All right, with all these whizzy new gas engines coming to market and electric this and that, along with mega $$$ YS four strokes, just how much thrust is really required to achieve the "stupid power" that everyone seems to crave? Last year at the US Nats it was windy and nasty and the electric setups didn't do so well in that. Can anybody actually quantify how much is enough and perhaps offer opinions on how much pitch you need to keep the thrust going at higher speeds? Put another way, for the mythical perfect power system, what prop would it turn at what rpm (static)?

I'm just trying to find the best power system for my new Pentathlon kit and it is getting a bit cloudy out there.

BTW, the new ZDZ F3A 40cc gasser is quite attractive at $550 with ignition. Much better than I was expecting...Still not cheap, but the operating costs are peanuts after that first big hit.


Thanks,
Mark

Just playing around w/ the Thrust program http://freespace.virgin.net/barry.hobson/ I try to guess what my equipment produces.

So I run a 18.1x10 APC on my YS 1.60 at about 8300 rpm, the program works that to 20-22lbs thrust; on a sub 10 lb plane is nice. I compare to a 17x12 APC at 17 lbs thrust.

The program also works the HP numbers.

So if you take ZDZ s word for there HP on the 40F3A and a 22x10 menz, reduce the RPM till the HP meets ZDZs number it shows 27lb thrust. So, that RPM is 6300 for this HP and prop. I think thats the RPM the Electric's run at or close to it..??

Ive never quantified this but just played around with it to get ideas.....ya..got to much time on my hands.[8D]

Depends who you talk to.. Chip hyde swears by none. Mixes rudder in. He makes a decent point. Not sure I'm buying though..

Chris

About having no thrust?

wow, he's even better than I thought.

Telekenisis. That is happening.

I have the opportunity to fly the same plane (Abbra) using gas engine (ZDZ 40) and glow engine. The ZDZ was not the F3A version and the plane was about 6 oz over 11 lbs. I built the gas plane for a friend of mine. The second Abbra (mine) has the OS 160 with ES carbon pipe. I flew the old Master schedule with both planes back to back. The Abbra glow was a little below 10 lbs. In fly the ZDZ 40 was a noticeable having harder time in the up lines. Vertical eight was a clear problem. I flew the gas version three or four times and I got the feeling that the Biela three blade 18x10 prop probably was too much load. The down lines and speed were very nice. I was using the DL 3 blade prop APC 15.75x11 in the glow version. My conclusion is that the ZDZ 40 was not a lot more powerful than the OS 160. However, I wish that I could test other props on the ZDZ 40. After this test, I will say that both engines are probably around the same in the power department. The ZDZ 40 has the ES petrol carbon pipe.

Note: The Abbra gas was flown without soft mount first. In one fly, the ailerons fluttered really badly. Fortunately, the plane was landed with no problem. Mr. Hyde built a soft mount for the engine. That was a very nice solution and the reduction in vibration and noise was evident. In conclusion, if you go gas do not attempt to run it on a hard mount.

Regards,

Vicente "Vince" Bortone

That's interesting, as the ZDZ should make a solid 20+lb of static thrust with the pipe and that should be LOTS to haul an 11lb aircraft around. I would bet that prop selection would sort that out.

There shouldn't be a 22oz difference between the OS160 and the ZDZ if they are both optimized, that seems way too much to me. Do you have a breakdown of where the weight is?

Dick Hanson would argue that point about the soft mount and gas engine combo. I plan to solid mount a gasser on my Pentathlon if that is what I settle on. We'll see what happens...


Funny guy, Chris. I WAS speaking of thrust as in the force that moves the aircraft through the air, not RIGHT thrust. I haven't worried about the trimming part yet...


Mark

There shouldn't be a 22oz difference between the OS160 and the ZDZ if they are both optimized, that seems way too much to me. Do you have a breakdown of where the weight is?

Yes, the 22 oz is about correct. In the engine deparment alone we have:

ZDZ 40 OS 160

Engines 52.4 oz 33.2 The ZDZ 40 includes the igniton
Pipe 4.4 4
Mount 5.5 4.4
Prop 4.7 4.3
Ig. Batt 4.0 Includes the switch
Headers 4.7 2.3
Total 75.7 48.2

Therefore, the difference is actually around 27.5 oz. The glow version is really 9lbs 12oz so the numbers appear to be correct. Remember that this is NOT the ZDZ-F3A version. From the specs. the F3A version is around 7 oz lighter so the gas engine penalty is reduced to around 20.5 oz. You should be able to make the weight assuming that the plane is as light as the Abbra.

In regard the soft mount, that is your choice. I just reporting what happened. The Abbra is composite construction. If you do all wood structure it will dampen a little better. However, if I were you I won't take the risk.

Regards,

Vicente "Vince" Bortone

Thanks for the weights, Vicente. That clears it up for me.

I agree, YMMV with the soft mounts. Some people swear by them, some swear at them...


Mark

Mark,

For sure, your mileage is going to change. First, your plane with soft mount is going to last longer. I know it is difficult to prove this one. Now, I have one easy one for you to prove. I did it more than 10 years ago. Take the same plane with same equipment and servos. Make sure that the battery is full charged. Fly the SAME sequence two or three times without soft mounting the engine. Charge the battery and measure the mah/flight that you put to fully charge the battery. Now, install a soft mount in this plane. Fly again and try to do exactly the same sequences you did before starting with fully charged battery. Get the new data mah/flight. You will surprise how much less mah you will use when the plane is equipped with soft mount. I did it and the reduction was over 20%. With digital servos could be a lot more.

Other good points, the noise reduction were anywhere between 5-10 db with soft mounted engine. I have been able to measure this in several occasions. In addition, you can use smaller capacity batteries and save some weight. Well, I agree 100% YMMV.....

Good luck in your new plane.

Vicente "Vince" Bortone

Vicente I agree with you 110% re the soft mounting---the maH drop per flight is an excellent demonstration----and the perceived noise is so much nicer to fly.
All the more irritating though, that these days you can just go out and buy an electric package, and have practically silent, vibration-free, flight!

Good point. I was just concentrated around internal combustion engines that were the original question. Actually, I had the opportunity to build the Abbra in electric version for a friend. We installed a soft mount in the electric version also. Yes, it sound crazy but the prop also generates vibration. It is a lot less vibration so the mount has less rubber. The weight of the electric version is 10 lbs 6 oz. Therefore, we have now a good reference for three different propulsion systems in the same model. The glow version was a couple of oz below 10 lbs. Besides the vibration and noise levels, the big advantage of the electric version is that the take off and landing weight are the same.

Best regards,

Vicente "Vince" Bortone

I C

I C


LOL

It was late when I posted..
Well, that's my excuse. haha

Ok, so how much thrust is required as in thrust from the prop.. I get it.. LOL

My answer is, well, well, you should use my setup. It works awesome. haha

Good luck with the setup. I'm interested in going gas also at some point..

Chris

Well, to let the cat out of the bag, I have been looking at using a Brillelli 46GT or the new 36GT with the rear exhaust for this plane:

http://www.scottellingson.com/brillelli_002.htm

I don't think the 36 will have enough poke, even on a pipe, though. Scott lists the baseline prop as a Xoar 20x8 @ 6800rpm. From what I can tell, that really needs to be a 20x10 or 12 @ 7000+rpm for that stupidly overpowered feeling... The 36 IS 6oz lighter than the 46, though, which is very significant. But, unless it responds amazingly well to a pipe, I don't think it will be enough.

The 46GT is about the same weight as the standard ZDZ40 RE, maybe a few ounces lighter. That will be offset by needing a wrap around header to put the pipe or canister on the centerline of the plane. It should have fantastic power, with the baseline of a Xoar 22x8 @ 6500rpm. This equates to a 20x10 at over 7000rpm on the muffler and should be several hundred rpm higher with a pipe, giving a static thrust around 25lb from Pe Reivers thrust calculator. If that isn't enough to get OOS vertical with an 11lb model, I don't know what is...

I am not competing with this, it is only a sport plane for me, so the 11lb limit is academic. But I would like to keep it close for a nice light wing loading and the excellent flight performance that accompanies it. I figure I will be around 16-18oz heavier than Mark Hunt's 10lb 6oz prototype, powered by an OS 160. If I use a carbon wing tube and take care with the equipment, I should be very close to 11lb when done. I plan to finish with .75oz glass cloth and Minwax Polycryllic, which seems to be coming in right about equivalent with film coverings on weight, from what I have seen.


Mark

Mark,

This past weekend I did get to see the 46gt in person. It was mounted in a lanier edge (73" span?) and it performed very nicely. I was not fully broke in yet, but had no problem swinging a xoar 21x8. The engine looks very well built. This one was hard mounted on beams and had the simple box muffler (loud). The owner did not know the RTF weight of the setup, but it was likely between 13-14 lbs. The airplane flew very well at this weight (1000+ sq. in. wing) and perhaps it's the only little lanier edge I've ever seen without 2 lbs. of lead in the nose to get it to balance.

The rear exhaust version although smaller, sounds very appealing for sake of keeping pipe setup simpler and cleaner....as well as lighter. However, I think your estimation of required rpm and prop are right on...and the 36 looks like a real longshot.

Your kit will be a few ounces lighter than my prototype due to changes in former web thickness, lightening hole sizing, etc. Small changes to the lite ply parts yield a nice little weight change in the end kit. I will be excited to see how your project turns out.


Regards,
Mark

Hey Mark,

Did your prototype have any of the coring done to the wing cores? Or honeycombing? There are several ounces there to be had, as well. Along the lightweight theme, what do you think of the digital mini servos from Hitec for the ailerons? Metal gears, 76oz-in torque on 6.0V and just over 1oz each.


Mark

Mark,

My prototype does not have the cored wings. I did not get my foam cutter going until after I built my prototype. With the cored wings, the savings are exactly 1oz. per panel. I guess they could be cored more aggressively and get a few grams more per panel.

As for servos, that would be enough torque for my setup....but I cannot say with any confidence what is really needed with a gasser up front. Perhaps Dick Hanson can comment on what servos he is using in his zdz test bed airplane.


-mark

Well, the Brillelli shouldn't shake any worse than your OS160, maybe less with the electronic spark ignition. Certainly far less than a 4 stroke glow engine. I guess there is really only one way to find out... Thinking ahead a bit, I think I will build servo boxes to take a standard size servo case, then add an adapter plate to install the mini's. If they don't work out, I can revert back to standard servos without a problem at that point.


Mark

It would be interesting to see the amp draw on servos by hard mounting a dz versus a gasser. Then soft mount both and compare readings as well. Mr. Bortone? Do you have a feel for comparative vibration after soft mounting the zdz in the abbras?

-mark

Another part of this equation... Since the slow flying electric set ups were not enough for the conditions at the US Nats this year, how much pitch at what rpm is enough to get through those windy days? Is the 18.1x10 @ 8300rpm on the YS160 enough for everything? It seems the gassers are spinning 20-22" x 10" props around 7000-7500rpm. Lots of thrust, but significantly less speed than the YS combo. Would this be enough? Or is this a question of power and not rpm? I'm trying to get a feel for what is really needed for the range of conditions that seem to be the norm and the info is scattered far and wide. What do the electric set ups run for prop and rpm?

Dick Hanson are you out there with the gas pattern perspective? Any electric flyers care to enlighten me?


Thanks,
Mark

If you look back, the only electric setups that "struggled" were the Hacker C50 setups with big 21 or 22" props and flyers who tried to push them too hard to get extra speed to help in the windy conditions mostly on day 4. The Pletty Evo outrunner (Chad) and Hacker A60 (Dave L) outrunner both were propped faster and handled the wind just fine. If the C50 guys propped for better speed, they would have faired better but the issue was setup more than available power. Some of the C50 setups were done for that extra slow presentation and got hurt by the wind. But in spite of what some say were the electrics falling down, they won Intermediate, Advanced, and FAI. Not too bad.

I think with the Axi 5330/F3A we are pulling about 5800 rpm with a 22x12. I haven't checked in quite some time though. But I did pull this off a thread that we had. Sick power!!!!!!

Thanks for the info, that is what I was looking for. So what were the guys running for props that propped for faster speeds? I'm not criticising the electrics, just going from what I read, they are all better than I am. I am just trying to get a handle on "enough" and what the various combinations were performing like. Is a 20x10 @ 7400-7500rpm a solid target to shoot for?


Mark

I will have to search this one. I know several that have started running the 20x13 and also the 20x15 for faster speed.
Not sure about the numbers. I'll try to find out. .

Chris

Most electrics used in FAI (with the exception of Dave L. with the A60) are running 12-15" pitch (20-22" dia.) at 5800-6500 rpm depending on packs, motor etc etc.

In regards to the winds during the finals, I would never expect any setup to have done well under those circumstances, glow, gas, electric or otherwise. If there was a very large advantage to glow in wind, Sean and Don had a great opportunity to show it, but from what I saw they suffered as much as anyone else. Lets not forget that Sean was in 2nd after the prelims and 1st after the semi's, with weather conditions that should have been an advantage to electrics. Personally, I was just happy to go home with my airplane in one piece after that day

Any way you slice it - more power on a higher pitched prop is better for handling just about any condition- vertical downlines are the only exception and a very low idle will work here .
The limitations of electrics are the batteries - the new 123 cells -IF n when second stage versions hit the scene may turn it all on it's ear as these can put out horrendous power without cell damage (compared to LiPo's)
On the gassers - you have to get the engine n pipe to work well throughout the 3000-6000-as well as flat out flying
So far -this takes a looong pipe but there is a performance increase in the slower flying speeds . I have been playing with my gassers (not in pattern planes ) to try and find best compromises . so far piping very long and adding more prop load seems to produce the best slower speed performance.
By better -I mean smooth, throttleable pull from slow flight or up vertical lines . When I did my Petrol Petrel in 2002 -I was after best power to weight and this really did that well. The slow speed transition was not the best -not bad just not silky smooth and the engine had that darn 3000 rpm shake .
As for glo?- frankly I am not into any of those new four stroke types -a BIG 2 stroke glow -on a trick spark ignition may still be the trick setup. The reason for the spark setup is that it will control timing to give best power and smoothness in different heat environments. Iran this combo on a ST2300 and 5% nitro - the setup beat any glow fuel/glow plug setup I have seen. total weight gain was 7 ounces. batt and ignition (custom made setup). all of this is pushing the 11 lb mark .