High Altitude Propellor Design Differences

bite.

On the ground the prop is straight, at altitude you increase the bite.

This subject must "be in the air" for I suggested it as a topic for Y Files to Moose.

Ship propellers in water have become similar to complex aircraft propellers.

Hi,

at high altitudes the density is lower, so the size should be bigger to yield the same (if necessary) thrust.

Lower density is also lower Reynolds number, so laminar to turbulence change (on convex side of wing and propeller) will happen later.

Air has viscosity and density and fluid dynamics on curved surfaces is not an easy job.

To get somewhat optimised propellers will need advanced fluid-dynamics programs and a team of specialists.

The lower the rotation rate the lower the shear losses (drag) but the bigger the necessary size so to be searched for a compromise.

RHABE

If you haven't discovered this already, it is pretty difficult to change propellers at 30,000 feet altitude..... Include turbofans in your search. Look at the specs for props for B-17 / B-29 vs. P-51, P-38 and compare the performance data for low vs. high altitude operations.

Most higher altitude prop planes use variable pitch or constant speed props the higher the pilot goes he adjusts the prop out put and on some it is done with flyweights

Thank You all very much for the help on this.

I will try to see these design changes/differences. Or I should say try to find examples of them.

What the project is for, is I'm working with a group of middle school students on a flight that they deamed up the idea, and I'm trying to see if it is feasable.

http://www.qsl.net/wb9sbd/educators.html

They are trying for a long or at least longer duration flight. Hopeing for at least 24 hours or more.

One problem is the day night transition. When the sun sets you loose the energy from it, and it comes down to on the average 10% of the lift provided by the balloon. So there are many senarios here on how to make a longer flight, But they came up with one that is pretty cool,

To cancel out the extra lift provided by the sun, have some solar panels running some propellors blowing upwards to keep the system from raising too high.

we can easily control when these will need to run and all that. And it's not a lot of force we need to overcome only about 6 ounces of lift do we need to cancel out.

so I'm trying to learn how possible this may be with some off the shelf items, and maybe some slight modifications of a standard prop too. Like i said, warping them to have a bigger bite "Pitch" etc.

I found an awesome site that give you a calculator of standard props that is in the hobby of model airplanes, and you choose the prop, and rpm, and altitude and it tells you the thrust it will make. so even with no modifications I can calculate the thrusts we could get with exact off the shelf items.

But if I can make it more efficiernt at altitudes, by simple changes to the prop by twisting it some to make a better bite, hey great. But just wondering if that has possibilities or now and again how far the twist can be,

thanks

you can purchase constant speed props for rc models now at rcuniverse.com or rcslot.com some other sights also now sell variable pitch props for rc fliers

Wow this I did not know that RC guys have goten this elaborate, How cool is that!?

Thank You!

Joe

http://www.e-fliterc.com/Products/Default.aspx?ProdID=EFLPVPP100

this site has a photo of an rc version of a constant speed prop

Hello NSS,

I have not had time to go to your site yet but am going on the content of your post.

My first thought is the propellors pointing upwards. You are more than likely going to get far more lift than these can alter or beat?

I assume you are talking of a fairly hi flight? You may or will have to contact the local flight control to let them know if it is in the sky for more than a few minutes. A small aircraft has no 'reference points' so size is not easy to guess, especially if you are in a 747 at 600 MPH (Miles Per Hour), ~960 KPH (Kilometres per hour).

With regard to the site you found, it sounds very handy indeed! Not sure why you are worrying about 'pitch' though. On the site you mentioned about propellor angles, speed etc, any high flying in thin air would have been 'designed into the prop'' already? The prop is going to be very small anyway, and by twisting it, you may end up with something which is unbalanced, and, not knowing the exact pitch dimension (mathematically), you cannot work on this in the class, unless you discuss theories, and any given prop' pitch and what power you may get from it?

Can you get a VP prop? Variable pitch seems to answer most questions as you can have it very 'thin' as it is starting, and 'flare' the prop (if that is the correct word) at altitude?

Another thought,.............. (I keep having them lately) are you flying the craft up pretty slowly and then flying round in a circle of say a mile radius, so you can recover the craft and possibly recover any info' you may have recorded on the 'plane' itself? I would suggest really broad wings to allow a gliding motion where possible. This could be set to a particular altitude and hopefully the plane will continue round in circles and will get enough updraft to continue flying through the night?

Giid luck.

Hello NSS,

(I wish all 'names' were so easy to remember and enter! ;=)

With regard to Propellor Design for high altitude; I would have thought a larger than usual propellor would be necessary for the relatively scarce 'air'?

If you are thinking of designing an engine or 'mod' to an engine for exceptional heights, you may need an on-board pumped air-supply? Is this just a design test or are you part of a team trying for an altitude 'Record'? And, what height will you be flying at, or envisage the propellor to be used at?

I will look later for propellor designs.

Take care.

the size of the prop does not make the performance the pitch angle and cord line of the prop as well as the type of engine turning the prop can determine the altitude the prop can pull the aircraft to a turbine engine doesn't care the altitude like a normally aspirated engine and an electric motor doesn't care at all. a good example is modern C130g flying at 40,000 ft and the original C130 only 25,000 ft (altitudes estimated for example)

Hi cburkovi,

I appreciate the info, thank you.

Hi NSS,

Check these sights on Variable Pitch RC Propellors:

http://www.google.com/search?client=safari&rls=en-gb&q=RC+variable+pitch+propellor&ie=UTF-8&oe=UTF-8

===============================================

Select a variable pitch propeller for an R/C airplane - How to ... Get free instructions on how to select a variable pitch propeller for an R/C airplane by Backyard Flyer Magazine.

www.findhow.com/.../how-to-select-a-variable-pitch-propeller-for-an-rc- airplane.php

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The first site above which is partly described has VP props.

Hi Bear,

Thanks for all the links I will be checking them out. There is a lot of them to look at.

Yeah check out the site. And it's not a lot of force i need to develop. about 6 ounces or so of thrust is all i need. And it wont be at any speed either. yeah check out the web site and it might be clearer too, This is removing the lift from a ballon, to make it stay at a certain altitude.

I'm fully aware of FAR-101 and have a great relationship with the FAA and all the ARTCC's

Our last flight ws flight 47, it went to 118,000 feet. here is a pic from 102,000 feet.

This project won't be going that high tho. But the air will still be very thin.
at 60,000 feet density is roughly 10% of that at sea level.

Hi NSS,

I have seen the site now and pretty good my friend! ..................

118,000 ft?........ WOW!

Is that the record for a craft like yours?

With regard to the FAA, I hope I was not 'preaching to the converted', so as to speak?!!! ;=)

Can you advise me as to where on the site I can see a pic' of this craft please?

Sorry but I have just had a mini flood in the bathroom and I have been running back and forth to remedy it and type this!

Take care and good luck.

View of system leaving

http://www.youtube.com/watch?v=NoUkgWOUbNQ

view from 100K

http://www.youtube.com/watch?v=GK15wUOqYKw

Joe

Hello NSS,

I have visited the two sites and it is pretty amazing stuff! Taking the camera up in the craft shows how stable it has become now.

I was figuring it to be a whole lot bigger than this but, having this type of launch saves on fuel so very little has to be taken up with the craft. And it moves up at a gradually exponential speed straight up. Are you going up to 60,000 + to test systems before going further and longer? Do you find the craft can be 'flown' more or less back to where it was launched, or does it drift with the wind?

Congrats to all!

And it moves up at a gradually exponential speed straight up.

Actually the rate of climb is pretty constant, averaging between 700 and 1400 feet per minute all depending on how much "Extra" lift we put into the balloon. but the average is close to 1000 feet per minute, And it stays once released prety close to the same rate all the way up.

Are you going up to 60,000 + to test systems before going further and longer?

No, we'd like to go higher, but the air is going to get soo thin that I doubt we ever get with the props develop enough downward force to cancel the extra lift. At the 100K level there is not even 1% of the atmosphere left. Even at 60K we are down to 10% density or so. But the erason choose the 60K level to try to stay at, is that we are above the controlled airspace, and all but the very rare military type of aircraft would be the only possible traffic and that would even be extremely rare. So it's thin air but maybe still dense enough, yet we should be more or less all by ourselves just hanging around.

Do you find the craft can be 'flown' more or less back to where it was launched,

That would be ultimately wonderful, But not possible anymore, after the 9/11 day, the FAA has for all practible purposes banned all UAV's (Un manned Air Vehicles), Unless you are the military, or a University with giant deep funding pockets, any type of UAV is no longer legal. You can NOT steer it in any way.

We went round and round with them on this too. explaining when we wanted to try after the balloon pops to via a parafoil type a of parachute to steer it and try to bring it back home or at least closer. But absolutely forbidden!

or does it drift with the wind?

Yup drift with the winds.

Hello NSS,

Really appreciate the full info' you sent.

Some of my thoughts were still on a type of 'Winged Aircraft'. It is not until you look at the project in more detail, the problems arise? You are trying something which is not all that common for sure! Just a thought.................. Would it be possible to try the ultimate 'flight' in a different Country like Japan or Australia or Mexico? Mexico being the best choice perhaps. It may be worth asking the Mexican Embassy for advice on this? My thoughts are, that there would perhaps be less restrictions there?

Take care and good luck.

after the 9/11 day, the FAA has for all practible purposes banned all UAV's (Un manned Air Vehicles),

Hi,

there is an infamous example what will happen with this type of precaution.

Nazi Germany officials banned any private shortwave radio communication in fear of spys.

So 10 years later as the first British RADAR systems evolved they had no idea what this might be.

It is private playing around with any of sophisticated toy that is driving one part of future technology and success.

Ban it and some time later the country and the people will be the loosers.

RHABE

As far as I know the ban on UAV's is a hoax If you recall there is an X-Prize for the worlds cheapest and highest green flight. if the craft has the words experimental plainly marked in 12in letters and a proper flight plan has been filed. then a UAV is totally legal being that you are a teaching institute like a school then you are legal to do an unmanned flight but then you also need to find your local rc fling club and be designnated an RC frequency the largest RC vehical that I know of flies at 30,000 feet and is a 1/4 scale b52 with real jet engines it is launched from a taxiway during airshows. the pilot uses camras mounted in the nose turret to see where he is It has a range of 1.5 miles and is just awesome to see fly. the guy that flies it got special permets to fly during airsows.

Talk to you local FSDO and local inspectors as well as local A&P's to assist in the build or design. a round trip flight would be most fun aswell as more data collecting. You might also want to try helo flight as well.

As far as I know the ban on UAV's is a hoax

Absolutely wrong,,,, Well, sort of, Yes you CAN still do a UAV, BUT it even if it's the size of a dragonfly, or the size of a full scale B-52 bomber it must passd the full airworthyness tests just like any plane! AND,, there in non military uses must have a fully licenced real PILOT at the controls and the very same PILOT MUST be in visual contact with the vehicle at all times. The military have different rules (go figure)

But i have been working with the FAA for over 20 years,and it was easier to get permission to launch a Super Loki rocket from right here in Wisconsin, check out these spec's
Launch Weight: 68 lb
Burnout Weight: 31 lb
Instrument Dart Weight: 18 lb
Booster Weight: 50 lb
(A 4.5 lb ballast weight is added to the booster for launches near populated areas. The ballast gives the booster aerodynamic stability on descent)
Propellant: ammonium perchlorate based
Burn time: 2.1 seconds
Height, Total: 10.5 ft
Height, Booster: 6.5 ft
Height, Instrument Dart: 4 ft
Booster diameter: 4 inches (excluding fins)
Altitude for booster/dart separation: approx 30,000 ft
Maximum Altitude (instrument dart): approx 250,000 ft
(185,000 ft w/ballast)
Time to apogee: 110 to 120 seconds
Top speed: 1 mile/sec (approx. mach 5)
Spin rate during ascent: approx 16 rev/sec (1000 rpm)
Payload: (main portion) 1 11/16 inch dia. x 11.2" long
Payload descent time: to 20km: 30 - 45 min with 10ft starute
to ground: 1.5 + hours (weather dependent)
Max Payload Weight: 4 lb (but is typically about 1 lb)
Initial acceleration (vertical): 60 g's (up)
Initial coasting acceleration due to air resistance: approx 30 g's (down)
Maximum centripetal acceleration on payload: 20 g's (horizontal)

Acceleration upon ejection: 100 to 250 g's along trajectory (depending on who you ask)

This was launched, But a UAV in Wisconsin, ever since 9/11 verboten PERIOD The only exceptions are the big pocket guys where they can get it fully air certified!

If you recall there is an X-Prize for the worlds cheapest and highest green flight. if the craft has the words experimental plainly marked in 12in letters and a proper flight plan has been filed. then a UAV is totally legal being that you are a teaching institute like a school then you are legal to do an unmanned flight

Again ONLY if it has been totally flight certified and just as if it was a boeing 747 pass all the tests,

but then you also need to find your local rc fling club and be designnated an RC frequency the largest RC vehical that I know of flies at 30,000 feet and is a 1/4 scale b52 with real jet engines it is launched from a taxiway during airshows. the pilot uses camras mounted in the nose turret to see where he is It has a range of 1.5 miles and is just awesome to see fly. the guy that flies it got special permets to fly during airsows.

If they tell you this they are really puling your leg, NO WAIVERS FROM THIS RULES WILL EVER BE GIVEN this is from WASHINGTON!!! Most RC clubs already break the most common rule in RC, the 500 foot rule, RC is NEVER EVER to exceed 500 feet. No Exceptions. it just is not enforced. But if they were to be at say 1500 feet and a cessna would hit them they would be totally liable and the insurance they think they have would say tooo bad you were above 500 feet so we do not have to pay.

Talk to you local FSDO and local inspectors as well as local A&P's to assist in the build or design. a round trip flight would be most fun aswell as more data collecting. You might also want to try helo flight as well.

Been there done all that,,, the key is the ability to steer it. if you can steer it it is forbidden. Period.

As an example when I was persuing this steering, we have had soo many flights we are on not only first name basis with the ARTCC and various flight services groups they even know our voices when we call they say Hi Joe what ya doing this weekend!

But we even used as an example to try to get permission of just a steerable parasail/parafoil, whatever you know the steerable parachute....

Even that is NOT LEGAL, get caught BIG Bucks fines AND jail time, no kidding!! I explained Ok our regular flights go up via the balloon, and we have absolute no control of where it's going just down wind,

the balloon pops and it starts to come down via the parachute, again wherever the wind pushes it. and it lands.

We have had them land at Nuke plants, and even at Ohare international airport!!!!

I said as an example of the Ohare landing, I said wouldn't it be great if it looked like it was drifting that way that we could be able to steer it away from there? And they said yes that would be nice, but if you did it youd be in jail for doing so,.

Crazy government.

Governments are worse than crazy.

They think about anything that can do harm and pass laws that shall prevent this harm (if benevolent).

But as in a family where (usually the mother) somebody is warning and forbidding the children anything that may do harm (screwdrivers, matches, playing on dirty grounds and endless more) then the result is an unable nonlearning grown up child.

No skills. No futire.

Same with the country. But politicians retired or dead. So nobody responsible.

Country will decline with time, may take decades. Have a look.

RHABE

I talked to my local fsdo which is a training facility for the FAA. Inspector Tersic a 20 year veteran has said that special experimental permits are granted every year to CMU for such flights out of his office that he also would grant a special permit with the propper documentation. aka 3120 form 337, and a few other forms of documentaion the scale of the vehical also must be totaly in these forms. he also said that a tetherd flight of this nature also reguires few permits but are less hassal to optain. see you local FSDO for information on your area.also be totaly aware of flight zoning totaly found on the FAA website never fly in a class a b or c zone without them.

I talked to my local fsdo which is a training facility for the FAA. Inspector Tersic a 20 year veteran has said that special experimental permits are granted every year to CMU for such flights out of his office that he also would grant a special permit with the propper documentation. aka 3120 form 337, and a few other forms of documentaion the scale of the vehical also must be totaly in these forms.

He needs to talk to WASHINGTON then, because we HAVE been for 20 years also talking to WASHINGTON and prior to 9/11 it was nothing, No Problems. but the rules have changed, And Ok, maybe he may have issued some of these permits but I do not have 100K or probably more to do a flight for some boy scouts!

he also said that a tetherd flight of this nature also reguires few permits but are less hassal to optain.

Ummm tehered flight, tethethered even if possible is also illegal to 100K feet,,

see you local FSDO for information on your area.also be totaly aware of flight zoning totaly found on the FAA website never fly in a class a b or c zone without them.


I think the guys in WASHINGTON somewhat trump anything a local thinks or says. When it comes to the laws and liabilities,, WASHINGTON absolutely trumps ANYTHING a local says.

Hello cburkovi,

Congrats on the info you sent about the Tethered flight and documentation necessary.

This shows the old idiom, "it is not what you know but who you know"!

Take care.

Hi Bear, and the rest, As far as the tethered balloon goes, this is pretty black and white, (a) Except as provided in paragraph (b) of this section, no person may operate a moored balloon or kite— (1) Less than 500 feet from the base of any cloud; (2) More than 500 feet above the surface of the earth; (3) From an area where the ground visibility is less than three miles; or (4) Within five miles of the boundary of any airport. b) Paragraph (a) of this section does not apply to the operation of a balloon or kite below the top of any structure and within 250 feet of it, if that shielded operation does not obscure any lighting on the structure. (a) No person may operate any moored balloon, kite, amateur rocket, or unmanned free balloon in a manner that creates a hazard to other persons, or their property. Kind of hard to go to 100,000 feet when the rules won't allow even 1000 feet. Yes you can get a waiver, Been there done that too, and it takes a LOT of time,, AND extremely deep pockets.

Hello NSS,

I hope you are fine my friend?

Thank you BTW for starting this post with my name. You are one of a very few who do this. It makes any confusion far less likely that's for sure, thanks again!

I did not feel the need to refer and answer the statement of "Tethered Aircraft", seeing as you had already done so, thanks BTW!

It really does not bear thinking about sending anything tethered to the 'maximum' height when or if there is likelihood to lightning?

Do they make the rules as convoluted as possible so they can be 'interpreted' only by an 'expert'?

Hi Bear No they don't care about the lightningaspect they are strictly thinking aircraft safety, and nothing else. Joe

Hi Joe,

Thanks for the name..........!

They and the 'Rules' might not worry about lightning,................ BUT I WOULD! ............... OWWWWWWWWWWWW.

Take care.

and you'd be amazed at the amount of voltage that can me generated if you did have wire instead of string,, been there done that,,

Hi Joe,

I mention this because I used to fly kites, "big boys toy" so as to speak?

I rigged a ten foot spar from the coiled rope release, with a copper wire leading to ground. Well I did get hit once, the power was so high it did go down the wire but at about the same instant also went to the coil of rope/wire. (It may have been wet rope?) I cannot recall which. I just know it burned my hands and for that I was thankful! I never flew a kite in anything but sunny weather after that. The kite which got hit was over half as mile high. I never went higher then 200 feet afterwards.

It hurt! And I feel lucky to be alive. I do not know but it may have been my wellington which stopped the earthing through me? I really do not know. Not exactly an expert on electrics, you know!

No need to answer this, just some silly musing which I thought may help and possibly save any burns to other 'kite flyers'.

Take care.

Just in case anyone need to fill out a FAA form 337, I found a blank form in this link http://goo.gl/Pkq0hm. This site PDFfiller also has several related forms that you might find useful.