I guess we will have to test both and evaluate the performance of each landing gear configuration.

On a project like this, you can waste a lot of time testing things that aren't really a big deal. Engineers are like that; they want to cover every possibility and do testing on every little thing to determine for themselves what they like the best. Good engineers learn from the past experiences of others and trust it so they can spend their time on the answers that no one has figured out yet. You guys have some major issues with your airframe design, so worry about that. We're telling you how the two gears behave, so listen to us. You're talking about a substantial structural change to go from trike to taildragger, so you're going to probably wind up with another airframe revision just for that. Set it up as a trike and give it a wide stance so it rolls well. The best ground handling model I've ever flown is my Kaos, so have a look at the wheel width and get close to that. A close second is my Ugly Stick which does happen to be a taildragger. One issue though that none of us regular RC pilots have to deal with though is that you're going to abuse your front wheel a lot. A Fultz nose gear would be a very good idea, and make your firewall nice and beefy with some good reinforcement. Nose wheels on models are notorious for bending and tearing out firewalls when models are landed on the nose, and I imagine that's about the same amount of stress you're going to be putting on yours.

I agree. Your taxi requirements over corrugated present some very unusual demands on the gear and the fuselage. I can see a tricycle geared airplane not only bobbing up and down due to the corrugations, but also see it rocking back and forth if the nosewheel is in a valley while the main gear is on a peak - the closer the nosewheel to the main gear, the greater the rock. A diagonal travel path across the corrugated may induce severe roll. Oh, well, same old rock and roll.

You are on the right track.

What was the taxi test last year?

They have given us 6 months to waste on a plane that can be build in 2 weekends. This is because they want us to go through the engineering process and test and document everything. A big part of this project is that 60 page detailed design report. All the testing we have been doing will end up in there and it will greatly improve our score if we can justify decisions made on the plane through testing.

I do believe that getting a top spot at this years competition requires to focus on many things that are not a big deal individual but together make a big difference in the score. Shaving off even 1 ounce could make as much as 10 point increase in the final score. If the pilot can do the same with conventional or tricycle landing gear but one saves 2-3 ounces - thats a big deal. If both weigh the same then we will figure out which one he is more comfortable with.

Looking the the Kaos models, I can see that the configuration provides a lot of stability because 2 of the wheels are mounted on the wings. That definitely works for low wing planes but the structure is much different on a high wing design like ours. Why not convert to low wing? There are addition obstacles on the taxi mission that make it very difficult if the wing cannot clear over them.

In my honest opinion, I think conventional landing gear will be better. When looking at stability, the tail wheel being far from the CG, will make it impossible for the plane to tip forward or backward when going over the bumps. In the tricycle configuration, all 3 wheels are relatively close to each other and stability would suffer. When looking at weight, I will have to add an extra servo and everything that goes with it to control the front landing gear when I can get away with using a tail servo to do both on conventional landing gear.

As for control I don't think that a single front wheel would perform better than steering with a back wheel. Someone brought up that its better to control object with front steering like cars. Cars have been around for a long time and it has become standard to use front steering, so it must be better? I think cars have front steering to avoid accidents and make it much easier for the driver. If a driver keeps turning it will be easier to see the position of his front end rather than his rear when driving forward. Boats have a rudder at the back end and planes also have a rudder at the end when in the air.

From a historical standpoint, 80%-90% of bush planes have conventional landing gear. There must be a reason for this.

Even despite all of my information of stability, control and past data, the RC community keeps pushing me to use tricycle landing gear. I cant ignore that, so I need to test it out to figure out whats best. The taxi mission plays a huge role in the competition. If we fail that, we instantly lose 80% of our score so any time wasted with configurations is not really time being wasted. I have over 10 members on my team, I might as well come up with tasks for everyone. To me its very fun to test out different stuff and thats one of the main reasons I am part of this project.

The taxi mission is unique this year. There has never been a mission like it before. Looking at past competition rules, there have always been just 3 flying missions. Some years, the planes were meant to be hand launched and didnt even require landing gear.

I love challenges and I wouldnt have it any other way. The contest makers know what they are doing and there is a reason why it is closely observed/sponsored by raytheon and cessna.

Pretty much everything you said in your post about landing gear was wrong Petkov. But go ahead and experiment. We who fly RC planes on a weekly basis don't know much at all about ground handling. A guy who has read a couple of books and spent two months on RCU probably realizes a lot of stuff that I haven't been able to figure out in 7 years. If you have any more questions I and others will be here.

I meant no disrespect jester, but I do believe I am approaching the problem the right way. I have a lot time and there are many resources at my school, it would be a shame not to take advantage and test everything.

Which parts of my post about landing gear do you recommend I do more research on?

there in one BIG thing missing from your comparison of conventional vs tricycle landing gear...
you're right of course, that 80-90% of bush airplanes have conventional (tail dragger) landing gear, and there are many reasons for that.
there are however two BIG differences between ALL full scale aircraft and ALL remotely controlled aircraft:
1) in full scale aircraft the person manipulating the controls is sitting inside the aircraft and can feel every control nuance and feedback (the pilot is essentially an accelerometer)
2) in full scale aircraft the pilot has specifically an airspeed indicator, a turn and bank indicator and most likely an artificial horizon or other method of precisely determining the aircraft's pitch angle.

in RC aircraft the pilot has neither of these items, and must 'guess'.
you will rarely see experienced full scale pilots 'ground loop' a taildragger because he has these 2 key items and knows how to use them.
you will regularly see experienced RC pilots 'ground loop' an RC taildragger because he does not have those 2 key items.

this is not a 'dig' on anyone's rc experience or flying abilities, and not ALL RC pilots WILL groundloop their taildraggers, but the simple fact is that tricycle gear RC airplanes are much more forgiving in their ground handling tendencies than are conventional gear RC airplanes generally speaking.

incidentally, no disrespect is meant by me either, (and none is taken )
not trying to blow my own horn, but as a reference point: I've been flying RC airplanes and helicopters of all types since 1968 when I was six, and have been flying full scale airplanes since 1985 (including tricycle gear, conventional gear, (from Cessna 152's to DC3's) single and multi engine recip and jets from Challengers and Gulfstreams to C-5 Galaxy's) I'm an A&P Mechanic and Flight Engineer also.

Having a bad day Jester?

Give the guy a break. He doesn't know you from a hole in the ground. And he is an engineer working on a problem. Testing and research is his job. Following your dictates is not.

Let's keep the tone of the posts as advisory and let him decide what to do with them. In the end he and his team will decide what is best for them. And whether they are successful or not will be theirs to own. We are just offering opinions and suggestions.

I know your post was well intended but your tone was nasty and .... not helpful.


That is what I thought. Thank goodness you don't have to land on that surface. If you did I would definitely think ski or pontoons with tiny wheels. Treat it as rough water rather than smooth runway.



AMA 74894,

Jim, thanks for your post. As an RC pilot who flies mostly belly landers and trike gear I have never landed a tail dragger but have always heard they are harder to land for RC pilots. Never knew the reason but you explained it well. Much appreciated.

New topic for today. I want to make sure my propulsion group has chosen the correct ESC. Can you guys help me where to start. To review my plane specs, we expect to run around 15 amps and 24 volts through to the motor. Should I go with 18 amps or 20 amps or 25 amps? Even with bursts we don't expect to go over 17 amps. Also what are recommended brands and would some show better performance than others?

All ESCs have the amp rating but few have a voltage rating. The ones that do, it tends to be lower than the 24 we expect to get. Another rating I see on the specs is NiMh/servo. What does this mean?

Just to add some more info RE conventional gear VS tricycle in models:
comparing a car's steering to an airplanes isn't IMO valid, mostly because of where the motive force to move the vehicle comes from.
(think of how long it took US car manufacturers to switch to front wheel drive... even though front wheel cars are easier to drive particularly in slippery conditions, they are not necessarily easier to manufacture... particularly when you need to re-engineer your cars and the production lines on which they are made)... so just because cars have the steering on the front wheels, that does not necessarily make them better or easier to drive.
Cars have front steering and boats have rear steering mostly because they are easier to manufacture that way.

with an airplane you have a relatively large propeller (imparting large amounts of torque in a different direction than the one the vehicle is moving in)
and here is where that long arm (between the main landing gear and the tail) can work against you. once the tail leaves the ground, you've got a VERY long lever, (from the wheels to the tail) with a VERY powerful control surface at the end (the rudder) and on the other relatively short arm (between the main landing gear and the prop) you've got a very large amount of torque trying to twist the aircraft in a different direction than the airplane is traveling.
the combination of those two things, aggravated by the lack of instrumentation and 'seat of the pants feel' (because the pilot is not sitting inside the airplane)
makes the airplane VERY sensitive to differences both in engine torque, and in rudder control. in short, it is much more difficult to 'tame' an RC taildragger than it is to tame the same airplane in a full scale version.
with a tricycle gear airplane, the plane is ONLY on two wheels once it's achieved flying speed, and the airplane is rotated for take off.

nose wheeled (full scale) airplanes have become the norm for just about everything except bush planes for a reason.... they ARE very simply MUCH EASIER to control on take off and on landing.
(perhaps that should read it's much more difficult to LOSE control on takeoff and landing. ;D )
Bush planes are designed for a very specific purpose: to be flown at or near their weight capacity from short and / or unimproved runways, and even from relatively flat surfaces off airport.
incidentally, (Full scale) Bush pilots are among the most capable, yet bush airplanes have the worst safety record than any other aircraft type.

your statement "When looking at stability, the tail wheel being far from the CG, will make it impossible for the plane to tip forward or backward when going over the bumps."
isn't true. what is far more important (with a taildragger) is the distance between the MAIN LG and the CG.
(if the LG is forward of the CG, but only slightly forward, the airplane will easily nose over when power is applied)
with a nose wheeled airplane, there is NO way the airplane is going to tip over forward, and since the main landing gear is well behind the CG, there's no chance of it tipping backward either.
(on full scale airplanes, a nose over / prop strike is SERIOUS business... a couple thousand dollars for the prop, complete engine tear down (sudden stoppage inspection) cost to repair the runway etc... and this for a fixed pitch prop)
nose wheeled full scale airplanes realistically only only have this issue on one occasion... when the pilot forgets to put the landing gear down it's almost unheard of on a fixed gear, tricycle airplane.


ALSO you can easily use the same servo to control both the rudder and the nosewheel steering... it's a very common practice.

Sorry for the long post!

Noted. Thank you very much!

if you don't expect bursts over 17 amps, I'd go with a 20 amp ESC, and if at all feasible, mount it so the ESC itself (the heat sink part) is outside the fuselage, in direct airflow.
(assuming external mounting is feasible, you could even go with a 15 amp.. if the ESC hasn't burned up after 10 flights or so, you'll know you're good to go )

Castle makes some of the best ESC's in the business IMHO... not the cheapest, but among the best. at 24 volts, you're looking at a 6 or 7 cell ESC. (they're rated for both voltage and amperage)

As far as tricycle or conventional gear, I do agree that you should test to determine which configuration optimally fits this mission. You appear to be on the right track already. I agree with you and Jester that conventional gear seems to be better suited for the task, but keep in mind that the location of the center of gravity with respect to the main gear has a big influence on stability. Also keep in mind that the force (propeller) that is trying to overturn the plane when the gear is on the corrugated can be somewhat ameliorated by "up" elevator. Testing will reveal what works best.

I have almost no experience in electric flight, but I have followed aeajr's posts and his advice to others seems spot on. For the EEs in your group, the motors used, if brushless, are electronically commutated motors and are very efficient. KV does not stand for kilovolt here. There are other words, but just like the term "tip stall", you will hear words used in the electric forum that will probably be foreign to the EEs.

I'm excited about your progress. Best of luck.

As you have noted you need to look at both the amp and volt rating of the ESC.

Since you will be limited to 15 amps a 17 amp ESC should work but I might suggest a 20 amp ESC so you KNOW you have plenty of headroom.

As for voltage, many ESC will not list voltage but will list rated CELL count. Now you have to be sure you know what kind of CELL count they are talking about.

24 V would be a 7 cell (actually 6.5 cell at 3.7V per cell) Lipo Pack

24V would be a 20 cell NiCd/NiMh pack (1.2V per cell)

So you are looking for the cell rating. As NiMh use in RC aircraft has dramatically declined you will most likely have to choose based on the lipo pack rating. (3.7V per cell) looking for a 7 cell rating if you are going to run at 24V.

LVC - low voltage cutoff. This is a feature of many ESC to insure that you do not damage LIPOs and so you leave enough power for the receiver/servos. NiMh can be run flat with only minimal damage. But a LiPo run down below 3V at rest starts to take damage and below 2.5V and the pack may be ruined. So the ESC and Low Voltage Cutoff chapters in the book for more information.

Since you are going to have a separate receiver pack and are using NiMh you really don't have to worry about LVC. I would use it for practice to see how far you are running the pack down. If you ever hit LVC that means you are becoming marginal on your motor power due to a depleted pack. you may have to make adjustments of some kind.

But during the competition I would turn it off if possible or at least turn it to a very very low setting. Being able to turn LVC off or to set it lower than normal would be an advantage. You don't want it cutting the motor during the event. Better to over drain the batteries than have the motor completely die.


If you see a rating for number of servos, ignore it. That is related to the internal BEC. (see the chapter for more info) If it has one you will disable it as you will be using a separate receiver pack. Most packs that run in the voltage range you will be using don't have internal BECs anyway. But if it does you will need to disable it. We can discuss that at the time, if it is an issue.

Sorry my tone was blunt. I see that after letting it sit a while. I got a little frustrated and should have just let it go.

To answer your question, what you need to research further is what it's like to fly an RC airplane, preferably both trike and taildragger. Your books won't help you with that. If there is an RC club nearby, it shouldn't be too hard to do that. Most aeromodelers own multiple aircraft, so asking someone to let you taxi a plane in both configurations won't be much trouble, While you're at it, maybe you and a couple of other guys on your team could get in some stick time on a well-designed and properly built model. There's nothing like having that reference point of knowing what something feels like that works right that you can then compare your designs to. But the main point here is that you should get some real world experience using these two kinds of landing gears to see what you're going to be dealing with. Ten minutes at the airfield will be worth more than 5 hours in the library for this particular part of your project.

Jester,

Great advice. Teaming with a club is a good idea.

Note that, according to the rules, the pilot who flies the plane is required to be an AMA member.

From the rules:

All team members (except for a non-student pilot) must be full time students at an accredited University or College and student members of the AIAA. At least 1/3 of the team members must consist of Freshman, Sophomores or Juniors. The pilot must be an AMA (Academy of Model Aeronautics) member. Teams may use a non-university member for the pilot if desired. We will provide qualified pilots at the contest on an as-available basis to assist teams who are unable to have their pilot attend.

Hopefully the team will have at least one member who is a qualified RC pilot who will be working with them every step of the way to test the designs. If not then they are headed for disaster.

Working a few of these events in Fort Worth (Sponsored by Lockheeed Martin), I can tell you that most teams don't bother consulting with a real RC pilot while developing their designs. They read books and make decisions. That's it. The planes show it too, some being nearly unflyable in real world conditions. I've seen designs that were so straight line lift oriented that they could barely turn without tip stalling, landing gears that were so complicated (RC models don't need suspension!) that they had a lot of trouble taxiing, and some planes that were just too stinkin' ugly to be allowed in the air. I respect Petkov for his willingness to go to people with practical experience in the field. He's an engineer so he'll want to approach tasks from a research and theoretical perspective, but he's at least willing to listen to users. That attitude will serve him well when's he's designing auto parts or oil drilling equipment or whatever he winds up doing because he'll put out products that are actually useful instead of just being technically elegant.

I could not find any ESCs in the 20-30 amp range that can handle over 20 volts. The smallest one I could find that covers the 20-25 volts we expect from our system is a high voltage 40 amp ESC but thats rated for 48+ volts. Could there be a problem with this besides extra weight?
http://www.castlecreations.com/produ...e-lite-hv.html

I like the idea. I have shared with group and I will try to organize something.

Yes our pilot is an AMA member.

MIN: 3S LiPo MAX: 12S LiPo

as long as you've got at least 11ish volts, that ESC series will work for you

Here is another ESC that meets your specs - Castle Creations Phoenix Ice Lite 50 - About $85 - less costly than the one above.
www.bphobbies.com/view.asp?id=A0780192&pid=D3265071

It also offers extensive data logging:

Thanks guys.

Good find aeajr, but I dont think those will be in stock. The item says out of stock and that product line is not longer made by castle. It seems They come out with a new line every year that is slightly different than the year before with a bigger price tag.

Good catch. Missed that it was discountinued.

Hi everyone, I wanted to give an update on the progress that the plane has made.

Since December we built 2 more prototypes.

Prototype 1:



The picture shows a side view with the hatch door open. We had 3 successful flights where we made small adjustments after each to improve performance or stability. On the forth flight, a gust along with pilot error took the plane into a tree.

Prototype 2:




The plane handled really well. We had an RC pilot who builds his own models from scratch fly it and he was impressed on how well it handled. Between this and the final plane we only added some light spars along the body to reduce drag and hope for faster flight times.

Final design:


The team left with the plane on Friday. I am awaiting to see how well we will perform. At competition, the plane has to pass tech inspection (making sure that it is safe to fly and meets all the requirements), taxi test (over the roofing panels), mission 1 (speed flight), mission 2 (payload flight), mission 3 (uneven payload flight representing medical passengers and nurses). Wish us luck!


Below is a link to the pdf of the report we submitted for anyone who wants to know specifics of the plane. It outlines everything that has been done on the plane including all the calculations, theories, construction and even what we changed after test flights. The report was submitted before the test flights of prototype 2 and we scored 83/100. I am not sure what the judges took points off yet but it compared very well with the top teams earning us a spot 38th out of 100 teams in the flight line.

https://www.dropbox.com/s/pke7skjxy1...s%20Lowell.pdf