Hello everyone,

I am considering replacing my second plane by a Tiger 2. The plane just looks and flies fantastic. I have seen it at the field and I have tried it. I have been looking through the forums searching for recommended modifications and have found plenty, mainly about increasing the rudder surface. I ampretty sure I will buy it ARF.
I wonder if anyone has ever modified the Tiger 2 - 40 to be taildragger BUT WITH RETRACTS installed in the main wing. If anyone has, please drop me a note

Take care
Carlos
Guatemala

Carlos:

If you can't find somebody that's done retracts on a Tiger 2 tail-dragger, I'd go look at the "Long Awaited UltraSport Build Thread" and see how the retracts are done there. Both planes are low wingers, the biggest difference is the US has a tapered wing where your Tiger's is constant chord.

If you're going to use mechanical retracts, your biggest problem may be getting the retract push rods to not bind where they connect with the retract servo arm. As I remember, the wing on my Tiger 2 wasn't too thick, and the top of the servo may be far enough above the top of the wing to create a problem.

I suppose you could go to a set of air up/spring down pneumatics, but it wouldn't be cheap.

You'll have a ball with your Tiger, it's a great 2nd plane.

Fred

Many thanks Fred,
I have not yet started but if the wing is thin, I may have to "give it a thought" as I will be using mechanical retracts. I guess some "mechanical engineering skills might be in order". I really want to set it and I see it as a challenge. I will be checking the thread you mention as a guideline and I hope to take pictures and let you all know (if I succeed).
Take care
Carlos

Fred,
just a quick question as it is my first set of retracts... Can I use a regular servo (Futaba S3004) or must it be a special servo?
Thanks
Carlos

IMO You need to use a RETRACT Servo. The Futuba S136G, Hitec HS-75(the ones that I've been using), or the Hobbico CS-63 are all good choices. These servos are designed for mechanical retracts and do a good job. Lots of torque. Mind you, each of these servos is not adjustable - they move through 180 degrees of travel (Stop to Stop). The 3004 would not have the strength to do the job. The Hitec and Hobbico only run about $30 each new from Tower. I just picked a Hitec HS 75 on RCU for $10.

Many thanks!
now I am set and will start the mods once the Tiger 2 is delivered
Carlos

PS:
sorry to ask, but what is the meaning of "IMO"

Carlos:

1) I'm pretty sure IMO is internet-speak for "In My Opinion". "IMHO" is "In my humble opinion". And for lots of the other letter combo's, I've gotta ask my kid. Sometimes I don't want to know the answer.

2) Bassfisher's got it correct. You need to use a retract servo, first for the higher torque needed to push/pull the gear, second for the longer arm travel, and third because the retract servo doesn't consume power when holding a fully open/closed position (which would happen with a regular servo). You need to make sure your push rod travel is adjusted correctly: meaning the rods open/close the gear completely, as well as moving just a bit further so that the gear lock into place. If you have insufficient travel, the gear can collapse because the locks don't engage. One the other hand, if you put in too much travel, the lock will be engaged, but the servo arm may be trying to move further, which will drain your flight battery because the retract servo isn't at the end of its travel. (This sounds more difficult than it really is.)

As I recall, to activate the Robart mechanicals on my UltraSport, I needed about 1-1/8" of total travel, and ended up using a 3/32" piece of birch plywood for the servo arm, mounted inside a Hitec adjustable arm mount on an HS75. I'll try to provide a picture when I get home tonight.

Fred

Carlos:

Maybe these pictures of the retract install on my US60 will help:

Picture 1: Shot of the bottom of my wing. Note the size of the wheel wells vs. the wheels. I will discuss this more below.
Picture 2: A (poor!) shot of the top of the wing, to give you and idea of where you'll need to mount the retract servo. (The servo you see further back controls the flaps.)
Picture 3: A shot of the retract servo installed in the wing. You can see how it sits so that the push rods operate just below the wing skin. In this picture, the pushrods have been moved far enough to engage the strut locks in the retracted position.
Picture 4: Another shot of the retract servo, beginning to extend the gear.

I measured the distance from the bottom of the servo to the top of the EZ connectors, and it's a little over 2 inches which (if my math doesn't fail too badly) is about 50mm. So you'll need that amount of depth in the forward portion of the wing to keep the bottom of the servo from sticking out of the bottom of the plane (or else you'd have to figure out how to mount the servo upside down, which I don't even want to think about). I also though about putting bends in the pushrods so the servo arm could sit above the top of the wing, but then threading the rods through the wing to the retracts might turn into a nightmare.

A couple of other things to consider. The wheel wells on the US are 3" in diameter, with 2" wheels. I'm not sure how much distance there is on a Tiger2 between the wing spar and the leading edge, but that will limit the size of your wheel wells. If the wells are too small in diameter, your wheels may hang up when retracting or extending because the landing gear struts will bend, especially if you're flying off a rough field or after a rough landing (but then you never do those, right? )

The wings on the Tiger2 are joined with a couple of small pieces of hardwood, but there's not an aluminum wing tube. And I think the center joint is wrapped with clear tape, but not something strong like fiberglass. If you have to cut away most of the center rib in front of the spar, you might end up weakening the wing joint, as well as weakening the wooden tab that holds the wing into the fuselage. There's probably enough room to mount the retract servo on one side of the center rib to avoid these problems.

Fred

Fred,

you cannot imagine how helpful your messege is. I am an engineer and I have built several planes from scratch but this is my first "major" modification. Even so, you just nailed the main problems I will face and even venture some answers. Many thanks!!

I have though about setting the retract servo upside down but I have to see the plane if there is enough room. I have a retract sevo but it has some years and is very thick. That is why I was asking about regular servos but I scratch that out. I will get a new thinner servo and try to work it out (either upright or upside down) to have a direct link to the retracts. I rather have a direct connection between the servo and the retracts as using linkages may jeopardize everything. What I see is that I will have to "tilt" the retracts so the wheels will be located well beyond the CG once the landing gear is deployed.

Referring to the wheel diameter, I do not want to use very small wheels as I usually fly from a concrete strip but my landings are still "rough on the edges" (need to say that the plane is for my son, he really does great landings, "most of the time"). I did think about using regular size wheels and cutting the leading edge and enlarge the root of the wing to fit the larger wheel (like the wing of a P51) but I will decide it once I get started to study the airframe.

The wing joint is critical, I am considering using dual servo for aileron and using the wing servo bay for flaps (if I dare modify the plane that much). In either case, the retract servo has to be mounted closer to the main spar so a new servo bay has to be fitted. I wil have to consider the wing joint ("small" thing I just have not thought about it. Thanks for bringing it up!)

Your pictures are very helpful and clarify most of my doubts. I hope I can be posting my own pretty soon and I will tell you how things go.

Take care
Carlos

Carlos:

At the risk of spending a bunch of your money, but simplifying the construction problems (hey, isnt that what engineering is all about?)...

All things considered, it might just be easier to spend the bucks on a set of air up/spring down pneumatic retracts, either Spring Air's or Robart's. It'd be simple to put a cheap micro server inside the fuselage to run the air valve, and there's only one piece of tubing that runs from the valve to each retract, which does away with all the problems of routing pushrods, cutting the root rib, and burying a retract servo in the wing.

There's enough room in the fuselage to mount a small air bottle, and you could use either 3/16 wire struts, or spend even more and get a set of robo-struts (VQ's got some that are about 1/2 the price of the Robarts). If you're flying off a concrete strip (you lucky man [sm=lol.gif]), you can probably get away with 1.75 or 2 inch diameter wheels, which should help with the wheel well problem.

I agree that you'll have to tilt the gear blocks foward to help get the gear in front of the CG (you can't tell from the pictures, but the retracts on the US are tilted about 15*). But I wouldn't cut into either the LE or the spar on the Tiger2; I think you'd risk weakening the wing structure. At MinnFlyer's recommendation, I moved the retracts out one rib bay from where the plans showed them. Since you've built from scratch, this is probably obvious, but don't forget to add plywood doublers to the ribs where you'll mount the retracts.

My Tiger landed just fine without the flaps. I found that I needed to keep approach speeds up just a touch more than with a semi-symetrical winged trainer, otherwise the controls got very "mushy" at stall speeds. This is not a good thing five feet off the ground if you need to abort a landing! My Tiger was a great airplane; I still rue the day my ground crew forgot to extend the antenna on my transmitter.

Keep us informed of progress. And whatever you do, don't even think about gear doors!

Fred

Fred,

you sure make an argument, and a pretty darn good one! I did not consider pneumatic retracts (because of the cost) but you are right, it is probably the best way to go... let me sleep on it for a little while. As an engineer, I rahter go the "difficult way" first... hahahahaha

As I read, you do not recommend cutting the ailerons to install flaps on the Tiger.. ok.. About the gear doors: thanks for the warning as I WAS CONSIDERING THEM!

Take care
Carlos

What kind of engineering do you practice? Mechanical/Civil/Structural/etc. A looooong time ago, before I went over to the dark side of the Force, I was a comical (oops, that's chemical) engineer.

I wouldn't do the flaps... no real need on a Tiger, especially the 46 sized model.

There are several phrases that can turn a guy's blood cold: marriage proposal, "I'm pregnant", IRS audit, etc. Having survived the first two (happily, I might add) and never been exposed to the last, "Gear Doors" are two words that currently reduce me to a quivering lump of jello.

But they wouldn't be that hard on a Tiger2. You could take the simple approach, which would be a hatch cover attached to the strut that covers the outer half of the wheel well, and leave the inner 50% of the wheel well open.

But if you decide to get fancy, on the inner doors you'd have to design some kind of spring loaded mechanism that holds the door open when the gear are extended, with a lever attached to the door that catches the wheel on the retraction stoke to hold the door closed. I think full sized T-34 Mentor's did it that way. The really sophisticated approach would be to use yet another servo, in conjunction with a Jomar door and gear sequencer, to open and close the inner doors as part of the retract/extend cycle. Which is probably more time and money than I'd want to spend, especially on a 46 size airplane.

I seem to be getting really good at spending your money! Just to keep you inspired, a couple of reminders of the end result.

Hello Fred,

I am a mechanical-industrial engineer and I like to "mess" with my hobby to make it fancy and difficult. Totally opposed to an engineering concept! But I loved the faces every one did when I showed up to a float plane meeting with a Northstar and how they drooled seeing it taking of and flying like a rocket! Currently at opur field ther is no Tiger II 40 with retrancts, only one taildragger. The rest (40 and 60) are all built stock. I set up my mind to make a different Tiger II 40 and I am starting with:

1. Taildragger
2. Retracts (mechanical with gear doors)
3. Flaps (for show off and trainning, but I am considering scratching this out on the Tiger II)
4. Larger rudder for possible knife edge
5. cowl (mounting the engine sideways)
6. and finally, setting up the plane with a OS .61FX engine

All starting from an ARF plane. Any experience you have on any point is always welcomed!

I was considering the gear doors mainly on the strut. But I have bought the hinge mechanism for the inner door (just in case) that is pushed closed by the weel as it enters the wheel well. Still not sure if I will do all of it.

On the side, I am mounting a Hobbico Nexstar on floats. This one will be equipped with dual aileron servos and flaps also (for show off as this planes definitely does not need them). Finally, I am building a P47 from TOP FLITE and it will be equipped with retractas and flaps so it is my excuse to "train myself" on both accessories. this last project, as it is a kit, is relaly lagging due to work (poor excuse but it is real).

Please feel free to write me at my email
[email protected]

Take care
Carlos

Carlos:

A great light dawns... you're gonna build a rocket ship!

Wow... an OS61! I flew my Tiger on a Magnum 46 XLS, 10x6 or 11x5 prop. There was plenty of power, and while vertical wasn't unlimited, it went up far enough for me. The combination I always wanted to try was the Tiger and a Magnum 52 2S. One of our club members has that engine mounted in a flat wing trainer similar to a Nexstar, and the thing just screams. My other thought for yours was an OS 55 AX. I've got its big brother, an OS 75 AX, in my UltraSport, and I can't say enough good things about that engine. I'd almost think the 61 would be too much power.

I've currently got a TF Beech Bonanza and Wing Mfg B-25 sharing space on my table. Both are being slowed by (you guessed it!) gear door engineering and installation.

Fred