Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Engine input for contest

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Old 04-30-2014, 09:57 AM
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why_fly_high
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Default Engine input for contest

I am on a committee that writes rules for a speed based college engineering design contest. http://speedfest.okstate.edu/Speedfe...les_Alpha.html

We are contemplating upping the engine limit and was wondering how much more power the OS .55AX has over the .46AX. The specs only show .01mor hp. I know manufacturer hp info is pretty much worthless so I was hoping to get input from people that have run both engines. Is the power increase noticeable and worth the change to the rules?

Thanks,

Dan
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Old 04-30-2014, 11:27 AM
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Any ABC constructed, twin ball bearing, ".45 class" engine with Schneurle porting will give you ample power for pretty thrilling performance with a 9 x 8 prop on a clean, light ship.
I don't think there are any "dogs" out there.
I'd go for the .46 OS or the .46 Thunder Tiger engines. The only issue I used to have with Thunder Tiger was the 2 piece muffler coming apart, but that was several years ago.
If you can visit a local RC pylon racing event and have a talk with some guys [during lunch, not while they are hectically preparing to race] you will come away with some good advice and a first hand look at it.
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Old 04-30-2014, 11:30 AM
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How many years has your school been running this program..? It would be very cool to see video of past competitions.
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Old 04-30-2014, 11:48 AM
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Originally Posted by combatpigg View Post
How many years has your school been running this program..? It would be very cool to see video of past competitions.
This past weekend was the 4th year. until this year we have always done electric planes for the Alpha Class. we decided to try something different this year with the glow. he planes were larger and slower than the little electric planes going nearly 200mph. The main reason for going to glow this year was cost. With only about 5-6 weeks for flight testing before the contest, if we bent a motor shaft, the motor could not get back to the manufacturer and then back to us before the contest was over, effectively rendering the motor worthless to the teams.

This is from 2 years ago. 180mph, vertical launching, fire breathing, completely bad to the bone electric. https://www.youtube.com/watch?v=g36Y...ature=youtu.be
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Old 04-30-2014, 11:52 AM
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Originally Posted by combatpigg View Post
Any ABC constructed, twin ball bearing, ".45 class" engine with Schneurle porting will give you ample power for pretty thrilling performance with a 9 x 8 prop on a clean, light ship.
I don't think there are any "dogs" out there.
I'd go for the .46 OS or the .46 Thunder Tiger engines. The only issue I used to have with Thunder Tiger was the 2 piece muffler coming apart, but that was several years ago.
If you can visit a local RC pylon racing event and have a talk with some guys [during lunch, not while they are hectically preparing to race] you will come away with some good advice and a first hand look at it.
I know some pylon racers and we have been doing speed planes for over 6 years now. We have built planes that go over 200mph. Up until this year we have always done electric. We are looking for info on reasonably priced glow engines. We don't want to make the teams by Jett engines or something like that. the teams this year designed planes that met the task we laid out and beat a Q500 plane with the same engine. We don't have a Q40 airframe to compare their planes against.

Dan
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Old 04-30-2014, 12:07 PM
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To me the actual top speed is not the issue, is it what you do with the limits that defines the quality/skill of the entrants. Is it important to go as fast as the electrics, or is it more important to use engineering skills to make the best of what you have available (which seems more real world)? Curious.

I only say this because of the diverse assortment of .45-.46 size engines on the market, versus .55, which makes me wonder is is restrictive or counterproductive to bump to a displacement size that has fewer offerings in the marketplace.
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Old 04-30-2014, 12:23 PM
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Originally Posted by MJD View Post
To me the actual top speed is not the issue, is it what you do with the limits that defines the quality/skill of the entrants. Is it important to go as fast as the electrics, or is it more important to use engineering skills to make the best of what you have available (which seems more real world)? Curious.

I only say this because of the diverse assortment of .45-.46 size engines on the market, versus .55, which makes me wonder is is restrictive or counterproductive to bump to a displacement size that has fewer offerings in the marketplace.
Valid points!

No, we are actually wanting things to slow down in hopes it might attract more teams and also increase safety for inexperienced teams. The main reason for this question is that we are planning on requiring the planes to carry a payload that will add some drag and about a pound of weight and don't want the planes to get "slow". We also want an engine that is readily available to everyone.

Yes, it is supposed to be an optimization exercise for the students. we are in fact not that concerned about top speed other than the students that have been watching year after year get pretty excited about how fast the planes go.
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Old 04-30-2014, 12:53 PM
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Those electric racers are stupendous..!
Nice job..!
If you are looking for best bang for the buck with glow engines I think the Thunder Tigers are the most universally popular brand in entry level pylon racing. The relatively low price might allow you to include the Jett muffler as an upgrade.
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Old 04-30-2014, 02:16 PM
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I agree with CP, add a Jett muffler to a .45 and gain more power. Be sure to talk to Dub Jett and explain what you are trying to do and the 16,000 rpm limit. He would also know which sport motors work best with his tuned mufflers. I changed out a stock muffler on a ST .40 some years back and picked up about 1500 rpm on the same prop, which is a lot more power.

Since you are writing the rules, I'd dump the RPM limit and I would also raise the voltage allowed for the airborne receiver pack. Some 2.4 systems work much better with two cell lipo battery packs with a regulator.

Now if the goal is to control speed, the easiest method is to add drag, not weight. A flat plate of plywood or aluminum can limit speeds easily. Since you have tight turns at speed, adding a pound of weight is a easy way to fold wings in a turn, especially if the event is flown on a gusty day. I don't see any restrictions on the airframe. The standard AMA quickie for 426 or 424 pylon racing would do well in your event, and easy since ARF's are available. It might help turnout if you just spec'ed a quickie design as standard. Otherwise a high aspect high wing design with a 10% airfoil would be very good for both the climb and tight turns of the speed course.

I forgot to add:

To get the most laps, you have to design the flight path based on the wind conditions. If the wind is aligned with the course, climb when going downwind, dive into the wind. Much of the altitude change can be done in the turns with little loss of speed (you will be pulling 25 to 35 g's anyway, +/-1 more makes no difference). If you want to read up on it try to find a paper that Jimmy Doolittle wrote on the subject around 1928 or after he received his PhD in Aeronautics at MIT. This is the same guy that planned and flew the B-25 raid on Tokyo and flew the Gee Bee R1 racer that killed everybody else that flew it.

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Old 04-30-2014, 03:08 PM
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I'd like to see how well these guys could do with the good ole COX TD .049s.
Prepping for the event would take students through some very basic engine "detailing" and the very limited power adds a lot of spice to the design exercise. They can go fast enough to be fun and the overall cost to campaign one of these is about as cheap as it gets. You could have 2 planes ready to run for about the same amount of investment as one .40 sized racer.
Another idea is to base an event on the very inexpensive ASP .12s. You can use basically the same weight building methods and equipment as you would for the .049 class and these planes will do 130 mph.
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Old 04-30-2014, 06:03 PM
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Originally Posted by HighPlains View Post
I agree with CP, add a Jett muffler to a .45 and gain more power. Be sure to talk to Dub Jett and explain what you are trying to do and the 16,000 rpm limit. He would also know which sport motors work best with his tuned mufflers. I changed out a stock muffler on a ST .40 some years back and picked up about 1500 rpm on the same prop, which is a lot more power.

Since you are writing the rules, I'd dump the RPM limit and I would also raise the voltage allowed for the airborne receiver pack. Some 2.4 systems work much better with two cell lipo battery packs with a regulator.

Now if the goal is to control speed, the easiest method is to add drag, not weight. A flat plate of plywood or aluminum can limit speeds easily. Since you have tight turns at speed, adding a pound of weight is a easy way to fold wings in a turn, especially if the event is flown on a gusty day. I don't see any restrictions on the airframe. The standard AMA quickie for 426 or 424 pylon racing would do well in your event, and easy since ARF's are available. It might help turnout if you just spec'ed a quickie design as standard. Otherwise a high aspect high wing design with a 10% airfoil would be very good for both the climb and tight turns of the speed course.

I forgot to add:

To get the most laps, you have to design the flight path based on the wind conditions. If the wind is aligned with the course, climb when going downwind, dive into the wind. Much of the altitude change can be done in the turns with little loss of speed (you will be pulling 25 to 35 g's anyway, +/-1 more makes no difference). If you want to read up on it try to find a paper that Jimmy Doolittle wrote on the subject around 1928 or after he received his PhD in Aeronautics at MIT. This is the same guy that planned and flew the B-25 raid on Tokyo and flew the Gee Bee R1 racer that killed everybody else that flew it.
We did allow tuned pipes this year. The main reason for the rpm limit is that we did not want the teams blowing up engines trying to squeeze the last little bit out of the engine. The plan was in fact to up the limit to 17K. The rules will be different for next year. Most likely the OS 46ax will be the choice. We are not adding weight for the sake of adding weight. We will be adding a payload that the plane must carry and then drop. The main purpose of the payload is two prevent a stock racing arf from being the best option driving the teams to design something new.

You are correct about the rx voltage. We have already changed that in next years rules.

in previous years when competing in other design contests with limited power and endurance we would do that exact climb and dive profile as you described. The difference in the distance covered was quite surprising.

Here are pictures from this years contest. The Uproars are from the high school category of our contest.


https://www.flickr.com/photos/tchays...7644383999655/
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Old 04-30-2014, 06:19 PM
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Holy snappers, those are some great models!
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Old 04-30-2014, 06:39 PM
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What's the purpose of this event if ARFs are allowed in any way, shape or form..?
I would assume that a video build log would be required to authenticate the entries.
That said, in the hands of the best pilot the race can be won with the slowest model...so I do not understand what is learned from this as an engineering exercise...?
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Old 04-30-2014, 07:05 PM
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Originally Posted by combatpigg View Post
What's the purpose of this event if ARFs are allowed in any way, shape or form..?
I would assume that a video build log would be required to authenticate the entries.
That said, in the hands of the best pilot the race can be won with the slowest model...so I do not understand what is learned from this as an engineering exercise...?
We have not disallowed them previously because the rules were written as such that an arf or off the shelf plane would not be the best solution. This last year was the first time an arf could have been competitive. I fly for both OSU teams so they have an equal footing for pilot. Both of the OSU teams beat the Q500 plane we put together for comparison. I flew all 3 planes and all 3 had the same engine. We have not set the rules for next year yet but I am sure that next year's payload and rules will make it very hard for an off the shelf plane. A couple years ago a team showed up with an off the shelf plane and they got beat handily by purpose designed planes.
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Old 04-30-2014, 07:27 PM
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OK...I'm a little bit slow to catch on. Thanks for clearing that up.
Yes, I can see how an ARF could possibly be made obsolete, especially the run of the mill variety. I visualized this deal differently. I had a mental image of well trained video gamers [your students] driving their RC creations around the pylon poles like they were born with joy sticks in their hands.
I'm really impressed with your program and your students are very fortunate to take part in this program.
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Old 04-30-2014, 07:40 PM
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I wouldnt increase the displacement. You are looking for ingenuity and engineering acumen.. A clipped wing quickie 500 racer, os 46 with a pipe and and a properly trimmed glider as a delivery system is probably the norm? I would think you would want to make things more interesting..most of last years stuff looked like they focused too much thought on the speed plane not the delivery system though. With the 16000 rpm limit the planes should all be within a few mph of each other so making the delivery system stay airborne the longest is the real challenge. How many exceeded the three minutes?

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Old 04-30-2014, 10:11 PM
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Thanks for the photos. I would say that you have already exceeded my expectations with your designs. Either you have a great engineering program or someone has done the research on induced drag. It would be very interesting to put a racing engine into your designs instead of a mildly timed sport engine. You could easily touch 200mph with a Q40 engine or FAI engine, though I would stick with the Q40 engines (Jett or Nelson) because they are much easier to operate and APC makes carbon props that work well.

If you have good bearings, it is nearly impossible to blow up a .40 sized engine. Most of the top racing classes operate in the 25 to 30K+ range in the air, and the internal construction is not that much different from any of the sport engines. The mild sport engine timing will limit them to under 20K, but you want any engine to operate at it's peak power rpm in the air, so prop selection is key especially with flight profiles you are running.
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Old 05-01-2014, 05:30 AM
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Originally Posted by HighPlains View Post
Thanks for the photos. I would say that you have already exceeded my expectations with your designs. Either you have a great engineering program or someone has done the research on induced drag. It would be very interesting to put a racing engine into your designs instead of a mildly timed sport engine. You could easily touch 200mph with a Q40 engine or FAI engine, though I would stick with the Q40 engines (Jett or Nelson) because they are much easier to operate and APC makes carbon props that work well.

If you have good bearings, it is nearly impossible to blow up a .40 sized engine. Most of the top racing classes operate in the 25 to 30K+ range in the air, and the internal construction is not that much different from any of the sport engines. The mild sport engine timing will limit them to under 20K, but you want any engine to operate at it's peak power rpm in the air, so prop selection is key especially with flight profiles you are running.
We do have a great engineering program! The reason we started this contest was that OSU had won the AIAA Design, Build, Fly contest 6 out of 7 years. They were beating 50-80 schools from all over the world. The basis for that contest was building the lightest electric planes you could to carry the prescribed payload. The way things worked out, teams were forced to build ultralight stick built film covered planes. We wanted to allow our students more material options using composites. Speedfest was born. The other reason for a speed based contest is that as you can imagine we have a lot of wind here in Oklahoma. Flying a plane with a 40mph cruising speed in 30-35mph winds does not work well. flying a 150mph plane in 30mph winds is not big deal as we have proven the last couple years.

Keep in mind, very few of the students have previous rc experience. Virtually none with glow engines. We did have fear of it becoming an engine tuning contest and that was one of the reasons behind the rpm limit. After running these engines for a season now I think we are comfortable raising the rpm limit some.

Thanks for the kind words and input. HighPlains, you are not that far away. You should come down and check it out.

Dan
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Old 05-01-2014, 05:41 AM
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Originally Posted by 2walla View Post
I wouldnt increase the displacement. You are looking for ingenuity and engineering acumen.. A clipped wing quickie 500 racer, os 46 with a pipe and and a properly trimmed glider as a delivery system is probably the norm? I would think you would want to make things more interesting..most of last years stuff looked like they focused too much thought on the speed plane not the delivery system though. With the 16000 rpm limit the planes should all be within a few mph of each other so making the delivery system stay airborne the longest is the real challenge. How many exceeded the three minutes?
Both teams had exceeded 3 minutes in practice. On the day of the contest with 30mph winds, the teams struggled keeping the gliders close. The Black team (flying wing glider) was able to reach 3 minutes. The orange team was unable to reach 3 minutes at the contest with their best time being about 2:30. It was interesting because the Orange plane was a little larger and slower but was able to turn better. on the course they were both very close. it did come down to the glider time and the black teams planes being lighter so they were able to climb higher in the 10 second climb portion.
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Old 05-01-2014, 06:09 AM
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The .55AX will spin a slightly larger prop and top RPM would be slightly less. If the goal was for speed, a 46AX commonly uses an 11x6 prop. The 55AX could start with an 11x8 or 11x10. Basically you get to prop about 'one size up' with the 55AX.

The 55AX is a bigger, more powerful motor. There's no denying it. If I had to choose I'd pick the 55 every time. Similar weight and size but more power.

Now if speed is the goal and you know how to tune an engine, Super Tigre is the way to go They are finicky but boy they scream.

Note that most brands seem to have something in the .5x category. There are a few .51 and .55 engines.
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Old 05-01-2014, 06:59 AM
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HighPlains, you are not that far away. You should come down and check it out.
I was thinking the same thing.
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Old 05-01-2014, 08:36 AM
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To answer your question, going from the .46 to the .55 is a torque upgrade. You'll see pattern pilots with .40 size planes or very light .60 size planes use it. You can turn a bigger or higher pitched prop with a .55 instead of a .46 at roughly the same RPM. The .55 was designed for pilots flying .40 size planes who wanted more pep without having to go to a tuned pipe exhaust.

Since everyone else is offering advice, I will too. Don't move up to the .55 unless you simply want to let them run as much speed as possible. Pick a powerplant that is plentiful and inexpensive and stick with it. Both of these engines qualify there, but the .46 will give them a lot to work with. Don't limit the RPM either. As stated above, the porting of the engines won't allow them to turn fast enough in the air to damage themselves anyway, at least not with a prop that is actually usable on a real airplane. If you're really that worried about it, go ahead and spec a realistic prop for them to use.

All that said, I'd reconsider abandoning electric power. The big issue you're going to have with glow is having the teams learn how to tune glow engines. It's not really that hard, but just 2-3 clicks in one direction or another will take a plane from a top contender to an also ran. You've been around pylon racers so you probably know how much effort they put into engine tuning. You'll be adding yet another set of skills and variables to an already complicated task by going the wet power route.

If the issue is broken prop shafts, buy motors with replaceable shafts and keep an inventory of them in stock. It is so much easier to level the playing field with electric, because you can simply set a watt limit on the ground and be done with it. Teams can play around with their prop selection and get the one that works best with their airframes without going over the limit. It takes all of a minute to put a watt meter on the plane and measure the current, so there will be no question on race day if the plane is legal.
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Old 05-01-2014, 09:49 AM
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Originally Posted by jester_s1 View Post
To answer your question, going from the .46 to the .55 is a torque upgrade. You'll see pattern pilots with .40 size planes or very light .60 size planes use it. You can turn a bigger or higher pitched prop with a .55 instead of a .46 at roughly the same RPM. The .55 was designed for pilots flying .40 size planes who wanted more pep without having to go to a tuned pipe exhaust.

Since everyone else is offering advice, I will too. Don't move up to the .55 unless you simply want to let them run as much speed as possible. Pick a powerplant that is plentiful and inexpensive and stick with it. Both of these engines qualify there, but the .46 will give them a lot to work with. Don't limit the RPM either. As stated above, the porting of the engines won't allow them to turn fast enough in the air to damage themselves anyway, at least not with a prop that is actually usable on a real airplane. If you're really that worried about it, go ahead and spec a realistic prop for them to use.

All that said, I'd reconsider abandoning electric power. The big issue you're going to have with glow is having the teams learn how to tune glow engines. It's not really that hard, but just 2-3 clicks in one direction or another will take a plane from a top contender to an also ran. You've been around pylon racers so you probably know how much effort they put into engine tuning. You'll be adding yet another set of skills and variables to an already complicated task by going the wet power route.

If the issue is broken prop shafts, buy motors with replaceable shafts and keep an inventory of them in stock. It is so much easier to level the playing field with electric, because you can simply set a watt limit on the ground and be done with it. Teams can play around with their prop selection and get the one that works best with their airframes without going over the limit. It takes all of a minute to put a watt meter on the plane and measure the current, so there will be no question on race day if the plane is legal.
Thanks for the input. It is much appreciated. Also, for our teams, there are about 20 people per team. There is a propulsion team that does test stand tests and experiments. They actually do learn how to operate and tune the engines but learning the glow engines and their temperament was probably the steepest learning curve. It appears that having an inventory of .46s already and the input from you guys that the power increase is negligible, keeping the .46 is the way to go.
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Old 05-01-2014, 10:43 AM
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Hello Dan!!!!

Dad
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Old 05-01-2014, 11:51 AM
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Here are my thoughts.
most 55 engines will give you 500-800 more rpm on the same prop over the 46.
The strongest 45-46 size engine out there with 9" props is the supertiger 45. Run it stock with a Black Jett muffler on a 9x8 and be over 17,000.
A 10 inch pitch prop on these engines with a high drag plane will not be the fastest. you will find that props in the 8" pitch range will be the fastest.
For the OS 55AX and a "red" jett muffler the APC 11x8 will produce good speed and thrust run a 11x7 for a bit more RPM.
The 55AX on a "Blue" Jett muffler you can run the 11x8-11x9 prop or a 12x7-12x8 prop
The 46 AXII on red Jett muffler the 9x8 -10x7 is the best prop.
The 55AX on the stock porting doesnt like to rev much over 15,000.
Also break in of the engine is very important. the MFG directions are good but not the best for max power.
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