Funbuild 5 Stinson Model A Tri-motor - Page 3 - RC Groups
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Jan 28, 2012, 09:06 AM
a.k.a. skcope
AVGDAY's Avatar
Originally Posted by glewis
Scott, thanks for the enlarged pics of the gear. I think it makes sense now.
What I see is the black parts are all one piece. Looking at the main strut there is a silver what looks to be a hydraulic cylinder connected at the top of the black arch over the wheel. If the cylinder were to pull straight up the wheel would travel in an arc forward and up. The whole assembly would pivot at the rear of the diagonal struts.
I knew it had to be simpler that I was making it up to be.
Kind of hard to duplicate with small hobby retracts that rotate. Or is it?
I wish the pictures showed a little more detail, but I think you are right. It does look like there may be a hydraulic cylinder which pulls the gear straight up (and probably acts as a shock absorber as well; I've read that Sikorsky used an arrangement such as this on his S-40 amphibious flying boat). It does look as though the rear struts and yoke around the wheel are all one piece. Perhaps you could design a mini air retract system using parts like those available from Hobbyking The price is right.
Otherwise, a mechanical version could be worked out I'm sure.
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Jan 28, 2012, 10:06 AM
It's a Great Day to Fly
LenBFP's Avatar
Maybe the gear works like this. Pivot on the back, top and just above the wheel. Probably the actuator is angled higher at the rear.
Jan 28, 2012, 11:27 AM
Or current resident
glewis's Avatar
Spent some time goofing with geometry of how this gear would retract.
A couple of balsa scraps and some pins and it looks like the only way this will work is for the main gear leg cylinder to pull the wheel straight up. The cylinder would have to pivot at the wheel arch attachment point which is evident in the picture. The top of the cylinder would need to be mounted on a pivot too as the whole assembly travels in an arc.
I did think of a couple of possible mechanical solutions, but they would be very fiddly and prone to damage on all but the smoothest landings.
A pneumatic system wouldn't really possible to do at this small a scale, there just isn't room in the weight budget.

Quit goofing around with the landing gear and went back to working on the model.
I'll say this, this plan leaves a LOT to be desired. It's not so much that there aren't a lot of details showing how things go together, I can handle that. But what is really getting me annoyed is the dang patterns that are there aren't correct! There's also a few that are missing altogether. There's nothing more frustrating than to cut out a bunch of parts THEN find out they don't fit the model.
I'm not talking just a little bit off here either, but so far off they're never going to fit!
Not like I have a ton of <6lb balsa laying around that I want to waste!
So far I'm only into it a few sticks and a quarter sheet of my good contest balsa.

I'm still going to build this model but I might have to rethink this thing and stop using this plan for now. I'm that aggravated with it!

Think I'll order a plan from Cleveland and see what it looks like before I waste much more time and materials on this one.
Since they have a 30% off sale on now a plan the same size as this will only cost like 15 bucks plus shipping.
Only bummer about ordering from them is they are kind of slow. Not nearly as bad as Carstens though.....

Jan 28, 2012, 11:47 AM
Registered User
E-Challenged's Avatar
I would opt for a larger scale plan, if possible, at least 48" w/s for more wing area. It will be a challenge with a scale twin to select an adequate but light twin power system with a small model. With a larger model, built light, you could consider making the gear functional and still have scale like flight performance. Sup to you!
Jan 28, 2012, 12:28 PM
Or current resident
glewis's Avatar
That's what I was thinking. Cleveland lists the plan at 45".
That will give a bit more room for the equipment and possibly other details.

Only one problem, the scale prop size is 7.5". The most the 1811 motor could handle in my tests is a 7x3.5. It spins that prop at 7800rpm with a pitch speed of 28mph and generates only 4.4oz of thrust. I don't think it will be a big deal that the prop is 1/2" smaller. Biggest problem is if that prop proves inadequate that is all the motors can handle and the whole power system will have to be redesigned. More power means a bigger battery and more weight.....

This is why my first potential fun build entry didn't pan out. It was stuck between power system choices. The 1811 wasn't powerful enough. The next size up is a 20mm motor but they weigh twice as much. I couldn't find a KV that was suitable to two cell use on the scale size prop. I would have to make my own 20mm motors so I could customize the KV and didn't want to make 4 of them!
Jan 28, 2012, 02:39 PM
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danrc's Avatar
The 16 gram motor has the 7" prop right in its wheelhouse.
Jan 28, 2012, 02:54 PM
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glewis's Avatar
Yes it is Dan. There's only 2 problems.
One is the Kv is low and it needs a 3 cell pack to make any power on a prop that small.
The other is the 16g is without a mount. It's more like 20g ready to actually use.
Right back where I started and this is what killed my original proposed entry.
If the motor weighs 20g I might as well make my own motors and tailor the KV to exactly what I want.

I already ordered the 45" span Cleveland plan but it will take at least a week to get here.

Jan 28, 2012, 06:26 PM
Registered User
Bill Smudge's Avatar
Danged Bummer on your plan problems Glenn!!!

It's no fun to get all warmed up on a project and have the rug pulled out from under you

When you get to it, I think the dark blue/red paint scheme looks great.

I'll be watching your build when you get reloaded, good luck with the new plans.

I really like the subject matter, and yes the plane does have the SR-7 wing appearance.

Jan 28, 2012, 06:46 PM
Or current resident
glewis's Avatar
Thanks Bill. I'm a bit bummed about it but I'm still stoked about building this unique looking model.

Also found another problem with that plan. The front view isn't the exact same scale as the side view. The front formers of the nacelles and fuselage have to come from the front view....
There are also a few patterns of parts of the nacelles and wing center section missing too.
Think it's best to cut my losses now before I waste too much time and material on this version.

So now we wait for a better plan....
To be continued....

Jan 28, 2012, 06:58 PM
It's a Great Day to Fly
LenBFP's Avatar
I picked up a motor from HK that weighs 20 grams with prop adapter and motor mount, it comes in 2050kv and 2200kv. I am using the former with a 6x3x3 and a 350mah 2 cell battery. I like it. I really like the prop adapter that comes with it.

Last edited by LenBFP; Jan 28, 2012 at 07:06 PM.
Jan 28, 2012, 06:59 PM
Or current resident
glewis's Avatar

HTX D1811-2000 motor tests

I tested an 1811 with all the props within it's operating limits and tabulated the data into a spreadsheet. Included is the measured current, prop rpm, thrust and pitch speed. I would like to share it with the community but can't post an .xls file.
Tried importing it into open office to convert to a .doc but it doesn't work.

Anybody have an idea how I can format the spreadsheet into something I can post and share?

Jan 28, 2012, 07:10 PM
It's a Great Day to Fly
LenBFP's Avatar
Open it on your monitor and hit print screen then open Paint and paste. Save as a jpg.

Jan 28, 2012, 07:15 PM
Or current resident
glewis's Avatar
Thanks Len.
Dan had suggested that motor too. Looks to be a good possibility if the 1811's don't have sufficient motivation I'll have to snag a few.

I also have 2 of these new in the bag in my stash, plus one 2500Kv version.
They might be the ticket for the larger model.

Jan 28, 2012, 07:18 PM
It's a Great Day to Fly
LenBFP's Avatar
I have a couple of those too, they seem to like 6x3 props, not much more, but they really crank.


I need to look at it, It may be a 6x5 I have on it.
Jan 28, 2012, 07:24 PM
Or current resident
glewis's Avatar
You mean the 2100 likes only a 6" prop? Crap, not enough.

I did what you suggested on the spreadsheet and it works. It's a tad on the blurry side but is better than nothing. Thanks for the suggestion.


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