results in just about 9 mm of travel instead of the original 20 or so .I also seriously doubt my ability to drill and tap two new holes accurately enough, and besides....will the insert now be too weak with 4 x holes in it

Have I goosed it

Is it too late to send them off to a pro ( you ! ) - and see if he can get me out of the sticky stuff

[Brian Parker]

It’s only serrated to allow for loose manufacturing tolerances.

You need to make a new bush, (does it need to be as long as 17mm? Probably not).

Take up Alan’s offer or start making swaff.

Edited By Brian Parker on 07/07/2011 19:05:21

[Tim Mackey]

I can make swarf, but how do you do make swaff ? LOL

[Brian Parker]

It's my accent

Edited By Brian Parker on 07/07/2011 19:08:19

[Tim Mackey]

LOL - I spotted the un-edited version first

[Brian Parker]

[Tim Mackey]

Actually, I am thinking that the inserts probably do need to be about that long - in order for the socket to give proper support to the 5 mm "con rod".

I may be able to shave a few mm off, but wouldnt like to shorten the socket TBH.

This still leaves me with the problem of having sufficient room left in the leg tube for a spring..... and its compression.

Maybe thats the reason why all these larger sized oleos seem to be around 115mm long

[Tim Mackey]

Update. First, the Lander DSrs arrived, and I am not best pleased TBH.

One unit showed too much slop in the "down " position, and I emailed the supplier in China to complain. he suggested that there was an adjusting screw which would compensate - but it simply doesnt.

After adjusting as instructed, the unit stopped working altogether - so will now have to be returned to China for exchange

I have also ordered some smaller sized E-Flite ones for my new flyfly Hawk, so will be interested to see how the quality compares. Seems so far, that in this particular department, you do get what you pay for .

On the good news front, Alan 4made a terrific job of altering the oleos for me - and got a bit creative with the lathe and a couple of O rings!

Im sure youll agree, they look a whole lot better than before!

The new look and size

[Alan Cantwell]

and heres me wanting to make a comment on Tims luverly legs, pretty, arnt they? and quite a challenge to get them to 90 mm, full blow by blow account later if anyones interested, think you need a bigger shot Tim, cant see all the detail there

 

forgot to mention,   the 3mm pan head that slides up the slot,  i did not secure it, thinking you may want to play with the tension, dont forget to thread lock it when you are happy

Edited By Alan 4 on 29/07/2011 16:47:24

[Tim Mackey]

Ah, OK, Ill do that now....

And heres the close up.

By all means lets have the full story Alan