stunthanger.com
Design => Engineering board => Topic started by: t michael jennings on September 23, 2013, 12:30:01 PM
-
Gentlemen,
How does one go about deciding the Better engine for a particular aircraft?
For Example:
1) Would a Fox 35 (6 oz.) be too light for a SIG Twister?
2) Would a OS Max 46 with muffler (11.4 oz.) be too heavy for a SIG Twister?
For both examples above, consider that the CG (center of gravity) to be maintained at the Plan location.
Additionally, which would be considered a Better predictor for engine size?
1) Total aircraft weight,
2) Wing area,
3) One can never have too much power.
Thanks for your input.
T Michael Jennings :!
Knoxville, TN.
-
Maintaining the center of gravity at the plan location should not be your first consideration in choosing an engine.
There has been a huge amount of discussion on engines, engine runs, and engine sizes in this forum over the years. I suggest that you do a search on "engine" or "engine size" (with quotes) and see what pops up.
If you have a stunter of "normal" proportions (i.e., airfoil thickness, aspect ratio, etc.), then the amount of power you need from the engine is going to be determined by the engine size -- BUT -- if the plane is too heavy it'll never fly right, and there's a contingent out there that feels that if the plane is too light then it'll be a great fair-weather plane, but won't be happy in the wind.
Having said all that:
The Fox 35 is what the Twister was designed for, but most folks feel that engine technology has marched on. Your best bet in a Twister is to put an LA 46 in it, and adjust the needle setting until you like the performance.
(I highly recommend finding a set of plans for Fancherizing your Twister. Folks feel that airframe technology has marched on, too, and that a Twister makes a great starting point for a stunt training with good modern "numbers". I know that I'm doing very well indeed with my rather overweight Fancherized Twister; I'm past due to be moving up to advanced with it.)
Note that there are plenty of people out there who disagree with me on these -- I'm just kind of distilling the zeitgeist, and presenting it through a lens composed of my own meager experience. You'll find plenty of people who think that useful engine development stopped at the Fox 35, that way heavy (or way light) planes fly just fine, etc. -- part of learning stunt is to learn how to separate the good suggestions from the bad, and who in general makes good suggestions and who doesn't.
-
I can't answer the question, but it reminded me of a story. Half a century ago, lots of kids in my neighborhood flew control line in a vacant lot behind my house. The kid next door had a Fox .35. He was miffed at its lack of power, it not having enough to maintain line tension with the poorly trimmed airplanes we flew. His solution was to build ever smaller, denser airplanes. One was plywood; the next was all aluminum. He gave up.
-
Gentlemen,
How does one go about deciding the Better engine for a particular aircraft?
For Example:
1) Would a Fox 35 (6 oz.) be too light for a SIG Twister?
2) Would a OS Max 46 with muffler (11.4 oz.) be too heavy for a SIG Twister?
For both examples above, consider that the CG (center of gravity) to be maintained at the Plan location.
Additionally, which would be considered a Better predictor for engine size?
1) Total aircraft weight,
2) Wing area,
3) One can never have too much power.
Thanks for your input.
T Michael Jennings :!
Knoxville, TN.
Choose the engine based on the run characteristisc, don't overly concern yourself with the weight of the engine. A good-running high rev/low pitch engine can go on a very wide range of airplanes. A weak 4-2 break engine has to be carefully tuned to the airplane.
Most of what you have heard over the years about weight is wrong, at least with current engines. It doesn't make much difference if everything else is right. That is significantly different from the past. If you use a Fox you need to make the airplane as light as you can.
Brett
-
His solution was to build ever smaller, denser airplanes. One was plywood; the next was all aluminum. He gave up.
I think that's going a bit farther than what Brett said about weight.
I think my current ride is based on that principle -- and at the moment I have an airplane that flies better than me, although I'm anticipating that this will change sometime in the coming year, either through continuous improvement of my flying, or a crash. Assuming that my right arm doesn't get too long to fit in my clothing from flying it.
-
I think this is something you develop a feel for based on experience and your own personal likes, again developed with time. The best course if not sure is to copy what others are doing for a while and you will figure it out. There are too many possible scenarios in airplane/engine combos that will work if you you don't get too close the the edges. I remember back in the 70s Dave Addleman lived in the KC area and came to the field with a Nobler and ST .46 in the nose. We kind of thought he needed 'coaching'. Turns out he showed us the future even though nobody saw it then.
Dave
If there is one universal rule to follow I'd say it would be to NOT underpower your airplane. If an engine range is suggested for the airplane, go for the larger end of the range. I'll also say (yet once again) you are not limited to two engines. There are many good .29-.40 engines of many brands out there. I've picked up quite a few new or near new Stallions, Vecos, Enyas, Greenheads, the 'good' McCoys, and even O&Rs recently. They fill the gap between .25 to .46 and will serve you well during the training phase and are 'classic' ready.
-
T Mike
"The Fox 35 is what the Twister was designed for, but most folks feel that engine technology has marched on. Your best bet in a Twister is to put an LA 46 in it, and adjust the needle setting until you like the performance." Tim W.
" Most of what you have heard over the years about weight is wrong, at least with current engines. It doesn't make much difference if everything else is right. That is significantly different from the past. If you use a Fox you need to make the airplane as light as you can. " Brett
You can take either of these approaces, but hanging a 12 oz. engine with muffler in the same place as an unmuffled Stunt 35(6.5 oz) will cause some problems. You do have to make sure the CG ends up reasonably close to where it has to be to fly right.
The Twister will fly just fine with the Fox 35 with no muffler, the modified version is better still. But it will have limited power so it will require more careful flying.
The LA 46 is a much easier engine to run and delivers gobs more power. It will take some tweaking to the airframe. Hopefully someone here can post what they did to make it work. Some combination of a shorter nose and a longer tail moment will do the trick, but unless you want to hack several planes it would be helpful to get the numbers from someone who as already done some testing.
-
The LA 46 is a much easier engine to run and delivers gobs more power. It will take some tweaking to the airframe. Hopefully someone here can post what they did to make it work. Some combination of a shorter nose and a longer tail moment will do the trick, but unless you want to hack several planes it would be helpful to get the numbers from someone who as already done some testing.
The Fancherized Twister lengthens the tail and puts on bigger tail feathers, without changing the nose length.
Mine has an LA 46 and it needed over an ounce of nose weight -- but mine is embarrassingly heavy.
A better example is the late, lamented KISS. This was a Fancherized Twister built by Mike Haverly from the Seattle area. It had a fairly winning life in the hands of two different pilots before I took ownership of it and crashed it through sheer stupidity. It sported a Magnum 36 with an OS E3020 (big heavy) muffler in the nose. It needed about an ounce of lead shot and JB Weld in the nose before its second owner was satisfied with it.
So there's your combo, with no nose shortening necessary.
A stock Twister may, indeed, be nose heavy with the LA 46, though.
-
I have built and flown two Twisters with Fox stunt 35s. I balanced the second one at 1 5/8 inches back of the leading edge and really liked how it flew. Won a couple of local Advanced contests with it.
My Fox 35s run to suit me, but then I bought them in 1977. I do a lot of things wrong: full ST NVA, 11 x 5 prop, Sig 10% nitro, 20% oil, half castor, half synthetic, and find the hemihead makes too much power.
The LA engines are much better for a beginner or sport flier. I would not advise a beginner to get a Fox 35 unless I could impart my evil ideas whilst coaching them.
-
I would not advise a beginner to get a Fox 35 unless I could impart my evil ideas whilst coaching them.
Whilst? Blimey.
-
Come, come Howard, you obviously do not appreciate the beauty of the English language!
Regards,
Andrew.