Borrow some gross weight?

23 posts in this topic

Posted

Hey everyone

so the plane is finally completed and some CG issues addressed. 

I've been fortunate enough to have an experienced aerobatic show pilot offer taildragger lessons in my plane. However, my gross in the MKIV is 1150 but I think our weight will put us over that. I'm 205lbs and I'm guessing he's another 205-225lbs. With minimum 30lbs of fuel and the plane at 720 I'll only have room to accommodate 200 beyond my 205, but I believe he's over that. Do you feel this causes a big issue or is a handful of lessons going over 1150 manageable?

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Posted (edited)

If your loaded CG is in the allowable range, lets say not more than 17" the plane should be controllable - I would rather be more over gross than short on fuel.  These planes can still be flown heavier than the kit-maker suggests.  I just wonder if two "large" fellows can be able to fit into that cabin and operate the controls without interfering with each other?  I know the MkIV is wider, but I have never sat in one.  You are going to need a longer takeoff run and have less climb rate and faster stall speeds with the extra weight, so be prepared for that.  The Airdale flys at 1400 GW on the same HH wings and 100 HP Subaru - I would be more worried about the landing gear stress.   EDMO

Edited by EDMO

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Posted

Thanks EDMO,

I am going to ask his exact weight. I'm yet to meet him and everything has just been by phone. I've only seen his airshow pictures so I'm completely guessing based on his pics. But last night I calculated myself at 205, him 220, 30 for fuel then CG will be at -15.1 and total weight will be 1175lbs. So if we can fit more fuel and 1200lbs is OK for now to be at then I'll feel comfortable with everything. 

Ive been doing taxiing practice and getting up to speeds to lift the TW. But before I continue I'd rather have the safety net and expertise of someone with experience. Who knows, I may be doing something that is just yet to bite my ass so I'd like to know lol. 

My grass strip is 1280' long. Regarding fitting in the cabin. He doesn't appear to be a wide built person. Just average I guess. Same with myself. My dad is 6'2, 225 but shoulders like an outhouse and he and I were snug.

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Posted (edited)

If you read the "Kitfox Pilot's Guide" by Ed Downs, (sold by Kitfox), you would read his statement against "High Speed Taxi" - "Don't Do That!".  I recommend that book to all new Kitfox and Avid flyers.  That's about the only advice I can quote on your preparing to fly the bird.  EDMO

Edited by EDMO
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Posted

What wings and engine do you have?  720lbs is the heaviest I've ever heard of a MK4 weighing. If you do fly it at 1200lbs I wouldn't do it off your grass strip or in any turbulence the first time. It'll fly but it's not going to perform anywheres near what they were intended for. 

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Posted

720lbs ? My plane comes in at 545lbs with a 582 and speed wing . I think my gross weight is only 1150 lbs . Is 1200lbs the normal gross weight? 

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Posted (edited)

Yeah unfortunately that's what she's weighing in at, I'm not proud of it. I even went out and bought good scales because I didn't trust the numbers I was getting. 

It has a Subaru ea81, belted redrive, single weber carb and custom intake manifold. Also has speed wings. 

Also forgot the 29lb battery in the back plus 10lb lead weight. Those didn't help my cause. For CG issues yes, but not overall weight. 

I finished this project with the plan of flying on my own and wife (she's tiny) then either upgrading to a bearhawk or finish the BMW engine I have and consider a conversion. We'll see I guess

Edited by fusionfab

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Posted

If you read the "Kitfox Pilot's Guide" by Ed Downs, (sold by Kitfox), you would read his statement against "High Speed Taxi" - "Don't Do That!".  I recommend that book to all new Kitfox and Avid flyers.  That's about the only advice I can quote on your preparing to fly the bird.  EDMO

I am sorry I didn't mean high speed taxiing. I meant short run ups. So I'd set up, full throttle, raise tail, and drop throttle to gently bring tail down. But if that's considered the same then I will for sure stop. 

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Posted (edited)

If you read the "Kitfox Pilot's Guide" by Ed Downs, (sold by Kitfox), you would read his statement against "High Speed Taxi" - "Don't Do That!".  I recommend that book to all new Kitfox and Avid flyers.  That's about the only advice I can quote on your preparing to fly the bird.  EDMO

I am sorry I didn't mean high speed taxiing. I meant short run ups. So I'd set up, full throttle, raise tail, and drop throttle to gently bring tail down. But if that's considered the same then I will for sure stop. 

I will have to leave the interpretation of that to the more experienced Avid taildragger pilots.  I guess as long as you are confident of your control enough to prevent a ground loop, then it is OK.  EDMO

Edited by EDMO

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Posted

If you read the "Kitfox Pilot's Guide" by Ed Downs, (sold by Kitfox), you would read his statement against "High Speed Taxi" - "Don't Do That!".  I recommend that book to all new Kitfox and Avid flyers.  That's about the only advice I can quote on your preparing to fly the bird.  EDMO

I am sorry I didn't mean high speed taxiing. I meant short run ups. So I'd set up, full throttle, raise tail, and drop throttle to gently bring tail down. But if that's considered the same then I will for sure stop. 

I will have to leave the interpretation of that to the more experienced Avid taildragger pilots.  I guess as long as you are confident of your control enough to prevent a ground loop, then it is OK.  EDMO

yeah I am not sure if it's considered the same thing, but nonetheless I'll stop lol. I appreciate the headsup. 

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Posted

daaaaaaumn.  She is way on the heavy side.  If you are fast enough to get the tail up, your fast enough to fly.. well, not sure with that one.  720 pounds in a speed wing.. your stall is going to be way up there.  Hopefully its an extended speed wing.

 

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Posted (edited)

daaaaaaumn.  She is way on the heavy side. 

 

We had a VP-! like that around here.  Joke was while doing touch and goes after take off he needed to fly around the pattern twice  to get to a safe altitude to set up to land.

Edited by TJay
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Posted

daaaaaaumn.  She is way on the heavy side.  If you are fast enough to get the tail up, your fast enough to fly.. well, not sure with that one.  720 pounds in a speed wing.. your stall is going to be way up there.  Hopefully its an extended speed wing.

 

I think they're an extended speed wing, or clipped wings? Each wing from butt rib to tip is 11'6" plus cabin 38" so total span is 26'2". 

Can anyone tell me what their Subaru powered mk4's weigh?

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Posted (edited)

I thought extended or STOL wings are about 29', but I am no Avid expert, and 26' may be right.  We have been thru this before, but my memory is shorter than the wings!  ;<)   Full Kitfox wings are 32'.  Subaru Avids/Kitfoxes/Airdales usually weigh around 700+.  I think it is hard to build one less than 700 lbs.  Trying to keep my "Heavy SuberFox" under 750 to 800, but that's another story.   EDMO

Edited by EDMO

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Posted

Standard STOL or Heavy Hauler wings are 29' 10 1/2"   I had 2 MK IV Avids.  Both weighed 585 lbs.  One had a 582, the other a Jabiru.  Both had the HH wings.  What's in the plane that you don't need?  If the Subaru is 75 lbs heavier than the Jab or Rotax, and you use 25 lbs of lead in the tail to offset the extra 75, where is the rest of the weight coming from.  JImChuk

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Posted (edited)

Standard STOL or Heavy Hauler wings are 29' 10 1/2"   I had 2 MK IV Avids.  Both weighed 585 lbs.  One had a 582, the other a Jabiru.  Both had the HH wings.  What's in the plane that you don't need?  If the Subaru is 75 lbs heavier than the Jab or Rotax, and you use 25 lbs of lead in the tail to offset the extra 75, where is the rest of the weight coming from.  JImChuk

I've read through a number of threads here and kitfox forums, that it is rare to keep a Subaru conversion under 700lbs as EDMO said also. 

My Subaru engine weight 206lbs with everything on it and oil. But minus plumbing, coolant and rads which came out to 24lbs. I may be wrong but the 582 is around 130lbs? Then the battery size needed is 26lbs mounted at the back, plus an additional 10lb weight in tail. With that said. Your bird at 585lbs would then weigh close to my 720 (roughly)

Its a popular conversion with good success rate. Would I do things differently now having run into limited payload, absolutely. But for the time being I am happy with it all and am just hoping this instructor who is at least my size will be able to fit. Fingers crossed.

Edited by fusionfab
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Posted

Standard speed wing on a mkIV is 24ft extended is 26ft. Hopefully the extended will help with your weight.

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Posted (edited)

Standard speed wing on a mkIV is 24ft extended is 26ft. Hopefully the extended will help with your weight.

I thought the Speedwing extensions were long enough to make it the same 29'+ as the STOL wings?  If I had an Avid with a Subaru engine I would seriously consider putting 32' Kitfox wings on it, or modifying the Avid wings to make them that long.  Extensions added plus the Kitfox droop tips should give better lift too.  The rounded Avid tips only count for about 2/3 of the area of the same length squared tips.  The modifications I have made to my 32' wings with 4" Leading edge extensions, modified Riblett (Kitfox 4+) ribs, modified Cessna 210 droop tips and 15" flaps and ailerons gives me about 160 square feet of wing area - compare that to the area he has on his short Speedwings, and figure the wing loading differences for a plane at 1200 lbs Gross Weight.  Mine is about 7.5 lbs/square foot.  If you substitute "Performance" and "stall speed" for "wing loading", it begins to mean a lot more.   EDMO

Edited by EDMO
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Posted (edited)

Standard speed wing on a mkIV is 24ft extended is 26ft. Hopefully the extended will help with your weight.

I thought the Speedwing extensions were long enough to make it the same 29'+ as the STOL wings?  If I had an Avid with a Subaru engine I would seriously consider putting 32' Kitfox wings on it, or modifying the Avid wings to make them that long.  Extensions added plus the Kitfox droop tips should give better lift too.  The rounded Avid tips only count for about 2/3 of the area of the same length squared tips.  The modifications I have made to my 32' wings with 4" Leading edge extensions, modified Riblett (Kitfox 4+) ribs, modified Cessna 210 droop tips and 15" flaps and ailerons gives me about 160 square feet of wing area - compare that to the area he has on his short Speedwings, and figure the wing loading differences for a plane at 1200 lbs Gross Weight.  Mine is about 7.5 lbs/square foot.  If you substitute "Performance" and "stall speed" for "wing loading", it begins to mean a lot more.   EDMO

Any idea what droop tips would do for my speedwing ? I could be wrong about the length of the extended speed wings . 

Edited by chopndrag

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Posted (edited)

 Biggest boost in Take-off, climb, Performance is more wing area - does not help cruise speeds - extensions would help a lot - square tips should help a little more - I think they add 18" to each wing.   I really like the tips that are on that Yellow tipped Kitfox 4 tcj posted in "Pictures" posts - They may be for Just Aircraft or Stewarts tips?    Looks like they add lift, reduce drag and give more cruise?   EDMO

Edited by EDMO

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Posted

I like more cruise speed . I have the regular wing tips but I'm always looking for mods to add less drag . I still haven't done any of the gap seals yet bit that's coming as soon as I paint it .

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Posted

Ed - those are the Hoerner wing tips available from Kitfox, I'm using them on my Avid+. I found a set that had already been trimmed for the KF 4-7 wing so I needed to do a little work at the trailing edge. I believe new ones come with the trailing edge of the tips unglued just like the KF droop tips did, so each builder can custom fit to his/her plane. I think it would take a bit more work to fit the Hoerner tips to an Avid under camber rib/wing, but I'm pretty sure someone here did it not that long ago (Tjay maybe?). I traded in my oem Avid tips to use these, prefer the aesthetics and wanted quick removeable tips. I suspect there are performance benefits as well.

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Posted (edited)

Ed - those are the Hoerner wing tips available from Kitfox, I'm using them on my Avid+. I found a set that had already been trimmed for the KF 4-7 wing so I needed to do a little work at the trailing edge. I believe new ones come with the trailing edge of the tips unglued just like the KF droop tips did, so each builder can custom fit to his/her plane. I think it would take a bit more work to fit the Hoerner tips to an Avid under camber rib/wing, but I'm pretty sure someone here did it not that long ago (Tjay maybe?). I traded in my oem Avid tips to use these, prefer the aesthetics and wanted quick removeable tips. I suspect there are performance benefits as well.

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Doug,  I thought tcj's tips looked different than the Kitfox Hoerner tips that I had, and sold - anyway, I like the looks of them - they were too short on the chord to fit my extended wings, so I got a bargain on some Cessna 210 semi-droop tips that are also light weight.   EDMO

Chopndrag,  The Hoerner Kitfox tips are supposed to produce less drag than most other kinds of tips.   My design book also says that they give less drag if angled in at the front about 7 degrees so the front is shorter than the trailing edge.   EDMO

Edited by EDMO

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