Difference between Viojett & Viofan?
10-29-2003, 10:50 PM
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Difference between Viojett & Viofan?
Are these two fan units interchangeable? Do they both work with either the BVM .91 or .96SE? I realise the Viofan is a newer design and has more thrust, but are there reasons why you would choose one over the other?
10-29-2003, 11:23 PM
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RE: Difference between Viojett & Viofan?
Mav,
The major differences between the two, is the afterbody fairing and the mounting bolt hole locations.
The VIOFAN uses the four bolt pattern in the front of the engine case (around the crankshaft) to mount the engine. The Viojet uses the standard beam mount lugs to mount the engine. The VIOFAN has a more streamlined afterbody/pipe exit fairing to smooth out the airflow aft of the crankshaft area of the engine.
The difference in the amount of induced drag produced by the engine is noticeably lower in the VIOFAN, due to the mounting bolt arrangement and the streamlining of the fairings. This gives more thrust at any engine RPM than the VIOJET. The afterbody blending is responsible for the drag reduction and it's corresponding thrust gain.
Both the .91R and the .96 are alternate and interchangeable in either fan unit.
One advantage with the .96 is the ability to run it a little richer (slower) than the .91R while making the same thrust. It seems to be a little easier on the rotating/jumping-up-and down parts.
Both fan units utilize the "Constant Area Rule" to compensate for the loss of area that the engine creates within the duct.
Both use the same rotor and shroud.
The VIOJET is only available for the OS .91.
If you want to buy a new one, the VIOFAN is the only one available from BVM to run the BVM .91R or BVM .96. Used VIOJET's are out there for sale, if you want one for your BVM .91 or .96. Always install a new rotor in a used fan if there is any question about the condition of a used rotor.
Hope this answers your question.
Harley Condra
BVM REP
Teqam Jetcat
The major differences between the two, is the afterbody fairing and the mounting bolt hole locations.
The VIOFAN uses the four bolt pattern in the front of the engine case (around the crankshaft) to mount the engine. The Viojet uses the standard beam mount lugs to mount the engine. The VIOFAN has a more streamlined afterbody/pipe exit fairing to smooth out the airflow aft of the crankshaft area of the engine.
The difference in the amount of induced drag produced by the engine is noticeably lower in the VIOFAN, due to the mounting bolt arrangement and the streamlining of the fairings. This gives more thrust at any engine RPM than the VIOJET. The afterbody blending is responsible for the drag reduction and it's corresponding thrust gain.
Both the .91R and the .96 are alternate and interchangeable in either fan unit.
One advantage with the .96 is the ability to run it a little richer (slower) than the .91R while making the same thrust. It seems to be a little easier on the rotating/jumping-up-and down parts.
Both fan units utilize the "Constant Area Rule" to compensate for the loss of area that the engine creates within the duct.
Both use the same rotor and shroud.
The VIOJET is only available for the OS .91.
If you want to buy a new one, the VIOFAN is the only one available from BVM to run the BVM .91R or BVM .96. Used VIOJET's are out there for sale, if you want one for your BVM .91 or .96. Always install a new rotor in a used fan if there is any question about the condition of a used rotor.
Hope this answers your question.
Harley Condra
BVM REP
Teqam Jetcat
10-29-2003, 11:37 PM
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RE: Difference between Viojett & Viofan?
ORIGINAL: Harley Condra
If you want to buy a new one, the VIOFAN is the only one available from BVM to run the BVM .91R or BVM .96.
If you want to buy a new one, the VIOFAN is the only one available from BVM to run the BVM .91R or BVM .96.
Does this make sense?
10-30-2003, 12:07 AM
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RE: Difference between Viojett & Viofan?
1. Yup, sho nuff.
There isn't any economic sense for BVM to make both fan units available for the BVM engines. The reason for the survival of the VIOJET is the existance of the OS engine. The major difference being the mounting arrangement and the fiberglass fairings.
Was I you, I would make sure that the seller has a VIOFAN for sale. It makes more blow than the VIOJET.
What airframe are you intending to power?
2. Makes sense to me.
VIOFAN part number is 6070, lists at $295.00
BVM .96 engine part number 6075, lists for $625.00
Harley Condra
BVM REP
Team Jetcat
There isn't any economic sense for BVM to make both fan units available for the BVM engines. The reason for the survival of the VIOJET is the existance of the OS engine. The major difference being the mounting arrangement and the fiberglass fairings.
Was I you, I would make sure that the seller has a VIOFAN for sale. It makes more blow than the VIOJET.
What airframe are you intending to power?
2. Makes sense to me.
VIOFAN part number is 6070, lists at $295.00
BVM .96 engine part number 6075, lists for $625.00
Harley Condra
BVM REP
Team Jetcat
10-30-2003, 12:09 AM
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RE: Difference between Viojett & Viofan?
ORIGINAL: Harley Condra
What airframe are you intending to power?
What airframe are you intending to power?
10-30-2003, 12:22 AM
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RE: Difference between Viojett & Viofan?
The Maverick Pro is a great airplane, and either fan will fit perfectly. I bought one from a friend that had started it before he discovered helicopters.
One of these days I'll finish it if I have the time, or maybe sell it. I've got everything except the engine, that I sold to a guy in Atlanta Ga. who needed it for Superman a couple of years ago.
Harley Condra
BVM REP
Team Jetcat
One of these days I'll finish it if I have the time, or maybe sell it. I've got everything except the engine, that I sold to a guy in Atlanta Ga. who needed it for Superman a couple of years ago.
Harley Condra
BVM REP
Team Jetcat
10-31-2003, 12:33 PM
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RE: Difference between Viojett & Viofan?
Both the .91R and the .96 are alternate and interchangeable in either fan unit.
One advantage with the .96 is the ability to run it a little richer (slower) than the .91R while making the same thrust. It seems to be a little easier on the rotating/jumping-up-and down parts.
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Harley, if you use the same fan (pick one from Viojett or Viofan), how can you make more thrust at a lower RPM? The fan always absorbs more Horsepower by gaining some RPM.
I think the Timing of the 96 may be milder, so it may not UNLOAD to a high RPM in a dive, but it cannot make MORE power in the SAME fan at slower RPM.
I feel the 96 may be a better choice for heavier or draggier aircraft because it probably makes more takeoff (loaded) power (and higher take-off RPM) due to more displacement. (The RPM (and thrust) may be lower ONLY when unloaded and/or diving)
The 91R may be better for people who want to go fast with lighter and cleaner planes because it probably unloads better in the air due to higher timing.
Does this make sense? Seems like your conclusions and comments are right, but the more thrust/slower comment is incomplete or misleading.
(Granted, the Viofan makes a bit more thrust with the same horsepower regardless of engine, and it probably does it more from efficiency (drag/turbulence/pressure), and not with increased RPM much.)
Best Regards,
David
One advantage with the .96 is the ability to run it a little richer (slower) than the .91R while making the same thrust. It seems to be a little easier on the rotating/jumping-up-and down parts.
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Harley, if you use the same fan (pick one from Viojett or Viofan), how can you make more thrust at a lower RPM? The fan always absorbs more Horsepower by gaining some RPM.
I think the Timing of the 96 may be milder, so it may not UNLOAD to a high RPM in a dive, but it cannot make MORE power in the SAME fan at slower RPM.
I feel the 96 may be a better choice for heavier or draggier aircraft because it probably makes more takeoff (loaded) power (and higher take-off RPM) due to more displacement. (The RPM (and thrust) may be lower ONLY when unloaded and/or diving)
The 91R may be better for people who want to go fast with lighter and cleaner planes because it probably unloads better in the air due to higher timing.
Does this make sense? Seems like your conclusions and comments are right, but the more thrust/slower comment is incomplete or misleading.
(Granted, the Viofan makes a bit more thrust with the same horsepower regardless of engine, and it probably does it more from efficiency (drag/turbulence/pressure), and not with increased RPM much.)
Best Regards,
David
10-31-2003, 05:01 PM
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RE: Difference between Viojett & Viofan?
"Harley, if you use the same fan (pick one from Viojett or Viofan), how can you make more thrust at a lower RPM? The fan always absorbs more Horsepower by gaining some RPM."
..by improving the efficiency of the DF propulsion unit.
Yes, the HP extracted by the fan will be lower if the RPM drops, but if the fan unit efficiency is improved (i.e. by means of all the fairings etc) to a level that exceeds the reduced HP extraction, the overall thrust of the propulsion system can increase.
In reality, I suspect that the difference in the output of the engines is probably negligible and the system thrust gains can be attributed primarily to the improved fairings (and thus overall system efficiency).
Peter
..by improving the efficiency of the DF propulsion unit.
Yes, the HP extracted by the fan will be lower if the RPM drops, but if the fan unit efficiency is improved (i.e. by means of all the fairings etc) to a level that exceeds the reduced HP extraction, the overall thrust of the propulsion system can increase.
In reality, I suspect that the difference in the output of the engines is probably negligible and the system thrust gains can be attributed primarily to the improved fairings (and thus overall system efficiency).
Peter
10-31-2003, 08:40 PM
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RE: Difference between Viojett & Viofan?
Yup,[8D]
The fan efficiency is higher as a result of the fairings, but it probably, nah, would have been more correct if I had said that the .96 engine can be run a little richer than the max RPM setting, thus being a little easier on the engine. It should still outperform the .91 in either fan unit.
That's what I really meant, but failed to state properly.
Dave, you know that propulsion tract efficiency is the key to the whole thrust thing...regardless whether it is low energy ducted fan air, or high energy air coming out the hot end of a turbine.
That's why the VIOFAN performs better than the VIOJET.
I'll do a better job of proof reading this time, and next time too.
Harley Condra
BVM REP
Team Jetcat
The fan efficiency is higher as a result of the fairings, but it probably, nah, would have been more correct if I had said that the .96 engine can be run a little richer than the max RPM setting, thus being a little easier on the engine. It should still outperform the .91 in either fan unit.
That's what I really meant, but failed to state properly.
Dave, you know that propulsion tract efficiency is the key to the whole thrust thing...regardless whether it is low energy ducted fan air, or high energy air coming out the hot end of a turbine.
That's why the VIOFAN performs better than the VIOJET.
I'll do a better job of proof reading this time, and next time too.
Harley Condra
BVM REP
Team Jetcat
10-31-2003, 08:48 PM
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RE: Difference between Viojett & Viofan?
Interestingly enough, it seems that (in the practical arena, anyway) the BVM .91 makes a given airplane fly faster than the .96. Of course, there could be explanations for this, but in the airplanes we used both in, they seemed to have more performance with the .91. Explanations?
10-31-2003, 10:08 PM
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RE: Difference between Viojett & Viofan?
"Interestingly enough, it seems that (in the practical arena, anyway) the BVM .91 makes a given airplane fly faster than the .96."
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I attempted to explain it above already.... The timing (porting, etc) in the 91R is probably higher, so it will UNLOAD to a higher RPM... So, at higher RPM... in cruise or dive, it probably makes more HP than the 96.
The 96, with more displacement probably makes more horsepower at (near static load) take-off RPM when the load on the fan is the heaviest.... The horsepower peak is at a lower RPM. Conversely, as the fan unloads, the 96 engine as timed is probably getting past peak horsepower, so the RPM does not climb further.... So it is more self limiting/constant speed.
(keep in mind, all engines have a power (torque x rpm) curve that climbs as RPM's climb, then reach a peak at some point, then decline (due to torque at ouput dropping off fast). The HP peak can be at different RPMs for a variety of reasons (ports/timing, bore, stroke, bearings... everything really). I am proposing that the 91R's peak HP is at a higher RPM than the 96. The 96 HP is probably higher, but it probably drops faster above the fans fully static loaded RPM.) At some RPM, if the engine does not break, the friction of the engine and pumping of air, etc will cause the torque, and therefore HP to drop back to 0.
If all else is the same, the lower timing of the 96 would likely make it easier to needle, and less likely to go toward a lean run. At the same time, the lower RPM (at high throttle cruise) would lower stress on the engine. These factors could make the 96 easier to run in a fashion that is less stressful.
I have run a lot of 91Rs, but have not owned a 96... just observing.
(By the way, there are some comments above mixing the fan type in as part of my HP comments, but for all engine comparisons, I removed the fan as a variable, and said... Just pick one fan....) The two issues need to be kept separate, and there seems to be a consensus that the Viofan will make more thrust out of your horsepower.
No problem Harley... I recognise that you had all the correct conclusions, and advise... just wanted to clarify the actual conditions/reasons. I also see what you mean about your comments... if you had said "slower than its peak RPM" instead of "slower than the 91R", it would be quite correct.... Oh well.... you left the door open... Consider yourself nit picked!
That is my feeling about it.
David
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I attempted to explain it above already.... The timing (porting, etc) in the 91R is probably higher, so it will UNLOAD to a higher RPM... So, at higher RPM... in cruise or dive, it probably makes more HP than the 96.
The 96, with more displacement probably makes more horsepower at (near static load) take-off RPM when the load on the fan is the heaviest.... The horsepower peak is at a lower RPM. Conversely, as the fan unloads, the 96 engine as timed is probably getting past peak horsepower, so the RPM does not climb further.... So it is more self limiting/constant speed.
(keep in mind, all engines have a power (torque x rpm) curve that climbs as RPM's climb, then reach a peak at some point, then decline (due to torque at ouput dropping off fast). The HP peak can be at different RPMs for a variety of reasons (ports/timing, bore, stroke, bearings... everything really). I am proposing that the 91R's peak HP is at a higher RPM than the 96. The 96 HP is probably higher, but it probably drops faster above the fans fully static loaded RPM.) At some RPM, if the engine does not break, the friction of the engine and pumping of air, etc will cause the torque, and therefore HP to drop back to 0.
If all else is the same, the lower timing of the 96 would likely make it easier to needle, and less likely to go toward a lean run. At the same time, the lower RPM (at high throttle cruise) would lower stress on the engine. These factors could make the 96 easier to run in a fashion that is less stressful.
I have run a lot of 91Rs, but have not owned a 96... just observing.
(By the way, there are some comments above mixing the fan type in as part of my HP comments, but for all engine comparisons, I removed the fan as a variable, and said... Just pick one fan....) The two issues need to be kept separate, and there seems to be a consensus that the Viofan will make more thrust out of your horsepower.
No problem Harley... I recognise that you had all the correct conclusions, and advise... just wanted to clarify the actual conditions/reasons. I also see what you mean about your comments... if you had said "slower than its peak RPM" instead of "slower than the 91R", it would be quite correct.... Oh well.... you left the door open...
Consider yourself nit picked!That is my feeling about it.
David
