I have a lt 40 kadet and i just put a OS 40 la on it.. What size prop should i put on this?</p>

The OS manual recommends a 11x5 prop as a starting point. On my engine a 10x6 or 11x4 seemed to work better.

That airplane is a Trainer. You will have much better success using a 11-4 0r 11-5. A 10-6 being the proverbial .40 size will work however you will have a better landing experience with the longer diameter and less pitch.

I do not recommend the APC although many will argue that. For a trainer I want good steady performance in all realms of the flight profile, not the best in just one profile.
I forget the brand because in all my other areas I use wood props.

It's the black one with squared tips. Performs well in all regimes. It's been many many years since I called for, "Mixtures, Rich, Props full increase" but on an RC models the lesser pitch is far better on the landings than vice-versa of such as the 10-6, 9-7, etc.

Some years ago a number of area clubs participated in a 4-Star Racing club competition. ST 40s, Sig 4-Star machines. Had to use 9-7 props. Everyone had problems landings unless they killed the engine. For fun put a 11-4/5 on it and landings were a piece of cake.
Like a pylon racer, short and high pitched prop, try to land with the engine running and you need a 1/2 mile of low final approach. Best to kill the engine.

The prop brand Horrace is thinking of is the MASTER AIR SCREW. As far as performance goes they aren't so good but for trainers they are perfect. Students tend to have a number of ground strikes with the prop on landings. The MAS is almost bullet proof and doesn't break like other props.
There is also a prop Sticky at the top of the page you may want to read just for the fun of it.

IMHO The shorter the prop when you start out the better....less chance of a prop strike while learning to land... I doubt starting out you'd notice much of a difference between a 10X6 or an 11X4.....the Kadet is a great trainer and like all trainers it is not extermely fast. After you become better at landings by all means go with an 11X6 or 7......Good Luck

Thank You much Gray Beard. You are 100% correct. I was "thinking" but somewhere the process was taking a nap.


You may well have a valid point there. However when I instruct a newbie I explain the roundout procedure in detail Once he understands the process, he will not need a "shorter prop". Once he sees and understands the process of a gradual power to idle, while ever so gently increasing elevator back pressure, the nose will be elevated adequately to allow the prop being well away from the surface providing his landing gear is correctly installed.
In addition, given 5 proper approach landings with a 10-6 and then 5 landings with a 11-4 or 5 on the standard .40-.45 engine the student will, IMO, well understand the difference.
Now with all that expertise, [:-] yes I do screw it up every so often. That is why my main interest in sport flying is simply shooting approaches and landings. Some say practice makes perfect. Well I have been practicing and practicing, and sometimes I think I am about there for that elusive "perfect" then, DARN, perfect slips away. [&o]

The OS 40 LA is not a powerhouse it won't pull an 11x7 well.

In a trainer it will be much happier on an 11x4 and the gray Graupner is preferred by at least one UK based flight school as it survives ground strikes better than others. Black Master is second choise. APCs are brittle and break easily.

If an 11 inch prop gives you ground clearance problems then a 10x5 works well. [ Or fit a larger nosewheel. ]

I concur 100% but state side the Graupner props aren't found in a lot of hobby shops. I have several hobby shops in my area and only one has a Graupner in stock and the pickens are mity slim! That being said every hobby shop I have ever been in has the Master Air Screws and most state side hobby shops stock the Zinger wood props for gas passers.
Some years ago I was an LA man, the .46 more then the .40 but it seems every time someone gives me a trainer there is a .40 stuck up front. That's fine with me, it makes my students learn to fly on the wing but there is no OS Factor in the .40 LA.
Back to the prop question, I wouldn't use a MAS prop on any of my own planes, I use APC on all my glow powered planes. I don't use anything else except the MAS on a trainer. I have taught 3 people once with the same prop and many ground strikes. I also agree, the 10X5 and up to the 11X4 or so on a trainer with a .40 engine.
Students don't strike the ground because the prop is too long but I'm sure it happens for that reason, my students get ground strikes because they come in with the nose down too much or just did a hard pancake.
I give my trainers over to my students after there solo to fly until they get there own plane. Usually they are good with that but every once in a while I loose a trainer. No big deal, a lot of the guys I fly with have a old trainer or two in there hanger they don't want so I get them for free and have a lot of old gear to set them up with.
Instructing is fun, up to that point just before the student can solo, then it's just holding a switch all day!

LT40 plans call for a 10" prop on a 40 motor. I believe it is recommended to be a 10x6 on the plans, but I don't have them in front of me.  The short nose wheel on the Kadet will give you clearance issues in grass with anything bigger than a 10.  I have an 11 on mine, but I turned it into a tail dragger with 4" wheels, so grass clearance is a non issue, but when I laid the motor and prop on the plans, there was not enough clearance for grass T&amp;L.

MODELERS can always adjust landing gear length to suit a prop length within reason. Plans are drawn for commercial reasons. Flying machines are set up to fly. Modelers can make adjustments.
I have an LT that I use strictly for AMA's TAG instructing. Not only does it have ample room for an 11 inch prop (even a 12" one) but it also has Barn-door ailerons
which makes it about 300% better as a flying trainer.

Those "plans" don't come from thin air. Someone has to know enough to make something then sell the plans/kit/ARF etc. to those that don't care to do the work.
Revising a plan doesn't require a lot of savy. If it did I would be in one "L" of a bad fix. [:'(]

Tried to upload some pictures of models that have no look-alikes of the kits they were modeled from. Seems like RCU is still having their troubles.

Hoss is correct. I bent a number of extra wire gear legs for several of my planes just for that reason. I used to fly from both grass and asphalt. I finally just left the tall gear legs on my planes. The longer stance did look a bit funny but an extra inch or two didn't mater. On my Hots and Kaos I was running bigger engines and props that the engines liked so some of the gear legas had to be long enough to allow 16 inch props instead of 12 and 13 inch.

Hi!
A 11x5 or 11x6 are the best sizes for a high winged trainer if flown from sea level and APC, RAM or Graupner (not the old blunt tipped gray prop though, are the best props to use.
10x6 and 11x4 does not give enough performance.
As always : Stay away from MA white tipped props! No good!

I am interested in what you mean by not enough performance. Do you mean, not enough take off thrust or speed when airborne or what.

The MAS props aren't as efficient as most other props, they tend to flex and there air foils aren't that well designed as other props. Thing is, it's a trainer, who cares, as long as it works and will fly the plane and MAS props will do just that. The beauty of them is how tough they are, it takes a lot to kill a MAS prop. When one brreaks you know you did something wrong. My students beat a prop to death when learning to land and after there solo. If MAS props didn't work they would have gone under decades ago. I tease Jaka about making everything sound so final and like his words are etched in stone someplace all the time. The MAS props just aren't the best but they do work just fine on a trainer. You can etch that in stone if you want.

Ditto! For my Kadet, I am using a Master prop for that very reason. It is my first taildragger, and I just KNOW it will be hitting the ground a few times before I get the hang of not having a nose wheel. Both of my electric planes use a thin bladed plastic prop that is no where near as sturdy as the MA prop, but have held up through quite a few ground clips, especially the Apprentice, it has so much down thrust that it will pull itself into the ground if the grass is too tall.

In fact I flew it the other day from my rear pasture and the horses have left quite a few divits, so two out of 3 landings wound up with a prop strike and a nose flip when the nose wheel fell into a divit. My first landing though caught the ground just right and skimmed over the bad parts, but #2 and 3 landings hit the ground at just the wrong spot. If I had a wodden prop, it would have been busted.

Now on my DLE20 it has a XOAR prop, but it is also a 16x8, and I haven't seen any plastic props in that size except for electric.

If a beginner is landing too fast, it is most likely because he/she hasn't trimmed the airplane for the slower landing speed (higher angle of attack). A one or two inch difference in pitch and/or diameter is not the culprit. A properly trimmed trainer flying on speed on a standard glide path will in most cases need a power setting ABOVE idle (thanks to the backside of the drag curve).

I have raced Skyraiders, Q500, and Q40 for many years. Skyraiders and Q500 airframes are more than draggy enough to land at throttle settings above idle. The only problem with Nelson/Jett powered Q500 airframes is that the engines do not have low speed needle valves, and as a result, don't idle very well - when you move the throttle to idle, the engine normally dies. Landing Thundertiger .40 powered Skyraiders at idle is no problem. They slow down like kites and the idle allows us to taxi back.

Fly a trainer slow enough on final and you will need more than idle. Full scale pilots learn early on pitch/power settings and the resulting airspeeds and descent/ascent rates.

Kurt

There is a lot of difference between an RC model and full scale and a trainer with a newbie. Prop has a lot to do with the landing, especially since we fly fixed pitch like many small private full scales do. Flying "....slow enough on final ... is a technique that most initial beginners don't really yet have the proficency to even recognize, much less accomplish. Besides what beginner is going to be retrimming while learning to fly?

Since you - on your profile claim to be an EXPERT Pilot and I would never question such, you just might expect a tad too much from the beginner. People that are really naturals in any endeavor seem to have less understanding of those that are less than "automatic" in a skill being learned. Having instructed in USAF T-33, T-38, and in Navigation and Bombardment, SAC B-47, I agree with those scholars that state such. I was good but not a natural. I had to WORK to stay at the upper levels.

In my navigator school, 30 started, 14 finished, I was 2nd. In my Pilot Training class, 28 started, 14 finished, I was 1st in flying but 4th overall as the physical training found me wanting, like REALLY wanting. As an RC Instructor, I demand a bit more proficiency than most, yet those I solo know how to fly, and the Safety precautions, but they are not then 3D pilots.

As far as "Full scale pilots..." maybe I dropped a ball here and there. Almost 20,000 hours, including a couple years in a C-123 with R-2800s, maybe I never learned what your full scale learned. However I survived 41 years of it. I still stick to it that a low pitch prop is much easier to land an RC model with than a high pitch. Student RC pilots don't have to be able to land out of a tight inside loop over the runway. I don't have to, but I like to!

Wow. I didn't know I was messing with the mamma bear of RCU (well, I kinda knew). I too flew in the USAF, like many of us here on RCU.

My comments were not about you nor directed at you...but your comments were definitely about me and directed at me. But that's ok; I'm a big boy and I can take it.

I think you should stick to the thread and offer comments/suggestions based on your experience and/or facts. We now know your resume, but that doesn't help answer the OP's questions.

It's entertaining how many beat their chest rather than objectively respond when someone differs from their opinion. Amazing, but fun.

Kurt

First off I have never seen anyone trim a Trainer plane for landing?? I trim a trainer for hands off straight and level at 1/2 throttle. I teach how to land, nothing tricky, just bring it in and land. By the time a student lands he has seen the air speed a lot and knows it. I land a trike geared sort of like a tail dragger, a bit nose high so the front gear isn't slammed into the ground, for tail draggers I teach the three point so the nose isn't going to hit. APC makes 16 inch props, I use a lot of them on my YS engines but they won't take a ground hit any better then a Xoar. I have never used a Xoar smaller then 20 inch but it would be fun to do a test compare between the Xoar and APC 16 inch. No real reason, I just like both brands and would like to see if one is any better then the other. I'm thinking the price would be about the same??

The XOAR is recommended for the DLE20, so that is why I have it. ;P  I have a nadful of of brand 16" props for it, but since it is a new engine, I will use what is recommended.

I use wood props on all my gassers except one, That engine is an old RSC 1.40 22 cc high performance engine. Depending on the plane that engine likes the APC 17 or 16 inch prop. I have had it before Xoar came out or got to the states? My bigger gas engines I have and have had I always start out with Zinger props. They sure aren't the best prop on the market but most every hobby shop stocks them. They are also cheap!! I use them first for maiden flights and to get my planes in trim. With a new plane I have been known to nip the props on landing!! Wood props tend to break as soon as they touch the ground!! Once I get past that little thing and get the landing part of a new plane figured out I switch over to Xoar props. They are way more efficient and it's like installing a new engine in the plane, much better performance then the Zinger, more money but worth the added cost!! I have just never used one of the smaller Xoar props. I usually don't run wood props on glow engines. Next time I install the RCS engine in another plane {I have the kit already} I will give the 16 inch Xoar a try when I am doing my prop testing.