Gear box on a Zagi? - RC Groups
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May 02, 2001, 11:40 PM
Registered User

Gear box on a Zagi?

Has anybody ever tried to put a gear box on a Zagi for longer, slower flights, and/or increased duration? I hear all of these charactistics are from gear setups and I wouldn't mind maybe changing up my zagi just for kicks.

I am especially interested in the possibilities of longer duration.

What do you guys think?
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May 02, 2001, 11:44 PM
Fun Flyin
Im sorry but this is probably a stoopis question..But whats a gear box. I have never heard of it befor!

May 03, 2001, 12:04 AM
Registered User
I hope I'm using the correct wording. I am referencing a little gear setup that mounts on the front of the motor and lets you turn the prop slower. Thus, you run longer props with more pitch.

Instead of me running a 4.5x5 or whatever that stock prop is on my zagi I maybe could run a 9x6 prop or something like that. (at a reduced speed of course)

[This message has been edited by Munch (edited 05-02-2001).]
May 03, 2001, 12:17 AM
Frequent User
yb2normal's Avatar
The FMA Razor can be purchased with a gearbox and a big propeller. They call it their "parkflyer" version.

I imagine you could do the same thing on your Zagi.
May 03, 2001, 12:29 AM
Registered User
I have heard a number of people say that they would like to try a gearbox or geared motor, but I do not remember anyone ever saying that it worked all that well.

The Zagi isn't really a slow flying plane. I've seen a couple float around a bit at DEAF, but the Zagi seems to really come into its own at higher speeds.

Since the Zagi has been around a while now and since so many have built, flown, and modified, just about everything that you can imagine has been tried on the Zagi. I would think that if a gearbox setup worked well on a Zagi, then a fair number of people would be doing it. However, do not let that stop you if you want to try it. I always love to hear about people’s new experiments.
May 03, 2001, 12:39 AM
Registered User
I'm running a gearbox on my Zagi...

Using a 1.85 ratio (Soarstar gearbox) and won't ever go back direct drive unless it's with a cobalt of something. With an 8x4 I can tool around for around 20 mins with the 1700AE pack. Spirited full throttle aerobatics last around 10-14 mins. I haven't actually tried a -part throttle see how long it will fly being extremely conservative- test yet.

Most noticeable is the increased thrust. The plane will just climb far better. No need for flat runs to gain speed after launching. Top speed is either the same or slightly slower.
I'm running the long-can 480 from Dymond (Jamara, Permax, Dymond, take your pick). I've experimented with 8x4, 8x5, and 7x7 extensively. About $15 from Dymond.
8x4 is a great overall prop with excellent efficiency. It pulls around 10.5 amps static. Much less at part throttle.
The 8x5 is even more efficient than the 8x4. It's especially noticeable at part throttle. Unfortunately, it doesn't spin very fast at the higher throttle range so its top speed ain't great, but from about 1/2 throttle to full, this thing is thrusting like crazy. This is a good lazy flying prop with good flight longevity. For instance, draw at 50% throttle is around 3.5-4 amps.
The 7x7 is a neat little prop. Definitely the speed prop of the group, and it thrusts well. Of course, it draws more current, but not by much. Probably about 12.5-13 amps static. Great in high-speed dives. I don't know if I'd run it on a 6V Speed 400, though.

I clipped 5 inches out of the center of my Zagi. With the 7x7 I can easily pull straight up from level and roll 3+ times and pull out with a quarter outside loop back to level.

For comparison, a 6V S400 with the Gunther prop was pulling about 13-14 amps static and thrusting far less (better top speed though). While the amp draw at part throttle (50%) on the geared setups was 3.5-5 amps, the direct drive Gunther part throttle draw was higher (I think around 6 or so, I can't remember).

The 8x4 is a Soarstar prop... the 8x5 and 7x7 are APC props.

The next experiments will be with higher ratios and 9" props, although I suspect they'll turn to slow.

It's definitely a worthy experiment, and it does work quite well...

BTW, that Soarstar gearbox is great. Fully enclosed with ball bearings and metal gears for about $15. Not too bad.


[This message has been edited by Jeff Goldman (edited 05-02-2001).]

[This message has been edited by Jeff Goldman (edited 05-02-2001).]
May 03, 2001, 12:47 AM
Registered User
I did do this with mine a while back and it gave me 30% longer duration and a much higher climb rate.

I used a 1.8 gear ratio with an 8.5x5 Aero Naut prop (cuz that's what I had in my bag of tricks at the time)

If you want to do this, You will need to cut away some additional tail material.

On Tom Hunt's Modelair-Tech website he talks about a speed 400 that is their enduro model that can turn a 7x6 gunther prop without a gearbox. This might be an even better combo if that is the desired performance you are after.

Have Fun,
May 03, 2001, 04:01 AM
Registered User
Gearboxes usually add efficiency, but take away top speed. Most experiments that involve a failure with a gearbox are usually a result of poor gear ratios.

Be sure to use a low ratio, such as 2:1 or less (such as the flyers above have done) and you should have good performance. But trying to make it work with a 3:1, 4:1 or higher ratio seems like the top speed would be too slow for any type of sport plane. This is fine for a sailplane that can fit a 12 inch diameter prop with no problem, where top speed is not an issue.
May 03, 2001, 04:59 AM
Registered User
Jeff, Who makes the Soarstar 1.85-1 ratio gearbox and where can I buy it? Thanks much!
May 03, 2001, 09:43 AM
Registered User
I have tried to fly a Zagi with a Speed 400 and 4:1 gearbox with a 9 x 6 prop because that was what I had in my box but I think it was too slow. Although it climbed slowly and majestically away, as soon as I tried to turn either to the left or the right, it didn't want to play any more!! I think I will try a lower ratio gearbox if I can get my hands on one.
May 03, 2001, 12:17 PM
Super Senior Member
I have been flying combat with some fellas out here who fly the Soarstar 1.85:1 box on a 9x6 prop or so. Their duration is about a minute longer than mine, but my Zagi is a tad faster on a direct Dymond 480 direct with the gunther spoon prop (long live the spoon prop!). So, I am landing (or trying to evade a forced landing) and they get another minute of flight.

I personally prefer the shorter duration and higher top end of direct drive on this ship.

May 03, 2001, 03:37 PM
Registered User
Fraser, I would think that a 9x6 prop is a bit on the small side for a 4:1 reduction. A 10x8 or something in that region would probably give more thrust.

Problem is, you end up cutting so much of the elevons away and then you have a lot less control authority. Then you turn up the throws and it gets twitchy. Landings are a pain too.

If you are going to mess around with gear ratios, props, etc, I would definately suggest downloading motocalc (30 day trial) @ <a target="_blank" href=""></a>. It's very useful.

Ben C

[This message has been edited by Ben C (edited 05-03-2001).]

[This message has been edited by Ben C (edited 05-03-2001).]
May 03, 2001, 03:49 PM
Registered User
You guys are great. Now one more question....

Somedays I want to keep flying and when my flight packs are empty I will hook up my RC car battery packs. Would the more thrust but less speed be helpful on a grossly overweight zagi?

May 03, 2001, 10:19 PM
I have no friends
I was thinking about this also. I was going to use a 1.5 - 1.86 gearbox with a 7x6 prop on the 6v Speed 400 motor.

With my 8 cell 600AEs I think I would get good performance and longer runs with only a small loss of speed.

Anyone else think so?

[This message has been edited by mt_100 (edited 05-03-2001).]
May 03, 2001, 11:11 PM
Registered User
I don't know who makes the Soarstar gearbox. I know it comes with the Soarstar which is made by Super Flying Models, which is probably a pseudonym for someone else...

Suffice it to say, you can pick the gearbox up from Horizon Hobby for $18.00... In fact, the unit also includes a 6V S400 (380) in that price which makes it a good deal in my book. Just do a search on brands for Super Flying Model, and select accessories. It's a nice light box that has so far been very trouble free.
I don't know if it's the same unit, but Hobby Lobby sells what looks to be the same unit (plus an 8x3.8 prop and spinner) for $83.90!!! Seems excessive to me.

BTW, if you go with the Horizon unit, you'll still need a spinner.

Personally, I don't see a huge difference between direct drive and a geared 7x7 as far as top speed, but the overall vertical performance with the geared 7x7 is seemingly much better.

I also heard about the 1.85 gearbox thing while flying in Albuquerque! After seeing them there, a mile high, I was sold...