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#11
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Aero engineer for designing homebuilt aircraft.
Peter Dohm wrote:
"cavelamb" wrote in message news brian whatcott wrote: cmyr wrote: I chose what I believe is the best of both worlds by going with a Jodel design. Efficient and economical on low H.P.,no apparent vices, and most of the designs are former production aircraft with years of goverment oversight to weed out any problems. John G. Good move! I have flown various Jodel flavors and can confirm that they fly well. They are well liked and without vice. Though how that trademark cranked wing does it, I'm not sure... Brian W Low wing load, moderate power loading, and a lot of leading edge. No secrets there. Actually, I envy you that one, Brian. I've never had the pleasure. I've heard they are really sweet. -- Richard Lamb I, too, have always heard that they were well known for extremely docile handling; and my very limited experience with models as a kid suggests that the docile handling is a common trait of that geometry. You could certainly do much worse, and I did once think of building a D9. I might even consider one of their designs again--but the obvious problem is that scratch building in wood is a lot of work and not a lot cheaper that a prepunched metal kit from Vans! Peter For me the concern is the wooden structure. I know that spruce is not a durable wood - it qualifies because it is among the highest strength to weight materials. I continually marvel that an aluminum structure can be left outside year after year and still hold up. I don't think you could expect that performance of wood. Brian W |
#12
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Aero engineer for designing homebuilt aircraft.
On Tue, 01 Jun 2010 22:57:57 -0500, brian whatcott
wrote: Peter Dohm wrote: "cavelamb" wrote in message news brian whatcott wrote: cmyr wrote: I chose what I believe is the best of both worlds by going with a Jodel design. Efficient and economical on low H.P.,no apparent vices, and most of the designs are former production aircraft with years of goverment oversight to weed out any problems. John G. Good move! I have flown various Jodel flavors and can confirm that they fly well. They are well liked and without vice. Though how that trademark cranked wing does it, I'm not sure... Brian W Low wing load, moderate power loading, and a lot of leading edge. No secrets there. Actually, I envy you that one, Brian. I've never had the pleasure. I've heard they are really sweet. -- Richard Lamb I, too, have always heard that they were well known for extremely docile handling; and my very limited experience with models as a kid suggests that the docile handling is a common trait of that geometry. You could certainly do much worse, and I did once think of building a D9. I might even consider one of their designs again--but the obvious problem is that scratch building in wood is a lot of work and not a lot cheaper that a prepunched metal kit from Vans! Peter For me the concern is the wooden structure. I know that spruce is not a durable wood - it qualifies because it is among the highest strength to weight materials. I continually marvel that an aluminum structure can be left outside year after year and still hold up. I don't think you could expect that performance of wood. Brian W you cant expect that performance in any material unless the surfaces are passivated or coated to diminish any hydroscopic effect. most of us have invented the hangar. Stealth Pilot |
#13
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Aero engineer for designing homebuilt aircraft.
On Jun 1, 8:43 pm, "Peter Dohm" wrote:
I, too, have always heard that they were well known for extremely docile handling; and my very limited experience with models as a kid suggests that the docile handling is a common trait of that geometry. I have a Jodel D-11 and don't consider it particularly docile, certainly not like a Cub or Champ. It stalls at 40 mph but long before you get that slow it will start a dangerous sink. Short wings will do that. 1.3 Vso approaches are too slow. The gear, placed as per plans, makes the tail really light and easy to nose the airplane over. My mains are a bit further ahead but it's still light in the tail and much twitchier in the rollout than many other light taildraggers. If you're using Falconar's plans, be aware that the airplane might come out tail heavy. The original French plans called for mahogany ply, no fabric on the fuselage or stab, and a tailskid. With birch ply and fabric and a tailwheel, you'll be out the aft limit unless you lengthen the engine mount or use a heavier engine. His F11/12 spring gear is far heavier than the oleos, I think, and I wish I had the oleos. More work but much more useful load in the end. Empty weight numbers on the plans are way off. I don't know why anyone would want flaps on this airplane. It glides like a brick as it is, and if you want to drop faster just slip it. It will scare the daylights out of you the first time. No other airplane I've ever flown slips as aggressively. This one has the all- flying rudder; the F-series fin and stab might not have such authority. Flaps and their mechanism would just add more weight and build time. Keep that wood dry. If rot gets into the spar, the airplane would be a writeoff. Building the spar is a major part of the whole project. Get it straight and get those ribs glued on in perfect alignment. If they're off, they're off permanently. There's no adjustment once the glue sets. You need a really long shop, as the 27- foot spar is all one assembly. There are no tiedowns provided for. Mine has hand-holes in the wingtips for maneuvering it on the ground and for tiedowns but they're too far out and place stress on the tips in a strong wind. Better to make up some aluminum bands to go around the spar and stick out through the wing's bottom fabric three or four feet outboard of the gear attachments. Dan |
#14
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Aero engineer for designing homebuilt aircraft.
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#15
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Aero engineer for designing homebuilt aircraft.
wrote in message ... On Jun 1, 8:43 pm, "Peter Dohm" wrote: I, too, have always heard that they were well known for extremely docile handling; and my very limited experience with models as a kid suggests that the docile handling is a common trait of that geometry. I have a Jodel D-11 and don't consider it particularly docile, certainly not like a Cub or Champ. It stalls at 40 mph but long before you get that slow it will start a dangerous sink. Short wings will do that. 1.3 Vso approaches are too slow. The gear, placed as per plans, makes the tail really light and easy to nose the airplane over. My mains are a bit further ahead but it's still light in the tail and much twitchier in the rollout than many other light taildraggers. If you're using Falconar's plans, be aware that the airplane might come out tail heavy. The original French plans called for mahogany ply, no fabric on the fuselage or stab, and a tailskid. With birch ply and fabric and a tailwheel, you'll be out the aft limit unless you lengthen the engine mount or use a heavier engine. His F11/12 spring gear is far heavier than the oleos, I think, and I wish I had the oleos. More work but much more useful load in the end. Empty weight numbers on the plans are way off. I don't know why anyone would want flaps on this airplane. It glides like a brick as it is, and if you want to drop faster just slip it. It will scare the daylights out of you the first time. No other airplane I've ever flown slips as aggressively. This one has the all- flying rudder; the F-series fin and stab might not have such authority. Flaps and their mechanism would just add more weight and build time. Keep that wood dry. If rot gets into the spar, the airplane would be a writeoff. Building the spar is a major part of the whole project. Get it straight and get those ribs glued on in perfect alignment. If they're off, they're off permanently. There's no adjustment once the glue sets. You need a really long shop, as the 27- foot spar is all one assembly. There are no tiedowns provided for. Mine has hand-holes in the wingtips for maneuvering it on the ground and for tiedowns but they're too far out and place stress on the tips in a strong wind. Better to make up some aluminum bands to go around the spar and stick out through the wing's bottom fabric three or four feet outboard of the gear attachments. Dan Well, I certainly stand enlightened on more than a few items, and that tie down location does sound like a poor choice. Personally, I have mixed feelings about the low speed performance that you described--and feel that I have to ask about the glide ratio at the best glide speed. Part of my reason for asking is that I personally liked the Piper Tomahawk, despite its sordid reputation, and it had a good gilde ratio at its best glide speed--but the version with four stall strips also had a fast sink. I recall the characteristic, but not the flap postition involved (possibly due to old timer's disease) and I never got to fly a Tomahawk with two strips or with no strips--but IIRC, the manual implied that the high sink might have been replaced with a dramatic stall, at a much lower speed, on the version with no stall strips. My best recollection is that there was a 6 knot difference in the stall speed without the strips--but the manual is inaccessible if I still have it. OTOH, the balance problems are "interesting" because, although I have yet to build my own project, I have seen a few interesting issues crop up in kits as well as plans built aircraft. The most glaring problem that I can recall was a two seat tandem kit that resembled a high wing ultralight in appearance, but was always intended to be a very simple registered airplane. I'll alow the type and manufacturer to remain nameless, but the factory welded fusalage had been jigged incorrectly when it was welded with the result that the wind was too far forward and the aircraft was tail heavy--so that forward pressure was required on the stick as there was no provision for trim. The good news was that the design CG position was shown in the plans relative to the wing--and just happened to be the same place as the wing strut attachment points with provision for balancing points to be easily attached. That last part really qualifies as an outstanding design feature--especially in the homebuild arena--and we were easily able to properly balance the airplane with about 15 pounds of balast added to the nose. After that, it flew perfectly hands off. (I know that a purist would criticise the estra weight, and I basically agree, but it made a lot more sense to the owner/pilot than cutting and rewelding the factory welded fusalage.) The point of this long winded dissertation is simply that you never know until you do a full weight and balance, both with and without people and fuel, and any amateur-built aircraft may very well require adjustment. Peter |
#16
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Aero engineer for designing homebuilt aircraft.
Peter Dohm wrote:
wrote in message ... On Jun 1, 8:43 pm, "Peter Dohm" wrote: I, too, have always heard that they were well known for extremely docile handling; and my very limited experience with models as a kid suggests that the docile handling is a common trait of that geometry. I have a Jodel D-11 and don't consider it particularly docile, certainly not like a Cub or Champ. It stalls at 40 mph but long before you get that slow it will start a dangerous sink. Short wings will do that. 1.3 Vso approaches are too slow. The gear, placed as per plans, makes the tail really light and easy to nose the airplane over. My mains are a bit further ahead but it's still light in the tail and much twitchier in the rollout than many other light taildraggers. If you're using Falconar's plans, be aware that the airplane might come out tail heavy. The original French plans called for mahogany ply, no fabric on the fuselage or stab, and a tailskid. With birch ply and fabric and a tailwheel, you'll be out the aft limit unless you lengthen the engine mount or use a heavier engine. His F11/12 spring gear is far heavier than the oleos, I think, and I wish I had the oleos. More work but much more useful load in the end. Empty weight numbers on the plans are way off. I don't know why anyone would want flaps on this airplane. It glides like a brick as it is, and if you want to drop faster just slip it. It will scare the daylights out of you the first time. No other airplane I've ever flown slips as aggressively. This one has the all- flying rudder; the F-series fin and stab might not have such authority. Flaps and their mechanism would just add more weight and build time. Keep that wood dry. If rot gets into the spar, the airplane would be a writeoff. Building the spar is a major part of the whole project. Get it straight and get those ribs glued on in perfect alignment. If they're off, they're off permanently. There's no adjustment once the glue sets. You need a really long shop, as the 27- foot spar is all one assembly. There are no tiedowns provided for. Mine has hand-holes in the wingtips for maneuvering it on the ground and for tiedowns but they're too far out and place stress on the tips in a strong wind. Better to make up some aluminum bands to go around the spar and stick out through the wing's bottom fabric three or four feet outboard of the gear attachments. Dan Well, I certainly stand enlightened on more than a few items, and that tie down location does sound like a poor choice. Personally, I have mixed feelings about the low speed performance that you described--and feel that I have to ask about the glide ratio at the best glide speed. Part of my reason for asking is that I personally liked the Piper Tomahawk, despite its sordid reputation, and it had a good gilde ratio at its best glide speed--but the version with four stall strips also had a fast sink. I recall the characteristic, but not the flap postition involved (possibly due to old timer's disease) and I never got to fly a Tomahawk with two strips or with no strips--but IIRC, the manual implied that the high sink might have been replaced with a dramatic stall, at a much lower speed, on the version with no stall strips. My best recollection is that there was a 6 knot difference in the stall speed without the strips--but the manual is inaccessible if I still have it. OTOH, the balance problems are "interesting" because, although I have yet to build my own project, I have seen a few interesting issues crop up in kits as well as plans built aircraft. The most glaring problem that I can recall was a two seat tandem kit that resembled a high wing ultralight in appearance, but was always intended to be a very simple registered airplane. I'll alow the type and manufacturer to remain nameless, but the factory welded fusalage had been jigged incorrectly when it was welded with the result that the wind was too far forward and the aircraft was tail heavy--so that forward pressure was required on the stick as there was no provision for trim. The good news was that the design CG position was shown in the plans relative to the wing--and just happened to be the same place as the wing strut attachment points with provision for balancing points to be easily attached. That last part really qualifies as an outstanding design feature--especially in the homebuild arena--and we were easily able to properly balance the airplane with about 15 pounds of balast added to the nose. After that, it flew perfectly hands off. (I know that a purist would criticise the estra weight, and I basically agree, but it made a lot more sense to the owner/pilot than cutting and rewelding the factory welded fusalage.) The point of this long winded dissertation is simply that you never know until you do a full weight and balance, both with and without people and fuel, and any amateur-built aircraft may very well require adjustment. Peter If the purists give you static about it, just name it Static Stability Augmentation System, and paint it bright red! Seriously, why would anyone complain about properly balancing an airplane??? It's rather important! -- Richard Lamb |
#17
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Aero engineer for designing homebuilt aircraft.
"cavelamb" wrote in message ... Peter Dohm wrote: -----------------snipped----------------- OTOH, the balance problems are "interesting" because, although I have yet to build my own project, I have seen a few interesting issues crop up in kits as well as plans built aircraft. The most glaring problem that I can recall was a two seat tandem kit that resembled a high wing ultralight in appearance, but was always intended to be a very simple registered airplane. I'll alow the type and manufacturer to remain nameless, but the factory welded fusalage had been jigged incorrectly when it was welded with the result that the wind was too far forward and the aircraft was tail heavy--so that forward pressure was required on the stick as there was no provision for trim. The good news was that the design CG position was shown in the plans relative to the wing--and just happened to be the same place as the wing strut attachment points with provision for balancing points to be easily attached. That last part really qualifies as an outstanding design feature--especially in the homebuild arena--and we were easily able to properly balance the airplane with about 15 pounds of balast added to the nose. After that, it flew perfectly hands off. (I know that a purist would criticise the estra weight, and I basically agree, but it made a lot more sense to the owner/pilot than cutting and rewelding the factory welded fusalage.) The point of this long winded dissertation is simply that you never know until you do a full weight and balance, both with and without people and fuel, and any amateur-built aircraft may very well require adjustment. Peter If the purists give you static about it, just name it Static Stability Augmentation System, and paint it bright red! Seriously, why would anyone complain about properly balancing an airplane??? It's rather important! Richard Lamb I agree, and it all was several years ago; but I will definitely use your nomenclatu Static Stabiliby Augmentation System. That's really outstanding! Peter |
#18
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Aero engineer for designing homebuilt aircraft.
On Sun, 6 Jun 2010 23:27:43 -0400, "Peter Dohm"
wrote: "cavelamb" wrote in message ... Peter Dohm wrote: -----------------snipped----------------- OTOH, the balance problems are "interesting" because, although I have yet to build my own project, I have seen a few interesting issues crop up in kits as well as plans built aircraft. The most glaring problem that I Richard Lamb I agree, and it all was several years ago; but I will definitely use your nomenclatu Static Stabiliby Augmentation System. That's really outstanding! Peter The Auster J1B isnt a kit aeroplane. down in the tail there is a location where the fuselage tubes form a "V" shape. on each side of this V shape is some 1/8" steel riveted in position to make a box. in the standard aircraft there is a 10lb triangular lead weight bolted in front of this "V". if you put a metal prop on the aircraft instead of a wooden prop there is a couple of pounds of lead in a triangular wedge to go in the box. if you add the exhaust muffler on to the straight stacks there is another triangular lead piece to go in the box. all told I think there can be 21lbs of lead in the tail. in flight you notice nothing if the CG is in the right place. I wouldnt feel embarassed about some lead ballast to get the cg correct. the aircraft will be a lethal trap if you dont get the cg right. your passengers wont even see the lead so why worry about it. of course if you make a second aircraft the way is open for some tweaking to remove the need. Stealth Pilot |
#19
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Aero engineer for designing homebuilt aircraft.
"Stealth Pilot" wrote in message ... On Sun, 6 Jun 2010 23:27:43 -0400, "Peter Dohm" wrote: "cavelamb" wrote in message ... Peter Dohm wrote: -----------------snipped----------------- OTOH, the balance problems are "interesting" because, although I have yet to build my own project, I have seen a few interesting issues crop up in kits as well as plans built aircraft. The most glaring problem that I Richard Lamb I agree, and it all was several years ago; but I will definitely use your nomenclatu Static Stabiliby Augmentation System. That's really outstanding! Peter The Auster J1B isnt a kit aeroplane. down in the tail there is a location where the fuselage tubes form a "V" shape. on each side of this V shape is some 1/8" steel riveted in position to make a box. in the standard aircraft there is a 10lb triangular lead weight bolted in front of this "V". if you put a metal prop on the aircraft instead of a wooden prop there is a couple of pounds of lead in a triangular wedge to go in the box. if you add the exhaust muffler on to the straight stacks there is another triangular lead piece to go in the box. all told I think there can be 21lbs of lead in the tail. in flight you notice nothing if the CG is in the right place. I wouldnt feel embarassed about some lead ballast to get the cg correct. the aircraft will be a lethal trap if you dont get the cg right. your passengers wont even see the lead so why worry about it. of course if you make a second aircraft the way is open for some tweaking to remove the need. Stealth Pilot The truth is: I agree! It's just that I have run into so many people over the years, who seem to place so much enphasis on weight that they seem willing to add a pound of drag to save two pounds of weight, and frequently have seemed willing to make some other questionable trades in other areas as well, that I just felt compelled to make a comment about it--even if a few minutes more thought might have provided a little better phrasing. Peter |
#20
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Aero engineer for designing homebuilt aircraft.
On Mon, 7 Jun 2010 16:56:32 -0400, "Peter Dohm"
wrote: The Auster J1B isnt a kit aeroplane. down in the tail there is a location where the fuselage tubes form a "V" shape. on each side of this V shape is some 1/8" steel riveted in position to make a box. in the standard aircraft there is a 10lb triangular lead weight bolted in front of this "V". if you put a metal prop on the aircraft instead of a wooden prop there is a couple of pounds of lead in a triangular wedge to go in the box. if you add the exhaust muffler on to the straight stacks there is another triangular lead piece to go in the box. all told I think there can be 21lbs of lead in the tail. in flight you notice nothing if the CG is in the right place. I wouldnt feel embarassed about some lead ballast to get the cg correct. the aircraft will be a lethal trap if you dont get the cg right. your passengers wont even see the lead so why worry about it. of course if you make a second aircraft the way is open for some tweaking to remove the need. Stealth Pilot The truth is: I agree! It's just that I have run into so many people over the years, who seem to place so much enphasis on weight that they seem willing to add a pound of drag to save two pounds of weight, and frequently have seemed willing to make some other questionable trades in other areas as well, that I just felt compelled to make a comment about it--even if a few minutes more thought might have provided a little better phrasing. Peter I had a fellow pilot complete a rebuild of his aircraft after the 3rd crash destroying it. you think you'd write him off at 82 after the third prang :-) "how'd the rebuild go mitch?" "3 lb lighter overall than last time" he said with some excitement. Mitch earned my undying respect that day. the accidents are just part of an active flying pasttime in an unforgiving environment but to have the focus on weight control at age 82 when the temptations must have been to 'make it a bit stronger' showed me that he is focussed on what matters. doesnt pay to become jaundiced in life. some people surprise you when you least expect it. :-) Stealth Pilot |
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