true DF thrust/ hp claims?
 

Hi all,

I notice that Rossi claim nearly 7 hp@23000rpm from their 105 DF- this compared with the OS .91 that claims 4.5 hp@22000rpm. The Rossi also claims upt to 28,000 rpm in some sources. (!!??)

I know that thrust is a function of ductwork, blade pitch, number of blades and blade diameter, as well as torque and rpm, BUT...

where do i get info on what is the most powerful possible commercial configuration available?... i am after thrust, not speed in this case, particularly low speed thrust.

based on folklore and anecdotes , the os .91 can be good for around 13 lb thrust at a duct, so with claims and a simplistic correlation of 46% more power, you'd think that the Rossi would be capable of near 20 lb if setup correctly.

Now i hear that Rossi are temperamental, take time to run in, and do not perform anywhere near their commercial claims, whereas the os .91 is off the shelf ready to live up to it's word.

i dont really care if it's "os", or "rossi" or "tommy porridge", what i want to know is what i can get from what, so i can design with a weight budget...i'd be interested to get some comments and anecdotal evidence/experience on this topic please...

cheers....:D

RE: true DF thrust/ hp claims?
 

It's all about RPM's, not HP. The BVM fan is the most efficent and with his motor makes the most thrust. I understand it's somewhere in the 9 - 12 lb range ?? Depends onwho you believe. You are correct that the efficency is also determined by the ductwork, and the entire systems as a whole. Not just the fan unit.

Because the RPM's are much lower than a turbine (100k +) the fan disk actually starts to act as a break at high speeds. This is also a limiting factor in thrust.

RE: true DF thrust/ hp claims?
 

True, but RPM is limited by hp and pitch angle isnt it?

you cant generate high rpm at a certain pitch without hp...?

for instance, at high pitch, and a fixed hp at revs, you aint gunna go very high thrust as you aint going to generate high revs...but you are moving more ait right?...which is thrust isnt it?

im confused.

the os .91 can get 13 lb from 23000 rpm using the ramtec fan..this ia a fixed pitch fan unit at 5 inch diamater. this is the best it can do..it is supposedly rated at 4.5 bhp. at that speed.

so if at 23000 rpm you have a power unit that jams 7 hp, surely the correct pitch and diamter would yield more thrust?

power is work done over time right?, work done is force times distance...force is mass times acceleration.

now thrust is airflow., or air velocity.

airflow is proportionate to revs and prop pitch and prop diamter right?

force is proportional to pitch, number of blades, and revs.

the mass flow of a higher hp engine must be greater than the lower hp engine, provided setup correctly. dont it?..(to avoid blade stall and blowback)..

does anyone have any perfoamcence curves for the ramtec/or any fan and the os .91?

does anyone have a formula that calculates thrust from pitch, d/f diam, revs, hp?

i cant see how the rossi doesnt generate more thrust than the os engine...other than false performance claims...and /or improper test setup..i.e. testing both engines on the same rig...

my dumb arse guess is that the extra hp should be absorbed by more lblades at a different pitch for optimisation...the tests ive heard of simply dont absord the power that rossi claim...

RE: true DF thrust/ hp claims?
 

Assuming the Rossi performance figures quoted above are authentic, there isn't a fan unit on the market that can absorb the the extra 2.5HP at 23k rpm. The Ramtec/Dynamx fans will absorb the 4.5hp of the OS at 22-23k rpm, but will need to spin a few 1000 rpm faster in order to absorb the extra 2.5hp. The problem you now have is that the Rossi can't deliver 2.5 hp extra at those higher rpm because it (HP) peaked out at 23k, and is now on the back side of the HP curve if it spins any faster. THAT is why NO-ONE has ever been able to harness the "power" of the Rossi 105, and all field experience to date with that engine in a Dynamx/Ramtec indicates performance no different from an OS. It doesn't suprise me in the slightest.....

In conclusion, if the Rossi perfomance data is indeed genuine, the only way you will be able to harness 7hp @23k rpm is to have a fan rotor+stator configuration designed to absorb 7hp@23k rpm .... as far as I know, no such fan unit exists.

So, if you are truely intesested in a successful .91 sized DF powerplant, you have 2 basic choices: BVM Viojet/fan+BVM 91/96 or OS 91 +Dynamax/Ramtec, period.

Regards,
Peter

RE: true DF thrust/ hp claims?
 

i still dont get it...why does it need to spin faster for more thrust?..doesnt more blades give more thrust?

more blades would also absorb the extra hp wouldnt it?

rossi's claims are up to 28000 rpm- so im still totally confused.

when a fan is selected, it is selected to match the motor's characteristics, including hp and revs. the fan then is superimposed on the rev and power profile...superimposing the rossi onto a fan designed for a different engine will give you data that leads to the wrong conclusions...

the rossi hp claim is at 23k rpm anyway...so the back end is beyond this peak..as with any fan curve...

im still not convinced...i really appreciate the info though, and would like to keep messaging until it is proven...i am happy to be wrong...absolutely...

i am also aware that everyone and their dog say that the os is the best setup..and it well may be...does anyone have any performance data/test data for these engines?

there are various d/f software programs that apparently calculate these things..so that the correct blade numbers, pitch and diamtere are selected. all you need is the power curve. then of course, the bench test to see if what was calulated is near actual...

RE: true DF thrust/ hp claims?
 

I think MiragePilot is trying to say that even if the 105 has a higher power-output than the 91 at the same RPM, it will not make much difference as the fan is designed for a given power-output at a given RPM...
Basically it requires 4,5 hp to run the fan at 23k, and at 23k it will load the engine with 4,5 hp regardless of it being a 4,5 hp OS or a 7 hp Rossi.
You wouldn't need full power on the Rossi to reach 23k, and you wouldn't gain much by giving it full power since the Rossi would go passed it's peak-power RPM (23k), meaning that as soon you run the Rossi passed 23k, it's power-output would drop. The Rossi 105 would never get to use it's 7 hp on a standard 5-inch fan.

The problem is that there are no fans designed for a 7 hp output at 23k RPM, so if you want more fanblades or more pitch, you'll have to make the fan yourself.

RE: true DF thrust/ hp claims?
 

I think Hurricane make them.

They claim to be able to absorb up to 10 hp with their 6 inch unit....

thanks for the message...it pretty much falls into line with what the claims anf theory states...which is enouraging.

and this also falls inline wihh the info ive ad from fan manifacturers...man my typing is rank isnt it?..lol..

RE: true DF thrust/ hp claims?
 

There is an performance curve that gives the best performance. The proper blade length, pitch, number of blades, the pitch of the blades, individual blade design, diameter of the fan, length of the fan, size of the inlets, shape of the inlets and on and on. That is why the BVM fan design is patented. It's very complicated to get the last bit of thrust from a fan.

RE: true DF thrust/ hp claims?
 

Peter,

Thank you! After a few years of fan-flying your explanation *finally* hit home & the little light bulb (dim at that) went on in my head! I've always wondered why the Rossi's weren't popular given the HP ratings on them, now it makes sense.

Bob

RE: true DF thrust/ hp claims?
 

Don't forget to consider dynamic thrust when you get to the point of making performance predictions. Many people look at static thrust as the best way to determine the best engine/fan combination, but what you really need to understand is how all that stump-pulling thrust at zero airspeed decays once the bird starts rolling down the runway.

Point of reference: a ByroFan with OS .91 puts out somewhere between 13 and 15 lb of static thrust, but 90% of the Byron-powered aircraft never get past about 130 mph. Massively draggy installations aside, a big part of the reason is that its thrust decays rapidly with airspeed. Compare that to a Dynamax or Ramtec-powered installation that also puts out around 13-15 lb static, and you can list several airplanes that are capable of 150 mph +. Again, discounting the fact that the Ramtec/Dynamax birds usually have much more efficient ducting than the ByroFan-powered aircraft, both the Ramtec & Dynamax have much better dynamic thrust. The Viojett is of course the most efficient unit on the market, pretty much spanking all the other fans as soon as any airspeed is desired.

I'm sorry I don't have any thrust curves to share with you. Maybe somebody else on the forum can help you find the data you need. Good Luck.

RE: true DF thrust/ hp claims?
 

Hi Bobman and Flanker...you are right, but regarding the dynamic thrust, in this instance, i am not interested in it...the current off the shelf units are optimised for the best compromise between ststic and dynamic thrust and best mix of takeoff and fast flying..

im interested in what thrust you can get at 0-5mph with the right nuber of blades, pitch and the rossi @ 23000 or somewhere where it is generating greater than 6 hp. We all go on about the bench limit of around 12 lb. But this seems to be fairly arbitrarily fixed by marketability, the popularity of engines and conventional wisdom, rather than the prospect of forward thinking...

why would you buy a turbine for $3000 that egenrates 18 lb thrust and weighs 2-3lb when you can get a ic engine and fan rig that weighs 2 lb, generates 20 lb thrust and costs $1000...(?)..the answer is probably the fact that at speed the thrust is generated by the turbine and the hp comes as expanding gasses, therrefore pressure, so it's alot more usable and easier to run down ducting...but for the layman, who merely wants thrust at a certain speed...it becomes a viable option doesnt it?

let's say that jet modellers merely want to be able to fly their b ird as a jet..i.e. no prop hanging off the nose or tail...alot of jet guys want to scream around and set the sky on fire..that's fine...

but those who want a powerpack that gives them a jet appearance probably want scale like flying..now, low level jets rarewly go beyond 600 mph, which, when you are flying a 1/4 scale jet is obviously 150mph, and a eight scale jet is around half that...now, since the flying speed compromises the aerofoil used, that may become the comrpomise or limitation..i dont know...

it's an interesting topic...and one that needs a range of fans for selection in the market. it seems the market is just catering to the models. if the powerpaks were varying and numerous, the models could select the powersource..as it should be...it's a bit of the cart drawing the horse in my opinion.

RE: true DF thrust/ hp claims?
 

The fact of the matter is that you can't even get close to your 20# thrust figure with a IC ducted fan. Don't you think the specs on the Rossi might be exaggerated? It would not be the first time a manufacturer made their product sound better than it is. The fact is, that the Rossi 105 has been around for a long time and you haven't had a single person chime in on this thread to say that their 105 was the most powerful engine they ever owned. I have heard some say that the 105 is a little more powerful than the OS.91 in a Byron fan.
But the only fan that I have seen fly big heavy planes with authority is the Dynamax/OS.91 combination. Take the JMP T-33. It's fairly large at 85" wingspan and I saw a 30# one fly very well with the Dynamax/OS.91 combination at speeds up to about 140mph. There was a very large Vulcan bomber flown at Superman with 4 Dynamax/OS.91 combos in it. I wasn't there but heard that it was the most impressive flying plane there.
My point is, don't get too wrapped up in specs and claims of manufacturers. Go see what really works before you invest a lot of time and money in your project

RE: true DF thrust/ hp claims?
 

What the?!?

I authored an article in RCJI a few years ago that dealt specifically with the calculation of DF thrust (both dynamic and static) as a function of fan diameter, engine HP, air density and inlet+fan+thrust tube efficiency.
The article covers the development of the governing equations and well as their solution, and corresponding results. As Flanker-RCU mentioned, there is a fundamental difference between static and dynamic thrust, and its effect on the ultimate performance of your jet. The problem with the equations provided in (all) of the DF-related books published out there to date, is that they are all only valid for the static thrust case. NONE of them consider the dynamic thrust case. My article addresses that omission.

I suggested you go ahead an read that article carefully before pursuing this thread any further. Take a look at pg 54 of the Feb/March 2000 issue of RCJI (Issue 40). It's all there....

Regards,
Peter

RE: true DF thrust/ hp claims?
 

GRBaker...

no-one has tested the rossi properly as far as i can see..everyone i 've spoken with go quiet when asked if they tested the rossi using different pitches, diameter fans etc...so im not convinced.

mirage pilot...please read my post that states that im not that interested in dnamic thrust.

furthermore grbaker, you need to run the theory first before testing, otherwise you have no way to know where to start. i was told by a certain ducted fan manufacturer that you need to do testing BEFORE you do the theory. What a crock. And this is from the "experts".

until i see the proof of the exaggeration beyond doubt, then i think ill reserve judgement.

Emperical data supplied also by a very reputable Fan desginer gives a relationship that results in almost exactly the os figures on the 5 inch setup. substituting the rossi data for a 6 inh fan results in 25 lb thrust...now these are empeical, not theoretical...so it is curious, perplexing, and interesting.

hurricane claim to be able to absorb 10 hp thrust, the current fans on the market no doubt can only absorb near 4.5-4.8 hp...which is why any engine with more poer than that does not yield any more thrust..it's really a no brainer.

furthermore, if you made a turbine that yielded 18 lb thrsut (ok ok, the dynamic thrust of a turbine is the advantage here), but you wouldnt be too interested in exploring the efficacy of a df that could generate 23 lb would you?

AND if your engine had the entire DF market cornered as preferred and also recommended powerplant for most kits, why would you assist in development of something else, esp if not yours?...

next question, why hasnt os tried to develop a 105 or 110 powerpack yet themselves?..something that could easily crank out 20 b plus on the 6 inch fan...

on top of all this, using the 4.5-4.8 hp and 6 inch hurricane fan combo, even the os seems to have a thrust output of near 20 lb...so this is all very interesting isnt it...?

im totally confused about it...and cannot accept that things are "just because"...

u ntil someone tables proper test results actually showing the data, and the calcs done, i cant see why or how it can be dismissed. Even if the HP claims are exagerrated, lets look at it this way...

the k&b df claims @ 0.21 ci and 25k revs, 1.25 hp
the k&b df claims at 17k revs and .45 ci, 2.2 hp

the k&b df claims @ 25k revs and .48 ci, 2.75 hp

the os .46 df @ near 20k revs , 2.5 hp

the irvine .46 df @ 23k revs, .1.9 hp


k&b at .82 ci and 23k revs, 4.2 hp
k&g at 1.0 ci and 22k revs, 4.8 hp

the rossi at 28k revs @ 6.1 hp
and the rossi at 23k revs at 6.97 hp

considering all the rossi data seems higher than the rest, lets suppose it is exagerrated...the fact is that there is a very evident trend here and relationship between df engine size and revs and thrust.

and so, a 105 engine should almost without doubt, generate more thrust than the .91. perhaps as much as 46% as claimed, but conservatively at least 20%.

There is something fishy going on here....

RE: true DF thrust/ hp claims?
 

please view this chart...

[link=http://www.users.on.net/tnewman/cmfc/DFCALCS.htm]DF charts[/link]

RE: true DF thrust/ hp claims?
 

It appears that you've already made up your mind, so why don't you spend a lot of money and test the Rossi 105 in a lot of different fan configurations and then post the results for all to see. But I think I can make a real safe prediction that you will never see 20# of thrust from any of these combinations and I doubt if you'll get 15#. But I've only been flying ducted fans for about 15 years so what do I know.

I'm out.

RE: true DF thrust/ hp claims?
 

well im convinced then grbaker...instead of being condescending and rude, why not look at the detail?

ive worked with ppl whove had 50 years experience and still dont know what they're doing so unless you've got a very solid explanation, your 15 years experience really doesnt mean anything to me.

what if i said my head was the biggest in the world?..would that mean im the smartest?

the facts are here to see...my mind is not made up..but blind freddy can see something's not right...

you can bury your head in the sand if you like, and be happy that "you know all there is to know"..but since you cant explain it to me, then i cant be convinced as all you have are scattered anecdotes that arent even backed up by thorough testing...

you go ahead and be blissful in ignorance...im glad your'e out..

oh, and BTW, you dont need to test in alot of different configs..that's plain dumb trial and error..that's why we have calcs, both perfect theory, emperical, relative and comparative...so you know around about where to start.

if anyone wants to post something constructive and value added, please do...i'm not really into this "defensive", persnal stuff..if you cant take it as non-personal, please dont post..it just irritates me..

RE: true DF thrust/ hp claims?
 

what the

a strange thing happens from theory to practice. reality creeps in. if you can get a rossi to turn a ramtec fan to the 23-24k threshold you are really achieving something. i personally spent the better part of two weekends trying to dial in the motor. we could sometimes get it to peak out at 23 k for seconds, but never beyond that, and not with any consistency. Rarely would the motor even get up on the pipe. We used the rossi pipe, several different fuels, all to no avail. contacted the us distributer, followed their suggestions, again nothing near the claims. ended up returning the set after the tuned pipe came apart during a run.

if you want to play on the bench and see what you can get, have fun. if you actually intend on flying, I think you will end up with the OS from a standpoint of reliability.

there is a thread here on rcu from about a year ago indicating all the mods a gentleman did to get his rossi to run. new porting was the least of his mods. i still do not think he was anywhere near what rossi claims. if they were as good as their numbers claim to be, there would be some flying.

RE: true DF thrust/ hp claims?
 

what fan? can i please see the test results?

if it was the 5 inch ramtec, byron, etc..then your results are exactly as expected- and as calculated...

it is not a surprise. and please, do you think i dont know the diff between reality and theory?...sigh...

RE: true DF thrust/ hp claims?
 

possibly...but this assumes that the rossi was tested correctly...and was it?... no-one seems to be able to conclusively tell...

in fact, after conversations with the major df manufacturers, i highly doubt that it was...im just trying to get to the bottom of this... all evidence suggests that the 105 HAS to jam out more thrust..the relationship is almost linear!!...

take out the rossi hp claims, and just look at the trend...extrapolate beyond the .91 and voila...more thrust...

RE: true DF thrust/ hp claims?
 

the k&b 100 should have had more power than the 91 as well. it may very will have on paper. again, once in real live pilots hands, it simply did not do the job. again some people were able to make it run after swapping carbs, connecting rods, and other mods. if someone could have made it run with any consistancy, it would have made a dent in the market, especially when it was priced less than the os.

yes the rossi should outperform the os. the reality is that it does not. or has not proven itself in the hands of guys who really wanted to see it perform. i have known several who have had all types of rossi df engines simply give up on the 105. perhaps the lack of people on this forum offering anything positive to say about the engine might be a sign as well.

the engine may claim to have 10 hp for all rossi claims, if it does not run, it does not do you any good.

RE: true DF thrust/ hp claims?
 

I have been reading this thread and have been reluctant to reply..

But...... I used to run Rossi .82 in Byron fans back in the 80s they worked fine. Hadta' screw with the carbs too much tho. Rossi came out with the .90 and I could't see much improvement. :(

Now, I have in my possession a TGA Mig-29 / Rossi 105 / Byron fan / Hurricane impeller. The owner is unhappy it will not fly faster than 86 MPH. :(

I changed the thrust tube and ran up the engine, and I don't think it will go over 110, about par for the course with Rossi / Byron.

No scientific calculations required.:D

RE: true DF thrust/ hp claims?
 

i say again..what fan, what pitch, what diameter..they simply wont generate more power on a os.91 tweaked fan...you could put t a v8 on the os .91 fan and it wont generate more thrust...

and yes, the anecdoates suggest what you say is true...but they are anecdotes.

anecdotally the biggest guy in the gym knows the most about weight training, the fastest sprinter knows all the secrets, the fastes drag car is the most poweful, and so on... anecdotally....what if?...

i am waiting on hurricane as we speak, as well as rossi.. FYI the os should be able to go near 20 lb on a 6 inch fan..has anyone tested the .91 on this setup?

oh, and BTW, the K&B should not have gone better..it's rating is the same as the os...

RE: true DF thrust/ hp claims?
 

EXACTLY...you should not expect it to go more than 80-100 mph if thrust (static) is the goal..and that is what is measured in engine tests...as mentioned previously, the fan becomes a brake at higher speeds.

Would you be so kind as to test the hurricane (i hope it's a 6 inch as otherwise it's basically the same as the ramtec unit so it's no surprise)...at various pitches, and then scale the thrust versus rev versus pitch? How many blades are being used?..what is the blade area? Apparently the blade area should be 2.2-2.5 inch per HP. if it isnt, then we have issues yet again.

still ever interesting eh?

what revs do you get also with that setup please...? it's great to have someone with the hardware...

RE: true DF thrust/ hp claims?
 

our experience was with the ramtec fan. again, the engine did not perform to a point the plane was even airworthy. the rossi would not turn up a ramtec to the same rpm as an os would. so the thrust of the rossi combo was less than that of the os combo. if the rossi was that much more powerful, it should be able to turn the same fan to a higher rpm, which it would not.

read terry's post again, if the rossi were indeed 46% more powerful harnessed to the hurricane byron replacement 6" fan, it should perform better than the os. his comment is that performance is on par with the rossi 90.

i am curious as to your experience with the 105 when you receive it. please share with us.