a typical trainer with an os .46 ax and 11x7 hits a max of 75mph leveling out after dive with a tailwind. realistic max full throttle speed is more like 45-50. (I've flown various gps's in planes, so I can't get the actual speed during a dive, but it is relatively close when leveling out.)

gauging the speed of rc planes is TOUGH to do without actually measuring it, especially when you watch the larger planes fly, they seem to be barely moving when in fact they are usually quite fast.

Your top speed example is actually a little low. The OS 40/46 LA, or TT 42 GP powered trainers typically hang around at ~50 mph, but good BB 46 powered trainers usually hit closer to 70 mph in level flight with an 11-5 or 11-6 prop (an 11-7 is just a little too much for best power from a healthy 46). Even a large trainer can get close to 70 mph --- a Nexstar, for example, with brakes & droops removed, hits very close to 70 mph with an 11-5. prop. My Superstar hot rod with full span (unclipped) wings & a TT 46 Pro, has been measured @ 75 mph in level flight with an 11-6 prop.

Regarding my general comments above.

Dr.1 points out “Most is not all� and my comments are “true in generalization only.� That’s very correct. My comments were aimed at the “beginner� for whom this forum is dedicated. They give a basic feel for it all, especially for the traditional middle of the road stuff they are likely to be involved with in their early stages of pursuing this hobby.

I was just commenting on another thread about the very large range in performance that today’s modelers are asking for, and getting, from manufacturers. No doubt the future will only bring more diversity.

Multiflyer

The ice skater/bar stool analogy is not valid in this instance because it ignores the effect of blade area and pitch.

jess

I wasn't trying to explain the effects of the pitch.

P.S. how does one not see arms don't have pitch ?

No' you weren't and you did not. You indicated that the ONLY factor affecting RPM was diameter.See your words below:

"Have you ever sat on a bar stool that spins around 360 degrees, and spun your self with your arms near your body and then away from your body ?

Well if you didn't , the speed of you spinning lessons the further out you stick your arms. The closer you bring them back to your body the faster you begin to spin.

Apply this example to a prop. the bigger the diameter = less rpms. " [RC-FIEND]

You should also realize that you failed to consider the power from the engine. As you may be aware neither the bar stool or the skater is connected to an external power source. On the same engine a large diameter, low pitch prop may well deliver higher RPM than a higher pitch prop of smaller diameter.

As stated, the skater/stool analogy is invalid and irrelevant. I hope this explanation helps'

jess

Given the pitch is the same the larger the prop THE LOWER THE RPMS.

If you took the time to read the beginning of the post this was obvious because the thread starter stated he understood the pitch. I re-wrote it down below for you.

RC-FIEND....I think your intention was good but you gave a wrong analogy. Maybe a better one would have been a helicopter rotor because that's an extreme example of a very large diameter prop. It turns slow but gives huge thrust.

I am glad you admit you don't understand so lets take it step by step.

A prop, lets say that folds up and down like on a glider, will A rotate much faster while the prop is reaching it's peak extension and will spin slower when the prop is full extended . How much slower I am not going to prove, but its obvious the longer the prop is, means more resistance while it is in motion and thus for it spins slower


A heli prop is no different from an airplane prop , it is only mounted differently and because of the size of it , more thrust is created allowing it to lift the heli straight into the air. OH that would be the same as an airplane doing 3D hovering ! [X(] .

So although I may not explain every thing to a tee I hope this clears things up a little.

Thanks RC-FIEND. Your vast experience, training, and general scientific expertise are much appreciated. Your encyclopedic knowledge of aerodynamics and physics are a great resource for all subscribers to these fora.

You have also demonstrated absolute mastery of the dynamics of the barstool.

Thanks!

jess

First of all you follow me around in this forum like a lost puppy I really need to understand why ? If are not man enough to respond and say I am right then please don't when I am wrong . [sm=redface.gif]

It's fine to correct wrong info, but I see nit-picking starting so I'll nip it in the bud right now. It's time to play nice folks and stop bashing on each other. People can disagree but please do it in a civil manner

Thanks

Gosh, RC. I try to pay you a compliment and you come back with this insult! I am sorry if I triggered some insecurity response you may have. I try not to offend anyone but cannot anticipate bizzare reactions.

Please accept my sincere apology for whatever ruffled your feathers.

Again your expertise is appreciated.[8D]

jess

(Now I defy anyone to say that was not civil.)

My feathers , what a PUN unintended

No you didn't , but you have a weird way of making your point , it's borderline dictatorship, no subtleness about and it can really be annoying if you attempt to do it every time I try to make a point . So please, if nothing else , understand this is how I feel. Thanks.

Sorry Bubbagates , my responses end here.

Back to props.
When I first started to fly my trainer I installed the O.S. recommended 11X7 on my .46. I know that I was at the upper limit here, but I am incorrigible. My instructor, on the second day, had me install a 10X6, which he provided. Wow. Flight stability made me wonder why they recommended the 11X7 at the hobby store in the first place, and landings were easier as well. I think that the vert. performance idea is not an issue until you solo, I have no idea if you have or not, and save your own plane from a fiery death a few times. Top speed is not necessarily a concern either, except as something to avoid until your second plane. These little two strokes like to be near the top of their recommended RPM range. They run better, last longer and teach you throttle control. I said near, not at the top as a safeguard against weird things that happen when in the air. I have referred to my instructor and his prop. theories when newbies ask me about what prop they should run, and when someone has problems with the way their plane handles. People usually want to go too fast and slowing the plane down really helps. Of course I promptly took the .46 out and installed a .75 when I needed an engine for my 40 sized pattern trainer. The 75 breaks all the rules for trainers.[sm=spinnyeyes.gif]

Gee, RC-Fiend, you manage to build and fly a Lanier Shrike (with LOTS of help) and suddenly you're an expert? The analogy is so totally non-sequiter that it borders on ludicrous.

MANY things govern engine RPM. Prop diameter, pitch, blade width and blade airfoil thickness, blade shape, engine reserve power, and even airframe parasitic drag. To make a blanket statement that a larger diameter prop lowers RPM is totally in error.

Confucious say: Man who make analogy of spinning on barstool must spend lot of time researching this.

Dr.1

solafein,

I do agree with almost every part of your statement. I will add something here to clarify one part of it.

True vertical performance is something you really do need during training. The need to pull out as quick as possible is something most every instructor loves to have. It can and will help save a plane from near doom. I've been there and done that more than I want to admit. In some cases, students have shown up with 11X7 props on an OS46AX and I will allow them one flight with that prop. We will then land and change out the prop to an APC 11X5 and it usually makes a lasting impression on the student. He now has more positive control and the plane has slowed considerably which give the student more reaction time.

I've had to put 2 trainers this past season into vertical climbs to save them. Both were Nexstars, both had OS46AX's on them, one had the 11X6 and the other had the 11X5 and both were APC's. The 11X6 sorta hovered and started to torque roll, which looked pretty cool, but would not climb out until I lowered the nose. The one with the 11X5 pulled out vertically, a little slow at first but very quickly gained altitude

So as I said, I do agree with your statement but I think for the OS46AX engines, you'll find that an APC 11X5 is even better on a high wing/high drag trainer. Both for takeoff punch and vertical "rescues" and landing.

If you have the ground clearance, a great prop for the OS46AX is the APC 12.25X3.75. I had this on a converted to tail dragger LT-40 and it would easily hover it as well as a trainer could hover, pull it vertical right from liftoff and slow it WAY down for landing. When using this prop and diving at the ground it really helped control the dive.

I also used the engine/prop combo a H9 Twist and it really worked well.

OK do you have anything else to offer toward the length of the prop , NOT DEALING WITH DIFFERENT PITCHES, BLADE WIDTHS,ENGINES POWER......

As far as the SHRIKE IT CRASHED do to poor elevator surface, DID YOU HELP with that also TEACH ?

I don't mind getting help but for one man to follow me around in here to ridicule me is just not acceptable.

Thanks again.

This has gotten into a three way argument
I have closed this thread