Whats the best propeller to use?

[DV50]

Hey!

Anyone know what propellers the more competitive teams use? Im just using the Ikara 24cm propeller and its giving me mediocre results. I hear different people talking about different propellers all the time but I never manage to find them on google.

[coachchuckaahs]

Unless you are building your own prop, the Ikara is a good prop to use. They have several, including the 24cm symmetric prop, the "wide blade" prop that many people call the "flaring" prop. While it has a flaring shape, it will not flare much unless sanded to be more flexible. There is also a 12" (approx" Ikara prop, but I have not heard of people trying that yet. It would not be suitable for C Div, due to box limitations, but should be able to fit a B div box. You would need notably thicker rubber for that prop.

While there is some advantage for a well-built balsa prop, you will not realize any such until you are regularly at 2:30 or more under a 20-24' ceiling in Div B with the Ikara prop.

Be sure the Ikara prop pitch is correct, starting with a Pitch/Diameter ratio around 1.6. You can adjust form there during your optimization, but that provides a good starting point. Some have reported the Ikara props come somewhat under-pitched, and the as-delivered pitch may vary quite a bit.

If you are not making 2:30, then you need to be looking at your basic trim, your winding technique, and your matching of prop and rubber. A different prop will not make up of shortfalls in those basic areas. Last year's Nationals winners, as far as I know, used stock Ikara props.

Coach Chuck

[pumptato-cat]

If you are not making 2:30, then you need to be looking at your basic trim, your winding technique, and your matching of prop and rubber. A different prop will not make up of shortfalls in those basic areas. Last year's Nationals winners, as far as I know, used stock Ikara props.

Do you think this year's Nats winners will use stock Ikaras as well? Also, do you think custom props would have beat Ikaras last year, or was the stock prop genuinely one of the best choices? I recognize that not a lot of the best Flight competitors make it to nationals due to SO's team-based structure(bjt4888's teams come to mind), so I was wondering if that had something to do with it. Do you know if previous seasons' winners used customs?
Also, what would be a good time to aim for before moving on to props for Div. C? I think I've gotten my basic trim pretty good and am testing rubber right now. Not sure if I moved on too quickly or need to work on winding instead, though. How many tests do you usually go through before moving on to custom props?

[coachchuckaahs]

The question asked appeared to be about commercial props.

In the past I have seen very few custom props at nationals. It's not something a lot of teams do. The margins are thin, compared to the number of new variables introduced. There is a lot of work and testing involved, and that time is often better spent on the basics. We often, by the time getting to nationals, had tested over 25 props.

I don't have a lot of thought on when it's the time to move on for C div. It really depends on your time, skill, etc. I put that 2:30 mark out there because that is a fairly pedestrian point at which some of the basics are worked out. The OP is substantially below that. An equivalent threshold for C might be 1:45. But, TBH, those might be more realistically 3:30 foot B and 2:15 for C. Those are reachable times with standard effort.

But when you move there is really personal preference. It is a lot of work. I wanted to be clear that it is not a pot at the end of the rainbow, instant doubling if time. If you are not making good time, a custom prop won't be a magic fix, but rather a time sink.

That said, we only do custom props, but we have the experience in SO and LPP to have a starting point. Our starting props are on par, usually, with ikara, because I know the variables and pitfalls. But if my current team were to win State, that's when the real prop work would start.

If already doing props, I would keep what you have. If not sure if it, pop on an ikara, see if yours is at least equal.

The bottom line, very few do customs, and those that do very few will do enough effort to make it work well. To me the strongest driver is the possibility of a proper flare for very low ceiling flight, but that is a very very fine balance.

Coach Chuck

[pumptato-cat]

Oh, I see--thanks! I want to work on custom props after Regionals, so what's a good starting place for prop shape/mold? LPP wasn't that time-consuming because there was a lot of data from previous testing that was available, but that's not the case with SO. Also, do you think it's worth building a prop with polyamide tubing on the hub to allow pitch change without wetting/twisting prop spars, sort of like the ones seen in F1D?

[coachchuckaahs]

Cat:

I think the prop starting point has been discussed elsewhere here. While LPP may have pitch around 24 or so(P/D of 2.0), a more reasonable starting point for these planes seems to be a P/D of 1.6 give or take, so I would start there. Similar camber (2-3 %), fairly soft flaring (usually people are custom making props to add flaring). Prop planform I have not changed much from the Ikara flaring shape forward of the spar. I have tried a few other planforms, but this is what I currently use on SO and LPP. I do scale it some depending on diameter, but since you are C-div, the diameter will be about the same as Ikara. You may want to trim the inner end of the blade a little to expose a little more spar for more twist (flare), depending on how flexible your spar is in twist.

As far as repositionable, you could do that but it adds another thing to come loose, and it stiffens up the spar in twist. I think the hard part of these props is getting enough flare for the low ceilings without distorting the blade badly, so I do not think you want a stiffer spar. The adjustment of pitch with water and a heat gun is quick adn easy (quicker than resetting the poly tubing spar), and can adjust over a pretty large range. If you build the carbon (Gowen) hub, there is less ability to adjust pitch, and may be hard to add a poly tube adjustment.

Keep it simple!

Coach Chuck

[DV50]

If the ikaras dont come with enough pitch, What should i use to adjust it? I have a pitch gauge, but i have never been familiar with it.

[coachchuckaahs]

{itch gage and two pair needle nose.

I think Josh has a video

It will only take a few adjustments before the spar fails, so be careful.

Coach CHuck

[jgrischow1]

The question asked appeared to be about commercial props.

In the past I have seen very few custom props at nationals. It's not something a lot of teams do. The margins are thin, compared to the number of new variables introduced. There is a lot of work and testing involved, and that time is often better spent on the basics. We often, by the time getting to nationals, had tested over 25 props.

I don't have a lot of thought on when it's the time to move on for C div. It really depends on your time, skill, etc. I put that 2:30 mark out there because that is a fairly pedestrian point at which some of the basics are worked out. The OP is substantially below that. An equivalent threshold for C might be 1:45. But, TBH, those might be more realistically 3:30 foot B and 2:15 for C. Those are reachable times with standard effort.

But when you move there is really personal preference. It is a lot of work. I wanted to be clear that it is not a pot at the end of the rainbow, instant doubling if time. If you are not making good time, a custom prop won't be a magic fix, but rather a time sink.

That said, we only do custom props, but we have the experience in SO and LPP to have a starting point. Our starting props are on par, usually, with ikara, because I know the variables and pitfalls. But if my current team were to win State, that's when the real prop work would start.

If already doing props, I would keep what you have. If not sure if it, pop on an ikara, see if yours is at least equal.

The bottom line, very few do customs, and those that do very few will do enough effort to make it work well. To me the strongest driver is the possibility of a proper flare for very low ceiling flight, but that is a very very fine balance.

Coach Chuck

Is there scaling factor to see how excess weight affects those benchmark times? My two Div B teams split up the light parts of their kits (and I'm sure some unscrupulous glue usage was a factor) and one plane is about 9.5 g and another is in the mid to high 8s. We plan to use all the lightest parts of our next kit for our state plane and hopefully be just above 8.00, but it would be nice to have a sense of where we are with our excess weight. I mentioned in another thread one of the planes is doing 2:10 and you and others mentioned it should be doing better with just trim adjustments and without substantially denser rubber or different props, but it would be nice to know how much the weight is depressing its max time. Thanks!

[pumptato-cat]

I'm interested as well--I did hear from bjt4888 that below 8.25g is probably okay in terms of time loss.