---------------------------------------------------------- Kolb-List Digest Archive --- Total Messages Posted Tue 10/05/21: 14 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:20 AM - thrustline (Peter Cowan) 2. 07:36 AM - Re: Reducing power on take off versus thrust line. (Richard Pike) 3. 07:48 AM - Re: thrustline (Richard Pike) 4. 08:15 AM - Re: Kolb-List Digest: 2 Msgs - 10/04/21 (Richard Swiderski) 5. 08:20 AM - Re: Re: Reducing power on take off versus thrust line. (william sullivan) 6. 08:56 AM - Re: thrustline (Rick Neilsen) 7. 09:08 AM - Mark III weight and balance (ridefst) 8. 10:53 AM - Re: Mark III weight and balance (Rick Neilsen) 9. 01:22 PM - Thrust line (james.vanlaak@gmail.com) 10. 01:37 PM - Re: Thrust line (Jay Dub) 11. 02:54 PM - Re: thrustline changes (1957grnchev@bluemarble.net) 12. 04:26 PM - Re: Thrust line (1957grnchev@bluemarble.net) 13. 07:14 PM - Re: Mark III weight and balance (Richard Pike) 14. 09:37 PM - Re: Re: Reducing power on take off versus thrust line. (lane jones) ________________________________ Message 1 _____________________________________ Time: 04:20:26 AM PST US From: Peter Cowan Subject: Kolb-List: thrustline Re: : 10:48:03 PM PST US Subject: Kolb-List: Re: Reducing power on take off versus thrust line. From: "chic" Okay, so I am a little confused here..... If I raise (just) the rear of the engine on my Firestar 2 for more prop clearance off the boom tube, am I adding positively or negatively to the thrust Raising just the back motor mount so that the thrustline points lower at the front is down thrust which results in an in flight nose up force.. ________________________________ Message 2 _____________________________________ Time: 07:36:42 AM PST US Subject: Kolb-List: Re: Reducing power on take off versus thrust line. From: "Richard Pike" Reading this thread jarred loose a memory from back in the 70's when guys were first starting to put gokart engines on Quicksilvers - Don't remember who it was that said it, but I do remember it was an article in Glider Rider. (Anyone else used to get that one?) Basically it was that you wanted the engine thrust line to have the prop perpendicular to the horizon when the wing was at it's normal angle of attack in level flight. -------- Richard Pike Kolb MKIII N420P (420ldPoops) Kingsport, TN 3TN0 Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=503423#503423 ________________________________ Message 3 _____________________________________ Time: 07:48:13 AM PST US Subject: Kolb-List: Re: thrustline From: "Richard Pike" Correct. Don't know what you call it, but picture progressively lowering the rear motor mount (pretend that prop length is not a problem) and you can see that eventually your thrust line is going to want to make the airplane just do outside loops. Obvious exaggeration, but you get the idea. When I went from a 68" prop to a 72" prop, I had to raise the engine to get prop clearance, and also ended up adding two extra washers under the rear motor mounts, working on trim. So the rear of the engine is now about 1/8" higher than the front. But subject to change. -------- Richard Pike Kolb MKIII N420P (420ldPoops) Kingsport, TN 3TN0 Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=503424#503424 ________________________________ Message 4 _____________________________________ Time: 08:15:42 AM PST US From: Richard Swiderski Subject: Kolb-List: Re: Kolb-List Digest: 2 Msgs - 10/04/21 chic, Since your engine is behind the CG, if you raise the rear of your engine (direct some of your thrust downward) you will take away some of your forward thrust and add to your downward thrust, which in turn will cause the nose to be pushed up. Picture a teetter-todder: the CG is the fulcrum; the engine is on the tail side; and the nose is on the other side. If the engine is pointed down it will be pushing the whole teetter-todder downward, but since it is on the tail side, it is also causing the nose to go up. On Tue, Oct 5, 2021 at 2:39 AM Kolb-List Digest Server < kolb-list@matronics.com> wrote: > * > > ================================================= > Online Versions of Today's List Digest Archive > ================================================= > > Today's complete Kolb-List Digest can also be found in either of the > two Web Links listed below. The .html file includes the Digest formatted > in HTML for viewing with a web browser and features Hyperlinked Indexes > and Message Navigation. The .txt file includes the plain ASCII version > of the Kolb-List Digest and can be viewed with a generic text editor > such as Notepad or with a web browser. > > HTML Version: > > > http://www.matronics.com/digest/digestview.php?Style=82701&View=html&Chapter 21-10-04&Archive=Kolb > > Text Version: > > > http://www.matronics.com/digest/digestview.php?Style=82701&View=txt&Chapter 21-10-04&Archive=Kolb > > > =============================================== > EMail Version of Today's List Digest Archive > =============================================== > > > ---------------------------------------------------------- > Kolb-List Digest Archive > --- > Total Messages Posted Mon 10/04/21: 2 > ---------------------------------------------------------- > > > Today's Message Index: > ---------------------- > > 1. 06:33 AM - Re: Fitting request (Rick Neilsen) > 2. 10:48 PM - Re: Reducing power on take off versus thrust line. > (chic) > > > ________________________________ Message 1 > _____________________________________ > > > Time: 06:33:53 AM PST US > From: Rick Neilsen > Subject: Re: Kolb-List: Fitting request > > Paul > > I have a Kolb MKIIIC. It is located at the Hart/Shelby County airport in > Michigan. Take the Badger (car ferry) across lake Michigan to ludington and > it is app 20 miles south. You are welcome to test fit in it. I'm heading to > Florida for the winter Oct 21 so if you are going to check it out please do > so quickly. > > Rick Neilsen > Redrive VW Powered MKIIIC > > > On Sat, Oct 2, 2021 at 7:49 PM prhutson wrote: > > > > > Is there anyone with a Mark III anywhere near south-central Wisconsin > that > > would let me sit in their Classic or Xtra for a fitting? I am 6'3" but > > longish torso. Failed a fit in a Sonex today. There was no one around > at > > Airventure this year when I stopped by for a fitting in a Mark III there. > > Thanks! > > Paul > > > > -------- > > Paul Hutson > > Middleton, WI > > > > > > Read this topic online here: > > > > http://forums.matronics.com/viewtopic.php?p=503382#503382 > > > > > > ________________________________ Message 2 > _____________________________________ > > > Time: 10:48:03 PM PST US > Subject: Kolb-List: Re: Reducing power on take off versus thrust line. > From: "chic" > > > Okay, so I am a little confused here..... If I raise (just) the rear of > the engine > on my Firestar 2 for more prop clearance off the boom tube, am I adding > positively > or negatively to the thrust line? > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=503414#503414 > > -- *Click on to Richard's Blog: * *Thoughts On God And Life -**Prose, **Prayers, Poems & Ponderings * ________________________________ Message 5 _____________________________________ Time: 08:20:50 AM PST US From: william sullivan Subject: Re: Kolb-List: Re: Reducing power on take off versus thrust line. If you pick up the rear, it will push the nose down. Imagine picking up th e rear about 2 feet. On Tuesday, October 5, 2021, 01:48:07 AM EDT, chic wrote: Okay, so I am a little confused here..... If I raise (just) the rear of the engine on my Firestar 2 for more prop clearance off the boom tube, am I ad ding positively or negatively to the thrust line? Read this topic online here: http://forums.matronics.com/viewtopic.php?p=503414#503414 S - WIKI - - =C2- =C2- =C2- =C2- =C2- -Matt Dralle, List Admin. ________________________________ Message 6 _____________________________________ Time: 08:56:06 AM PST US From: Rick Neilsen Subject: Re: Kolb-List: thrustline I am concerned people might not understand the negative impact of using thrust to counter power induced pitch changes. First, your effective thrust will be reduced. The impact is related to total thrust and the amount of change of thrust line. Second, the down thrust needs to be countered by increasing the angle of attack of the wings which adds drag and increased stall speed. What is the total impact? Really hard to say but just grabbing an unrealistic number out of the air does a disservice to our readers. There have been a lot of smart people designing and building Kolb airplanes for a lot of years. If it was beneficial and that easy everyone would be flying our planes that way from the very start. Rick Neilsen Redrive VW Powered MKIIIC On Tue, Oct 5, 2021 at 7:22 AM Peter Cowan wrote: > Re: > : 10:48:03 PM PST US > Subject: Kolb-List: Re: Reducing power on take off versus thrust line. > From: "chic" > > > Okay, so I am a little confused here..... If I raise (just) the rear of > the engine > on my Firestar 2 for more prop clearance off the boom tube, am I adding > positively > or negatively to the thrust > > Raising just the back motor mount so that the thrustline points lower at > the front is down thrust which results in an in flight nose up force.. > ________________________________ Message 7 _____________________________________ Time: 09:08:19 AM PST US Subject: Kolb-List: Mark III weight and balance From: "ridefst" Getting close to my first flight, and I've found that I need 82lb of steel shot in front of the passenger seat to get my CG around 30% (20.2" back from LE) Does this seem normal, or is something weird? Total flying weight would be 748lb (326 left, 371 right, 50 tail) I'm 195lb / 6', so pretty average size. Rotax 582, three blade composite prop BRS in front of engine Both fuel tanks full (about 10 gal total) No doors, just windshield Original mesh seats Seems to be in good shape like this, just way more weight that I was expecting to need! Thanks, Franklin Read this topic online here: http://forums.matronics.com/viewtopic.php?p=503429#503429 ________________________________ Message 8 _____________________________________ Time: 10:53:58 AM PST US From: Rick Neilsen Subject: Re: Kolb-List: Mark III weight and balance Franklin 82 lbs does sound excessive. I have a MKIIIC with a redrive VW engine. I seem to recall that my engine is a bit heavier than normal and was a bit behind the CG so I moved my battery to the nose cone. When all weighed and calculated my plane will stay in the safe aft CG range as long as the only person on board weighs at least 160lbs. The forward range couldn't be too far forward with passengers loading well over max allowable weight. Revisit your calculations but stay safe. For your first flights anchor some weight on the floor of the passenger area just to be safe. Rick Neilsen Redrive VW powered MKIIIC On Tue, Oct 5, 2021 at 12:11 PM ridefst wrote: > > Getting close to my first flight, and I've found that I need 82lb of steel > shot in front of the passenger seat to get my CG around 30% (20.2" back > from LE) > Does this seem normal, or is something weird? > Total flying weight would be 748lb (326 left, 371 right, 50 tail) > I'm 195lb / 6', so pretty average size. > Rotax 582, three blade composite prop > BRS in front of engine > Both fuel tanks full (about 10 gal total) > No doors, just windshield > Original mesh seats > > Seems to be in good shape like this, just way more weight that I was > expecting to need! > > Thanks, > Franklin > > > Read this topic online here: > > http://forums.matronics.com/viewtopic.php?p=503429#503429 > > ________________________________ Message 9 _____________________________________ Time: 01:22:23 PM PST US From: james.vanlaak@gmail.com Subject: Kolb-List: Thrust line I have been biting my tongue on this thread for a while but have to say a few things. And yes, I am an engineer. Remember that thrust losses from pitching the engine are going to be very small. The thrust loss varies with the cosine of the angle. So for small angles the loss is small. The pitching force of the airplane results from the sum of the forces acting on it at that moment. The sum yields a resultant force vector and its relationship to the center of gravity tells whether it is up or down. On takeoff, there is negligible aerodynamic drag so the thrust line is a major force to accelerate the airplane. If it is not pushing through the center of gravity there will be a pitching moment. On Kolbs, it is obviously down. During the takeoff roll, there is a force from the rolling friction of the wheels. It is obviously well below the center of gravity, so it also pitches down. Early in the takeoff the drag on the wing is relatively low so its contribution is fairly low, but as airspeed increases it grows. At maximum level speed the drag of the wing is a major part of the total drag that obviously equals the thrust from the engine (hence maximum level speed). Other sources of drag, like the fuselage and landing gear legs will tend to pitch nose down. But remember that the thrust of the engine on a Kolb is pushing pretty close to the centerline of the wing, so those two forces are largely offsetting. Finally, the downforce on the tail is what we use to balance the rest. If we had the horizontal tail in the wake of the prop we would see a downforce proportional to the power setting. High power with high tail downforce. Look at certified pusher prop planes, mostly amphibians. Lake Amphibian, Seabee, and others all have big tails in the middle of the propwash. There is a reason for that. I built an original Firestar and owned a Mark 3X. Both were nice flying airplanes with large pitching moments. I also owned a Buccaneer amphibian, Rans S-12, Sportflight Talon, Drifter, CGS Hawk, and Super Hornet. All had similar but different pitching responses. I thought the S12 was the worst, but the Buccaneer was close behind. In general it is not hard to learn to control this, but it does require attention. A power loss on takeoff may require a strong nose down push to keep from stalling. If you forget that you will be in trouble. I never worried about it for myself because I flew the planes a lot, but I did not want to loan them to someone who was not familiar with the characteristics. Frankly, I love pushers but not this pitching moment. Someday I will build a custom machine with the horizontal tail in the slipstream to minimize the effect. ________________________________ Message 10 ____________________________________ Time: 01:37:05 PM PST US From: Jay Dub Subject: Re: Kolb-List: Thrust line "Someday I will build a custom machine with the horizontal tail in the slipstream to minimize the effect." I was glad to see you had a CGS Hawk. They still have a high thrust line but the curved boom tube was to get the tail into the prop wash so you had some response once you added some power. Also, in my Hawk the engine sat a lot lower than on the Firestar 2 I'm building. My prop centerline was about even with bottom of the wing on my 1991 Hawk Arrow. The drag on the landing gear definitely gave a pitching down moment but I'm surmising the Firestar I'm building will be a lot worse since the engine will sit so high in comparison. Jay ________________________________ Message 11 ____________________________________ Time: 02:54:43 PM PST US From: 1957grnchev@bluemarble.net Subject: Kolb-List: Re: thrustline changes Re: Thrust line comments Put a tractor prop on the nose, and it has a fairly long arm. But mounting 2X the HP above and behind (AND CLOSE to) the CG will be different. Seeing all of these posts, reminds me of the following: Prop thrust is greatest as slow speeds Stab/Elevator effectiveness is least at slow speeds Take off roll requires ground roll drag, also causing an additional forward pitching moment. Wing pitching moment is variable (on most airfoils, depending on AOA and airspeed(?) When considering thrust angle variables.. to what? CG, center of mass, or center of drag?: There is the CG measured with the AC level. Does anyone know the center of mass on their Kolbs?? Or the center of drag which changes a lot with airspeed, loading, and being on the ground, or in the air. I would assume induced drag is near constant above stall speed, if level flight is maintained with trim. But parasitic drag goes up with the cube of the speed, and drag on take-off depends upon grass height, tire pressures, ground firmness and TOW. What doesn't change, is the number of questions asked when a perfectly good airplane flies very differently with 2X the horse power initially intended. A very small increase in opposing leverage could be accomplished with only slightly larger Stab and Elevator! My Drifter is very similar to my Kolb configuration, and yet the tail areas must be twice as large! I never noticed ANY pitch issues flying the Drifter. But I didn't bolt on 100 HP either! If people are going to be arbitrary with a design which had minimal tail area initially, why not improve THAT!?!? Oh, I forgot, you can't do that with just a few washers! LOL There isn't hardly anything that can be changed on an airplane, that doesn't affect a LOT of different aspects. ________________________________ Message 12 ____________________________________ Time: 04:26:17 PM PST US From: 1957grnchev@bluemarble.net Subject: Kolb-List: Re: Thrust line Very Weird! I only see and reply to the list via my email. I no longer log on. I only saw the response from James Vanlaak JUST NOW.. and very much appreciate what he wrote! What I found odd, was having not seen his post before I wrote mine! So I was not trying to trump his words. Thanks James for the much better (technical) description! ________________________________ Message 13 ____________________________________ Time: 07:14:59 PM PST US Subject: Kolb-List: Re: Mark III weight and balance From: "Richard Pike" Something doesn't sound right. I have done a lot of mods to my MKIII but nothing to move the weight fore or aft much, I have a 582 and need no ballast. I assume you are using the Kolb forms on page 41, 42 & 43 of "The Yellow Book"? If not, PM me, I'll email them to you. FWIW, here is my W&B: -------- Richard Pike Kolb MKIII N420P (420ldPoops) Kingsport, TN 3TN0 Forgiving is tough, being forgiven is wonderful, and God's grace really is amazing. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=503443#503443 Attachments: http://forums.matronics.com//files/mkiii_wandb_166.jpg ________________________________ Message 14 ____________________________________ Time: 09:37:18 PM PST US From: lane jones Subject: RE: Kolb-List: Re: Reducing power on take off versus thrust line. 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