low power sport heli designH

[slowrotor]

Hello,
I am new to this forum but not new to aviation,(30
years as pilot/mechanic,experimenter).
For the past few months I have searched for a suitable sport helicopter (one seater) and have not found anything I want to own. It seems the choices available are either an outright scam or unproven or overpriced.
What I want is a very slow (30-50kt cruise) but efficient and light, maybe ultralight helicopter.
It appears I may have to design this ship myself.

Is anyone interested in low speed helicopters available for design consultation either free or for a fee?

Recently, I used the X-plane simulator,that comes with a robinson r-22 and bell jetranger but also can be used to design and fly any helicopter. X-plane is very useful and entertaining. Is anybody on this forum using X-plane to design helicopters?
I highly recomend x-plane simulator for training also. Go to www.x-plane.com Price varies $40-$99.
Anyway, I have several helicopter designs on x-plane with rotor diameters around 30 feet and gross weight of 550 lbs that hover with less than 20 horsepower.
Is anyone interested in low speed, low tip speed sport helicopters?

thanks, slowrotor

[Dave_Jackson]

slowrotor,

The upcoming European - JAR - VLR (Very Light Rotorcraft) may be what you are looking for. Supposedly, the FAA is considering similar regulations.

The Dragon Fly and the Masquito are intended to go into JAR - VLR.

[CRAN]

Welcome to Rotorheads Slowrotor,

There have been some discussions in the past on the Rotorway product and some mention of the Masquito, but little else of relevance from what I can remember...

Have you seen:

www.ultrasport.rotor.com

www.dynali.com

www.lafhelicopters.com

www.pra.org/directory/Helicopters/helicopter1.htm

I've done some quick calculations on the back of an envelope, and the 20hp you quote is in the right ball park if you use the very basic theory. I actually think you would probably require at least 30hp to hover safely...if you include increased profile drag due to scale effects, realistic inflow, cut-outs, tip losses, transmission losses and manufacturing inaccuracies of blades and then include a small power reserve etc etc etc.

The main problem that I foresee with giving your helicopter such a low disk loading is that the downwash velocity will be very slow - 3.9m/s (770fpm). This will give rise to a number of problems, firstly the region of decent velocities in which Ring Vortex State can occur, sits right over the range of velocities typically used in normal descents for single engine helicopters, i.e. 383 -> 770 fpm. Therefore, you would be more likely to have a mishap flying a machine with this disk loading, when flying 'normally' than you would in a higher loaded helicopter. Robinson has hit a sensible limit of around 132 N/m^2 in his efforts to reduce induced power losses in the hover. The machine you have specified is less than a third of this at a tiny 40 N/m^2! The other problem of disk loading this low is the response to gusts, and generally handling qualities in disturbed air. It would only be possible to fly this machine on the finest, stillest days!

You are right there is a gap in the market for low cost recreational rotary wing aircraft, but there are good reasons for it. Helicopters have a number of characteristics that make them expensive.

(1) They need a lot of power. (From engines with an exceptionally high power to weight ratio) Since helicopters use very high power settings all of the time, typically never dropping below 70% of max cont power, substantially larger engines have to be specified and the de-rated to ensure robust reliability. This is very expensive and heavy.

(2) Helicopters require a great deal of expertise to design, develop, build and maintain. When this is all lumped together as an overhead figure it makes for a very expensive vehicle.

It is possible to design a safe kit build helicopter, but it cannot be done in the same way as current kit build aeroplane projects. If one was to embark in the design of a kit helicopter then I would suggest the following key principles:

(1) The helicopter must be well designed, by an expert or group of experts. [Note: I'm NOT saying kit aeroplanes are not well designed!!! - But they are much easier to design.]

(2) The helicopter should meet either JAR/FAR-VLH or JAR/FAR-27

(3) The helicopter must be designed such that all of the critical components, such as key load paths, controls, rotors, power-train, etc are 'assembly only tasks' - Absolutely no fabrication.

(4) The only components on which any fabrication should be carried out by the builder are cosmetic components - fairings cabin fittings etc.

(5) There should be a high degree of supervision of the build.

(6) The build process should include substantially more component/sub-system/system testing and inspection.

(7) All builders should attend compulsory courses on: Engineering Principles & Practises, FATIGUE, NDT & Inspection, along with the standard build and maintenance courses that are usually part of the deal.

(8) Thanks to rotorusa: All builders must show proof of having a helicopter pilot's license prior to receiving (insert critical component such as T/R gearbox)

Can you see the cost yet!!!!! :(

In answer to your original question - yes, i'm interested in low cost recreational helicopters and I think there are many people out there that would buy one, if they thought that they were safe - that’s the catch.

Hope this helps
CRAN
:{

[slowrotor]

To: Cran
Very helpful!
Your comment about slow downwash velocity being a problem is news to me, thank you for alerting me to this. I do not understand how a slower downwash would be worse but I will certainly check into the subject, it sounds to me, you know the physics.
I did research the Ultrasport ultralight helicopter that you linked in your reply. In fact, I had sent a deposit to purchase one to the manufacturer but later requested a refund after talking with two Ultrasport builders.They listed many problems such as clutch failure in a few hours, main rotor gearbox worn with less than 10 hours. Also severe high frequency vibration from the engine which is hard mounted to the seat. The low disc loading of the Ultrasport does apparently offer about a 700fpm autorotation. They show a 25 foot high hovering auto on the video.
All of the sport helicopters, and certificated helicopters as well use high output engines running near full power most of the time and they get hot and fail more often than is desired. My thought was to build a low performance helicopter that would only use about half of the installed horsepower and last a good bit longer.

I have been using the X-plane simulator as a design tool for preliminary design hoping that X-plane is reasonably accurate.Then I would like to confirm the X-plane data with standard performance math to determine the actual power required. I do not have the needed math skills at this time. The hover power formula in my book (Helicopter Theory by Wayne Johnson) looks relatively simple but I cannot get the proper units figured out. I wish the book had included several examples explained. Oh well.

Thanks for the heads up on the downwash problem, I will look into that.

slowrotor

[rotorusa]

Cran,

May I suggest that you add

'all builders must show proof of having a helicopter pilot's license prior to receiving (insert critical component such as T/R gearbox).'

to your list of key principles, to reduce the attrition rate of your pool of builders.

[RobboRider]

I was wanting to ask a question about your desire for a cruise of about 30 or 40 knots. Why so slow?

After the first few hours of enjoying the scenery you'll actually start wanting to go somewhere, do some cross country flights or something and at that speed it will get awfully long hours in the saddle, especially if you end up in a headwind.

[Specnut727]

Might be worth keeping an eye on Jabiru's website (www.jabiru.net.au)

I have heard that they're developing a single seater using one of their own engines, but I haven't seen any detaiils or time frame yet.

[slowrotor]

Robborider,
Most helicopters cannot be safely operated lower than 500 feet because of the need to stay above the height-velocity envelope. Also they are noisy and disturb the neighborhood. I want a helicopter that is very quiet and will autorotate from 100 feet. To achieve that I figure I will need a large rotor and therefor be limited in cruise speed.
Thousands of hot air balloons, powered parachutes,ultralights and gliders exist just for the fun of flight.
I just want to hover for the fun of it.
There really isn't a dependable sport helicopter and that is because the designers sought high cruise speed and high disc loading. That works for the big boys with high power to weight to ratio turbine engines. Sport helicopters are running there piston engines at a high output. High power piston engines are not reliable in general.
The solution is low disc loading for the sport pilot.

[RobboRider]

Specnut727
Jabiru's helicopter is still in building phase and I'm told is probably going to have flight trials later this year. I had a look at the very early fuselage prototype last year on our 2002 yearly touring trip.
Have a look at http://secretmensbusiness.homestead.com/realday6.html
The photo of the helicopter is right down the bottom of the page.

At that time they were planning on kevlar belt drive to the fenestron tail rotor. Later I believe they went back to a metal drive shaft and gear box but then returned to the original idea of belt drives.

Slowrotor

Why 100 ft? The old aviation adage is something like "altitude is life and speed is life insurance" and it applies to helicopters as well. I make a point of never flying that low unless I'm taking off or landing. That's just about the height that power lines live.

I'm not sure how fast your design would drop while you set up your auto but I'd have to to say it doesn't give you much time to to allow for that initial drop you get as the auto is initiated.

I would have thought you'll need some huge rotor inertia to stop the sudden drop as the donk goes quiet and that means high rotor mass usually. Turning a big mass means lots of power needed.

Seems like a number of contradictory needs.

[slowrotor]

Robborider,
In a R22, altitude is your friend, as the R22 has low rotor inertia. Low disc loading does offer better autorotations and I don't know if an autorotation from 100 feet is realistic but I do think a sport copter should have a relatively high inertia rotor. The Ultrasport company video shows a 25 foot high, hovering, power cut landing. Probably just uses rotor inertia as the Ultrasport does have a lot of rotor inertia. A builder told me that the Ultrasport high inertia rotor takes time to spool up but otherwise is very good.It would'nt take more power as you suggest once the rotor is up to speed.
Today I was thinking it might be better to use twin smaller engines and then not give much consideration to autorotation performance. If level flight could be maintained on one engine then a twin might be the best way to go. Chances of a double engine failure are remote and therefor training for autorotations may safely be eliminated. I know twins are used in larger helicopters but I never heard of a twin sport copter.
What do you think?

[Spaced]

Slow rotor, just a point on using 2 donkeys instead of one. While the chances of a double enigine failure may be remote you have increased the chances of a single engine failure.
Piston engines seem to be very reliable these days with few inflight failures.
One problem you wont overcome is the possibility of fuel contamination stopping the engine. If bad fuel stops one then it will more than likely stop the other as well.
Another area you will have to consider is the vibration of the two engines setting up a resonance and the helo shaking itself out of the sky.
In my personal opinion you would be better off sticking with the single engine as it reduces your complications.
As far as yourhovering autos from 100ft, how often would you beable to hover at that height anyway, in most countries you wont be able to do it near anything interesting without breaking the rules.
Rember as well that once above 500 feet that in most aircraft you are above the HV curve, enabling an auto rotative recovery.
Im in no way trying to discourage you from designing a chopper, just think that perhaps some of your design goals need a little tweaking.

[RobboRider]

I've got agree with Spaced.
Your design goals seem to be simple but when looked at in greater depth are kind of contradictory and open further cans of worms.

I may be wrong but your posts seem to be saying you are basically wanting to execute hovering autos from 100 ft as a standard event. I'm afraid that sounds a bit far fetched. Even standard high inertia helicopters can't do that sort stuff. You need forward speed to maintain enough RPM and to maintain directional control.

All helicopters (low inertia or high inertia) require height and forward speed for a safe auto. (I'm not talking about low level hovering autos from 5 feet etc - or 25 in the case of ultrasport if what you say is correct). I'm talking about autos from heights where the starting inertia is not sufficient to conduct the whole auto - which isn't much more than about your stated 25 ft) At heights above that there is a need for airflow through the disc to contribute to the RPM and the energy that is stored in the blades.

Low inertias have a rapid drop off in RPM followed by an equally rapid return of RPM so long as you have some good airflow up through the disc. High inertias still need forward airspeed to maintain the rotation and once they drop RPM need lots of airflow through the disc to get the RPM back up again, and all of them need forward airspeed just prior to the final flare and pitch pull at the bottom.


High mass rotors still have to be got up to speed and every bit of turbulence, every pitch adjustment etc needs bursts of extra grunt to keep the blades going. The input, the drag and the subsequent RPM are dynamic states that are constantly needing adjustment and power inputs, hence the widespread use of governors even in light pistons.

Twins mean twin amounts of everything - weight, work on them, cost, vibrations. The russians have a twin light in development. I think there was a mock-up out here early this year for an airshow, but I didn't get there. Don't know if its a real option or just an idea looking for an outlet.

[bugdevheli]

Slowrotor. We have a Helicopter Experimental Group here in the UK . We have a lot of data that might assist you should you decide on a homebuilt machine.

[slowrotor]

Quite a response from Australia (Robborider,Spaced,Specnut) must be a lot of interest in sport heli's down under. Thanks for your views. I am trying to get a overview of why the sport copter never caught on. With only about half a dozen designs world wide compared with over 700+ sport plane designs, what is the reason?

As for the twin idea I will definetly seek out more pro and cons. Yes a twin may have a resonance problem on the other hand I think two power drives would give half the torque stress pulse to the rotor drive. I notice the Ultrasport seems to be surging (on the video) and maybe two engines would avoid that. The engines I have in mind come with built in governors,cooling fan and are four stroke.The Ultrasports two stroke powerplant may not be the best even with the higher power to weight ratio.Anybody with experience with twins please comment.

Robborider, I do not plan to auto from 100 feet for fun, I just don't want to die if the engine quits while I'm flying low.Some forward speed would be normal as there is no real need to hover. I just want a much smaller dead man curve and am willing to sacrifice high cruise for a larger,safer disc.

Spaced,I agree with your comments, separate fuel tank for each engine would help.

Bugdevheli, How can I access your helicopter experimental groups information?

slowrotor

[Dave_Jackson]

slowrotor

You might want to look at the Mosquito (http://www.innovatortech.ca/) , if you haven't already. It is an ultralight, very low cost and the manufacturer is not to far from you. I have spoken to John Uptigrove on a number of occasions and he appears to be a very straight forward person.

Of course, this is not a recommendation of the craft.

[slowrotor]

Dave,
I did try calling John to ask about the Mosquito ultralight helicopter last week. Have not heard back, I assume its a busy time,probably at the PRA or Oshkosh convention. The construction looks good,made of bolted aluminum bars and tubes. Looks like maybe a bit small in disc size to suit me,but the actual size is not listed on the website.

Here is some of the designs I have looked at pretty close:
1)Rotorway Exec- I almost bought one, an unfinished kit for less than $10k but found a rather long list of problems. Secondary shaft failures,engine outdated and prone to failure,rotorhead outdated (according to RotorWay). Numerous roll overs and often the ship burns up.(exhaust pipes run red hot inches from the plastic fuel tanks or the coolant leaks and burns). In support of the Rotorway I did not find any case of in flight rotor separation.

2)Ultrasport- Almost bought one as well. I called two builders that reported numerous serious mechanical problems that required redesign.Flies great, they said, just stay above suitable landing area at all times.

3)CH-7 ANGEL one seat and two seat KOMPRESS:Looks very good on video, hovering on mountain tops.I don't have much info other than what is posted at http://www.usbusiness.com/helicopter/index.htm
Price is rather high.

4)Canadian Home Rotors SAFARI Good design for the most part. One owner reported the engine runs hotter than he would like. As a retired military helo pilot, he was forced to give in and seek some dual instruction after a near disasterous test flight. The Safari cyclic had a delay that he was not prepared for on the test flight but later found to be OK. To costly for me and I want a One seater.

[bugdevheli]

Slowrotor you can e mail me for info [email protected]

[Spaced]

I know that I definately am. I have been toying with my own ideas for about 8 months now. Gone through about 6 different designs, gave up completely, now back into it again.
Im going a different route to you, leaning toward something a little quicker.
I think there are definately a few holes in the chopper market, which good designs will fill.
As CRAN said in a previous post helicopters are hard, much harder than fixed wing to design, with alot of factors to thinkabout.
My thoughts to lean towards safety as well, and Ive got a few ideas that I think will work, only time will tell.
One thing you may have not considered is an autogyro. Some designs allow for a touchdown speed of nearly 0, and an effective hover in about 15knts of headwind.
I dont know if youve thought of it, but RC scale versions are a great way to figure things out. If you allow for scale effects, a 1/3 model can give some good flight characteristic information, as well as some possibly good data. Then if the results seem good, you could hire an engineer to look over load factors, stress and fatigue analisis, ect...........
Couple of other things Ive personally found useful, a good CAD program (Rhino 3D has a free demo which can be downloaded) is a must. Aircraft Designs inc has some very good books and programs available on helicopter and gyro design, as well as books on composites. If you havent been to Dave's site yet I highly recomend it, lots of good info.
I agree with you about the lack of good kits out there. The only ones I would even think about buying would be Helicycle, or the Mosquito, or Daves syncrolight (later two not available yet). The horror stories from the others make me feel safe in the 22.
Would you care to share your current resources, Im always looking for more stuff to read. That applies to any one with good tech info.

[Vfrpilotpb]

Hey Slowrotor,

100 ft would give you just enough time to cross you legs, before impact, remember 1kg of lead and 1 kg of feathers fall at the same rate, and from 100 ft terra firma is about 2.5 to 3 secs away from your rear end, but count me in if you find a safe design ;)

[RDRickster]

Here is some good info on the Rotorway Secondary Drive failure problem. If you take the time to view his research, he follows the scientific method and has the equipment / knowledge to provide useful information.

http://www.epi-eng.com/RW_TOC.htm

If I were considering a piston design of somekind, I would probably keep a company like EPI-ENG on retainer. It may take longer, but implementing strategies and lessons learned from someone who specializes in this limited field will save you headaches later.

[3top]

Hey Slowrotor,

did you already check on the "Eagles Perch"?

Unfortunately I can´t find their website, but you see it on quite a few sites if you google it with "Eagles Perch Inc." or "Eagle´s Perch Inc." eg:

http://www.geocities.com/chopperjoker/eagle.htm

It was in some Aviation Mags in the past and seems to be able to do a lot of "impossible" maneuvers.
No autorotation possible, as the blades have a fixed pitch. Climb/Descent by varying Rotorspeed. Twin Hirth engines + a parachute (I understand shoots to the side and then cuts the wooden blades with the chute steel cable!).

Set it up for Parachute-auto-deployment when the 2nd donk quits and you are safe.........or so!

Personally I will stay away from Rotorcraft that cannot autorotate or have some non-destructive way to come down in one piece!

3top
:cool:

[slowrotor]

Spaced,
I think anybody considering the design of an experimental helicopter ought to have their head examined.But I want a simple sport copter and I hav'nt seen anything worth buying yet.
What is needed is a group of skilled engineers to take on the task of the small sport helicopter.
Since that has not happened,the only alternative is for an individual to do the best he can,hopefully with some professional engineering assistance.
BJ Schram has been the most prolific sport heli designer with the Rotorway and now Helicycle and I dont think he had any formal engineering training.

My main resource is the X-Plane simulator.See the current issue of Popular Science (August 2003) for a review of X-Plane.The simulator uses blade element analysis. I believe the data obtained from the simulator is better than a 1/3 scale RC model.
I was hoping another X-Plane user would comment on the accuracy of the program.You can do autorotations on the sim and clearly the larger the rotor, the slower the descent. I tried about 15 different rotor sizes,rpm's and tip speeds. It gives a good understanding of the physics and you dont have to perform any calculation,the computer does it all.
Also have Helicopter Theory By Wayne Johnson. I will be shopping for more books,any suggestions?

That Eagles Perch is the opposite of what I am doing! I am working on milder autorotation performance, not interested in hanging from a fixed propeller.

[Dave_Jackson]

slowrotor

I find the technical study of rotorcraft to be very complex, but very, very interesting, The more you know, the more you realize the more you need to know. :uhoh:

"Also have Helicopter Theory By Wayne Johnson. I will be shopping for more books, any suggestions?"

Here's a list of books. (http://www.unicopter.com/B281.html)

'Helicopter Theory' leans strongly toward mathematical explanations. However, it is the only book I've found that adequately covers 'delta-3'; a subject that Nick Lappos and I are currently in total disagreement on. :p

Helicopter Performance, Stability, and Control' by Prouty explains a lot without going too deeply into the math, but it is expensive. 'Rotary-wing Aerodynamics' by Stepniewski and Keys is good and a lot less money.

[Spaced]

find the technical study of rotorcraft to be very complex, but very, very interesting, The more you know, the more you realize the more you need to know
If there were ever truer words spoken I would like to hear them.


BJ Schram has been the most prolific sport heli designer with the Rotorway and now Helicycle and I dont think he had any formal engineering training
Good to know maybe there is hope for me yet.

Youre right I probably do need my head read, but I find designing alot more fun than a rubics cube to pass the time.
I just bought 3 books,
MODERN HELICOPTER DESIGN by Dr. Eric Hollmann and M. Hollmann
COMPOSITE AIRCRAFT DESIGN. NEW REVISED 2003 Issue. By Dr. Hal Loken and Martin Hollmann
HOW TO BUILD COMPOSITE AIRCRAFT by Martin Hollmann
All available from Aircraft designs inc (http://www.aircraftdesigns.com/books.html) . I spoke with Martin Hollman a couple of times and he was very helpful with choosing books.
The latter 2 are more fixed wing orientated, Modern Helicopter desgin, may not be what youre after though, its more to do with higher speed choppers. It does come with some programs though, which once you figure them out are very useful. The performance calculator is very useful, I put the numbers in for the R22, and the figures were within 10%.

The next one on my list is the last one mentioned by Dave, Rotary Wing Aerodynamics. You can purchase it online and isnt that expensive.
Its interesting that you have had such good results with X-Plane, Ive got the demo, and Ill have to consider purchasing the full version.
One thing I would recomend is learning some of the math. Its good to be able to understand whats actually happening, without having to rely on the computer for everything.
One benefit of doing the scale model, is in the construction area. Many of the items and techniques you use on the small one, can be transferred onto the big one, especially if you are going to use composites.
I gotta confess though, if mine dosent make it past the scale stage, I dont mind to much, I really enjoy figuring things out.

[slowrotor]

Spaced,
I think maybe the reason we dont see more sport heli designs is the complexity of the machine combined with the fact that new designs often need to be completely redesigned.
I was thinking of getting into RC model heli's to learn more but I'm afraid I may get too involved and stick with models. I did that with RC airplanes, got started to test a new design then got sidetracked with a local club flying models in competition.
Models operate at a vastly lower reynolds number,which is a factor in comparing scale size.
The X-Plane simulator uses actual full size reynolds numbers and everything else is full size as well. Takes just a few minutes to modify a design. You can watch the blade pitch readout change as collective is increased and watch the engine power go up. Then translate into forward flight and watch the power decrease. It's great for learning while having fun experimenting.
I dont have stock in the company, in fact I always have a hard time getting the newest version of x-plane to install.So consider looking for an older version(V-6) if your computer is not almost new.Later versions are more accurate as it is continuously improved by the creator Austin Meyer Works on MAC or PC.

[Dave_Jackson]

This may be of passing interest (http://www.endlessflyers.com/news.htm)

[Graviman]

Regarding controlability for low disk loading, particularly at low altitude, the following may be helpful. The conclusions are repeated below:

http://www.pprune.org/forums/showthread.php?s=&threadid=177241&perpage=15&pagenumber=3


And repeating from post:

Best control system for a light heli is:

1. Lockheed gyro augmentation of rigid (or do i mean articulated) rotor system cyclic pitch.
2. RRPM control electric motor force feedback to collective pitch, as part of (R22) auto throttle to assist the pilot make fast but safe decisions.
3. Non-augmented pedal system, primarily to keep the tail rotor forces sensible (use top rearward rotation to stop occasional R22 tail rotor vortex ring).


The whole idea is for the machine design to have inherent stability, and fast response to eng-failure, greatly reducing pilot workload/risk. I don't see either the cyclic gyro or collective servo as being that difficult to implement as part of a new design.

Mart

[quadrirotor]

good video about this very interesting small hello!
http://www.wartowne.com/Videos/Flying%20Video/TheMosquitoMontage.wmv

[Dave_Jackson]

Owner/builder Forum (http://www.innovatortech.ca/forum/index.php)