1. Q: Will you sell a reduction drive unit for a fixed pitch prop like the SoloProp while you work on your Constant Speed hub and blade redesign?
A: An excellent question, and one that has come up over the last several months with regularity.
Our current drive frame is designed around the DA-50R motor. It is designed to connect to our Constant Speed propeller hub and allows for us to actuate the internal workings of the hub based on its specific design. It has a reduction ratio of 2.6:1, so that at 7800 engine RPM, the propeller will be spinning at 3000 prop RPM. The propeller is specifically designed to provide optimum performance and to handle all the dynamic loads at 3000 RPM.
This is not a problem for the CS prop as it is designed to have as much as 40 degrees of pitch change and will be low pitch for takeoff and high pitch for max speed and cruise.
The reduction drive mated to a fixed pitch prop (we made a SoloProp adaptor specifically for this application) is going to create the following performance considerations.
As you can imagine, at 3000 RPM on the prop, things aren't going to be moving very quickly!! If you set the pitch on the prop to be high enough for cruise or max speed, it is going to make the takeoff roll much longer, and will greatly reduce the vertical performance
You can set the pitch much lower to allow for better takeoff performance, but you will sacrifice top speed and cruise speed.
If you look at the link here, you can see what we did with the H9 1/3 Scale CAP 232. This is a 97" W/S, 26 lb airplane. We flew it with a 3-blade SoloProp as well as the original 4-blade prop that I was going to import from overseas. This was with a previous design 2:1 reduction drive. We tried everything from 12" of pitch (ok takeoff roll but no top speed) to 22" of pitch (ok on the top end, but the takeoff roll was scary long, and this on a lightly wing loaded aerobatic plane with 1750 sq. in. of wing area. When we went to the 4-blade prop, the effect was even more pronounced (due in large part to the aerodynamic design of the blade. it is not a SoloProp design). With the 4-blade prop, we ran at 17 degrees of pitch, or just about 20" of pitch. Takeoff was very long, cruise was pretty good.
Another consideration is that there is no governor on a fixed pitch design. Since you control the throttle, you control the max motor RPM. Normally, you select a prop with enough pitch to give you a short takeoff roll and good vertical and accept what ever top end you get. The F1 Racing guys use SERIOUS pitch on their prop and pay for it in dramatically increased takeoff roll. They don't worry about overspeeding their engines because they are designed to run at much higher RPMs than we run our stock RC gas motors.
Since you have a nice pulley (reduction) system with a fixed pitch prop (instead of a variable pitch which will change in flight and put enough load on the motor so it won't go over a constant speed), you will start to get higher and higher RPM's as you go faster, to the point where if you don't have enough pitch dialed in, you can easily overspeed your motor!!
How do I know? I flew the DA-50R on the 1/3 CAP 232 with a 2:1 reduction. I thought I had tightened the SoloProp tight enough, but on takeoff I "mowed the grass" a little bit and loosened the prop adjusting mechanism enough so it went to a flatter, lower pitch than I had set. (totally my error, nothing wrong at all with the design) Originally I had 22" of pitch set, but now I was flying on 6" of pitch!. Wow, the sound of a DA 50 at 12,400 RPM is AMAZING!. It flew really slowly at normal RPM of 7000 engine RPM.
So, with a fixed pitch prop spinning at 3000 RPM, performance is going to be a consideration
2. Q: So, why don't you just change the ratio for more prop RPM and be done with it already!
A: Another good question. We selected the ratio of 2.6:1 to give us 3000 RPM on the prop. This gave us the RPM (7800) we measured the DA 50 making the most power (not its highest RPM).
When we change the ratio to another number we have to consider the following
Will the motor be powerful enough to spin the prop at max motor RPM and not bog down and overheat the motor?
Belts come in fixed lengths, in 10mm increments. Change the diameter of the pulleys and you change the required length of the belt.
If you make the large pulley even larger, will it still fit in the cowl, and will it clear the other smaller, driven pulley?
If you make the smaller pulley larger, will it clear the other pulley and still fit in the bottom of the cowl (you can move the center distances of the pulleys, but they still need to fit in the cowl AND have the proper length belt.
There is a minimum radius for the belt to work and not be prone to premature failure
3. Q: If you make the current reduction drive for a fixed pitch setup, will it also work when you get your Constant Speed, variable pitch propeller hub and propeller redesign finished so I can purchase that and put it on the front of the drive that I bought for the fixed pitch propeller?
A: I don't know. One of the benefits to not having to be backwards compatible is that when we get the Constant Speed, variable pitch propeller hub and blade done, we may have made so many changes to the existing drive that you won't recognize it. If we don't have any fixed pitch reduction drives out there, we don't have to worry about backwards compatibility.
We don't know if that is important to you or not. At this stage, if we did sell a fixed pitch compatible reduction drive we could not state that it would be backwards compatible
4. Q: Will you make a Constant Speed propeller for my Turboprop motor?
A: We sure do want to! We think that a CS prop on a Turboprop would be way cool. Beta, full reverse, wow, what could you do with that!!! It's also several orders of magnitude harder to do that compared to just the run of the mill, Constant Speed variable pitch propeller (tongue in cheek here). First we need to get this "regular" CS prop done, THEN we can look at the TurboProp version. I've had some nice conversations with the TurboProp mfgs and some other folks on this subject, so believe me we have given it some serious thought.
So, what we hope that you will now do is to email us and let us know if you would accept a fixed pitch reduction drive designed for the DA 50 and ZDZ 50. It may or may not be backwards compatible. We may change the ratio, but most likely not due to packaging constraints. It would consist of the front and side drive frames, rear frame specific to one motor or the other, driven pulley (large), drive pulley (small) PolyFlex JB v-belt, flywheel. The driven pulley would have a hole in it to accommodate a pitch actuation rod; this may or may not be the configuration in the Constant Speed variable pitch propeller reduction drive.
5. Q: When will the drive and prop be available for purchase?
A: We are targeting selling the drives and prop in June. If the fight tests go well, we should make that date (late June). If we have any issues (hey, who here knows Murphy?) then there will be a delay. Believe me, we’d really like to exchange drives for money, but no sales until we know it's right.
6. Q: What will the whole thing cost?
A: The drive is priced at $300 USD, the Constant Speed Prop hub and governing computer at $375 USD, and the blades at $30 USD each.
7.Q: What about a 3 blade hub?
A: We do have a 3 blade hub and the price is the same as the 4 blade hub.
8. Q: I have a Composite-Arf Mustang-Will you make a prop for this airplane?
A: We have one too!! Yes, we will.
9. Q: Will a 50cc motor fly a 38# plane like the Ziroli Mustang or Composite-Arf Mustang?
A: That’s a darn good question. We have successfully flown the Bruce Tharpe Super Flyin King, a 132" Wing Span, 94" long, 35# plane with the P-51 Mustang Blades without using the governor. It flew the plane with authority, wifh snappy accelleration, short take off roll, and good vertical. This is a 35# plane that is very draggy, and is designed for a 80 to 100cc motor. We had the SKF up to 90 MPH (admittedly at a fast RPM) but the prop will do the job. More testing to come. Since the Constant Speed prop has a pitch range of approx 18” to 50” of pitch, we think that it will fly the Big Iron just fine. If the Ziroli or Comp-Arf Mustangs will fly on a 70-80cc motor and a fixed pitch prop, we think that it will fly on a Constant Speed prop turned by a DA-50R or ZDZ 50.
10. Q: If I buy a Constant Speed hub now and the 26” blades for the TF Mustang, can I use the hub for the Composite-Arf Mustang?
A: Yes you can. The hub is designed for growth, and can accommodate blades up to at least 31” overall diameter.
11. Q: How am I supposed to fit your prop into a spinner? Who makes one that will look scale, with the prop blades not flat against the backplate?
A: We know what you mean, and we will be coming out with an all composite spinner with the blades placed in the scale position. If you look at the pictures of the drive in the plane, the position of the blades are in the scale position.
12. Q: I have an XXXX motor, will your drive fit my motor?
A: Our drive is designed to accept the DA-50R and the ZDZ 50. We are looking at other motors (we have about 20 different motors people would like to see us make drives for). We will make drives to accept other motors after we get some of the 50cc sized drives out in the market. Some motors will be relatively easy to adapt (think ZDZ 80 single) while others will be more development time.
13. Q: What is the next motor you are going to design a drive for?
A: That is an excellent question. We are looking at 80cc singles, and there is a lot of interest in the G-62. We will keep you posted.
14. Q: What’s the deal, just come out with a drive for my motor!!
A: We do listen to our customers, so it is tough saying no to anyone (I know I don’t like to hear no!).
The big issue is that with a motor that has side induction and side exhaust, there isn’t a lot of “real estate” to make every thing fit. Motors that have really short noses (G-62) have a different solution than ones with medium length noses (DA-50R) vs long noses (Revolution 52). Anything with linkages from carb to spark advance (Brison) is a whole different solution set. Beam mounted motors are another solution set. Finally, each engine has an optimal RPM range and that, coupled with the optimal RPM of our prop design, makes the requirement for different ratios a real possibility. Different ratios require either a different belt length (a finite number of choices here) or different sized pulleys (limited by the geometry of center distance) and trying to fit the whole thing in the cowl.
Not trying to make excuses, but as you can see, the design solutions become more complex depending on a lot of different factors.
Finally, if there is a demand for 1 copy of a drive for one type/size of motor, it is not practical for us to make a unique design for just one motor. That’s why we have been asking people to tell us which motor they would like to see a drive for, because we need to know more about what the market wants, so we can meet the overall markets needs.
15. Q: What is the next prop design you are coming out with?
A: There is a fair amount of interest in the FW 190, Spitfire, P-40. We haven’t made a final decision, but we are trying to follow your interests closely.
16. Q: What about us Aerobatic guys, are you going to make something for us?
A: Absolutely!! The design for the Aerobatic CS prop will be totally different because the demands on a 3-D type plane are very different from a Warbird platform. The requirement to only swing 2 blades and desire to have the pitch go to beta and reverse requires a different solution. Weight is also a much bigger consideration on an IMAC type plane, so our design will accommodate those unique needs