FTFC20 Martian Space Ship designed by Horseman3381

[Hai-Lee]

In my initial test I had around 4 degrees, and on the ground it didn't seem to do much. I have been going back and forth in my head as to weather thrust angle would do any good on this. I'll do some testing and let you know what I discover.

I am particularly interested in any effect that side thrust would have on the tendency for the model to roll on the application of throttle!

Have fun!

 

[Horseman3381]

This ship looks like it relies on the Coanda effect for thrust as the airflow wraps around the bulbous fuse, which is why it doesn't need a wing span but more of a wing chord. And like a football it has the same profile on the roll axis all around. In my uneducated theories I would say using a smaller diameter high pitch prop on the F Pack would work better. That's where I am putting my money.

As for the pendulum effect you mentioned that makes so much sense. Center of gravity is completely different from center of mass. The combination of the landing gear and the battery being low would give you the swinging action. You changed both at once though right? what if you still had the landing gear on and only centered the battery? This ship would be fun to tinker with and figure out. I'm jealous, good on ya man. Cheers

The original free flight model calls for a .049 motor and 6" prop, though the model also only weighed 6 oz. The F-pack motor will put out significantly more power that a .049 motor, so my bet is that will be what the final ship uses.

Once I get it flying I will try to get the landing hear back on and see how it does as I am not a big fan of hand launching.

 

[Horseman3381]

I am particularly interested in any effect that side thrust would have on the tendency for the model to roll on the application of throttle!

Have fun!

I was just looking at the original plans and it specifically calls for there to be zero thrust angle. I wonder if the angle I had put in was causing part of the problem with the pendulum motion.

I will say that with this ship the faster it went the less roll there was. I believe this was because more air was moving between the fins allowing them to track the ship better.

 

[Captain Video]

How about tripod landing gear to help the pendulum effect but add a little ballast to the rear to balance the dirigible.

 

[Piotrsko]

Obviously, for centerline mounts, down trust will tend to make it dive SO there might be a requirement to the 0 degree offset. Some of the variants with the pods utilize the nose up trend. The nose vertical fin does a lot of weird stuff according to NASA, typically working backwards to the rudder but also inducing roll moments. However this is so far beyond what I know, anything I suggest is SWAG.

How about large area elevons for countering torque roll? Does it HAVE to use the rudder? Make another 2/3 size rudder and mount it underneath the original.

 

[BATTLEAXE]

I was just looking at the original plans and it specifically calls for there to be zero thrust angle. I wonder if the angle I had put in was causing part of the problem with the pendulum motion.

I will say that with this ship the faster it went the less roll there was. I believe this was because more air was moving between the fins allowing them to track the ship better.

If like i am right thinking that it is the Coanda effect wrapping air around the fuse i agree that 0 thrust angle is the answer. More direct thrust on one side over the other theoretically should make it bobble around. Again just a newbies opinion

 

[Piotrsko]

https://www.rcgroups.com/forums/showthread.php?1688355-A-Spaceship-for-Lazy-Martians
https://www.rcgroups.com/forums/show...&postcount=881

Aha!! was correct about the nose dorsal sub rudder, wrong about lower rudder, sort of correct about the elevons, CG needs to be further back by about 1 1/3" .

 

[Horseman3381]

I was able to make the modifications I mentioned above to the Ship and got it out to the flying field. Unfortunately I forgot to take my B Pack motor power pod and the contra rotating power pod with me. I was able to test fly it with the F-pack motor using a 6x4 2-blade prop (I also forgot my spare props).

For the first flight I added all the additional fins that I had mentioned in the previous post and re-balanced the ship with the CG moved 1 1/3” back from where it was shown in the plans based on discussion that @Piotrsko link to.

There was no sign of torque roll with this setup, however it went straight vertical before slowly falling back to the ground. I gradually added weight to the nose until it was able to fly horizontally. However, at that point it was too heavy for the motor to keep it in the air. Oddly enough this put the CG back where it was shown on the original plans.

To shed weight I removed all the extra fins which allowed some of the nose weight to be removed. There was still no sign of torque roll but it was just shy of being able to sustain flight, it was more of a long glide.

I think it is close. I am going to rebuild the ship and redo where I can mount the battery to be able to remove more of the nose weight. I was running the motor on 3s, I will give it a try on 4s and play musical props to see if I can get a good combination that works.

I won’t be able to get much done on this for the next 2 weeks, so hopefully I can get it rebuilt and back out in in the next 3-4 weeks.

 

[Vimana89]

I am particularly interested in any effect that side thrust would have on the tendency for the model to roll on the application of throttle!

Have fun!

The thing in this video is a little fixed wing indoor flyer. I ordered one a while back, they haven't been manufactured in some years. It didn't work, probably a defective battery, but I noticed a diagonal side thrust angle on the prop, which is the mechanism by which it does the torque roll stunt on full throttle. The design of this little toy is a lot different from the Martian Space Ship, but it is a good example of using side thrust and throttle to roll.

 

[Piotrsko]

Never ever had anything Airhog actually fly without buggering up. That video suggests they are on fly fishing line.

Sorry, @Horseman3381 about the bad CG data but the forum swore by it. Might be other subtle things going on. Congrats on the success so far.

 

[Horseman3381]

Never ever had anything Airhog actually fly without buggering up. That video suggests they are on fly fishing line.

Sorry, @Horseman3381 about the bad CG data but the forum swore by it. Might be other subtle things going on. Congrats on the success so far.

It's not a problem, I learned a lot form that forum and glad you posted the link, thanks for posting it. Since a number of people who had built it agreed the CG needed to move back it seemed like something to try. If I had a bigger motor on it would probably have flown at a high alpha with the CG 3/4" back.

 

[SlingShot]

It's not a problem, I learned a lot form that forum and glad you posted the link, thanks for posting it. Since a number of people who had built it agreed the CG needed to move back it seemed like something to try. If I had a bigger motor on it would probably have flown at a high alpha with the CG 3/4" back.

When sorted out, it should fly like a fancy Nutball right?

 

[L Edge]

When sorted out, it should fly like a fancy Nutball right?

I like different shapes to flying objects that make it look unique. Good choice.

It is going to fly nose up due to the shape as it plods forward.
One area to explore is a larger prop dia to get flow to the control surfaces.
Don't fly it in the wind until you solve your problems.
I have three different shapes that others don't have and they plod along and please don't punch the throttle for it will go vert and will spin like a top if little contro.
I have some suggestions if you want to try it out.