R/C Phile

I have a question regarding an old Great Planes Sportster Bipe that I am finally building.

I am contemplating putting four micro servos (HS 85) or Mini Servos (HS 225) in the wings.

This setup would allow turning the the top wing ailerons on and off from the transmitter and also get the possibility of having 4 ailerons to play with for Flaperons and Flaperons / Elevator coupling or whatever combination of mixes.

Would this affect the roll rate tremendously? Would flaps be any good?

Keeping in mind that this thing will be diesel powered (Not fast) Would the HS85 suffice? is this worth the extra weight to be able to play with the mixes?

I am an experienced flyer, I do like a fast roll rate and I am anxious to play with my 9Z's mixing capabilities..

Any feedback appreciated

MinnFlyer

My Feedback: (4)

I can't answer all of your Q's, but if you like a fast roll rate (me too) 4 ailerons are a must. And if I had 4 small servos at my disposal, that's how I would do it.

CafeenMan

I agree with MinnFlyer. I have several projects in the works right now, but I've been itching to build a bipe with four full span ailerons.

First, I want the roll rate. Every bipe I've had that had 2 ailerons also had a sluggish roll. You can get by just two servos though.

The reason I'd want four servos is so that I can try a few things out such as flaps (independent per wing or coupled) and also a crow type thing. I.e. top ailerons up, lower ailerons down. I suspect the crow won't be much use or much fun, but I have to prove that to myself by actually doing it.

CafeenMan

PS. I have no clue about hitec servos, so I can't give you advice there. Mini servos with about 35+ torque should be fine if it's not moving too fast. What engine and what is the expected weight and wing area?

R/C Phile

Hi guys and thanks for the reply's To answer CefeenMan's Questions

The Engine is a PAW .60 TBR Diesel which Weighs about 16 ounces including exhaust and turns a 12-10 prop in the 8100-8400 RPM range if I remember correctly.

The wing area is in the neighborhood of 750-780 square inches

This time I will try to "swiss cheese" the wood with lightening holes / try to build as light in every way possible. I am shooting for a flying weight around of 5 lbs.

And this bring me to the servo question:

Here are the specs:

HS-85 Micro Ball Bearing
English Metric
Torque 4.8/6.0v : 42 / 49 oz. 3.0 x 3.5 kg.
Speed 4.8/6.0v : 0.16 / 0.14 second
Size : 1.1"x 0.5"x 1.1" 29 x 13 x 30 mm
Weight - Nylon 0.67 oz. 19.2 g.
Metal gear 0.77 oz. 22 g.

HS-225MG BB Mini M.G. Servo Specifications:
Bearing Type: Top Ball Bearing
Torque @ 4.8v: 55oz\in (3.9kg\cm)
Torque @ 6.0v: 67oz\in (4.8kg\cm)
Speed @ 60 degrees @ 4.8v: 0.14
Speed @ 60 degrees @ 6.0v: 0.11
Standard Size L x W x H:
1.3" x 0.7" x 1.3 "
(33mm x 18mm x 33mm)
Weight: 0.98oz plastic (32 g)
1.1 Metal gear

The reason I am thinking about the micro's is that I am going for super light weight and since that Diesel is no speed demon I would not be too worried about flutter or high aero loads on the control surfaces.

On the other hand I don't know if the weight difference is significant enough to forgo the peace of mind afforded by the mini's 4 screw mounting and larger gears.

From the specs only it seems the micros might do the trick..

tiggerinmk

I used HS-81's in my Zephyr for rudder, elevator and throttle. They work fine but the plane is only 36oz.

Goes vertical with the OS15

Main thing to consider is that the micro only has one screw at each end to hold it down. That means if you mount the servo sideways you risk the servo rocking when movement is applied. Ultimately, the servo could work loose and fall out!

With the servo mounted length ways it shouldn't be a problem.

The other main thing to consider is to keep the servos inboard especially on the top wing to minimize the length of the servo lead.

The HS-81's are a little lighter than the 85's and should be adequate for one on each aileron.

CafeenMan

Those servos have plenty of torque at either voltage as long as you don't put the plane in terminal velocity power dives.

I don't think I'd use a single HS-85 servo for two ailerons though. The 225 servo should be fine.