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Open Forum / Re: Vast facebook stunt pics.
« Last post by Dick Byron on July 02, 2025, 11:58:16 AM »Thanks Doc.
- July 05, 2025, 10:19:40 AM
Recent Posts
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Open Forum / Re: Propeller load changes with diameter
« Last post by Brett Buck on July 02, 2025, 10:06:26 AM »But as Brett mentined, you must remember it is static or pitch speed difference at the same RPM, in flight difference on C/L stunter which will fly the same air speed with any of those props (that larger will have smaller RPM), is much smaller as both needs to deliver the same power, so difference is only in prop efficiency. Best example is comparation of our 11x5 and 12x5 flat back props. There is very small difference (less than 10%) in consumption between both, reason is 12x5 has slightly better efficiency and they both deliver the same cruise power. That measurable difference comes from better pull in corners where the prop is loaded close to static thrust, which is better with 12x5 than with 12x5 and therefore it takes more power. That is why I wrote that note in that other thread that the speed stability in fugures is in relation to used power. That means better speed stability (at constant RPM) is payd by higher consumption.
And to finish the thought, pitch is an even bigger driver for efficiency. As far as I know, nobody it using anything like a typical tuned pipe prop (like mine - Eather 12.5-3.9 flat back 3-blade) on an electric - because it is so inefficient for most of the flight you would require a HUGE battery. This is where the low energy density of electric is precluding some options, I am doing it with 6.5 ounces of fuel, instead of a maybe 20-25 ounce battery. Electric makes up for it in different ways, and so it doesn't require you to use inefficient props for performance reasons.
Brett
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Open Forum / Re: Propeller load changes with diameter
« Last post by Mike Alimov on July 02, 2025, 09:40:31 AM »Thanks for responding. Something is sucking the life out of the batteries and nothing is jumping up saying "Me, Me, Me"! Since I cannot do anything about the weight (it is now 68oz after changing ESCs), I am stuck trying to stretch available mah. [snip]
Ken
I suspect that it is the weight of the airplane and the associated drag from the wing required to support that weight that is sucking the juice out of the batteries. Lighter plane would need less mAh, but I agree, not much can be done about it right now. I would then recommend flying on shorter lines. This translates to less work required to do the flying, and so less mAh. At this weight, I doubt there will be any problems with line tension. And you will have an added benefit of having the plane closer to you, which (some reported) somehow makes it easier to nail the bottoms.
Just my $0.02
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Open Forum / Re: Vast facebook stunt pics.
« Last post by john e. holliday on July 02, 2025, 09:30:14 AM »Dick glad to see you are still with us. Those pictures brought a lot of memories back. Yes a lot of the familiar faces are now gone. You were the man in scale to me. Take care. 
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Open Forum / Re: Rule of thumb for wheel size for grass
« Last post by Perry Rose on July 02, 2025, 05:41:39 AM »2 1/2 min. Even then I use full up elevator until the plane gets rolling. The plans generally list the wheel size.
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Open Forum / Re: Rule of thumb for wheel size for grass
« Last post by Dave_Trible on July 02, 2025, 05:30:12 AM »I use 2 1/4 or 2 1/2" very narrow wheels on my grass field and do well. However there are a few variables that make a lot of difference. One is simply how thick or dense is the grass. In general the nicer looking the grass the harder it is too take off from-the wheel drag is a bunch. Another is wheel location. The best grass location is further forward to compensate for that wheel drag but then the airplane lands like a kangaroo on pavement. Landing gear length and how stiff it is will also matter. The more prop you can keep clear of the grass the better. The weight and power of the airplane matter and whether you are taking off more into the wind or not. The wheels that are a little larger but narrow and very light have worked best for me. I wish the Maxx aluminum hub wheels were still around-worth their weight in good balsa....Something like a Ringmaster though should be able to mostly jump off in a couple feet at most , don't weigh much and usually have the gear ahead of the leading edge. You might do OK with 2" but it will likely flip over on most landings.
Dave
Dave
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Open Forum / Re: Propeller load changes with diameter
« Last post by Igor Burger on July 02, 2025, 03:20:37 AM »I have read a bit about the diameter changing the load something akin to the 5th power.
Martin Hepperle has all equations on his home page. But it is necessary to understand. It is 5th power if whole prop is resized linearly. Diameter gives power of two, pitch, blade width and blade area makes linear ratio. So if you resize all of that linearly it gives power of 5. if you resize all except of pitch, you get power of 4. if you shorten existing blade, you are changing diameter, but you keep blade width and pitch so it is only aproximately power of 3. (it is all approximate of course)
But as Brett mentined, you must remember it is static or pitch speed difference at the same RPM, in flight difference on C/L stunter which will fly the same air speed with any of those props (that larger will have smaller RPM), is much smaller as both needs to deliver the same power, so difference is only in prop efficiency. Best example is comparation of our 11x5 and 12x5 flat back props. There is very small difference (less than 10%) in consumption between both, reason is 12x5 has slightly better efficiency and they both deliver the same cruise power. That measurable difference comes from better pull in corners where the prop is loaded close to static thrust, which is better with 12x5 than with 12x5 and therefore it takes more power. That is why I wrote that note in that other thread that the speed stability in fugures is in relation to used power. That means better speed stability (at constant RPM) is payd by higher consumption.
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Building techniques / Re: Control throw measurement.
« Last post by Brett Buck on July 02, 2025, 12:32:54 AM »That’s interesting. PW said to set the original, flat, round-leading-edge Impact stabilizer parallel to the wing chord. This made for about a 4.5 degree elevator downrig, tweaked as required. I have been doing the same with the new, pointy-LE stabs, but maybe I should try positive incidence with faired elevator.
Again, I am not at all sure, but I am not surprised at all by the flat stab requiring a 0-0 incidence. I think the lift/AoA curve almost has to have some large slope right near zero due to separation on the "top" surface at infinitesimal angles. About 50% of the local "flat stab" airplanes ended up with issues that were fixed by taping wires around the LE. Making it pointy but otherwise flat is a less-ugly variant of that that, reducing the pressure gradient variation where the flat part starts, but still permitting very accurate alignment measurement. I gave up on that issue and made the stab airfoiled - effectively making the "pointy" section go all the way to the hinge line. Other types of airfoils where the high point is ahead of the hinge line still have occasional odd behavior.
And, maybe I am slow on the uptake, but I have learned almost nothing new about this particular problem in 25ish years. But I not that neither VGs nor tripper/zigzag strips seem to make much difference, where they are pretty dramatic on the point-flat-stab airplanes.
Brett
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Building techniques / Re: Control throw measurement.
« Last post by Howard Rush on July 02, 2025, 12:22:06 AM »That’s interesting. PW said to set the original, flat, round-leading-edge Impact stabilizer parallel to the wing chord. This made for about a 4.5 degree elevator downrig, tweaked as required. I have been doing the same with the new, pointy-LE stabs, but maybe I should try positive incidence with faired elevator.
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Open Forum / Re: Li-on vs Li-po?
« Last post by Howard Rush on July 01, 2025, 11:39:01 PM »Howard, which costs more if you leave it at the field?
You’re mean.